Cracks in reinforced concrete structures due to restrained imposed deformations – case studies

Abstract

Effects due to indirect actions such as thermal loading and shrinkage strains are very often neglected in the design of reinforced concrete structures. In elements with partial or full restrain of free deformations, tensile concrete stresses resulting from thermal - shrinkage effects can cause severe cracking. These elements can be long retaining walls, tank walls or other structures restrained by soil or previously casted elements like foundations. Reinforced concrete floor slabs, as integral parts of long buildings and buildings with stiff vertical elements, can be considered in this group of elements too. It is well known that effects due to restrained thermal and shrinkage movements can be avoided or minimized by undertaking suitable measures at the design and/or construction stage (construction and thermal joints, selection of optimal stiffness of vertical bearing elements, choice of proper construction methodology and concrete curing, concrete mix design etc.). Otherwise, the structure has to be designed and built to be able to withstand those effects. This paper presents the consequences of neglecting the effects due to restrained deformations of two case studies: RC flat slab in multistory building and RC wall as a part of water-retaining structure. In both cases, cracks that extend through the whole element depth have appeared during the construction process itself. The causes of occurred damages at early-age of considered structures are confirmed by comprehensive theoretical and numerical analysis. The analysis encompasses simulation of real construction history, modeling of different thermal effects (release of hydration heat and ambient temperature change) and includes real characteristics of the embedded construction materials.