VALIDITY AND APPLICABILITY OF TWO SIMPLE HYSTERESIS MODELS TO ASSESS PROGRESSIVE SEISMIC DAMAGE IN R/C ASYMMETRIC BUILDINGS

The coupled lateral-torsional vibration in R/C asymmetric structures under seismic loading leads to larger lateral deformation in the load-resisting elements located at one edge, compared to the other resisting elements. This may cause earlier yielding of the elements of that edge in localized form. Strength and stiffness degradation due to successive inelastic excursions of these R/C structural elements at one edge may make these elements more flexible and weaker as compared to those at the opposite edge. This may cause progressive shifting of stiffness and strength centres away from this flexible edge, leading to consequent increase of effective eccentricity in successive loading cycles. This, in turn, causes a progressive increase in torsional effect in R/C structures. This damaging effect cannot be predicted by using the bilinear hysteresis models devoid of degradation characteristics. Existing sophisticated hysteresis models representing the degrading behaviour of the R/C structural load-resisting elements require a number of parameters to be specified, the evaluation of which requires extremely case-specific calibration study. In this context, the present paper studies the suitability of two alternative simplified hysteresis models, which are capable of predicting the strength and stiffness degrading behaviours with simple input parameters. Responses of idealized asymmetric R/C building systems are studied using these two hysteresis models under design spectrum-consistent synthetic ground motions and idealized near-fault ground motions. The comparison between the responses of the R/C asymmetric structures with deteriorating structural elements and the similar structures having elasto-plastic structural elements proves the suitability of the proposed models in recognizing the progressive damaging effect of torsion in R/C asymmetric buildings.