8 - Modelling the dynamic response of concrete with mesoscopic heterogeneity

Abstract

Concrete is heterogeneous in nature. The needs of modelling concrete with explicit inclusion of the heterogeneity will arise when the mechanical processes at this level become of particular interest, either due to the target scale of observation, or more so if the heterogeneity is deemed to play a critical role in the material response under a particular loading condition. This chapter deals with modelling mesoscopic heterogeneity of concrete for high strain rate loading. For completeness in the treatment of this subject, both tensile and compressive loading as applied externally will be included. In fact, at the mesoscale the mechanisms underlying the damage process are closely associated with fracture or generalized tension even under compression. The chapter begins with an overview of the nature of the mesoscopic heterogeneity and its computational representation. Different modelling techniques are briefly reviewed and discussed. A finite element based mesoscale modelling framework is then described in more detail. The model is employed in various investigations into the meso-mechanisms affecting the dynamic behaviour of concrete in high strain rate compression and tension, and representative numerical simulations are introduced and the main observations summarized. In particular, the contribution of the heterogeneity in the dynamic compressive and tensile strengths of concrete, the dynamic structural (inertia) effects, and the strain rate limits in dynamic compression and Brazilian splitting tension tests are highlighted from a mesoscopic numerical simulation point of view. In the last part of the chapter, a simplified scheme for representing concrete heterogeneity, in which regular spatial discretization is utilized in conjunction with a stochastic material property distribution, is introduced along with example applications.