Structural Behavior of Pre-Loaded Fire-Damaged RC Columns Rehabilitated with UHPC

This study presents an experimental investigation into the rehabilitation of fire-damaged reinforced concrete (RC) columns using Ultra-High-Performance Concrete (UHPC) under an eccentric load of (e = 45 mm). The experimental program comprised nine small-scale RC column specimens, which were divided into two groups based on exposure temperatures of 500 °C and 700 °C, applied using a specially designed furnace. A control column that was not exposed to fire was also tested for comparison. The study included two fire exposure durations: 60 and 120 min. During the heating phase, the columns were subjected to a pre-applied axial load equal to 50% of their ultimate capacity (Pu). After sustaining fire-induced damage, the columns were rehabilitated using UHPC jacketing. The experimental results revealed a reduction in the ultimate load-carrying capacity of the RC columns with increasing fire temperature and exposure duration. Specifically, the load capacity decreased by 22.68% and 33.89% when exposed to 500 °C for 60 and 120 min, respectively, and by 42.02% and 49.02% when exposed to 700 °C for 60 and 120 min, respectively, compared with the control column. However, strengthening the fire-damaged columns with UHPC significantly enhanced their structural performance, resulting in an increase in ultimate load capacity ranging from 81.88% to 157.14% compared with their corresponding fire-damaged unstrengthened specimens. Based on the experimental findings, the load lateral displacement response at mid-height, load–axial deformation curves, failure modes, ductility, and stiffness characteristics of the columns were analysed. The study concludes that the use of UHPC in rehabilitating fire-exposed columns substantially improves most of these structural properties.