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Long-Term Bridge Performance – Past Research

 

Developmental Phase

Roadmap

A roadmap was developed to guide the Long-Term Bridge Performance (LTBP) Program over the course of its life. The roadmap was the basis for many of the early communication and marketing products that were used to garner support and champions for the LTPB Program. The roadmap is expected to evolve as the Program advances to include anticipated future research needs that will be generated as a result of studies conducted by the LTBP Program.

Specific Questions to Answer and Data to Collect

The objective of this task was to identify the questions to be answered and the data elements that are most relevant to support the objectives of the LTBP Program. This included examination of the questions to be answered for all members of a bridge; feasibility and economics of collecting reliable and quantitative data; evaluation of the potential for practical use of this data in evaluation of bridge performance; and recommendation of data to be collected.

To meet these objectives, the research team held a series of focus groups involving 15 States (figure 1), and sent a survey to other States to gather information related to bridge performance issues and questions to which they would like answers; specific modes of deterioration for bridge decks, superstructures, substructures, and ancillary systems; as well as functional and operational aspects of bridge management.

Participating State DOTs
Figure 1: Participating State Departments of Transportation (DOTs) in the Initial Focus Groups.

The research team, Federal Highway Administration, State coordinators, and the Transportation Research Board (TRB) LTBP Advisory Committee recognized that all topics suggested by the States could not be addressed immediately and the number of topics to be addressed would be constrained by LTBP Program resources. Therefore, a short list of top priority topics was developed for immediate consideration. Table 1 presents the top six priority topics recommended for the Long-Term Data Collection phase. As time and resources permit, additional topics may be incorporated into the Program.

Table 1: Initial study topics for the LTBP Program.
Category Issue
Decks Untreated Concrete Bridge Decks
Decks Treated Concrete Bridge Decks
Joints Bridge Deck Joints
Bearings Bridge Bearings
Steel Bridges Coatings for Steel Superstructure Elements
Concrete Bridges Embedded Prestressing Strand and Post-tensioned Tendons

 

Development of a Data Infrastructure

The LTBP Bridge Portal has been created and populated by LTBP staff and its contractors. The LTBP Bridge Portal is the data infrastructure for storing, describing, updating, and accessing multiple data models (for primary data and associated metadata) with appropriate considerations of security. The Bridge Portal is open, extensible, and scalable to meet the goals and objectives of the LTBP Program. Due consideration is given to future needs of the LTBP Program and to new and upcoming technologies. The LTBP Bridge Portal is being designed to serve both as a robust and comprehensive repository of scientific data and for ease of use and utility to a broad array of potential users, and as the launching spot for data-driven deterioration and life-cycle cost forecasting tools. It will also support the implementation of automated data mining tools and standard queries.

Protocols for Data Sampling, Data Collection, and Quality Assurance

The contractor has developed protocols for data sampling, data collection using inspection techniques and instrumentation, and data quality assurance to carry out these functions. Protocols are compatible with the data infrastructure developed for the LTBP Program. These protocols are being developed and documented sufficiently so that various State DOTs, contractors, or researchers can use these protocols to collect and analyze data so that their research can be compared to data already gathered by the LTBP Program. These protocols accommodate visual inspection, a variety of sensors and associated instrumentation, physical and material sampling, and nondestructive evaluation (NDE) and destructive test methods. To date, more than 80 protocols have been developed. The protocols are living documents and will be updated frequently to include new methods and technologies.

LTBP Program Bridges (Quantity, Type, Location, etc.)

The LTBP Program has developed a methodology and rationale for selecting a representative sample of bridges from the National Bridge Inventory (NBI) database. The Pilot Study bridges were selected and data were collected for all seven of these bridges. The bridges for the LTBP Program Long-Term Data Collection phase are currently being selected. Culverts, tunnels, and complex bridges (suspension, cable-stay, and movable) were excluded from the sample.

The bridges in the Pilot Study were selected based on many factors, such as the NBI information, geographic location (climate and environmental conditions), traffic volume, bridge type, geometry, span length, maintenance practice, substructure, and age.

The transition from the Developmental phase to the Long-Term Data Collection phase is being done systematically in order to address the critical performance issues that have been identified. It is important to recognize that the current funding level for the Program will not be adequate to address all of the identified performance issues at once. Additionally, Program resources will not allow all types of bridges to be studied. Restraints on Program resources will not allow each and every bridge studied to be examined at the same depth done on the bridges in the Pilot Study. Therefore, the LTBP Program has developed a strategy that ensures maximum impact in the near-, mid-, and long-terms.

