Concrete under tension exhibits a great degree of post-peak non-linearity. Current design codes assume the tensile strength of concrete to be negligible, which is not only a gross oversimplification of the fracture process of concrete in tension, but is also overly conservative. However, research in the field of fracture mechanics has produced models that can accurately predict crack propagation in concrete using fracture parameters determined from testing. One of these models, which is both simple and reasonably accurate, estimates the post-peak tensile behavior of concrete as a bilinear approximation of the softening curve, known as the bilinear cohesive crack model. The American Concrete Institutes Committee 446 is developing a draft test method, ACI 446-5, which determines the key fracture parameters of the bilinear cohesive crack model using three-point bend notched beam tests. ACI 446-5 currently contains errors and some impractical methods, combined with complex and often obscure equations for the determination of the bilinear cohesive fracture parameters. To remedy this, the equations for the calculation of the fracture parameters of the bilinear cohesive crack model are derived, and the experimental methods examined and criticized. Experiments of normal strength concrete notched beams of three different sizes were also performed using the guidelines for Level II testing, provided in Chapters 2 and 4 of ACI 446-5, with modifications as needed in the case of ambiguity or impracticality. The results are analyzed and discussed, and potential size dependence of the fracture parameters is discussed. With the corrections provided in this thesis, ACI 446-5 is concluded to be adequate for the determination of the fracture parameters of the bilinear cohesive crack model, and modifications are suggested to improve the test method.'
Concrete beams--Testing, Concrete beams--Fatigue, Fracture mechanics.
Level of Degree
First Committee Member (Chair)
Second Committee Member
Chapman, Scott. "Clarification of the notched beam Level II Testing Procedures of ACI 446 Committee Report 5." (2012). http://digitalrepository.unm.edu/ce_etds/57