Developments in sandwich construction

Abstract

The research is divided into two parts. In the firstpart the structural behaviour of sandwich beams usingtimber-based facings and foamed plastic cores wasstudied. Various available theories were examined andthe most appropriate theory for this type of panel wasidentified. In an extensive test programme the relevantproperties of the constituent materials were measuredand the data used in the proposed theory of structuralbehaviour to predict beam deflections and core andfacing stresses. Corresponding sandwich beam tests werecarried out on the range of skin/core combinations andthe theoretical and experimental behaviours werecompared. Good agreement was confirmed within the rangeof span/depth ratios investigated, confirming theapplicability of the theory for semi-thick timber-basedfacings. A variety of timber based facings wereinvestigated and those most suitable for sandwichconstruction were identified.This type of panel construction has many advantages butlacks the benefit of good fire resistance. The recF.iiredfire resistance could be provided by a suitable corematerial.Part two of the research concentrated on the developmentof a new core material which was intended to have goodstructural properties at reasonable density, and to haveadequate fire resistance free from the production of smoke and toxic fumes. Coated paper honeycombs werechosen for the study. The properties of the constituentmaterials were investigated in detail and then thestructural properties of the developed cores weremeasured using methods drawn from national andinternational standards. One particular coatingcombination proved to be effective in terms ofstiffness, fire resistance, freedom from micro crackingand strength retention at high temperature. This wasbased on a mixture of sodium silicate and ball clay.Cores were tested both with cells empty (to be blockedby intumescence) and with cells filled (e.g. withlightweight filler). In the best of the developed cores,shear stiffness and transverse stiffness were muchhigher than in normal core materials. On the basis ofthe test programme, panels can be designed to give afire resistance defined by insulation of up to two hours