Study on Axial Load Mechanical Behavior of Square Concrete-Filled Tubular Steel Stub Column with Gap

Square concrete-filled tubular steel stub column (SCFTSSC) is of great mechanical performance, which has been broadly used in the construction of engineering structures. For the purpose of avoiding the buckling and bulging in the steel tubes and then making full use of the steel tubes to constrain the core concrete, in this paper, an experiment is conducted to study the effects of different preset gap modes on the mechanical performance of SCFTSSC, and a comparative study is carried out to investigate the failure mode, load–deformation response and load–strain results of two types of specimens, including ones with a gap on the top end and others with a middle gap. The obtained results indicated that the preset gap changes the force transmission mode, then enhances the mechanical performance of specimens, which shows better plasticity, and the failure mode can be observed as the tube has cracked along corners. The findings of the comparative study showed that the introduction of a gap on the top end can make the corresponding load–deformation curve show a form of a threefold line and accompanied by a relatively persistent strengthening stage; meanwhile, the existence of a middle gap also makes the vertical load cannot be transmitted by the tube, so that the horizontal strain will increase; further, the rectangular section of the specimen will be changed to a circular form, and finally, the cracks will emerge in corners.