Evaluation of Seismic Acceleration Demands on Building Nonstructural Elements

As proven by several past earthquakes, seismic losses associated with nonstructural damage in modern buildings are likely to significantly exceed those associated with structural damage. Hence, to satisfactorily assess the overall seismic performance of a building and consequently the associated losses, it is paramount to properly account for the nonstructural damage through the adequate estimation of acceleration demands that are imposed on its acceleration-sensitive nonstructural elements in any one-floor level during an earthquake. Component acceleration amplification factors, ap, which measure how much the acceleration of a component is amplified relative to the peak floor acceleration are evaluated by floor motions recorded during earthquakes on instrumented buildings in the United States. The study shows that component amplification factors currently used in codes significantly underestimate acceleration demands for components whose periods are tuned or nearly tuned to modal periods of the supporting structure. Simplified equations are proposed to estimate component acceleration amplifications. The study also evaluates inelastic floor acceleration spectral ordinates. As a result of the filtering and amplification of the ground motion by the structure, the results show that even small levels of nonlinearity in the nonstructural element or its attachment to the structure lead to significant reductions in acceleration demands.