The strategy by which the Long-Term Data Collection phase will be conducted is referred to as the Reference Bridge/Cluster Bridges (RB/CB) approach. Briefly, this concept involves identifying small groups of similar bridges (Clusters) and studying one or more of the high-priority bridge performance issues using data collected from those bridges. Two to four of the bridges within each cluster will be selected as Reference Bridges and will undergo periodic inspection and monitoring using a detailed visual inspection protocol supplemented with advanced methods that utilize sensors, NDE tools, and simulation technology in a manner appropriate to the issue(s) being studied. In contrast, the supporting cluster of bridges will only undergo detailed visual inspection and very limited NDE or physical testing and will be compared directly to their Reference Bridges to ascertain consistency. In cases where discrepancies are identified, certain Cluster Bridges may be subjected to more advanced assessment approaches to further examine the discrepancies and to identify the root cause(s).

During the 20-year or longer duration of the LTBP Program, it is intended that there be many different Cluster Bridges and each will have an associated Reference Bridge. The number of bridges in any one cluster will vary, but will usually be in the range of 75–100 bridges. In many cases, the clusters will be concentrated in a small geographic area and may be on a contiguous section of highway (known as Corridor Bridges).

One of the goals of the sampling methodology is selecting bridges to maximize the information they can provide to the LTBP program while minimizing the cost of obtaining that information. The RB/CB approach not only places the Reference Bridge in context, but it also allows for the assessment of variability, alleviates the potential for non-representative/anecdotal findings, and is cost effective as each bridge cluster is located within a concentrated geographical area.

The general approach to data interpretation and performance assessment for the Reference Bridge program will involve multiple levels:

  • Comparison of the Reference Bridge to its cluster in order to identify detailed, bridge-specific behavior/performance. 
  • Comparison of bridges within a given cluster or corridor. 
  • Comparison of clusters of similar bridges from different regions across the United States to identify the influences of climate, maintenance practices, truck traffic, etc. 
  • Comparison of clusters across bridge classes to identify the relative performance of one bridge type to another.
  • Comparison of the Reference Bridge and its cluster to associated (but larger) families of bridges that can be evaluated through available legacy and production data, such as NBI, AASHTOWare Bridge Management software, design and construction records, and the like.

These perspectives are enabled by the clustering methodology that allows the representative nature of each Reference Bridge’s performance data to be assessed. Assuming that the Reference Bridges and their cluster are consistent in terms of performance, reliable comparisons can then be made to other Reference Bridges (and clusters) of similar type to ascertain influences such as climate, truck traffic, maintenance practices, etc.  In the case where discrepancies between the Reference Bridge and its cluster are identified, the root cause(s) of the discrepancies will be identified through additional investigations before comparisons with other clusters occur. Such investigations have great promise to begin to establish the expected variability of bridge performance within a given region and to identify the reasons why seemingly identical bridges in some cases perform quite differently.

 

LTBP: Research

Office of Infrastructure R&D Links

» Office of Infrastructure R&D
» Infrastructure R&D Program
»Long-Term Bridge
  Performance Program

»Long-Term Pavement
  Performance Program
» Infrastructure R&D Experts
» Infrastructure R&D Laboratories
» Infrastructure R&D Projects
» Infrastructure R&D Publications
» Infrastructure R&D Topics

 

Updates

» FHWA Launches Flagship Initiative to Collect Nationwide Data on Highway Bridges
  
» FHWA Deploys LTBP Program

 

Related Links

» National Bridge Inventory
  
» AASHTO Bridges Subcommittee
  
» Strategic Highway Research Program 2

 

Contact Us

» Hamid Ghasemi, Ph.D
LTBP Program Manager
202-493-3024
E-mail ltbp@dot.gov
  
»Address
Turner-Fairbank Highway Research Center
6300 Georgetown Pike
McLean, VA 22101
  
»Driving Directions/Map Click here for directions and a map to theTurner-Fairbank Highway Research Center facility.

 

Federal Highway Administration | 1200 New Jersey Avenue, SE | Washington, DC 20590 | 202-366-4000
Turner-Fairbank Highway Research Center | 6300 Georgetown Pike | McLean, VA | 22101