The National Academies

NCHRP 12-28(11) [Completed]

Development of Site-Specific Load Models for Bridge Rating

  Project Data
Funds: $200,000
Research Agency: Imbsen & Associates, Inc.
Principal Investigator: Drs. W. David Liu and C. Allin Cornell
Effective Date: 2/9/1987
Completion Date: 3/30/1990

Throughout the United States bridges are evaluated for their capacity using standard design loads and truck configurations. In some cases bridges are judged to be structurally deficient for the current design loadings and therefore require load posting. The public pays a high price when bridges are posted, either in increased travel time or in costs associated with bridge rehabilitation and replacement. Bridge design loads and design load frequencies are typically used as inputs to the rating process. However, the bridge location determines the actual loads, load frequencies, and truck configurations that an existing bridge will experience. These factors may differ substantially from the current design loadings for which the bridge is presently rated. Data on truck traffic show considerable variation with respect to the functional highway classifications and locations on which they had been collected. More realistic evaluations of bridges may be possible by developing site-specific loading models.

The objective of this research was to develop rational site-specific load models for bridge rating that accurately reflect bridge site characteristics. The project was to also have produced procedures for incorporation of these site-specific models into the bridge rating process in accordance with the AASHTO Manual for Maintenance Inspection of Bridges. The models were to consider the bridge location, highway system functional classification, expected vehicle types and configurations, multiple presence of vehicles, peak load spectra, and the degree of legal load limit enforcement.

The final report was not published.

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