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Mr. M. G. Stevens: The layout and load capacity of a typical king pile is given in Fig 1.
The empirical design method recommended by design Codes for flat slab structures assumes that ribbed and plain panels behave in the same manner under load. However, there are significant differences between the behaviour of ribbed and plain plates, the
increased ratio of flexural to torsional rigidities in a ribbed plate resulting in a substantial reduction in the load that is transmitted by torsion of the plate elements. In the existing design method, the total ultimate load design moment for each panel, which is based on thequilibrium requirement of the panel, is distributed
according to specified coefficients derived from an elastic analysis of square plain panels. A theoretical study of the moment distributions within plain and ribbed flat slab panels has been carried out, and the theoretical moment coefficients for internal,
edge, and corner panels are presented. It is concluded that the recommended coefficients should be modified for the design of ribbed panels. Suitable alternative coefficients for internal and external ribbed panels are presented. The effect of solid regions around columns is considered, and it is shown that solid regions attract higher negative moments in the column strip than are allowed for in existing design coefficients. An additional design rule that allows for these effects is proposed.
I.E. Tebbett and J.E. Harrop
We remarked in March that an arboriculturist friend considered that oak trees in this country were regenerating satisfactorily and their conservation was not at risk. That comment was engendered by a correspondent's concern over the felling of six oak trees; since then we have heard that some experts are seriously concerned about the possible invasion of oak wilt which is endemic in America and which can be carried in the American oak sapwood imported into this country for its highly decorative value. The
disease apparently spreads with great rapidity and, like Dutch elm disease, there is no treatment for it. The suggested precaution is to ban the importation of American oak wood.