Seismic Behavior of Code-Designed Bidirectionally Eccentric Systems

Extreme seismic vulnerability of bidirectionally eccentric structural systems such as street corner buildings has been demonstrated repeatedly during past severe earthquakes. Inelastic range response of such structural systems may vary considerably depending upon the sense of eccentricities regulated by relative quadrant wise position of center of stiffness with respect to center of mass particularly for reinforced concrete (RC) structures with strength and stiffness degrading behavior. Recognizing the same, an effort has been made in the present paper to analyze the inelastic range response of bidirectionally asymmetric structures designed as per the existing codal standards. Such response helps to perceive the adequacy of the code provisions to minimize the progressively damaging effects expected to arise in RC bidirectionally eccentric structural systems due to strength and stiffness degradation under severe seismic excitation. The effect of change in stiffness eccentricity due to cracking of reinforced concrete members is also attempted to be studied in the limited form. Inelastic seismic response of code-designed bidirectionally eccentric structural systems with only strength deteriorating and only stiffness degrading structural elements are also investigated to examine the potential of such comparatively simpler hysteresis models. Effort has also been made toward assessing the response of similar elastoplastic structural systems. The study clearly indicates the limitation of the design code provisions to take adequate care of seismic torsional vulnerability of bidirectionally eccentric structures made up of strength and stiffness degrading RC structural elements. However, the performance of the same seems satisfactory for elastoplastic structural systems.