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21st Century Operations Using 21st Century Technologies

North Dakota's Bridge Load Testing Project - 2017 ATCMTD Application: North Dakota Department of Transportation

I. Project Description

1. Introduction

The Bridge Division of the North Dakota Department of Transportation (NDDOT) performs load rating calculations for all bridges within the state, including locally owned structures. The NDDOT is proposing a project to use diagnostic load testing technology to load test bridges that have load ratings near legal load capacities but are restricted for weight because of the calculated load ratings. The expectation is that this technology will allow these structures to become unrestricted, hereby shortening the travel time and distance to move agriculture and industrial products to markets.

The technology that is being proposed uses instrumentation on the existing structural members that measure deflection and strain while moving a known load across the structure. The measured deflections and strains in the beams allow for the maximum allowable safe load calculations. This technology was used on a limited basis on two local bridges and, in these cases, the results increased load ratings on the structures that were restricting free movement of goods to markets.

American Association of State Highway and Transportation Officials (AASHTO) has created the Manual for Bridge Evaluation (MBE) which outlines the bridge inspection process and the process to load rate existing bridges for safe loads. The local structures to be evaluated with diagnostic testing are on structures where plans are no longer available. The individual member sizes have been measured, however, assumptions have been made on the material strength and how the loads are distributed from the deck to the beams. The other structures being proposed for this analysis are reinforced slab bridges on the state highway system. While plans are available, slab bridges typically perform much better than the rating calculations indicate, so we anticipate being able to increase the load rating on the slab bridges. Overweight permitted vehicles are detoured around these slab bridges because of the lower rating calculations even though they can safely carry legal highway loads.

2. Entity Entering Into Agreement

The NDDOT will be the entity that will enter into the agreement to complete this project. Approximately one-third of the structures are locally owned and maintained. The NDDOT will partner with the owners of these structures to participate in this project. An RFP process will be created to select a consulting service that will be able to perform the work with NDDOT oversight and project control.

The NDDOT will set up multiple project numbers for this project. Each local agency will have a project number to better assist us to assign costs to specific owners and their bridges. The state owns the majority of the structures in this program and will monitor the progress of the selected consultant.

3. Geographic Area

The local bridges are concentrated in 3 Counties within North Dakota. Grand Forks County is in the northeast area of the state while Morton and Burleigh Counties are in the central portion of the state. The map below shows the local bridge locations proposed for this project.

Map of local bridge load testing locations in the state of North Dakota with two clusters of red dots signifying bridges to looked at: one around Bismark and one around Grand Forks

The state owned structures are located across the state on highways that are designated as a route for 129,000 lb. vehicles as well as local non-designated highways. The map below shows the location of the state structures being proposed for use of this project.

Approximately half of the slab bridges are on the designated interregional routes that will carry the increased legal load of 129,000 lbs. on the NHS and Interstate Highway System.

State slab bridges with inventory less than legal load.  Throughout the map are green plus signs denoting bridges that qualify.

4. Issues and Challenges

While a few mile detour may not seem like a huge issue, additional miles create more fuel consumption, emissions and time to the haulers. Using these bridges with lighter than legal loads creates more trips which leads to a similar increase in fuel, emissions and time. The most direct route is the most efficient as long as legal loads can be hauled. Achieving the goal of creating the most direct routes saves time, fuel, reduces emissions and creates the most efficient transportation system for transporting agricultural, manufacturing, and other goods. More than 27 million truck miles within ND are traveled on detour routes annually because of lower capacity bridges. This conservative estimate is based upon detour lengths and average annual truck traffic. North Dakota's Upper Great Plains Transportation Institute (UGPTI) performed a study noting that the cost to operate a semi on a paved road is $2.18/mile. Eliminating these detour miles would equate to an estimated annual savings in trucking costs of $58.9 million.

5. Transportation Systems Included in Project

North Dakota's State Strategic Freight System identifies three levels of highways that move freight statewide and connect to neighboring states and Canadian provinces. The map below from the ND State Freight Plan, adopted in 2015, shows the route levels for freight movements within the state as well as to other states and Canada through identified Gateways, indicated by an asterisk (*). All three counties partnering with NDDOT on this project contain Freight Level 1 routes and those are top priority level for freight movements.

State Strategic Freight System - Highways.  All over the North Dakota state map are red lines denoting roads at level 1, blue lines denoting roads at level 2, and green lines denoting roads at level 3.  There are red astericks denoting gateway to state roads, and gray areas denoting urban areas.

The Interregional Highway System is designed to transport goods within as well as outside of the state, region, and U.S. Some of the highways on the Interregional System include:



Interstate 29

  • Main north south corridor from Kansas City, MO to the Canadian border at Pembina, ND.
Map of North south corridor from Kansas City, MO tothe Canadian border at Pembina, ND.  Road to Kansas City is in red.

