Advanced material modelling of concrete in Abaqus

Abaqus is a complex finite element (FE) package widely used in civil engineering practice. The choice of material models for concrete is limited in Abaqus to (i) the smeared cracking model, (ii) the brittle cracking mode and (iii) the damaged plasticity model. The smeared cracking model can handle only monotonic loading that limits the range of its applicability. The damaged plasticity model is by far most complex concrete model incorporated in Abaqus that can be used in any loading regime. However, it is not “user friendly”, includes multiple parameters and its calibration can be very challenging. Additionally, this model does not allow damaged elements to be deleted form the FE analysis. The brittle cracking model can be used in any loading regime and is very “user friendly” and easy to calibrate. The main disadvantage of this model is that it assumes linear elastic material behaviour in compression.
In this paper the brittle cracking model is extended by introducing nonlinear compressive behaviour using the user subroutine VUSDFLD. This subroutine allows to redefine material properties at a material point as a function of a field variable such as stress, strain, temperature, etc. The field variable is updated at each analysis step and the value of the relevant material property is recalculated. The nonlinear compressive behaviour of concrete is introduced into the brittle crack model by formulating the modulus of elasticity of concrete (Ec) as a function of strain (ε). The Ec-ε relationship is derived using the stress-strain curve obtained based on FIB Model Code 2010. Additionally, the concrete material is modelled to be able to develop damage defined by the maximum strain and damaged elements are deleted from the FE model. The extended brittle crack model is used to examine strain rate effects and also to simulate a three point bending experiment, a standard brittle failure test and reinforced concrete columns under blast. In all cases the results favourably compared with those observed in experiments. Overall, the extended brittle crack model offers a robust reliable way for modelling of concrete.