EVALUATION OF THE EFFICIENCY OF GROUND MOTION SELECTION METHODS IN ASSESSMENT OFTHE SEISMIC DEMANDS WITH SIGNIFICANT HIGHER MODE EFFECTS

An important step for the Nonlinear Time History Analysis (NLTHA) of structures is to select a reliable set of ground motions. An effective selection can reduce the possible scatter in the results due to the intrinsic uncertainties of recorded Strong Ground Motions (SGMs). Following the described purpose to achieve a more reliable estimation of the seismic behaviour of structures; Different SGM selection and modification methods have been proposed. In this paper the “structure-specific” selection, is evaluated quantitatively. Two proposed selection methods based on the spectral shape and the ability of reliable prediction of dynamic collapse capacity of group structures are chosen and the sensitivity of response characteristics to the selected SGMs in case of MDOF systems is investigated. Selection methods are based on some simplifying assumptions that may not be true in case of complex structures. Also, most of proposed selection and scaling methods are claimed to be efficient in case of building structures, while many researchers in the field of earthquake engineering are interested in the seismic evaluation of soil systems or special non-typical structures. MDOF systems including a 3-story steel frame, a 12-story steel frame and two typical soil profiles are modelled. The features of frames and soil profiles are selected such that the efficiency of methods can be compared both for “soft” and “stiff” dynamic systems.The results show that when the selection method consider only the spectral shape at the first mode of vibration, significant reduction in the reliability of EDPs is possible. To resolve the mentioned problem it is suggested that new scaling and selecting methods be designed in which the role of higher modes of vibration and more complex mechanisms of failure as a part of selection problem is considered.

کلیدواژه ها:

Time-history analysis ، Ground motion selection ، Evaluation