Modified virtual internal bond fracture constitutive model for concrete

- A Modified Concrete Virtual Internal Bond model (MC-VIB) for concrete is presented.
- The proposed model is a 'fracture-constitutive' model.
- The model's seven material parameters are calibrated for compressive strength of 27.6 MPa.
- MC-VIB model is fairly insensitive to mesh size and shows structure size effect.

The goal of the research presented here is the development of a Modified Concrete Virtual Internal Bond model (MC-VIB) for concrete. Concrete is often used as a primary material to build protective structures and this paper focuses on the development of a material model for concrete and its application in LS-DYNA in order to simulate the behavior of reinforced concrete (RC) structures under impact and blast loading. This 'fracture-constitutive' VIB model is the further development of earlier work which accounted only for the tensile behavior and fracture of concrete. The proposed model includes the differences in the behavior of concrete in tension, compression and shear. Consequently, while the previous VIB model had only two material parameters, the MC-VIB model has seven material parameters. The model parameters are calibrated based on the stress-strain behavior of single element and cylinder models of concrete with a uniaxial compressive strength of 27.6 MPa. The material models currently available in LS-DYNA require a number of input parameters that are often automatically generated by giving the compressive strength of concrete. The stress strain curves from the MC-VIB model are compared to the material models for concrete available in LS-DYNA and standard curves obtained by an accepted equation and has shown good correspondence. It is shown that the MC-VIB model is fairly insensitive to mesh size and size effect studies presented here has successfully demonstrated the ability of the model to account for the inherent inertial confining effect as the structure size increases. The effect and sensitivity of the material parameters has been studied using the simulated stress-strain response of concrete in tension and compression under dynamic loading and finally recommendations have been made for the material parameter values for a standard concrete mix of 27.6 MPa.