Dimensional effects on failure of concrete loaded in Mode II and III

Concrete collapse is seldom governed by crack propagation in pure Mode I (opening) , due to loading and geometrical complexities. Usually, a superposition of the three modes of propagation occurs. In the laboratory, instead, the tests are normally performed by loading structures in Mode I. Moreover, such tests are conducted on smaller samples with respect to the real dimension. These two factors should be analyzed in order to get the actual strength and toughness for real structural members. The Authors proposed the so-called Multifractal Scaling Law, largely validated in presence of failure in pure Mode I and especially in absence of large pre-notches. In the present work, the MFSL is applied to failures in Mode II (sliding ) and Mode III (tearing ). The interpretation of experimental tests for shear and torsion permits to affirm that the interaction between the microstructural characteristic length and the external structural size governs the scale effects also in Mode II and III.