Reliability-Based Seismic Assessment of Multi-Story Box System Buildings under the Accidental Torsion

Abstract

ABSTRACT Performance analysis of reinforced concrete (RC) buildings during past earthquakes has shown that irregular distribution of mass, stiffness, and strength may cause severe damage in structural elements. Accidental torsion, one of the most common reasons of damage and failure under the strong ground motions, is a complex phenomenon in which several variables are involved. The box-type structural system is considerably sensitive to torsion due to shear wall arrangement and that the torsional mode which governs structural response. Thus, understanding and evaluating accidental torsion is a fundamental step in seismic reliability evaluation of this structural system in comparison with other common structures. Therefore, in this study, seismic sensitivity of the box-type structural system is evaluated for various configurations of mass, stiffness, and strength centers. Several analyses, such as eigen-value, push-over, nonlinear time history, and seismic reliability analysis are performed using artificial records to predict structural characteristics and probabilities of failure. The results show that the mass eccentricity has a greater effect on the seismic response in comparison with the strength and stiffness eccentricities. The most critical condition occurs when the mass and stiffness centers are shifted in the same direction, so the story drift under the design and maximum credible earthquakes are 2.45 and 2.26 times the symmetrical model drift, respectively. Furthermore, it is shown that this box-type structural system demonstrates acceptable seismic reliability under the accidental torsion since the main elements of lateral bearing system remain in an immediate occupancy performance level under the design earthquake.