Fatigue crack growth prediction in concrete slabs

A new method to predict crack growth and fatigue life of concrete slabs is presented based on similar models for 2-D specimens. Four large-scale concrete slabs on ground subjected to three different stress ranges have been tested to fatigue failure. Geometric correction factors to calculate the effective crack length and stress intensity factor from the experimental fatigue compliance are derived based on 3-D finite element modeling. Crack length versus the number of cycles curves are constructed and fitted to a modified logistic function, which enables for the calculation of the crack propagation rates and critical crack lengths from the first and second derivative of the logistic function. Fatigue crack growth is separated into a decelerating and accelerating crack growth functions based on the initial crack length and the applied stress intensity factor, respectively. The proposed method is able to predict the fatigue life of the tested slabs and the fatigue resistance of several independent slabs cast with the same geometry and material. The analysis of the tested slabs shows that load pulses with higher minimum loads generated more fatigue damage as indicated by greater crack growth rates. The principles of this slab fatigue crack growth procedure can now be extended to estimate the remaining life in uncracked or partially-cracked concrete slabs on ground.