Integrated effect of R-factor and height on seismic vulnerability and damage index in IS code-designed RC buildings

Seismic vulnerability in earthquake-prone areas is a key concern; choosing a suitable response reduction factor (R-factor) is crucial for assessing the seismic performance of reinforced concrete structures. This study presents a comprehensive analysis of the effects of the Response Reduction Factor (R-factor) on the seismic vulnerability of symmetrical buildings with 3 to 20 stories at different seismic intensities (DBE and MCE). The buildings are designed for varying R factors, ranging from 3 to 6, and the non-linear response parameters have been evaluated using both pushover and time-history analyses. The fragility curves of the buildings are developed according to the Hazus manual, and the probability of damage is estimated for each case. A unique relationship has been established between DI and SVI. The results indicate that both the height of a building and the R-factor collectively influence its seismic vulnerability. The result shows that the collapse damage of buildings increases by up to 20% when the R factor is increased from 3 to 6, and by 16% when the building height is increased from 3 storeys to 20 storeys. From the combination of height and R-factor on the selected models, it has been observed that buildings up to 15 stories can be safely designed with an R-factor of up to 6. In contrast, for a 20-storey building, the maximum recommended R factor is 5 because a 20-storey building with R=6 experiences more than 30% collapse damage. The DI value exceeds 3, and the SVI value exceeds 0.7 at the MCE level of earthquake. Finally, a 3d graph has been prepared, which shows the combined effect of height and R factor value, which can help to make a decision about the selection of R factor for multistoried buildings based upon seismic vulnerability as per performance level and damage states criterion.