Effect of concrete rate dependent behaviour on structural progressive collapse

This contribution focuses on the need to take into account the material rate dependence in the modelling of reinforced concrete structures for progressive collapse analyses. Since progressive collapse is a dynamic phenomenon which depends strongly on stress redistribution, the strain rate effects may play a significant role in the overall structural response. A viscoplastic model is adopted to couple strain rate effects to the plastic response of both concrete and steel. The rate dependence in the elastic domain is also considered. The introduction of 1D constitutive laws for concrete and steel in a layered beam model provides strain rate dependent relations between generalised stresses and strains at the cross-sectional level. This multilevel approach is used in progressive collapse simulations where the structural response of a RC planar frame undergoing a sudden column loss is studied. Inertial effects are also taken into account. The results obtained using rate dependent material laws are compared to those provided by a rate independent approach. The influence of the column removal time on the structural resistance is also assessed. Noticeable differences are observed in terms of the degree of progressive failure. It can be concluded that the material strain rate effects might lead to an increased structural resistance to the sudden loss of a load-bearing member.