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Structures should perform adequately under normal service conditions. The deformation of the structure, or any part of it, should not adversely affect its efficiency or appearance. Deflections should be limited so that other elements, such as partitions, glazing or services, are not damaged.
For buildings, BS 8110 (now superceded byby Eurocode 2, BS EN 1992, Design of concrete structures, Part 1-1, General rules and rules for buildings) gives limiting span/effective depth ratios for beams and slabs that should limit the total deflection to span/250. Calculation methods are also given for use when more accurate estimates of the deflection are required.
Traditionally, liquid retaining structures have been designed to BS 8007, Design of concrete structures for retaining acqueous liquids´. This extended BS 8110 with particular emphasis on the provision of reinforcement to control crack widths. The widths of cracks that form should be limited for aesthetic reasons or, in some structures, for watertightness, by the provision of adequate amounts of reinforcement. BS 8110 and EC2 limits widths to 0.3 mm while BS 8007 and BS 5400 give lower limits, additionally relating the permissible width to the environment. BS 8007 has now been replaced by Eurocode 2 Part 3, Liquid retaining and containmnt structures.
Vibration may be a problem in slender structures, leading to discomfort for occupants or possible damage to the structure. If possible, the source of the vibration (e.g. machinery) should be isolated from the structure.
Acknowledgement: The Concrete Society
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