- What the Long-Term Bridge Performance (LTBP) Program Is
- What We Do
- Why We Do It
- How We Do It
The LTBP Program is a long-term research effort, authorized by the U.S. Congress under the Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (SAFETEA-LU) to collect high-quality bridge data from a representative sample of highway bridges nationwide that will help the bridge community to better understand bridge performance. The products from this program will be a suite of data-driven tools, including predictive and forecasting models that will enhance the ability of bridge owners to optimize their management of bridges.
The overall objective of the LTBP Program is to inspect, evaluate, and periodically monitor representative samples of bridges nationwide to collect, document, maintain, and manage high-quality quantitative performance data over an extended period of time. This will require taking advantage of sensing technologies, nondestructive evaluation (NDE), and testing tools in addition to typical bridge inspection approaches. It will also require close collaboration among stakeholders, State transportation departments, academia, and industry to collect data that are available but not currently gathered into a single database by the bridge community. The LTBP Program is designed in part to collect critical performance data that are not available elsewhere and merge it with data gathered from available sources.
LTBP Program researchers will conduct detailed periodic inspections, monitoring, and evaluation of the population of bridges representing the national bridge inventory by taking advantage of NDE techniques and visual inspections. NDE techniques are used to detect flaws and corrosion inside the structures and cracks because of fatigue, corrosion, overloads, and environmental conditions. For the selected bridges in the study, researchers will conduct recurrent, periodic evaluations throughout the life of the program and may perform forensic autopsies of decommissioned bridges to learn more about their capacities, reliabilities, and failure modes.
The wealth of data collected through the LTBP Program and the subsequent data analysis will do the following:
- Improve knowledge of bridge performance.
- Advance research in deterioration and predictive models.
- Apply cost analysis effectively.
- Improve inspection/condition information through NDE and structural health monitoring.
- Further the advancement of technology used for the assessment of critical but hidden bridge elements and components.
- Support development of improved design methods and maintenance/bridge preservation practices.
- Quantify the effectiveness of various maintenance, repair, and rehabilitation strategies.
- Improve the operational performance of bridges with the potential to reduce congestion, delay, and accidents.
- Promote the next generation of bridge and bridge management systems.
Ultimately, improved understanding of bridge performance will promote safety, mobility, longevity, and reliability of the Nation's highway transportation assets and allow bridge owners to make better data-driven decisions regarding their bridge inventory.
Understanding bridge performance is the key to creating "the bridge of the future." Bridge performance is a multifaceted issue involving the performance of materials and protective systems, individual bridge components, and the structural system as a whole. The performance of any single bridge or bridge element depends on multiple factors, many of which are closely linked. They include: the original design parameters and specifications (bridge type, materials, geometries, and load capacities); the initial quality of materials and the as-built construction; varying conditions of climate, air quality, and soil properties; and corrosion and other deterioration processes. Other factors influencing performance include traffic volumes; counts and weights of truck loads; truck live load impacts; and damage sustained as a result of scour, seismic events, and wind.
A final critical factor influencing performance is the type, timing, and effectiveness of preventive maintenance, of minor and major rehabilitation actions, and ultimately of replacement actions applied to the bridge. All of these factors combine to affect the condition and operational capacities of the bridge and its various structural elements at any given point in the life of the bridge. Currently, some important aspects of bridge performance are not well understood, and some of the main factors related to bridge performance are not well documented. Attempts to assess how bridges are performing are partly based on expert opinion and/or analyses that are hampered by lack of crucial data, and thus are dependent on one or more assumptions or generalizations.
Bridge performance measures have different uses depending on the perspective and responsibilities of those persons using the performance measures. Bridge performance measures are useful for the following reasons:
- Identifying clear links between specific policies (such as the type and quantity of anti-icing materials), actions, and the resulting change in the performance level of a bridge element.
- Improving knowledge of how and why bridges deteriorate.
- Gaining a better understanding of the effectiveness of various design, construction, inspection, and preservation strategies, as well as management practices.
- Gaining a better understanding of the effectiveness of durability strategies for new bridge construction, including material selection.
- Improving bridge management practices using qualitative and quantitative data.
- Evaluating serviceability and durability.
- Setting priorities for resource allocations and evaluating organization-wide policies and programs such as the split between maintenance and capital funds.
- Establishing risk-based evaluations of bridges that are vulnerable to failure.
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 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 multitiered sampling approach. This approach determined the most common bridges types and factored in climate/environmental conditions as well as geographic location to allow the maximum number of States to participate and to implement the most effective, cost-efficient data collection effort.
In all, 14 geographic clusters and 10 corridors were identified. Figure 1 shows the clusters and corridors overlaid on a Department of Energy (DOE) climate zone map.
Figure 1. Map. LTBP Program clusters and corridors.
To determine the actual bridges that would participate in the program, the following specific selection criteria were used:
- Untreated deck (for untreated deck clusters).
- State owned.
- Bridge types:
- Steel multigirder bridges.
- Prestressed multigirder bridges.
- Adjacent prestressed box beam bridges and cast-in-place box girder bridges.
- Not over a railroad.
- Max span length is between 10 and 50 m.
- Maximum of four lanes on bridge.
- Average daily traffic (ADT) is less than 50,000 (removed for corridor bridges).
- Built after 1960.
More information about the bridge selection methodology, the selected bridges, and data collection progress can be found on the Data Collection page.
The framework for LTBP Program is to collect data to improve the understanding of bridge performance and provide hard data on bridge condition that supports the decisionmaking process of bridge maintenance, restoration, and rehabilitation.
The objective of the data collection portion of the LTBP Program is first and foremost to collect research quality data to support data-driven decisions. Collecting research quality data requires data be collected in an accurate, repeatable, and reliable manner, allowing comparison of data sets gathered from the same bridge over time, and revealing the changes in performance attributed to aging of a bridge. Concurrently, the data collected must allow for comparison of a population of bridges with similar attributes to understand performance trends for that population and to compare populations with dissimilar attributes and environmental exposures.
Figure 2. Photo. Long-Term Bridge Performance (LTBP) Program Protocols, Version 1, published January 2016.
These objectives are achieved through the employment of data collection protocols that establish a consistent methodology covering the planning, field execution, and post processing of the data. A set of approximately 185 LTBP Program data collection protocols have been developed for the program covering visual inspection, material testing, and NDE. The protocols address visual data collection approaches and manual data collection. Protocols currently under development will address the employment of innovative technology such as the Robotic Assisted Bridge Inspection Tool, or RABIT™. The RABIT™ bridge deck assessment tool was developed to automate NDE data collection resulting in a safer, more efficient, and therefore cost effective approach to bridge condition and performance data collection.
More information about the LTBP Program Protocols and the RABIT™ bridge deck assessment tool can be found on the Products page.