For many concrete structures the avoidance of thermal cracks is essential, in particular when high requirements for water-tightness and durability must be met. In practice, many measures are taken to inhibit or prevent crack formation. Most of them are based purely on empirical analyses. Besides, computer-aided engineering models emerged in the past decade to, primarily, validate the effectiveness of a chosen preventive measure. Currently, complex commercial programs for computer simulations are available, which in general are deterministic processes and employ the Finite Element Method. In contrast, cracking criteria are mostly crude. Such models rely strongly on accurate data of hydration and thermomechanical properties. In consequence, the differences on forecast of cracking are substantial. In this paper, the commonly applied crack criteria are discussed. The effects of aging, stress-strain relation, micro-cracking and stress relaxation on crack formation are studied in a cut-out from an axially restrained slab. Aspects of reliability-based cracking criteria are also discussed.
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