Time-Dependent Nonlinearity of Compression Softening in Concrete

As nonlinear post-peak mechanics is time dependent in nature and the transient process of collapse is influenced by loading rates, post-peak analyses have to be conducted considering softened structural concrete under varying rates of straining. To meet this challenge, a new time-dependent constitutive model, which encompasses both near- and post-peak regions in concrete compression, is proposed. Towards better evaluation of structural collapse under extreme loads, a coupled plastic-damaging law is presented. For the purpose of identifying evolution laws of plasticity and continuum damage, experimental investigation into rate-dependent nonlinearity was performed under different levels of lateral confinement. The plastic and damage evolutions were formulated with respect to paths of intrinsic stress intensity of damage continua and time. The combined law of short-term elasto-plastic and fracture successfully convey nonlinear creep deformation and rate dependent strength, as well as delayed creep rupture of material instability.