EWPAA Structural Plywood and LVL Design Manual - Engineered ...

11 Plywood Stressed Skin Panels11.1 IntroductionBecause of its lightness, directional strength properties and inherent stiffness plywood is an excellentmaterial to fix to timber beam (stringer) elements to produce a composite construction. Such a structuralsystem can have the plywood skins affixed to one or both sides of the stringers. Structurally, the functionof the plywood skins is to develop the flexure stresses as in-plane tension and compressive stresses as aresult of loading the panel perpendicular to its surface.To be categorised as a stressed skin panel as shown in FIGURE 11.1 the plywood sheathing must beglued to the stringers. The necessary pressure required to effect curing of the adhesive can be applied bynailing, screwing or stapling. If plywood/stringer interconnection is sought through mechanical fastenersonly (no adhesive) full composite action will not be attained and a stressed skin system as referred to hereinwill not result.FIGURE 11.1: Component parts of a stressed skin panelThe plywood skins of roof, wall or floor panels fulfil a number of important functions, e.g. they:• develop I or tee beam action thus minimising stringer size for a given span;• provide a trafficable surface for floors or roofs which can be covered by other materials such as tiles,vinyl, etc. or sanded and suitably coated to provide an aesthetically pleasing floor;• provide a feature ceiling;• develop diaphragm action to resist in-plane horizontal wind or earthquake loads;• provide a void between skins which can be filled with insulation.The plywood stressed skin panel is also highly amenable to prefabrication thus allowing process controlprocedures to be implemented therefore ensuring the quality of the glue bonds.Maximum spans of simple stringer members is generally constrained to the 7 to 9m range, however with theavailability of LVL this range can now be extended.142