ROLE OF TIMBER ENGINEERING HAS GROWN IN IMPORTANCE

Press, Volume CVI, Issue 31113, 16 July 1966, Page 12

ROLE OF TIMBER ENGINEERING HAS GROWN IN IMPORTANCE

(Specially written for “The Press” by

RODGER KINGSBURY)

WOOD was among the first structural materials in the primitive world; it still maintains an indispensable place in the modern age. In contrast to so many other engineering materials, it is a crop, and the supply can be renewed indefinitely.

Trees are the oldest living things. A Sierra juniper in the Stanislaus National Forest, California, is estimated to be. at least 6000 years old, while actual age determination. by ring count of the California Big tree (Sequoia gigantea) indicates an age of 4000 years. Our own oldest kauri is estimated to be 1200 years to 2000 years.

In building the Ark, probably of cedar, Noah had little knowledge of the properties of the highly complicated material with which he worked, and suffered little from the lack. The same was true later when the Egyptians invented plywood, and for the Romans in the building of their galleys.

But, when the skilled craftsmen centuries ago constructed the ingenious arches and trusses that support the high vaulted roofs of the great cathedrals of Europe, they no doubt recognised the joints and fastenings as the Achilles heel of wood construction. They would have yearned for the present day connectors and techniques had they been able to foresee them.

Many wood structures in Europe are centuries old. The most notable are the trusses in the Basilica of St. Paul at Rome, part of which was constructed in A.D. 816. Certain trusses are known to have given service for more than 1000 years. Wood users of the world have a wide choice of species, each of which exhibits to some degree properties and characteristics that are individual. Each species with its different inherent properties may be considered as a different alloy, but among the large variety of species are many sufficiently alike in properties to be used interchangeably in closely designed engineering structures.

The variety of tree species in the world Is enormous, running into many thousands, but for relatively few is systematic strength data available. In New Zealand, however, practically all the 26 indigenous and six exotic species in commercial use have their strength characteristics published. More Exact

In a paper on modern timber engineering Mr A. H. Johnston, chief structural engineer for the Ministry of Works in Christchurch, says that, since wood has been the servant of man from time immemorial, there has naturally accumulated an empirical background regarding its use. Prejudice and rule of thumb have largely been dispelled in recent decades by extensive and intensive research.

Mr Johnston says that in spite of this a great deal of timber' construction and design is still governed by that same rule of thumb and prejudice. Because wood is relatively light in weight and easy to shape and form, it lends itself readily to fabrication even by pioneer methods and tools. Where close design was not critical, wood was made to serve effectively through the centuries by employing experience, and trial and error methods, without the critical need of more intimate knowledge of properties on which many modern applications depend.

“A thorough understanding of wood, and a basic knowledge of its properties are fundamental to its intelligent use,” Mr Johnston says. “Wood is unique in that, on the one hand it can be used without much deliberation, while on the other hand it presents a greater complexity and variety of problems than perhaps any other single engineering material." Service’s Work

Virtually all the data available and timber research done, has been brought about by the New Zealand Forest Service. The forest products section of the Forest Service was split in 1947 and the Forest Research Institute set up in Rotorua. In 1962 an advisory committee on timber research was set up, membership of which represents as wide a variety of timber interests as possible, covering nearly all aspects of forestry and wood usage. At least three major developments have revolutionised timber engineering in the last 30 years. They are the modern connectors, glued laminated construction, and timber preservation techniques. Over the last decade there has been a definite trend to advanced thinking on the part of architects and engineers in terms of modem timber engineering and construction. As a result there has appeared a wide variety of imaginative structures made possible by the latest techniques. In the United Kingdom much of the credit for the impetus given is due to the Timber Research and Development Association (T.RJLD.A.). A direct result of the association’s approach was the construction of the largest hyperbolic paraboloid shell roof in the world. It was built for the Wilton carpet factory at Salisbury. While it was a product of advanced engineering design, its construction required little more than run of the mill timber, and no other [skill than that of ordinary carpenters. From the United States

almost every engineering journal shows some interesting development in timber engineering. The initial interest in the glued lamination industry was- sparked off by war-time demands, and later by the enterprise of firms. Today the timber engineering industry is competing successfully with steel and concrete.

