A note on strength-reduction factors for design of structures near earthquake faults

Strength-reduction factors are analyzed for simplified near-fault, fault-normal and fault-parallel strong-motion displacements. It is shown that the common design rules for selection of the strength-reduction factors are conservative and properly 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 should 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 all periods and equal to (2μ−1)1/2, where μ is ductility.