U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
The goal of the Long-Term Bridge Performance (LTBP) Program's data collection effort is to inspect, evaluate, and periodically monitor representative samples of bridges nationwide to achieve the following:
This data collection effort will benefit the following:
The LTBP Program is collecting quantitative, research-quality bridge performance data on a national basis over time to facilitate quantifying the effects of external inputs and internal attributes at an individual and population level.
The initial data collection effort is focused first on untreated concrete bridge decks and is then focused on treated concrete bridge decks. Data collection for joints and bearings occurs concurrently with deck evaluations which permits addressing several of the LTBP Program's high priority issues concurrently. As time progresses the program will expand to include additional bridges and will collect data more efficiently in subsequent cycles.
Mining bridge documentation and legacy data provides a broader context and comparative framework for the reference and cluster bridges (see below) and allows for the identification of potential trends that may merit further examination.
Bridge performance is a multifaceted issue involving performance of materials and protective systems, performance of individual components of the bridge, and performance of the structural system as a whole. The LTBP Program was initiated to collect, store, and analyze the data necessary to better understand high priority bridge performance issues. The success of the program depends on first being able to identify the most important performance issues that bridge owners face. To identify these issues, input was sought from those bridge owners and other key stakeholders. As part of this outreach, bridge experts in 15 State transportation departments were interviewed and asked to name the performance issues in their bridge inventory that are most common and/or most difficult to solve. The findings of these interviews are included in report FHWA-HRT-14-052, LTBP High Priority Bridge Performance Issues, published in 2014.
To supplement these interviews and identify high priority issues related to bridge substructures, a workshop on substructure performance issues was held. The findings from the interviews and the substructure workshop were used to develop a list of 22 high priority performance issues. From this list, a shorter list of six bridge performance issues was recommended as the first group of issues for study under the LTBP Program.
Based on input from stakeholders and considering current resources of the program, the following key topics in table 1 will initially be addressed:
|Decks||Untreated concrete bridge decks|
|Decks||Treated concrete bridge decks|
|Joints||Bridge deck joints|
|Steel Bridges||Coatings for steel superstructure elements|
|Prestressed concrete bridges||Detection of condition of embedded pretensioned strands and post-tensioning tendons|
Each of these high priority performance issues will be examined in detail, and the specific data necessary to study the issues will be identified.
To ensure that LTBP Program data are collected in a consistent manner over the duration of the program, data collection protocols are being developed by the Federal Highway Administration (FHWA) for use by practitioners, LTBP researchers, and decisionmakers involved with the research, design, construction, inspection, maintenance, and management of bridges. The LTBP Program protocols are for research purposes and intended primarily for use within the LTBP Program. Report FHWA-HRT-16-007, Long-Term Bridge Performance (LTBP) Program Protocols, Version 1, was published in January 2016.
The LTBP Program is currently collecting data on approximately 500 bridges throughout the United States. Figure 1 shows the bridge regions that the LTBP Program has determined for its data collection efforts. These regions provide the names of the concentrated areas of bridges, known as clusters and corridors, that were selected using a multi-tiered sampling approach.
Figure 1. Map. LTBP Program bridge cluster and corridor regions.
Given the large and diverse population of bridges throughout the United States, one of the most significant challenges to the LTBP Program is selecting a sample of bridges that is large enough and diverse enough to be representative, yet small enough to permit data collection efforts within current resource constraints. To meet this challenge, the LTBP Program designed a multi-tiered sampling approach. While theis approach used is an elegant and iterative one, the following are the primary steps taken during bridge selection:
Step 1: Determine the most common bridge types that predominate now and are likely to do so in the future. Specifically, the program focused on the performance of the following three types of bridges as these represent a majority on the National Bridge Inventory:
Step 2: Identify representative clusters of each primary bridge type within various regions of the United States, considering the following factors:
Step 3: Determine the level of detail appropriate for data collection efforts for each bridge within geographic clusters and corridors. It is important to recognize that carrying out the most detailed NDE, structural characterization through field instrumentation, material sampling, visual inspection, etc., for each bridge identified—which number in the thousands—is neither realistic nor cost effective.
Step 4: Perform legacy data mining for all the candidate bridges to determine which bridges will be a cluster or a reference bridge within a geographic clusters or corridors.
