This paper mainly focuses on the cracking problem of concrete structures, researches on the biaxial tensile strength of cement concrete. The biaxial tensile instrument is used for material test, the biaxial tensile strength formula is proposed, and the theoretic formula is deduced by Hill criterion. With the test data analysis, it shows that the calculating value and the testing value fit well. The biaxial tensile strength of cement concrete is about 15%~30% lower than its uniaxial tensile strength, putting up significant biaxial tensile strength weakening effect. This kind of weakening effect is important for designs of large-span beam, plate and shell structures under complex stress.
Using PCER (post-crack energy ratio) method, the influence of strength grade and curing age on flexural toughness of plain concrete were analyzed. Results show that along with the increase of strength grade and curing age, the flexural toughness of plain concrete decrease; and along with the increase of the K value used in the calculating equation, the flexural toughness of plain concrete decrease too. Meanwhile, the changing tendency of PCER value along with the K value manifests that when evaluating the flexural toughness of different quality concrete, the same K value should be used.
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