Damage-based inelastic response spectra for seismic design incorporating performance considerations

Modern seismic design allows a structure to develop inelastic response during moderate to severe earthquakes. The emerging performance-based design requires more clearly defined levels of inelastic response, or damage, to be targeted for different earthquake hazard levels. While there are a range of factors that could influence the level of damage and hence the performance, the design strength remains to be a fundamental design parameter that is inherently related to the structural performance. In this paper, the response reduction factor, which is a normalized form of the design strength, is investigated on a direct damage basis. The implications of the damage-based strength reduction factor (SRF), denoted as RD factor, on multiple performance targets are discussed. A series of RD spectra are generated from a large set of ground motions in different groupings to examine the effects of local site condition, earthquake magnitude and distance to rupture on the RD spectra. The overall mean and standard deviation of the RD spectra for different levels of damage are obtained, and simple empirical formulas are proposed.