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20 Pages

FractureMechanicsofConcrete : Concepts , ModelsandDeterminationofMaterialProperties

Concrete structures are full of cracks. Failure of concrete structures typically involves stable growth of large cracking zones and the formation of large fractures before the maximum load is reached. Yet design is not based on fracture mechanics, even though the basic fracture mechanics theory has been available since the middle of this century. So why has not fracture mechanics been introduced into concrete design? Have concrete engineers been guilty of ignorance? Not at all. The forms of fracture mechanics which were available until recently were applicable only to homogeneous brittle materials such as glass, or to homogeneous brittle-ductile metals. The question of applicability of these classical theories to concrete was explored long ago - the idea of using the stress intensity factor appeared already in the early 1950’s (e.g., Bresler and Wollack, 1952) and serious investigations started in the 1960’s (e.g., Kaplan, 1961, and others). But the answer was, at that time, negative (e.g., Kesler, Naus and Lott, 1971). As is now understood, the reason was that in concrete structures one must take into account strain-softening due to distributed cracking, localization of cracking into larger fractures prior to failure, and bridging stresses at the fracture front. A form of fracture mechanics that can be applied to such structures has been developed only during the last decade.