Comprehensive Truck Size and Weight Limits Study - Bridge Structure Comparative Analysis Technical Report

Appendix A: Revised Desk Scan Report

Table of Contents

• Chapter 1. Introduction
  • 1.1 Purpose
• Chapter 2. Structural Impacts Due to Overweight Trucks
  • 2.1 Documents on Methods and Impacts of the Bridge Strength Limit State
  • 2.2 Documents on Methods and Impacts of the Bridge Fatigue Limit State
  • 2.3 Methods and Models Related to Accrued Bridge Damage Costs and Bridge Serviceability Limits
• Chapter 3. Bridge Deck Deterioration, Service Life and Preventative Maintenance
  • 3.1 A Survey of Analysis Methods and Synthesis of the State of Practice in Modeling Bridge Deck Impacts
  • 3.2 3Data Needs and an Evaluation and Critique of Available Data Sources for Bridge Decks
  • 3.3 Assessment of the Current State of the Understanding of the Impact and Needs for Future Research, Data Collection and Evaluation
  • 3.4 Past Studies with Past Prospective And Retrospective Estimates in Each Category of Effect
  • 3.5 List of References
• Chapter 4. List of Agencies
  • 4.1 National Academy of Sciences
  • 4.2 Federal and State Transportation Agencies
  • 4.3 Universities
  • 4.4 Industry Standards and Publications
  • 4.5 Foreign Resources

CHAPTER 1 - Introduction

This report presents a revised version of the Bridge Task Desk Scan developed to support the Bridge Structure Comparative Analysis of the 2014 Comprehensive Truck Size and Weight Limits Study (2014 CTSW Study). This revised Desk Scan addresses the recommendations made by the National Academy of Science (NAS) Peer Review Panel concerning the originally submitted version of this scan.

1.1 Purpose

The purpose of the revised Desk Scan is to:

• Reorganize and enhance the original Desk Scan; and
• Add any additional, relevant content that may have been identified since the submission of the original Desk Scan.

Specifically, the NAS Peer Review Panel recommended that the original Desk Scan be reorganized to address four issues:

• Correlation of findings and discussions of cited references;
• Clarifications including to several references to and from prior studies; and identification of findings or correlations in prior studies common to the 2014 CTSW Study.

The purpose of this desk scan is to assess the extent to which specific changes in Federal truck size and weight limits might impact the nation's bridges. The potential impacts to be considered include direct and immediate structural effects and the resulting accrued damage to bridges over time. In addition, study subtasks include the effects of the proposed scenario truck configurations on the fatigue life of bridges; and on bridge deck deterioration, service life and maintenance. The NAS Peer Review Committee also enquired into the absence of discussion regarding bridge barriers, median barriers, railings, etc. The effects on these elements with respect to their capacity to resist errant 'Scenario' vehicles would more aptly be considered under the Safety Task. For this CTSW 2014 Study, the scope of the strength limit (structural analysis) case was confined to the evaluation of the primary member load bearing capacity. However, the dead load for those elements was accounted for in the ABrR bridge models.

There are of necessity fundamental differences in approach to these study areas. This is most evident with respect to the application of structural analysis. The assessment of structural impacts is based on a straight forward analysis of the structural effects of the proposed scenario trucks vs. those attributable to the control vehicle. As the load rating factor is based on specific truck configurations and assumed axle weights acting on specific bridges; the determination of the number of bridges, and in the end the costs associated with additional posting issues that arise, are directly derived from this straightforward structural analysis for the representative sample of bridges. So, for the purposes of this study the load rating of bridges and the identification of resulting posting issues and costs is in the end a simple comparison of the structural effects of one truck to another: each scenario truck vs. the control vehicle. For load rating purposes, the maximum axle loads for each axle configuration are applied.

For the fatigue sub-study, one could use WIM data to perform a simple fatigue life analysis for representative bridges for a modal shift fleet vs. the existing truck fleet. But those results would be inherently limited to a comparison of the effects of the truck count for the existing fleet vs. that for the modal shift fleet. That approach treats all trucks as equal, ignoring the incremental effects of one truck vs. another. Alternatively, a comparison can be made between the incremental fatigue effects of the scenario trucks vs. the control vehicle, a direct comparison of truck vs. truck in terms of the resulting stress ranges at specific fatigue details on representative bridges. This is the approach adopted in the 2014 CTSW Study.

Several approaches have been employed historically to study bridge damage costs including: incremental costs associated with different truck weights applied to specific bridges; application of a very simplified structural analysis of idealized bridge types for a large bridge inventory using WINBasic; and, allocation of bridge damage responsibility share based on a factor reflecting an assumed causal relationship between some 'allocator' and overall damage costs. Some studies have also used fatigue analysis to help derive damage related bridge costs. Studies have been designed to answer different questions, and in some cases agencies have simply applied the methods developed for pavement costs to bridges; such studies have been limited to a relatively small sample of bridges, or just to a corridor. So, the past approaches to this study area have not been consistent. But it has been a goal of the bridge task team from the outset to answer the question of 'what are the impacts (damage costs) associated with the proposed introduction of the scenario trucks' on a national scale. This led the team to consider the viability of the various study approaches or methods to compare the effects of the modal shift fleet as a whole to those of the existing fleet. The general purpose of the Bridge Task Desk Scan is to conduct and document a literature search and provide literary technical support of various educational and industry supported institutions in the United States, Canada, Australia, Europe and Japan to inform the methods and means used in this 2014 CTSW Study's Bridge Desk Scan. The primary intent is to identify any resources that may inform as to new approaches or refinements to existing approaches to: 1) the quantifying of structural demands on bridges due to 'heavy' truck loads (specifically with respect to six (6) alternative truck configurations; and/or 2) the derivation of resulting bridge capital costs. The process then involves an assessment as to the relevance and applicability of those approaches to this study.

This Desk Scan first considers the potential impacts resulting from the introduction of the six 'Scenario Vehicles', relative to those associated with the 80 kip Control Vehicles for the AASHTO strength, fatigue and serviceability limit state categories. The sub-study area of concrete deck deterioration is more general in nature, with a consideration of impacts due to both overweight trucks and environmental effects.

Accordingly, this report is organized as follows:

2.0 Structural Impacts due to Overweight Trucks

• 2.1 Documents on Methods and Impacts related to the Bridge Strength Limit State:
  • Under this section, methods and practices regarding one time bridge costs due to strength issues, such as load rating, are examined, summarized, and assessed with respect to their relevance to the current study.
• 2.2 Documents on Methods and Impacts related to the Bridge Fatigue Limit State:
  • Under this section Methods and practices of analyzing fatigue impacts are examined, summarized, and assessed.
• 2.3 Documents on Methods and Cost Impacts related to Bridge Serviceability:
  • Under this section, methods of modeling bridge long term deterioration and allocating associated accumulated bridge damage cost are examined, summarized, and presented.

3.0 Documents Modeling and Discussing Bridge Deck Impacts due to Overweight Trucks and Environmental Effects:

• • Under this section, previous studies of deck deterioration are be examined, summarized, and assessed.

CHAPTER 2 - Structural Impacts due to Overweight Trucks

2.1 Documents on Methods and Impacts related to the Bridge Strength Limit State

2.1.1 A survey of analysis methods and synthesis of the state of the practice

National Bridge Inspection Standards in Section 23 of Code of Federal Regulation Part 650.313(c) specifies that a bridge's safe load-carrying capacity is to be determined in accordance with the AASHTO Manual for Bridge Evaluation (MBE). Within the MBE there are three (3) methods to determine the safe load-carrying capacity, the Load and Resistance Factor (LRFD) method, the Load Factor (LRD) method, and the Allowable Stress (ASD) method. No preference is given to a specific method within the MBE. However, the AASHTO LRFD Bridge Design Specifications states in Section 1.1 that the methods provided within the LRFD manual are "encouraged". The LRFR methodology provides a systematic and more comprehensive approach to bridge load rating that is reliability based and provides a more realistic assessment of the safe load capacity of existing bridges. Therefore, the Load and Resistance Factor Rating (LRFR) method is generally accepted and many states have switched to or are switching to this method of analysis. AASHTO has analysis software (AASHTOWare Bridge Rating^®; ABrR) which is used to calculate the Rating Factor (RF) for all three methods. If the RF is below 1.0 then that bridge is considered to have strength limit issues and some action is required. Potential actions or repairs include posting, strengthening, and/or replacing the bridge.

2.1.2 An identification of data needs and an evaluation and critique of available data sources

In order to perform a structural analysis and cost estimate for bridge strengthening or replacement three (3) key data categories need to be defined.

1. Bridge data: bridge geometry, member size, bearing fixity, and material properties are needed to model a bridge. The bridge data usually can be obtained through a review of record plans and field verification, if needed, but would not be feasible for a comprehensive national study. This bridge data necessary to build the models is readily available, but the shear effort involved in reviewing hundreds of plan sets, let alone tens of thousands, would be daunting. Instead the team relied on obtaining existing and verified bridge models from various state DOTs and from NCHRP Project 12-78.
2. Live load data: for the ASD and LFD methods, AASHTO H20 and HS20 trucks or lane loads are used. For the LRFD method, three levels of evaluation are used, i.e.; design load (HL93) rating, legal load rating, and permit load rating. All three ratings should be calculated and the lowest rating determines the safe-load capacity for that bridge. More details pertaining to the LRFD safe-load analysis vehicles can be found in the MBE. In addition, states can designate their own live load configurations to determine safe-load capacity. In general, the bridge data have been inputted into computer models such as AASHTO's ABrR (VIRTIS) for bridge load rating purposes at the states' level. Historically ABrR (VIRTIS) models had been constructed using ASD or LFD methods, but in recent years ABrR (VIRTIS) models have been converted to the LRFR method. However, at the time of this study Load and Resistance Factor Rating (LRFR) capability was not available in AASHTO's ABrR software for the structural analysis of two specific bridge types: trusses and girder-floor-beam bridges.
3. Unit costs for bridge strengthening, replacement or posting: unit cost data is typically referenced to past construction projects within a specific state or region. However, average unit costs vary greatly by state and region, and the reporting format also tends to vary. The cost of posting bridges is typically buried in the states' maintenance and operations programs. As such, it is not readily discernable as a distinct cost category and it is likely to be small relative to the replacement cost.

2.1.3 An assessment of the current state of the understanding of the impact and needs for future research, data collection and evaluation

The methods to determine the load capacity based on ultimate strength has been extensively researched and standardized by AASHTO. AASHTO continues to refine these methods and implement updates to the Manual for Bridge Evaluation and the AASHTO LRFD Bridge Design Specifications. The flexibility providing for a bridge owner to use their own standard rating vehicle is already given and widely used among bridge owners. Once a bridge is determined not to meet the strength requirement in response to the live loads concerned, the owner would typically analyze replacement or strengthening costs versus the direct and indirect costs related to posting the bridge to determine the appropriate action.

2.1.4 Quantitative results of three past studies

2.1.4.1 Results of the 'USDOT Comprehensive Truck Size and Weight Study, 2000'

Bridges from 11 states were studied to extrapolate to the number of bridges requiring replacement in the US. The truck scenarios analyzed were the 2000 CTSW Study Base Case, the Uniformity Scenario (short wheel bases), the North American Fair Trade Act (triple axle vehicles), Longer Combination Vehicles, Triples, and H.R. 551 (intended to phase out trailers longer than 53', terminate state grandfather rights, and freeze national highway system weights). The National Bridge Inventory (NBI) and the FHWA WINBasic analysis software were used to determine the number of bridges that would need to be replaced. The 2000 CTSW Study was the first study to include both Live Load and Dead Load effects. However, the data obtained within the NBI is insufficient to determine the exact stresses. Using WINBasic, all bridges on the NHS were assigned to one of several archetypal bridge types, reflecting assumptions about the number of spans, length of longest span, etc. This approach doesn't yield precise results for any specific, real bridge, but it did allow for a quick, general assessment of the totality of the effects of truck loadings on bridges of various types on the NHS. A three part threshold was set to determine if a structure would be overstressed.

• Bridges rated up to H-17.5 with stresses exceeding 71.5% of the yield stress were assumed to be structurally deficient.
• Bridges with a rating greater than H-17.5 with stresses greater than 63% of the yield stress were assumed to be deficient.
• Bridges with an HS-20 rating with stresses greater than 57.5% of the yield stress were assumed to be structurally deficient.

If a bridge was determined to be overstressed, the proposed bridge replacement cost due to that vehicle was calculated. In addition to the one time replacement cost, a user cost was estimated to account for delays due to congestion during construction of the replacement bridge. A summary from the 2000 CTSW Study is included below.

Table VI-2. Scenario Bridge Impacts

Analytical Case		Costs ($Billion)			Change from Base Case ($Billion)
		Capital	User	Total	Capital	User	Total
1994 Base Case		154	175	329	0	0	0
2000 Base Case		154	175	329	0	0	0
SCENARIO
Uniformity		134	133	267	-20	-42	-62
North American Trade	44,000-pound tridem axle	205	378	583	51	203	254
	51,000-pound tridem axle	219	439	658	65	264	329
LCVs Nationwide		207	441	648	53	266	319
H.R. 551		154	175	329	0	0	0
Triples Nationwide		170	276	446	16	101	117

This chart depicts the bridge capital (replacement) costs and the user costs calculated to result from the various alternative truck types studied, vs. the 'Base Case' costs.

2.1.4.2 Results of the 'Western Uniformity Scenario Analysis':

This study was to evaluate the cost effects of heavier, Longer Combination Vehicles (LCVs) in 13 western states. The bridge data obtained from the NBI was screened using WINBasic to bridges on the Interstate System and on the non-Interstate portion of the National Highway System. A base case vehicle was determined for each state based on existing fleet vehicles as a point of comparison with the ratings of the scenario vehicles. The cost to strengthen or replace a bridge was also calculated. Each of the 13 states reported a unit cost per square foot to replace a bridge. The deck area was increased by 25% because FHWA data shows that replacement bridges are on average 25% longer then the bridge they replace. Also, it was assumed that 50% of the bridges requiring replacement would be rehabilitated or strengthened. The rehabilitation cost was assumed to be 1/3 the replacement cost.

The number of overstressed bridges and the cost of strengthening or replacing the bridge was calculated in increments from 0% overstressed to 36.6% overstressed. It was also assumed that most states would not replace the bridge until the overstressing threshold was approximately half way between the Operating Rating and Inventory Rating. Based on this data and reflecting the two threshold overstress ranges, the one-time bridge replacement and/or rehabilitation cost for the corresponding 2,773 to 3,182 bridges in the 13 western states affected would cost between $2.329 Billion and $4.125 Billion.

2.1.4.3 Results of the 'Wisconsin Truck Size and Weight Study, 2009'

The Wisconsin Truck Size and Weight Study evaluated the potential bridge replacement cost for six (6) overweight trucks. For this study, only bridges on state roads were used for analysis. The data was screened to select 84 bridges representing the type, length and age of Wisconsin bridges. Each scenario vehicle was analyzed using SEP. A minimum inventory rating was set for each vehicle type and bridge type to determine what bridges would require remediation. The results from the analysis of the 84 bridges was extrapolated to determine the number of bridges within the state that would require posting or replacement. For cost estimating purposes any bridge with a rating lower than the minimum limit set was assumed to require replacement. The study reported annual costs over a projected period of 10 years expected to result from the potential introduction of specific alternative truck configurations and weights. The total annual capital cost ranged as high as $8.5 Million ($85 Million over the 10 year period), for the six-axle 98,000 lbs. tractor-trailer. The results from the Wisconsin study are shown below.

Table 7.2 Estimated Annual Bridge Replacement Costs

Special Vehicle Configuration	State Route Bridge Replacement Costs	Local Route Bridge Replacement Costs
Six-Axle Tractor-Trailer, 90,000-Pound GVW (6-90)	$0.04M	$2.14M
Seven-Axle Tractor-Trailer, 97,000-Pound GVW (6-90)	$0.04M	$2.80M
Eight-Axle Tractor-Trailer, 108,000-Pound GVW (8-108)	$0.04M	$2.22M
Seven-Axle Tractor-Trailer, 80,000-Pound GVW (7-80)	$0.78M	$5.24M
Six-Axle Tractor-Trailer, 98,000-Pound GVW (6-98)	$1.54M	$6.94M
Six-Axle Tractor-Trailer, 98,000-Pound GVW (6-98 Pup)	$0.72M	$3.5M

Excerpt from Wisconsin Truck Size and Weight Study, 2009.

2.1.5 Summary of Three Past Studies

In the 2000 CTSW Study, we find an increase in the one-time national bridge replacement costs associated with the introduction of specific alternative heavier trucks ranges up to a maximum of $65 Billion for the NAT truck with a 51,000 lb. triple-axle.

The 'Western Uniformity Scenario Analysis' study summarized the one-time rehabilitation/replacement costs for bridges in the thirteen western states (only) for Longer Combination Vehicles (LCVs). The range of one-time costs attributable to the introduction of those vehicles was found to be between $2.3B and $4.1B.

The 'Wisconsin Truck Size and Weight Study, 2009' reported annual bridge replacement costs over a projected period of 10 years expected to result from the potential introduction of specific alternative truck configurations. The total annual capital costs predicted ranged as high as $8.5M ($.085B over the ten year funding period) for the six-axle 98,000 lb. tractor-trailer.

In summary, there is a large range of disparity in the costs, scale, parameters, methods and purpose of previous studies, which makes a comparison between them and to the 2014 CTSW Study extremely difficult.

