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Verulam

Shear in concrete slabs having concentrated loads close to supports In February, we published two letters from readers responding to a request from Mr R. N. Morgan (19 December 1989) for opinions on how to deal with this problem, he having found that the requirements contained in BS 8110 and BS 5400 could lead to significant differences in the resulting required depths of slabs. While our correspondents were able to contribute some information, they both concluded that much remained unknown. This it appears is also the opinion of Angus Low of Ove Arup & Partners. Mr Low finds in this an illustration of the necessity for more openness in our attitude to 'areas of ignorance' in the drawing up and interpretation of Codes: Mr Morgan asks about the 'black hole', otherwise known as BS 5400's treatment of shears due to wheel loads in deck slabs. This omission in the Code has been unfortunately masked by an excessively detailed treatment of punching shear. When remote from a support, shear can be considered to disperse from a wheel in four directions. When near a support almost all the shear will go direct to the support so the shear intensity will be about four times greater. Even allowing for the common haunching of deck slabs it is difficult to imagine a situation where punching shear is critical. Verulam