Direct tensile behavior of steel fiber reinforced ultra-high performance concrete at high strain rates using modified split Hopkinson tension bar

This paper aims to investigate the dynamic tensile behavior of steel fiber reinforced ultra-high performance concrete (SF-UHPC) under impact loading. The investigated SF-UHPC were designed to have a compressive strength in excess of 200 MPa. A modified split Hopkinson tensile bar (SHTB) has been designed to obtain the dynamic behavior of SF-UHPC with fiber volume fraction of 2% and 4% under high strain rates ranging from 55 to 156 s-1. Wave shaping technique was used to achieve stress equilibrium and constant strain rate during testing. The average dynamic impact factor (DIF) of the tensile strength for SF-UHPC with a fiber volume fraction of 2% and 4% was found to be 3.2 and 1.9 at an average strain rate of 118 s-1 and 131 s-1, respectively. The designed SHTB in combination with high speed digital image analysis of notched specimens was able to measure the stress versus crack opening relationship of the SF-UHPC. Based on the results obtained from the current study and results obtained from twelve other studies, an equation is suggested to calculate the DIF of the tensile strength of SF-UHPC.