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Glued laminated timber, commonly referred to as glulam, is a type of structural
engineered wood Engineered wood, also called mass timber, composite wood, man-made wood, or manufactured board, includes a range of derivative wood products which are manufactured by binding or fixing the strands, particles, fibres, or veneers or boards of woo ...
product constituted by layers of
dimensional lumber Lumber is wood that has been processed into dimensional lumber, including beams and planks or boards, a stage in the process of wood production. Lumber is mainly used for construction framing, as well as finishing (floors, wall panels, wi ...
bonded together with durable, moisture-resistant structural adhesives so that all of the grain runs parallel to the longitudinal axis. In North America, the material providing the laminations is termed ''laminating stock'' or ''lamstock''.


History

The principles of glulam construction are believed to date back to the 1860s, in the assembly room of King Edward VI College, a school in
Southampton Southampton () is a port city in the ceremonial county of Hampshire in southern England. It is located approximately south-west of London and west of Portsmouth. The city forms part of the South Hampshire built-up area, which also covers Po ...
, England. The first patent however emerged in 1901 when Otto Karl Freidrich Hetzer, a carpenter from Weimar, Germany, patented this method of construction. Approved in Switzerland, Hetzer’s patent explored creating a straight beam out of several laminations glued together. In 1906 he received a patent in Germany for curved sections of glulam. Other countries in Europe soon began approving patents and by 1922, glulam had been used in 14 countries. The technology was first brought to America by Max Hanisch Sr. who had been associated with the Hetzer firm in 1906 before emigrating to the United States in 1923. With no financial backing, it wasn’t until 1934 that Hanisch was able to first use glulam in America. The project, a school and community gym in Peshtigo, Wisconsin, took time to get started as manufacturers were hard to find but eventually the Thompson Brothers Boat Manufacturing Company took on the project. The Wisconsin Industrial Commission, however, rejected the arches as they had no previous experience working with glulam. A compromise was reached in which the arches could be used if they were used in conjunction with bolts, lags, metal strapping, and angles to reinforce the structure. Though the reinforcements were unnecessary, ground finally broke in late 1934 featuring four spans of three-hinged arches with clear spans of 64ft. The partnership for this project lead to the creation of Unit Structures Inc. a construction firm for glulam owned by both the Hanisch and Thompson families. In 1936, the Unit Structures patented both the forming equipment used to produce glulam arches and the glulam arches themselves. A second project, this time for the Forest Products Laboratory (FPL), gave Unit Structures the opportunity to prove the strength and stiffness of glulam members to architects and engineers. Full-scale load tests conducted by placing 31,500 pounds of sandbags on the roof exceeded the design specs by 50%. The noted deflections were also in favor of the system. While the results took some time to get published, the test enabled Unit Structures to continue building with glulam. At this time, I-sections featuring plywood webs and glulam flanges became popular in Europe while rectangular sections became the norm in America. The I-sections saved on lumber which was beneficial to Europeans as they had high lumber costs but were more labor intensive which was expensive in the states. The glulam system piqued the interest of those on the west coast and many firms began to engage with it. In 1942, the introduction of a fully water-resistant phenol-resorcinol adhesive enabled glulam to be used in exposed exterior environments without concern of glue line degradation, expanding its applicable market. During the midst of World War II, glulam construction became more widespread as steel was needed for the war effort. In 1952, leading fabricators of engineered and solid wood joined forces to create the American Institute of Timber Construction (AITC) to help standardize the industry and promote its use.The first U.S. manufacturing standard for glulam was published by the Department of Commerce in 1963. Since then, glulam manufacturing has spread within the United States and into Canada and has been used for other structures, such as bridges, as well. It is currently standardized under ANSI Standard A190.1.


