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Well-known seismic design codes have offered an alternative equivalent static procedure for practical purposes instead of verifying design trials with complicated step-y-step dynamic analyses. Such a pattern of base-shear distribution over the building height will enforce its special stiffness and strength distribution which is not necessarily best suited for seismic design. The present study, utilizes a hybrid optimization procedure to seek for the best stiffness distribution in moment-resistant building frames. Both continuous loading pattern and discrete sizing variables are treated as optimization design variables. The continuous part is sampled by Harmony Search algorithm while a variant of Ant Colony Optimization is utilized for the discrete part. Further search intensification is provided by Branch and Bound technique. In order to verify the design candidates, static, modal and time-history analyses are applied regarding the code-specific design spectra. Treating a number of building moment-frame examples, such a hyper optimization resulted in new lateral loading patterns different from that used in common code practice. It was verified that designing the moment frames due to the proposed loading pattern can result in more uniform story drifts. In addition, locations of the first failure of columns were transmitted to the upper/less-critical stories of the frame. This achievement is important to avoid progressive collapse under earthquake excitation.

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Steel plate shear walls have long been used as a lateral load resisting system. It is composed of beam and column frame elements, to which infill plates are connected. This paper investigates the progressive collapse-resisting capacity of 50-story building 3D model of the strip model of steel plate shear wall comparing with X-braced and moment frame system based on the removing structural elements from a middle and corner of the exterior frame, in the story above the ground. The collapse behavior is evaluated by different nonlinear static and dynamic analyses using conventional analysis software. In this study, vulnerability of structures is also assessed by sensitivity index (SI) regarding the sensitivity of structures to dynamic effect induced by progressive collapse. To identify vulnerable members, resulting actions of nonlinear static analysis, considering load factor to account for dynamic effect, at the failure mode of structure at the specific performance level are compared by the factor of redundancy related to overall strength of structure, with the linear static analysis of damaged model without considering dynamic effect,. Comparing analysis results indicated that in the steel plate shear wall system, the progressive collapse resisting potential is more than X-braced and moment frame. Sensitive index of highly sensitive elements to dynamic effect stated that in the structural models, beams are more vulnerable in moment frame than X-braced frame and SPSW structure, significantly, and vulnerability of columns in X-braced frame and SPSW system is more than moment frame.