Seismic vulnerability mitigation of RC building in reclassified seismic zone through fiber-reinforced concrete retrofitting as jacketing in cover region

Abstract

Reinforced concrete (RC) buildings designed without modern seismic provisions pose significant risks in seismically active regions. The reclassification of a structure’s location from low seismic zone to high seismic zone, as per the Indian seismic code IS 1893:2016 Part 1, significantly increases the seismic demand on existing structures. This increased seismic demand necessitates advanced retrofitting techniques to mitigate the building’s vulnerability and ensure compliance with current safety standards. Fiber-reinforced concrete (FRC) is a retrofit material that offers an innovative solution to enhance seismic performance. The role of fiber reinforcement in improving the seismic performance of reinforced concrete (RC) buildings, particularly in the context of retrofitting at both local and global levels, has not been thoroughly investigated. This study conducts a risk-based assessment of retrofitted RC buildings with FRC (1.5% Polyethylene fiber (PE) or 2% Hook-end steel fiber (HS)) jacketing in the outer periphery under varying seismic hazard scenarios. The analysis considers a case where the building was initially located in Seismic Zone 2 but has been reclassified to Zone 5 due to updated seismic zoning maps. Pushover analysis has been performed to assess key performance metrics such as capacity curves, base shear capacity, displacement capacity, energy dissipation capacity, global ductility, and the initiation of the first plastic hinge. Additionally, fragility analysis is employed to estimate the probability of damage to the building. Results demonstrate that incorporation of FRC retrofitting in the outer cover region significantly improves the seismic performance by enhancing base shear capacity (by up to 28.9%), displacement capacity (44%), and global ductility (27%) and delaying plastic hinge formation, which subsequently reduces the collapse probability (14%), damage index (17%), recovery time (122 days), and repair cost (7.36%) of the building. The PE 1.5% FRC shows superior performance compared to the HS 2% FRC.