Manufacturing

The manufacturing of glulam is typically broken down into four steps: drying and grading the lumber, joining the lumber to form longer laminations, gluing the layers, and finishing and fabrication. The lumber used to produce glulam may come to the manufacturers pre-dried or will have to be dried onsite. A hand-held or on the line moisture meter is used to check the moisture levels of the lumber. Each piece of lumber going into the manufacturing process should have a moisture content between 8% and 14% in accordance with the adhesive used. If a piece of lumber is above this threshold it is redried. Once the lumber is dry, knots on the ends of the lumber are trimmed and grading occurs. Lumber is then grouped based on the grading it receives. To create lengths of glulam longer than those typically available for sawn lumber, the lumber must be end-jointed. The most common joint for this is a
finger joint A finger joint, also known as a comb joint, is a woodworking joint made by cutting a set of complementary, interlocking profiles in two pieces of wood, which are then glued. The cross-section of the joint resembles the interlocking of fingers ...
, 1.1in or 2.8cm in length cut on either end with special cutter heads. A structural resin, typically RF curing melamine-formaldehyde (MF) or PF resin, is applied to the joint between successive boards and cured under end pressure using a continuous RF curing system. After the resins have cured, the lumber is planed on each side to ensure smooth surfaces for gluing. Once planed, a glue extruder spreads the resin onto the lumber. This resin is most often Phenol-resorcinol-formaldehyde, but PF resin or melamine-urea-formaldehyde (MUF) resin can also be used. For straight beams, the resinated lumber is stacked in a specific lay-up pattern in a clamping bed so that a mechanical or hydraulic system can press the lumber together. For curved beams, the same process occurs but lumber is instead stacked in a curved form. These beams are cured at room temperature for 5-16 hours before the pressure is released unless the hydraulic pressure is combined with RF curing which can reduce the length of time needed for curing. Once the glulam beams are completely cured, they are removed from the clamping system the wide, side faces are sanded or planed to remove any resin that is squeezed out between the boards. The narrow top and bottom faces may also be sanded if necessary, based on the desired appearance. The corners are often rounded as well. Specifications for appearance govern whether or not additional finishing is completed. Additional finishing may include filling knot holes with putty, sanding the beams further, and applying sealers, finishes, or primers.


Technological developments


Resin glues

When glued laminated timber was introduced to the building technology in the early twentieth century,
casein Casein ( , from Latin ''caseus'' "cheese") is a family of related phosphoproteins ( αS1, aS2, β, κ) that are commonly found in mammalian milk, comprising about 80% of the proteins in cow's milk and between 20% and 60% of the proteins in hum ...
glues, which are waterproof but have low
shear strength In engineering, shear strength is the strength of a material or component against the type of yield or structural failure when the material or component fails in shear. A shear load is a force that tends to produce a sliding failure on a materi ...
, were widely used. Joints with casein glues had detachment failures due to inherent stresses in the wood. The invention of cold-curing synthetic resin glues in 1928 ("Kaurit") and other
urea-formaldehyde Urea-formaldehyde (UF), also known as urea-methanal, so named for its common synthesis pathway and overall structure, is a nontransparent thermosetting resin or polymer. It is produced from urea and formaldehyde. These resins are used in adhesiv ...
glues solved these problems - resin glues, which are inexpensive and easy to use, are waterproof and enable high adhesive strength. The development of resin glues contributed to the wide use of glued laminated timber construction.


Finger joints

The use of
finger joint A finger joint, also known as a comb joint, is a woodworking joint made by cutting a set of complementary, interlocking profiles in two pieces of wood, which are then glued. The cross-section of the joint resembles the interlocking of fingers ...
s with glulam allowed for production of glulam beams and columns on large scale. Glulam finger joints were developed to provide broad surface area for gluing. Automatic finger-jointing machines help cut the finger joints, connect and glue them together under pressure, allowing for a strong, durable joint, capable of carrying high loads comparable to natural wood with the same cross-section.


Computer numerical control

Computer-controlled fabrication (CNC) allows architects and designers to cut glued laminated timber into unusual shapes with a high degree of precision. CNC machine tools can utilize up to five axes, which enables undercutting and hollowing-out processes. The cost-effective CNC machines carve the material using mechanical tools, like a router.


