Comparison of the Hu-Duan boundary effect model with the size-shape effect law for quasi-brittle fracture based on new comprehensive fracture tests

The boundary effect model (BEM) for concrete fracture and the effects of specimens size and crack length has previously been criticized on theoretical grounds, but the experimental evidence found in the literature, when taken alone, has been too limited to judge the validity of BEM conclusively. New, separately published, comprehensive fracture experiments, which were made on specimens cast from one and the same batch concrete and featured a broad ranges of both the size and the crack length (including a zero crack length), change the situation. The optimum fit of the data by Hu and Duan's model shows major deviations from these new test results. On the other hand, the Type 1 and 2 size effect laws (SELs) and their amalgamation in the universal size effect law are found to give a far better fit of the test results. Thus, regardless of the previously expounded theoretical objections, the comparison with experimental evidence alone suffices to conclude that Hu and Duan's model is not realistic.