Interstate 94

  • Northernmost east-west Interstate Highway connecting the Great Lakes and Intermountain regions of the U.S. This route runs from Detroit, MI to Billings, MT where it connects with Interstate 90 and continues to Seattle, WA.
Map of NorthWestern US.  With East-West Interstate 94 Highway connecting the Great Lakes and the Intermountain regions of the U.S. highlighted in red.

US 2

  • Disconnected US highway from Everett, WA through Duluth, MN to St. Ignace, MI and Rouses Point, NY to Houlton, ME.
Map of US 2 which runs East-West accross Northern US; from Everett, WA through Duluth, MN to St. Ignace, Mi and Rouses Point, Ny to Houlton, ME.

US 83

  • One of the longest north-south routes in the U.S. from Canada to Brownsville, TX on the Mexican border.
Map of mid-west of the U.S.  US 83 is displayed as a red line running north-south from Canada to Brownsville, TX on the Mexican border.

US 85

  • CanAm Highway from Canada through the mountain-northern plains to El Paso, TX at the Mexican border.
Map of US as US 85 runs North-South from Canada through the mountain-northern plains to El Paso, TX.

US 281

  • Longest north-south route from the International Peace Gardens at the Canadian border to Brownsville, TX at the Mexican border.
Map depicting US 281 in red.  Longest north-south rounte from the International Peace Gardens at the Canadian Border to Brownsville, TX ast the Mexican Border.

The state highway system includes some of the slab bridges not on the interregional system. This system is used to transport goods from the interregional system to the end-use location.

The local county systems included in the project are mainly farm-to-market roads that producers use to transport their agricultural products to local markets.

6. Deployment Plan

NDDOT plans to create an RFP and use quality based selection to hire a consulting firm that will perform the field analysis and result calculations on a bridge by bridge basis. Coordination with bridge owners will be handled by the consultant to fit their schedule as it falls within the NDDOT timelines. Bridges will be grouped geographically and by type to provide efficiency while providing better coordination with bridge owners. The NDDOT will remain active in this project by monitoring progress and results. As the responsible agency for all bridge load ratings within the state, the NDDOT will utilize this information for the potential increase of load limits on our transportation system.

During the field testing phase, the superstructure will be instrumented with a combination of strain transducers, deflection sensors, and tiltmeter rotation sensors (See Figure 1). Once the structure is instrumented, controlled load tests will be performed with a 3-axle dump truck along three lateral positions. Data obtained from the load tests will then be evaluated for quality and subsequently used to verify and calibrate a finite-element model of the structure.

Figure 1 showing strain transducer and rotation sensor near girder end (typical).

Figure 1 showing strain transducer and rotation sensor near girder end.  Devices are mounted on girder with red electrical wires coming from them.

During the structural investigation, all available geometric data will be recorded and compared with any previously collected data. Additionally, beam details including the location and sizes of both the stirrups, Post-Tension (PT) ducts, and the deck reinforcement will be determined using GPR techniques (See Figure 2). All of the information obtained from this investigation will then be compiled into As-Inspected drawings.

Figure 2 showing GPR scan along bottom of a girder (typical).

Figure 2 showing GPR scan along bottom of a girdr (typical).  Workman is holding equipment above his head mounted on the girder.

Although much of the crucial information will be determined from structural investigation, it may still be necessary to make some educated estimates on certain parameters critical in the calculations of the structure's capacity; namely the design material properties and the number of PT wires in each duct. Using design and fabrication information obtained from structural plans from a similar structure (e.g., same bridge type built in the time frame in the same geographic area), it may be assumed that a bridge was designed for a specific loading and that the design was based on certain methodologies.

7. Regulatory, Legislative, or Instructional Environmental Challenges

This project does comply with accepted practices in the American Association of State Highway and Transportation Official's Manual for Bridge Evaluation (MBE). While formulas and calculations provide safe capacities of the bridge systems, assumptions are made on many inputs into the load rating formulas. Assumptions include:

  • Strength of steel
  • Strength of reinforcing steel
  • Strength of concrete
  • Load distribution to various members and;
  • Interaction between separate elements within the bridge

The diagnostic load testing combines all of the interactions, determines assumptions and shows how the bridge actually reacts to a specific loading. A more realistic capacity can be determined based on the as-constructed mechanics and interactions of the individual bridge members.

The NDDOT does not anticipate any Legislative challenges with this project.

Environmental impacts will be significantly reduced if load ratings can be increased by reducing fuel usage as well as vehicle emissions associated with the 27 million truck miles traveled as a result of truck detours. Another environmental benefit will be eliminating the impacts caused by the unnecessary removal and replacement of bridges. In addition, the environmental impacts associated with disturbances to the streambed is avoided as well as the production of the materials necessary to construct a new bridge.

