Evaluation of Seismic Design Criteria for Highway Bridges

After an overview of the development of U.S. seismic design specifications for highway bridges an evaluation of current Caltrans and AASHTO seismic criteria is presented. Linear and nonlinear response spectra of ground motions recorded on different soil conditions in the Loma Prieta earthquake and other recent earthquakes are compared with code recommendations. Special emphasis is placed on how present design procedures reduce elastic forces to take into account the energy absorption capacity of the structure, and on the estimation of maximum inelastic deformations. Results indicate that current design recommendations may underestimate strength and deformation demands, particularly for short-period bridges and for bridges on soft soils. Finally, recommendations are made on how seismic design specifications may be improved.