Study On Fire Resistance Of Steel Fiber Reinforced Concrete Beams

Steel fiber concrete(SFRC)is a kind of concrete composite material formed by adding steel fiber into the concrete matrix,which can enhance the tensile performance of concrete and prevent the generation and development of cracks.At present,the mechanical properties of steel fiber reinforced concrete(SFRC)members under normal temperature have been fully studied,but the mechanical properties of SFRC members under high temperature are less studied.This paper studies the mechanical properties of steel fiber reinforced concrete beams at high temperature.The main research contents and conclusions are as follows:(1)Based on the stress-strain law of ordinary concrete and the relevant parameters of SFRC at high temperature,the constitutive relationship of SFRC at high temperature is obtained,which lays a foundation for subsequent numerical simulation research.(2)Two reinforced concrete beams are made,one is ordinary reinforced concrete beam,the other is reinforced concrete beam mixed with steel fiber.The results show that when the two types of concrete beams reach the critical state,both positive and negative bending moment zones have cracks.Among them,ordinary reinforced concrete beam crack development distribution is more dense,wider range,wider crack width.Under the same load condition,the mid-span deflection of steel fiber reinforced concrete beam is larger than that of ordinary reinforced concrete beam,and the critical temperature is higher.(3)The mechanical properties of steel fiber reinforced concrete beams under high temperature were studied by using ABAQUS finite element model.The results show that under the same loading conditions and high temperature,the ductility of steel fiber reinforced concrete beams is better than that of ordinary reinforced concrete beams,and the width and length of cracks are smaller.The failure mode in the positive moment zone of steel fiber reinforced concrete simply supported overhanging beam is the same as the flexural failure mode of ordinary reinforced concrete beam with proper reinforcement,which is marked by the reinforcement in tension zone and concrete in compression zone.The failure sign of negative bending moment zone is mainly concrete in compression zone.In addition,the shear failure of steel fiber reinforced concrete beams under high temperature is smaller than that of ordinary reinforced concrete beams,mainly because steel fiber exerts its tensile performance in concrete beams,which limits the development of oblique cracks in reinforced concrete beams under high temperature.Secondly,the fire resistance limit temperature of steel fiber reinforced concrete beam is 600℃,which is higher than that of ordinary reinforced concrete beam of 400℃,which can prove that the fire resistance of steel fiber reinforced concrete beam is better.(4)ABAQUS finite element model is used to analyze the parameters that affect the fire resistance of steel fiber reinforced concrete beams,including load ratio,reinforcement ratio and steel fiber content.The results show that the ultimate deflection of steel fiber reinforced concrete beam increases with the increase of load ratio.By comparing the fire resistance of steel fiber reinforced concrete beams with different reinforcement ratio,the most suitable reinforcement ratio is 1.9%.The fire resistance deflection of reinforced concrete beams with steel fiber content of 0.5%,1.5% and 2.0%is about 25 mm,and that of reinforced concrete beams with steel fiber content of 1.0%is about 45 mm.It can be proved that the steel fiber concrete with 1.0% steel fiber content has better fire resistance than other steel fiber concrete.(5)Based on the research of fire resistant design method of reinforced concrete beam,the fire resistant design method of steel fiber concrete beam is further studied.The influence of steel fiber content on the high temperature bearing capacity and fire resistance limit of reinforced concrete beams is studied according to experiments and theoretical calculations,and a simplified method for fire resistance design of steel fiber reinforced concrete beams is obtained.