Axial Compression Performance Of High-strength Recycled Aggregate Concrete-filled Steel Tubes With Different Connectors

The influence of section shape and internal structures of steel tube on the axial compression performance of recycled concrete-filled steel tube(RCFST)is a very important problem in engineering field.In this thesis,the axial compression properties of high-strength RCFST with circular or square sections and different inner structures are studied.The stress mechanism is revealed,and reasonable internal structures are put forward,which has important engineering value and certain theoretical significance.Main research work and contributions are as follows:1.Axial compression tests of 33 circular specimens of high-strength RCFSTs were carried out.The internal structures include the cavity with no additional structures,witn studs,vertical ribs,tie bars,steel partitions,or circular ribs.Concrete include C60,C70 normal concrete and C60 recycled coarse aggregate concrete.The failure process,loaddisplacement curves and strain of each specimen were analyzed.The axial compression capacity and energy dissipation capacity of different specimens were obtained.And the reasonable internal structure of circular high-strength RCFSTs was put forward.2.Axial compression tests of 22 square specimens of high-strength RCFSTs were carried out.The internal structures include the cavity with no additional structures,witn studs,vertical ribs,tie bars,steel partitions,or circular ribs.Concrete include C60 normal concrete and C60 recycled coarse aggregate concrete.The failure process,loaddisplacement curves and strain of each specimen were analyzed.The axial compression capacity and energy dissipation capacity of different specimens were obtained.And the reasonable internal structure of square high-strength RCFSTs was put forward.3.Based on the tests,the finite element analysis model was established to reveal the damage evolution and yield mechanism of each specimen.And the calculation method of axial compression capacity of high-strength RCFSTs with different internal structures was given.The calculation results are in good agreement with the test resuts.Main conclusions:(1)The built-in reinforcement cage can strengthen the confinement to the core concrete,improve the bearing capacity,and slow down the performance degradation of specimens after ultimate load.Vertical ribs,internal cirular steel tubes and steel partitions can improve the bearing capacity,stiffness and energy dissipation capacity of specimens,and slow down the damage evolution and performance degradation of steel tubes.(2)With the same internal structures,and the same concrete strength grades,the axial compression properties of high-strength CFSTs and high-strength RCFSTs are similar.(3)Considering the different steel tube shape,vertical ribs,circular ribs,built-in reinforcement cage and steel partitions,the calculation method of axial bearing capacity is given.The finite element analysis model is established.The calculation analysis and finite element simulation of the bearing capacity of specimens are carried out.And the calculation results are in good agreement with the test results.