Prediction on Crack Propagation of Concrete due to Time-Dependent Creep under High Sustained Loading

To investigate the effects of sustained loading on crack propagation of concrete, three-point bending tests were conducted on prenotched concrete beam specimens under 90% and 95% of the ultimate load until failure. The load versus crack mouth opening displacement ($P–\mathrm{CMOD}$) curves and the failure age of the beam specimens were obtained from experiments. A numerical model was also proposed to investigate the crack propagation of concrete under sustained loading. The combination of the model with the Norton and cohesive stress relaxation models can reflect the viscoelastic property of uncracked concrete and its fracture process zone. Moreover, an initial fracture toughness-based criterion was proposed to determine the crack propagation under sustained loading. By calibrating the creep parameters of the Norton model and using necessary fracture parameters of concrete, the time-dependent crack propagation and failure time of concrete structures could be predicted. The numerical results indicated that for failure of the concrete specimens under high sustained loading, both the CMOD and crack growth rate first decreased and then increased during the sustained loading duration. There existed an inflection point on both the CMOD and crack growth rate versus time curves, which can be used to characterize the stability of concrete structures under sustained loading. Also, the crack propagation length corresponding to the inflection point was found to be approximately equal to that under static loading.