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Home > Publications > International Concrete Abstracts Portal
The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts.
Title: Span/Thickness limitations for Deflection Control
Author(s): N. J. Gardner
Publication: Special Publication
Appears on pages(s): 95-114
Keywords: code provisions; deflections; long term deflections;
Abstract:Predicting the deflection serviceability of reinforced concrete members in service is fraught with uncertainties which include imperfect knowledge of the limiting serviceability criteria, the material properties and the load history including construction loads and the service load. The serviceability criteria can be immediate deflection/curvature or incremental deflection/curvature. Most codes offer two methods for control of deflections. The designer may choose to calculate the deflections and check that these computed deflections are less than arbitrary, specified allowable limits. Calculating the immediate deflections of reinforced concrete members is difficult due to the concrete cracking in the tension zones of such members. Calculating the additional deflections due to the shrinkage and creep of the concrete and the consequent redistribution of stress is extremely difficult. Alternatively the codes give specified maximum span/depth ratios for which serviceability can be assumed to be satisfied and deflections do not need to be calculated. This paper compares the deemed-to-comply span/thickness limits of AC1 318-99, CSA A23.3-94, BS 8110-85, AS 3600-94, Eurocode 2 (1992 draft), AC1 435-78 and the proposals of Gardner and Zhang (1995), Thompson and Scanlon (1988), Asamoah and Gardner (I 997) and Scanlon and Choi (1999).
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