Behavior of reinforced concrete short columns exposed to fire

Fire could dramatically reduce strength of reinforced concrete columns. The objective of this work is to study columns exposed to fire under axial load and to evaluate reduction in column compressive capacity after fire. The first part of this research is experimental investigation of fifteen-column specimens (15 × 15 × 100) cm exposed except one specimen to (600 °C) fire. The second part is a theoretical analysis performed using three-dimensional nonlinear finite element program. The main studied parameters were concrete strength, fire duration, level of applied loads, longitudinal reinforcement yield strength, percentage of longitudinal reinforcement, and bar diameters. Comparison between experimental results and theoretical analysis indicated that for columns not exposed to fire, the first crack appeared at 80% of column failure load while the first crack occurred at 50% of column failure load for columns exposed to fire. Columns with the same reinforcement percentage but with smaller bar diameters gained less lateral strain and smaller vertical displacement than columns with bigger bar diameters. Using high-grade steel as main reinforcement showed failure load higher by 55% than that of column reinforced by mild steel. Cooling column by jet water resulted in 17% reduction in failure load than columns cooling gradually in room temperature