PSI - Issue 70

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

135

The results from the nonlinear IDA are presented in Figure 5, which illustrates the IDA curves generated for the SMRF model. Based on these curves, the PGA values required to achieve the target 2% IDR is found to vary between 0.24 g and 1.11 g across the set of ground motions. At these PGA levels, the corresponding V y ranged from 2416 kN to 3436 kN, with an average value or V y-avg of 2834 kN. Likewise, the V e , obtained from linear dynamic analysis at the same PGA levels, ranged between 2667 kN and 4017 kN, with a mean value or V e-avg of 3647 kN. Figure 6 the illustrative representation of the V y-avg and V y-avg values. Using the V d of 582 kN, along with the average values of V y and V e , the R μ , the Ω d , and R -factor are evaluated as 1.29, 4.87 and 6.26 respectively as shown in the Table 2. This indicate that Ω d -factor plays a larger role than the R μ -factor for satisfying the desired R -factor.

Table 2. Analysis obtained seismic response modification factors.

V d (kN)

V y-avg (kN)

V e-avg (kN)

Ω d

R µ

R

582

2835

3647

4.87

1.29 1.67

6.26

IS Values

3

5

6. Conclusion This study investigates the seismic response modification factors – structural overstrength factor ( Ω d ), ductility reduction factor ( R μ ), as well as the overall seismic response reduction factor ( R ) for a 4-storey special steel moment resisting frame (SMRF) proportioned according to relevant Indian design standards. A two-dimensional nonlinear numerical model of the frame is developed in OpenSees, and both nonlinear incremental dynamic analysis (IDA) and linear time history analysis are carried out using a suite of representative seismic ground motion records. From these analyses, the average base shear at the fully yielded state ( V y-avg ) corresponding to a 2% inter-storey drift ratio (IDR) is obtained, along with the mean elastic base shear ( V e-avg ) at the same Peak Ground Acceleration (PGA). These values, along with the design base shear ( V d ), are used to compute the R μ , Ω d and R -factor for the frame. The output results indicated that the evaluated R -factor is approximately 25% higher than the Indian standard code-specified value, while the Ω d is about 62% greater than the corresponding code-defined value for the studied frame. These findings underscore the acceptable seismic response capabilities of the selected SMRF system, with a comparison to code recommended values offering insights into the earthquake-resistant design practices in India. Further, this study investigated only a regular, symmetric, 4-storey SMRF. For more generalized and acceptable results, the study needs to be extended to SMRFs with varying heights, bay-span lengths, relevant structural irregularities, and other pertinent parameters. Acknowledgement The authors acknowledge the financial support provided by the DST-SERB, Government of India, under the CRG scheme (Grant No. CRG/2023/006530) for carrying out this research. References Aditya, P.A., Navvar, K.M., Bahubali, J.K., Pandikkadavath, M.S., & Mangalathu, S. (2025). Near-fault seismic vulnerability assessment of corrosion inflicted steel moment resisting frames. Journal of Constructional Steel Research, 229, 109527. Anand, A.P., & Pandikkadavath, M.S. (2024). Near-fault seismic vulnerability assessment of corrosion inflicted 8-storey steel moment resisting frame. Lecture Notes in Civil Engineering, 897 – 906. https://doi.org/10.1007/978-3-031-70431-4_64 Anand, T.P., & Pandikkadavath, M.S. (2022). Effect of bay-span length on ductility demand in steel-core buckling restrained braces under near field seismic disturbances. Materials Today: Proceedings, 65, 1634 – 1641. https://doi.org/10.1016/j.matpr.2022.04.697 Anand, T.P., Pandikkadavath, M.S., & Mangalathu, S. (2024). Near-field seismic response assessment of buckling-restrained braced frames for different engineering demand parameters. Journal of Constructional Steel Research, 216, Article 108583. https://doi.org/10.1016/j.jcsr.2024.108583 Anand, T.P., Pandikkadavath, M.S., Mangalathu, S., & Sahoo, D.R. (2024). Machine learning models for seismic analysis of buckling-restrained braced frames. Journal of Building Engineering, Article 111398. ANSI/AISC 341-22. (2022). Seismic Provisions for Structural Steel Buildings. American Institute of Steel Construction, Chicago, IL. ANSI/AISC 360-22. (2022). Specification for Structural Steel Buildings. American Institute of Steel Construction, Chicago, IL.