Abstract
In this study the seismic performances of axi-symmetric steel building structures with circular plan shape were evaluated based on the ATC-63 approach. For analysis models, thirty-three-story vertically convex, concave, and gourd-type axisymmetric buildings were designed using diagrid structure system, and their seismic performances were compared with those of the cylinder type regular steel structure. Seismic fragility analyses were carried out using twenty-two pairs of earthquake records to obtain the probability of failure for a given earthquake intensity. The validity of the response modifcation factor used in the seismic design of the model structures was also investigated. Based on the analysis results it was concluded that the response modifcation factor of 3.0 used in the design of the model structures is acceptable for the ATC-63 methodology. It was also observed that the seismic safety margin for a specifc level of earthquake decreases as the vertical irregularity of the structure increases.
1 Introduction
Recently the geometric complexity and irregularity of building structures have been rapidly increasing, which signifcantly afects the seismic performance of the structures. Al-Ali and Krawinkler (1998) investigated the seismic behavior of building structures with vertical irregularities, and found that the seismic response of building structures is more sensitive to stifness and strength irregularities than to mass irregularities. Soni and Mistry (2006) carried out review of studies on the seismic behavior of vertically irregular structures along with their fndings. Scott et al. (2007) explored the structural challenges that are created by buildings with unique geometries or articulated forms, and discussed some of economic design and construction techniques.
6 Conclusions
In this study the seismic performances of axi-symmetric diagrid building structures with various vertical irregularities were evaluated based on the procedure recommended in the ATC-63. Seismic fragility analyses were carried out using twenty-two pairs of earthquake records to compare the probability of failure for a given earthquake intensity. The thirty-three story analysis model structures with diferent elevations were designed to have similar total foor areas, the aspect ratios of the model structures range from 2.0 in the case of the concave structure with low center of mass and to 6.2 in the case of convex structure with high center of mass.
