Modeling of strain rate effects for concrete with viscoelasticity and retarded damage

Abstract

Especially the tensile strength of concrete may by far exceed the quasistatic values under high strain rate conditions. Due to present knowledge this is predominantly caused by the higher resistance of water in the capillary system of concrete on one hand and by the limited speed of the evolution of micro and macro cracks on the other hand. This contribution combines a viscoelastic approach for the first case with a gradient damage approach for the second, whereby damage is retarded due to inertial effects under high strain rates. The combined material law includes quasistatic behavior as a special case and covers dynamic material behavior up to a strain rate in a magnitude of 103 s−1. The material law is implemented in a Finite Element Method and first of all applied to uniaxial wave propagation problems. Thus, typical experimental results for dynamic tensile strength increase factors may be reproduced within a calibration procedure for the three dynamic material parameters of the material law. Furthermore, the structural behavior of a plain concrete beam under impact loading is investigated. The effects of structural mass inertia and the material's strain rate sensitivity to the dynamic load bearing capacity are exemplarily outlined. Finally, it is demonstrated how the dynamic load bearing capacity depends on load duration beneath load amplitude.