In-plan distribution of peak floor acceleration demands in torsionally irregular buildings

Abstract

The precise estimation of peak floor acceleration demands is essential to ensure the seismic safety of building contents and attachments. The present study aims to investigate the distribution of the peak floor acceleration demands across the floor plan in torsionally irregular buildings. To achieve this objective, 28 mid-rise reinforced concrete buildings with torsional irregularities are analyzed under 5600 bidirectional earthquake excitations, considering various strength ratios in buildings. A total of 2,59,200 in-structure amplification factors are estimated at multiple locations within the building plan and also at different floors. It is observed that current seismic design codes tend to underestimate the in-structure amplification factor for torsionally irregular buildings, particularly at locations distant from the center of rigidity (towards flexible frames), by up to 137 % for elastic buildings, and up to 54 % for moderately inelastic buildings. Even in the case of frames closer to the stiff frames, the seismic design codes underestimated the in-structure amplification factor by up to 68 % for elastic buildings. It is observed that a strong relationship exists between the torsional amplification of the peak floor acceleration and displacement amplification due to building torsion at the floor of interest. The torsional amplification of peak floor acceleration is found to be approximately equal to torsional displacement amplification for the flexible frames at the floor of interest. Simplified equations are developed for their integration with existing building codes to precisely estimate the in-plan distribution of peak floor acceleration demands in torsionally irregular buildings.