| Concrete filled steel tube(CFST)structures are widely used in engineering structures for its high bearing capacity and good ductility.However,when the strength of filled concrete is high,brittle failure will occur.Therefore,researchers put forward the shortcomings of reinforced concrete-filled steel tube(R-CFST)structure formed by inserting steel bars into CFST to improve the plasticity and ductility of CFST members.At present,the research on the influence of concrete strength on R-CFST is rare.Therefore,this paper studies the energy influence mechanism of concrete strength on the axial stress of R-CFST short columns by means of experiment and finite element simulation.The research includes the following contents:(1)Experimental study: the axial compression tests of plain concrete,reinforced concrete,CFST,R-CFST filled with 6 concrete strengths were carried out with the concrete strength as the variable parameter,and 72 specimens(3 repeated specimens)in total were tested.The influence of the concrete strength on the failure mode,axial compression characteristics,bearing capacity,hoop coefficient and ductility was analyzed.Finally,it was found that the reinforcement had a good effect on CFST The improvement effect of.(2)Research on finite element numerical simulation: in order to further clarify the role of reinforcement in improving the performance of R-CFST,the numerical simulation is carried out.In the simulation,the concrete constitutive model and simulation method suitable for R-CFST are put forward first,and then the reliability of the finite element simulation method is verified by the test data.Finally,the comparative analysis of 36 R-CFST and CFST specimen models with the same steel content of 6 kinds of steel content and 3 kinds of concrete strength grades is carried out by using this model.It is found that the action of longitudinal reinforcement is similar to that of steel tube,that is to say,it can restrain the core concrete.(3)Bearing capacity calculation: according to the test and finite element simulation results,the bearing capacity calculation of R-CFST can not directly use the formula of CFST.Therefore,the calculation method of the bearing capacity of R-CFST under axial compression is studied and a more reasonable calculation expression is given.Through the above research,the following conclusions are drawn:(1)The concrete strength has no great influence on the failure mode of the specimen;with the increase of the concrete strength,the bearing capacity of the R-CFST will increase all the time,but when the concrete strength exceeds a certain value,the bearing capacity of the CFST will decrease,and it is easy to produce brittle fracture;with the increase of the concrete strength,the ductility coefficient and the hoop coefficient of the R-CFST and the CFST will decrease,but the R-CFST will decrease The decrease degree of CFST is always smaller than that of CFST,and the difference is more obvious with the increase of concrete strength.(2)An effective and reliable finite element simulation method for R-CFST is established;(3)The results of finite element analysis show that: the longitudinal reinforcement can be equivalent to steel tube to calculate the side stress of the longitudinal reinforcement to the core concrete;when the steel content is the same,the bearing capacity,ductility and contribution rate of the longitudinal reinforcement to the bearing capacity of R-CFST are higher than that of CFST,and the difference is more obvious when the concrete strength is higher.(4)The formula suitable for R-CFST bearing capacity is put forward,and the accuracy and stability of the formula are verified by comparing and analyzing the experimental data. |
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