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Abstract: The seismic performance of structures with irregular distribution of mass, stiffness and strength along the height, may be significantly different compared to regular structures, depending on the limit-state or the level of seismic intensity considered. In the framework of probabilistic performance based earthquake engineering, it is possible to quantify the effects of vertical irregularities on the seismic performance of structures. In this study, the seismic performance of different non-geometric vertical irregular structures is compared to a regular structure at various performance levels with a probabilistic approach. The results show that the non-uniform distribution of lateral resisting properties over the height of structure influences the seismic performance, especially at the limit-states close to collapse until global dynamic instability. These effects may be on the seismic intensity capacity and/or on the ductility capacity of the structure, based on the type and the position of vertical irregularities. Also from the standpoint of a probabilistic seismic performance based design, the vertical irregularities increase the mean annual frequency of exceeding the GI performance level by about 5% to 30%. [Copyright &y& Elsevier]

Abstract: This paper presents the seismic vulnerability and rehabilitation of a steel building with semi-rigid connections in Tehran. This 19-storey building with an asymmetric plan was constructed 30 years ago in three blocks. The qualitative vulnerability of the building was evaluated in the first step of the study, indicating its high seismic vulnerability. In the next step of the study, the quantitative vulnerability of the structure was investigated. The results show that the building was strong enough to resist gravity loads but the strength was not adequate for seismic loads. Finally, three seismic retrofitting methods consisting of concrete shear wall, steel shear wall, and steel bracing were proposed. The comparison of the three retrofitting alternatives in terms of architecture, implementation, and seismic performance showed the superiority of using the concrete shear walls over the two other alternatives. [Copyright &y& Elsevier]