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.
