Effect of steel fibers on the performance of ultrahigh-strength concrete columns

This study investigates the effect of the volume fraction of steel fibers on the axial load response of 200 MPa ultrahigh-strength concrete (UHSC) columns. Behavioral aspects investigated include strength, ductility, and delay and control of brittle concrete cover spalling. In addition, the influence of the amount of transverse reinforcement and the combined effect of transverse reinforcement and steel fibers on the postpeak behavior of the 200 MPa UHSC columns were investigated. Two series of columns, having different amounts of transverse reinforcement, ρ_sh = 3.6 and 6.1%, were constructed and tested under pure axial compressive loading. Each series consisted of three columns with three different steel fiber volume fractions (υ_f = 0, 1, and 1.5%). Test results demonstrated that an increase of transverse reinforcement amounts in 200 MPa UHSC columns improves the maximum confined concrete strength and significantly improves the postpeak ductility. The addition of steel fibers resulted in increased peak loads for both the poorly and well confined 200 MPa UHSC columns by delaying and controlling initial cover spalling. The addition of steel fibers improves the confined concrete strength and significantly improves postpeak ductility only for the well confined UHSC columns.