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U.S. Department of Transportation U.S. Department of Transportation Icon United States Department of Transportation United States Department of Transportation
OFFICE OF RESEARCH, DEVELOPMENT, AND TECHNOLOGY AT THE TURNER-FAIRBANK HIGHWAY RESEARCH CENTER

LTBP Research Projects and Products


LTBP Research Projects

Accelerated Bridge Performance Testing

To date, bridge deterioration is almost exclusively studied using either direct observations of the performance of in-service bridges (using visual inspection, non-destructive evaluation (NDE), 
structural health monitoring, etc.), or using material level tests on small-scale specimens. These 
approaches cannot generate the type of objective, quantitative, and reliable information needed in 
a timely or cost-effective fashion to understand the underlying mechanisms of the deterioration of 
bridges. This research project utilizes accelerated testing of a full-scale bridge superstructure system subjected to live loads with varying environmental conditions. It is envisioned that this research will complement both field observations and material-level tests and fill an important gap in our current understanding of bridge performance and deterioration.

This project has the potential to provide valuable insights and understanding of deterioration of bridge systems and bridge components through accelerated testing in a controlled environment. 
The ability to not only test a full-scale bridge under variable environmental conditions but also with continuous live load application has never been attempted. Due to the controlled and accelerated nature of testing a full-scale bridge specimen, this research project has the potential to not only reach quicker conclusions on infrastructure performance but will also enable the Long-Term Bridge Performance program to assess newer materials, more bridge types, and new assessment technologies in a cost-effective manner and reasonable timeframe.

Objectives

The goal of this research is to expand understanding of long-term bridge performance through large-scale accelerated testing. There are three primary objectives for this research:

  1. Detect and quantify the onset and propagation of deterioration of various components of a full-scale bridge such as the reinforced concrete bridge decks, deck joints, and coatings of structural steel bridge components.
  2. Quantify long-term performance of various materials and protection systems such as deck reinforcement types, steel coatings, and deck overlay systems and materials.
  3. Evaluate the applicability of various NDE technologies in assessing concrete bridge decks with various overlay materials and systems.

Project Status

The test specimen was constructed in the Summer of 2019 and accelerated testing began the following October. The bridge superstructure consists of four 50 ft long W27x84 grade 50 steel girders coated with hot-dipped galvanized, inorganic zinc, 85 percent / 15 percent zinc and aluminum respectively, and 100 percent aluminum coatings.  The bridge deck is 8 inches thick and constructed with ordinary Portland cement class A mix, with # 5 black reinforcing bars located at the top and bottom of the deck.  The formwork for the bridge deck includes one bay of stay-in-place forms and two bays of removable forms.

The testing facility provides for full scale accelerated testing of a bridge superstructure, imposing both environmental and traffic loads.  It is designed as a closed environmental chamber capable of imposing freeze-thaw cycles on the specimen while also allowing for the application of load with a moving carriage that has the configuration of a standard truck rear carriage. The load carriage moves back and forth at up to 20 mph while applying a 60,000-pound force to the bridge deck along a specified transverse location which varies throughout the testing regimen.

"The specimen is shown in the open environmental chamber. The tandem axle loading mechanism is shown above the specimen."

Figure 1. Completed bridge specimen located within the accelerated testing facility.  (Source: Rutgers, The State University of New Jersey)

The first phase of testing, which comprised application of both live and environmental loading to the bridge specimen starting from its initial as-constructed condition, was completed in late 2021.  During phase 1 of the accelerated testing program, approximately 2 million load cycles and 85 freeze-thaw cycles were applied to the specimen along with a total of 4,000 gallons of a 6 percent brine solution. 

The second phase of the project continues with preparation of the surface of the deteriorated deck for the installation of 2 different cementitious overlays using hydrodemolition. Ultra-high-performance concrete (UHPC) and latex modified concrete (LMC) overlays on each longitudinal half of the deck were selected in order to better understand the performance of each material.  Construction of the overlays was completed in the Spring of 2022 and subsequent accelerated testing commenced in the Summer of 2022. 

Project Data

During the conduct of this project, 8 different NDE technologies were used:

  • Electrical resistivity
  • Half-cell potential
  • Ground penetrating radar
  • Ultrasonic surface waves
  • Impact echo
  • Ultrasonic tomography
  • Infrared imaging
  • High-definition imaging

NDE data was collected 30, 45, and 90 days after deck construction was completed.  Periodic NDE data was also collected immediately following application of approximately 200,000 load cycles.

In addition to NDE data, various sensor data are also collected throughout the testing cycles including strain, displacement, and temperature at specific locations throughout the specimen.

Periodic NDE data for phase 1 of this project can be found on InfoBridge™ under the data tab and clicking the experimental bridges box on the left.

For more information, contact Rob Zobel at robert.zobel@dot.gov.

