Developments in sandwich construction
The research is divided into two parts. In the first part the structural behaviour of sandwich beams using timber-based facings and foamed plastic cores was studied. Various available theories were examined and the most appropriate theory for this type of panel was identified. In an extensive test programme the relevant properties of the constituent materials were measured and the data used in the proposed theory of structural behaviour to predict beam deflections and core and facing stresses. Corresponding sandwich beam tests were carried out on the range of skin/core combinations and the theoretical and experimental behaviours were compared. Good agreement was confirmed within the range of span/depth ratios investigated, confirming the applicability of the theory for semi-thick timber-based facings. A variety of timber based facings were investigated and those most suitable for sandwich construction were identified. This type of panel construction has many advantages but lacks the benefit of good fire resistance. The recF.iired fire resistance could be provided by a suitable core material. Part two of the research concentrated on the development of a new core material which was intended to have good structural properties at reasonable density, and to have adequate fire resistance free from the production of smoke and toxic fumes. Coated paper honeycombs were chosen for the study. The properties of the constituent materials were investigated in detail and then the structural properties of the developed cores were measured using methods drawn from national and international standards. One particular coating combination proved to be effective in terms of stiffness, fire resistance, freedom from micro cracking and strength retention at high temperature. This was based on a mixture of sodium silicate and ball clay. Cores were tested both with cells empty (to be blocked by intumescence) and with cells filled (e.g. with lightweight filler). In the best of the developed cores, shear stiffness and transverse stiffness were much higher than in normal core materials. On the basis of the test programme, panels can be designed to give a fire resistance defined by insulation of up to two hours.