Inelastic floor spectra for designing anchored acceleration-sensitive nonstructural components

Abstract

In this study, inelastic floor spectra are developed for designing acceleration-sensitive nonstructural components (NSCs). The parameters response modification (reduction) factor, $R_{\text{cc}}$, and inelastic displacement ratio, $C_{\text{cc}}$, are evaluated to quantify the effects of NSCs inelasticity on their seismic-induced force and displacement demands, respectively. The results of the conducted response history analyses illustrate that the inelastic behavior of NSCs can significantly de-emphasize the effects of their tuning period ratio and viscous damping ratio, and of the characteristics of the primary structure and ground excitation. Due to the quasi-harmonic characteristic of building floor motions, NSC inelasticity is more effective for NSCs attached to buildings than for those attached to the ground. NSC inelasticity is most effective for a low-damping roof-mounted NSC tuned to the first modal period of an elastic building (i.e., the most critical NSC from the design point of view). Adopting even a mild level of inelasticity for tuned NSCs not only decreases their seismic force demands significantly but also reduces their displacement demands. For non-tuning conditions, particularly for rigid NSCs, achieving even a relatively small $R_{\text{cc}}$ (i.e., a small reduction in force demand) leads to a significant increase in NSC displacement and ductility demands suggesting that these NSCs should be designed to remain elastic. Results illustrate that the amplitude of $R_{\text{cc}}$ and $C_{\text{cc}}$ depends on the tuning ratio, viscous damping, and level of inelasticity of NSCs, and to a lesser extent, on the characteristics of the primary structure and ground motion. Simplified yet reliable equations are proposed for the estimation of the parameter $R_{\text{cc}}$ for non-rigid NSCs with different levels of inelasticity and viscous damping.