Glued Laminated Timber
Glulam frame for the roof of a building.
Glued laminated timber, also called Glulam, is a type of structural timber product composed of several layers of dimensioned timber glued together.
By laminating several smaller pieces of timber, a single large, strong, structural member is manufactured from smaller pieces. These structural members are used as vertical columns or horizontal beams, as well as curved, arched shapes. Connections are usually made with bolts or plain steel dowels and steel plates.
Like other engineered wood products, glulam represents an efficient use of available resources. Whilst demand for lumber continues to increase worldwide, the reduction in availability of high-quality, large-diameter logs has combined with environmental concerns and changes in forestry management practices to make larger sections and long lengths of solid timber increasingly less economical and more difficult to procure. Glulam utilises smaller readily available sections that are efficiently end-jointed using bonded finger joints. Glulam is stronger and stiffer than similar-sized members made of solid wood. This is achieved by grading during manufacture, together with the statistical effects of dispersing defects. Glulam also suffers less from movement due to moisture changes in use, because the individual laminations are dried to a close tolerance during manufacture.
Glulam is a demonstrably sustainable alternative[citation needed] to concrete and steel. Furthermore it has much lower embodied energy than these, although of course glulam does entail more embodied energy than solid timber. However the laminating process allows timber, a generally environmentally benign material, to be used for much longer spans, heavier loads and complex shapes.
One of the earliest still-standing glulam roof structures is generally acknowledged to be the assembly room of King Edward College, a school in Southampton, England. Other examples of 19th-century British glulam have also been identified. The first industrial patented use was in Weimar, Germany. Here in 1872 Otto Hetzer set up a steam sawmill and carpentry business in Kohlstrasse. Beginning in 1892, he took out a series of patents. DRP No. 63018 was for a ventilated timber floor deck that could be tightened laterally after installation, to compensate for shrinkage. Hetzer continued to patent various ingenious systems, but the first of these that could be compared with subsequently standardised horizontal glulam was DRP No. 197773, dated 1906. This entailed vertical columns which transitioned into curved glued laminated eaves zones, and then became sloped rafters, all in a single laminated unit. Each component, bonded under pressure, comprised three or more horizontally arranged laminations. In other words, the glulam portal frame was born. In 1895, Hetzer moved his company to Ettersburger Strasse, still in Weimar. At the height of production, in around 1917, he employed about 300 workers, and Mller includes a fine engraving of the railway sidings and works in 1921
Glulam dome roofing the tower of Universitt Zrich, built using Hetzer system in 1911.
In 1909, the Swiss engineering consultants Terner & Chopard purchased permission to use Hetzer's patent, and employed glulam in a number of projects. These included the the former Hygiene Institute, Zurich, 1911, now the main building of the university, where the bell-shaped roof dome is still to be seen.
The technology arrived in North America in 1934 when Max Hanisch, Sr., who had worked with Hetzer at the turn of the century, formed a firm in Peshtigo, Wisconsin to manufacture structural glued laminated timber.
Glulam bridges As well as being used in buildings, glulam is applied to construct timber bridges. The ability described above to form large cross sections, long lengths and curved shapes makes it advantageous for this purpose. Laminated timber bridges include not only pedestrian footbridges, of which many examples are found, but also road bridges. An example in North America of the latter is at Keystone_Wye, South Dakota, constructed in 1966 - 7. Here two associated glulam arch bridges create a unique interchange having impressive architecture.
References
^ a b c Mller, C. Laminated timber construction, Birkhauser, ISBN 3-7643-6267-7, Basel, 2000
See also
Engineered wood
Fiberboard
Hardboard
Masonite
Medium-density fiberboard
Oriented strand board
Particle board
Plywood
Pressed wood
Laminated veneer lumber
External links
American Institute of Timber Construction
Glued Laminated Timber Association (UK)
Glulam 'the naturally engineered solution' from BKTS (UK)
Glulam Beam Repair/Reinforcement - An article (Printed in STRUCTURE magazine, Sep. 2006) by Gary W. Gray P.E. and Paul C. Gilham P.E.
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