Fracture Analysis of Cracking in Concrete Beams

by Neil M. Hawkins, (M.ASCE), Prof. of Civ. Engrg.; Univ. of Washington, Seattle, Wash.,
Alan H. Mattock, (F.ASCE), Prof. of Civ. Engrg.; Univ. of Washington, Seattle, Wash.,
Andreas N. Wyss, Consulting Engr.; Bern, Switzerland,

Serial Information: Journal of the Structural Division, 1977, Vol. 103, Issue 5, Pg. 1015-1030

Document Type: Journal Paper

Discussion: Albrecht Pedro (See full record)
Closure: (See full record)

Abstract: An energy balance criterion, based on fracture mechanics concepts, is proposed for predicting the loads at which concrete members develop rapidly propagating cracks. After an initial period during which microcracks increase slowly in length and extent over a critical region of the member, an unstable running crack develops when the rate of energy released by continuing microcrack growth exceeds the energy inputed to the system. The shape of the growing microcrack zone is determined by the stress intensity factors for the extremities of the principal axes of that zone. A critical strain energy release rate, Gc, is determined from direct tensile data and its appropriateness verified by showing that strength and size effects are correctly predicted for modulus of rupture specimens. Diagonal tension cracking load expressions for reinforced concrete beams are developed using that Gc value and energy criterion. Those expressions correctly predict the effects established from tests of the moment of shear ratio, reinforcement ratio, type of loading, and size of member.

Subject Headings: Cracking | Ultimate strength | Concrete beams | Load factors | Reinforced concrete | Load tests | Strain rates |

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