There are approximately 580,000 bridges in the FHWA National Bridge Inventory (NBI). The NBI is a collection of key information used to identify and characterize the type, usage, size, location, and condition of bridges in the United States. Approximately 90,000 of the bridges in the NBI have been identified as having unknown foundations. Because of inadequate foundation information, expensive bridge countermeasures are often implemented even though they may not be necessary. However, taking no action at all may involve unacceptable risk.
Current methods to investigate unknown foundations are limited and costly. Bridge owners know intuitively that it is often prudent to use countermeasures, monitor sites, or even take the risk of failure rather than use limited resources for costly foundation investigations, especially for bridges with limited remaining service life. Risk-based guidelines are needed to assist bridge owners in determining when a detailed foundation investigation is warranted. If an investigation is warranted, guidelines are needed to assist bridge owners in determining the type of investigation to be conducted considering the applicability and costs of various investigation techniques. If an investigation is not warranted, guidelines are needed to assist bridge owners in determining if a hydraulic or structural countermeasure is warranted, and if so, the level of protection commensurate with the estimated risks.
The objective of this research is to develop risk-based guidelines to assist bridge owners in evaluating and prioritizing various courses of action (i.e., investigations, countermeasures, monitoring, rehabilitation, or replacement) for managing bridges with unknown foundations.
Accomplishment of the project objective(s) will require at least the following tasks.
) Review relevant practice, literature, performance data, research findings, and other information related to risk-based analysis of various courses of action for managing bridges with unknown foundations. The review should include information from unpublished experiences of engineers and bridge owners. (2.
) Identify existing data sources, in addition to the NBI database, that will be used in developing risk-based guidelines. Evaluate the data sources to determine parameters available for use in developing the guidelines. The parameters may include but are not limited to costs, bridge type and age, substructure, soil characteristics, traffic volume, scour, seismic vulnerability, remaining life of the bridge, value of lost time, traffic volume, detour lengths, types of foundations, bridge condition, bridge geometry, and potential loss of life. Select parameters to be used in guideline development. Evaluate the data sources to determine, in addition to the above, actual bridge sites for use in demonstrating the application of the guidelines. (3.
) Evaluate the parameters selected in Task 2 and assign risk factors for each parameter. Using the selected parameters and risk factors, develop preliminary risk-based guidelines for evaluating and prioritizing various courses of action for managing bridges with unknown foundations. (4.
) Submit an interim report documenting the information developed in Tasks 1, 2, and 3. An updated work plan for completing Phase II should be included as a separate appendix. The interim report should include a thorough discussion of the data sources, parameters, and associated risk factors used to develop the preliminary guidelines. The report should also discuss the actual bridge sites selected for use in demonstrating the application of the guidelines. Meet with the NCHRP panel to review the interim report and updated work plan. Work on Phase II will not begin without approval of the NCHRP.
) Based on panel guidance during the interim meeting, finalize the risk-based guidelines. Demonstrate the guidelines by developing detailed examples of their application, using information from actual bridge sites approved during the interim meeting. (6.) Submit a final report that documents the entire research effort. Include the final risk-based guidelines and examples of their application as stand-alone appendices.
The final report is available online as NCHRP Web-Only Document 107