Experimental and numerical study on the compressive behavior of micro-expansive ultra-high-performance concrete-filled steel tube columns

In concrete-filled steel tube (CFST) columns, conventional ultra-high-performance concrete (UHPC) has a large shrinkage and could easily be deboned from the steel tube, resulting in a failure of the effective lateral restraint of the steel tube to the core concrete. To solve this problem, a new type of micro-expansive and self-compacting UHPC was adopted to short CFST columns, which were further subjected to push-out and axial compressive tests. Test results indicated that the UHPC with the expansive agent could achieve an effective bonding between the core concrete and the steel tube. Compared with the compressive behavior of conventional UHP-CFST columns with a low confinement factor, the load-shortening curves of micro-expansive UHP-CFST columns do not show any obvious softening section. Furthermore, a finite element model of the micro-expansive UHP-CFST column was developed to predict the relationship of load and displacement by ABAQUS. Finally, the axial capacities of the short micro-expansive UHP-CFST columns obtained by the finite element analyses (FEA) were compared with that calculated by different design codes. It was concluded that the axial capacity of the composite members calculated by current codes is less than the FEA results and the formulas provided by the codes need to be further validated or modified. (C) 2020 Elsevier Ltd. All rights reserved.