Structural Damping and Displacement Ductility Effects on Input Energy Spectrum of Earthquake

To improve seismic design of structures, providing more comprehensive criterion than the common criterions in structural seismic design is essential for the engineering community. The concept of energy has been considering as a seismic design philosophy in research communities; But there are some gaps for application of energy concept and its development in seismic design, and filling a small part of these gaps is the main objective of this study. Energy criterion is simple, scalar and conceptual quantity. Easy using of spectrum as an efficient tool in engineering is noteworthy; therefore, study on effects of damping and ductility on input energy spectrum is effective step to exert the energy criterion in structural seismic design. In this research, by using nonlinear dynamic analysis for 4 damping ratios and 4 ductility factors, relative input energy spectra per unit mass of structure have been produced for 4 Iranian earthquakes. Then 64 spectra that produced in this study have been reviewed and obtained-results have been discussed. Scrutiny of spectra show that increasing of damping ratio and ductility have reduced spectrum’s changes. Also, variation of ductility factor is more effective than the variation of damping ratio on relative input energy spectrum. Variation of damping ratio and ductility factor have little effect on changing of peak corresponding period in relative input energy spectrum. Overall, with engineering estimate and in the range of damping ratios and ductility that have been studied in this research, has been concluded that in inelastic behavior range, input energy spectrum per unit mass has little sensitivity to changes of damping ratio and ductility in wide range of periods, and it is a function of structure’s period. Because lack of design engineer's awareness on real amounts of damping ratio and ductility when designing structure, it is one advantages of relative input energy spectrum.