بكارگيري الگوي بار سختي براي مدلهاي اول و بالاتر در تحليل استاتيكي فرآيند غيرخطي

Sufficient seismic performance implies that available strength and deformation capacities exceed the demand imposed on a structure by the design earthquake. Ideally, performance evaluation should be based on nonlinear time history analyses utilizing suitable of representative ground motions. However, complex analyses cannot be justified economically except in very special cases, and presume that sufficient knowledge exists to accurately represent the cyclic load-deformation behavior of structural elements. A simpler option to evaluate strength capacities and deformation demands is the nonlinear static pushover analysis. This procedure involves applying a predetermined lateral load pattern that approximately represents the relative inertia forces which are generated at locations of substantial mass, and pushing the structure under this load pattern to the level of deformation expected in a design earthquake. The objective of the pushover analysis is to obtain estimates of the member forces and the global and local deformations to in which are likely experienced by a structure in a design earthquake, and to use these estimates for evaluation of structural response. In this paper, first the nonlinear static procedure is reviewed, then the effect of stiffness load pattern on first and higher modes are studied. Different moment resisting frames and braced frame are evaluated by nonlinear static and nonlinear dynamic time history procedures and the results obtained from two methods are compared.