Introduction

Bridges that cross faults can be subjected to large dynamic and static ground motions. As there are very few actual ground motions recorded very close to ruptured faults ($<$ 100m), ground motion simulation is the only viable way to obtain time histories for structural analysis. Professors Dreger (BSL) and Chopra (CEE) are collaborating on a Caltrans funded project investigating the response of bridges that cross faults with the objective of developing simplified methods that can be applied to bridge design. In this report the ground motion simulation part of the effort is described.

The bridges being considered have a minimum span of 30m, and therefore the simulation method must be capable of calculating seismic response time histories at this small distance from the fault. In addition, the method must accurately account for the near-fault source radiation pattern, far- and near-field seismic radiation, and have the ability to characterize motions for a broad range of fault types (e.g. vertical strike-slip and reverse faulting), as well as variable slip and full kinematic description of the rupture process. We must be able to accurately simulate the directivity effect as well as the sudden elastic rebound sometimes referred to as fling.

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