Mechanical performance of self-stressing CFST columns under uniaxial compression

Abstract

Applying the expansive concrete in concrete-filled steel tube (CFST) columns can prevent the debonding between the steel tube and internal concrete. Self-stresses are on the steel tube and internal concrete before an external load is applied because of the concrete expansion. Mechanical performance of self-stressing CFST columns under the uniaxial compression were studied in this paper by tests and finite element analysis. A calculation method was proposed to calculate the self-stress based on the free deformation of concrete. Ten CFST columns with different amounts of expansive agent, tube thicknesses, and curing ages were tested under the uniaxial compression. The results indicated that the axial load bearing capacity of CFST columns improved significantly after adding the expansive agent to the internal concrete. Besides, the improving degree was related to the initial self-stress. Subsequently, a finite element analysis was carried out on self-stressing CFST columns to investigate the interaction mechanism between the steel tube and internal concrete further. The simulated results agreed well with the experimental results through some response comparisons. According to the simulated results, contact stresses were observed between the steel tube and internal concrete of self-stressing CFST columns throughout the loading process. Furthermore, a parameter analysis was carried out, which indicated increasing the compressive strength of concrete, yielding strength of steel tube, and thickness of steel tube increased the axial load bearing capacity of self-stressing CFST columns and the corresponding load shared by concrete. Finally, a calculation formula considering the effect of self-stress was proposed to predict the axial load bearing capacity for short self-stressing CFST columns with reasonable accuracy.