2.1.6 List of References

Methods and Impacts of the Bridge Strength Limit State

Reference No.	Document No.	Document Title and Link	Relevance to Study
2.1.6-1	FHWA NHI 12-049	Bridge Inspector's Reference Manual, BIRM https://www.fhwa.dot.gov/bridge/nbis/pubs/nhi12049.pdf	General Reference
2.1.6-2	TRB SR 267	Special Report 267: Regulation of Weights, Lengths, and Widths of Commercial Motor Vehicles, 2002 http://www.nap.edu/catalog.php?record_id=10382	CTSW
	This study follows a series of investigations of the regulation of commercial motor vehicle size and weight conducted by the U.S. Department of Transportation (DOT) and by earlier TRB committees. The study charge in TEA-21 asked TRB to take into account the conclusions of the 1990 report Truck Weight Limits: Issues and Options (TRB Special Report 225), which was also produced at the request of Congress. In 2000, DOT published the final version of its Comprehensive Truck Size and Weight Study; the TRB committee that conducted the present study interpreted its task as complementary to the DOT study. The objective of the latter study was to develop an analytical framework that could be applied to assess a range of policy options; the study did not generate policy recommendations. One of the findings of Report 267 was that “The methods used in past studies have not produced satisfactory estimates of the effect of changes in truck weights on bridge costs”. Instead, they have estimated the cost of maintaining the existing relationship of legal loads to bridge design capacity through bridge replacement strategies and they ignore other options state agencies may have in maintaining their bridges.” The study also recommended the authorization of pilot studies to better understand the impacts of the larger heavier trucks on the states' infrastructure.
2.1.6-3		Western Uniformity Scenario Analysis, USDOT, 2004 https://www.fhwa.dot.gov/policy/otps/truck/wusr/wusr.pdf	CTSW
	In 2000 the U. S. Department of Transportation (DOT) issued the Comprehensive Truck Size and Weight (CTS&W) Study, the first such study by DOT since 1981. The CTS&W Study analyzed five truck size and weight scenarios varying from a rollback of size and weight limits to nationwide operations of longer combination vehicles (LCVs). Due to time constraints, the scenario could not be included in the CTS&W Study Volume III, but the Department agreed to analyze the scenario in a follow-up report. All of the studies performed by the Federal Highway Administration (FHWA), the Transportation Research Board (TRB), and several universities in the last ten years that examined potential impacts of truck size and weight (TS&W) increases have found that the estimated damage to bridges would be the greatest single infrastructure cost caused by larger, heavier trucks. This study uses the FHWA WINBasic tool to analyze bridges included in the Region. It uses the NBI to get basic geometry and material data. The tool uses estimated bridge dead-loads and live loads are computed based on the scenario trucks using operating and inventory load rating. This method may have been appropriate for 2004 however the means and methods would not be compliant with current AASHTO load rating requirements and regulations. The tool is only capable of recommending bridge replacements therefore the final impact cost would be at best the extreme high end or upper bound of cost and not representative of the most likely impact costs.
2.1.6-4	AASHTO 27-MBE-2-M	The Manual for Bridge Evaluation, 2nd Edition with interim updates to 2013; American Association of State Highway Transportation Officials https://bookstore.transportation.org/	Load Rating, Posting
	This document provides guidelines, rules, and specifications for the inspection and load rating of existing bridges. Owner agencies are required to load rate each of their bridges at least biennially to assure they can carry legal loads. This document provides the basis for assessing the load capacity of these bridges by calculating allowable stresses and load factors, which are functions of the bridge material, age and condition. This will be used as the guiding document for the structural analysis, load rating and posting assessment of the bridges.
2.1.6-5	NCHRP Report 700 (12-78; 12-83)	Evaluation of Load Rating by Load and Resistance Factor Rating; Mark Mlynarski, Michael Baker; Modjeski & Masters, Work in Progress (Report 12-78 completed 2011; Report 12-83 in Progress) http://apps.trb.org/cmsfeed/TRBNetProjectDisplay.asp?ProjectID=1629 http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_700Appendices.pdf	Load Rating
	This report documents the analysis of 1,500 bridges that represent various material types and configurations using AASHTOWareTM Virtis® (Now AASHTOWare Bridge Rating, ABrR) to compare the load factor rating to load and resistance factor rating for both moment and shear induced by design vehicles, AASHTO legal loads, and eight additional permit/legal vehicles. The report includes recommended revisions to the AASHTO Manual for Bridge Evaluation based on a review of the analysis results. This is work in progress for developing load rating methods in LRFR format using a database of 18,000 bridges nationwide with actual load rating analysis on 1500 of those bridges. The purpose of this report is to make final recommendations for AASHTO's Manual of Bridge Evaluations for methods and means of conducting load ratings in LRFR. As such, this is still a work in progress and no concrete resolutions have been made for changes to the manual, and in any case the recommendation will not be totally relevant to the current 2014 CTSW Study. However, it may be a good source for obtaining bridge files for analysis
2.1.6-6	AASHTO 27- LRFDUS-6	LRFD Bridge Design Specifications, 6TH Edition 2011 https://bookstore.transportation.org	Load Rating, Design
	The provisions of these specifications are intended to govern the design, evaluation and rehabilitation of bridges and is mandated by FHWA for use on all bridges. It employs the load resistance factor design (LRFD) methodology using factors derived from current statistical knowledge of all loads and structural performance. This will be used as the guiding document for the structural analysis, load rating and posting assessment of the bridges
2.1.6-7	AASHTO 27-HB 17	Standard Specifications for Highway Bridges, 17th Edition https://bookstore.transportation.org/	Load Rating, Posting
	This document provides guidelines, rules, and specifications for the design of new bridges and rehabilitation of existing bridges. Moreover it provides truck and lane design loads such H20 and HS20, wind, snow and seismic load combinations and factors for bridge design This will be used as a supplemental guiding document for the structural analysis, load rating and posting assessment of the bridges. The AASHTO defined rating trucks such as the H20 and HS20 are defined in this manual. These trucks will be used in the ABrR (VIRTIS) program and will be used in part as a basis for evaluating the bridges for their capacity to carry the existing fleet and the proposed future fleet of vehicles.
2.1.6-8	NCHRP SYN 453	NCHRP Synthesis 453: State Bridge Load Posting Processes and Practices, Transportation Research Board, George Hearn, University of Colorado at Boulder, 2014 http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_syn_453.pdf	Load Rating, Posting
	This report is a synthesis of the practices of U.S. state governments in restricting weights of vehicles that can cross highway bridges and culverts. Bridges and culverts restricted for vehicle weights are called load posted structures. The load posting practices of bridge owners include the identification of structures to post for load, the evaluation of safe load capacities of these structures, and the implementation of restrictions on vehicle weights at structures. Practices for load posting operate within a system of legal loads established in law and regulation of federal, state, and local governments. Posting for load is one possible outcome of states' greater activities in evaluation of safe load capacities of bridges and culverts. States post for load, but also grant permits that allow overweight vehicles to travel on designated routes. Overall, states identify and regulate routes that can carry overweight vehicles, routes that can carry legal weight vehicles only, and routes or individual structures that must be restricted to less than legal loads. The LRFR method adopted in the 2014 CTSW Study by necessity eliminates the need to refer to individual state policies and practices with regard to posting vulnerable bridges. All LRFR bridge ratings were normalized to the Base Case Control Trucks. Normalized rating factor values less than 1.0 indicated that there was a posting issue for that representative bridge and the class of bridges of that type. In the final analysis, each state agency or bridge owner have to structurally analyze their bridges in accordance with AASHTO and their state regulations to determine if posting is required.
2.1.6-9	NCHRP RPT 575	NCHRP Report 575: Legal Truck Loads and AASHTO Legal Loads for Posting, Transportation Research Board, Bala Sivakumar, Lichtenstein Consulting Engineers, Inc., 2006 http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_575.pdf	Load Rating
	Summary: In the US trucks are allowed unrestricted operation on the nations highways' and are generally considered legal provided they meet the weight guidelines of the Federal Bridge Formula B (FBF), up to 80,000 lbs. GVW and if any single axle load does not exceed 20,000 lbs. Tandem axles cannot exceed 34,000 lbs. (Each state has additional guidelines and restrictions.) The current AASHTO truck design loads consisting of the H20 and HS20 family of trucks do not adequately represent the fleet of trucks that operate in the United States. It has been found that on certain bridges, the FBF compliant trucks may overstress those bridges by as much as 22%. One of the goals of Report 575 was to investigate through state surveys and WIM data a representative set of trucks that would more adequately represent the class of trucks that are currently operating and attempt to formulate new design guidelines. Other goals as stated in the report included the provision of load factors for use with the LRFD method of design and the LRFR method of load rating. The NCHRP Report 575 goes to the heart of the CTSW study as it relates to structural impacts on bridges and load postings. It was designed to answer the question of “what is the structural effect of the current fleet of legal vehicles on the nation's bridges?” However, the report only answers this question on “a set of generic spans”. The results and findings of this study could not be wholly inclusive of Steel Trusses, and Girder Floorbeam type spans.
2.1.6-10	FHWA-PD-96-001	Recording and Coding Guide for the Structure Inventory and Appraisal of the Nation's Bridges; 1995; Office of Engineering, Bridge Division	Bridge Inventory, NBIS
	This Guide has been prepared for use by the States, Federal and other agencies in recording and coding the data elements that will comprise the National Bridge Inventory data base. By having a complete and thorough inventory, an accurate report can be made to the Congress on the number and state of the Nation's bridges. The Guide also provides the data necessary for the Federal Highway Administration (FHWA) and the Military Traffic Management Command to identify and classify the Strategic Highway Corridor Network and it's connectors for defense purposes.
2.1.6-11	Idaho
		129,000 Pound Pilot Project: Report to the 62nd Idaho State Legislature. Idaho Transportation Department, January 2013. https://rosap.ntl.bts.gov/view/dot/26522/Email	Truck Size & Weight Study
	This study quantifies damages based on NBI ratings before, during, and after the study for several different categories of bridges. This study does not consider the shift in modes of transport, or comment on the effects on other routes not included in the scope.
2.1.6-12	Indiana
	FHWA/IN/JTRP-2007/10	Long-Term Effects of Super Heavy-Weight Vehicles on Bridges; http://docs.lib.purdue.edu/jtrp/236/	Permitted Truck Study
	Abstract: A permit truck which exceeds the predefined limit of 108 kips is defined as a superload in Indiana. This study was conducted to examine the long-term effects of superload trucks on the performance of typical slab-on-girder bridges and to assess the likelihood of causing immediate damage. Typical steel and pre-stressed concrete slab-on-girder type bridges were analyzed using both beam line analysis and detailed finite element models.
2.1.6-13	FHWA/IN/JTRP-2010/12	A Synthesis of Overweight Truck Permitting; http://docs.lib.purdue.edu/jtrp/1118/
	For purposes of safety and system preservation, trucking operational characteristics are regulated through legislation and policies. However, special permits are granted for trucks to exceed specified operational restrictions. Thus, the Indiana DOT not only seeks highway operations policies that retain/attract heavy industry including those that haul large loads but also seeks to protect the billions of taxpayer dollars invested in highway infrastructure. As such, “it is sought to avoid policies that may lead to premature and accelerated deterioration of assets through excess loading or undue safety hazard through oversize loads. ... “Using data from a national study, the report quantifies the extent to which each additional payload increases pavement deterioration. The data also suggests that having more axles on a truck reduces pavement deterioration and consequently, damage repair cost, but could decrease the revenue to be derived from overweight permitting. In conclusion, the study recommended the conduction of a cost allocation study to update these load-damage relationships as well as the overweight permit fee structures, to reflect current conditions in Indiana.
2.1.6-14	FHWA/IN/JTRP-2011/15	Evaluation of Effects of Super-Heavy Loading on the US-41 Bridge over the White River http://docs.lib.purdue.edu/jtrp/1491/	Super Loads, Fatigue
	Built in 1958, the US-41 White River Bridge is a two-girder, riveted steel structure located in Hazelton, IN. The bridge is comprised of two, sixteen span superstructures sharing a common substructure. Each superstructure also contains four pin and hanger expansion joint assemblies. Long-term remote monitoring was used to quantify any negative effects due to the series of superloads. Five primary tasks were undertaken as part of this study: Perform controlled load testing to gain insight on the typical behavior of the bridge. Monitor the effect of individual superloads on the bridge structure to detect any notable damage. Perform an in-depth fracture critical evaluation. Evaluate the effects of multiple super-heavy loading events on the bridge. Collect stress range histograms to be used as part of a fatigue life evaluation
2.1.6-15	Louisiana
	LTRC_398	Effects of Hauling Timber, Lignite Coal and Coke Fuel on Louisiana Highways and Bridges, LTRC Report No. 398. Roberts, Freddy L.; Saber, Aziz; Ranadhir, Abhijeet; Zhou, Xiang. USDOT. March 2005. http://www.ltrc.lsu.edu/pdf/2005/fr_398.pdf	Truck Study, Load Demands
	This study provides a report on the performance of simple span as well as three span bridges of varying lengths. The performance is examined based on the ratios of maximum moment and shear of the exclusion vehicle compared to that of the bridge design vehicle. The sample bridges selected were designed with either H15 or HS20 truck loads. An in depth fatigue evaluation was not performed for this study. Instead the bridge life was determined using a simplified formula involving the performance ratio that was calculated. The added costs for these heavy trucks was then determined using the calculated bridge life.
2.1.6-16	Maine
		Engineering Analysis of Maine's Intestate Bridges, 100,000 Pound Six Axle Trucks, 2011 Sweeney, Kenneth L.; Getchell, Chip; http://www.maine.gov/mdot/docs/EngineeringAnalysis-of-MaineInterstateBridges8-15-11.pdf	Truck Size & Weight Study
	In December 2009, the United States Congress authorized a one year Pilot Program that allowed Maine (and Vermont) to use State weight limits on the Interstate instead of the Federal cap of 80,000 pounds. Through two Executive Orders and then State legislation, Governor Baldacci and the Maine Legislature modified State law to allow a three-axle truck-tractor with a three-axle semi-trailer at 100,000 pounds to use Maine's entire Interstate system, effectively diverting large trucks from non-Interstate highways to the Interstate. Previously, this configuration was only authorized on the Maine Turnpike.
2.1.6-17		Interstate Highway Truck Weights - White Paper; Prepared by Maine DOT; September 20, 2010 https://www.maine.gov/mdot/ofbs/docs/MaineDOTTruckWeightPaper091020.pdf	CTSW Web Site, Truck Size & Weight Study, Safety
	In Maine, 100,000-pound six-axle semi-trailers have long been allowed to operate on approximately 22,500 miles of non-Interstate highways in the state. These same vehicles are unable to operate on approximately 250 miles of Maine's 367 miles of Interstate highways. This situation forces these semi-trailers to exit the controlled-access Interstate system and travel on secondary roads with numerous villages, intersections, driveways, schools, crosswalks and many other potential conflict points
2.1.6-18	Executive Summary, Final Report , Appendices	Study of Impacts Caused by Exempting the Maine Turnpike and New Hampshire Turnpike from Federal Truck Weight Limits; June 2004; Wilbur Smith Associates	Truck Size & Weight Study
	Abstract: Regulations governing truck size and weight have impacts on highway safety, infrastructure preservation and economic efficiency. In the United States (U.S.), federal laws govern truck size and weight (TS&W) on the Interstate Highway System. Federal TS&W laws are of particular importance to U.S. border-states heavily impacted by the North American Free Trade Agreement. Nearly all this trade travels by truck. Both Canada and Mexico allow significantly higher truck weight limits in their respective counties. As a result, U.S. companies competing against cross-border rivals in natural resource based industries, where profit margins are typically low find it difficult to compete against foreign competition that is able to use more efficient means of transportation.
2.1.6-19	Position Paper	Impact and Analysis of Higher Vehicle Weight Limits on Minnesota Interstate System; March 2011; Minnesota DOT http://transportationproductivity.org/templates/files/minnesota-dot.pdf	CTSW Web Site, Truck Size & Weight Study
	Mn/DOT's Minnesota Truck Size and Weight Project (June, 2006) established Mn/DOT's position with regard to heavier trucks. The study views the topic from a standpoint of balancing infrastructure preservation, safety and economic benefits. Several neighboring states in the upper Midwest and Canada have higher vehicle weight limits than Minnesota. Many agricultural industries in Minnesota are impacted competitively by lower vehicle productivity in Minnesota. Current Truck Size and Weight limits (80,000 pounds on Interstate system) control the amount of payload that can be carried in a truck. An increase in vehicle weight limits would increase the allowable weight per trip, so fewer truck trips would be necessary to carry the same weight. Freight transportation cost savings due to increases in vehicle weight limits would benefit not only shippers and carriers but all consumers. There are two current bills in Congress (HR 763 and HR 801) that proposes increasing vehicle weight limits of vehicles using the national interstate system. These bills both display “opt-in” language, meaning that enabling State legislation is a requirement of the proposed law. This paper was cited in the CTSW Web Site in light of the bridge study. Many bridges on the interstate system would potentially be impacted by this legislation.
2.1.6-20	FR2	Minnesota Truck Size and Weight Project Final Report; 2006; Cambridge Systematics http://www.dot.state.mn.us/information/truckstudy/pdf/trucksizeweightreport.pdf	Truck Size & Weight Study
	This report summarizes the approach, findings, and recommendations of the Minnesota Truck Size and Weight (TS&W) Project led by the Minnesota Department of Transportation (Mn/DOT) in cooperation with other public and private stakeholders. The purpose of the project is to assess changes to Minnesota's TS&W laws that would benefit the Minnesota economy while protecting roadway infrastructure and safety.
2.1.6-21	Texas
	FHWA/TX-10/0-6095-1; FHWA/TX-10/0-6095-2	Potential Use of Longer Combination Vehicles in Texas: First & Second Year Reports (multiple documents); ftp://ftp.dot.state.tx.us/pub/txdot-info/rti/psr/0-6095.pdf	Truck Study, LCV
	Trucking remains the only major freight mode not to benefit from increases in size and weight regulations since 1982. The need for more productive trucks-both longer (LTL) and heavier (TL)-is growing with economic activity, rising fuel costs and concerns over environmental impacts from emissions. This study covers the first year activities of a two-year TXDOT-sponsored study into potential LCV use in Texas. It describes current U.S.LCV operations and regulations, operational characteristics of various LCV types, safety issues, and environmental and energy impacts, together with pavement and bridge consumption associated with LCVs. Methods to measure both pavement and bridge impacts on a route basis are described. A survey of current U.S. LCV operators provides an insight into business characteristics, vehicles, drivers, performance, and safety. The overall study benefited from three sources of direction: an advisory panel from TXDOT, an industry panel comprising heavy truck and LCV operators, and finally an academic team from the University of Michigan Transportation Research Institute. In the second year of the study, a series of routes and LCV types will be evaluated in Texas using methods developed in the first year and approved at a study workshop.
2.1.6-22	Maine and Vermont - multiple studies
	ME_VT_Pilot - 6 month Report; Vermont Final Report	Maine and Vermont Interstate Highway Heavy Truck Pilot Program- 6-Month Report, Congressional Reports, Multiple Documents; Maine and Vermont Pilot Program Congress Report. The Report was prepared by a team of Federal and State Agencies (VDOT, MeDOT); December 2010 https://ops.fhwa.dot.gov/freight/sw/reports/me_vt_pilot_2012/	Truck Size & Weight; Fatigue
	Section 194 of the Consolidated Appropriations Act, 2010 (Public Law (P.L.) 111-117), directs the Secretary of Transportation to study the impacts of the Maine and Vermont truck pilot programs, which replace Federal commercial-vehicle weight regulations with State limits on Interstate highways in those States. Public Law 111-117 also exempts Maine and Vermont from following Federal Bridge Formula B requirements mandated by Section 127 of Title 23, United States Code. Abstract: The purpose of this initial assessment is to report “...to the House and Senate Committee on Appropriations no later than six months after the start of the pilot program on the impact to date of the pilot program on bridge safety and weight impacts.” Accordingly, this report presents the findings of the U.S. Department of Transportation (DOT) analysis which focuses on bridge safety and pavement performance. It discusses truck size and weight regulations in Maine and Vermont prior to and after passage of P.L. 111-117 and provides the most recent weigh-in-motion, registration, and permit data. The report also summarizes the findings of previous truck size and weight studies and highlights methodologies used to determine bridge load and operating ratings. The Final report was a continuation of the findings in the earlier 6-month report, but it also included steel fatigue study on a sampling of bridges. It concluded that the pilot trucks would have little cost and structural impacts on Vermont's network of Interstate bridges. See the Final Report reference under the Vermont Truck Size & Weight Study
2.1.6-23	West Virginia
		An Analysis of Truck Size and Weight FOR WVDOT. (ksowards@njrati.org) Appalachian Transportation Institute, Marshall University, Huntington WV http://www.njrati.org	Truck Size & Weight Study; Cost Allocation
	Abstract: A gap in the body of knowledge in the areas of cost allocation/infrastructure recovery and safety regarding increases in truck size and weight has been identified. The goal of this research is to critically evaluate the claims made by groups advocating for heavier and longer trucks and to update knowledge potential impacts to safety and infrastructure, including economic and fiscal consequences. Given that a Congressionally mandated study will be conducted over the next two years, the focus will be on completing this research effort to supplement the work that is being done by the Federal Highway Administration. The study will be divided into three main areas: safety, infrastructure, and cost recovery
2.1.6-24	Wisconsin
		2009 Wisconsin Truck Size and Weight Study. Multiple documents. Wisconsin Traffic Operations and Safety Laboratory. Cambridge Systematics and Department of Civil and Environmental Engineering: University of Wisconsin-Madison. Available at http://www.topslab.wisc.edu/workgroups/wtsws.html	Truck Size and Weight Study
	This is a valuable study that considers the inclusion of six new heavy truck configurations. Study focuses on the inclusion of these configurations on both state highways as well as the combination of both state and federal highways. The Study does look into several of the other areas that need to be addressed with heavier trucks including permitting and safety; however the evaluation of potential changes to shipping modes is lacking full attention. This is seen in the study's examination of rail-to-truck diversion. This portion of the study lack concrete data and partially relied on expert opinion.
2.1.6-25		Bloomberg- "Kraft Pushes for 97,000-Pound Trucks Called Bridge Wreckers" J. Plungis. Bloomberg.com, December 2011. http://www.bloomberg.com/news/2011-12-12/kraft-leads-push-for-97-000-pound-trucks.html	Truck Size and Weight Study
	Emboldened by U.S. legislation allowing Maine and Vermont to keep 97,000-pound trucks rumbling on their interstate highways, Kraft Foods Inc. and Home Depot Inc. are pressing more states to follow. Companies including Kraft, which says its trucks would drive 33 million fewer miles a year with higher weight limits nationwide, say they need to carry loads more efficiently to combat high diesel-fuel prices. Safety advocates say more heavy trucks would accelerate an increase in truck-related accident deaths, and question whether bridges can withstand the added weight. This was another article sighted by the CTSW web site regarding trucks with GVW over the Federal Limits. It is included here for informational purposes and for understanding issues in general regarding overweight/oversize trucks as perceived by the public.
2.1.6-26	NCHRP 20-07 (303)	Directory Of Significant Truck Size And Weight Research; Jodi L. Carson, P.E., Ph.D. ; Texas Transportation Institute; Texas A&M University System ; October 2011	Truck Size & Weight Study
	A Directory of Significant Truck Size and Weight Research was to provide a brief, well organized summary of significant research related to large truck size and weight for use by decision-makers. In particular, this reference document will benefit those involved in considering possible changes in regulations related to truck size and weight limits. This Directory is intended to address the breadth of all related topic areas and consider research performed by various sponsoring agencies but is not intended to be inclusive of all related research. Instead, this reference guide will be limited to only that related research that is considered to be relevant, significant, and useful. This is a significant document in that it emulates the elements of the current CTSW underway
2.1.6-27	NCHRP 20-68A, Scan 12-01	Advances in State DOT Superload Permit Processes and Practices; NCHRP Project 20-68A U.S. Domestic Scan, April 2014	Superload Permits
	In addition, for documents referencing Methods and Impacts of Bridge Strength Limit State see “Reference Nos.”: 2.2.7-17; 2.2.7-18; 2.3.6-32; 2.3.6-46; 2.3.6-47

2.2 Documents on Methods and Impacts of the Bridge Fatigue Limit State

2.2.1 Introduction

Load induced fatigue has been observed in steel components for over 140 years. The modern day approach to fatigue design of fabricated steel structures was primarily developed during the 1960s and 1970s. This research identified the following major factors impacting fatigue life: stress range, stress cycles, and steel fatigue details. The current code approach is based upon Miner's linear damage rule concerning the cumulative process of fatigue and the determination of stress range as it relates to the stress-life approach. The evaluation of fatigue effects of overweight trucks requires either calculating the effective stress range at the un-cracked details of concern or utilizing site specific stress measurements under the fatigue truck. The overall desk scan on fatigue studies is summarized as follows:

2.2.2 A survey of analysis methods and synthesis of the state of the practice in modeling Fatigue Impact

2.2.2.1 History of steel fatigue study and development

AASHTO published the first fatigue design provisions in 1965. They were completely revised in the 1977 AASHTO Highway Bridge Design Standard Specification, 12th Edition, based on the research results of Dr. John Fisher of Lehigh University and his colleagues. Many specification changes associated with specific details were incorporated annually by AASHTO to improve design as well as fabrication and field performance, however the S-N approach remained unchanged. In 1994 the introduction of the AASHTO LRFD Bridge Design Specification incorporated a reliability-based approach with significant changes to the load models for fatigue design.

2.2.2.2 - State of the Practice in modeling load induced fatigue effect in steel bridges

2.2.2.2.1 - AASHTO Specifications for fatigue design and evaluation

The AASHTO Highway Bridge Standard Specifications and AASHTO LRFD Bridge Design Specifications are referred to for fatigue analysis. Even though the load models are different in these two specifications, the classification of fatigue details, detail illustrative examples, and fatigue detail resistance (Constant Amplitude Fatigue Threshold (CAFT)) remain essentially unchanged. CAFT is a stress range or limit state below which an applied, constant stress range will not create fatigue damage and for which the detail will theoretically have infinite life. A structure rarely experiences a constant stress range. Therefore, the calculated stress range due to site specific data shall be considered to be below half of the CAFT or the variable amplitude fatigue threshold (VAFT) in order to ensure no fatigue damage and to theoretically experience infinite fatigue life for the detail being considered. If the particular detail of concern fails to achieve these thresholds, a more complex finite life fatigue evaluation is required.

For estimating the remaining fatigue life in bridges, the AASHTO Manual for Condition Evaluation and LRFR of Highway Bridges, and the AASHTO Guide Specifications for Fatigue Evaluation of Existing Steel Bridges, have been widely used.

2.2.2.2.2 - Bridge Modeling Methods

Three modeling methods have been commonly used in previous studies as follows:

1. 2D beam model: in this method, the bridge is only modeled in the longitudinal direction and steel stringers are modeled as beam elements. Effects in the transverse direction are considered by utilizing AASHTO's live load distribution factors.
2. 3D beam model: in this method, bridge components including the deck and stringers are modeled as beam elements in both the longitudinal and transverse directions.
3. 3D Finite element model: in this method, more complex elements such as plate element, shell element, etc. are used to model a bridge.

2.2.2.3 Distortion Induced Fatigue Study

Distortion induced fatigue is due to secondary stresses in the steel connection plates that comprise bridge member cross sections. Typically, the effects of secondary stresses are seen at the connections to primary members. However, distortion induced steel fatigue cannot be codified. And methods for prediction of secondary stresses are not speci?cally addressed by the AASHTO specifications. Analysis of distortion induced fatigue requires a detailed Finite-Element model for the specific bridge being considered. Accordingly, limited studies have been focused on using ?nite-element modeling to determine the magnitude of distortion-induced stresses, to describe the behavior of crack development, and to assess the effectiveness of repair alternatives. Importantly, the results indicate severe stress concentration at the crack initiation sites, and typically a low cycle fatigue phenomenon.

2.2.2.4 Fatigue Study on Concrete, reinforcement and pre-stressed concrete strands

AASHTO generally does not specify the investigation of fatigue in concrete decks, considering decks of greater than 9" thickness to have infinite fatigue life. However, decks constructed prior to the 1960s with thickness less than 9 inches or with girder spacing greater than 10 ft may be susceptible to longitudinal flexural cracking which could decrease their service life.

With respect to fatigue in rebar and pre-stressed concrete strands; there is increasing interest and several significant studies including perhaps most notably: The 2003 Minnesota DOT / University of Minnesota study entitled 'Effects of Increasing Weight on Steel and Pre-stressed Bridges' (Section 2.2.5 -1), and the 2013 South Carolina study titled the 'Rate of Deterioration of Bridges and Pavements as Affected by Trucks'. The South Carolina study referenced the following publications as resources:

• Altay, A.K., Arabbo, D.S., Corwin, E.B., Dexter, R.J., French, C.E. (2003)

Effects of Increasing Truck Weight on Steel and Pre-Stressed Bridges, Minnesota Department of Transportation, University of Minnesota.

• Bathias, C., and Paris, P. C., (2005) Gigacycle Fatigue in Mechanical Practice, Marcel Dekker, New York.
• Chowdury, M., Putnam, B., Pang, W., Dunning, A., Dey, K., Chen, L., (2013)
• Rate of Deterioration of Bridges and Pavements as Affected by Trucks, SPR 694, Columbia, South Carolina.
• Helgason, T., Hanson, J. M., Somes, N. F., Corley, W. G., and Hognestad, E., (1976) Fatigue Strength of High-Yield Reinforcing Bars, NCHRP Report 164, Transportation Research Board, National Research Council, Washington D.C.
• Overman, T. R., Breen, J. E., and Frank, K. H., (1984) Fatigue Behavior of Pretensioned Concrete Girders, Center for Transportation Research, University of Texas at Austin, Austin, Texas.
• Paulson, C., Frank, K. H., Breen, J. E., (1983) A Fatigue Study of Pre-stressing Strand, Center for Transportation Research, University of Texas at Austin, Austin, Texas.

