Comparative Analysis of Structural Performance of Plain and Step-back RCC Building

Abstract

This study compares the performance and structural response of two buildings: a 4 Storey RCC building built on plain ground, and a Step-back RCC building, built on a sloping ground. The step-back model has a single bay in the lowermost floor and 2 bays at every other level along one direction. Two models were developed in FEM tool ETABS. Both buildings were analysed by 3 methods, Equivalent Static Method, Response Spectrum Analysis, and Pushover Analysis following the guidelines in NBC 105:2020 code. Key response parameters such as storey drift, storey shears, modal mass participation, fundamental time period, and various performance point parameters were evaluated. The findings suggest that despite being stiffer, the step-back building showed similar maximum displacement values along weaker direction, indicating higher inter- storey drift values. The storey shear values continuously increased from top storey to bottom for the plain RCC building, but for the step-back building, there was a sudden change in nature of storey shear between 1st and 2nd storey due to the supports provided at differing levels. The results of model analysis indicate that step-back configuration is stiffer than plain one. Non-linear pushover analysis shows that plain building can withstand higher base shear and displacements at performance point. These results suggest that more precautions is necessary during step-back building construction to ensure stability and safety.