Document Type : Article
Authors
1
Science and Research Branch Islamic Azad University
2
International Institute of Earthquake Engineering and Seismology
Abstract
In this paper, the effect of the deterioration behavior of hysteretic loops in nonlinear static analyses (pushover) on special concrete moment-resisting frames with shear walls has been studied. One of the shortages in pushover analysis is that it approximately considers the effects of deterioration pertaining to hysteretic loops for structural elements. To evaluate this effect, it is necessary to perform nonlinear static and dynamic analyses and compare the results. To this end, six different planar frames, each one part of a three-dimensional design structure, have been modeled. All structures are the same in plane and different in height. After conducting the pushover analyses for defining the target displacement, dynamic analyses are also performed, considering the two different employed behavioral models. Because OPENSEES software has various behavioral characteristics for steel and concrete, and also has the ability to suitably model structural elements, it was used for performing the nonlinear static and dynamic analyses. In order to find the capacity curve of the structure, the displacement of the control node and the shear force of the base level were calculated using this software. For accurate calculation of the target displacement and bilinear idealization of the capacity curve, a computer program was developed in the Matlab environment to determine the target displacement, strength ratio (R) and etc. The employed material models are reinforcing steel material, concrete02 and hysteretic material. Deterioration behavior, as well as non-degrading behavior, is considered in nonlinear dynamic analyses. For modeling the structural elements, stresses and strains for each designed section are considered, with respect to confinement effects. The required backbone curve includes cracking point, yielding point and ultimate stress point, which are all derived from USC-RC software, and, of course, by considering element cross section, arrangement, number and size of reinforcing bars. Also, twelve ground motion records, which are scaled to 0.35g hazard level, have been used in time history analyses. Finally, maximum displacement amounts derived from inelastic dynamic analyses for 0.35g hazard level are compared with the amounts of target displacements, which express the maximum displacement of the structure under design earthquake, and we consider the effects of different parameters, such as deterioration, with the coefficient, c2. Results show that by increasing the height of the frame, the variance between frame displacement, with both deteriorating and non-degrading behavior, will be decreased, so that the effect of the deterioration behavior could be neglected in the target displacement calculation for high-rise frames.
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