Effect of Conventional Retrofitting Methods on the Seismic Fragility of Substandard RC Buildings: A Cost-Benefit Analysis

Past earthquakes demonstrate that most significant part of losses in buildings are due to the poor seismic performance of substandard reinforced concrete (RC) buildings. It is necessary to retrofit substandard buildings to reduce/prevent casualties and economic losses. Two of the most widely preferred conventional seismic retrofit approaches are the integration of new structural walls and/or RC jacketing of existing RC columns. This paper presents an attempt for comparison of the effectiveness of these conventional seismic retrofitting methods for substandard RC buildings. For this purpose, an existing four-story RC moment frame building is considered as a case study. The building represents typical substandard RC frame buildings common in Türkiye. After conducting a seismic assessment of the building according to Turkish Building Earthquake Code-2018 (TBEC-2018) and demonstrating its unsatisfactory performance, a retrofit design is made to satisfy the target seismic performance level (controlled damage-life safety) specified in TBEC-2018. Then, a series of nonlinear structural analyses were performed by using Incremental Dynamic Analysis (IDA) technique for the original state of the building (before retrofitting) and for the seismically retrofitted states, Peak Ground Acceleration (PGA) based fragility curves were obtained for each state. Furthermore, based on the obtained fragility curves and making use of new construction, repair and retrofitting costs, cost-benefit analyses were conducted to compare the original state of the building and the two retrofitted states. The results of the fragility and cost-benefit analyses indicate that seismic retrofitting of such buildings by integration of new shear walls or column jacketing provided a remarkable improvement in both seismic performance and loss reduction, compared to the original state of the building. The relevant quantitative comparisons, which may be critical for seismic mitigation decisions are also presented. Finally, it was also shown that the value assumed for human life in the calculations has a remarkable impact on the expected loss.