Glued laminated timber
Glued laminated timber, also called glulam, is a type of structural engineered wood product comprising a number of layers of dimensioned lumber bonded together with durable, moisture-resistant structural adhesives. In North America the material providing the laminations is termed laminating stock or lamstock.
By laminating a number of smaller pieces of lumber, 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. Glulam is readily produced in curved shapes and it is available in a range of species and appearance characteristics to meet varied end-use requirements. Connections are usually made with bolts or plain steel dowels and steel plates.
Glulam optimizes the structural values of a renewable resource – wood. Because of their composition, large glulam members can be manufactured from a variety of smaller trees harvested from second- and third-growth forests and plantations. Glulam provides the strength and versatility of large wood members without relying on the old growth-dependent solid-sawn timbers. :3 As with other engineered wood products, it reduces the overall amount of wood used when compared to solid sawn timbers by diminishing the negative impact of knots and other small defects in each component board.
Glulam has much lower embodied energy than reinforced concrete and steel, although of course it does entail more embodied energy than solid timber. However, the laminating process allows timber to be used for much longer spans, heavier loads, and complex shapes. Glulam is two-thirds the weight of steel and one sixth the weight of concrete – the embodied energy to produce it is six times less than the same suitable strength of steel. Glulam can be manufactured to a variety of straight and curved configurations so it offers architects artistic freedom without sacrificing structural requirements.
The high strength and stiffness of laminated timbers enable glulam beams and arches to span large distances without intermediate columns, allowing more design flexibility than with traditional timber construction. The size is limited only by transportation and handling constraints.
One of the earliest still-standing glulam roof structures is generally acknowledged to be the assembly room of King Edward VI College, a school in Bugle Street, Southampton, England, dating from 1866, designed by Josiah George Poole. The building is now the Marriage Room of Southampton Register Office.
Two churches in Northumberland are now thought to have the earliest extant uses: Holy Trinity, Cambo (1842), and Holy Trinity, Horsley (1844), and four 1850s Merseyside churches also feature laminated timbers: St Mary, Grassendale, St Luke, Formby, St Paul, Tranmere and Holy Trinity, Parr Mount, St Helens.
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. The result was the first glulam portal.
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 Müller includes a fine engraving of the railway sidings and works in 1921.
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 distinctive bell-shaped roof dome of the former Hygiene Institute, Zurich, 1911, now the main building of the University of Zurich.
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.
A significant development in the glulam industry was the introduction of fully water-resistant phenol-resorcinol adhesive in 1942. This allowed glulam to be used in exposed exterior environments without concern of gluline degradation. The first U.S. manufacturing standard for glulam was Commercial Standard CS253-63, which was published by the Department of Commerce in 1963. The most recent standard is ANSI/AITC Standard A190.1–02, which took effect in 2002.:4
The roof of the Centre Pompidou-Metz museum is composed of sixteen kilometers of glued laminated timber. It represents a 90-metre wide hexagon with a surface area of 8,000 m². The glued laminated timber motif forms hexagonal wooden units resembling the cane-work pattern of a Chinese hat.
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Glulam versus steel
A 2002 case study comparing energy use, greenhouse gas emissions and costs for roof beams found it takes two to three times more energy and six to twelve times more fossil fuels to manufacture steel beams than it does to manufacture glulam beams. It compared two options for a roof structure of a new airport in Oslo, Norway – steel beams and glulam spruce wood beams. The life cycle greenhouse gas emission is lower for the glulam beams. If they are burned at the end of their service life, more energy can be recovered than was used to manufacture them. If they are landfilled, the glulam beams result in greater greenhouse gas emissions than the steel beams. A more recent study by Chalmers University of Technology was not so optimistic. Nevertheless, it showed that while the absolute greenhouse emissions are strongly dependent on the method used to calculate them, the environmental profile of glulam is typically as good or better than steel in an example structural application. The cost of the glulam beams is slightly lower than the steel beams.
