The crack propagation velocity as a reason for the strain rate effect of concrete: An analytical model

An analytical model is presented in this paper which, based on the maximum crack velocity, provides a hypothesis for one of the reasons of the increase in tensile strength of concrete under high loading rates. Due to the fact that the formation of cracks needs a certain time to pass through the cross section and not happens suddenly, stresses can still be transmitted over the remaining uncracked cross section during this time. The hypothesis is that at high loading rates, the increase in externally induced stresses can be greater than the decrease in the load-bearing cross-sectional area due to limited crack propagation velocity, which results in an externally measurable increase in strength. This measured strength increase depends on the stress distribution in the crack plane. In this paper two variants of this stress distribution during the failure process are described, and their effect on the increase in strength is mathematically evaluated.