Evaluation of Strong Ground Motion Record Selection & Scaling Methods in Case of Regular and Irregular Generic Frames

Abstract eng:
In performance based earthquake engineering, Nonlinear Time History Analysis (NLTHA) is recognized as an efficient tool for reliable estimation of seismic demands. Knowing the fact that nonlinear structural response can be highly sensitive to the selection and scaling of input Strong Ground Motions (SGMs), many SGM selection and modification methods have been proposed in the literature, however, most of them are evaluated quantitatively just in case of several typical regular structures. Despite the importance of this issue, few studies have focused on the comprehensive evaluation of available methods to assess their performance by using a series of benchmark structures and find the applicability scope of each approach. This paper presents an evaluation of three well-known SGM scaling methods (PGA-based, S a (T 1 )-based and the conventional code-based scaling approach) as well as a recently introduced method known as modal pushover based scaling and selection. To have a comprehensive assessment, forty of 2-D one bay vertically regular frames designed with general features as: five different heights (N= 3, 6, 9, 12 and 15 stories), two types of seismic behavior i.e. stiff and flexible frames with periods of 0.1 and 0.2 time of the number of stories, respectively and four ductility capacities (μ =1, 2, 4 and 6). Furthermore, for all frames three types of irregularity (stiffness, strength, and combined stiffness and strength) have been applied in four different locations along the height (top story, middle story, first story and lower half of the frame) using four modification factors (0.2, 0.5, 2 and 5). A set of 22 pairs of horizontal far-field SGMRs which was used in the ATC63 project is selected for response history analysis of total 1960 frames. Engineering Demand Parameters (EDPs) considered in this study are: Maximum Inter-story Drift Ratio over building height, absolute acceleration of each story, base shear, and etc. The results illustrate that the efficiency of each method is affected by properties of the structure that is subjected to NLTHA. Ductility capacity is a property that may significantly threaten the accuracy of predicted EDPs if it is not involved in the method of selection and/or scaling. On the other hand, the results indicate that although vertical irregularities are important, but they may not produce the meaningful bias in the results. It is shown that the efficiency of each method depends on the desired EDP selected to be controlled, i.e. the proper performance of any method in the prediction of a specified EDP does not guarantee its acceptable efficiency for predicting other EDPs keeping the same level of accuracy.

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