- Size Effects
Size effect is one of the salient characteristics of fracture mechanics. Classical linear elastic fracture mechanics exhibit a size effect on strength, which was mentioned in Chapter 2 and worked out in Appendix 1. For a long time there has been interest in size effects. In their days Leonardo da Vinci and Galileo Galilei studied the effect of structural size on strength. The issue is of considerable importance, namely, can the strength of real-size structures be predicted from small-scale laboratory experiments? It turns out that larger structures are generally weaker and their behavior is more brittle than structures that are geometrically scaled down. Testing full-scale structures in the laboratory is, however, rather impracticable and expensive. Often sufªciently large loading equipment is simply not available. Only a few exceptional labs are ªtted to do really large-scale work, for example, the large structural labs at the University of San Diego. The rule is, however, that most laboratories are limited to test structures up to the 10-[m] scale (this means, for instance, beams with a depth up to 1 [m]). Figure 9.1, from Bažant and Yavari (2005), quite clearly illustrates the lack of large-scale data. The largest existing tests measuring the shear capacity of reinforced concrete beams are likely those carried out by Shioya et al. (1989) with a depth of 3,000 mm for the largest beams. Once in a while it is possible to test a full-scale structure, prior to demolishing, but in those cases one obviously has no in¸uence on the composition of the materials used, or on the structural design and all the relevant details.