Experimental study on the uniaxial compression performance of ultrahigh-performance concrete constrained by stirrups and fibers

摘要

The influences of stirrups and steel fiber content on the compression performance of ultrahigh-performance concrete (UHPC) were investigated through the axial compression test of ten groups of UHPC short columns with stirrups and one group of columns without stirrups. The effects of volume stirrup ratio, stirrup form, stirrup spacing, and volume fraction of steel fiber on the peak stress and strain of confined UHPC were analyzed. Results showed that the failure modes of the specimens are the sharp increase and protrusion in circumferential deformation caused by core UHPC crushing, stirrup yielding, and "cracked but not broke into pieces. The protective layer of UHPC did not spall due to the pullout resistance of the end-configuration steel fiber. Constrained UHPC specimens with high stirrup ratio, small stirrup spacing, and large fiber content demonstrated enhanced constraining effects. The slope of the descending section of the constrained UHPC stress-strain curve was small, and the deformation capacity of the short column was improved. Compared with the constraint coefficient of the steel fiber content, the stirrup constraint coefficient exerted greater influence on the restraining effect of UHPC. A calculation formula for the constrained UHPC peak stress and the corresponding strain that considered the stirrup and fiber constraint coefficients was proposed on the basis of the experimental results and theoretical analysis. The proposed complete stress-strain curve equation of UHPC constrained by composite stirrups and steel fibers demonstrated consistency between the theoretical and experimental curves.