AN EVALUATION OF EQUIVALENT LINEAR MODELS FOR MODAL ANALYSIS OF NONLINEAR SYSTEMS SUBJECTED TO EARTHQUAKES

摘要

The purpose of this paper Is to summarize a study for the evaluation of the validly of the use of the modified dynamic properties of a structure in conjunction with elastic response spectra for the performance of modal analysis when the structural response is in the nonlinear range. To evaluate this technique, two small-scale nine story reinforced concrete structures were excited by six widely known earthquake records all of which caused significant yielding to the structures. In each case, the maximum displacement of each structure, found from its response history, was compared with the corresponding response maximum spectral displacement, which was estimated based on an "effective" period. The effective period is determined from the corresponding history of the structure. The comparison demonstrated clearly that the results from the modal analysis, using an effective period, do not generally agree with the results from the more realistic response history analysis. The use of the elastic response spectra, when nonlinear response is predominant, was found to yield results of a nonuniform trend, sometimes overestimating and sometimes underestimating the structural response.