A COMPREHENSIVE STUDY OF BRIDGE LOADS AND RELIABILITY -- FINAL REPORT

The provision of safe bridge structures is an activity that occupies many engineers and design agencies. The loading features in current AASHTO provisions for short and medium span bridges were based on truck data recorded almost a half century ago. Recent development of discrete and unbiased weigh-in-motion systems have provided an opportunity to revise the specifications to use current data base including truck weights, configurations and headway, girder distribution and impact values. This data is incorporated in the present study with a reliability analysis. This provides uniform and consistent reliabilities over a variety of bridge spans and configurations. The reliability model incorporates prediction of extreme loads and the uncertainties in loading variables, strength and failure consequences. Maximum load spectra are compared with simulation, theoretical and approximate modelling. Two extensive examples are illustrated including fatigue design of steel attachments and static strength design. Recommended design provisions are given for each example. In each application, design loading vehicles are derived with measured characteristics to provide uniform reliability over a complete range of application. This includes simple and continuous spans. Allowable stresses are adjusted to provide consistent component reliabilities. Load factors are introduced to incorporate truck weight intensities and volume. Numerous examples and sensitivity studies are discussed on the impact of the data base on the recommended design provisions. Further discussion is made on extending the loading model to evaluation and rating of existing bridges and decisions regarding posting, permit vehicle and legal load changes. (Author)