Effect of specimen geometry on the dynamic direct tensile responses of ultra-high-performance fiber-reinforced concrete

Abstract

Direct tensile responses of ultra-high-performance fiber-reinforced concrete (UHPFRC) at high strain rates were investigated using a high-rate hydraulic universal testing machine (HR-UTM) with modified cylindrical specimens. The modified cylindrical UHPFRC specimens containing 2 vol% steel fibers exhibited tensile strain-softening behavior even at static strain rates, in contrast to the tensile strain-hardening responses commonly reported in previous studies. The modified cylindrical UHPFRC specimens containing 0.5 and 2 vol% steel fibers exhibited average tensile strengths of 8.8 and 10.0 MPa, respectively, at static strain rate (ε̇[jls-end-space/]=5.55 ×10−4s−1). As the strain rate increased from 5.55 × 10−4to 162.96 s−1, the tensile strength of the specimen with 2 vol% steel fibers increased from 10.0 to 17.1 MPa. Moreover, the elastic modulus of UHPFRC in direct tension increased from 59.4 to 124.7 GPa as the strain rate increased from 5.55 × 10−4to 99.53 s−1. However, at strain rates exceeding 162.45 s−1, accurately determining the tensile elastic modulus became difficult because of vibrations and early damage to strain gauges. Overall, the results demonstrate that specimen geometry plays a critical role in governing the dynamic tensile response of UHPFRC, emphasizing the need to consider geometric effects in material design and structural applications subjected to high strain rates.