GLULAM – THE NATURAL STRUCTURAL MATERIAL
The long term resource security of timber as a structural material is assured with sound forestry management and adherence to sustainable development principles established in Australia and around the world. The sustainability of a forest is measured by determining whether it can produce products, goods and services over time and maintain its own productivity. Controls are set to protect soil and water values and the diversity of plants and animals, while carrying out the production potential of the forest.
The principles of sustainable forest management are: control by a government body dedicated to a high standard of forestry management; saw log yield levels which are sustainable over time without reducing the quality and extent of the forest resource; and scientific measurement of new forest growth to ensure sustainable levels of harvesting.
The preservation of legislative security for wood production forests at all Government levels is most important, as this will safeguard future timber supply.
Australia has about 43 million hectares of native forests, predominantly made up of eucalypt. Approximately 32 million hectares is publicly owned and 11.5 million hectares of this is managed by State Forestry agencies for multiple uses. The management of multiple use forests carefully plans for the protection of habitats for plant and animal species, water catchments and soil quality. Less than 7 million hectares of native forest is available for sustainable wood production.
The waiting period for re-harvesting an area of native forest is approximately 100 years and consequently, in order to ensure sustainability of native forests, less than 1% of the sustainable wood production forests are logged each year. This production accounts for approximately 40% of Australia’s domestic timber needs.
Almost a million hectares of plantation forests have been progressively established in Australia to help meet the growing demand for timber and pulpwood products. The majority of plantation forests are fast-growing softwood and a large proportion are on land which is of marginal value to farming. The flexibility and soil requirements of the softwoods mean they are able to thrive in less fertile and acidic soils. In general, native hardwoods require more fertile, higher rainfall areas. As these are limited, to date, only 60,000 hectares of hardwood plantations have been established to supplement the seven million hectares of native wood production forests. Research is continuing into ways of making hardwood timber plantations more viable.
Approximately 30% of Australia’s domestic need for timber is supplied by plantation forests and the remaining 30%, is met by imported timber.
The global per capita consumption of timber is approximately 0.67 cubic metres per year. The fact that this figure has remained largely unchanged since 1960, indicates that the growth in world timber demand is almost precisely following the growth of world population. This is a significant trend, since world population is expected to more than double within the next century.
Less than half of the harvested timber in the world is used for industrial log uses and the greater portion is used for fuelwood. With the expected increase in demand for timber, it is vital that the timber resources world-wide are properly managed and that sustainable forest management principles are adhered to with planning for increased volumes through plantations and channelling of native resources into greater valued products.
As regrowth material increases, the yield of high grade timber will decrease, while the yield of timber suitable for structural material will increase. The sawn sizes, however, will decrease. As the demand for timber and pulpwood products increases, it will be more important to obtain the maximum value of return for the log. There is no doubt that all select grade timber that can be recovered from a log will be used by the furniture industry, however, structural grade material which may not be of sufficient size or length, may end as waste with a poor return value. This trend towards greater volume of waste from a sawn log can be diminished with glue laminating.
Glued laminated timber (glulam) is a valued added product which utilises short pieces of timber of relatively small size and joins them by gluing into large structural timber. The process of laminating removes a number of natural features which reduce the strength of timber, such as knots, sloping grain, gum vein, etc., and produces a structural member with known properties of less variability than solid timber.
There has been substantial research in glulam properties, timber adhesives used in the laminating process, lamination joints and glulam behaviour in both in-service environments and long term, over the past three decades and glulam is now accepted world-wide as a structural material of known behavioural properties.
With the acceptance of the structural adequacy of glulam and the implementation of quality control procedures, timber has retained or recaptured its traditional markets. These were previously threatened by the lack of solid timber in sizes suitable for use as structural members, and by an increased number of alternative structural products.
As trees grow, photosynthesis results in the production of oxygen and the absorption of carbon dioxide, the major cause of the greenhouse effect. Carbon dioxide is removed from the atmosphere firstly by phytoplankton in the oceans and secondly by forest cover around the world.
Trees absorb carbon dioxide and store it in wood fibre. Young, vigorously growing forests absorb far more carbon dioxide than a mature forest. As trees age, the carbon absorption process slows up and the release of carbon dioxide increases through death and decay. In the latter part of their life, trees tend to release more carbon than they absorb. This unique ability to absorb and store carbon as wood fibre means the production of forest products can make an important contribution to reducing the impact of the greenhouse effect. The harvesting of native forests and replanting, and increasing forest cover with plantation forests are important contributors.
The structural framing in a typical 180m2 house is an example of the contribution to reducing the impact of the greenhouse effect that can be made by forest products. The carbon that is stored in the timber frames is approximately 7.5 tonnes. The energy needed to convert iron ore into steel frames for the same house would add approximately 2.9 tonnes of carbon to the atmosphere
Trees use solar energy to grow and only the manufacture of the finished timber products requires other forms of energy. The energy needed to produce a tonne of structural timber is only 580 kilowatt hours, whereas producing a tonne of structural steel requires 13,920 kilowatt hours. A structural timber member is 60% of the weight of a similar structural steel member, however the energy requirement of the latter can be as much as 40 times greater.