Floor and Attached Component Seismic Amplification Factors from Nonlinear Time-History Analysis

Abstract eng:
Seismic forces for attached nonstructural building components can be quite different from forces obtained from the current design code. This is because the current code is based on measured building motions where the buildings remained largely linear and past analysis studies that focused on linear building response – clearly a significant limitation since buildings are designed for nonlinear response. Maximum floor accelerations of frame buildings subjected to major earthquake loading are often amplified over the peak ground acceleration (PGA). Furthermore, maximum accelerations of nonstructural components that are attached to a given floor can be amplified several times over these already large maximum floor accelerations. Hence, attached component accelerations of above 5g are possible, even under design-basis earthquake events. This paper provides floor and attached component acceleration and amplification results determined from nonlinear time-history analyses of a suite of low and mid-rise steel moment frame buildings designed to current US code provisions. All possible attached components from flexible to stiff were considered at each floor level. Ten significant earthquake motions were selected and scaled to match a design ARS curve for the highest seismic regions in California. A simple hand equation for determining maximum possible floor accelerations is presented and validated based on the local strength characteristics of the structure above and below the floor of interest. Of particular note is that the maximum possible floor acceleration is independent of earthquake loading, as it is based on the plastic capacity of the girder hinges.

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