Weathering Steel Research

Existing guidance on the performance of uncoated weathering steel (UWS) structures was published by the Federal Highway Administration (FHWA) as Technical Advisory (TA) 5140.22 in 1989.  This gave broad guidance on situations where UWS should not be used or used with caution. The TA noted that work is needed to quantify and understand the performance of uncoated weathering steel in a variety of circumstances and conditions.  This research project contributes toward that goal, particularly considering the lack of longer-term performance of UWS structures than was available at the time of the writing of the 1989 TA.  

The scope of this effort included soliciting owner feedback on contemporary UWS issues, compiling a comprehensive national database of UWS structures and their environments, evaluating a subset of these structures using field work protocols developed herein, conducting laboratory analysis of field samples, reviewing owners’ inspection reports of UWS structures, and performing a statistical analysis of the UWS database.  As a result, quantitative combinations of influential parameters (including climate, geography, geometry, and traffic volume) that were consistently associated with inferior environments for UWS bridges in coastal and heavy deicing environments were identified.  This research is of interest to owners and bridge designers who are involved with the specification or maintenance of UWS structures, material scientists, and those interested in the long-term performance of highway infrastructure.  

Data from this research project, including the compiled database, has been incorporated into InfoBridge™ and can be found under the data tab and then under Special Projects at the bottom left of the screen.

For more information, contact Rob Zobel at robert.zobel@dot.gov.

Pooled Fund Project TPF-5(283): The Influence of Vehicular Live Loads on Bridge Performance

Introduction

The principal objective of this pooled fund study is to quantify the influence of vehicular live loads—particularly truck loads—on the long-term performance and durability of highway bridges. Bridge owners have much interest in this objective because of the diversity of truck loads and configurations currently operating on the Nation's highway bridges and because the freight industry has proposed increasing the allowable truck loads. Currently, the data available for evaluating the influence of truck loads on the performance and durability of highway bridges are incomplete and are largely qualitative or empirical in nature. This pooled fund study seeks to answer the principal objective through robust and systematic data collection to: quantitatively characterize the current truck loads on the Nation's highway bridges, measure and quantify how various bridge elements respond to different truck loads and configurations, and track the long-term changes in the measured bridge responses to truck loads.

In addition to the principal objective described above, the pooled fund study includes a number of related objectives including the following:

  • Develop a national bridge traffic database.
  • Develop protocols for collecting high-quality bridge traffic data.
  • Develop tools and products that bridge owners can use to better quantify and manage loading conditions on the existing network of highway bridges.

Scope

The pooled fund study includes a number of tasks that were devised to meet the project objectives. The following is a summary of these tasks:

  1. Conduct a literature review of available weigh-in-motion (WIM) data collection technologies and systems. This task has been completed. Report FHWA-HRT-16-024, LTBP Program’s Literature Review on Weigh-In-Motion Systems, was published in June 2016.
  2. Review the Long-Term Pavement Performance (LTPP) Program’s experiences with WIM systems and traffic data collection obtained through the execution of pooled fund study TPF-5(004): Long-Term SPS Traffic Data Collection.
  3. Identify and evaluate alternative approaches for collecting the necessary data to meet the project objectives.
  4. Identify optimal bridge sites for data collection and the number of test sites to be included in the study.
  5. Develop a data collection program for the study that includes recommended methods and protocols for measuring and analyzing bridge traffic and bridge responses at the test sites.
  6. Implement the data collection program, maintain the measurement systems, and collect and analyze the data at selected bridge sites for a period of 2 years.
  7. Archive the data collected in this study in a format suitable for inclusion in the Long-Term Bridge Performance (LTBP) Bridge Portal.
     

The bridges selected as data collection sites for this study will also be classified as reference bridges in the LTBP Program. Reference bridges in the LTBP Program are subject to a spectrum of detailed data collection efforts and protocols that are in addition to the data collection efforts specific to the pooled fund study.

Periodic reviews of the progress and deliverables for each task have been provided by the Federal Highway Administration (FHWA) LTBP Program team, a Technical Advisory Committee consisting of representatives from the State transportation departments participating in the pooled fund study, and the Transportation Research Board (TRB) LTBP Expert Task Group on Traffic and Truck Weights.

Project Status

As of July 2016, the first five project tasks have been completed, and the data collection program is being implemented. A prestressed concrete multibeam bridge in Oregon and a steel multibeam bridge in Wisconsin have been identified as initial test sites for the data collection program. The sites were chosen from bridges located in States participating in the pooled fund study using selection criteria consistent with that used by the LTBP Program to select reference bridges. Several additional criteria were also considered, including proximity to existing weigh stations or WIM sites, average daily truck traffic (ADTT) characteristics, ease of access, and proximity to electrical power service.