The South Carolina study in particular provides a significant amount of data on their 9,271 bridges with respect to truck impacts measured with the fatigue limit state as an indicator of relative bridge damage.

2.2.3 An identification of data needs and an evaluation and critique of available data sources

2.2.3.1 Data needs - Bridge data and fatigue truck data

In order to perform fatigue analysis of overweight truck effects, specific bridge data and truck data are needed. In general, bridge data can be obtained through record drawings to meet the research needs. Typically information in the NBI database is not sufficient to build a bridge model. For truck data, both AASHTO LRFD and Standard specifications (17th Edition) use the 72,000 lb. HS-20 truck as the fatigue truck to represent the large variety of actual trucks of different configurations and weights. The fatigue truck has a constant dimension of 30' between main axles of 32,000 lb. This arrangement approximates the 4 and 5 axle trucks that do most of the fatigue damage to bridges. In previous overweight truck and fatigue studies, various overweight trucks up to 119,000 lb. GVW, were analyzed as fatigue loads. For example, research in Louisiana limited truck GVW to 100,000 lbs., and research in Indiana used trucks ranging in GVW from 54,400 lb. for Class 9 vehicles to 119,500 lb. for Class 13 vehicles. In some cases, Strains measured in the field have also been used to calibrate stress ranges obtained from analysis and modeling.

2.2.3.2 Critique of available data sources

• The fatigue mechanism has been extensively researched and S_N curves were developed primarily based on fatigue test data derived by Dr. John Fisher and his colleagues under constant amplitude cycle loading.
• Previous studies on overweight truck effects have primarily been a product of state sponsored research using limited WIM data in accordance with the state's needs. There hasn't been a uniform standard for overweight trucks used for the fatigue studies across the nation.
• The results of previous studies are not consistent. For example, the 1983 "Steel Bridge Members under variable amplitude, long life fatigue loading" study, by Dr. Fisher, et al. concluded that the results obtained from variable amplitude tests were consistent with the previously reported constant amplitude test. However, NCHRP Report 721 'Fatigue Evaluation of Steel Bridges' stated that "the S-N curve development based on constant amplitude stress range testing results is different from that derived from variable amplitude test data, because the latter involves a new dimension of uncertainty associated with the load effect". The authors did not elaborate on the difference in the report, but mentioned that the Eurocode and the Australian code both use multiple slopes instead of a single slope developed based on the constant amplitude stress range testing results.

2.2.4 An assessment of the current state of the understanding of the impact and needs for future research, data collection and evaluation

2.2.4.1 Assessment of the current state of the understanding of the impact

Load induced fatigue in steel bridges was extensively studied in the 1970s and developed into the current AASHTO standards. Specifically, bridge connection details are grouped into categories A to E' based on their level of fatigue strength/resistance. Based on Dr. Fisher's study, the 5 ksi stress range represents an approximate upper bound of stress ranges observed on actual bridges. The majority of the stress ranges observed on actual bridges have been between 1 ksi and 3 ksi. The expected stress cycles on most bridges are between 10 million and 150 million. Through damage accumulation analysis, it was found that actual truck traffic closely correlates the effects of the fatigue design truck and that heavy traffic will not cause severe fatigue problems on steel girders with fatigue details of categories A, B and C. The AASHTO LRFD Design Specifications C6.6.1.2.3 state that "Experience indicates that in the design process the fatigue considerations for Detail Categories A through B' rarely, if ever, govern". The S-N curves for fatigue detail categories D through E' are within this area of greater concern. This observation is consistent with experience in that fatigue failure has not been reported for categories A through C, but has occurred in categories D, E and E'.

It was also found that factors influencing the level of fatigue damage caused by a given vehicle are axle weights and spacing. In general, state specific overweight truck studies have been performed in accordance with AASHTO specifications and guidance, plus field strain measurement. These studies did not distinguish the impact and passing cycles of trucks of specific types or axle weights and configurations, therefore they were not configured to answer the questions the 2014 CTSW Study is intending to address.

2.2.4.2 Need for future data collection and research

The following areas of further study are recommended in order to better understand and quantify the fatigue life impacts due to load induced fatigue in steel bridges:

• Further study using WIM data and strain values on multiple bridge types and fatigue category details in heavy load corridors to more definitively predict long term fatigue behavior under low magnitude and variable amplitude cycle loading.
• Calibration of S-N curves for the potential new fleets under variable amplitude cycle loading on steel bridges.
• Further study of fatigue behavior on concrete and pre-stressed concrete bridges of varying span lengths and support fixity under low magnitude and variable amplitude cycle loading.

2.2.5 A synthesis of quantitative results of past studies with past prospective and retrospective estimates in each category of effect, including reasonable ranges of values for impact estimates

1. Results of 2003 Minnesota DOT "Effects of Increasing Truck Weight on Steel and Pre-stressed Bridges", (Altay et al., 2003). This study evaluated the effects of increasing the legal truck weight by 10 or 20% on 5 steel girder bridges and three pre-stressed I-girder bridges that were instrumented. It was discovered that: (1) Fatigue is insensitive to loading that occurs less frequently than 0.01% of all load cycles; (2) an increase in truck weight of 20% would lead to a reduction in the remaining life in their older steel bridges of up to 42% and a 10% increase would lead to a 25% reduction in fatigue life; (3) typical Minnesota pre-stressed concrete girders and concrete decks were found not to be susceptible to fatigue for truck weights increased by 20%.
2. Results of 2005 Wang et al. "Influence of Heavy Trucks on Highway Bridges": it was observed that: (1) traffic induced flexural stress does not necessarily increase with Gross Vehicle Weight (GVW), but is highly related to axle weights and configurations; (2) there was very little difference in maximum strain (and stress) ranges induced by a 5 axle 80,000 lb. truck and the 134,000 lb. 9 and 11 axle trucks. The 5 axle 80,000 lb. truck did however produce the largest maximum strain range.
3. Results of 2006 FHWA "Fatigue of older Bridges in Northern Indiana due to Overweight and Oversized Loads" indicated that less than 1 percent of the trucks induce a strain range that exceeds the variable amplitude fatigue limit of the fatigue critical details in the structures in spite of heavy loads (more than 200,000 lbs) being carried.
4. Results of 2008 FHWA "Monitoring System to determine the impact of Sugarcane Truckloads on Non-Interstate Bridges" indicated the estimated fatigue cost is $11.75 per trip per bridge for a 120,000 lb. GVW truck and $0.90 per trip per bridge for a 100,000 lb. GVW truck.
5. Results of 2013 LTRC "Load Distribution and Fatigue Cost Estimates of Heavy Truck Loads on Louisiana State Bridges" indicated that if bridges are exposed to high cycles of repetition of heavy loads, the life span of the bridges will be reduced by about 50%.

Of the previous studies reviewed, only the 2003 Minnesota DOT "Effects of Increasing Truck Weight on Steel and Pre-stressed Bridges" study evaluated the effects of increasing the legal truck weight on fatigue detail categories E and E'. But this study was limited to (presently) legal trucks of up to 66 kips GVW. The 2013 SCDOT Final Report of the 'Rate of Deterioration of Bridges and Pavements as Affected by Trucks', conducted jointly with Clemson University, was based on a finite element analysis of four 'archetypal' concrete bridge types in response to typical truck types determined to best represent the existing fleet based on WIM data analysis. It focused on fatigue in steel rebar and pre-stressed strands in slabs and beams respectively, concrete being the by far the most prevalent material type in South Carolina bridges. The following table compares these two studies to the 2014 CTSW Study.

Major Fatigue Study Results

Study	2003 Minnesota DOT Study	2013 SCDOT Study	2014 CTSW Study
Fatigue Trucks	54 kip Truck (HS15) 58 kip Truck 66 kip Truck	Multiple axle groups of 2 through 8 axles, with range of axle weights reflecting WIM data analysis	3S2-80 kip Truck 3S2-88 kip Truck 3S3-91 kip Truck 3S3-97 kip Truck 2S1-2-80 kip Truck (28.5' trailer) 2S1-2-80 kip Truck (33' trailer) 2S1-2-2 105.5 kip Truck 3S2-2-2-129 kip Truck
Bridge Data	4 span continuous (Category E') 3 span continuous (Category E) Multiple span continuous plate girder (Category C) 2 span continuous (Category E')	Reinforced concrete slab, 33 ft. span Pre-stressed: Conc. beam, < 66' span; Conc. Beam, 66' to 115'; Conc. Beam, 115' to 148'	Short span (42') simply supported bridge (Category E') Long span (133') simply supported bridge (Category E) 3 span continuous bridge (Category E) 5 span continuous bridge (Category E)
Results	Bridges that did not have E or E' details had infinite fatigue lives under all situations including a 10% increase in truck weight; bridges with category D or better details and with connection plates attached to both flanges are not as susceptible to fatigue. An increase in truck weight of 20% would lead to a reduction in the remaining life in these older steel bridges of up to 42% and a 10% increase would lead to a 25% reduction in fatigue life.	“A 10% to 20% increase allowable gross vehicle weight did not have a significant impact on the fatigue life of bridges” (quoting Helgason et al, 1976) Fatigue damage (unitless share of all damage) attributable to each truck model Annual South Carolina bridge damage costs	12% higher main axle weights result in an incremental 25 to 27% negative effect on fatigue life. The addition of the third axle to the rear axle grouping results in a negative effect on fatigue life on the order of 29 to 54%. A negative incremental effect on fatigue life will be up to 66% due to the closely spaced axles.

2.2.6 Summary

Load induced fatigue behavior on steel bridges has been well studied under constant amplitude cycle loading and AASHTO has established design specifications and evaluation specifications for fatigue behaviors based on those studies. Essentially, fatigue life is inversely proportional to the cube of the effective stress range per AASHTO. With the increase of size and passing cycles of overweight trucks, fatigue behavior under low magnitude and variable amplitude cycle loading has attracted more attention from engineers and researchers recently and would be a direction of future research.

