Issue 6

Continuous steel-concrete composite bridges develop longitudinal tensile stresses in their deck slab as a result of differential strains caused by shrinkage. Analytical procedures are described whereby the shrinkage stresses along continuous, non-uniform composite beams can be estimated. The accuracy of these predictions is assessed in relation to the results of a laboratory test on a two-span continuous beam. In addition, existing design recommendations are examined and typical distributions of stresses in medium span bridges are presented. A.E. Long and P. Csagoly

The paper describes a method of estimating the elastic critical loads of multi-storey rigid frames unbraced against side-sway. A standard, linear elastic analysis is performed, choosing a defined loading pattern, and the critical load ratio is derived simply from the maximum sway index occurring in any of the storeys of the frame. The method gives estimates which are on the safe side, but always within 20 per cent of the correct result. This accuracy is shown to be sufficient for practical purposes. M.R. Horne

Professor M. R. Horne (F) : Dr. Wood has rendered an enormous service to structural engineers by the publication of this paper. The concept of effective length has been too loose a one as far as most engineers are concerned, and Dr. Wood has shown how powerful and exact a tool it can become. Its use is crucial for the design of column in no-sway frames, and its accurate exploitation for such frames, as opposed to its hitherto empirical application, must surely form the basis for any future design procedures.

I shall confine myself to fairly obvious generalities when dealing with the subject of housing. But the fact that a generality is obvious does not mean that it is universally perceived. It is one of the features of British life that the more obvious a generality, the less likely it is to be noticed. Lord Goodman

Soon British reinforced brickwork design will shift from a permissible stress approach to a limit state approach similar to that already accomplished for reinforced concrete. For the limit state shear design of reinforced brickwork beams, ultimate shear stress values must be defined as a function of the main shear parameters. The main parameters, similar to the case of reinforced concrete beams, were assumed to be the ratio of shear span to effective depth a/d, and the percentage of tensile reinforcement p. Since a review of published evidence provided little systematic data on the influence of a/d and p on reinforced brickwork strength, the authors carried out a systematic experimental investigation involving a/d and p. Results indicate a significant increase in ultimate shear stress with decreasing a/d values similar to the case of reinforced concrete beams, but, in contrast to the case of reinforced concrete beams, a virtual independence of p on ultimate shear stress. G.T. Suter and A.W. Hendry

Mr. Gordon Rose's dilemma in establishing the capacity of load-bearing walls of old buildings to the satisfaction of Authority (April) has drawn further comment; Mr. Stephen Revesz (F) considers it is timely to air this issue and offers practical, commonsense suggestions drawn from experience. He writes: We have had to deal with similar problems when converting existing buildings. In most cases the floors were found to be just adequate for domestic loading (1.5 kN/m2) but had been in use as offices for a considerable number of years. The owners had controlled storage of papers or office machinery to avoid overloading by commonsense. Verulam