Numerical investigation of the dynamic increase factor of ultra-high performance concrete based on SHPB technology

This work numerically investigates the dynamic increase factor (DIF) of ultra-high performance concrete (UHPC) under compressive impact by employing a split-Hopkinson pressure bar (SHPB). The DIF test values of UHPC are collated at six different sizes of SHPB devices, and the effectiveness of the formulas to calculate the DIF proposed by the specification for normal concrete (NC) is evaluated. An analysis model simulating the SHPB test of UHPC in the LS-DYNA is established by calibrating the Karagozian and Case concrete (K & C) model, and the DIF-strain rate curves of UHPC are further supplemented and improved. The expressions of DIF under six different specimen sizes for UHPC are obtained by regression analysis. The results indicate that (1) the proposed formulas by the specification for NC will overestimate the strain rate effect of UHPC under impact compression; (2) the calibrated K & C model can simulate well the dynamic stress-strain curve of UHPC in compression under different specimen sizes; (3) the DIF value increases with the increase of the specimen size and decreases with the increase of the uniaxial compressive strength, while the variation trends of the threshold of strain rate in the DIF-strain rate curves are opposite to those of the DIF value; (4) the proposed formulas to calculate the DIF can match well the numerical results, and avoid overestimating the DIF of UHPC to a certain extent.