Investigation into Pure Rate Effect on Dynamic Increase Factor for Concrete Compressive Strength

Dynamic increase factor (DIF) has been used to consider rate effect on compressive strength of concrete in both design and analysis of concrete structures loaded with high rate. Until now, a variety of DIFs have been suggested by various researchers, and these DIFs are adopted in design guidelines and model codes, e.g., ACI 349-13, ACI 370R-14, fib MC2010, and UFC 3-340-02. However, the DIFs includes the axial and radial inertia effects, which cause confining effect and resistance to deformation. Therefore, additional strength enhancement due to the inertia effects is included in the DIFs, so applying the DIFs to design and analysis can lead to nonconservative results. In this study, in consideration of the strain acceleration and geometry of a specimen, a new DIF, which is exclusive of the inertia effects, was suggested based on concrete split Hopkinson pressure bar (SHPB) test results. Furthermore, to validate the new DIF, finite element analyses to which the existing and new DIFs were applied were performed for concrete SHPB tests. The verification results indicated that the DIF proposed in this study improve predictions of the dynamic strength enhancement of concrete compared with the existing DIFs.