Sports structures are a particularly suitable application for wide-span glulam roofs. This is supported by the light weight of the material, combined with the ability to furnish long lengths and large cross-sections. Prefabrication is invariably employed and the structural engineer needs to develop clear method statements for delivery and erection at an early stage in the design. The PostFinance Arena is an example of a wide-span sports stadium roof using glulam arches reaching up to 85 metres. The structure was built in Bern in 1967, and has subsequently been refurbished and extended.
The roof of the Richmond Olympic Oval, built for speed skating events at the 2010 Winter Olympic Games in Vancouver, British Columbia, features one of the world's largest clearspan wooden structures. The roof includes 2,400 cubic metres of Douglas-fir lamstock lumber in glulam beams. A total of 34 yellow-cedar glulam posts support the overhangs where the roof extends beyond the walls.
Pressure-treated glulam timbers or timbers manufactured from naturally durable wood species are well suited for creating bridges and waterfront structures. Wood’s ability to absorb impact forces created by traffic and its natural resistance to chemicals, such as those used for de-icing roadways, make it ideal for these installations. Glulam has been successfully used for pedestrian, forest, highway, and railway bridges. An example in North America of a glulam bridge is at Keystone Wye, South Dakota, constructed in 1966–1967.
The Kingsway Pedestrian Bridge in Burnaby, British Columbia, Canada, is constructed of cast-in-place concrete for the support piers, structural steel and glulam for the arch, a post tensioned pre-cast concrete walking deck, and stainless steel support rods connecting the arch to the walking deck.
European Standards Organisation (CEN) standards
The following CEN standards are relevant to the topic of glulam. They are used by all of the countries that subscribe to the European Committee for Standardisation:
- EN 386 — Glued laminated timber — Performance requirements and minimum production requirements
- EN 387 — Glued laminated timber — Large finger joints — Performance requirements and minimum production requirements
- EN 390 — Glued laminated timber. Sizes. Permissible deviations
- EN 391 — Glued laminated timber – Delamination tests of glue lines
- EN 392 — Glued laminated timber – Shear test of glue lines
- EN 408 — Structural timber and glued laminated timber — Determination of some physical and mechanical properties
- EN 1193 — Timber structures — Structural timber and glued laminated timber — Determination of shear strength and mechanical properties perpendicular to the grain
- EN 1194 — Timber structures — Glued laminated timber — Strength classes and determination of characteristic values
- EN 14080 — Timber structures — Glued laminated timber — Requirements
- I joist
- Medium-density fiberboard
- Oriented strand board
- Particle board
- Pressed wood
- Laminated veneer lumber
- Timber framing
- A Guide To Engineered Wood Products, Form C800 (PDF). APA – The Engineered Wood Association. 2010. p. 7.
- Product Guide, Form No. EWS X440 (PDF). APA – The Engineered Wood Association. 2008.
- Timber Engineering Europe Ltd. Glulam beams. Timberengineeringeurope.com. Retrieved on 2015-09-27.
- "About Glulam". American Institute of Timber Construction. Retrieved 3 February 2015.
- Smith and Wallwork. "Faculty of Education". Retrieved 19 April 2016.
- Müller, Christian (2000). Laminated Timber Construction. Birkhäuser. ISBN 978-3764362676.
- Leonard, A.G.K. (Spring 2008). "Josiah George Poole (1818–1897): Architect and Surveyor serving Southampton" (PDF). Journal of the Southampton Local History Forum. Southampton City Council. pp. 19–21. Retrieved 2 June 2012.
- Sandin Peters Svanström (2014) Life cycle assessment of construction materials: the influence of assumptions in end-of-life modelling. International Journal of Life Cycle Assessment 19:723-731
- FPInnovations A Synthesis of Research on Wood Products and Greenhouse Gas Impacts page 61. Forintek.ca. Retrieved on 2015-09-27.
- Naturally:wood Richmond Olympic Oval. Imagelibrary.bcfii.ca. Retrieved on 2015-09-27.