Two Important Issues Relevant to Torsional Response of Asymmetric 8-Story RC Building Designed with Direct Displacement based Design Approach

Direct displacement based design (DDBD) is a conceptual framework that directly designs a structure to achieve an expected performance level under specified seismic intensity. In this study, two important issues relevant to torsional response of mass eccentric 8-story RC building designed with DDBD approach are investigated. These issues are including the effects of unbalanced mass distribution scenario on the torsional response parameters and the study of these parameters with reference to diagonal displacement. Diagonal displacement is the SRSS combination of the displacement demands along the direction of excitation and orthogonal direction. Three different unbalanced mass distribution scenarios which produce the same mass eccentricity were applied to the plan of the generic structural model to determine the general range of the mass moment of inertia (MMI) variation due to different unbalanced mass distribution scenarios. Expressions were established to correlate MMI and mass eccentricity in each scenario. Results show that for slight eccentricities the variation of the MMI is negligible but as eccentricity is increased the range of the variation is extended. Then, sensitivity analyses based on finite element method and inelastic time history analysis have been carried out on 8-story RC building frame designed with DDBD approach with different levels of mass eccentricity and different MMI. Torsional response parameters in terms of maximum displacement demands of edge elements, diaphragm rotation, nominal relative displacement and nominal rotation is compared with diagonal and horizontal displacement demands along seismic excitation.