2.2.7 List of References

Methods and Impact of the Bridge Fatigue Limit State

Reference No.	Document No.	Document Title and Link	Relevance to Study
2.2.7-1	ASCE JBE 2005 10:1 -12	Truck Loading and Fatigue Damage Analysis for Girder Bridges Based on Weigh-in-Motion Data. Wang, Liu, Huang, Shahawy, ASCE Journal of Bridge Engineering, 2005 http://ascelibrary.org/doi/pdf/10.1061/%28ASCE%291084-0702%282005%2910%3A1%2812%29	Fatigue
	Based on data collected by weigh-in-motion (WIM) measurements, truck traffic is synthesized by type and loading condition. Three-dimensional nonlinear models for the trucks with significant counts are developed from the measured data. Six simply supported multi-girder steel bridges with spans ranging from 10.67 m (35 ft) to 42.67 m (140 ft) are analyzed using the proposed method. Road surface roughness is generated as transversely correlated random processes using the autoregressive and moving average model. The dynamic impact factor is taken as the average of 20 simulations of good road roughness. Live-load spectra are obtained by combining static responses with the calculated impact factors. A case study of the normal traffic from a specific site on interstate highway I-75 is illustrated. Static loading of the heaviest in each truck type is compared with that of the AASHTO standard design truck HS20-44. Several important trucks causing fatigue damage are found.
2.2.7-2	NSBA	A Fatigue Primer for Structural Engineers; Fisher, John W., Lehigh University; Kulak, Geoffrey L, University of Alberta; Smith, Ian F. C., Swiss Federal Institute of Technology; National Steel Bridge Alliance; 1998 http://www.aisc.org/store/p-1638-a-fatigue-primer-for-structural-engineers-pdf-download.aspx	Fatigue, Fracture Critical, Design
	This publication from the NSBA provides guidelines for the understanding of fundamentals in the fatigue of metals, and the recognition of fracture critical details. The purpose of this publication is to provide a background of (information) to understand the design rules for fatigue strength that are currently part of the design codes for fabricated steel structures
2.2.7-3	AISC -1977	Bridge Fatigue Guide Design and Detail; 1977; Fisher, John W., Lehigh University, 1977 http://www.aisc.org/search.aspx?id=3852&keyword=Bridge Fatigue Guide Design & Detail	Fatigue Guide
	This document is a guide and introduction to the fatigue problems in bridges, provides design details to optimize fatigue strength, concepts, considerations and examples for bridge engineers and designers.
2.2.7-4	NYSDOT TA 12-002	Fatigue Evaluation 100% Hand-on Exemption; NYSDOT Technical Advisory for Bridge Engineer / Inspectors, 2012 https://www.dot.ny.gov/divisions/engineering/structures/repository/manuals/inspection/bim_ta12-002.pdf	Fatigue, Inspection
	This document provides the means and methods for exempting the inspection of fatigue sensitive and fracture critical details by NYSDOT using various AASHTO publications. It is an indication of current practice by DOT's around the country.
2.2.7-5	NCHRP Project 12-15	Members Under Variable Amplitude, Long Life Fatigue Loading, Final Report; 1983 Fisher, J. W., D. R. Mertz, and A. Zhong. Steel Bridge Lehigh University, Bethlehem, Pa. http://preserve.lehigh.edu/engr-civil-environmental-fritz-lab-reports/2246.	Fatigue
2.2.7-6	FHWA/IN/JTRP-2005/16-1	Fatigue of Older Bridges in Northern Indiana due to Overweight and Oversized Loads - Volume 1& 2: Bridge and Weigh-In-Motion Measurements; 2006; James A. Reisert and Mark D. Bowman; Purdue University; Indiana DOT; Joint Transportation Research Program http://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1726&context=jtrp	Fatigue, Over-weight Truck Study, WIM
	Abstract: This report is the first of a two-volume final report presenting the findings of the research work that was undertaken to evaluate the fatigue behavior of steel highway bridges on the extra heavy weight truck corridor in Northwest Indiana. The purpose of the study was to evaluate the type and magnitude of the loads that travel along the corridor and then assess the effect of those loads on the fatigue strength of the steel bridge structures. This volume presents the results of the experimental field study conducted to evaluate the load and load effects on one steel bridge structure on the corridor. A weigh-in-motion (WIM) system was installed near the bridge structure to evaluate the loads that would cross over the bridge being monitored. Strain values were monitored on two spans of the ten-span continuous bridge. Comparisons were then made between strain measurements in particular girders and strain values predicted using the measured truck axle weights. The WIM data indicated that 15% of the Class 9 trucks and 26% of the Class 13 trucks travel heavier than their respective legal limits. Extreme weights of more than 200,000 lbs were observed. In spite of the heavy truck loads being carried, it was found that less than 1 percent of the trucks induce a strain range that exceeds the variable amplitude fatigue limit of the fatigue critical details in the structure being monitored. Lastly, it was found that three dimensional analytical models provide the best agreement between predicted and measured strain values in the bridge. The titles of the two volumes (Report Number in parentheses) are listed below: Volume 1: Bridge and Weigh-In-Motion Measurements (FHWA/IN/JTRP-2005/16-1) Volume 2: Analysis Methods and Fatigue Evaluation (FHWA/IN/JTRP-2005/16-2)
2.2.7-7	TRB Report 299	Fatigue Evaluation Procedures for Steel Bridges; F. Moses, C.G. Schilling, K.S. Raju, Case Western Reserve University http://www.trb.org/Publications/Pages/262.aspx	Fatigue
	The primary purpose of this study was to develop improved procedures for the fatigue evaluation of existing steel bridges. A secondary objective was to develop improved procedures for the fatigue design of new steel bridges. The evaluation procedures are recommended for inclusion as Section 6 in the AASHTO Manual for Maintenance Inspection of Bridges and the design procedures are recommended for inclusion as Articles 10.3.1 and 10.3.2 in the AASHTO Standard Specifications for Highway Bridges.
2.2.7-8	FHWA-IF-12-052	US Department of Transportation Federal Highway Administration, Steel Bridge Design Handbook, Design for Fatigue https://www.fhwa.dot.gov/bridge/steel/pubs/if12052/volume12.pdf	Fatigue
	Fatigue in metals is the process of initiation and growth of cracks under the action of repetitive tensile loads. If crack growth is allowed to go on long enough, failure of the member can result when the uncracked cross-section is sufficiently reduced such that the member can no longer carry the internal forces or the crack extends in an unstable mode. The fatigue process can take place at stress levels that are substantially less than those associated with failure under static loading conditions. The usual condition that produces fatigue cracking is the application of a large number of load cycles. Consequently, the types of civil engineering applications that are susceptible to fatigue cracking include structures such as bridges. This document provides the practicing engineer with the background required to understand and use the design rules for fatigue resistance that are currently a standard part of design codes for fabricated steel structures.
2.2.7-9	NSCC2009	Fatigue Prone Details in Steel Bridges; El Emrani, M; Kliger, R.; Chalmers University of Technology, Göteborg, Sweden http://www.nordicsteel2009.se/pdf/147.pdf	Fatigue
	Abstract: This paper reviews the results of a large investigation of more than 100 fatigue damage cases, reported for steel and composite bridges. The damage cases were categorized according to the type of detail in which they were encountered and the mechanisms behind fatigue damage in each category were identified and studied. It was found that more than 90% of all reported damage cases are of the deformation-induced type and are generated by some kind of unintentional or otherwise overlooked interaction between different load-carrying members or systems in the bridge. Poor detailing, with unstiffened gaps and abrupt changes in stiffness at the connections between different members, also contributed to fatigue cracking in most details.
2.2.7-10	ASCE-SE-1995	Fatigue-Based Methodology for Managing Impact of Heavy-Permit Trucks on Steel Highway Bridges, Dicleli, Bruneau, ASCE Journal of Structural Engineering, 1995 http://www.tucsa.org/images/yayinlar/makaleler/ASCE-SE-1995-high-cycle-fatigue-in-steel-bridges.pdf	Fatigue
	Currently, in many areas of North America, special permits are issued to extra heavy vehicles without a detailed evaluation of individual components, considering only the ultimate capacity of the bridge inventory as a whole. Based on this, a large number of special permits have been issued to extra heavy vehicles. In this perspective, the ultimate and cumulative effect of such overloads on steel bridge components was studied. It was found that steel bridge members have adequate ultimate capacity to accommodate such overloads; however, they may suffer fatigue damage due to the cumulative effect of these overloads. Accordingly, a fatigue-based methodology was developed to assess the reduction in service life of bridges due to heavy-permit trucks. It is found that a reasonably large number of special permits can be issued at small reductions in fatigue life, but because stress ranges in excess of the constant-amplitude fatigue limit significantly alter the shape of the S-N curve, it is essential to appreciate that the concept of infinite fatigue life cannot be relied upon anymore.
2.2.7-11	FL/DOT/RMC/6672-379	Influence of Heavy Trucks on Highway Bridges, Ton-Lo Wang, Chunhua Liu, Florida International University, 2000 http://www.dot.state.fl.us/research-center/Completed_Proj/Summary_STR/FDOT_BC379_rpt.pdf	Fatigue
	The objective of this study includes the following aspects: (1) synthesize truck traffic data collected through WIM measurements; (2) establish live-load spectra; (3) perform fatigue damage analysis for typical bridges; (4) carry out static and dynamic analyses. Three-dimensional nonlinear mathematical models of typical trucks with significant counts are developed based on the measured axle weights and configurations. Road surface roughness is simulated as transversely correlated random processes. The multi-girder bridges are treated as a grillage beam system.
2.2.7-12	FHWA/LA.06/418	Monitoring System to Determine the Impact of Sugarcane Truckloads on Non-Interstate Bridges; Saber Aziz, Freddy Roberts, Louisiana Tech University, 2008 http://www.ltrc.lsu.edu/pdf/2009/fr_418.pdf	Fatigue
	The study included in this report assessed the strength, serviceability, and economic impact caused by overweight trucks hauling sugar cane on Louisiana bridges. Researchers identified the highway routes and bridges being used to haul this commodity and statistically chose samples to use in the analysis. Approximately 84 bridges were involved in this study. Four different scenarios of load configuration were examined: 1. GVW = 100,000 lb., with a maximum tandem load of 48,000 lb., 2. GVW = 100,000 lb., with a maximum triple axle load of 60,000 lb., 3. Uniformly distributed tandem and triple axle loads, and 4. GVW = 120,000 lb., with maximum tandem of 48,000 lb., and maximum triple axle of 60,000 lb. It is to be noted that a GVW of 120,000 lb. for sugarcane haulers was the highest level currently considered in this investigation. The methodology used to evaluate the fatigue cost of bridges was based on the following procedures: 1) determine the shear, moment, and deflection induced on each bridge type and span, and 2) develop a fatigue cost for each truck crossing with a) a maximum GVW of 120,000 lb., and b) a GVW of 100,000 lb. with a uniformly distributed load. Through the use of a field calibrated finite element model, Structure 03234240405451 was analyzed and load rated for loading vehicles HS-20, 3S2 and 3S3 (sugar cane loading cases 1 thru 4). The structure had adequate strength to resist both bending and shear forces for all six loading vehicles. It should be noted that all of the rating factors were acceptable for all 17 spans as long as the construction and the structural condition of each span were the same. Results indicate that among the four cases of loading configurations, Case 4, which was a GVW=120,000 lb. with maximum tandem and triple axle loads, generated the worst strength and serviceability conditions in bridges. Therefore, Case 4 is the loading configuration that controls the strength analysis and evaluation of fatigue cost for bridge girders. Based on the controlling load configuration, Case 4 with a GVW = 120, 000 lb., the estimated fatigue cost is $11.75 per trip per bridge. In Case 3, which was a GVW = 100,000 lb. uniformly distributed load; the estimated cost is $0.90 per trip per bridge. The results from the bridge deck analyses indicate that the bridge deck is under a stable stress state, whether the stresses are in the tension zone or the compression zone. Moreover, the decks of bridges with spans longer than 30 ft. may experience cracks in the longitudinal direction under 3S3 trucks. Such cracks will require additional inspections along with early and frequent maintenance. Based on the results of the studies presented in this report, it is recommended that truck configuration 3S3 be used to haul sugar cane with a GVW of 100,000 lb. uniformly distributed. This will result in the lowest fatigue cost on the network. It is recommended that truck configuration 3S3 not be used to haul sugar cane with GVW of 120,000 lb. This will result in high fatigue cost on the network and could cause failure in bridge girders and bridge decks.
2.2.7-13	2010 Vol. 4:10-35 ISSN 1934-7359	Economic Impact of Higher Timber Truck Loads on Louisiana Bridges; Saber Aziz, Louisiana Tech University, Journal of Civil Engineering and Architecture, 2010 http://www.davidpublishing.com/davidpublishing/Upfile/5/21/2013/2013052171895729.pdf	Fatigue
	Due to the limited amount of funds available for bridge inspection, maintenance and rehabilitation, the evaluation of load capacity for existing bridges is crucial to the Louisiana Department of Transportation to development in general. This paper includes the development of a methodology to assess the economic impact of overweight vehicles with permits, hauling Louisiana harvest products on state bridges. The proposed higher truck loads are applied on the existing bridges and their effects are determined using deterministic load capacity evaluations as well as reliability assessments. The target reliability level is derived from bridge structures designed to satisfy AASHTO Standard Design Specifications and also satisfy safe and adequate performance levels. The amount of harvest produced is used to select a representative sample of bridges to provide specific examples of expected changes in load ratings and safety levels. The bridges include simple and continuous span behavior. Strength and serviceability criteria are investigated under current legal loads and the expected changes, due to the proposed new weights, are determined. The results are used to assess the cost of crossing a bridge and the permit fees for the proposed truck weight regulation.
2.2.7-14	FHWA/LA.13/509	Load Distribution and Fatigue Cost Estimates of Heavy Truck Loads on Louisiana State Bridges, Aziz Saber, 201, LDOT, Louisiana Tech University http://www.ltrc.lsu.edu/pdf/2013/FR_509.pdf	Fatigue
	The bridge in this study was evaluated and a monitoring system was installed to investigate the effects of heavy loads and the cost of fatigue for bridges on state highways in Louisiana. Also, this study is used to respond to Louisiana Senate Concurrent Resolution 35 (SCR-35). The superstructure of the bridge in this study was evaluated for safety and reliability under four different kinds of truck configuration and loads hauling sugarcane. The bridge model was verified by performing live load tests using 3S3 trucks with a gross vehicular weight (GVW) of 100,000 lb. on the structure. The bridge finite element model was analyzed under the different kinds of loading and the effects were listed and compared. The results of the analyses show that the pattern of response of the bridge under the different cases follows the same trend. Among the four different cases of loading configurations, case 4, which was GVW =148,000 lb. and a vehicle length of 92 ft., produced the largest tensile and compressive stresses in the members. The results from the bridge deck analyses confirm that the bridge deck is under a stable stress state, whether the stresses are in the tension zone or the compression zone. The heavy load as indicated in SCR-35 will cause damage to bridges. The data from the monitoring system indicates that the average number of heavy loads during October, November, and December is 3.5 times higher than the rest of the year. The bridges are exposed to high cycles of repetition of heavy loads that will reduce the life span of the bridges by about 50%. The bridges that are built to last 75 years will be replaced after about 40 years in service. This seasonal impact is due to the sugarcane harvest and confirms the cost of fatigue, $0.9 per truck per trip per bridge, as determined in the previous study. Based on the results of the studies presented in this report, increasing the gross vehicle weight of sugarcane trucks is not recommended. The heavy loads indicated in SCR-35 will cause premature fatigue damage to the main structural members and could cause their eventual structural failure. In addition, the majority of the Louisiana bridges currently in service were designed to accommodate lower loads than the bridge tested on this project. Therefore, based on the test results, one should expect that the proposed trucks will significantly shorten the remaining life span of Louisiana bridges. All these bridges should be rehabilitated prior to implementing SCR 35. The data from the monitoring system will provide a good source of information to review the current serviceability criteria used by the Louisiana Department of Transportation and Development (LADOTD) for the design of prestressed concrete bridge girders. It appears that the ultra-heavy weight trucks will subject the bridges to excessive stresses in the girders and may be approaching the ultimate strength of the superstructures. Indeed under such circumstances the bridges will suffer. However, the fatigue design is a separate issue. Bridges are not necessarily replaced when they reach the end of the fatigue life. Rather fatigue details are retrofitted or removed allowing the bridge to continue to service traffic in its original form.
2.2.7-15	ASCE JBE 2003 8:5-259	Finite-Element Analysis of Steel Bridge Distortion-Induced Fatigue, Roddis, Zhao, 2003 ASCE Journal of Bridge Engineering http://ascelibrary.org/doi/pdf/10.1061/%28ASCE%291084-0702%282003%298%3A5%28259%29	Fatigue
	Welded plate girder bridges built before the mid-1980s are often susceptible to fatigue cracking driven by out-of-plane distortion. However, methods for prediction of secondary stresses are not speci?cally addressed by bridge design speci?cations. This paper presents a ?nite-element study of a two-girder bridge that developed web gap cracks at ?oor truss-girder connections. The modeling procedures performed in this research provide useful strategies that can be applied to determine the magnitude of distortion-induced stresses, to describe the behavior of crack development, and to assess the effectiveness of repair alternatives. The results indicate severe stress concentration at the crack initiation sites. The current repair method used at the positive moment region connections is found to be acceptable, but that used at the negative moment region connections is not satisfactory, and additional ?oor truss member removal is required. Stress ranges can be lowered below half of the constant amplitude fatigue threshold, and fatigue cracking is not expected to recur if the proposed retro?t approach is carried out.
2.2.7-16	TRB 2003 Annual Meeting	Finite Element Study of Distortion-Induced Fatigue in Welded Steel Bridges http://www.ltrc.lsu.edu/TRB_82/TRB2003-001245.pdf	Fatigue
	Out-of-plane distortion-induced fatigue cracking is caused by relative rotation and displacement between longitudinal girders and transverse members framing into these girders. Procedures for determination of secondary stresses are not specified in the design or rating process. This paper presents appropriate finite element method procedures to analyze distortion-induced fatigue behavior. A multi-girder bridge developed web gap cracks near the girder bottom flange in a positive moment region. The affected diaphragm-girder connections were repaired by installing additional reinforcing splice plates to the web and attaching connection stiffeners to the flanges. Since no structural modifications were made to similar details in the bridge that had not developed fatigue cracks, concerns remain that these details may also be subjected to high magnitude fatigue stresses that may lead to future cracking. By using finite element sub-modeling techniques, potential crack initiation sites in the bridge were identified and the corresponding distortion-induced stresses were determined. The most stressed detail reached yielding with an out-of-plane displacement of only a few thousandths of an inch. Based on the analytical results, a linear stress displacement correlation was established for prediction of the secondary stresses. Repair analysis indicated that web gap stresses can be significantly reduced if a rigid stiffener-to-flange attachment is used. Thus, a bolted repair is recommended for the positive moment region connections and a welded repair is recommended for the transition and negative moment region connections.
2.2.7-17	MN/RC-2003-16	Effects of Increasing Truck Weight on Steel and Pre-stressed Bridges http://www.dot.state.mn.us/ofrw/PDF/200316.pdf
	Any increase in legal truck weight would shorten the time for repair or replacement of many bridges. Five steel girder bridges and three pre-stressed concrete I-girder bridges were instrumented, load tested, and modeled. The results were used to assess the effects of a 10 or 20% increase in truck weight on bridges on a few key routes through the state. Essentially it was found that all pre-stressed girders, modern steel girders, and most bridge decks could tolerate a 20% increase in truck weight with no reduction in life. Unfortunately, most Minnesota steel girder bridges were designed before fatigue-design specifications were improved in the 1970's and 1980's. Typically, an increase in truck weight of 20% would lead to a reduction in the remaining life in these older steel bridges of up to 42% (a 10% increase would lead to a 25% reduction in fatigue life). Bridge decks are affected by axle weights rather than overall truck weights. Transverse cracks in bridge decks are primarily caused by shrinkage soon after construction and are not affected by increasing axle weight. However, decks with thickness less than 9 inches or with girder spacing greater than 10 ft may be susceptible to longitudinal flexural cracking which could decrease life. This is an important finding for the current study in general and as it relates to crack propagation in bridge decks.
2.2.7-18	FHWA/TX-07/0-1895-1	Evaluation of Serviceability Requirements for Load Rating Pre-stressed Concrete Bridges; Wood, S. L., M. J. Hagenberger, B. E. Heller, and P. J. Wagener. 2007. Texas Department of Transportation, Jan. 2007 http://fsel.engr.utexas.edu/publications/detail.cfm?pubid=626092718	Load Rating, Pre-Stressed Concrete; Fatigue,
	Within Texas, the procedures in the AASHTO Manual for Condition Evaluation of Bridges (MCEB) are used to determine the load rating of existing structures. A large number of pre-stressed concrete bridges that were constructed in the 1950s and 1960s have load ratings that fall below the minimum design vehicle specified in the MCEB. The load ratings for this group of bridges are typically controlled by the serviceability limit state criterion related to the tensile stress in the concrete. A low load rating implies that these bridges have experienced damage under service loads. However, observations made by TXDOT personnel during routine inspections indicate that the condition of these bridges is very good, and that there are generally no signs of deterioration. Based on the results of the diagnostic load tests and laboratory fatigue tests, it was concluded that the tensile stress criterion in the MCEB should not be used to evaluate existing pre-stressed concrete bridges. The calculated tensile stress in the concrete is not a reliable indicator of the stresses induced in the strand due to live load. Conservative guidelines for considering the fatigue limit state explicitly in the load rating process were developed.
2.2.7-19	MN/RC - 2005-38	Analysis of Girder Differential Deflection and Web Gap Stress for Rapid Assessment of Distortional Fatigue in Multi-Girder Steel Bridges; MN/DOT http://www.lrrb.org/media/reports/200538.pdf	Steel & RC Fatigue
	Abstract: Distortion-induced fatigue cracking in unstiffened web gaps is common in steel bridges. Previous research by the Minnesota Department of Transportation (Mn/DOT) developed methods to predict the peak web gap stress and maximum differential deflection based upon field data and finite element analyses from two skew supported steel bridges with staggered bent-plate and cross-brace diaphragms, respectively. This project aimed to test the applicability of the proposed methods to a varied spectrum of bridges in the MN/DOT inventory. An entire bridge model (macro-model) and a model encompassing a portion of the bridge surrounding the diaphragm (micro-model) were calibrated for two instrumented bridges. Dual-level analyses using the macro- and micro-models were performed to account for the uncertainties of boundary conditions. Parameter studies were conducted on the prototypical variations of the bridge models to define the sensitivity of diaphragm stress responses to typical diaphragm and bridge details. Based on these studies, the coefficient in the web gap stress formula was calibrated and a linear prediction of the coefficient was proposed for bridges with different span lengths. Additionally, the prediction of differential deflection was calibrated to include the influence of cross bracing diaphragms, truck loading configurations and additional sidewalk railings. A simple approximation was also proposed for the influence of web gap lateral deflection on web gap stress.
2.2.7-20	ACI 215R-74	ACI 215R-74 Consideration for Design of Concrete Structures Subjected to Fatigue Loading ACI Code	Concrete Fatigue
	In recent years, considerable interest has developed in the fatigue strength of concrete members. There are several reasons for this interest. First, the widespread adoption of ultimate strength design procedures and the use of higher strength materials require that structural concrete members perform satisfactorily under high stress levels. Hence there is concern about the effects of repeated loads on, for example, crane beams and bridge slabs. Second, new or different uses are being made of concrete members or systems, such as pre-stressed concrete railroad ties and continuously reinforced concrete pavements. These uses of concrete demand a high performance product with an assured fatigue strength. Third, there is new recognition of the effects of repeated loading on a member, even if repeated loading does not cause a fatigue failure. Repeated loading may lead to inclined cracking in pre-stressed beams at lower than expected loads, or repeated loading may cause cracking in component materials of a member that alters the static load carrying characteristics. This report is intended to provide information that will serve as a guide for design for concrete structures subjected to fatigue loading. However, this report does not contain the type of detailed design procedures sometimes found in guides.
2.2.7-21	ENGINEERING JOURNAL Volume 17 Issue 1	Finite Element Analysis of Distortion-Induced Web Gap Stresses in Multi-I Girder Steel Bridges, Akhrawat Lenwari1, (Chulalongkorn University), Huating Chen (Beijing University of Technology), 2012 http://engj.org/index.php/ej/article/view/322/271	Distortion Fatigue
	Abstract: Unstiffened girder web gaps at the ends of transverse stiffeners that also serve as diaphragm connection plates are subjected to high local stresses during cyclic out-of-plane distortion. The out-of-plane distortion is mainly caused by the differential deflection between adjacent girders. The purpose of the paper is to investigate the effects of bridge parameters including span length, girder spacing, slab thickness, and girder stiffness on the differential deflection and distortion-induced web gap stresses. Dual-level finite element analyses that consist of both global model and sub-model were performed. The global model was used to investigate the critical truck position and maximum differential deflection between adjacent girders, while the sub-model was used for the critical web gap vertical stress. A base case bridge was a simply supported composite superstructure with three steel I-girders that support two traffic lanes, which is typical for steel bridges over intersections in Bangkok, Thailand. A parametric study was conducted by varying one bridge parameter at a time. The analysis results show that the maximum differential deflections and web gap stresses caused by one-truck loading are higher than those caused by two-truck loading (one truck on each lane). Under one-truck loading, the maximum web gap stress occurs at the interior girder. In addition, both the differential deflections and web gap stresses are primarily dependent on the bridge span length.
2.2.7-22	NCHRP SYN 354	NCHRP Synthesis 354: Inspection and Management of Bridges with Fracture Critical Details; Conner, Robert, Purdue University; Dexter, Robert, University of Minnesota, 2005 http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_syn_354.pdf	Fatigue
	This report is focused on inspection and maintenance of bridges with fracture-critical members (FCMs). The AASHTO LRFD Bridge Design Specifications (LRFD Specifications) defines an FCM as a “component in tension whose failure is expected to result in the collapse of the bridge or the inability of the bridge to perform its function.” Note that the FCM can refer to a component such as a flange of a girder and does not necessarily include the whole “member.” Approximately 11% of the steel bridges in the United States have FCMs. Most of these (83%) are two-girder bridges and two-line trusses, and 43% of the FCMs are built-up riveted members. The objectives of this synthesis project were to: Survey the extent of and identify gaps in the literature; Determine best practices and problems with how bridge owners define, identify, document, inspect, and manage bridges with fracture-critical details; and Identify research needs
2.2.7-23	TRB 1696	Highway Network Bridge Fatigue Damage Potential of Special Truck Configurations; International Bridge Engineering Conference; National Research Council; 2000, Jeffrey A. Laman, John R. Ashbaugh; http://academic.research.microsoft.com/Publication/27566789/highway-network-bridge-fatigue-damage-potential-of-special-truck-configurations	Fatigue; Truck Configuration
	A study of the fatigue damage potential of special truck configurations was conducted to facilitate informed decisions by state transportation agencies in considering various truck size and weight and permit policies as well as to provide relative damage information that will be useful in ongoing network damage evaluations. The primary objective was to evaluate 78 existing common and FHWA-proposed truck configurations for relative fatigue damage potential. To accomplish this objective, an analytical fatigue evaluation tool was developed to determine the relative fatigue damage induced in highway network bridges by simulation of a highway fleet mix database crossing actual bridges modeled analytically. Additional objectives were to evaluate the influence of impact values and endurance limits used for a fatigue analysis. The semi-continuum analysis method, the Palmgren-Miner hypothesis, and the rain flow cycle counting algorithm are incorporated. A 39-bridge database statistically selected as representative of bridges in the United States allowed a network level fatigue analysis of several hundred fatigue-prone details. Seventy-eight special truck configurations were studied, 25 of which were developed by FHWA as part of the comprehensive truck size and weight study. The remaining 53 vehicles were taken from the Turner proposal, Michigan, Pennsylvania, Canada, military, AASHTO, and other sources. It was found that fatigue damage potential is primarily a function of axle weight, spacing, and vehicle length instead of gross vehicle weight. The importance and relevance of this study was that it suggested a method to rate fatigue damage relative to truck GVW and configuration as it analyzed numerous truck configuration (including similar trucks proposed on the Turner Proposal (TRB Special Reports 225 & 227) as well as this study) on real representative bridge types.
2.2.7-24	ASCE JBE 2003 8:5-(312)	Predicting Truck Load Spectra Under Weight Limit Changes and Its Application to Steel Bridge Fatigue Assessment. Cohen, H., G. Fu, W. Dekelbab, and F. Moses. 2003. Journal of Bridge Engineering, Vol. 8, No. 5, pp. 312-322. Available through American Society of Civil Engineering Journal Library: http://ascelibrary.org/doi/pdf/10.1061/(ASCE)1084-0702(2003)8%3A5(312)	Fatigue
	This document was included in the list of references in NCHRP Report 495. However the NAS Peer Review Committee asked for specific reference herein. This article specifies a method to select the most appropriate fatigue truck given a certain truck histogram under a specific modal shift. The method seeks out the average truck and standard deviation used in an equation to derive an amplification factor to apply to the AASHTO designated fatigue truck.
2.2.7-25	NCHRP Rpt 721	NCHRP Report 721: Fatigue Evaluation of Steel Bridges, Bowman, M. D., G. Fu, Y. E. Zhou, R. J. Connor, and A. A. Godbole, 2012. Purdue University, Transportation Research Board of the National Academies, Washington, D.C. http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_721.pdf	Fatigue, Fatigue Truck
	There were three objectives on NCHRP Project 12-81 Validation of the AASHTO Fatigue Truck since the fatigue provisions of the AASHTO Manual of Bridge Evaluation appeared to be overly conservative in the view of many practicing engineers. The research program aims toward the revision of Section 7 of the MBE to advance the state of the art and the practice. Items specifically identified as in need of improvement include: 1. Improved methods utilizing a reliability-based approach to assess the fatigue behavior and aid bridge owners in making appropriate operational decisions. 2. Guidance on the evaluation of retrofit and repair details used to assess fatigue cracks. 3. Guidance for the evaluation of distortion-induced fatigue cracks.
2.2.7-26	FHWA/TX-83/8+247-4	Estimation of the Fatigue Life of a Test Bridge from Traffic Data. Research Hoadley, P., K. Frank, and J. Yura. 1983. Center for Transportation Research, University of Texas at Austin. http://library.ctr.utexas.edu/digitized/TexasArchive/phase1/247-4-CTR.pdf	Fatigue
	Fatigue studies were conducted on a twin-girder, multi-lane highway bridge. Two types of stress histories were measured at several locations on the bridge. One type of stress history was measured during the passage of a test truck of known weight. Stress histories were measured for velocities of the test truck of 5, 35 and 50 m.p.h. The second type of stress history was measured under normal traffic conditions. An effective stress range, SRE' and number of cycles were computed from each measured stress history using the Rainflow Cycle Counting method in conjunction with Miner's linear damage rule. Other cycle counting methods are considered and compared with the Rainflow Cycle Counting method. The values of SRE and number of cycles are used to compute fatigue-life estimates for the bridge. The fatigue life estimates were computed as a function of the amount of fatigue damage occurring per hour and per day, and future increases in traffic and axle loads were considered. The longitudinal-transverse stiffener intersection, LTSI, detail was found to control the fatigue life of the bridge. The estimated fatigue life for this detail was 50 to 85 years. A modified LTSI detail increased the fatigue life by a factor of three.
2.2.7-27	Paper 98-0417	Fatigue Impacts on Bridge Cost Allocation; Laman, J.A.; Ashbaugh, J.R., 1997 http://trid.trb.org/view.aspx?id=540784	HCAS, Fatigue
	The objectives of this project was to develop an analytical tool to evaluate relative user responsibility for fatigue damage on highway bridges. The tool was a FORTRAN program designed to read standard format FHWA files on vehicle data including Vehicle Miles Traveled (VMT) and the output is a relative fatigue damage matrix for each weight group. The relative damage factors are then used in a cost allocation study to assign the cost of fatigue damage. 39 representative bridges throughout the United States were selected. This was an interesting study in two ways. First it was a cost allocation method attempting to allocate cost not by a load based allocator but rather by a generic VMT allocator. This was a deviation from the Incremental Method. Secondly it is the only attempt at conducting a study on bridges on a national scale. There are potential weaknesses in terms of the allocators used and the number of bridges selected, however this may be due to computational power and technology available during the mid to late 90's.The results of the analysis was used in 1997 HCAS
2.2.7-28	LTRC_228 TRB 09_228	Effects of Heavy Truck Operations on Repair Costs of Low-Volume Highways, LTRC Report No. 228. Saber, Aziz; Morvant, Mark J.; Zhang, Zhongjie. USDOT. 2009. http://docs.trb.org/prp/09-0228.pdf	Truck Study; Fatigue
	Abstract: The economic impact of overweight permitted vehicles hauling sugar cane on Louisiana highways is evaluated. The highway routes that are used to haul this commodity are identified and statistical samples are selected and analyzed. Two different vehicle types and three different gross vehicle weights are chosen including 100,000-lb. and 120,000-lb. AASHTO design guidelines are used to determine the effects of heavy loads on pavements and bridges. The approach requires the overlay thickness needed to carry traffic from each gross vehicle weight for the design period and costs based on 20-year period. The state bridges are evaluated to satisfy regulations for the loading requirements and a fatigue cost is estimated for each safe crossing of a bridge.
	In addition, for documents referencing Methods and Impacts of Bridge Fatigue Limit State see “Reference Nos.”: 2.3.46; 2.1.6-14; 2.1.6-16; 2.1.6-22

2.3 Methods and Models Related to Accrued Bridge Damage Costs and Bridge Serviceability Limits

2.3.1 Introduction

The bridge team was tasked to conduct a study of the potential effects of the general legalization of the 2014 CTSW Study six (6) Alternative Truck Configurations (Scenarios) on bridges on the National Highway System (NHS) and the National Truck Network (NN), and by inclusion specifically on the Interstate System (IS). The scope of this sub-study area focuses on the serviceability related impacts on the existing bridge inventory, and the bridge capital cost effects that would accrue over time due to resulting bridge damage.

2.3.2 A survey of analysis methods and a synthesis of the state of practice

Historically, there has been a large volume of studies and research related to truck size and weight and attempts by agencies, university academics and consultants to determine means and methods to assign cost responsibility for infrastructure investments to a diverse set of roadway users. The breadth of these studies, diverse interests and funding levels by the supporting agencies make them a challenge to compare. Various studies were employed to answer fundamentally different questions. A lack of consensus on methodologies and on the parameters studied has had a detrimental effect on the consistency of the results and has severely limited the possible conclusions. The research team started with existing literature references that were previously identified in the course of the Washington, DC, District of Columbia DOT (DDOT) Truck Size and Weight Study, titled "District-wide Truck Safety Enforcement Plan", May 2010, KLS Engineering and Wilbur Smith Associates (CDM Smith). The team drilled down through the bibliographies to find additional sources of information, and used various search engines on the world-wide web. We also identified domestic and foreign universities' and transportation agencies' web sites to obtain more data and information. Finally the team used CDM Smith's Internal Library System to find and obtain additional literature and articles. With our subscription to the ASCE journals and access to the Knovel Online Library we were able to obtain archived or proprietary studies. A few other resources were provided as a result of research conducted by the other internal Task Teams engaged in this current 2014 CTSW Study.

The following provides a brief history of the most relevant documents found.

2.3.2.1 Other Cost Methodologies

A number of different cost allocation methodologies have been reviewed. The most prevalent method used in the United States in the recent past (1997-2012) has been the 'Federal Method', as described in NCHRP Report 495 (2003) - "Effect of Truck Weight on Bridge Network Costs", which was derived from the 1997 FHWA Highway Cost Allocation Study. Both of these documents are a refinement of the previous incremental methods developed in the 70's and 80's. The Federal Method was developed for use by individual states and/or local highway network authorities and has not been adapted to national or even regional studies. To implement the Federal Method on a national scale would require a level of detail not available in the National Bridge Inventory (NBI) or not available in a consistent format, and potentially not available at all. The required information includes: detailed structural data for each bridge; bridge specific condition data; current detailed cost/expenditure data; and WIM data specifically applicable to the bridges. The various states have different policies and procedures as they relate to bridge preservation, rehabilitation and replacement. It would be extremely difficult to reflect all of those policy differences in such a national study.

States have used the Federal Method in modified formats to allocate bridge costs along with varied allocators (Vehicle Miles Traveled (VMT), Passenger Car Equivalent (PCE), Passenger Car Units (PCU), Average Gross Mass (AGM) or Equivalent Single Axle Load (ESAL)) for different bridge elements and for various other bridge related costs. It should be stressed that there has been no uniformity or consensus in regard to what is included in a bridge cost allocation study. Perhaps most importantly, the states have designed the methodologies used in those studies to answer their different questions. The Federal Method cannot generate cost allocation at the level of detail envisioned under this 2014 CTSW Study, or with a similar degree of transparency as one would hope to have for a study of this national scale. However, some aspects of the Federal Method, as set forth in NCHRP Report 495 (2003) might augment other models or approaches.

Two reports chronicle previous U.S. cost responsibility efforts. NCHRP Synthesis 378 (2008) provides a detailed history of U.S. based cost allocation studies by state from the early 1940's through 2008. NCHRP 20-07 Task 303 (2011), "Directory of Significant Truck Size and Weight Research" is similar to the Synthesis 378 report but adds additional studies through 2011.

