Plywood as a structural medium
THE efficient use of timber in struc- tural engineering has come about by the development of durable synthetic resin glues with a shear strength and permanence equal to, and often better than, the timber which they bond together. One result of this develop- ment is the production of exterior grade plywood with many valuable structural uses, particularly in the fabrication of components.
Although wood veneers were used decoratively in Ancient Egypt (1500 BC) it was not until the beginning of this century that plywood became established as a new sheet form of wood.
The aircraft industry recognised plywood's advantages of strength/ weight ratio and rigidity but its struc- tural use could not be developed until the use of adequate waterproof ad- hesives provided the necessary durabi- lity. In the 1930's came the develop- ment of hot pressed plywood with synthetic resin adhesives which has a durability nearly always emphasised by the term 'Weather and Boil Proof (WBP plywood): during World War II this sheet form of timber was available for extensive use in aircraft, boats and building construction.
With standardised production to a rigid specification along with struc- tural design data, mechanical proper- ties and low cost, Canadian fir ply- wood became particularly suitable for general structural use in the building industry. The Plywood Manufacturers of British Columbia (PMBC) establish- ed overseas offices in the 1950's to advise on and promote the use of fir plywood which, from 1962 have been backed by information from their own structural testing and research labora- tory in Vancouver.
Standardisation of production of Finnish Birch structural plywood and clarification of its structural strength and elasticity characteristics (by Niskanen in Finland 1960-62) was followed by the Finnish Plywood Development Association (FPDA)
By Ian H. Paxton
A partner in the chartered civil and structural engineering firm of lan H.Paxton, G. Thompson and Associates, UK, Mr. Ian H. Paxton, MA(Cantab), MICE, AMIStructE, AIWSc, first became interested in plywood as a structural material in 1955 when he was consulted for the design of a shallow roof slab incorporating a cantilever with a light in-place weight, to be supported mainly on a glazed shop front. Since then he has designed plywood structures throughout the UK and for export to Ghana, Aden and Bahrein, and has provided a structural design service for plywood components manufac- tured from local plywood in Canada and Portugal.
establishing overseas offices to provide technical information and promotion for Finnish Birch plywood.
British-made structural plywood is manufactured from imported tropical hardwoods and a standard specifica- tion was laid down in 1965 by the Association of British Plywood and
Veneer Manufacturers (ABPVM), which enabled the manufacture publi- cation of structural design data and properties for this plywood type.
These events, set beside the establi- shment of rapidly expanding plywood industries in other timber producing areas such as Malaysia, testify to
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One of the louvred canopies, constructed of plywood, over the two main entrances to the Mersey Tunnet. They act as screens to soften the glare of the sun and provide a transition from darkness to light for drivers leaving the tunnel
Far East BUILDER, November 1969
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