Calculation of Deflections in Reinforced Concrete Flexural Members

. . spare that tree Mr. C. G. H. Jofeh is clearly a man concerned about nature conservancy. He writes: I read with interest the letter from Mr. A. Billingham (November 78). What interested me was not the question of what the building regulations do or do not say, but the attitude of mind of the author that I inferred from what he said about the trees. Verulam

Professor A. L. L. Baker (F): At one time it appeared that we might use a limited tensile strain normal to uniaxial load of cube strength x Poisson's ratio / E as the general criterion for ultimate strengths for all practical purposes. Indeed, if we assume that the ratio of stress over strain at the ultimate limit state is 2 x l0 to the power 6, and that the Poisson's ratio is 1 over 4.5, we can derive, for a multiaxial strained cube, an equation that fits the mean values shown in Fig A1 in the paper. It also fits the higher ranges, if E is reduced in all the terms of the basic strain equation to agree with low values indicated by the curves in Fig A4 and provided that secondary strains do not at some point reverse.

Whilst I am a firm believer in the economy obtained by the intelligent use of grade 50 steel, the submission by Mr. Needham that the present cost differential is an extra £3.50 per tonne compared with grade 43 steel is somewhat misleading. This figure is applicable only when comparing the cost of grade 43A steel with that of grade 50A steel, and is thus limited only to certain rolled sections. Significant economy by the use of grade 50 steel with rolled steel sections is doubtful, especially where deflection is the criterion. When using structural hollow sections in lattice construction, where the maximum economy in weight is possible, it is necessary to compare the cost differential between grade 43C and grade 40C. This is, I am given to understand, as much as 50 per tonne depending on the sections used. B.J. Jessup