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In the past decade design procedure changed to �performance-based design� from�force-based design�, by this mean many researchers focused on nonlinear static analysis (NSA)and the procedure named �PUSHOVER�. Advantages of this method are defining the inelasticbehavior of structure without nonlinear dynamic analysis (NDA) effort and also defining plastichinges formation in critical elements, and the order of formed plastic hinges. In spite of these goodadvantages NSA is limited to short and planar structures and application of that in tall andtorsionaly asymmetric structures may yield unreliable results.In this study reliability of NSA is investigated by performing both nonlinear static and dynamicanalysis on six 2D moment resisting concrete frames. Non linear dynamic analysis has been doneby the suggested method in FEMA356 guideline called �Target Displacement Method�. A groupof 4 different lateral increasing loads were used in pushover analysis and 3 different groundmotions were applied in NDA. Results indicate that same responses can be obtained by performingNSA, but errors will be increased by frames height increment.

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The nonlinear static procedures (NSPs) proposed by design codes do not lead to reliable results especially for tall buildings.

They generally provide inconsistent estimates of inelastic seismic demands, especially for the top floors due to their inabilities in

considering the higher modes effects. In this paper, a new enhanced pushover procedure is proposed which is based on the

envelope of the structural responses resulting from two separate pushover analyses as a combination rule. Also, the suggested

pushover analyses are performed using a newly proposed modal load pattern, i.e., the Modal Spectra Combination (MSC), and

the ASCE41-06 required first mode load pattern. The MSC load pattern is consisted of a number of mode shapes combined with

appropriate weighting factors that depend on their modal participation factors, modal frequencies and design spectral values. A

number of 2-D steel moment resisting frame models with different number of stories are used to investigate the efficiency of the

proposed method. The inter-story drifts and the maximum plastic beam moment and curvature responses are used as a measure

to compare the results obtained from the nonlinear time-history analyses (NL-THA) and some other NSPs. The results obtained

through rigorous nonlinear dynamic analyses show that the application of the proposed method leads to acceptable results for

steel MRF systems in comparison to other available enhanced NSPs. The OpenSees program is used for numerical analysis.

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The current building codes provide limited prescriptive guidance on design for protection of buildings due to progressive collapse. Progressive collapse is a situation in which a localized failure in a structure, caused by an abnormal load, such as explosions or other happenings. Three procedures, often employed for determination of the structural response during progressive collapse i.e. linear static procedure (LSP), nonlinear static (NSP) and nonlinear dynamic (NDP) analyses. In nonlinear static analysis, a force-based method is applied and the structure is pushed down to the target force. In this research, a new displacement-based method will be proposed for nonlinear static analysis. In displacement-based method, the structure is pushed down to target displacement instead of target force (similar to the one in seismic pushover analysis). To make a nonlinear static analysis, instead of increasing the load around the area of the removed column, a maximum displacement is calculated and the upper node of the removed column is pushed up to target displacement. Here, to determine the target displacement, results from nonlinear dynamic and linear static analyses are compared. This paper tries to present a formula to calculate the target displacement using the linear static rather than the nonlinear dynamic analysis. For this reason, 3 buildings with 3, 5 and 10 stories have been seismically designed and studied. The results show that, this method is much more accurate in comparison to the recommended approach in current codes. Also, this method does not have the limitations of force-based nonlinear static analysis.