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This volume consists of papers presented at the First International Conference on Bridge Management, held at The University of Surrey, Guildford, UK, from 28-30 March 1990.
In this study, a reliability-based calibration of live load factors for design and rating specific to the State of Michigan was conducted. For this study, high fidelity WIM data from 20 Michigan sites were analyzed. Using vehicle weight and configuration filtering criteria developed for the project, the WIM data were filtered to best capture Michigan truck traffic. From this data, multiple presence frequencies were calculated for two truck data pools. Load effects were generated for bridge spans from 20 to 400 ft, considering simple and continuous moments and shears, as well as single lane and two lane effects. Load effects were then projected to 5 (for rating) and 75 (for design) years. Bridge structures considered for the calibration included steel, prestressed concrete, reinforced concrete, and spread box beam girder structures, side-by-side box beams, and special long span structures. The calibration considered design; legal load rating; routine permit load rating; and special permit rating.
TRB’s National Cooperative Highway Research Program (NCHRP) Report 700: A Comparison of AASHTO Bridge Load Rating Methods documents an analysis of 1,500 bridges that represent various material types and configurations using AASHTOWareTM Virtis® to compare the load factor rating to load and resistance factor rating for both moment and shear induced by design vehicles, American Association of State Highway and Transportation Officials (AASHTO) legal loads, and eight additional permit/legal vehicles.
In recent years, requests to move heavy vehicles across bridges have risen dramatically. Highway agencies find it necessary to calculate safety margins under loads significantly above legal levels. For some regions of the U.S., permits have effectively raised the legal vehicle weight. Reliability analysis is used in this study to model live load uncertainties (using bridge weigh-in-motion data) and other dead load and resistance variables. Target safety indices are introduced by calibration with existing bridge rating and posting practices. Simulation of the expected maximum load effects of permit vehicles plus alongside vehicles has been carried out for both frequent permits, for different traffic classifications including volume and traffic enforcement levels, and single passage permits. Load factors are calibrated to achieve the target safety indices for different simple and continuous spans. A checking format for permit vehicles is proposed for possible inclusion in a bridge evaluation code. For the covering abstract of the Conference see IRRD Abstract No. 807839.