Behavior of Reinforced Concrete Beams in Fire Considering Various Structural Conditions

This paper aims to analyze the influence of parameters on the deflection–time behavior and fire resistance of reinforced concrete (RC) beams under combinations of load and fire. To achieve this aim, a tested full-scale RC beam in fire was selected to model using SAFIR software. The model was verified and used for parametric studies. Two criteria based on the critical deflection and deflection rate were used to determine the fire resistance. The results showed that the load ratio, the thickness of the concrete cover, and the steel ratio exhibit a significant influence on the deflection–time behavior of RC beams under combinations of load and fire. The load ratio, the thickness of the concrete cover, and the steel ratio improve the fire resistance by up to 55.5%, 65.0%, and 61.2%, respectively. In contrast, deflection–time behavior and fire resistance are marginally affected by the tensile strength of steel and the compressive strength of concrete. The deflection–time behavior of RC beams in fire can be generalized by three phases: linear, nonlinear, and collapse. The criteria based on the critical deflection and deflection rate in current code seem to be unsafe for determining fire resistance because they fall into the collapse phase. Therefore, a safer criterion, which is based on the end of the linear phase or in the transition phase, should be considered for fire resistance. The outcomes of this study can be useful for engineers in practical evaluations of RC beams in fire.