Experimental Study On Flexural Fatigue Of Reinforced Concrete Beams With Mixed Aggregates

With the development of engineering structure to high strength and light weight,it is bound to put forward higher requirements for materials such as reinforcement and concrete.Lightweight aggregate concrete has been greatly developed due to its advantages of light weight,high strength,good seismic and crack resistance.However,in engineering practice,more and more reinforced concrete structures are subjected to alternating loads,and the research on their fatigue properties has become the focus of the engineering and academic circles.The research on the fatigue properties of concrete mainly comes from the mechanical fatigue theory,and is aimed at ordinary concrete.However,there are few studies on fatigue of lightweight aggregate concrete.This experiment is aimed at the fatigue performance of composite lightweight concrete beam members in lightweight aggregate concrete.The specific contents are as follows:(1)By making 8 rebar-mixed aggregate concrete beam specimens,two kinds of reinforcement ratio.Two of the beams were subjected to static tests,and the ultimate be aring capacity of the beams was obtained as the basis of fatigue tests.The fatigue test was carried out with the three-point loading method.The failure pattern,crack variation and expansion trend under static load and dynamic load were studied,and the test datawere recorded.Analysis of the similarities and differences with ordinary reinforced concrete beams.The results show that the composite concrete beam with reinforced concrete can meet the requirements of China’s current specifications,and the bending fatigue performance of the composite concrete beam is similar to that of the ordinary reinforced concrete beam.(2)Under different stress levels,the change of load deflection relation in the fatigue process and the change of strain with the change of cycle times were studied to observe and analyze the law of crack extension.The fatigue test of reinforced concrete beams with mixed lightweight aggregate was studied and the S-N curve was obtained by regression method.The results show that: when the ratio of reinforcement is the same and the stress level is different,the higher the stress level is,the greater the rate of deflection increase is,the wider the crack extension is,and the cracks appear in the compression zone in advance.(3)Under different reinforcement ratios,the load relationship changes and the strain changes with the number of cycles in the fatigue process of specimens were studied,and the law of fracture extension was observed and analyzed.The results show that the deflection and strain of reinforced concrete beams with different reinforcement ratios are very similar,but the width of crack development and the crack spacing in the extension process are slightly different,and inclined cracks appear in the bending and shear section of test beams with larger reinforcement ratio during fatigue.Compared with ordinary reinforced concrete beams,the deflection of reinforced concrete beams with rebar and mixed aggregate is slightly larger,the width of crack development and the crack spacing in the extension process are larger,which is mainly related to the small elastic modulus of light aggregate.