Assessment of Floor Accelerations in Yielding Buildings

Abstract

The large investment in nonstructural components in buildings and severe damage to these components in recent earthquakes necessitates improved design provisions for these components. The present study uses OpenSees finite element framework to develop full three dimensional models of four steel moment frame buildings. The incremental dynamic analysis method is employed to evaluate the floor response of inelastic steel moment frame buildings subjected to all three components of a suite of 21 ground motions. To better understand the acceleration demands on nonstructural components, this study focuses on the influence of structural period, level of ductility of the structure, and relative height in the building on the horizontal and vertical floor acceleration response. The horizontal floor acceleration response is shown to decrease with increasing structural period and ductility while varying nonlinearly along the height of the building. In contrast, the vertical acceleration response was found to be independent of structural period, level of ductility, and relative height. Variation in the vertical acceleration response is primarily attributed to the out-of-plane flexibility of the floor system. Significant vertical acceleration amplification is only observed away from the column supports. As a result of this study, a more realistic formulation of the peak floor acceleration response accounting for the effect of structural period and ductility is proposed and may be used to improve current code estimations is proposed. In addition, a direct method for developing an envelope horizontal floor response spectrum is developed.