Response Spectral Matching of Two Horizontal Ground-Motion Components

Accurate performance-based earthquake engineering analysis requires that engineering seismologists and structural analysts employ consistent characterizations of bidirectional seismic demand. In current design, the seismic demand is generally given as a geometric mean response spectrum, which does not give a direct measure of the maximum spectral demand for all possible orientations of the ground motion with respect to the axes of the structure. Although this may be appropriate for most applications, it is shown that for some structures in which the lateral-load resisting system is not decoupled into two orthogonal subsystems, the maximum rotated spectral demand (major axis demand) may be the most appropriate characterization of bidirectional seismic hazard. On the basis of this observation, a new program is developed for matching the major and minor axis spectra of two horizontal ground-motion components simultaneously to two target spectra, using wavelets. The program, RspMatchBi, is based on the original single-component version of the code, RspMatch2005, written by Hancock and coworkers. It is shown in an example application that the new program can effectively match the major and minor axis spectra of the record to two individual target spectra, where the two targets are representative of either expected major and minor axis demand or the mean demand. The latter may be used to derive effectively orientation-independent ground motions. DOI: 10.1061/(ASCE)ST.1943-541X.0000227. (C) 2011 American Society of Civil Engineers.