Advantages

There are several advantages to using glulam in construction: * ''Size and Shape -'' By laminating a number of smaller pieces of lumber into a single large structural member, the dimensions of glulam members are only limited by transport and handling rather than the size of a tree like sawn lumber. This also enables the use of smaller trees harvested from second-growth forests and plantations rather than relying on
old-growth forests An old-growth forestalso termed primary forest, virgin forest, late seral forest, primeval forest, or first-growth forestis a forest that has attained great age without significant disturbance, and thereby exhibits unique ecological featur ...
. Glulam can also be manufactured in a variety of shapes, so it offers architects artistic freedom without sacrificing structural requirements. * ''Versatility -'' Because the size and shape of glulam members can be so variable, they are able to be used as both beams and columns. * ''Strength and Stiffness -'' Glulam has a higher strength to weight ratio compared to both concrete and steel. Glulam also reduces the impact defects in the wood have on the strength of the member making it stronger than sawn lumber as well.  Glulam has also been proven to have a higher resistance to lateral-torsional buckling than steel.Hassan, O.A.B. and Johansson, C. (2018). Glued laminated timber and steel beams. Journal of Engineering, Design and Technology, 16(3), pp.398–417. doi:10.1108/jedt-12-2017-0130. * ''Environmentally Friendly -'' Glulam has much lower
embodied energy Embodied energy is the sum of all the energy required to produce any goods or services, considered as if that energy was incorporated or 'embodied' in the product itself. The concept can be useful in determining the effectiveness of energy-produ ...
than reinforced concrete and steel because the laminating process allows the timber to be used for much longer spans, heavier loads, and more complex shapes than reinforced concrete or steel. The embodied energy to produce it is one sixth of that of a comparable strength of steel. Also, as glulam is a wood product, it naturally sequesters carbon, keeping it from being released into the atmosphere. As long as the wood used to manufacture the glulam members comes from a sustainably managed forest, glulam is a renewable resource. * ''Fire Safety -'' While glulam is inherently flammable because it is made of wood, if it catches on fire a char layer forms that protects the interior of the member and thus maintains the strength of the member for some time.


Disadvantages

As with any system, there are some drawbacks to using glulam: * ''Material Cost -'' Glulam is generally noted to be more costly than concrete at high axial loads, though this can depend on location and its abundance of either material. While glulam beams may be cheaper than HEA steel beams in some cases, it is not a significant difference. * ''Moisture -'' Glulam, especially when used for bridge projects, is susceptible to changes in moisture which can impact its strength. When glulam was exposed to a number of wet/dry cycles, the bending strength decreased dramatically, 43.5%. * ''Dimensions -'' When compared to more common structural materials, glulam generally requires larger members to support the same load. Compared to steel, the cross-sectional area and height of a glulam member are significantly greater which may even make it impossible to use. Compared to concrete, glulam columns will be smaller for small axial loads, but once large axial forces come into play, concrete columns have a smaller cross-sectional area. * ''Biodegradation -'' As a wood product, glulam is subject to concern regarding biodegradation. In regions where there is a high risk for biodegradation, additional measures to protect the glulam need to be taken.