Vermont Pilot Program Study (2012): Under Vermont Public Law 111-117, the State raised truck size and weight limits on its Interstate System (IS) for a period of one year, beginning in December, 2009. The state allowed the 99,000 pound, six-axle trucks that were operating on Vermont's State Highway System to be on the State's 280 miles of interstate highways and on the affected 265 bridges. The method involved estimating the fatigue lives of the 23 steel bridges for a baseline Control Loading with trucks in the existing fleet and then comparing it to the fleet of trucks (including the 99,000 lb. pilot study truck) representing the year 2010. A similar study of longer duration with a calibration of the limit state to the recognized service life of the bridges might yield another cost allocation approach.

Methodologies used in Europe and Australia were also reviewed. The European Union (E.U.) Cost Allocation of Transport Infrastructure (CATRIN, 2008) synthesis document is a summary of methods of cost allocations used in the transportation industry (including roadways, railway, air transport and maritime) in Europe. Countries submitting studies included Austria, the UK, Belgium, Denmark, Finland, Germany, Poland, the Netherlands, Sweden and Switzerland. They approach the allocation of roadway costs (including bridges) from an econometric or "top-down" approach as well as from an engineering or "bottom-up" approach. What is clear from this document is that there is a huge disparity of approaches between these countries due to: data type, cost categories and elements, etc. In the end the document does not sum up the cost responsibilities from each country, but rather summarizes the 'approaches' in tabular form. So, all we can surmise from this tabular matrix is that in some cases load based allocators were used for highway cost allocation, including for bridges (either directly or in-directly). The Netherlands and Switzerland used them on their roadways and then broke out bridges as a percentage of overall costs. In Finland they used them directly in their bridge cost allocation. As far as we understand it, no new engineering methods were introduced, except for in Germany (the Maut Study) which used a "Club" type approach, applying PCEs. Another observation is that the number of vehicle classes used in the cost responsibility procedures shows a great variance among the countries, ranging from 6 to as many as 27 (Netherlands), 30 (Switzerland), and 37 (United Kingdom) vehicle classes.

The Australian Method, as reported in the National Transport Commission's 'Third Heavy Vehicle Road Pricing Determination Technical Report' (October 2005), uses a number of allocators to determine shares of vehicle cost responsibility. The study lumps all costs under "roadway" costs and then breaks out pavement and bridge costs. Bridge costs are compiled from the various regional transport industries and are categorized as Attributable and Non-attributable Costs. Original and new construction costs of bridges are considered as Non-attributable costs, and are allocated by vehicle usage or Vehicle Kilometers Travelled (VKT). These costs were estimated at 85% of all bridge costs. As we understand it, for them Attributable Costs include preservation and maintenance, repairs and rehabilitation. The Attributable bridge cost, estimated at 15% of all costs, was allocated based on Passenger Car Equivalent Units (PCUs). The Australian report acknowledged that there was a relationship between load based allocators and bridge deterioration, but it stopped short of suggesting a method other than using PCUs. The report states "For other non-pavement expenditure (i.e., bridge) categories, there is little international consensus, and little information on which to judge to what extent alternative approaches might be applicable to Australia." In other words the Australian report does not endorse any other method for allocating bridge costs.

In summary, the following results were developed:

• In the U.S. no nation-wide studies had been done to-date purely of bridge costs utilizing a load-induced cost responsibility allocator.
• Internationally, there has been little consistency of data across states or other political boundaries.
• In part due to the lack of uniform data collection policies, there has also been little consistency in the methodologies used by the various agencies for assigning cost responsibilities across states (or provinces) and other political boundaries.
• These studies have used various metrics to help apportion, allocate or assign costs to the various truck classifications. The pros and cons of these metrics can be described as follows:

2.3.2.1.1 Weigh-in-Motion (WIM) Data

The initial data records include station description, traffic volume and count, speed data, vehicle classification based on the Highway Performance Monitoring System, HPMS), and weight data.

The data provides axle load estimates and counts including frequency and magnitude. Every state monitors movement of trucks, which makes the data readily available and standardized as reported to the FHWA. The data provides detail for HPMS Vehicle Classification by Highway Classification.

However, there are drawbacks to using WIM data. As stated above, the initial raw data provides a lot of the basic information needed. It cannot be used in its raw form since the data is highly fragmented and must be processed by scrubbing, aggregating and weighting (by other parameters such as VMTs) and translated into a usable format. In this final format much of the original detail may have been altered. For example, truck counts are collected at individual stations. However, these are only a snapshot of the data for a given day and hour of data collection. Different stations in the state may collect data at different times so as the data is aggregated there will be gaps and overlaps. In order to compensate for these inconsistencies, the data are processed with subroutines to derive a sub-data set that represents the truck traffic stream in a given state.

2.3.2.1.2 Vehicle Miles Traveled (VMT)

VMT is a metric which is an indicator of the travel levels on the roadway system by motor vehicle class. VMT's are estimated for the given time period that is based upon traffic volume counts and roadway length. This metric has been used as one of many allocator types to estimate consumption of wearing surfaces on pavements and bridge decks.

The problem with VMT as an allocator by itself is that it assumes equal consumption based on the relative miles traveled and does not account for the vehicle weight. For example in applying VMT it is assumed that a 3500 pound car consumes the same stretch of pavement as an 80,000 lb. 5-axle (3-S2) tractor semitrailer for the same distance traveled. Another problem with VMT is more specific to bridges; we would be assuming that bridges are distributed proportionally to the number of highway miles. However, we know that the bridge density (length of bridges and their count) per mile of highway varies geographically based on rural and urban environments, and on the number of water crossings and overpasses of intersecting roadways.

2.3.2.1.3 Passenger Car Equivalents (PCE)

PCE is a metric which equates any of the HPMS vehicle classes to a Passenger Car Equivalent or Unit (PCE or PCU) and is essentially the impact that a mode of transport has on traffic variables (such as headway, speed, density) compared to a single car. It is derived from taking a certain mixed traffic stream and heuristically or statistically converting it into a hypothetical passenger-car stream.

Similar to VMTs, PCEs do not take into account axle loads. As an allocator it might be more useful to estimate delays and backups that may occur at a certain location (such as a bridge under construction). But the PCE is more a capacity based allocator and cannot provide a suitable estimate of the physical load impacts those trucks would have on the bridge itself.

2.3.2.1.4 Equivalent Single Axle Load (ESAL), Load Equivalency Factor (LEF)

The ESAL was originally derived in the 1940s after large trucks started to populate US highways and was introduced by AASHO (now AASHTO) in a rather complex formula that was based on a standard truck axle weight of 18,000 pounds. The premise was that the standard 18,000 lb. axle induced a unit of damage on pavement. The complex formula was eventually reduced to a more simple ratio of actual axle load divided by the standard axle (i.e., 18,000 pounds) raised to the 4th power or Load Equivalency Factor (LEF). Many transportation agencies in the US and Europe (CATRIN, 2008) used variations of this formula to estimate impacts to bridges and various power ratios were selected ranging from 2.0 to 4.0. Some agencies used the method directly to estimate pavement (highway) impacts and pulled out bridge costs simply as a percentage, while others applied the ESAL damage index directly to their bridges.

New pavement damage methodologies have been developed such as the Empirical-Mechanistic Pavement Models. In spite of this the ESAL/LEF methodology continues to be used by transportation agencies, because it provides a method of incorporating axle loads and frequency of occurrence to estimate pavement and bridge damage.

2.3.2.2 Pros and Cons of Specific Cost Responsibility Assignment Methods

2.3.2.2.1 Incremental/Federal Method (as described in NCHRP Report 495, 2003)

The concept presented therein is rather simple however its implementation is very complex, and increasingly so for large systems. The cost impacts are categorized as 1) impact to existing bridge superstructures, 2) impact to new bridge superstructures, 3) impact to steel fatigue details and 4) impacts to reinforced concrete deck crack propagation (termed reinforced concrete fatigue in Report 495). The method allows one to prescribe a course of action that has a certain cost to perform, but it does not provide for a measure of the actual level of damage. The effective use of this method requires a familiarity with each state's repair philosophies and practices. For instance, does the state lean towards repair and preservation or does it favor pro-active replacement of deficient structures? With respect to the fatigue methods described in this document, the document itself addresses its own limitations in that ... due to "uncertainty observed in reported physical test results and practice" in determining end of service life., "the real service life of the deck (for instance) is not certain." In this, the report recognizes the lack of available data in a consistent format, sufficient to implement its use for a large regional or national study. With respect to the term 'practice', they mean at what threshold visible condition level, do different owners determine that a deck has failed or that a specific intervention (action option) is warranted.

"The Federal.method is more advantageous at the state level or a local level [for which] cost impact estimation could be conducted in more detail, because more detailed bridge data are available and the number of bridges becomes smaller" (NCHRP Report 495, 2003). Conversely stated, the disadvantage of this method is that the level of detail and data needed to analyze bridges on a national scale would be time and cost prohibitive. The method provides bridge selection guidelines that may end up excluding representative bridges if there is a large population of bridges in the study area.

2.3.2.2.2 KLS/Wilbur Smith Associates Study, Washington, DC DDOT, 2010 District Wide Truck Safety Enforcement Plan: Task 3 - Infrastructure Impacts of Overweight Trucks

The bridge cost allocation portion of this study was based on a model that utilized a bridge deterioration mechanism prevalent where states use chlorides in de-icing roadways and bridges. This study employed ESAL/LEFs as its allocator for estimating damage and assigning cost. District Axle Load Charts were used to determine which sets of axle weight increments would be considered compliant or non-compliant. Accordingly, a relative damage distribution profile was determined (by percent) of legal and over-weight trucks by vehicle class (HPMS Classes 4 through 13). Based on the literature review (Ohio DOT Impacts of Permitted Trucking on Ohio's Transportation System and Economy, Final Report of 2009, and the 1997 FHWA HCAS methodology), it was observed that between 59% to as much as 79% of bridge damage could be attributed to non-truck related (or non-load induced) factors. These would include environmental factors, site related conditions, usage patterns, age and the cumulative effects of light weight vehicles.

A detailed, annualized capital cost estimate was developed for the 139 of the District's non-parkway bridges that carry truck traffic. The truck distribution profile of the 10 truck vehicle classifications was applied to the annualized bridge costs providing a clear picture of the impact of trucks (both compliant and non-compliant) on the District's bridges.

This methodology utilized the ESAL/LEF allocator to assign cost responsibility, and this approach is somewhat flawed as it ties damage to an arbitrary standard axle load and to a powered exponent that was not well understood at the time.

This study was not published, but has been made available to FHWA and NAS reviewers by permission of the District Authority.

2.3.2.3 South Carolina's 'Rate of Deterioration of Bridges and Pavements as Affected by Trucks'

One recent (released in late 2014) addition to the desk scan was South Carolina's 'Rate of Deterioration of Bridges and Pavements as Affected by Trucks' report.

This report included the following:

• Bridge Damage Model: the authors modified AASHTO S-N curves and created a new curve called "Service-Level Fatigue Curve" for the "Giga-Cycle Low Stress Region" based on the 2005 Bathias and Paris giga-cycle fatigue study and on the 5 million cycle AASHTO limit, arguing that the number of fatigue cycles would be well beyond 5 million within the design life of 75 years per AASHTO assumptions. The fatigue details considered consisted of steel reinforcement in concrete decks and tendons in pre-stressed bridge members.
• Cost Allocation Model: the authors first calculated the maximum allowable fatigue cycles based on the new fatigue curve for each truck model, and on annual cycles for each truck model based on WIM Data, and then proportioned the annual cycle counts over the maximum allowable cycles to obtain annual bridge fatigue damage costs, then added the annual bridge maintenance cost to obtain the overall annual bridge damage cost. Shares of bridge damage cost for each truck model were proportioned based on the percentage of each truck's volume in the fleet.
• Potential applications of the Study: (1) the study establishes a new method of allocating bridge damage cost due to overweight trucks based on axle weight groups. The method could be a blueprint for other studies; 2) the South Carolina study concluded that the "bridge damage increased exponentially with an increase in truck weight", which supports CDM Smith's bridge damage model that is an exponential power formula.
• Potential limitations of the study: 1) In the bridge damage model, it is debatable that the slope of S-N curve in the Giga-Cycle Low Stress Region would be the same as that in the AASHTO High Cycle High Stress Region. There is insufficient data to verify this assumption; 2) it is also debatable that the bridge damage within the design life span is attributed to the reinforcement or pre-stressed tendon fatigue damage.

The most common deterioration in bridges is typically the prevalence of concrete spalls in decks that lead to major bridge rehabilitation and/or replacement. It's rare to observe rebar fracture failure due to fatigue, even at the end of the bridge design life span, but particularly within the design life. It's very common to have at least one full deck replacement due to deck failure, and the authors' equating the time frame of bridge replacement to that of bridge fatigue failure didn't consider this issue. It is logical to assume that the bridge will only exhibit damage after passing the 5 million cycle threshold, but the authors calculated the annual fatigue damage cost assuming that it would be same for every year in the design life span. The assumption is contradicted by the bridge damage model. The South Carolina report allocated bridge damage costs based on miles traveled. But this didn't take into account variables such as bridge length, number of spans, and the number of bridges in a given mile. Finally, the authors didn't consider that the number of stress cycles might be different for each truck model on different bridges due to variance of bridge span lengths, number of spans, and truck axle configuration in the model. This last issue poses a limitation on evaluating the net effects due to a specific bridge.

In the South Carolina report bridge types studied were reduced to a few archetypes based on the predominant bridge types found in the state, with an emphasis on concrete vs. steel superstructures.

2.3.3 An identification of data needs and an evaluation and critique of data sources

With respect to the Incremental/Federal Method, the process for all cost categories includes selecting a number of bridges in the region or state. These bridges would need to be load rated in accordance with AASHTO's Manual of Bridge Evaluation. To estimate the cost impact of the truck; if the rating factor is less than 1.0 the bridge is considered to be inadequate for the truck, and one of five action options could be selected: 1= do nothing, 2 = rehab or retrofit, 3 = post, 4 = combination of 2 and 3, 5 = replace. The cost of the action then is estimated for that truck on that type of bridge. The same general steps are repeated for the four cost categories with variations in the actual details.

Report 495 did introduce a 'probabilistic approach', a formulaic expression (Equations 3.4.2.7 and 3.3.3.1) to deal with the uncertainty with respect to reported physical test results and practice. (NCHRP Report 495, pages 46 and 51, Section 3.4.3). However, the amount of data required and the shear scope of work relative to its application to large numbers of specific, real bridges is considered to be untenable at this time.

The KLS/WSA 2010 D.C. DDOT Truck Safety Enforcement Plan study used the NBI database to get most of the bridge data, minus the structural details. WIM data in the form of axle load weight increments and counts for each vehicle class was employed.

Data types and categories have varied greatly for the various studies reviewed, and at the time of this study there was a general lack of consistently formatted data throughout the various states. This has been referred to as the data gap issue. Quality and quantity of viable information in the format desired are inconsistent. The data (particularly WIM data) can be 'mined' and 'scrubbed' and often must be reconfigured to address the needs of a particular study.

2.3.4 An assessment of the current state of understanding of the impact and needs for future research, data collection and evaluation

The FHWA is engaged in the development process for the Long Term Bridge Performance (LTBP) program, intended to provide a more detailed and timely picture of bridge health, improve knowledge of bridge performance, and lead to better bridge management tools.

2.3.5 Quantitative results of past studies

Numerous past studies having been reviewed, we can conclude the following:

• The differences in the methods employed, the parameters and allocators chosen, and the assumptions about the relationships between those parameters and bridge costs have yielded a plethora of results that simply don't lend themselves to direct comparison.
• U.S. DOT has confirmed their position, and the desk scan confirms, that there is presently no generally accepted methodology for deriving the bridge damage costs associated with trucks and most particularly with allocating shares of those costs to specific trucks in the traffic stream.
• A few of the study methods reviewed appear to have relative merit or potential, but all of them have limitations. They all include assumptions, the application of which introduces varying degrees of uncertainty and in some cases skepticism.

 

