Softening of Concrete in Torsional Members - Theroy and Tests


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Title: Softening of Concrete in Torsional Members - Theroy and Tests

Author(s): Thomas T. C. Hsu and Y. L. MO

Publication: Journal Proceedings

Volume: 82

Issue: 3

Appears on pages(s): 290-303

Keywords: angle of twist; beams (supports); building codes; compatibilitymethods; compressive strength; computer programs; cover; cracking (fractur-ing);

Date: 5/1/1985

In 1929 Rausch derived an equation to predict the torsional strength of reinforced concrete members based on a space truss model. This equation, however, overestimates the actual torsional strength of a member. During the past five decades three approaches have been proposed to modify this equation: (I) the addition of an efficiency factor for reinforcement, (2) an arbitrary definition for the centerline of the shear flow, and (3) the deletion of the concrete cover. Al-though these methods are satisfactory for practical design purposes, in theory they are unsatisfactory because arbitrary assumptions were made to artifically bring Rausch’s equation in line with the test results. The unconservative nature of Rausch’s equation is caused by the softening of concrete due to diagonal cracking. Using a new stress-strain curve for softened concrete, a new theory is presented in this paper which predicfs the torsional behavior of 108 test beams available from the literature. This theory can predict not only the torsional strength but also the angles of twist, the steel strains, and the concrete strains throughout the loading history.