Fracture parameters by polylinear tension-softening analysis

Elastic-plastic fracture parameters for concrete were proposed based on the cohesive force model (CFM) and polylinear approximation analyses of the tension-softening diagram (TSD). The prediction method for the load-displacement relationships of concrete with cracks was developed by means of the fictitious crack model concept with the K-superposition method and the constitutive law of the polylinear TSD. In this method the nonlinear crack equation was solved by an iteration program for evaluating the optimum softening inclinations of TSD. The polylinear approximation method for calculating the complete TSD from the actual load-displacement curve was established by using the stepped inverse analysis. The energy consumed by fracturing (dW(f)) was calculated by integrating the work done by a cohesive force acting on the fictitious crack surface. Fracture parameters for elastic-plastic materials such as G(p), which is the energy release rate of CFM, R-curve, and fracture energy were estimated based on the value of dW(f). The energy consumption measured by the offset test for the notched concrete beam specimen agreed with the energy consumption calculated from the value of G(p). Fracture parameters for normal-strength concrete (NSC) and high-strength concrete (HSC) were measured, and their characteristics are discussed.