عنوان مقاله [English]
Response modification and deflection amplification factors are used in the current seismic design codes to account for the inelastic behaviour of structural systems without the need for complicated nonlinear analyses. A deflection amplification factor, cd, is used to compute the expected maximum inelastic displacement from the elastic displacement induced by the design seismic forces. The response modification factor, R, expressed as either a force reduction factor or a behavior factor, is used to reduce the linear
elastic design response spectra. It is generally expressed as the product of three factors: overstrength factor, ductility factor, and redundancy factor.This paper tries to evaluate these factors for steel intermediate moment-resisting frames. For this purpose, two-dimensional steel building models with different number of stories have been designed and analyzed. After obtaining pushover curves of the models, two different approaches have been adopted to calculate the effective parameters of the response modification and deflection amplification factors from pushover curves; the first approach that is suggested by seismic code provisions, like ATC-19, FEMA-356 and Iranian Standard No. 2800, uses the idealized pushover curve to specify the effective parameters, and the other approach that is recommended by FEMA-P695 gets the parameters directly from pushover curves. The obtained results from these two approaches for the above-mentioned factors have then been compared with each other and with the recommended values of these factors in the Iranian Standard No. 2800. In this evaluation, ductility factor of the response modification factor has been calculated based on the relations proposed by Newmark and Hall, Lai and Biggs, and Nassar and Krawinkler.According to the obtained numerical results, the average response modification factor resulted from the FEMA-P695 approach is 5.26, while this factor was obtained 3.98 based on the Iranian Standard No. 2800 approach. Considering the recommended R factor of the Iranian Standard No. 2800 for the ultimate limit state design of steel intermediate moment-resisting systems equaling 5, it is obvious that the results from the FEMA-P695 approach are more compatible with the code recommendation. In addition, the average overstrength factors, according to the FEMA-P695 and Iranian Standard No. 2800 approaches, are 2.37 and 1.80, respectively, when the recommended value of this factor in the Iranian Standard No. 2800 is 3. The average deflection amplification factor obtained from both approaches is 3.67 that is slightly less than the recommended value of 4 for this factor in the Iranian Standard No. 2800.