Author: Kerensky, OA;Henderson, W;Brown, W C
First published: N/A
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Kerensky, OA;Henderson, W;Brown, W C
The paper discusses the problem of design of rafts resting on soft subgrades in which long-term deformations lead to a redistribution of reactions. Design moments and shears are calculated by assuming a uniform upthrust, and it is usual to analyse an inverted raft on column supports subjected to a uniformly distributed loading. Errors
inherent in such an approach are discussed and an alternative method is suggested. This assumes an elastic subgrade composed of very soft springs giving prominence to raft stiffness and ensuring uniform distribution upthrust. The method automatically satisfies local and overall equilibrium. A comparison of the two approaches on a raft analysed by the author for consulting engineers demonstrates the differences in design moments predicted by the two methods.
As announced in the March 1971 issue of The Structural Engineer (page 112) the Council awarded the 1971 Drury Medal to Mr. Peter Ellis, an Associate-Memberaged 24. The design submitted by Mr. Ellis was for an elevated tank for supplying water to an exhibition site. As well as the Drury Medal, Mr. Ellis receives a premium of £100.
Mr. Parkhouse has presented a simple model to represent a cellular deck without intermediate diaphragms. The model has then been analysed for various loadings to determine the corresponding transverse distribution coefficients based on deflexion and moment. The loadings and deflexions have been represented as a sinusoidal series.