Material based dynamic increase factor models for UHP-FRC under compression and tension

Abstract

Ultra-high performance fiber reinforced concretes (UHP-FRC) exhibit strain rate sensitivity when subjected to dynamic loadings. In recent years, concerns have been raised among researchers that structural effects, such as lateral inertial confinement and frictional confinement at the specimen’s face, could contribute to the strain rate sensitivity under high strain-rate testing using a split Hopkinson pressure bar (SHPB) besides material inherent property. The enhanced material strength by structural effect is often misinterpreted as material strain rate effect, and hence overestimating the material’s dynamic increase factor (DIF). If the overestimated DIF is used in numerical simulations, and some constitutive models have already adopted such overestimated DIF, the structural effects will be double-counted and misinterpreted as material property, leading to overestimated material resistance. To the best knowledge of the authors, there exists (1) no empirical equations for the nominal DIF models of UHP-FRC, which is directly obtained from experimental tests with structural effect; (2) no material based DIF models of UHP-FRC, which consider isolating structural effects. In this paper, based on the authors’ previous research on isolation of structural effects of UHP-FRC subjected to dynamic loadings, material based DIF models of UHP-FRC under compression and tension are proposed.