Accounting for Torsional Response in Direct Displacement-based Design of Plan-asymmetric Reinforced Concrete Frame Buildings

The torsional response of Reinforced Concrete (RC) frame buildings within the Direct Displacement-Based Design (DDBD) framework is considered by using semi-empirical equations developed for wall-type asymmetric structures. These equations when applied to RC frame buildings result in the underestimation of engineering demand parameters such as drifts. To alleviate this problem, it is proposed that first-mode effective masses of the frames are connected with rigid bar, constraining the system so that the critical frames' design displacements are not exceeded and displacement compatibility for all frames is maintained. The proposed method of seismic design is verified by a Nonlinear Time History Analysis (NTHA) of two six-story plan-asymmetric RC frame buildings, the only difference in the buildings being that one is applied with equal mass and the other variable mass along the height. Eleven ground motions are selected and scaled to match a design response spectrum of a given seismic hazard level at the building site. The proposed design procedure produces reasonable response outputs when verified by NTHA of the case studies. Thus, it is a step toward minimizing the use of NTHA for plan-asymmetric frame buildings, thereby saving computational resources and effort.