Step 5: Select the clusters and reference bridges in a geographic cluster on which to conduct the data collection. The supplemental interstate corridor sampling provided an opportunity for the maximum number of States to participate in the program and to leverage efficiencies related to corridor analysis. For the selection of bridges in various corridors, the LTBP Program removed the ADT criteria, performed similar steps for cluster bridge selection, and examined the distribution of climatic environments for corridor bridges.
The goal of this general framework is to allow the influences of various bridge inputs and attributes on the performance of bridges to be uncoupled and better understood. For example, by comparing the results of geographic clusters/corridors, the influence of climate and environmental conditions may be identified. Within each geographic cluster/corridor, the influence of more detailed attributes (e.g., deck cover, span length, age, skew, and girder spacing) and inputs (e.g., ADT, ADTT, maintenance activities, and winter deicing operations) can be studied and identified. In addition, this framework will allow for the possibility of bridges being moved within the various categories if their performances warrant.
The LTBP Program has identified 14 clusters and 10 corridors encompassing over 6,000 bridges. They group together bridges with similar attributes (steel, prestressed concrete, and concrete box multigirder bridges) in varying environmental regions; these groupings form the population of candidate bridges for data collection.
Figure 2 through figure 4 present the location of the 14 clusters with the following distributions:
Figure 2. Map. Five steel multi-girder bridge clusters.
Figure 3. Map. Six prestressed multi-girder bridge clusters.
Figure 4. Map. Three concrete box girder bridge clusters.
Ten corridors on existing Interstate highway alignments (figure 5) were identified in the analysis, thereby providing complete State coverage and enabling the investigation of bridges on corridors which span multiple climate zones while maintaining heavy truck traffic. The following are the ten corridors the LTBP Program identified:
Figure 5. Map. Interstate corridors included in the LTBP Program.
Detailed inspections and data collection are being performed by Michael Baker International, Professional Service Industries, Inc. (PSI), Rutgers University, and WSP | Parsons Brinkerhoff. This team of LTBP Program contractors is collecting data on 72 bridges throughout the United States, including 24 bridges each inthe Mid-Atlantic and Gulf Coast clusters and 12 each in the Southwest and Northwest clusters. The following is a summary of the progress as of the summer of 2016:
Rutgers University and Arora Engineers, Inc. have completed visual inspection and NDE testing on 24 bridges in the Mid-Atlantic cluster—11 prestressed concrete bridges and 13 steel bridges. This includes visual inspection and NDE with the use of the RABIT™ bridge deck assessment tool (figure 6). The bridges are located in the following States:
Figure 6. Photo. RABIT™ bridge deck assessment tool collecting NDE data in the Mid-Atlantic cluster.
Rutgers finished data collection in May 2016 and completed data analysis in June 2016. Data from all 24 bridges are available on LTBP Bridge Portal.
WSP | Parsons Brinkerhoff is currently working on collecting data on 12 bridges in the Northwest Region—2 reference prestressed and 10 cluster prestressed—with ongoing data collection activities on bridges in the following States:
WSP | Parsons Brinkerhoff is currently working on data collection (figure 7) activities on 12 bridges in the Southwest Region—2 reference CIP post-tensioned and 10 CIP post-tensioned box—with ongoing data collection activities on bridges in the following States:
Figure 7. Photo. Verifying crack width on bridge I 2699 in Nevada.
Data collection efforts for the bridges in Arizona and Nevada have been completed. Data collection for the four bridges in California is underway.
Michael Baker International has completed data collection (figure 8) activities on 24 bridges in the Gulf Coast Region and is currently working on data validation and input activities. The contractor examined 2 reference concrete, 10 cluster concrete, 2 reference steel, and 10 cluster steel bridges in the following States:
Figure 8. Photo. Michael Baker International's data collection efforts in the Gulf Coast Region.
PSI has collected bridge documentation data for 434 bridges in the 4 clusters in the Mid-Atlantic and Northeast cluster regions of the U.S. The contractor has completed the legacy data mining study and is currently working on revising the final reports.
Future plans in FY 2017 include data collection on the remaining 10 clusters, 10 corridors, and all reference bridges. Also, reference bridges will be instrumented for long-term structural health monitoring.
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LTBP Program Coordinator
Turner-Fairbank Highway Research Center
6300 Georgetown Pike
McLean, VA 22101
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