Behavior of Reinforced Concrete Beams Exposed to Fire

Abstract

. There is a shortage in researches that discuss the effect of fire on building and represent solution for structural elements that exposed to fire [1-19]. Improving the fire resistance for beams, requires studying the response of reinforcing steel and concrete under fire attack. Concrete has a good behavior under fire due to its low thermal conductivity and non-combustibility. Concrete can act as protective cover to steel reinforcement. To understand the thermo-mechanical response of reinforced concrete beams under fire, experimental researches have been carried out to investigate the performance, resistance, and residual strength of beams under elevated temperature [14,15]. There is a lack of numerical studies addresses these types of analysis. This paper numerically investigates the fire performance of reinforced concrete beams subjected to fire exposure. A series of models of RC beams has been studied. Firstly, RC beams were studied under fire exposure on three surfaces following the temperature time history by ISO 834 standard fire curve. Secondly, studying heat transfer in RC beams and its effects on concrete and reinforcement steel with changing concrete cover and many factors through a parametric study. A finite element model using ANSYS program was carried out and accomplish a good correlation with the experimental results in both thermal and structural performance. The element type used for concrete in thermal analysis is Solid 70 while Link 33 is the element type used to represent reinforcing steel. The validated finite element model was used to conduct a parametric study on the behavior of RC shallow beams under fire. Materials nonlinearity was taken into consideration because there effects of the heat transfer in concrete, thermal expansion, and yielding of reinforcing steel. In addition, investigate the residual capacity of RC beams. The parametric study investigates the effects of: (1) concrete compressive strength (f cu ); (2) concrete cover (d`); (3) steel reinforcement yield strength (f y ); (4) ratio of main reinforcement (  %); (5) specific heat of the outer layers (C); (6) thermal conductivity of the outer layers (K); (7) voids area percentage in beam cross-section; (8) shear –span to depth ratio (a/d); and (9) compression reinforcement steel ratio (  ` %).