Codes of practice principally focus on design to resist externally applied loads, deriving the reinforcement needed to resist axial loads, bending moments and shear forces. However, many concrete elements are lightly loaded or are affected principally by other actions, such as early-age contractions, temperature and humidity effects, creep, and long-term drying shrinkage. These all generate movements, and although they rarely determine the ultimate capacity they often affect serviceability, particularly cracking. This Report considers the various types of movement and their timescales. Any cracking or deformation is usually at least the result of shrinkage and temperature added to early-age effects, and often with contributions from other sources. The importance of movement is highly dependent on whether it is restrained or not; all restraint is partial as restraints will usually give under the huge forces that can be generated. In addition, creep is beneficial in reducing the stresses induced by restraint, especially at early ages. The likelihood cracking occurring is very difficult to predict, and the strategy proposed by the Report is to assume that cracks will occur and to provide enough reinforcement to control them.
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