Live Load Effects on Response of Bridges during Earthquakes

Most bridge design specifications have few requirements concerning the inclusion of live load in the seismic design of bridges. Although it is recognized that live load provides not only additional gravity load but also dynamic force effects due to its sprung nature, the significance of these effects on the seismic response of a bridge is not clear. The main objective of this study is therefore to investigate and obtain insight into the effect of vehicle-bridge interaction during earthquake shaking. The study consists of both experimental and analytical investigations. This paper focuses on the experimental work, which includes shake table testing of a 0.4-scale model of a horizontally curved steel girder bridge loaded with a series of representative trucks. Preliminary experimental results show that the presence of the live load clearly had a beneficial effect on performance for small amplitude motions, but that this improvement diminished with increasing amplitude of shaking. Parameters used to measure performance include column displacements, abutment shear forces, and concrete spalling.