Applications


Sport Structures

Sport 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 The PostFinance-Arena (originally known as Eisstadion Allmend and Bern Arena) is an indoor arena in Bern, Switzerland. It is primarily used for ice hockey and is the home arena of SC Bern. It was opened in October 1967 and currently accommodates 1 ...
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.
Eastern Kentucky University Eastern Kentucky University (Eastern or EKU) is a public university in Richmond, Kentucky. As a regional comprehensive institution, EKU also maintains branch campuses in Corbin, Hazard, Lancaster, and Manchester and offers over 40 online u ...
's Alumni Coliseum was built in 1963 with the world's largest glued laminated arches, which span . The roof of the
Richmond Olympic Oval The Richmond Olympic Oval (french: Anneau olympique de Richmond) is an indoor multi-sports arena in the Canadian city of Richmond, British Columbia. The oval was built for the 2010 Winter Olympics and was originally configured with a speed skati ...
, built for speed skating events at the 2010 Winter Olympic Games in
Vancouver, British Columbia Vancouver ( ) is a major city in western Canada, located in the Lower Mainland region of British Columbia. As the most populous city in the province, the 2021 Canadian census recorded 662,248 people in the city, up from 631,486 in 2016. The ...
, 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. Anaheim Ice, located in
Anaheim, California Anaheim ( ) is a city in northern Orange County, California, part of the Los Angeles metropolitan area. As of the 2020 United States Census, the city had a population of 346,824, making it the most populous city in Orange County, the 10th-most ...
, is also an example of using glued laminated timber. Disney Development Company desired to build an aesthetic ice rink with less cost, and glulam was one of the most qualified materials in order to meet the owner's requirement. Architect Frank Gehry suggested a design with large double-curved
Yellow pine In ecology and forestry, yellow pine refers to a number of conifer species that tend to grow in similar plant communities and yield similar strong wood. In the Western United States, yellow pine refers to Jeffrey pine or ponderosa pine. In the ...
glulam beams, and the ice rink was constructed in 1995.


Bridges

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. One North American glulam bridge is Keystone Wye in the Black Hills of South Dakota, constructed in 1967. The da Vinci Bridge in Norway, completed in 2001, is almost completely constructed with glulam. The Kingsway Pedestrian Bridge in
Burnaby, British Columbia Burnaby is a city in the Lower Mainland region of British Columbia, Canada. Located in the centre of the Burrard Peninsula, it neighbours the City of Vancouver to the west, the District of North Vancouver across the confluence of the Burrard ...
, Canada, is constructed of cast-in-place concrete for the support piers, structural steel and glulam for the arch, a post tensioned
precast concrete Precast concrete is a construction product produced by casting concrete in a reusable mold or "form" which is then cured in a controlled environment, transported to the construction site and maneuvered into place; examples include precast bea ...
walking deck, and stainless steel support rods connecting the arch to the walking deck.


Religious Buildings

Glulam is used for the construction of multi-use facilities such as churches, school buildings, and libraries. The Cathedral of Christ the Light in
Oakland, California Oakland is the largest city and the county seat of Alameda County, California, United States. A major West Coast of the United States, West Coast port, Oakland is the largest city in the East Bay region of the San Francisco Bay Area, the third ...
, is one such example and uses glulam to enhance the ecological and aesthetic effect. It was built as the replacement of the Cathedral of Saint Francis de Sales, which became unusable after the Loma Prieta earthquake in 1989. The ,
vesica piscis The vesica piscis is a type of lens, a mathematical shape formed by the intersection of two disks with the same radius, intersecting in such a way that the center of each disk lies on the perimeter of the other. In Latin, "vesica piscis" litera ...
-shaped building formed the frame with a glued-laminated timber beam and steel-rod skeleton covered with a glass skin. Considering the conventional way of construction with steel or reinforced concrete moment-frame, this glulam-and-steel combination case is regarded as an advanced way to realize the economy and aesthetic in the construction. As an alternative to new-felled oak trees, glued laminated timber is proposed as the structural material in the replacement spire of , destroyed by fire in 2019.


Other

In 2019, the world's tallest structure employing the use of glulam was Mjøstårnet, an 18-story
mixed-use Mixed-use is a kind of urban development, urban design, urban planning and/or a zoning type that blends multiple uses, such as residential, commercial, cultural, institutional, or entertainment, into one space, where those functions are to som ...
building in Brumunddal, Norway. However, in 2022, the Ascent MKE building in Milwaukee, Wisconsin surpassed it with 26 stories, measuring over 86 meters tall. The roof of the Centre Pompidou-Metz museum in France is composed of sixteen kilometers of glued laminated timber intersecting to form hexagonal units. With a surface area of 8,000 m², the irregular geometry of the roof, featuring various curves and counter-curves, resembles a Chinese hat.


