Stress and strain of cracked sections

Cracks occur in reinforced and partially prestressed members when the stresses exceed the tensile strength of concrete. After cracking, the stresses in concrete normal to the plane of the crack cannot be tensile. Thus, the internal forces in a section at the crack location must be resisted by the reinforcement and the uncracked part of the concrete cross-section. The part of the concrete cross-section area which continues to be effective in resisting the internal forces is subjected mainly to compression and some tension not exceeding the tensile strength of concrete. At sections away from cracks, concrete in tension also contributes in resisting the internal forces and hence to the stiffness of the member.