Effect of Torsion on Seismic Response of Single-Story Structures: an Energy-Based Design Approach (EBD)

Torsion of structural frames is one of the main causes of damage to structures during earthquakes. Accordingly, this study investigated the effects of torsion on frame structures with different asymmetries in stiffness when subjected to earthquakes with natural translational vibration period of less than 1.00 s. In this study, an idealized single-story lateral load resisting system was considered, and an energy-based design approach was used to analyze and investigate the effect of the resulting eccentric center of rigidity on the seismic response of frames. First, the stability of the energy spectrum due to torsional behavior was verified by conducting a nonlinear dynamic analysis. A series of nonlinear dynamic analyses was then used to investigate the responses of torsionally flexible systems with different eccentricity ratios in terms of total energy input, plastic strain energy distribution, cumulative plastic deformation ratio, and displacement ratio which found to be sensitive in different translational vibration of system. The results demonstrate that the energy input into asymmetric systems is less than that input into symmetric systems under the same accumulated plastic deformation ratio. Moreover, the vertical members that are located farthest to center of rigidity (flexible-edge member) were observed to suffer greater damage than other vertical members, particularly under large eccentricity ratios.