3D Restraint Analyses of Typical Structures with Early Age Cracking Problems

The content of this report is related to the so-called one-point method for estimation of cracking risk in young concrete. Using this type of method, the degree of restraint must be determined from linear elastic analysis, while the cracking risk thereafter may be determined by means of a time dependent uniaxial one-point stress calculation. The report considers through cracking only. Restraint factors have been calculated for three typical structures where early age cracking frequently occur; (1)Slab on grade restrained by adjoining slab (slab to slab problem); (2)Wall restrained by subgrade and foundation; (3)Top slab restrained by wall, foundation and subgrade. For the slab on grade and wall problems, the geometry has been varied over the main part of the practical range, while for the top slab a limited number of calculations have been carried out. When the critical position (i.e. the point with largest cracking risk) is assumed to lie approximately one thickness away from the casting joint, the degree of restraint vary within the following range: Slab to slab problem: 0.05-0.52 Wall on slab: 0.37-0.70 Top slab: 0.12-0.52 The critical position is strongly dependent on the thickness of the hardening structure, and is a major parameter influencing the degree of restraint.