Floor displacement-based torsional amplification factors for seismic design of acceleration-sensitive non-structural components in torsionally irregular RC buildings

Abstract

In this study, the effects of inherent building torsion on the seismic response of acceleration-sensitive non-structural components are investigated. To achieve this objective, a group of elastic torsionally irregular step-back reinforced concrete moment-resisting frame buildings are analyzed under bi-directional earthquake excitations. The floor torsional amplification factors, defined as the ratio between the floor spectral ordinate at the flexible/stiff edge to the floor spectral ordinate at the center of rigidity, are obtained as a function of the tuning ratio for varying damping ratios of non-structural components. The correlations of the peak torsional amplification factors at different floors for the rigid and flexible non-structural components are studied with their floor displacement-based torsional irregularity indices, recommended in the national building codes of the United States and India. It is observed that the torsional amplification factors are building characteristics and tuning ratio-dependent. These torsional amplification factors are further observed to be well-correlated with the corresponding floor displacement-based torsional irregularity indices for both the rigid and flexible non-structural components. Contrarily, the torsional amplification factors for the very flexible non-structural components tend to unity and are thereby observed to be independent of the characteristics of both the building and the non-structural components. Simplified and numerically validated, floor displacement-based models are proposed to compute the torsional amplification factors, which can be used in aggregation with the existing codes to design acceleration-sensitive non-structural components in torsionally irregular buildings.