Experimental study on structural performance of UHPC and UHPFRC columns confined with steel tube

Structural performance of circular steel tube confined ultra high performance concrete (UHPC) columns under uniaxial compression was presented in this study. In addition to plain UHPC, steel fibers reinforced UHPC (UHPFRC) with 1% and 2% by volume were also investigated. A total of eighteen composite columns including short and intermediate columns were constructed and tested. Test results indicated that a substantial improvement in the strength and ductility was obtained by means of loading on only the concrete core. All specimens exhibited a shear plane failure of the UHPC and UHPFRC core which is normally associated with the softening behavior. The incorporation of steel fibers can enhance the ductility only for the intermediate columns and minimize the localized deformation of the columns. The influences of steel fibers and steel tube thickness on the axially compressive behavior were also identified. The analysis of test results demonstrated that the addition of steel fibers has negligible effect on the response of axial load versus axial strain. Furthermore, the impact of steel tube thickness and the confinement index on the strength and ductility was found to be more dominant than that of steel fibers.