Study On Pure Bending Mechanical Properties Of Recycled Concrete-filled Circular Steel Tube Under Simulated Acid Rain Environment

In this paper,the effects of acid rain corrosion environment on the mechanical properties of recycled concrete-filled circular steel tubes are analyzed by simulating the corrosion test in acid rain environment and the pure bending test after acid rain corrosion.Finite element analysis software ABAQUS is used to analyze the whole process of pure bending force of all specimens.The corrosion effects of the acid rain environment on the specimens were considered based on the wall thickness reduction and double reduction(thickness and material reduction)methods.The resistance bending capacity of each specimen was calculated using the formulas for the corresponding bearing capacity in the technical regulations for concrete-filled steel tube(CFST)in Jiangxi Province and China respectively,and the effect of corrosion on the bearing capacity was analyzed.On this basis,according to the correlation between the corrosion depth and the corrosion time of the steel,the flexural bearing capacity of the CFST under acid corrosion environment is suggested.The main research work based on this article have been undertaken as followed:(1)Three specimens of ordinary concrete-filled circular steel tube and three specimens of recycled concrete-filled circular steel tube were placed in simulated acid rain solution respectively for corrosion test.When the target corrosion was 10%,20%,30%,the corrosion test was stopped.Through the detailed description of the corrosion test,the methods,steps and the phenomena in the corrosion process are introduced.The results show that the reduction of the thickness of the CFST is in good agreement with the theoretical calculation value of Faraday's first law in a certain period of corrosion.(2)The mechanical properties of all the specimens(8 specimens,including 2 non corroded specimens)were tested.Under the different corrosion degree(no corrosion,target corrosion 10%,target corrosion 20% and target corrosion 30%)and different aggregate types(ordinary and regeneration),the failure modes,bending moment-stain,bending moment-mid span deflection and other correlation curves were compared and analyzed.The results show,under pure bending loads,the concrete type has no obvious effect on the failure morphology of the specimens.However,different acid rain corrosion rates have great influence on the mechanical properties of the specimens.It can be seen that the elastic stage stiffness and its ultimate bearing capacity of all specimens show a significant decrease trend with the increase of corrosion rate.(3)The corrosion effect of acid rain environment were considered from two aspects of wall thickness reduction and double reduction respectively,and all the specimens weremodeled and analyzed using the finite element analysis software ABAQUS.Comparing the calculation results obtained by the finite element method with the experimental results,based on the verification of the correctness of the modeling method,the typical pure bending specimen were established and its failure morphology,load distribution and interaction between steel tube and core concrete were analyzed theoretically.(4)On the basis of considering the effect of acid rain corrosion by two ways of wall thickness reduction and double reduction,the flexural capacity of CFST after acid rain corrosion is calculated by using the corresponding bearing capacity formula of Jiangxi provincial standard and national standard respectively.According to the correlativity between corrosion depth and corrosion time of steel,the theoretical calculation method of flexural bearing capacity of CFST under acid rain corrosion environment is suggested.