ACI 446.4R-04

This report summarizes information regarding the analysis of concrete systems subjected to rapid loading. Engineers will obtain an overview of the subject matter along with recommended approaches for analysis and selection of material properties. Researchers will obtain a concise source of information from leading authorities in the field conducting research and applying these concepts in practice. This report describes how, as strain rates increase above 10 -4 to 10 -3 s -1 , concrete in tension and compression becomes stronger and stiffer, with less prepeak crack growth and less ductile behavior in the postpeak region. The rate dependence of bond is shown to be due to local crushing around deformations of the bar and to have the same relationship to rate as compressive strength. The practical effect of this local crushing is to concentrate strains in a small number of cracks, thus lowering the overall ductility of reinforced members. Finally, it is concluded that computational models of postpeak behavior under either dynamic or static load should use a localization limiter so that strain softening into arbitrarily small regions is prevented. The models should also properly pose the equations of motion; one appropriate way to do this is to represent softening through rate dependence, such as viscoplasticity.