2.3.6 List of References

Methods and Cost Impacts of Bridge Serviceability

Reference No.	Document No.	Document Title and Link	Relevance to Study
	In this subsection cost allocation studies of 15 states are presented. Some states like Oregon conduct Highway Cost allocation studies biennially, however only the latest studies are shown herein. Indiana has conducted a 2013 HCAS, however their latest report is not available through the internet. There will be an ongoing effort to obtain that report (as well as others) as the methods and conclusions are of vital interest to this study. The majority of the US HCAS reports conducted by each state follow the Federal HCAS method recommended in 2003with some modifications. The exception would be the Washington DC, District DOT Truck Size & Weight Study, 2010 conducted by CDM will be used as a basis of this study. It should be noted that the Federal Cost Allocation Method for bridges has not been used on a nationwide basis and the data requirements presents considerable difficulties in expanding it to a national scale. The method was devised to provide uniformity for state and local agencies to conduct the studies on network of roads (toll road, trucking network) and could be expanded to the whole state if needed. California, Maryland and New York are states that have examined a limited network of roads. Most other states have studied a sampling of their bridges and extrapolated the results to the state-wide array of bridges. We have also included the Australian HCAS study and the European Union CATRIN study as they provide alternate views, means and methods for such studies. A discussion of these studies is provided in the Bridge Task Project Plan. In brief, the Australians conducted a nationwide highway cost allocation study but used Passenger Car Equivalents (PCE) and Vehicle Kilometers Traveled (VKT) as the basis for the bridge cost share allocator. The European Cost Allocation Report (CATRIN) was a compilation of cost allocation studies conducted independently by 15 European Union countries on their roadway (and other transportation) networks. Our focus was on the bridge costs and the allocators used to proportion out cost responsibilities. What was apparent was that only a handful of countries like the Finland, Switzerland, the Dutch tracked bridge costs separate. In each case the same allocator (Load related allocator - ESALs or ESAL KM) that was used on the pavements was also applied to the bridges. A few countries like Germany approached the allocation problem from a Top-Down or Econometric method as well as using Engineering type allocators like PCEs and VKTs. What is clear from all of the foreign studies was the difficulty in obtaining data in a uniform format across political boundaries and what cost items (construction, rehabilitation, maintenance, etc.) to include or exclude from the studies. Although the US Federal method provides a uniform method for cost allocation, the states use the cost data in the format that they are used to collecting and there is no standardization.
2.3.6-1	TRB 1990a (SR 225)	Special Report 225: Truck Weight Limits: Issues and Options. National Research Council, Washington, D.C., 1990	CTSW
2.3.6-2	TRB 1990b (SR 227)	Special Report 227: New Trucks for Greater Productivity and Less Road Wear: An Evaluation of the Turner Proposal. National Research Council, Washington, D.C, 1990	CTSW
	The thrust of both the TRB 1990a and TRB 1990b documents with respect to bridges was the speculation that the one-time cost for upgrading bridge superstructures due to the heavier Turner Trucks would be cost prohibitive to the states.
2.3.6-3	CTSW 2000 Volumes 1-4	Comprehensive Truck Size and Weight Study: Volume 1-4, USDOT - Office of Transportation Policy Studies; https://www.fhwa.dot.gov/policy/otps/truck/finalreport.htm	Historical Context & Commentary
	The Comprehensive Truck Size and Weight Study began in 1994 along with a companion study, the Federal Highway Cost Allocation Study that was submitted to Congress in August, 1997. The objectives of the 2000 Comprehensive Truck Size and Weight (CTS&W) Study were to: (1) Identify the range of issues impacting TS&W considerations; (2) Assess current characteristics of the transportation of various commodities including modes used, the predominant types of vehicles used, the length of hauls, payloads, regional differences in transportation characteristics, and other factors that affect the sensitivity of different market segments of the freight transportation industry to changes in TS&W limits; and (3) Evaluate the full range of impacts associated with alternative configurations having different sizes and weights. The document forms a historical basis for the current CTSW study and a basis for understanding on going issues with respect to trucks and bridges. Some of the goals were common with the 2014 CTSW Study, however many of the bridge related studies included in it were designed to answer a different question. A Highway Cost Allocation Method that included a modified “Incremental” method along with several interlinked spreadsheets had been introduced in 1997. This was called the Federal Incremental Method. Neither a nationwide nor regional bridge allocation study was provided, although some local examples of bridge allocation studies were included. In 2003 the Federal Bridge Cost Allocation Method was re-introduced in NCHRP Report 495 Based on our research a true national bridge cost allocation has not been done.
2.3.6-4	FHWA-IF-05-040	Transportation Asset Management Case Studies; Office of Asset Management https://www.fhwa.dot.gov/infrastructure/asstmgmt/bmcs701.cfm	Bridge Management, PONTIS
	This document is a case study covering several states that use the AASHTOWare PONTIS software (initially developed by FHWA) in their asset management practices. The Federal Highway Administration Office of Asset Management is promoting a different way for transportation agencies to distribute their resources among alternative investment options. This new way of doing business, "Asset Management," is a strategic approach for getting the best return on dollars spent for transportation improvements. Each State transportation agency will likely have different methods for implementing an Asset Management strategy. For example, some agencies will pursue a data integration strategy in order to ensure comparable data for the evaluation of investment alternatives across asset classes. Others will move to deploy economic analysis tools to generate fact-based information for decision-makers. Still others will want to integrate new inventory assessment methods into their decision-making process. Pontis® is a comprehensive bridge management system tool developed to assist in the challenging task of bridge management. Initially developed by FHWA, Pontis® now is an AASHTOWare Bridge Management® product. It stores bridge inventory and inspection data; presents network-wide preservation and improvement policies for use in evaluating the needs of each bridge in a network; and makes recommendations for what projects to include in an agency's capital improvement program for deriving the maximum benefit from limited funds. The software is continuously upgraded and improved based on various users' input.
2.3.6-5	FHWA - IF - 11-016	Framework for Improving Resilience of Bridge Design; Turner Fairbanks Transportation Research Center, Long Term Bridge Performance https://www.fhwa.dot.gov/bridge/pubs/hif11016/hif11016.pdf	Long Term Bridge Performance
	This document provides a framework for bridge engineers to design and build more robust and resilient bridges that are resistant to the forces of nature as well as to the ever growing truck numbers and sizes that frequent the nation's highways.
2.3.6-6	FHWA-HRT-11-037	FHWA LTBP Workshop to Identify Bridge Substructure Repairs; Turner Fairbanks Transportation Research Center, Long Term Bridge Performance https://www.fhwa.dot.gov/publications/research/infrastructure/structures/ltbp/11037/index.cfm	Long Term Bridge Performance
	The purpose of this workshop was to consider overall bridge performance and identify geotechnical performance metrics that may correspond to good and poor performance. This report describes the results of the workshop and presents them in the larger perspective of designing and implementing the LTBP program. This document will be of interest to engineers who research, design, construct, inspect, maintain, and manage bridges as well as to decision-makers at all levels of management of public highway agencies.
2.3.6-7	NCHRP SYN 397	NCHRP Synthesis 397: Bridge Management Systems for Transportation Agency Decision Making; 2009; Markow, Michael J.; Hyman, William A. http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_syn_397.pdf	Bridge Management
	The objective of this synthesis study has been to gather information on current practices that agency chief executive officers and senior managers use to make network-level investment and resource allocation decisions for their bridge programs, and to understand how they apply their agency's bridge management capabilities to support these decisions. The following areas of planning, programming, and performance-based decision making have been addressed. Condition and performance measures that are used to define policy goals and performance targets for the bridge program are: Methods of establishing funding levels and identifying bridge needs Methods and organizational responsibilities for resource allocation between the bridge program versus competing needs in other programs (pavement, safety, etc.) Methods of allocation among districts and selection and prioritization of projects The role of automated bridge management systems (BMS) in planning, programming, resource allocation, and budgeting Use of economic methods in bridge management Methods to promote accountability and communication of the status of the bridge inventory and the bridge program
2.3.6-8	NCHRP Rpt 668	NCHRP Report 668:Framework for a National Database System for Maintenance Actions on Highway Bridges, Principal Investigator: George Hearn, (University of Colorado), Paul Thompson, Walter Mystkowski, William Hyman, (Applied Research Associates), 2010 http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_668.pdf	Bridge Asset Management
	This report presents a potential framework for a National Bridge Maintenance Database (NBMD). This framework provides a uniform format for collecting, reporting, and storing information on bridge maintenance actions. Use of this framework could promote compatibility of maintenance data reported by different agencies and will provide an effective means for using these data in evaluating cost and performance of alternative maintenance applications or as a basis for cost-benefit analysis and evaluation of cost and deterioration models. The material contained in the report should be of immediate interest to state bridge and maintenance engineers and others concerned with the maintenance and management of bridges. In terms of standardizing owner agency bridge maintenance and preservation practices and cost reporting, this documentation has made advances. This type of data is of great interest to both bridge owners and others who may utilize and analyze the data for a variety of cost purposes. These may be for evaluating the cost effectiveness of a program or using it for cost allocation studies. It should be noted that standardization of cost reporting is still premature and owner agencies have to buy into the benefits of conforming to the standards. This program could be a great source of data that could be readily available.
2.3.6-9	CDOT 2012-4	Deterioration and Cost Information for Bridge Management; 2012; George Hearn, University of Colorado http://www.coloradodot.info/programs/research/pdfs/2012/pontis.pdf/view	Bridge Management, PONTIS
	Abstract: Study 87-60 uses contract bid tabulations and element-level condition records to develop element-level actions, costs for actions, transition probabilities for models of deterioration of bridge elements, and transition probabilities for improvements to elements due to actions. The information on actions, costs, and transition probabilities are input to a Pontis BMS bridge database. Study 87-60 applies transition probabilities for element deterioration to compute the number of years to possible loss of safety in bridges, and to compute the number of years for inspection intervals. Study 87-60 examines variations among CDOT regions of costs of actions and of deterioration of elements. Study 87-60 developed a set of software applications to handle bid tabulations, compute costs of actions, compute transition probabilities, and mediate the steps needed for movement of data into and out of PONTIS BMS.
2.3.6-10	USDOT PUB	Bridge Preservation Guide; FHWA Office of Infrastructure; https://www.fhwa.dot.gov/bridge/preservation/guide/guide.pdf	Bridge Preservation
	This guide provides bridge related definitions and corresponding commentaries, as well as the framework for a systematic approach to a preventive maintenance (PM) program. The goal is to provide guidance on bridge preservation.
2.3.6-11	SHRP 2 PREPUB R19A	Design Guide for Bridges for Service Life; 2012; Principal Investigator: Atorod Azizinamini, Ph.D., P.E.; Florida International University, HDR Engineering, etc.	Deterioration Models, Bridge Design
	The main objective of the Guide is to provide information and define procedures to systematically design for service life and durability for both new and existing bridges. The objective of the Guide is to equip the user with knowledge that is needed to develop specific optimal solutions for a bridge under consideration in a systematic manner using a framework that is universal, but with specifics being different. The general frame work for design for service life is described, followed by addressing specifics related to each step by topics covered in various chapters. In developing our bridge cost allocation method, we utilized a deterioration model based on our own experience and observations collected while inspecting thousands of bridges in the Northeast Region of the United States. The first step is understanding bridge behavior; the deterioration mechanism and the interaction of each element. Based on an understanding of bridges through extensive bridge inspection and rehabilitation design, the development of a deterioration model is at this point rather intuitive. Based on review of this document, it is evident that a scientific approach is being proposed using the engineering community's collective knowledge base. The R19A document provides a scientific method to enhance the service life of bridges. It is a major shift in thinking for bridge design and preservation. New design methods are being proposed as a result of understanding how bridges deteriorate over time. It should be noted that this document is a work in progress and is being updated.
2.3.6-12	SHRP 2 S2-R19A-RW-1	Bridge for Service Life Beyond 100 Years Innovative Systems, Subsystems and Components, Atorod Azizinamini, Ph.D., P.E.; Florida International University, HDR Engineering, etc. http://onlinepubs.trb.org/onlinepubs/shrp2/SHRP2_S2-R19A-RW-1.pdf	Deterioration Models, Bridge Design
	The Service Life Design Guide is a new reference volume that addresses design, fabrication, construction, operation, maintenance, repair, and replacement issues for both new and existing bridges. The Guide provides information and procedures to systematically design new and existing bridges for the service life and durability. It includes a framework for service life design and has 11 chapters, and 7 appendices each devoted to a certain bridge part or aspect of the service life design process.
2.3.6-13	SPR-P1 (11) M302	Developing Deterioration Models for Nebraska Bridges; Nebraska Department of Roads (NDOR), University of Nebraska, Lincoln, George Morcous, July 2011 https://dot.nebraska.gov/media/5688/final-report-m302.pdf	Deterioration Models, Bridge Decks
	Nebraska Bridge Management System (NBMS) was developed in 1999 to assist in optimizing budget allocation for the maintenance, rehabilitation and replacement needs of highway bridges. This requires the prediction of bridge deterioration to calculate life-cycle costs. The approach tries to predict the deterioration of bridge components based on national average deterioration rates but does not account for the impact of traffic volume, structure and material type, and environment impacts, in addition to being not specific to Nebraska bridges. The objective of this project is to develop deterioration models for Nebraska bridges that are based on the condition ratings of bridge components (i.e. deck, superstructure, and substructure). Recently, NDOR decided to migrate to AASHTOWare PONTIS software, to avoid the frequent updates of NBMS and stream line the data gathering process. PONTIS requires the use of a specific type of deterioration models with Transition Probability Matrices (TPM), which were not available for Nebraska bridges. Therefore, another objective of this project was to develop TPMs to customize the PONTIS deterioration models using the inventory and condition data readily available from the NBMS database. Procedures for updating and customizing the deterioration model were presented. This report highlights two areas that state agencies are grappling with. Proprietary type, legacy databases that have been used to develop predictive deterioration models to better manage infrastructure assets. On the other hand the agencies are struggling to migrate these databases to more nationally utilized and standard Bridge Information and Management systems such as PONTIS. In this case the NBMS data was successfully migrated and incorporated in TPMs for better predictive modeling. The migration process is on-going throughout the US. With respect to bridge decks it establishes a relative time frame where bridge components such as decks reach the end of their service life in comparison to the bridge service life. The more important finding of this study is that there is a strong correlation between Average Daily Truck Traffic (ADTT) and bridge deck deterioration (ratings) over time (Section 4.2.2.2, page 64). The data shows a rather steady decline in the early years, followed by a sharp decline in the later years, indicating a non-linear behavior.
2.3.6-14	NCHRP SYN 234	Settlement of Bridge Approaches (The Bump at the End of the Bridge); 1997; Briaud, Ph.D., P.E, Jean-Louis; James, Ph.D., P.E., Ray W.; Hoffman, Stacey B.; Texas A&M University; http://trid.trb.org/view.aspx?id=482992	Bridge Design, Settlement, Deterioration Mechanisms
	This synthesis describes the current state of practice for the design, construction, and maintenance of bridge approaches to reduce, eliminate, or compensate for settlement at the bridge/abutment/embankment interface or the bump at the end of the bridge. It discusses the geotechnical and structural engineering design and procedural factors, and includes numerous illustrations. This report of the Transportation Research Board presents data obtained from a review of the literature and a survey of the state DOTs. It is a supplemental update to Synthesis of Highway Practice 159: Design and Construction of Bridge Approaches (1990). The synthesis identifies and describes techniques that have been used to alleviate the problem of the bump at the end of the bridge including the location and cause of settlement and methods used to reduce settlement. In addition, the types of interaction between various divisions of the DOTs in the design, construction, and maintenance of bridge approaches are addressed. This synthesis was used as part of a comprehensive formulation of the Northeast Region deterioration model used (by CDM Smith Associates in 2010) for the District of Columbia Truck Size and Weight Study. The premise of the deterioration model was the progressive failure mechanism initiated by failure of the bridge deck joints. One key reason for the deck joint failure is settlement of the approach slabs. In turn the settlements would cause impact onto the bridge deck joint itself causing the header beams to crack, armor plating to separate or seals to fail. In either case this was an initial entry point for water intrusion into and below the bridge deck which caused deterioration of the beams, bearing and bridge seats/pedestals.
2.3.6-15		Truck Loads and Highway Bridge Safety: New Developments; Gongkang Fu, Center for Advanced Bridge Engineering, Wayne State University; 2002 http://www-personal.umich.edu/ ~nowak/Papers/Fu,%20paper%201-6-03.pdf	Cost Allocation, Modal Shift
	Abstract: This paper reports on some latest developments in efforts to balance truck loads and the capacity of highway bridges that carry the loads. One of them is the completion of the development of a method for estimating effects of truck weight limit change on bridge network costs, funded by the US National Cooperative Highway Research Program (NCHRP). Four categories of cost impact are addressed in this new method: steel fatigue, reinforced concrete (RC) deck fatigue, inadequate existing bridges, and higher design load for new bridges. This development has taken into account the constraints on data availability at the State infrastructure system level. Another recent development is the completion of a research effort examining the adequacy of bridge design load for the State of Michigan in the US, with respect to real truck loads measured. It was found that there is a need to develop a more rational design load to cover the risk represented. These developments offer effective tools for response to the trend of increasing truck loads. This article was quoted in the reference section of NCHRP Report 495. It is the main methodology used by Report 495 for utilizing the truck spectra (from WIM data) to predict truck load shift from one truck load fleet to another. As such it is a valuable document as we proceed with bridge cost allocation study.
2.3.16	SHRP2 S2-C20-RR-1	Freight Demand Modeling and Data Improvement; 2013; Chase, Keith M. Chase, Anater, Patrick; Gannett Fleming, Inc. Phelan, Thomas; Eng-Wong, Taub and Associates http://onlinepubs.trb.org/onlinepubs/shrp2/SHRP2_S2-C20-RR-1.pdf	Freight Demand; Modal Shift
	Determine freight demand modeling and data needs, in part by defining an optimal scenario or desired future state of what the freight planning process should be with all of the model parameters clearly identified and the necessary data available. Identify and promote innovative research efforts to help develop new modeling and data collection and processing tools in the near and long-term future. Establish and strengthen links between freight transportation planning tools and supporting data, and also consider the relationships between freight transportation and other areas of public interest, such as development and land use, in which freight movement has major implications. Leverage and link existing practices, innovations, and technologies into a feasible approach for improved freight transportation planning and modeling. Establish a recognized and regular venue to promote and support innovative ideas, modeling methods, data collection, and analysis tools as the basis for informing and sustaining further research.
2.3.6-17	NCFRP RPT 22	NCFRP Report 22: Freight Data Cost Elements; 21013, José Holguín-Veras, Jeffrey Wojtowicz, Carlos González-Calderón, Rensselaer Polytechnic Institute,Troy, NY Michael Lawrence, Jonathan Skolnik, Michael Brooks, Shanshan Zhang, Jack Faucett Associates, Inc., Bethesda, MD Anne Strauss-Wieder, A. Strauss-Wieder, Inc., Westfield, NJ Lóri Tavasszy, TNO, Delft, Netherlands http://onlinepubs.trb.org/onlinepubs/ncfrp/ncfrp_rpt_022.pdf	Freight, Cost Allocation
	NCFRP Project 26, “Freight Data Cost Elements,” had the following objectives: . Identify the specific types of direct freight transportation cost data elements required for public investment, policy, and regulatory decision-making; and . Describe and assess different strategies for identifying and obtaining these cost data elements
2.3.6-18	ASCE JBENF 2_13_6_556	Impact of Commercial Vehicle Weight Change on Highway Bridge Infrastructure; G. Fu; J. Feng; W. Dekelbab; F. Moses; H. Cohen; and D. Mertz; ASCE Journal of Bridge Engineering http://ascelibrary.org/doi/pdf/10.1061/%28ASCE%291084-0702%282008%2913%3A6%28556%29	Freight - Over Weight Truck Study
	Truck weight limit is one of the major factors affecting bridge deterioration and expenditure for maintenance, repair, and/or replacement. Truck weight in this paper not only refers to the truck gross weight but also to the axle weights and spacings that affect load effects. This paper presents the concepts of a new methodology for estimating cost effects of truck weight limit changes on bridges in a transportation infrastructure network. The methodology can serve as a tool for studying impacts of such changes. The resulting knowledge is needed when examining new truck weight limits, several of which have been and are still being debated at both the state and federal levels in the United States. The development of this estimation method has considered maximizing the use of available data such as the bridge inventory at the state infrastructure system level. In application examples completed but not reported herein, the costs for relatively inadequate strength of existing bridges and for increased design requirement for new bridges were found dominant in the total impact cost.
Arizona
2.3.6-19	FHWA-AZ-06-528	Estimating the Cost of Overweight Vehicle Travel on Arizona Highways; Sandy H. Straus' ESRA Consulting Corporation http://azmemory.azlibrary.gov/cdm/ref/collection/statepubs/id/3603
2.3.6-20	FHWA-AZ99-477(1)	1999 Update of the Arizona Highway Cost Allocation Study; Arizona Department of Transportation; Carey, Jason;
2.3.6-21	FHWA-AZ99-477(3)	Implementation of the Simplified Arizona Highway Cost Allocation Study Model; Arizona Department of Transportation; Carey, Jason http://wwwa.azdot.gov/ADOTLibrary/publications/project_reports/PDF/AZ477(3).pdf
Idaho
2.3.6-22	023-2010 Idaho HCAS	2002 Idaho Highway Cost Allocation Study; SYDEC, Inc.; R.D. Mingo Associates; Harry Cohen Consultants; http://itd.idaho.gov/taskforce/resources/1040-Cost%20Allocation%202002.pdf
2.3.6-23	017-2010 Idaho HCAS	2010 Idaho Highway Cost Allocation Study Final Report; Battelle; P Balducci; J Stowers; R Mingo; H Cohen; H Wolff; http://betterroadsforidaho.com/wp-content/uploads/2015/02/2010-Idaho-HCAS-Final-Report_Oct-24_RS.pdf
Indiana
2.3.6-24	FHWA/IN/JHRP-89/4	1988 Update of the Indiana Highway Cost Allocation Study; Sinha, K.C.; Saha, S. K.; Fwa, T.F.; Tee, A.B.; Michael, H.L; Joint Transportation Research Program; http://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=2510&context=jtrp
2.3.6-25	FHWA/IN/JHRP-84/20	Indiana Highway Cost Allocation Study: Final Report; Kumares C. Sinha; Tien Fang Fwa; Essam Abdel-Aziz Sharaf; Ah Beng Tee; Harold L. Michael; Joint Transportation Research Program; http://ia600401.us.archive.org/20/items/indianahighwayco00sinh/indianahighwayco00sinh.pdf
Kentucky
2.3.6-26	KTC-00-3	2000 Highway Cost Allocation Update; University of Kentucky, Kentucky Transportation Center; http://www.ktc.uky.edu/files/2012/06/KTC_00_03.pdf
Maryland
2.3.6-27	2009 MDTA HCAS	2009 Highway Cost Allocation Study for the Maryland Transportation Authority Toll Facilities; C. C. Fu; C. W. Schwartz; Erin Mahoney; University Of Maryland http://www.mdta.maryland.gov/Home/documents/Final_HCAS_FinalReport_052609.pdf
Minnesota
2.3.6-28	MN/RC 2012-14	2012 Highway Cost Allocation and Determination of Heavy Freight Truck Permit Fees; Gupta, Diwakar; University of Minnesota http://www.lrrb.org/media/reports/201214.pdf
2.3.6-29	1990 MN HCAS	1990 Results of the Minnesota Highway User Cost Allocation Study; Cambridge Systematics, SYDEC, The Urban Institute, Jack Faucett Associates http://www.dot.state.mn.us/research/pdf/1990-00.pdf
Nevada
2.3.6-30	2009 NV HCAS	2009 Nevada Highway Cost Allocation Study; Battelle; P Balducci; J Stowers; R Mingo; H Cohen; H Wolff; http://www.nevadadot.com/uploadedFiles/NDOT/About_NDOT/NDOT_Divisions/Planning/Performance_Analysis/Balducci%20Nevada%20DOT%20HCAS%20Compilation%20Report%20Jul%2030.pdf
New Jersey
2.3.6-31	FHWA-NJ-2001-030	Infrastructure Costs Attributable to Commercial Vehicles; Dr. Boilé, Maria; Ozbay, Kaan; Narayanan, Preethi , Rutger University, Center for Advanced Infrastructure & Transportation http://cait.rutgers.edu/files/FHWA-NJ-2001-030.pdf
New York
2.3.6-32		Effect of Overweight Vehicles on I-88 Bridges, Task 2.a &b Report - Draft for Part 1, March 2013; Graziano Fiorillo, Michel Ghosn; City College of New York	Cost Allocation
	The object of this report is to describe a procedure that quantifies the effect to bridges caused by overweight trucks.  The methodology is implemented on a representative sample of twenty three bridges along the I-88 corridor between Binghamton and Schenectady in New York State. The procedure is divided into three phases. In the first phase, the WIM data file which is assumed to be representative of the entire corridor is analyzed In the second phase, the maximum moment response of each vehicle contained in the WIM file is obtained for each bridge by sending each truck through the appropriate influence line. Finally, each truck's response is used to estimate the effect caused by each truck. The cost analysis is executed for two types of effects: 1) Overstress effect and 2) fatigue effect.  The overstress cost analysis follows the classical FHWA cost allocation model.  The fatigue cost analysis follows the AASHTO LRFD fatigue analysis method. The cost model presented in this report is still preliminary pending the updating of the bridge design methodology that is taking place based on input from the TWG.  Furthermore, the unit cost data for the steel and concrete are based on the unit costs obtained from the RS Means Heavy Construction Costs Database.  As indicated above this bridge cost allocation study was conducted on 23 of the 40± bridges located on the I-88 corridor between Schoharie and Binghamton, NY. As indicated the Federal Incremental Method of cost allocation was used with some modifications.
Ohio
2.3.6-33	2009 Ohio HCAS	Impacts of Permitted Trucking on Ohio's Transportation System and Economy; Director James G. Beasley, P.E., P.S. http://www.dot.state.oh.us/Divisions/Legislative/Documents/ImpactsofPermittedTrucking-Web.pdf
Oregon
2.3.6-34	2011 Oregon HCAS	2011 Oregon Highway Cost Allocation Study https://www.oregon.gov/das/OEA/Documents/2017report.pdf
Tennessee
2.3.6-35	2009 TN HCAS	Highway Cost Allocation for Tennessee Final Report; 2009; Garcia, Alberto; Huang, Baoshan; Dai, Yuanshun; Dong, Qiao; Celso, Jonathan. Document available upon request from TNDOT
Texas
2.3.6-36	0-1810-1	A Framework for the Texas Highway Cost Allocation Study; Luskin, David M.; Garcia-Diaz, Alberto; Lee, DongJu; Zhang, Zhanmin; Walton, C. Michael; University of Texas; Texas A&M University http://www.utexas.edu/research/ctr/pdf_reports/1810_1.pdf
2.3.6-37	FHWA/TX-02-1810-2	Texas Highway Cost Allocation Study; Luskin, David M.; Garcia-Diaz, Alberto; Zhang, Zhanmin; Walton, C. Michael; University of Texas; Texas A&M University http://www.utexas.edu/research/ctr/pdf_reports/1810_2.pdf
Vermont
2.3.6-38	1993 VT HCAS	1993 Vermont Highway Cost Allocation Study; SYDEC, Inc. http://www.ccrpcvt.org/library/freight/highway_cost_allocation_study_19930223.pdf
2.3.6-39	VT_Pilot_2012	Vermont Pilot Program Report - a Truck Size & Weight Study, FHWA Office of Freight Management and Operations, 2012 https://ops.fhwa.dot.gov/freight/sw/reports/vt_pilot_2012/	Truck Size & weight, HCAS, Fatigue
	Executive Summary Following the enactment of Public Law 111-117 (P.L. 111-117), Vermont raised truck size and weight limits on its Interstate highways for a 1-year period beginning December 16, 2009. Several heavier truck configurations that were previously limited to Vermont State highways, including a 6-axle 99,000-pound gross vehicle weight (GVW) truck, were allowed on the Interstate System during that period. As required by P.L. 111-117, the U.S. Department of Transportation (DOT) conducted a study to examine the effects of the heavier trucks on Interstate highways in Vermont during the Pilot period. Approach While the study made the most of available models and data, a 1-year time period is simply insufficient to make any meaningful conclusions relative to the full consequences of a permanent change in vehicle weight restrictions in Vermont, or elsewhere. The pavement and bridge conclusions are based on truck volumes applied to deterministic models rather than observed damage. Pavement and bridge models are well advanced and capable of reliably predicting infrastructure impacts, while empirical measurement of infrastructure effects would require many years of empirical observation. The truck volumes applied to these models, as noted in the Commerce section of this report, reflect temporary changes and may or may not indicate how truck volumes and weights would change if the Pilot were permanent. Findings: Bridges - Study results indicate that the Pilot Program had a negligible impact on Interstate bridges in Vermont. All of the analyzed bridges provided adequate capacity to safely support the Pilot loads. However, secondary members of two existing bridges will need strengthening if Pilot loads are allowed in the future. Vermont has typically designed its bridges to higher load standards than national specifications require. As a result, the superstructure components of both existing bridges and future designs that meet current national bridge design standards will have no problem supporting the Pilot loads. Bridge decks and deck wearing surfaces may be affected by heavier loads, but the costs to address these impacts are likely to be small in comparison to overall State highway expenditures. Other bridge components such as deck joints, bearings, piers, and abutments also may be affected, but these impacts cannot be quantified with currently available analytical tools. Long-term infrastructure costs will likely be less than for other States, especially given the relatively small truck volumes on those bridges.
Washington DC
2.3.6-40	DDOT TSW 2010	District Wide Truck Size & Weight Study, Wilbur Smith Associates (CDM Smith & KS Engineers) 2010 Available upon request from CDM Smith	HCAS
Wisconsin
2.3.6-41	WisDOT 0092-10-21 CFIRE 03-17	Aligning Oversize/Overweight (OSOW) Fees with Agency Costs: Critical Issues; Teresa Adams,Ph.D., Ernie Perry, Ph.D., Andrew Schwarts, Bob Gollnik, Myungook Kang, Jason Bittner and Steven Wagner; 2013	HCAS, OSOW Truck Study
	This document attempts to address a number of issues regarding OSOW trucks in Wisconsin. Of relevance to the 2013 CTSW is the attempt to allocate bridge cost to vehicles using the load based allocator - ESAL miles. This is one of the few states that have deviated from the Federal Cost Allocation method as outlined in this document.
Australia
2.3.6-42		Third Heavy Vehicle Road Pricing Determination Technical Report, October 2005, Prepared by the National Transport Commission (NTC)
	The paper provided details of the NTC's calculation of heavy vehicles' share of road costs, used in preparing recommendations for a Third Heavy Vehicle Road Pricing Determination, to be implemented in 2006. It should be noted that the Australian Bureau of Statistics is responsible for gathering both roadway cost data as well as vehicle usage data across states and territories and combining them in a uniform nationwide statistical database on an annual basis. This provides a common data bank with which to conduct cost allocation studies on a national basis.
Europe
2.3.6-43	FP6-2005-TREN-4	Cost Allocation for Transportation Infrastructure (CATRIN) - Cost Allocation Practices in the European Transport Infrastructure Sector; 2008; European Transport Sector http://www.transport-research.info/Upload/Documents/201210/20121031_161818_54329_Catrin_D1_140308-final.pdf
	The CATRIN project aims to collect cost allocations from 15 European Union countries including the UK, Sweden, Germany, Switzerland, the Netherlands, The Dutch, Hungary, Poland, Greece, Turkey and more. The document does not aggregate the costs across the countries, but does provide several charts and tables summarizing the various methods.
2.3.6-44		Guidelines for a Study of Highway Cost Allocation, Mudge, Kulash, Ewing; Natural Resources and Commerce Division of the Congressional Budget Office,1979	HCAS Methodology
	This 1979 document provides some recommendations for future cost allocations as related to bridges. It goes on to recommend separating out certain bridge components such as bridge decks and metal; fatigue and allocating costs by a different allocator than if part of the whole. It is of interest that it was recommended that different “workable” methods be used for more equitable allocation of costs and for the most part these recommendations went largely ignored and perhaps lost in the large volume of cost allocations conducted to date.
2.3.6-45	NCHRP SYN 378	NCHRP Synthesis 378: State Highway Cost Allocation Studies; A Synthesis of Highway Practice ; CONSULTANTS: Patrick Balducci, Battelle Memorial Institute, Joseph Stowers, Sydec, Inc.; 2008 http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_syn_378.pdf	HCAS Historic Summary and Methods
	This document provides a history of cost allocation studies and a compilation of methods used by various states. In that sense it is similar to the EU CATRIN document.
2.3.6-46		HCAS Bridge Analysis, (1997) -Guidelines for Conducting a State Highway Cost Allocation Study Using the State HCAS Tool, 2000 -Documentation for Using the State HCAS Tool, 2000 Provided by the FHWA Office of Transportation Policy Studies Main investigator: James March and a team of consultants managed by Battelle Memorial Institute consisting of Roger Mingo, Joe Stowers, Harry Cohen, Holly Wolff, Dan Haling & Tom Foody. https://www.fhwa.dot.gov/policy/hcas/final/index.htm	HCAS
	The 1997 HCAS Method outlines a uniform method to conduct state cost allocations. The bridge portion of the report attempts to standardize and refine the “incremental' method developed in 70's and 80's. The final report was published in 2000. The method provides a series interconnecting spreadsheets containing truck load spectra, WIM data, state cost data etc. to aid state conducting these studies.
2.3.6-47	NCHRP Rpt 495	NCHRP Report 495: Effect of Truck Weight on Bridge Network Costs; Gongkang Fu; Jihang Feng; Waseem Dekelbab; Center For Advanced Bridge Engineering, Wayne State University; Fred Moses; University Of Pittsburgh; Harry Cohen; Dennis Mertz; University Of Delaware; Paul Thompson (including the Software Module CARRIS 1.0, a series of interconnecting spreadsheet using WinBasic macros) http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_495.pdf	HCAS Methodology for Bridges
	NCHRP Report 495 has been the commonly used method in the US for state transportation agencies and jurisdictions to conduct cost allocation studies in a modified format for their entire network of bridges or for a specific trucking corridor. The method was a refinement of the Federal “Incremental” Highway Cost Allocation method of 1997. The full report provides appendices, look up tables, step by step procedures and examples for two states. In addition it includes a software CD for the CARRIS, excel based interconnecting spreadsheets. The method compiles costs based on four cost categories - Steel Fatigue Retrofits, Reinforced Concrete Deck Fatigue, Deficiency due to existing bridge overstress and Deficiency due to new bridge overstress. The method investigates the load impact or effects of increasingly heavier trucks on the cost of posting, retrofitting or replacing a vulnerable bridge. It then extrapolates those costs to similar bridges on the network. The method is capable of investigating the effects of altering the mix of the trucks (modal shift) on the same cost categories listed above. States have used this methodology in part or as whole to conduct bridge cost allocation studies. To our knowledge, a nationwide bridge study using this methodology has not occurred to date. As the name indicates, this is a “state” tool. The fatigue methodology and formulations presented in this document will be included in one of the sub task studies on the fatigue related effects on reinforced concrete decks.
2.3.6-48	SWUTC/10/476660-00064-1	A Road Pricing Methodology for Infrastructure Cost Recovery; Southwest University Transportation Center; Conway, Alison J.; Walton, C. Michael ; 2010 http://d2dtl5nnlpfr0r.cloudfront.net/swutc.tamu.edu/publications/technicalreports/476660-00064-1.pdf	HCAS Method
	Abstract: The purpose of this research is to provide a theoretical framework for future commercial vehicle user-charging using real-time vehicle weight and configuration information collected using weigh-in-motion (WIM) systems. This work provides an extensive review of both mechanisms and technologies employed for commercial and passenger vehicle user-charging worldwide. Existing commercial vehicle-user charging structures use only broad vehicle classifications to distinguish between vehicles for the pricing of user-fees. The methodology proposed in this study employs highway cost allocation methods for development of an “Axle-Load” toll structure. A theoretical case study, based on information from Texas State Highway 130, is performed to explore the equity improvements that could be achieved through implementation of this proposed structure. Some sensitivity analysis is also performed to examine the potential revenue impacts due to uncertainties in different data inputs under existing and proposed structures.
2.3.6-49		Cost Allocation By Uniform Traffic Removal Theoretical Discussion And Example Highway Cost Applications; 1992 Chris Hendrickson Department of Civil Engineering, Carnegie-Mellon University, and Kane, Anthony; Pergammon Press, UK Office of Program and Policy Planning, Federal Highway Administration, Washington. DC 20590. U.S.A.	HCAS Method
	Abstract: The paper proposes 4 methods for equitable roadway cost allocations: (a) allocated costs should be based on full cost recovery, (b) allocated costs must be non-negative for any traveler group, (c) cost allocations should be additive, and (d) cost allocations should be consistent where equivalency factors among traffic categories exist. For cases with well-behaved cost functions, the uniform traffic removal technique discussed here uniquely satisfies these four properties and should be used whenever the four allocation properties are desired. Example applications as well as cases in which cost functions are not well behaved are discussed
2.3.6-50		Highway Cost Allocation Methodologies; Alemayehi Ambo, F.R. Wilson and A.M. Sevens; Transportation Group, University of New Brunswick, Fredericton, N.B. Canada; January 1991	HCAS
	Abstract: Four methodologies of life-cycle highway cost allocation were examined using the province of New Brunswick, Canada as a case study. The first two methodologies were reported by Wong and Markov. The third methodology was suggested by Rilett et al. The fourth methodology was introduced as part of a research project. It was in line with the procedures practiced in public accounts for the construction and maintenance of roads on a continuing basis. The four methodologies were tested using the same data base pertaining to vehicle types; traffic measures (independent vehicle, passenger car equivalents, and equivalent standard axle loads); and costs of construction, maintenance, and rehabilitation. These data were applicable to a major two-lane highway in the study area. Six sites were selected for the case study. An analysis period of 60 years, three traffic growth scenarios, three pavement design periods were considered. Eleven types of vehicles comprising passenger cars, light trucks and vans, trucks, buses and recreational vehicles were used in the analysis. The assessment of the methodologies resulted in the recommendation of and suggestions for the costing of highways. This was the only document related to Bridge Cost Allocation study in Canada. Studies referenced at the Transport Association of Canada web site refer to US studies. We will continue to search for any relevant provincial or national Canadian Studies.
2.3.6-51	Freight Facts and Figures 2012	Office of Freight Management and Operations- Freight Facts and Figures 2012; Office of Freight Management; https://www.freight.dot.gov	Freight
	Freight Facts and Figures 2012 is a snapshot of the volume and value of freight flows in the United States, the physical network over which freight moves, the economic conditions that generate freight movements, the industry that carries freight, and the safety, energy, and environmental implications of freight transportation. This snapshot helps decision makers, planners, and the public understand the magnitude and importance of freight transportation to the economy. This report provides information on freight volume and movement between modes of transportation. It is referenced by the team to better understand modal shift data and issues.
2.3.6-52	FHWA/IN/JTRP-2004/12	Quality Control Procedures for Weigh-in-Motion Data; Andrew P Nichols; Marshall University; Darcy M. Bullock, Purdue University; http://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1647&context=jtrp	WIM Data
	Abstract: For the past two decades, weigh-in-motion (WIM) sensors have been used in the United States to collect vehicle weight data for designing pavements and monitoring their performance. The use of these sensors is now being expanded for enforcement purposes to provide virtual weigh stations for screening vehicles in traffic streams for overweight violations. A study found that static weigh stations in Indiana were effective for identifying safety violations, but ineffective for identifying overweight vehicles. It was also determined that the alternative approach to identifying overweight vehicles using virtual weigh stations requires a high level of WIM data accuracy and reliability that can only be attained with a rigorous quality control program. Accurate WIM data is also essential to the success of the Long-term Pavement Performance project and the development of new pavement design methods. This report proposes a quality control program that addresses vehicle classification, speed, axle spacing, and weight accuracy by identifying robust metrics that can be continuously monitored using statistical process control procedures that differentiate between sensor noise and events that require intervention. The speed and axle spacing accuracy is assessed by examining the drive tandem axle spacing of the population of Class 9 vehicles. The weight accuracy is assessed by examining the left-right steer axle residual weight of the population of Class 9 vehicles. Data mining of these metrics revealed variations in the data caused by incorrect calibration, sensor failure, temperature, and precipitation. The accuracy metrics could be implemented in a performance-based specification for WIM systems that is more feasible to enforce than the current specifications based on comparing static vehicle weights with dynamic vehicle weights measured by the WIM sensors. The quality control program can also be used by agencies to prioritize maintenance to more effectively allocate the limited funds available for sensor repair and calibration. This research provides a tool that agencies can use to obtain and sustain higher quality WIM data. This report provides detailed information on WIM sensors, how WIM data is collected, data mining and WIM data quality issues. It is essential in understanding the WIM data that will be provided by other task leads, quality and reliability issues.
2.3.6-53	NCHRP RPT 683	Protocols for Collecting and Using Traffic Data in Bridge Design. B. Sivakumar; M. Ghosn; F. Moses; TranSystems Corporation, 2011. http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_683.pdf	WIM Data Scrubbing
	This report documents and presents the results of a study to develop a set of protocols and methodologies for using available recent truck traffic data to develop and calibrate live load models for LRFD bridge design. The HL-93, a combination of the HS20 truck and lane loads, was developed using 1975 truck data from the Ontario Ministry of Transportation to project a 75-year live-load occurrence. Because truck traffic volume and weight have increased and truck configurations have become more complex, the 1975 Ontario data do not represent present U.S traffic loadings. The goal of this project, therefore, was to develop a set of protocols and methodologies for using available recent truck traffic data collected at different US sites and recommend a step-by-step procedure that can be followed to obtain live load models for LRFD bridge design. The protocols are geared to address the collection, processing and use of national WIM data to develop and calibrate vehicular loads for LRFD superstructure design, fatigue design, deck design and design for overload permits. These protocols are appropriate for national use or data specific to a state or local jurisdiction where the truck weight regulations and/or traffic conditions may be significantly different from national standards. The study also gives practical examples of implementing these protocols with recent national WIM data drawn from states/sites around the country with different traffic exposures, load spectra, and truck configurations.
	In addition, for documents referencing Methods and Impacts of Bridge Serviceability see “Reference No's.”: 2.1.6-12; 2.1.6-16; 2.1.6-17; 2.1.6-18; 2.1.6-22

