Near-fault ground motion effects on simple structures

Ground motion records obtained from sites at known locations relative to earthquake faults were used to study near-fault (NF) ground shaking effects on the inelastic response of simple structures. The structures were idealized as single-degree-of-freedom oscillators with periods ranging from 0.05 to 3.0 s, a damping ratio of 2%, and target ductilities of 2, 4, and 6. The severity of inelastic response was described by a relationship between the oscillator period, the target ductility, and the lateral force reduction factor obtained from analysis. It was found that the inelastic demands of medium and longer period oscillators responding to NF strike-normal shaking increased for sites close to the fault as the distance along the fault from the epicenter increased. The inelastic response of short-period oscillators was not affected as much by NF shaking. A methodology for obtaining average and design level demands for structures at specific locations relative to the epicenter and fault is described. A design example is provided.