Inelastic seismic response of code-designed reinforced concrete asymmetric buildings with strength degradation

The study presents the inelastic seismic response of code-designed asymmetric buildings idealized as asymmetric one storey systems. The strength eccentricity of the code-designed buildings are studied and accordingly, the strength of various load-resisting elements of the idealized asymmetric systems are adjusted in such a way that these systems have the strength eccentricities similar to those of the code designed buildings. Two categories of systems are studied. The first category has lateral load-resisting structural elements with ideal elasto-plastic hysteresis behaviour. The load-resisting elements of the other category have a strength-deteriorating characteristics representing the deterioration in yield strength of structural elements, which are known to arise in reinforced concrete (RC) members under successive yield excursions due to seismic loading. The study of the first category of systems shows that code-designed buildings may exhibit only a moderate increase in displacement and ductility demand if the load-resisting elements have a purely elasto-plastic behaviour. On the contrary, the study of the second category of systems reveals that the shifting of resistance centres due to asymmetrically localized yielding of load-resisting element at one edge under coupled lateral-torsional motion, and the progressive deterioration of strength of this edge element, may cause a displacement and ductility demand several times those of the similar symmetric systems. Hence, the existing code provisions for asymmetric buildings can be considered adequate for the same constructed by RC, only if the strength deterioration in RC structural elements can be minimized through adequate reinforcement detailing.