CHAPTER 3 - Bridge Deck Deterioration, Service Life and Preventative Maintenance

This sub-study area was originally conceived as two independent studies, 'Bridge Deck Deterioration Mechanisms' and 'Bridge Deck Preservation and Maintenance'. It was soon realized that these topics are intimately related and integrated in terms of agency program implementation. Accordingly they have been combined in this report.

3.1 A Survey of Analysis Methods and Synthesis of the State of Practice in Modeling Bridge Deck Impacts

3.1.1 Bridge Deck Deterioration Model

Analysis and design methods of reinforced concrete bridge decks are based on the AASHTO LRFD Bridge Design Specifications, 2011, 6th Edition. Reinforced concrete bridge decks behave in a complex manner, especially at the end of the serviceable deck life, however the design of decks is simply based on ultimate flexural strength. In order to understand the assumptions and limitations the bridge team explored other existing models that can define, measure and predict bridge deck damage. The desk scan included studies related to bridge deck deterioration mechanisms either based on 1) chloride contamination/freeze thaw action; or 2) mechanical-dynamic and repetitive loading. Studies and experiments that involved both deterioration mechanisms were limited in scope and only provided qualitative descriptions of the mechanisms and no quantifying metrics on deck damage.

Reports by Williamson and Weyers, et al., (Virginia DOT) 2008 and N. Hu and Syed, et al, (Michigan DOT) 2013 used a probabilistic framework based on chloride contamination of the reinforcement bars through a pre-existing network of micro-cracks and the eventual re-cracking and deterioration of the bridge deck due to freeze-thaw action. Y. Tanaka et al, 2009 (Japan Public Works Research Institute PWRI), Takashi et al (PWRI) in two separate reports studied the effects of truck axle loads (both static and dynamic) on bridge decks and the propagation of cracks from a microscopic scale to general deck failure in cold weather climates. The primary cause of failure in these studies was considered to be repetitive axle loading. In a Nebraska Department of Roads (NDOR) study, G. Morcous, 2011, used a data driven approach (using bridge deck ratings from inspection data) to predict when bridge (deck) ratings were likely to fall from a given condition state to a lower level. Further refinements were implemented by incorporating ADTT and cold/wet climatic data. It also demonstrated how the rate of deterioration of bridge decks increased non-linearly as the truck GVW increased. A general trend among current efforts is to develop predictive models following the data driven approach.

• Finding: These studies acknowledged the need to study the long term combined effects of axle loads and wet/cold climates. And metrics need to be established to quantify damage based on both mechanisms. The search for related studies revealed there is very little research in this area.

The search for deterioration models also considered service limit states as described by the Auburn University Study, Cost/Benefits of Employing Thicker Bridge Decks (Ramey, et al., 2000). Alabama bridge decks were cracking prematurely under regular truck axle loads and were found to be 1" to 1.5" thinner than comparable bridge decks in most other states. A California case study (as chronicled in NCHRP Report 495, 2003) compared two parallel alignment interstate bridge decks in Alameda County. One deck allowed only passenger cars and light trucks, while the other bridge deck, although slightly thicker (1"), allowed all truck traffic over a 37 year period. The thicker bridge deck with heavy truck traffic exhibited more surface damage even after a rehabilitation project at the end of the 37 years than the thinner bridge deck with no major rehabilitation.

S. Matsui (1991), P. Perdikaris (1993), and Tanaka (2003) conducted studies on the fatigue mechanisms in concrete decks combined with the effects of de-icing salts. The life cycle of bridge decks from construction to deck fracturing and failure were established and arching behavior of fractured bridge decks was investigated. It was further established that de-icing salts (chloride contamination) greatly accelerated the deterioration process.

• Finding: The clear indication is that chloride contamination accelerates bridge deck deterioration. But this is only observed at the mid- to near the end life cycle of the bridge, mainly due to the period of time it takes for the chlorides to permeate through the bridge deck and form oxidation or rust products around the reinforcement bars, which in turn causes delamination of the surrounding concrete.
• Finding: The desk scan revealed that there is no commonly accepted metric to measure the degree of bridge deck deterioration. However, some studies attempted to measure the density of surface defects while others measured the degree of internal cracking or fracturing. This may be due to the number of variables involved in developing such a model. These variables include concrete mix, construction methods (support/shoring and curing), deck thickness, beam spacing and actual truck axle loadings.

An Ohio DOT study by Ganapuram et al, 2012 looked at 12 bridges in Ohio District 3 and compared concrete slab bridges to stringer supported bridges. An Indiana DOT study by Frosch et al, 2010 studied early onset deck cracking with the objective of developing more effective design and repair methods to extend deck life. Another Indiana DOT study by Yang et al., 2004 investigated the interaction between micro-cracking and reduced concrete durability with the purpose of: assessing cumulative damage; finding common parameters among pavements that could quantify overall damage; and testing/calibrating non-destructive technologies. This study was conducted on concrete pavements and not bridge decks; but it may still provide insight into bridge deck deterioration mechanisms. None of these studies, while informative were conducted with the goal of establishing a uniform metric for measuring or quantifying bridge deck damage.

3.1.2 State DOT Policies on Repair, Replacement and Preservation

As indicated above, many states have deployed an integrated asset management system which combines (bridge) inspection data (condition reports) with the availability of their maintenance forces (crews, equipment and budget) and tries to target the repair and rehabilitation of bridges with the most critical needs. The scope of the activity determines whether the repairs are done with in-house maintenance crews (for such activities as patching and crack sealing of the decks) or if they become part of a capital program involving design and specialty contractors (such as deck replacement or a programmatic deck joint replacement). How these decisions are made depends on the DOT capabilities as well as their policies.

The desk scan of DOT web sites for maintenance and preservation policies found several DOT web sites that either had published manuals available with PDF downloads or had web pages/portals that listed their policies and practices for bridge deck preservation and maintenance. These included California (Caltrans Highway Maintenance Manual, Volume 1, 2006), Indiana (IDOT Highway Maintenance Manual, Chapter 72, Bridge Rehabilitation 2013), Michigan (Capital Scheduled Maintenance, Bridge Manual, 2010) and Ohio (ODOT, Web site only). The team also found secure portals that required credentials and were tied in with their bridge inspection software. As such we were limited to what could be gleaned from the various agencies.

Bridge Deck Asset Management TRB and NCHRP reports: The desk scan also addressed the national effort to standardize the data and reporting practices. On the bridge inspection side (NBIS), MAP-21 requires that FHWA start collecting element level bridge data for the NBI on the NHS within two years, and to conduct a study of benefits and costs associated with extending this requirement to non-NHS bridges. Many states are now using Element Level Inspection (ELI) in concert with a bridge management system (BMS). NCHRP Report 668, G. Hearn et al, 2010 investigated the use of Bridge (Asset) Management Systems (BMS) and setting up a national standard for collecting, reporting and storing information on bridge maintenance actions. The underlying reason for employing these systems is to provide a framework for developing a data-driven predictive bridge (deck) model that may alert agencies when a specific action is recommended to prolong and preserve bridge (deck) life. In other words, a bridge deck deterioration model would be built into the asset management system.

3.2 Data needs and an evaluation and critique of available data sources for bridge decks

3.2.1 Comparison of State Unit Cost Data

The following DOT web sites were found to readily provide public access information on bridge projects and provide unit cost data: Alabama, Arkansas, California, Colorado, Connecticut, Delaware, Florida, Georgia, Indiana, Louisiana, Missouri, Nebraska, New York, Ohio, Virginia, Pennsylvania, Tennessee, Washington, DC, and Wisconsin.

This unit cost data was valuable in that it generally consisted of real costs reported by contractors, however the reported cost categories varied widely in their description of what was included and therefore the range of costs for similar work items had considerable variation. Therefore the need for a national bridge asset management standard becomes inherently obvious. There must be an agreement on which cost elements to include in the quoted costs (such as design engineering, mobilization / de-mobilization, Work Zone Traffic Control (WZTC), Construction Inspection (CI), demolition and removal).

In order to augment some of our findings regarding the bridge deck deterioration mechanism the bridge team conducted a qualitative anecdotal survey (interview) of two agency bridge owners/managers. The bridge team contacted the Indiana DOT and the New York Bridge Authority in order to conduct informal interviews on the condition of their bridge decks on routes that routinely allow heavier (permitted) trucks, heavier than the current Federal weight limits. The information gained from these agencies confirmed our understanding of bridge deck deterioration mechanisms and the critical effects of heavy trucks and axle loadings.

NCHRP Project 14-15, led by principal investigator G. Hearn (Univ. Of Colorado), developed a framework that could be a model for collection of bridge inspection data to tie into state and national bridge management databases. States are beginning to develop bridge management systems based on element level inspection data, PONTIS and life cycle cost analysis. Georgia, North Carolina and New York are examples of states that are in various phases of development of such programs. New York DOT's Bridge Data Information System (BDIS) will be incorporated into an integrated total infrastructure asset management system that will include bridges, office buildings, parking facilities, rest areas, pavement, sign structures, high mast lights, cell towers, retaining walls, culverts and perhaps tunnel structures.

3.3 An assessment of the current state of the understanding of the impact and needs for future research, data collection and evaluation

• There is a lack of research combining the effects of the primary long term bridge deck deterioration mechanisms; the repetitive effect of dynamic axle loads and climatic effects (i.e., chloride contamination).
• There is no accepted uniform metric to quantify the degree of deck deterioration and to correlate it with inspection ratings. However, condition states for element level inspections represent an effort toward this goal, one that will likely be incorporated into the FHWA's greater goal of establishing a long term data driven transportation infrastructure program management system.
• There is a lack of consistency in data (cost) format and reporting methods between agencies, partly due to the lack of a uniform reporting standard. This is also partly due to different rehabilitation and preservation practices between the states. It's to a large degree a product of the policies that drive the states' capital programs. For instance, one state might include proactive minor repairs in their capital cost tabulation that would be considered as preventive maintenance by other states, the costs for which would be buried in the accounting for a general highway department. Another factor contributing to the lack of consistency in reporting bridge costs is the degree to which a given agency is proactive or on the other hand reactive with respect to bridge deterioration. At a national level FHWA's FMIS program collects and summarizes bridge related costs for each of the states. However, these are project costs and may include approach highway work. Due to the lack of detail in the FMIS data, it is difficult to segregate the bridge specific component of these costs. Also, many of these projects and/or parts of these projects would not be a result of load induced factors. There is an effort underway to establish a framework for building a national bridge database with standardized reporting methods. In addition many states have implemented or about to implement asset management systems which may include life cycle analyses to prolong the intended serviceable life of bridge decks. The BMS will help these states to comply with the overall national effort in developing the bridge (deck) database and all agencies will potentially benefit from it.
• Implied in developing this database and the BMS is that it may include or lead to a predictive data driven model on bridge deck deterioration.

3.4 Past studies with past prospective and retrospective estimates in each category of effect

• Past CTSW studies did not include sections specifically dedicated to bridge decks. This was a new and unique area of study for the 2014 CTSW Study. It represents one of the highest cost bridge elements (to state DOT agencies) and one of the most visible elements to the traveling public. Past CTSW studies investigated the structural behavior of the bridge, as a whole, with respect to truck impacts.
• NCHRP Report 495 (2003) Effect of Truck Weight of Bridge Network Costs provided a method for State Agencies to study the cost impacts on their bridges. One of the cost elements in that study was the effect of trucks on reinforced concrete bridge deck fatigue. The report provided insight and references for the bridge deck behavior and deterioration mechanism, however the limited time and scope of this project as well as its national scale, did not allow for a direct application of that very complex method with its numerous variable parameters to this study.
• There is what appears to be a flaw in using reinforced concrete fatigue life as a metric for estimating bridge deck health. The method uses AASHTO fatigue trucks as a baseline and typically bridge deck fatigue life ranges exceed hundreds of years. The current accepted average bridge deck serviceable life is 25 to 55 years in most regions. In this regard, there needs to be a calibration of the fatigue life estimation to actual bridge deck service life.

