Evaluation of Linear Static Approach in Performance-Based Design of Steel Bending Frames

In recent decades, the performance-based design of structures as a design philosophy has been implemented in many works. A performance-based design depends on the performance levels considered for the structure, and the design procedure is accomplished in such a manner that the respective defined demand and capacity of the structure are balanced. Consequently, an analysis should be carried out to specify the structural performance in terms of the deformation and strength capacity of that structure. Linear static approach is one of the approaches introduced in the guidelines for performance-based seismic evaluation of structures. This approach is superior to nonlinear and dynamic approaches due to the simplicity, high speed, and low computational burden of the related analysis method. The objective of this study is to evaluate the efficiency and accuracy of this approach in the performance-based seismic design of structures. In other words, the purpose of this study is to define that to what extent the linear static approach including the linear static analysis and performance criteria corresponding to the analysis proposed in the guidelines is reliable for design of structures. Moreover, designing a structure with a trial and error process and without a systematic method may lead to attaining a non-economic design in which the design capacities are much more than the design needs. Therefore, for a more appropriate evaluation of the approach, the design of the structure should be done in an optimal manner to avoid the effects of the structure over design in the results. In this study, the optimal designs of two two-dimensional steel bending frames, including a six-story frame and a twelve-story frame, at the performance levels of immediate occupation (IO), life safety (LS), and collapse prevention (LS) at the risk level of one (the earthquake with a 10% probability of exceedance in 50 years) are separately determined according to the linear static approach. Genetic algorithm is employed for solving the optimization problem. Having determined the optimum designs of the frames at any performance level, the nonlinear static approach is used to evaluate the efficiency of the optimum designs. The results show that the optimal designs obtained based on the linear approach meet the criteria of nonlinear approach even at a more conservative level. It means that the performance constraints associated to the linear approach are strict enough to address implicitly the acceptance criteria associated to the nonlinear approach.