Wave-passage effects on strength-reduction factors for design of structures near earthquake faults

Wave-passage effects are described for strength-reduction factors near faults, for fault-normal and fault-parallel strong-motion displacements. It is shown that the common design rules for selection of the strength-reduction factors are usually conservative and approximately describe the reduction amplitudes near faults of strong earthquakes for fault-normal pulses. However, for fault-parallel displacements, the same reduction factors are not conservative and must be changed. It is recommended that for design close to active faults, the strength-reduction factors for all components of motion should be constant for long periods and equal to (2μ−1)1/2, where μ is ductility. For periods shorter than about 1 s, these strength reduction factors should be further reduced by 30–40%.