The prestressed concrete bridge carries two lanes of I–84 West over County Road 1133 in Umatilla County, OR. The bridge, constructed in 1969, is located approximately 30 miles west of the Emigrant Hill Weight Enforcement Station. The bridge consists of three simple spans (deck continuous for live load) and has an overall length of 160 feet. The superstructure consists of a cast-in-place (CIP) reinforced concrete deck on American Association of State Highway and Transportation Officials Type III prestressed beams. The 2013 average daily traffic (ADT) for the bridge was 7,400, with 29 percent trucks.

The data collection program for the prestressed concrete bridge site includes the installation of a new WIM site in the pavement just east of the bridge and instrumentation of bridge components located in the middle span of the structure. The new WIM site includes an overview camera and will classify and measure the weights of vehicles in the two traffic lanes that cross the bridge. Various sensors installed on the bridge elements will measure and record how the bridge responds as the vehicles characterized by the WIM site cross the structure. Data collection from this test site is expected to begin in October 2016.

"The elevation of the prestressed concrete multigirder bridge is shown. A construction worker is standing under the bridge in the roadway."

Figure 2. Photo. Prestressed concrete multi-beam bridge site-side view. (SOURCE: FHWA)

The data collection program for this bridge will take advantage of the existing LTPP WIM site to collect classification and weight data for the vehicles crossing the structure. Various sensors will be installed on the bridge elements to measure how the bridge responds when the vehicles characterized by the WIM site cross the structure. Data collection from this site is expected to begin in the spring of 2017.

The results obtained and lessons learned from the data collection programs at these two bridge sites are expected to be used to further refine the design and execution of the data collection program for future bridge sites included in the study.

Project Participants

The current participants in the pooled fund study include the FHWA LTBP Program and the transportation departments from the following seven States: Georgia, Iowa, Minnesota, North Carolina, Oregon, Pennsylvania, and Wisconsin. 

NDE Data Utility Study

Introduction

To date, bridge deterioration is almost exclusively studied using either (a) direct observations of the performance of operating bridges (using visual inspection, sensing, etc.), or (b) material level tests that operate on small-scale specimens. Unfortunately, neither of these approaches can generate the type of objective, quantitative and reliable information on long-term bridge performance needed to implement modern asset management systems. In contrast, NDE technologies have been shown to reliably detect defects and corrosive conditions even when not visible.

A bridge deck is expected to safely carry the load and distribute it to other structural elements while delivering a smooth riding surface for the vehicles. As a bridge deck deteriorates, areas of concrete may spall off, degrading the riding condition, and reinforcement may corrode, causing expansive forces that may result in delaminations and spalls as well as threatening the strength of the deck. 

The ability of non-destructive technologies (NDTs) to identify current conditions such as delaminations has been extensively demonstrated through validation studies performed by many skilled researchers including members of FHWA’s NDT lab. This study will principally be focused on how NDE data can be leveraged to answer questions related to bridge performance and management. 

Project Objectives

The main objectives of this effort are to demonstrate how NDE data may be analyzed and interpreted to further the understanding of bridge performance and provide bridge owners with tools for predicting future bridge performance, to characterize and rank the types of NDE data that are most effective at answering questions related to bridge performance and management, and to identify and provide recommendations of other ways in which NDE data (obtained using methods practical for field-collection) may be used to further understanding of bridge performance. 

The research team will analyze existing data sets obtained from the current Accelerated Bridge Performance Testing project discussed above. These analyses will seek to establish the influence of environmental and structural demands, design and structural characteristics, and maintenance activities on bridge performance, and to the extent possible, develop predictive deterioration models. Throughout the process, the applicability and value of different NDE data sets to the established objectives will be assessed. Furthermore, in some instances, different types or quality of data may be identified, in which case recommendations will be made for future data collection efforts.

LTBP Research Products

The following links provide navigation to related research products which are located on the LTBP Tools and Products Page:

Bridge Deterioration Models  

Below you will find links to both the Bridge Component Condition Forecast Models and the Bridge Network Performance Forecast Models as described below and as implemented within InfoBridge. 

Bridge Components Condition Forecast Models:

  • Learn more about InfoBridge bridge component condition forecast models for implementing a data driven bridge asset management program.  

Bridge Network Performance Forecast Models:  

  • Learn more about the InfoBridge network-level Survival and Machine Learning Models. 

Bridge Performance Transition Forecast:

  • Learn more about this InfoBridge tool which produces a listing of bridges that may transition from one condition state to another within a user-specified time interval.  

Asset Valuation Tool:

  • Learn more about this InfoBridge tool which provides an estimate of the replacement value, existing value, and remaining value of user-specified bridge assets.

Historical Bridge Specification Changes:  

  • Learn more about this InfoBridge tool which provides a snapshot of chronological changes to various bridge and material specifications.

LTBP Program Protocols: 

  • Learn more about LTBP data collection protocols.
Last updated: Monday, November 14, 2022