PSI - Issue 70

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

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2. Seismic response reduction factors As previously outlined, the R -factor in seismic analysis design that accounts for a structure's inherent reserve strength, ductility, and redundancy. It enables the reduction of the elastic base shear force ( V e ) which represents the demand under a linear-elastic response to a reduced design base shear force ( V d ) that is more representative of the structure’s expected inelastic behavior during a seismic event. The R -factor can be numerically decomposed into two key components, the overstrength factor ( Ω d ), which reflects the excess strength available beyond the design level, and the ductility reduction factor ( R μ ), which captures the capacity of the structure to undergo acceptable level of inelastic deformations without significant loss of stiffness. Accordingly, the R -factor can be represented as the product of the above given parameters, as illustrated schematically in Figure 1 and mathematically by the following equation: = µ Ω (1)

V e

R µ =

V y

R =

Ω d =

V d

Δ vy

Δ u

Δ ve

Lateral Seismic Force (Base shear)

Lateral Displacement (Roof drift)

Fig. 1. Details of ductility reduction factor, overstrength factor and response reduction factor. Further, referring to Figure 1, R μ can be obtained as the ratio between V e & V y and Ω d can be obtained by ratio between the V y & V d . Here V y is the inelastic seismic base shear corresponding to fully plasticized structure. Thus, the expression for R -factor in terms of the seismic base shears can be formulated as given below. = ⁄ (2) 3. Study Adopted SMRF structure Figure 2 presents the elevation and plan of the 4-storey prototype building selected for this study (Kottalage et al ., 2022; Anand & Pandikkadavath, 2022; Jasir et al ., 2023, Jagruthi et al ., 2023). The structure features a regular and symmetric layout comprising 6 × 6 bays, with each bay spanning 8.0 meters. In addition, a 0.30-meter slab overhang is provided on all sides, resulting in an effective total floor plan dimension of 48.30 m × 48.30 m. The bottom floor has a storey height of 5.50 m, while each of the higher floors maintains a constant height of 4.0 m (Anand & Pandikkadavath, 2024; Anand et al ., 2024a; Anand et al ., 2024b; Aditya et al ., 2025).

Fig. 2. Plan and side view information of the investigating SMRF. Based on the structural and architectural configuration, the total seismic weight of the building is estimated to be 47,240 kN. The building frame consists of a combination of internal gravity frames and SMRFs strategically located along the building perimeter, as shown in Figure 2. Although SMRFs are present in certain interior frames, the investigation focus of this study is limited to the analysis and design of the perimeter SMRFs, which are designated as the primary lateral force-resisting system. These perimeter SMRFs extend continuously over four bays in both orthogonal directions, providing the main resistance against seismic lateral forces. The scope of the current