Evaluating and strengthening low-rise reinforced concrete buildings constructed in Nepal

Abstract

In Nepal, the reinforced concrete (RC) frame system is commonly used to construct low-rise buildings. In last three decades, a significant number of such buildings were proportioned and constructed in accordance with Nepal National Building Code NBC 205:1994 and NBC 205:2012—also known as the Mandatory Rule of Thumb (MRT). In the aftermath of 2015 Gorkha Earthquake (Mw 7.8) which resulted in large scale social and economic losses, the efforts to formulate improved seismic design provisions led to the development of NBC 105:2020. Considering that MRT-designed low-rise RC frame buildings still constitute a significant part of existing building stock, this study is aimed to conduct a comparative seismic performance evaluation of several case study structures under a comprehensive set of ground motions. Using the nonlinear analysis and seismic fragility assessment of four low-rise RC frame buildings (designed using all three code versions), it is shown that the structural performance and seismic losses can be significantly reduced by following NBC 105:2020 provisions. Several retrofitting solutions are also explored to improve the seismic performance of buildings designed using MRT. It is shown that the concrete or steel jacketing of RC columns can significantly increase the lateral strength and energy dissipation, and reduce the damage probability of such buildings. Lastly, based on the developed results, a machine learning approach is employed to correlate the peak ground acceleration with structural drifts for convenient practical applications.