Experimental Study On Fatigue Behavior Of Prefabricated Steel Reinforced Concrete Beams

Steel Reinforced Concrete(SRC)structures are structures with steel sections in concrete,with certain longitudinal reinforcement and hoops.In the context of China’s construction industrialisation,assembly-type structures are flourishing.In order to solve the constraints in the development of SRC structures,Prefabricated Steel Reinforced Concrete(PSRC)structures have been proposed at home and abroad.The fatigue strength must be considered as the floor beams of the PSRC structure are directly subjected to the frequent action of the train loads.There is a lack of understanding and research on the fatigue performance of PSRC beams and related design methods.The current design level of PSRC structures in China in terms of fatigue is not yet able to meet the needs of engineering design,which undoubtedly limits the application of PSRC structures under fatigue loading conditions.To this end,this paper presents an in-depth study of the fatigue performance of PSRC beams through experimental research.The main findings of this paper and the conclusions obtained are as follows:(1)Fatigue tests were carried out on eight PSRC beams and one SRC beam to investigate the full fatigue damage process,deformation and concrete crack development,fatigue fracture morphology of the steel components and other characteristics.The results show that the dominant mode of damage for both the SRC and PSRC beams is flexural fatigue damage,with cracks in the steel beam originating at the fillet weld between the web and the tensioned flange.Complete fatigue fracture of the tensile longitudinal bars generally precedes the tensile flange of the internal H-shaped steel beam,and complete fracture of the tensile flange of the internal H-shaped steel beam can be used as a sign of fatigue damage of the entire PSRC beam.(2)Based on the fatigue test phenomena and results of PSRC beams,the main stages of the damage process of PSRC beams under fatigue loading are summarised.The results show that the damage process is divided into five main stages: cracking of concrete in the tensile zone;formation of fatigue micro-cracks;crack expansion and damage development process of H-shaped steel beam and reinforcement;fracture of tensile reinforcement;fatigue cracking of H-shaped steel beam through its tensile flange plate thickness and collapse of the member due to loss of load carrying capacity.(3)Analysis of the factors influencing the fatigue life of PSRC beams based on the S-N curves obtained from the regression of PSRC beam fatigue life data.The study shows that: 1)The distribution of positive strain along the section height of the purely bending section of the PSRC beam after 1 million cycles,the observation of the shape of the precast and cast-in-place concrete laminated surfaces and the comparative analysis of the SN curves of the precast assembled and cast-in-place steel and concrete beams show that there is no slippage in the precast and cast-in-place concrete of the PSRC beam during the test and that the fatigue performance of the PSRC beam is not significantly affected by the precast and cast-in-place concrete laminated surfaces.2)The higher the strength of the cast-inplace concrete,the higher the strength of the precast concrete,the higher the fatigue performance of the beam.For the same number of stress cycles,the fatigue strength of the H-beam in group 1 PSRC beams(cast-in-place concrete strength class C50)is approximately 15% higher than that of group 2 PSRC beams(cast-in-place concrete strength class C30);the fatigue life of the H-beam in group 1 PSRC beams is approximately 1.53 times higher than that of group 2 beams for the same magnitude of stress amplitude.(4)A comparative analysis of the fatigue performance of prefabricated assembled and pure cast-in-place steel and concrete beams was carried out.The results show that the fatigue strength of group 1 PSRC beams is higher than that of pure H-shaped steel beams with the same strength class of H-shaped steel beams;the S-N curve obtained by combining the fatigue life data of pure cast-in-place steel and concrete beams and group 1PSRC beams were compared and found that the fatigue strength of group 1 PSRC beams is slightly higher than that of pure cast-in-place steel and concrete beams,but the difference is not significant The S-N curves obtained from the combined regression of Group 1 PSRC beams and cast-in-place SRC beams were compared with Group 2 PSRC beams and found that the fatigue strength or life of the beams could be increased to some extent by increasing the strength of the cast-in-place concrete without changing the strength of the precast concrete.