RATE EFFECTS IN UNIAXIAL DYNAMIC COMPRESSION OF CONCRETE

Corrections for stress-wave dispersion in a 76.2-mm-diameter split Hopkinson pressure bar (SHPB) system have produced more accurate data in the regime between yield point (elastic limit) and maximum stress of dynamic stress-strain curves of concrete, so that the rate dependence of the stress on the inelastic strain rate in this regime could be determined. Such results are published here for the first time, based on SHPB tests of two kinds of high-strength plain concrete specimens. In addition to rate dependence of the dynamic compressive strength (to more than twice the static strength), the critical strain to failure and the yield stress are reported. Records from axial and circumferential strain gages mounted on some specimens permitted estimation of lateral inertia effects and were useful in determining yield. It is shown that, in these ramp-loaded tests, the lateral acceleration of the specimen surface between yield and maximum stress was very small, so that the induced radial confinement stresses were too small to account for the enhancement of the dynamic compressive strength above the static strength, contrary to what has sometimes been suggested by experience with much higher-rate loading.