Effect of Design Seismic Loads on a Highway Bridge

The measured and calculated response of a five-span reinforced concrete highway bridge subjected to static lateral loads is presented. The experimental studies included nondestructive static tests of the bridge loaded by hydraulic jacks at the intersection of piers and the deck, as well as quick-release dynamic tests. The lateral deflection of the bridge deck was measured at the abutments and at the intersection of piers and the deck. The bridge was loaded to approximately 50% above the seismic design loads. No sign of distress was observed even though these very large loads were used. The analytical studies included several static elastic and inelastic analyses of the bridge for the test loads, the loads used in the design of the bridge, and the loads based on the current Applied Technology Council (ATC) guidelines for seismic design of highway bridges. An inelastic model was developed that accounted for the nonlinear action at the pier to foundation connections. In this model, the loads are applied monotonically in small load increments and the internal forces and deformations are determined for each increment. Comparison of the experimental and analytical results showed that, by ignoring the foundation flexibility (an assumption made in design of the bridge), the lateral displacement at the deck center was underestimated by approximately 50%.