Rigid-body-spring network with visco-plastic damage model for simulating rate dependent fracture of RC structures

The mechanical properties of concrete materials vary with the loading rate under dynamic conditions, which can influence the dynamic fracture behavior of structures. The rate dependency is reported as due to the microscopic mechanisms, such as a material inertia effect and the Stefan effect. In this study, the rigid-body-spring network (RBSN) is employed for the fracture analysis, and the visco-plastic damage model is implemented to represent the rate effect in this macroscopic simulation framework. The parameters in the Perzyna type visco-plastic formulation are adjusted through the direct tensile test with various loading rates as a preliminary calibration. As the loading rate increases, the strength increase is presented in terms of the dynamic increase factor (DIF), and compared with the experimental and empirical results. Next, the flexural beam test is conducted for plain and reinforced concrete beams under slow and impact rates of loading. At the failure stage, different crack patterns are observed depending on the loading rate. The impact loading induces the failure to be more localized on the compressive zone of the beam, which is due to rather the rate dependent material features. In structural aspects, the reinforcement exerts stronger effects on reducing crack width and improving ductility at the slow loading rate. The ductility is also evaluated through the comparison of loaddeformation curves until the final rupture of the beams. This study can provide understandings of the structural rate dependent behavior and the reinforcing effect under dynamic loadings.