Tension-softening constitutive model of concrete under sustained loading

The tension-softening constitutive model of concrete under sustained loading is the basis for analyzing the creep fracture behavior of concrete structures. Given the limited existing research in this area, this study aims to establish the tension-softening constitutive model of concrete under sustained loading through a combined experimental and theoretical approach. Initially, a series of creep fracture tests were conducted on 24 three-point bending beams subjected to sustained loads at 0.75, 0.80, 0.85, and 0.90 times the peak load. From the test results, a quantitative relationship between the external work and the energy dissipated by the elastic deformation, the creep deformation, and the crack propagation of specimens was established. Subsequently, the energy consumed by the crack propagation was extracted and then quantified in terms of the work done to overcome cohesive stress. By two-parameter regression analysis, the tension-softening constitutive model of concrete under sustained loading was established, describing the relationship between cohesive stress, crack opening displacement, and loading time. Finally, the effect of loading time and load levels on the cohesive stress under sustained loading was investigated. It was found that the cohesive stress decayed over time with three stages, i.e. decelerated reduction, stabilized reduction, and accelerated reduction stages. Moreover, the extent of cohesive stress reduction was associated with the load level, with cohesive stress decreasing at lower load levels when crack opening displacement remains constant. The tension-softening constitutive model developed in this study is a valuable reference for evaluating the serviceability of concrete structures throughout their service life.