3.5 List of References

Modeling and Discussing Bridge Deck Impacts due to Overweight Trucks and Environmental Effects

Reference No.	Document No.	Document Title and Link	Relevance to Study
The topic of bridge asset management was included to hi-light a series of topics germane to state policies toward the maintenance and preservation of bridges. Key questions addressed include: First, what are the tools that state agencies use (such as PONTIS and Bridge Management Systems) for asset management? Secondly what decision making process is used for preserving, retrofitting or replacing bridges? Thirdly what is included/excluded in their budgets? Ultimately we are interested in the bridge costs that the proposed future fleet of trucks will have on the nation's bridges. The link to the FHWA Long Term Bridge Performance (LTBP) web site and publications were included in this study. There is an apparent paradigm in thinking and philosophy that is occurring in light of the nation's aging bridges. In the past 100 years or so, bridges have been built with a planned life span of 75 years. What design standards do we use for trucks that have not yet been conceived and how will these bridges be designed and constructed to meet future needs for an extended life cycle? It's an interesting question, since we are attempting to address a similar issue with regard to bridges that are in service now. How will they perform under the load of a different set of vehicles? Another issue that has been raised with regard to bridge preservation and maintenance costs: as indicated by NCHRP Synthesis Report 397 each state has its own unique set of practices and cost factors that are tracked. How can this data be used to make comparisons between states that allow heavier vehicles vs. those that do not? Is it even possible to draw such conclusions? In a greater context can these costs be collected in a standardized way to conduct a national cost allocation study? References in this section were selected to address specific issues or were general informational topics relating to bridge decks. The first several reports refer to bridge deck durability, methods for preserving decks including different overlay methods and materials, design of orthotropic steel decks, non-destructive testing of reinforced concrete decks, and a few articles on causes of cracking in reinforced concrete decks whether they be caused by construction (early stripping of forms, improper curing, shrinkage), environment (temperature, rain, snow followed by application of de-icing salts) and/or load induced by vehicles and trucks. An effort is made to understand that initial cracking in bridge decks may not be necessarily caused just by vehicles and trucks, but by other means. However, the eventual development of cracks and other deterioration can be partially attributed to the traveling vehicles (i.e. load) on the bridge deck. An important reference for bridge decks is the NCHRP Report 495, Effect of Truck Weights on Bridge Network Costs. This report describes an approach for evaluating reinforced concrete bridge decks for crack propagation as it relates to cost allocations studies. However, a very detailed section is provided on describing the deck deterioration mechanism and ties the failure point of decks to the ultimate shear strength of the deck. (Based on independent studies conducted by Matsui et al at Osaka University Japan 1992 & by Perdicaris at Case Western Reserve University 1993).
3.5-1		California Department of Transportation (2006). Highway Maintenance Manual, Volume 1 Chapter H. https://dot.ca.gov/programs/maintenance/maintenance-manual	Bridge Asset Management
	This is a series of web based online highway maintenance manuals developed by Caltrans. Chapter H pertains to Bridge Maintenance and Repair Practices. Of particular interest was section H.08.0, which discouraged the use of asphaltic concrete overlay over concrete decks, which are commonly used elsewhere.
3.5-2		Indiana Department of Transportation (2013). Highway Maintenance Manual, Chapter 72, Bridge Rehabilitation	Bridge Asset Management
	Chapter 72, sub section 3.01(02) describes typical department practices with respect to bridge deck rehabilitation. The department does not proscribe the use of asphaltic concrete overlay. The Department is actively researching use of various other repair and rehabilitation materials to prolong bridge decks. See research under “Implementation of Performance Based Bridge Deck Protective Systems”, Frosch, et al 2013.
3.5-3	FHWA-HRT-08-004	History Lessons From the National Bridge Inventory; Analyzing data from the NBI can help predict how bridge decks will perform, Waseem Dekelbab, Adel Al-Wazeer, Bobby Harris, FHWA Turner Fairbanks - Public Roads - Vol. 71, No. 6 https://www.fhwa.dot.gov/publications/publicroads/08may/05.cfm	Bridge Deck Deterioration Models
	Researchers recently analyzed the numbers and data stored in the NBI. Their findings could offer insight and improve understanding of bridge performance based on 24 years of information compiled in the database. For example, information gained from this research will help answer the question, “How much longer is a bridge in a certain condition likely to stay in that condition before deteriorating further?” Deterioration Models for Bridge Decks Predicting performance is the main challenge in the life-cycle assessment and asset management of bridges. Performance of the bridge deck is a major maintenance and serviceability concern because the deck is the component most prone to problems that affect traffic and requires the most maintenance and replacement work. Loss of deck performance generally results from corrosion (caused by natural salinity or direct application of deicing agents), traffic loading and vibration, temperature fluctuations, and other factors. A modeling method based on medical “survivability” concept of “survival” function was developed. This article offers another bridge deterioration model based on NBI data. As with the other probabilistic models it is not yet able to predict behavior based on truck load-induced truck damage. Furthermore, it is a study in progress and no definitive methodology has been suggested.
3.5-4	FHWA-ICT-12-003	Superiority & Constructability of Fibrous Additives for Bridge Deck Overlays, Alhassan, Mohammad A, Ashur, Soleiman A, Indiana-Purdue University Fort Wayne; Illinois Center for Transportation https://apps.ict.illinois.edu/projects/getfile.asp?id=3054	Bridge Deck, Durability, Life Cycle Analysis
	This project outlined critical issues essential for successful and durable overlay applications with minimal cracking and delamination. Various micro- and macro-fiber combinations were added to the fibrous overlay mixtures, resulting in 13 fibrous mix designs (nine LMC, two MSC, and two FAC). For further evaluation of the constructability of fibrous overlay-taking into consideration actual field conditions-demonstration bridges were selected and received fibrous overlays through actual IDOT contracts. Life-cycle cost analyses were also conducted to assess potential savings from incorporating fibrous additives within the concrete overlays. This research is pioneering in terms of using fibrous FAC overlay, which could be a potentially sustainable overlay system for preserving bridge decks with lower cost and minimized adverse environmental impact.
3.5-5	FHWA-IF-12-027	Manual for Design, Construction, and Maintenance of Orthotropic Steel Deck Bridges; 2012, Conner, Robert, Fisher, John, et al. https://www.fhwa.dot.gov/bridge/pubs/if12027/if12027.pdf	Orthotropic Steel Decks
	This Manual covers the relevant issues related to orthotropic steel deck bridge engineering, including analysis, design, detailing, fabrication, testing, inspection, evaluation, and repair. It includes a discussion of some the various applications of orthotropic bridge construction to provide background with case study examples. It also provides basic criteria for the establishment of a cost-effective and serviceable orthotropic bridge cross section with detailing geometry that has been used on recent projects worldwide. The manual covers both the relevant information necessary for the engineering analysis of the orthotropic steel bridge and the requirements for complete design of orthotropic steel bridge superstructures. Additionally, design details such as materials, corrosion protection, minimum proportions, and connection geometry are addressed as well as basic fabrication, welding, and erection procedures. Portions of the manual also cover methods for maintaining and evaluating orthotropic bridges, including inspection and load rating. Wearing surfaces are also covered in depth. The culmination of all the information is demonstrated in two design examples.
3.5-6	NCHRP SYN 425	Waterproofing Membranes for Concrete Bridge Decks; Prepared by Russell, Henry G. for AASHTO http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_syn_425.pdf	Bridge Decks
	The objective of this synthesis is to update NCHRP Synthesis of Highway Practice 220: Waterproofing Membranes for Concrete Bridge Decks on the same topic published in 1995. This synthesis documents information on materials, specification requirements, design details, application methods, system performance, and costs of waterproofing membranes used on new and existing bridge decks since 1995. The synthesis focuses on North American practices with some information provided about systems used in Europe and Asia.
3.5-7	FHWA/OH-2012/3	Quantification of Cracks in Concrete Bridge Decks in Ohio District 3; 2012; Sai Ganapuram, Michael Adams, Dr. Anil Patnaik; University of Akron http://www.dot.state.oh.us/Divisions/Planning/SPR/Research/reportsandplans/Reports/2012/Structures/134564_FR.pdf	Bridge Decks, Cracks
	In this study, a quantitative measurement strategy was adopted by measuring the crack densities of twelve bridges in District 3. Two types of bridges were inspected: three structural slab bridge decks and nine stringer supported bridge decks. Crack densities were determined based on crack maps corresponding to the surveys for each bridge deck. The crack densities determined for the twelve bridge decks indicated that structural slab bridge decks have slightly higher shrinkage crack densities compared to the bridge decks constructed with stringer supports.
3.5-8	SHRP2 S2-R06A-PR1	Nondestructive Testing to Identify Concrete Bridge Deck Deterioration; Rutgers University - Center for Advanced Infrastructure and Transportation; University of Texas at El Paso; Federal Institute for Materials Research and Testing, BAM Germany; Radar Systems International http://onlinepubs.trb.org/onlinepubs/shrp2/SHRP2_S2-R06A-RR-1.pdf	Bridge Decks, Non-Destructive Testing (NDT)
	The ultimate goal of this research was to identify and describe the effective use of NDT technologies that can detect and characterize deterioration in bridge decks. To achieve this goal, the following four specific objectives needed to be accomplished: Identifying and characterizing NDT technologies for the rapid condition assessment of concrete bridge decks; Validating the strengths and limitations of applicable NDT technologies from the perspectives of accuracy, precision, ease of use, speed, and cost; Recommending test procedures and protocols for the most effective application of the promising technologies; and Synthesizing the information regarding the recommended technologies needed in an electronic repository for practitioners
3.5-9	FHWA/IN/JTRP-2010/04	Control and Repair of Bridge Deck Cracking, Robert Frosch, Sergio Gutuirrez, Jacob Hoffman; Purdue University; Indiana DOT; 2010 http://docs.lib.purdue.edu/jtrp/1125	Bridge Deck Cracking
	A large number of bridges across the state of Indiana had exhibited early age deck cracking. This presented a major threat to the lifespan of these bridges, as deck cracking often leads to corrosion of the reinforcing steel by creating a path for water and deicing salts to reach the steel. Therefore, the need to develop design and construction guidelines to control deck cracking in newly constructed bridges was recognized. In addition, a method to repair deck cracks must be developed to prevent corrosion of the reinforcement in bridges already in service. The objective of this research was to develop effective design, construction, and repair methods for the control of bridge deck cracking
3.5-10	FHWA/IN/JTRP-2013/12	Implementation of Performance Based Bridge Deck Protective Systems, R.J. Frosch, M.E. Kreger, and B. Strandquist; Purdue University, Indiana DOT; 2013 http://docs.lib.purdue.edu/jtrp/1533	Bridge Decks
	When considering the durability of a bridge, the concrete deck is often the most vulnerable component and can be the limiting factor affecting service life. To enhance the durability of both new and existing bridge decks, a protective system is often provided to prevent or delay the ingress of chlorides and moisture to the reinforcing steel. In the state of Indiana, this protective system typically comes in the form of a concrete overlay or a thin polymer overlay. Another protective system widely used in the United States and in many countries internationally consists of a waterproofing membrane overlaid with asphaltic concrete. Due to a history of poor performance in the 1970's and the 1980's, a moratorium has been placed on the installation of waterproofing membranes in Indiana. This study reevaluates the state-of-the-practice of bridge deck protection in Indiana with the goal of enhancing the Indiana Department of Transportation's toolbox of bridge deck protective systems. Consideration was given to the state-of-the-art and state-of-the-practice in bridge deck protective systems used by other state transportation agencies as well as by international transportation agencies. Research focused on the practice of installing waterproofing membranes and the latest technologies being used. Based on the information gathered, various protective systems were evaluated, and recommendations are provided on the selection of the most appropriate systems for various bridge conditions. Furthermore, a recommendation is provided to remove the moratorium on membrane systems so that the benefits of this system can be more fully explored and realized.
3.5-11	FHWA/IN/JTRP-2004/10	Interaction Between Micro-Cracking, Cracking, and Reduced Durability of Concrete: Developing Methods for Quantifying the Influence of Cumulative Damage in Life-Cycle Modeling; 2004; Yang, Zhifu ; Weiss, W Jason; Olek, Jan; Joint Highway Transportation Program; Indiana DOT, Purdue University http://docs.lib.purdue.edu/jtrp/	Cracking, NDT, Detection, Measurement
	While uncracked concrete exists as the best case scenario, frequent cracking occurs in real structures that could have a profound impact on life cycle performance. Cracks from several sources may accumulate and interact thereby accelerating the deterioration of concrete. For example, the distributed cracking caused by freeze/thaw damage can substantially increase the rate of water absorption and reduce the load carrying capacity of concrete. To accurately simulate the performance of actual concrete facilities, the role of cracking and its cumulative effect on the changes of material properties was intended to be accounted for in these models. The main goal of this investigation was to assess the influence of cumulative damage in concrete and to quantify its influence for use in life-cycle performance modeling. Samples were taken from five concrete pavement sections based on age, traffic, and overall performance to assess existing damage and to identify possible sources responsible for inducing the damage. These results were used as a baseline to assess the types of damage that merited laboratory investigation. After the field assessment, laboratory investigations were conducted to simulate the damage that may be expected in the field. After various levels of damage were introduced in laboratory specimens, durability tests (freezing and thawing and water absorption) and direct tensile tests were performed to develop an understanding of how the pre-existing damage accelerated the deterioration process. Specifically, it was determined that cracks caused by freezing and thawing dramatically increase the rate and amount of water absorption while cracks caused by mechanical loading only increased the absorption in a local region. Further, freeze-thaw damage dramatically reduces the direct tensile strength and modulus of elasticity of concrete until the aggregates begin to pull out of the matrix. This results in a larger fracture process zone in the damaged concrete than in the undamaged concrete.
3.5-12	VTRC 08-CR4	Bridge Deck Service Life Prediction and Costs, Gregory Williamson, Richard Weyers, Michael Brown, Michael Sprinkel; Virginia DOT, Virginia Polytechnic Institute, Virginia Transportation Research Council, 2008 http://www.virginiadot.org/vtrc/main/online_reports/pdf/08-cr4.pdf	Bridge Deck Deterioration, Chloride Contamination
	The service life of Virginia's concrete bridge decks is generally controlled by chloride-induced corrosion of the reinforcing steel as a result of the application of winter maintenance deicing salts. A chloride corrosion model accounting for the variable input parameters using Monte Carlo resampling was developed. The model was validated using condition surveys from 10 Virginia bridge decks built with bare steel. Life cycle cost analyses were conducted for polymer concrete and Portland cement based overlays as maintenance activities. The most economical alternative is dependent on individual structure conditions. The study developed a model and computer software that can be used to determine the time to first repair and rehabilitation of individual bridge decks taking into account the time for corrosion initiation, time from initiation to cracking, and time for corrosion damage to propagate to a state requiring repair. Virginia DOT uses the chloride contamination and intrusion mechanism in concrete to develop a predictive model based game theory on RC deck deterioration. Then it uses a life cycle cost analysis to determine the best course of action to preserve deck life. This modeling approach, however does not include the effect of axle load induced crack propogation as a factor in deck deterioration.
3.5-13	CEE-RR -2013/02	Development and Validation of Deterioration Models for Concrete Bridge Decks; Phase 2: Mechanics based Degradation Models, Nan Hu, Syed Haider, Rigoberto Burgueno, Michigan DOT, Michigan State University https://www.michigan.gov/documents/mdot/RC-1587B_435818_7.pdf	Bridge Deck Deterioration, Chloride Contamination
	This report summarizes a research project aimed at developing degradation models for bridge decks in the state of Michigan based on durability mechanics. A probabilistic framework to implement local-level mechanistic-based models for predicting the chloride-induced corrosion of the RC deck was developed. The methodology is a two-level strategy: a three-phase corrosion process was modeled at a local (unit cell) level to predict the time of surface cracking while a Monte Carlo simulation (MCS) approach was implemented on a representative number of cells to predict global (bridge deck) level degradation by estimating cumulative damage of a complete deck. The predicted damage severity and extent over the deck domain was mapped to the structural condition rating scale prescribed by the National Bridge Inventory (NBI). The influence of multiple effects was investigated by implementing a carbonation induced corrosion deterministic model. By utilizing realistic and site-specific model inputs, the statistics-based framework is capable of estimating the service states of RC decks for comparison with field data at the project level. Predicted results showed that different surface cracking time can be identified by the local deterministic model due to the variation of material and environmental properties based on probability distributions. Bridges from different regions in Michigan were used to validate the prediction model and the results show a good match between observed and predicted bridge condition ratings. A parametric study was carried out to calibrate the influence of key material properties and environmental parameters on service life prediction and facilitate use of the model. A computer program with a user-friendly interface was developed for degradation modeling due to chloride induced corrosion. This study is similar to the Virginia DOT study on RC deck deterioration in terms of approach and modeling. Similar to the VDOT study, no attempt is made to account for the effects of truck axle loads. In terms of policy and strategy to prolong the bridge deck life, the agency uses a different approach. In this study the DOT is using empirical data or the current deck condition ratings to verify the deterioration progression.
3.5-14	FHWA/TX-12/0-6348-2	Bridge Deck Reinforcement and PCP Cracking: Final Report; Oguzhan Bayrak, Shih-Ho Chao, James O. Jirsa, Richard E. Klingner, Umid Azimov, James Foreman, Stephen Foster, Netra Karki, Ki Yeon Kwon, and Aaron Woods; Center for Transportation Research, The University of Texas; TXDOT, 2010 http://www.utexas.edu/research/ctr/pdf_reports/0_6348_1.pdf	Bridge Deck Cracking
	Bridge decks composed of precast, pre-stressed panels (PCPs) overlain by cast-in-place (CIP) are popular in many states, including Texas. Optimization of top-mat reinforcement and reduction of collinear panel cracking were addressed in this project. Longitudinal top-mat reinforcement was found to be already optimized. Further optimization of transverse top-mat reinforcement is possible by slightly reducing the area of deformed reinforcement or by using welded-wire reinforcement. Collinear panel cracking can be reduced by reducing the initial pre-stress or by placing additional transverse reinforcement at panel ends. Measured pre-stress losses in PCPs were at most 25 ksi, much less than the 45 ksi previously assumed by TxDOT. The comparative efficiency of different types of high-performance steel fibers was examined. Double-punch testing, appropriately standardized as proposed in this report, was found to be a reliable and repeatable measure of the comparative efficiency of high-performance steel fibers.
3.5-15	PWRI Report 5-2tanaka	Fatigue and Corrosion in Concrete Decks with Asphalt Surfacing; Yoshiki Tanaka, Jun Murakoshi, Yuko Nagaya, Public Works Research Institute, Japan (PWRI, Japan) http://www.pwri.go.jp/eng/ujnr/tc/g/pdf/25/5-2.pdf	RC Deck Fatigue; Corrosion
	In 20th century, a large number of highway bridge reinforced concrete bridge decks in the U.S. suffered from corrosion due to deicing salt, however, similarly constructed bridge decks in Japan suffered from fatigue due to the cyclic loading of heavy truck axles. Lately, significant corrosion of concrete decks due to deicing salt have also been reported in Japan, giving rise to further concerns about combined deterioration from fatigue and corrosion in existing bridge decks designed according to old specifications. This paper provides a comparison of bridge decks chloride profiles in asphalt covered concrete decks in Japan and bridge decks in the US to see if there was a significant difference in deterioration rates. Additional research was conducted on the decks with regard to the interaction chloride contamination with RC concrete fatigue mechanisms with the rate of deterioration using dynamic wheel load testing. The study provided some insight in the behavior of concrete decks with regard to fatigue and studies the rate of deterioration of concrete decks when impregnated with chloride salts. However, there was no direct interactive testing of the two deterioration mechanisms that of are direct interest to the deterioration mechanism under study.
3.5-16	PWRI Report 23-2-4satoh	Fatigue Durability of Reinforced Concrete Deck Slab in a Cold Snowy Region; Takashi Satoh, Hiroshi Mitamura, Yutaka Adachi, Hiroaki Nishi, Hiroyuki Ishikawa and Shegeki Matsui; Civil Engineering Research Institute for Cold Region (CERI); PWRI, Japan http://www.pwri.go.jp/eng/ujnr/tc/g/pdf/23/23-2-4satoh.pdf	RC Deck Fatigue; Corrosion
	Repetitive wheel loading from heavy vehicles are known to be the major cause of the deterioration and fatigue failure of reinforced concrete (RC) deck slabs on road bridges. Additionally, the intrusion of rainwater into cracks significantly reduces the fatigue durability of RC decks. Other environmental conditions also accelerate the deterioration. In Hokkaido, the extreme cold causes freeze-thaw damage, and the spreading of deicing agents causes chloride damage. In order to manage the repair of RC decks in a cold region, it is necessary to determine how their states of deterioration relate to their lifespans. To study the fatigue durability of deck slabs, we performed fatigue tests using a wheel tracking test machine. Test specimens were cut from a bridge that was in service in Hokkaido for forty years and was tested to failure. Stress - cycle curves were developed to help predict the service of life RC decks. More insight was gained from this testing approach, however there are some obvious flaws in this study. The first 40 years of the deck was in the field experiencing real truck axle loads, cold wet climate and use of de-icing salts, however the number of axle load cycles over the 40 years can at best be estimated.
	In addition, for documents referencing Modeling and Discussing Bridge Deck Impacts due to Overweight Trucks and Environmental Effects see “Reference Nos.”: 2.3.6-4; 2.3.6-13

3.6 Conclusion

The reports, studies and articles presented above represent available information that is currently available from on-line university libraries, industry publications, State and Federal transportation agencies and other government and/or industry web sites. The collection provides a snapshot of ideas, methods, and research efforts from 1997 to 2013. Many articles and papers have been added to this edition of the Desk Scan since it was first released to the FHWA in November 2013. Every effort has been made to provide a link to every article, however a few of them are part of online libraries that require accounts and paid subscriptions. We obtained those articles through special requests from the CDM Smith InfoCenter, which has access to many of the private libraries. All the articles and documents that are sighted herein address the key issues that were investigated inthe 2014 CTSW Study as they relate to bridges.

CHAPTER 4 - List of Agencies

4.1 National Academy of Sciences

TRB - Transportation Research Board
National Cooperative Highway Research Program - NCHRP
Strategic Highway Research Program - SHRP 2
Conferences: International Bridge Conference, IBC

4.2 Federal and State Transportation Agencies

United States Department of Transportation (USDOT)
Federal Highway Administration (FHWA)
Turner Fairbanks Research Center
Long Term Bridge Performance
Arizona - ADOT
California-CalTrans
Colorado - CDOT
Illinois - IDOT
Indiana - INDOT
Joint Transportation Research Program (JTRP)
Kentucky - KDOT
Kentucky Transportation Cabinet
Louisiana - LDOT
Louisiana Transportation Research Center
Maryland - MDTA (MD SHA)
Michigan- MDOT
Minnesota - (MnDOT)
Nebraska - NDOR
Nevada - NVDOT
New York
NYSDOT, NYCDOT
Ohio - ODOT
Oregon - ODOT
Tennessee - TDOT
Texas - TXDOT
Vermont - VAT
Washington DC - District DOT
Wisconsin - WisDOT

4.3 Universities

Carnegie-Mellon University
Case Western Reserve University
City University of New York
Louisiana Tech University
Lehigh University
Purdue University
Rensselaer Polytechnic Institute
University of Kentucky
University of Nebraska (Lincoln)
University of Texas (Austin)
City University of New York (CUNY)
University of Leeds (Coordinator of CATRIN Study)

4.4 Industry Standards and Publications

AASHTO - American Association of State Highway Transportation Officials
ASCE - American Society of Civil Engineers
Journal of Structural Engineering
Journal of Bridge Engineering
AISC - American Institute of Steel Construction
(NSBA) National Steel Bridge Alliance
ACI - American Concrete Institute
PCI - Precast Concrete Institute

4.5 Foreign Resources

Canada - Transportation Association of Canada
UK - English Highway Agency
European Transport Commission:
(Cost Allocation of TRansit Infrastructure, CATRIN)
(UNIfication of Accounts and Marginal Costs for Transport Efficiency, UNITE)
(Generalization of Research on Accounts Cost Estimation, GRACE)
Dutch Ministry of Transport
Poland:
General Directorate of National Roads (GDDKiA)
Road & Bridge Research Institute (IBDiM)
Swedish Road Administration (SRA)
Australia:
Australian Transport Council (ATC)
National Transport Commission (NTC)
Australian Road Research Board (ARRB)
Japan: Public Works Research Institute

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