Cracks and Crack Control in Concrete Structures

Special Report Cracks and Crack Control in Concrete Structures Fritz Leonhardt Professor Emeritus Dr.-Ing. Dr.-Ing. h.c. mull. Consulting Engineer Stuttgart, FRG T he material presented in this paper is based on more than 30 years of re- search, observations and experience concerning causes, control, and conse- quences of cracking in concrete structures. This extensive background was helpful in the preparation of this paper which deals with questions of concrete cracking. The presence of cracking does not necessarily indicate deficiency in strength or serviceability of concrete structures. While currently available design code provisions lead to reasonable control of cracking, additional control can be achieved by understanding the basic causes and mechanisms of crack- Note: This paper is a revised and updated version of an article originally published in the Proceedings of the International Association for Bridge and Struc- tural Engineering (1ABSE), Zurich, Switzerland, 1987, p. 109. ing in concrete structures. In this paper, causes of concrete cracking are discussed, including tensile strength of concrete, temperature, shrinkage and creep effects. Recommended crack widths are presented along with design methods for sizing reinforcement to control crack widths. CAUSES OF CRACKING Concrete can crack due to a number of causes. Some of the most significant causes are discussed in detail. Tensile Strength of Concrete The tensile strength of concrete is a widely scattering quantity. Cracking oc- curs when tensile stresses exceed the tensile strength of concrete. Therefore, to control concrete cracking, the tensile strength of concrete is of primary im- 124

Cracks and Crack Control in Concrete Structures

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