A Survey on Displacement Resonance Factor Supplemented to Linear Analysis Responses for Actual Displacements

Regarding that several structures, especially moment resisting frames, which have been designed using recent seismic design Iranian codes, have shown some vulnerability against earthquakes it can be said that there is still a need for modification of some features of the seismic design codes for structural systems. Namely under provision of this code, displacement resonance factor (DRF) receives same values for all structural systems. To make a point, eighty concrete moment resisting frames by eccentric braces, designed based on the Iranian National Seismic Standard, has been considered to capture seismic parameters by performing two-dimensional nonlinear pushover analyses. Pushover Analyses have been conducted using SAP-2000 program, which can consider material nonlinearities almost near reality. In this case the applied forces have been considered as the lateral forces of the Seismic Standard. Seismic parameters including overstrength, ductility and behavior factors are excerpted by following Young Theory. Also studies based on Newmark and Hall practice has been pursued to withdraw coefficient of force reduction due to ductility.Analytical results show that in the case of reminded frames the value of DRF can be much higher than that recommended by Iranian Code. Furthermore, the nonlinear responses of these structures are very different from those estimated by static equivalent method. On the suggestion side, this problem can be devised by multiplying a coefficient of 1.85 to the former resonance factor.

Keywords:

Earthquake , Structure , Moment resisting frame , Nonlinear