Earthquake Response of Flat‐Slab Buildings

Abstract

System identification, three‐dimensional linear dynamic analysis, and code‐specified conventional equivalent static techniques are used to evaluate the response of a nine‐story flat‐slab building during the Loma Prieta, Calif., earthquake of 1989. Four different models are used in the finite‐element‐based dynamic and static analyses. The system identification results on natural frequencies, mode shapes, and interstory drifts are used to validate the four analytical models. It is found that the model with a 30% live load included in the mass computation, a 2/3 reduction in the stiffness of slabs, and 30% reduction in stiffness of columns and shearwalls appears to give a reasonable overall approximation of the measured response. The eccentricity of the central shearwall core in the east‐west direction promoted torsional response. Both the dynamic analysis and system identification results indicate that the shearwall kept the drift level at the central core within the code limit. At the east and west ends of the building, where frame action dominates, the drift level reached the code limit. The horizontal forces were mostly resisted by the core shearwalls. The base shear coefficient in the north‐south direction determined from the dynamic analysis was close to that of the equivalent static procedure. In the east‐west direction, however, the dynamic base shear coefficient was twice as much.