Research On Mechanism Of Concrete-Filled Steel Tubes Subjected To Local Compression

How to reasonably design concrete-filled steel tubes(CFST) under local compression is one of the hot topics in the relevant engineering field now. It was not solved in the past design code yet. The related research needs to do further, especially theory research. The research on CFST with square section under local compression is not reported to date. Behaviours and mechanism of CFST under local compression were investigated in this paper, including theoretical and experimental studies. Based on the systemic analysis of parameters, practical computational methods for local compression bearing capacity of CFST were given. In this paper, the main achievements were summarized in detail as follows: (1) The local compression area ratio, steel ratio and rigidity of end plates were chosen the main parameters. Experimental studies on the behaviours of CFST under local compression were carried out, including 26 circular CFST specimens and 56 square CFST specimens. Influence of local compression area, steel confinement, section shape, end plate and its size were studied. The differences between CFST and plain concrete, and between CFST with and without end plate were compared. Furthermore, push-out tests were conducted to investigate the bond stress in the interface between concrete and steel tube. (2) Based on a large amount of computational examples, the constitutive model of core concrete of CFST was suggested. Load-deformation curve of CFST under local compression was obtained by ABAQUS, which is a common analysis software by finite element method(FEM). From the results, it can be seen that the constitutive model of core concrete in this paper has the advantages of clear mechanics concept and easy using. By verifying lots of test results using the computational method in this paper, such as axially loaded 529 CFST members and 126 steel tube confined concrete members selected from other researchers, and 97 CFST members under local compression in this paper and from other researchers, it can be proved that this method is reliable. (3) Load-deformation curves of CFST under local compression were analysized through the computational method given by this paper. The influence of local compression area ratio, steel ratio and rigidity of end plates was investigated. It is the original work that the local compression mechanism of CFST was discovered deeply . (4) Influences of local compression area ratio, steel ratio, strength of steel and concrete, and relative rigidity radius of end plates on local compression bearing-capacity of CFST were investigated systemically. On this basis, the method to calculate the local compression bearing capacity was suggested. The results indicate that the method has clear mechanics concept, and easy using, which can supply practical engineering and specifications with reliable references.