8. System Performance Improvements

The anticipated results of this project will reduce the number of miles traveled, emissions produced, and misdirection of travel. A more efficient transportation system for moving agriculture and industrial commodities will help reduce costs to the eventual consumer as well as costs to the producers of those items.

Reducing capacities of bridges by posting with load limit signs creates a huge maintenance issue for the bridge owner. Signs are routinely vandalized, removed or destroyed and need repair or replacement to correctly identify the safe load capacity of the structure. If the restrictions can be removed, these maintenance costs can be spent on other more critical items such as maintenance of the bridges to keep them in good condition. The NDDOT spends many hours annually inspecting, notifying owners of deficiencies in posting signage, and following up on the accuracy of the posting signage across the state. With fewer posted structures, time can be spent on inspection of the bridge condition and safety rather than the condition of signs.

9. Safety, Mobility, and Environmental Benefit Projections

By reducing the total distance traveled, safety will be increased by reducing the interaction of large and small vehicles. The more direct route will be used rather than the detour route which adds time and length to every trip. A shorter trip reduces fuel consumption as well as reduces emissions from those vehicles. The interregional corridors within the state of North Dakota are designed for a safer interaction to the large and smaller vehicles. Keeping large permit vehicles on these routes increases safety to both the haulers and the smaller vehicle traveling public.

The perceived risk associated with structures being permanently damaged from overloads due to signs being removed or vandalized would be eliminated if it's determined that the load restrictions can be removed.

Mobility is increased by the option of using the shortest route rather than a longer less direct route to transport goods to market or to the end users.

10. Vision, Goals and Objectives of the Technology Deployment

One county utilized this technology on a very limited basis on 2 local bridges in 2012. The success of that pilot project has urged the NDDOT to try this technology on other bridge types in an attempt to reduce the number of posted bridges and increase the allowable capacity on some of the state mainline structures.

NDDOT will use this project as a way to determine the success rate to eliminate the postings on various types of structures. If the success rates are quite high or show a predictable pattern, more structures may be identified for a follow-up project to further reduce posting in other counties across the state.

11. Partnering with Private or Public Agencies

NDDOT does not believe the best use of this technology would be for the state to own this equipment. This type of technology and interpretation of the results should be left up to those who do the work daily instead of intermittently. The learning curve has been completed by those consultants who routinely perform this work and should be considered the experts in dealing with this technology.

The ND Soybean Council has expressed an interest in assisting the NDDOT in reducing the number of bridges that are restricted for load within the state. Other agencies who are also interested would be the ND Corn Growers and ND Wheat Producers. All of the farm organizations are also interested in the most efficient way to get products to markets.

The last legislative session in North Dakota included a bill to increase the legal load (with enough axles) to 129,000 lbs. While this increase will be limited to the state's Interregional System, some of the bridges on that system haven't been designed for this loading. This technology may be used to determine if some of the questionable bridges should be replaced earlier rather than later or if they are performing better than the calculated load rating would indicate. This project will look at several state structures on these routes. An attempt to get a correlation between the calculated ratings and the actual performance in slab bridge structures may allow NDDOT to justify a factor of increase for slab bridges in general within the state.

12. Leveraging & Optimizing Existing Local & Regional Technology Investments

The NDDOT provides federal funding to local governmental agencies to improve and maintain their systems. This technology will allow this funding to stretch further by partnering with local agencies to reduce the number of structures that must be replaced on the local and state systems. Other structures will be able to be funded and these structures will be able to become un-restricted for loads.

13. Project Schedule & Technology Deployment

The project will include field instrumentation, testing, analysis and final reporting for each of the bridge sites. After the award in the fall of 2017, the NDDOT would develop the RRP and select a consultant during the winter of 2017-2018. The field work would be completed in the summer of 2018 with final results and reports expected in early 2019. Annual reports and a follow-up project review and report would be written after final results from the consultant and would be expected to be completed in the summer of 2019 to be used in the determination of the value and continued use of this technology.


Approximate Due Date

Section 508 Compliant?

Kick-off Meeting – Conduct a kick- off meeting with DOT at mutually- agreed-upon location. Within 4 weeks after award. No
Develop RFP for consultant to perform site testing and analysis 6-8 weeks after grant award No Value
Award Contract to successful Consultant March after grant award to begin work during summer construction season No Value
Monthly Progress Reports – submit progress reports to document activities performed, anticipated activities, and any changes to schedule or anticipated issues. Monthly No
Report to the Secretary – submit a report describing the deployment and operational costs compared to the benefits and savings, and how the project has met the original expectations projected in the deployment plan. Annually beginning one year after grant award. Yes
Consultant delivers completed reports on each bridge regarding final load rating Quarterly at a minimum as field work is completed No Value
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