Should Design Codes Consider Fracture Mechanics Size Effect?


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Title: Should Design Codes Consider Fracture Mechanics Size Effect?

Author(s): Zdenek P. Bazant

Publication: Special Publication

Volume: 134


Appears on pages(s): 1-24

Keywords: diagonal tension; failure; fracture properties; pullout tests; punching shear; shear properties; standards; structural design; structures; torsion; Design

Date: 9/1/1992

Reviews recent theoretical and experimental results on the size effect in brittle failures of reinforced concrete structures caused by the release of stored energy After summarizing the size effect law and explaining the novel concept of a brittleness number, the results of recent tests of diagonal shear failure, punching shear failure, torsional failure, and pullout failure are discussed. These results, which were obtained on geometrically similar specimens with a broad range of sizes, are found to be in excellent agreement with the theoretical size effect law. The experimental evidence is much stronger than that which was previously obtained by analyzing a large amount of test results from the literature, which were not obtained on geometrically similar specimens and were limited to a narrow size range. It is also pointed out that the test data on diagonal shear disagree with the classical Weibull-type theory of size effect, thus strengthening the theoretical argument against using this theory for the size effect in concrete structures whose maximum load is much larger than the cracking initiation load. The test results indicate that the presently considered fracture mechanics size effect ought to be incorporated into the formulas for the contribution of concrete to the ultimate load capacity in brittle failures of concrete structures. It is shown that such formulas can be based on the brittleness number. For any given structure shape, this number can be determined from size effect tests. However, prediction of this number without such test data will require some further research.