PSI - Issue 70

Pradeep Ushakumari Abhinand et al. / Procedia Structural Integrity 70 (2025) 129–136

134

Fig. 4. Response spectra of selected records along with its mean spectra in logarithmic scale. As hinted previously, the incremental dynamic analysis (IDA) relied methodology is followed to evaluate the R factor of the selected SMRF (Vamvatsikos & Cornell, 2002). IDA quantify the inelastic capacity of the study structure under incrementally increasing seismic intensity measure to identify the base shear corresponding to a pre-set target response of the structure. Here, the SMRF model is applied with the suite of FF ground motion records as discussed just above, and the IDA is performed to capture the structural response with increasing seismic intensity in terms of the PGA. The target response level is defined using the inter-storey drift ratio (IDR) of 2%, which serves as the pre set performance threshold or the relevant engineering demand parameter (EDP). Numerically, the IDR can be calculated as the maximum relative lateral displacement between two consecutive floors, with respect to the storey height, at any instant during seismic excitation (Hasssan, 2022; Navvar & pandikkadavath, 2023; Aditya et al ., 2025). Initially, the ground motion inputs are scaled in increments of 0.1 g of PGA, and a trial-and-error (hit-and-trial) approach is employed to identify the specific PGA level at which the structure reaches the 2% IDR value. At this seismic intensity level, the corresponding fully yielded base shear or V y is noted, which in turn represents the inelastic strength demand required to reach the pre-set EDP limit. Finally, the average of the 44 seismic records is used to obtain the V y-avg . Following the nonlinear analysis, a linear elastic time history analysis is carried out using the same ground motion at the 2% IDR PGA level as well to the associated V e values. Successively, the maximum elastic base shear average obtained from this analysis is denoted as V e-avg (as explained before). Using these results, the desired seismic performance factors Ω d , R µ and R are derived as given in Equations (1) and (2) along with the Figure 1 information. 5. Analysis results The modal analysis of the SMRF revealed a first mode period of 0.92 seconds, indicating the dynamic characteristics of the structure under free vibration.

Fig. 5. Nonlinear IDA curve obtained for the study scenario.

Fig. 6. V y-avg and V e-avg variation of study SMRF with the seismic records.