ABSTRACT
Aer the 1933 Long Beach Earthquake, California began designing bridges for a small lateral earthquake force. Bridge damage during the 1971 San Fernando Earthquake prompted Caltrans to develop comprehensive seismic design criteria. Highway bridges in California were typically designed using a single-level, force-based design approach based on a “no-collapse” design philosophy. Seismic loads were determined on the basis of a set of soil conditions and a suite of four site-based standard Acceleration Response Spectra (ARS). Structures were analyzed using the three-dimensional elastic dynamic multimodal response spectrum method. Structural components were designed using a reduction Z-factor (Caltrans 1990) to reduce seismic forces for ductility and risk. Minimum transverse reinforcement con-nements were required.
