Effect of spatial variation of earthquake ground motion on seismic response of bridges

ABSTRACT

A methodology is presented to generate spatially varying seismic ground motion time histories at a number of prescribed location on the ground surface, complatible with prescribed response spectra and duration of strong ground motion, and reflecting the wave propagation and loss of coherence effects. The prescribed locations can correspond to differencial local soil conditions and therefore different response spectra can be assigned to each location. In such a case, the generated ground motion time histories will have different frequency contents. This methodology is the used in two case studies involving the SR 14/I-5 Interchange that has partially collapsed during the 1994 Northridge earthquake, and a typical three-span concrete bridge designed BERGER/ABAM Engineers for the Federal Highway Administration. Each case study considers a set of different scenario earthquakes with different apparent velocities of wave propagation and/or different angles of incidence of seismic waves with respect to the axis of the bridge and/or combinations of vertical and horizontal components of ground motion. It is concluded that the maximum stress at critical locations of the bridge can show increases up to 18