Influence of damping on seismic strength reduction factors: a study differentiated by ground motion frequency bandwidth

Building design codes typically specify seismic forces based on a 5-percent damped elastic design spectrum. To consider the case of structures with damping ratios other than 5%, damping correction factors are used. While these factors are determined for elastic systems, several studies have shown that the effects of damping are different for systems with nonlinear behavior. A study concerning the influence of damping on the nonlinear seismic response of building structures is presented. To separate the influence of nonlinear behavior, spectra of the ratio between the seismic strength demands corresponding to nonlinear and linear behavior, respectively, were computed, for damping ratios ranging between 2% and 10% and various constant ductility values. A database of ground motion records from the three strongest earthquakes that affected Romania during the last four decades was used in the study. The records were grouped into two sets, according to their frequency bandwidth. The spectral values computed for each set were processed statistically and results were expressed with reference to the 5%-damped spectra. It was found that, for the analyzed damping range, the influence of this parameter on the nonlinear response is weak to moderate, for both considered types of frequency content.