ABSTRACT
The large major crack in a typical concrete structures at maximum load has the same effect as the notches in fracture specimens. In effect, well-designed structures develop, in a stable manner, large cracks which behave the same as notches. However, there is a small difference. In fracture specimens, the notches are cut precisely. In real structures, the growth of large major cracks is influenced by the randomness of material properties, originating from material heterogeneity. Thus, the major fractures in similar structures of various sizes can be geometrically similar only on the average, in the statistical sense. The concept of brittleness of structural failure, which is the opposite of ductility, is an old one, but for a long time, the definition of brittleness has been fuzzy and has not stabilized. When the extended size effect is used, the fracture energy is easy to obtain by identification with the effective crack model, as done for the classical effective crack extension.
