Journals Proceedings

Abstract

Current structural design codes like ASCE/SEI 07-10 permit the engineer to use three number of ground motion records approximating to a uniform hazard spectrum on condition that the maximum of the obtained displacements should be used during seismic performance assessment. However, if at least seven number of ground motion records are selected and scaled to this aim, mean of the obtained displacements shall be used. It is rather arguable if the former compensates the latter considering the fact that dispersion of structural response parameters are generally too high under the effect or earthquake loading. In this work, initially a suite of seven ground motions all of which scaled to approximate the design response spectrum of ASCE/SEI 07-10 is prepared, afterwards all possible trio combinations of these seven records are determined and each subset re-scaled to fit the response spectrum. A total of 35 subsets are prepared in this sense. The amount of approximation to the target spectrum is also determined for each set, and eventually 5 subsets with maximum, minimum and medium approximation levels are chosen. In order to study the story drift distributions of steel special moment frames under the effect of these prepared sets, a ten story model frame is designed per US design codes. The results indicate that the use of record subset with the highest approximation to the target spectrum does not result in the maximum story drift ratios of the sub set to be close to the mean story drift ratios of the main set with 7 records. Moreover, the difference between the mean story drift ratios of the main set and the maximum story drift ratios of the subset can be considerably high especially for the floor level with the peak maximum story drift ratio among the other floor levels.