Rigid-Plastic Pseudo-Spectra: Peak Response Charts for Seismic Design

Seismic design generally involves the assessment of the maximum plastic displacement of elastoplastic structures under given earthquakes. Recent studies show that this displacement can be evaluated by referring to a simple rigid-plastic model. This can be done with the help of an appropriate rigid-plastic response chart, called here pseudo-spectrum. For a given earthquake it plots the peak displacement of a rigid-plastic oscillator as a function of its acceleration at the yield limit. Despite their simplicity, rigid-plastic pseudo-spectra have not been studied extensively. The present paper discusses the main features of such spectra and presents the rigid-plastic pseudo-spectra relevant to some 38 earthquakes of the last 50 years. These spectra show that the methods currently available to estimate the seismic response of a rigid-plastic oscillator may fail to give accurate results. To facilitate comparison between different earthquakes, the rigid-plastic pseudo-spectra are also presented in a non-dimensional form. The latter may come in handy when constructing conventional rigid-plastic pseudo-spectra for design purposes.