A SIMPLIFIED SEISMIC DESIGN METHODOLOGY AND EVALUATION FOR NEW AND EXISTING RC BUILDINGS IN PAKISTAN

Abstract

In seismic design, response spectrum analysis (RSA) stands as a prominent method to determine structural design forces under earthquake loading. However, its reliance on a single response modification factor (R) to account for nonlinearity can lead to underestimations of actual design forces. This research endeavors to introduce an enhanced design approach by refining the R factor within a linear model to incorporate nonlinearity. To achieve this, detailed analysis is conducted on three selected RC buildings as case studies, reflecting the broader sample. Initial designs of these structures are conducted using RSA in the ETABS software, followed by NLRHA performed in PERFORM 3D. Through a comparative assessment of RSA and NLRHA results, the substantial disparities in design forces estimation between the two methods become evident. To delve into the inelastic behavior of each vibration mode, UMRHA is executed. Upon scrutinizing individual modal responses, a noteworthy observation emerges: higher modes tend to exhibit either elastic behavior or lesser nonlinearity. Utilizing the modal findings, response modification factors (R) are calculated for each significant mode across the case study buildings. Using this R, results of modified versions of RSA procedures (MRSAHE and MRSAHI) are compared with NLRHA and UMRHA. Ultimately, a modified versions of RSA procedures are recommended for the design of RC buildings where higher modes are significantly participating. This research aims to provide a novel perspective on seismic design by addressing the shortcomings of traditional RSA methods and integrating more nuanced considerations of nonlinearity.