Evaluation of Seismic Design Procedures for Highway Bridges

Abstract

The seismic response of highway bridges designed by Cal‐Trans specifications in use before and after the 1971 San Fernando earthquake and hypothetical bridges designed by the latest American Association of State Highway Transportation Officials (AASHTO) specifications are evaluated. A computer code to analyze the dynamic response of bridges to a uniform base acceleration is developed with particular emphasis on modeling the overall nonlinear behavior of the piers. A spectrum‐compatible, artificial accelerogram is derived as a base input for the bridges. The degree of damage expected for the piers is evaluated by the use of a damage index derived from tests on reinforced concrete specimens. The results found that for bridges designed prior to 1971, the piers are in danger of collapse if the moments exceed the yield moments due to the limited amount of transverse reinforcing used. The bridges designed after 1971 and by the current specifications showed good calculated behavior of the piers. The method currently used for calculating the design force on the abutment, however, was unconservative in many cases.