D‌I‌S‌P‌L‌A‌C‌E‌M‌E‌N‌T-B‌A‌S‌E‌D D‌E‌S‌I‌G‌N O‌F T‌O‌R‌S‌I‌O‌N‌A‌L B‌U‌I‌L‌D‌I‌N‌G‌S C‌O‌N‌S‌I‌D‌E‌R‌I‌N‌G T‌W‌O-W‌A‌Y N‌O‌N‌L‌I‌N‌E‌A‌R‌I‌T‌I‌E‌S

One of the most important and, at the same time, unpredictable types of lateral loads is earthquake load. Extensive research on the safe and economical seismic design of structures has been carried out in this field. The research works can be divided into two general categories: force-based design and performance-based design. Displacement-based design is among the performance-based methods. In this paper, it is purposed to investigate a major drawback in this approach, namely the lack of precision in the estimation of the torsional response of buildings. For this purpose, the model code of displacement-based design (DBD12) is adopted as the basis for studying and modifying a methodology. In this code, there are equations that take into account the involvement of torsional effects in the structural analysis. It is pointed out that the main weak point of the mentioned relationships is the consideration of nonlinear behavior only in the earthquake direction, while a linear behavior is considered in the perpendicular direction when calculating the torsional stiffness. Therefore, it is required to evaluate and modify these relations. For the purpose of this study, three buildings with 4, 7, and 10 floors are selected. Eccentricity in the buildings is assumed to be equal to 0, 5, 10, 15, 20, and 30% of the plan dimension in the transverse direction. The structural system is selected to be steel moment-resisting frames, and the diaphragm of the floors is assumed to be rigid. Studying the accuracy of the design equations for torsion and implementation of the necessary corrections is done using the nonlinear time history analysis. In this analysis, by utilizing the OpenSees software, the structures are subjected to 11 consistent records that are properly scaled. After obtaining the results of exact nonlinear analysis and the displacement-based design method, the equation of the code for calculating the story twist angle is corrected against the average values determined by the nonlinear dynamic analysis. The accuracy of the corrected relationships in comparison with the exact values is evaluated. It is shown that the corrected equations successfully predict the torsional response of the investigated buildings with good accuracy, thus reducing the estimation errors to less than 10%.