The Behaviour of Purlins Subject to Wind Uplift (an Assessment of EC3: Part 1.3)

Code limits on deflections On 17 November last year, Dr J. B. Bellamy invited information concerning the origin of the deflection limits set out in the various structural Codes. He responds to comments that have appeared in Verulam from Roger Mead and Mr C. K. Lim: I would like to thank Mr Lim (20 April) for his quotation from Structural engineering by White, Gergely & Sexsmith which justifies the limit as a device to prevent tension craclung of plaster. Mr Lim does not give the date the book was published, but the reference to plaster rather than plasterboard suggests a date prior to World War 2, and that could explain the thinking behind the wording of current British Codes. More recent thinking would surely consider it more appropriate to control the tensile stresses in the plaster, not the deflection of that member. On that basis, the deflection clauses in many Codes are now archaic and need overhaul. Verulam

In July 1992 a colloquium was held at Pembroke College, Cambridge, to discuss the development and performance of tensioned fabric and airsupported structures. Participants included representatives from users and fabricators, as well as engineers and other specialists. The aim of the colloquium was primarily to review the performance of these structures, to understand where the shortcomings were, and to see how the reliability could be improved. The discussion did indicate that air-supported structures could be safe and reliable, but that there were many deficiencies in design, construction, and operation, which resulted in an unacceptably large number of failures. The same did not apply to tensioned fabric structures, which have a good record of reliability. The meeting to be held at the Institution on 2 September 1993 will address these problems and review whether the situation can be improved. W.I. Liddell

An all-steel sandwich punel consists of two steel facing flat plates spot-welded onto a core of stiffeners, which may consist of zed sections, tophats, channels, or corrugated sheeting. Such panels have been studied extensively, and both numerical and analytical comparisons have been reported. This paper presents a modified thick plate approach for the analysis of snndwich panels. To better appreciate the development of the proposed method, a brief review of the previous modelling techniques - i.e. closed-form solution, grillage analogy and the conventional finite element modelling - is given. K.H. Tan, T.C. Fung and T.S. Lok