In recent years, many challenges have emerged for design of structures against earthquake loads. In newer building codes, a design based on behavior is preferred over the traditional force-based design. This modern procedure is called the performance-based design. Meanwhile, the nonlinear static analysis methods have attracted more attention because of their simplicity, less time consuming compared to more rigorous methods, and better adaptation with the performance-based methodology.
In this research, targeting modification of the lateral force distribution pattern, the seismic behavior of two samples of steel structures with special moment resisting frames are studied using different shear-based push-over procedures and nonlinear time history analysis. The main goal is to present a shear-based push-over methodology that results in an accuracy enhanced over the existing methods. To make this end, five different approaches for combination of modal contributions are examined. In each method, use is made of the story shear in equilibrium with the inertial forces. After a suitable modal combination, these are converted to equivalent lateral static loads.
The criteria for the evaluation of accuracy is comparing the basic responses, including the story drifts, shears, and plastic hinge rotations, with the averages of those calculated using the nonlinear time history analysis with 7 consistent earthquakes. As the final result of this research, it is observed that selecting the maximum responses between three out of five suggested push-over procedures, results in a better accuracy compared with the existing methods.
KEY WORDS: shear-based nonlinear static analysis, conventional pushover, modal pushover, adaptive pushover, nonlinear time history analysis.