The estimation of inelastic displacement is an essential step in displacement-based design. Estimation of inelastic response using response spectra is a simpler and attractive alternative to nonlinear dynamic analysis. A number of methods based on different approaches are now available to estimate nonlinear response from design spectra. Equivalent linearization is one of the widely used approaches for this purpose. The approach is known to yield reasonably accurate results. However, an anomaly in the approach is observed, which results in significantly non-conservative estimates of inelastic displacement, particularly in displacement-controlled spectral range. This paper illustrates the anomaly using displacement modification factors and numerical examples of oscillators of different periods and ductility. The results from the equivalent linearization approach have been compared with the results of nonlinear dynamic analysis and yield spectrum approach.
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