Examples of outstanding timber construction in the United States are the great radial dome at Bozeman, Montana, which is 300 ft in diameter and one acre and two-thirds in area; and a geodesic dome at Cuyahoga Falls, Ohio, which is built around a central auditorium 222 ft in span. Supporting the roof is a dome of engineered glued laminated timbers, which rests on concrete pilasters. Some Progress In his paper on timber engineering Mr Johnston says the development of modern timber design and construction in New Zealand in the last 25 years has not been impressive, when compared with that overseas. However, there has been some progress. The first major use of split ring connectors was in the Centennial Exhibition building at Rongotai in 1940. During the Second World War the rapid construction of Army and Air Force camps, with some very large buildings, was only made possible by the use of timber connectors, and from then their use became standard practice. Glued laminated construction has become well known since the initial major project at Matamata racecourse in 1956. Nelson-type secondary schools have been built all over New Zealand with glued laminated portals, beams and trusses. Glued laminated structures are now numerous throughout the country, particularly in Auckland and Canterbury. Timber Prejudice In an article published in the Australian Timber Journal, Mr R. J. M. Sutherland, a civil engineer, of London, says that few persons would deny that there is a widespread prejudice against timber as a structural materiaL “The prospective building owner thinks of timber as a temporary, combustible material; at the best he may see images of fancy cricket pavilions, at the worst a shabby shed,” says Mr Sutherland. “The architect, on his side, frequently strives after woody finishes which sometimes he hopes to marry to the structure. This can be very successful, but it is significant that it is nearly always done on a small scale, and that when he has a large job the architect turns to steel or concrete. “The engineer, especially the younger one, looks on timber as beneath him. Steelwork is all right, reinforced concrete is proper engineering, and prestressed concrete is positively holy, but timber, no, that is the stuff for joiners.” Mr Sutherland says that it is quite clear that timber will only survive as an engineering material if a timber technology is established comparable to the existing steel and concrete tech- • nologies. This would call for . vastly greater education, ; research, mechanisation and • standardisation. “The future for structural timber could be very rosy indeed, but I suggest that ■ those with an interest in it . must choose between either ; full industrialisation or just ' the preservation of a craft. .. .” Ham Display In the last few years significant progress has been made by the Forest Research Institute towards the pro- ; vision of scientific and engineering data for the economic use of New Zealand’s timber resources. A display to demonstrate . the engineering qualities of timber was opened at Canterbury University, Ham on June 27, and wil run until August 5. Timber engineering has recently been incorporated in the degree course for the school of engineering. The display was arranged by the Forest Service at the request of the school of engineering to bring to the notice of students,, engineers, builders and architects the special features of timber as a building material. It is also open during the day from Mondays to Fridays to members of the public. It is being held on both

sides of the courtyard at the school of engineering. The display is divided Into sections on glued lamination, wood preservation, timber fasteners, non - destructive testing and research. Material for it has been provided by a number of firms and organisations including the Addington Timber Company, Ministry of Works, Railways Department, Lyttelton Harbour Board and the Timber Development Association. Much To Offer The timber officer for the Forest Service in Christchurch, Mr N. C. Clifton, believes there' are endless possibilities in the field of glued lamination for the imaginative architect and engineer. It is one of the fields in which timber has the most to offer.

Mr Clifton says an impressive example of this type of construction is the recentlycompleted Rotorua sportsdrome which has a gross floor area of 41,000 square feet. Considerable use has been made of timbers, both native and exotic, throughout the project.

The purlins and main arches to the stadium are all laminated from treated radiata. The purlins are vertically laminated in lengths continuous over two or more bays giving a total length of up to 90ft. Constant radius two-pin laminated arches span 120 ft. The arches are the largest glued laminated timber type built in New Zealand. With the purlins they required about 50,000 super feet of laminated stock.

Another major project incorporating glued laminated timber is the new forest products laboratory of the Forest Research Institute being built at Rotorua. Acoustics Good Mr Clifton said that glued lamination had excellent acoustic properties, compared with structural steel. This had been particularly noticeable in school assembly halls and church buildings. Like ordinary timber beams of large sections it had advantages over steel in a fire. “Whereas a steel beam buckles and collapses under heat, a large solid or laminated wood beam will char on the outside but will not fail. Efforts are now being made to have this attribute incorporated in the New Zealand standard building code,” he said. Sleepers and wharf decking figure prominently in the section of the display on wood preservation. Laboratory and field tests showing how wood preservatives are evaluated are also a feature of this section. As a result of the tests used, the Timber Preservation Authority has drawn up specifications based on their results which ensure that engineers can be confident in the durability of the product they are using. Treated pine has largely replaced Australian hardwood for railway sleepers, and it has been estimated that its use could save New Zealand up to £500,009 a year in overseas funds. Easy Treatment Treated timber has long been established for housing needs, and the ease of treatment of some exotic species such as radiata pine enables such timber to be used for special applications where other materials are unsatisfactory. Samples of machine stressgraded timber are shown in the section on non-destructive testing. Timber put through such a machine is tested over its total length for strength, and colour-branded according to the reading given. Standard colours have been adpoted for the different strengths. The Forest Service plays a three-fold role in timber engineering, covering research, growing the raw material and education. Years of work by the Forest Research Institute have gone into its timber design data handbook which is added to as each project is completed. A recently published section will enable engineers and architects to use glue lamination with greater confidence. In 1960-61 the Forest Service made new plantings of 9600 acres. In 1965-66 there were 20,500 acres of new forest planted, mostly in radiata pine. Douglas fir (imported as Oregon pine) Is being planted to an ever-increasing extent in New Zealand. This timber is particularly suitable for engineering, and has a considerable export potential. In the field of education the Forest Service arranges displays and exhibits at shows and fairs, and holds courses for those engaged in the timber industry. In his summary of what is

needed to stabilise and enlarge the timber industry, Mr Johnston says that continuing and increasing research, from the improvement of timber species to methods of application of new techniques must be accelerated. “With assured continuity of work, better organisation of production methods, and better labour utilisation, labour costs in the glued lamination field could be cut by up to 40 per cent. “In the New Zealand timber industry we have the men, we have the materials, we must and can acquire the ‘knowhow.’ All sections of the industry, both private enterprise and Government agencies, must co-operate and work in harmony, allowing no sectional interests or petty jealousies to hinder progress. “If it is done, I can see no reason why a flourishing timber engineering industry cannot be built up in New Zealand. If it can be done in the United States, in the United Kingdom, and in Europe, it can be done here,” Mr Johnston says.