Study On Behavior Of Square CFST Under Transverse Local Compression

For concrete filled steel tube (CFST), steel tube can effectively constrain its core concrete, thus delay the longitudinal cracking of concrete under compression and improve the ability of the plastic deformation of core concrete; and at the same time core concrete can delay or prevent premature local buckling of steel tube. The commonly cross-section of CFST used in practice includes circular and rectangular, and square section is a special one of rectangular section. Generally, the confinement to concrete core of square steel tube is not as good as that of circular steel tube; however, square CFST is favored by engineers because of its big section moment of inertia and simple joint configuration which meet the architectural design, and at present square CFST is very popular in high-rise and super high-rise buildings, bridge structures, industrial buildings and spatial structures. In practice, CFST may be subjected to transverse local compression, such as the intersection of the chord member and the web member in CFST truss or CFST laced member. The performance of CFST members under transverse local compression significantly affects the behavior of CFST truss or CFST laced member, even determines the safety of an entire structure.This paper experimentally and theoretically investigates the behavior and mechanisms of CFST under transverse local compression. The main research works are summarized below:(1) Reviewing of the past researches related to this study, including performance of joint with CFST chord, behavior of truss with CFST chords and performance of CFST under local compression, was carried out.(2) Twelve CFST specimens,4hollow structural section (HSS) specimens and4plain concrete (PC) specimens were tested under transverse local compression. The influence of width ratio between straight (inclined) bearing member (BM) and compression member, wall thickness of the steel tube and the type of BM (solid/hollow) on the performance and failure mechanisim of specimens under transverse local compression was investigated. In the meantime the comparison of performance between CFST and superposition of HSS and PC member was also carried out.(3) Based on the determination of constitutive model of steel and core concrete, a finite element analysis (FEA) model of square CFST under transverse local compression was developed using the software ABAQUS, and the predicted failure mode and load versus deformation curve generally agreed well with the experimental results. (4) Based on the verified FEA model, the effect of width ratio between BM and compression member, steel ratio, material strength and member dimension on the performance and mechanism of square CFST under transverse local compression was systematically conducted. Finally, the simplified formula for bearing capacity of square CFST under transverse local compression was proposed, and the simplified calculating results were generally in good agreement with the numerical and experimental results.