Time-Dependent Cracking and Crack Control in Reinforced Concrete Structures


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Title: Time-Dependent Cracking and Crack Control in Reinforced Concrete Structures

Author(s): R. I. Gilbert

Publication: Special Publication

Volume: 225


Appears on pages(s): 223-244

Keywords: crack control; cracking; creep; direct tension members; flexural members; reinforced concrete; restraint; serviceability; shrinkage; structural behavior; time-dependent behavior

Date: 3/1/2005

Cracking caused by both shrinkage and external loads in reinforced concrete members is examined both experimentally and analytically. The mechanisms of cracking and the factors affecting the time-varying width and spacing of flexural cracks in beams and slabs and direct tension cracks in longitudinally restrained members are examined. Laboratory tests on twelve reinforced concrete beams and slabs subjected to sustained service loads were conducted in order to measure and quantify the effects of steel area, steel stress, bar diameter, bar spacing, concrete cover, concrete strength and concrete shrinkage on the extent of flexural cracking and the width of flexural cracks both immediately after loading and in the long-term after almost 400 days under load. In addition, an analytical procedure is presented that models time-dependent cracking. Use is made of the tension chord model developed by Marti et al.1 which is here modified to study the tensile zone of a flexural member and the time-dependent effects of creep and shrinkage. A second series of tests on longitudinally restrained slab specimens is also reported and the analytical procedure is extended to model the time-dependent development of direct tension cracking.