Evaluation of Seismic Analysis Procedures for Concrete Moment-Resistant Frames with Horizontal Re-entrant Corners Irregularity

Abstract

Seismic design codes and standards such as the IBC 2012 and ASCE/SEI 7-10 allow using different seismic analysis procedures for buildings having horizontal re-entrant corner irregularity. However, such codes allow using Equivalent Lateral Force (ELF) procedure for buildings having re-entrant corner irregularity but not exceeding 50 m in height. The aim of this study is to quantify the limits on building height and on the percentage of re-entrant corner of building, where ELF procedure may not produce a reasonable results when compared to Response Spectrum (RS) and Response Time History (TH) procedures. Usually, these limits in seismic design standards are based on judgments and experience rather than quantification studies. Based on the results of this study, it is observed that using ELF method mostly overestimates maximum displacements and drift ratio. However, this method can be used safely up to 12-storey buildings, because the maximum underestimation of column shear forces for buildings with higher stories gives 30% less compared to other procedures. Moreover, it has been found that the maximum underestimation of column shear forces for buildings without re-entrant corner is 0% less than those with re-entrant corners. Furthermore, buildings analysed by ELF method are also exposed to have a higher percentage value of underestimation of column shear forces as the case of 12-story buildings with 40% less when compared to TH Procedure. In addition, the column at the re-entrant corner is not effectively affected until a re-entrant corner of 25% exists in buildings. Thus the ASCE/SEI 7-10’s limit for using ELF procedure for buildings with re-entrant corner irregularity may be increased from 15% to 25% with less conservative results.