Glued laminated timber

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, horizontal beams, and arches. Glulams are readily produced in curved shapes and is available in a range of species and appearances.[1] Connections are usually made with bolts or steel dowels and steel plates.

Glulam optimizes the structural values of wood. Because of their composition, large glulam members can be manufactured from a variety of smaller trees harvested from second-growth forests and plantations. Glulam provides the strength and versatility of large wood members without relying on the oldgrowth-dependent, solid-sawn timbers. [2]^: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 it entails more embodied energy than solid timber. However, the laminating process allows the timber to be used for much longer spans, heavier loads, and more complex shapes than reinforced concrete or steel. Glulam is one tenth the weight of steel and one sixth the weight of concrete; the embodied energy to produce it is one sixth of that for a comparable strength of steel.[3] Glulam can be manufactured to a variety of shapes, so it offers architects artistic freedom without sacrificing structural requirements.

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Glulam arches of the Sheffield Winter Garden

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.[4]

Glulam dome roofing the tower of the University of Zurich, built using the Hetzer system in 1911.

Curved glulam-framed building at the Faculty of Education, University of Cambridge.[5]

One of the earliest still-standing glulam roof structures is generally acknowledged[6] 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.[7]

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 in Parr Mount, St Helens..

The first industrial patented use was in Weimar, Germany. In 1872,[6] Otto Hetzer set up a steam sawmill and carpentry business in Kohlstrasse. Beginning in 1892, he took out a series of patents, including one 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 awarded in 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 1909, the Swiss engineering consultants Terner & Chopard[6] 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 the firm Unit Structures in Peshtigo, Wisconsin, to manufacture structural glued laminated timber. The first building in the United States to use structural glued laminated timber was a school gymnasium in Peshtigo.[8]

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 published by the Department of Commerce in 1963.[2]^:4

The roof of the Centre Pompidou-Metz museum in France 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.

It is made of dimensional lumber; trued, finished and glued on the faces; with the grain laying parallel to layers above and below. The individual lumber is selected and positioned according to defects and grain structure to maximize structural integrity. It can be made for straight, cambered and bent/arch applications, and other arrangements. It is available in standard dimensional and custom sizes.

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 are a worse alternative than steel because of the methane emission.[9] 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 as or better than steel in an example structural application.[10] The cost of the glulam beams is slightly lower than the steel beams.[11]

• Cross laminated timber
• Fiberboard
• Hardboard
• I joist
• Laminated veneer lumber
• Masonite
• Medium-density fiberboard
• Oriented strand board
• Parallam
• Particle board
• Plastic composite (disambiguation)
• Plywood
• Pressed wood
• Timber framing

• Glulam Beam Repair/Reinforcement – An article (Printed in STRUCTURE magazine, Sep. 2006) by Gary W. Gray P.E. and Paul C. Gilham P.E.
• Timber Engineering Europe Glulam
• Canadian Wood Council Glulam