Failures

In 2005, researchers at
Lund University , motto = Ad utrumque , mottoeng = Prepared for both , established = , type = Public research university , budget = SEK 9 billion Siemens velodrome arena in Copenhagen collapsed when a joint between glulam
truss A truss is an assembly of ''members'' such as beams, connected by ''nodes'', that creates a rigid structure. In engineering, a truss is a structure that "consists of two-force members only, where the members are organized so that the assembl ...
es failed at the point of its dowel fastenings. * In February 2003 the roof of a newly built exhibition hall in
Jyväskylä Jyväskylä () is a city and municipality in Finland in the western part of the Finnish Lakeland. It is located about 150 km north-east from Tampere, the third largest city in Finland; and about 270 km north from Helsinki, the capital of ...
, Finland, collapsed. It was found that during construction the specified number of dowels at joints between glulam timbers were missing or had been wrongly placed. There was a collapse of the Perkolo bridge, at
Sjoa The Sjoa is a river in Innlandet county, Norway. The long river runs through the municipalities of Vågå and Sel and it provides the outlet from lake Gjende at Gjendesheim in the Jotunheimen mountains of Norway's Jotunheim National Park. ...
, Norway, in 2016 caused by a design miscalculation of stresses at joints. Following this incident thirteen road bridges of glulam construction were checked, with only minor faults found. On 15 August 2022 Tretten Bridge in
Gudbrandsdalen Gudbrandsdalen (; en, Gudbrand Valley) is a valley and traditional district in the Norwegian county of Innlandet (formerly Oppland). The valley is oriented in a north-westerly direction from Lillehammer and the lake of Mjøsa, extending towa ...
, Norway, collapsed as two vehicles were crossing. It was made with glulam and steel construction and had been erected in 2012, with a design life of "at least 100 years". The cause of the failure was not immediately apparent, although during the 2016 inspection , one joint was found to have dowels that were too short.


See also

*
Engineered Wood Engineered wood, also called mass timber, composite wood, man-made wood, or manufactured board, includes a range of derivative wood products which are manufactured by binding or fixing the strands, particles, fibres, or veneers or boards of woo ...
* Cross laminated timber *
Fiberboard Fiberboard (American English) or fibreboard (British English) is a type of engineered wood product that is made out of wood fibers. Types of fiberboard (in order of increasing density) include particle board or low-density fiberboard (LDF), med ...
*
Hardboard Hardboard, also called high-density fiberboard (HDF), is a type of fiberboard, which is an engineered wood product. It is used in furniture and in the construction industry. Description Hardboard is similar to particle board and medium-densi ...
*
I joist An engineered wood joist, more commonly known as an I-joist, is a product designed to eliminate problems that occur with conventional wood joists. Invented in 1969, the I-joist is an engineered wood product that has great strength in relation to i ...
*
Laminated veneer lumber Laminated veneer lumber (LVL) is an engineered wood product that uses multiple layers of thin wood assembled with adhesives. It is typically used for headers, beams, rimboard, and edge-forming material. LVL offers several advantages over typi ...
*
Masonite Masonite is a type of hardboard, a kind of engineered wood, which is made of steam-cooked and pressure-molded wood fibers in a process patented by William H. Mason. It is also called Quartrboard, Isorel, hernit, karlit, torex, treetex, and ...
*
Medium-density fiberboard Medium-density fibreboard (MDF) is an engineered wood product made by breaking down hardwood or softwood residuals into wood fibres, often in a defibrator, combining it with wax and a resin binder, and forming it into panels by applying high te ...
*
Oriented strand board Oriented strand board (OSB) is a type of engineered wood similar to particle board, formed by adding adhesives and then compressing layers of wood strands (flakes) in specific orientations. It was invented by Armin Elmendorf in California in 1963 ...
*
Parallam Parallel-strand lumber (PSL) is a form of engineered wood made from parallel wood strands bonded together with adhesive. It is used for beams, headers, columns, and posts, among other uses. The strands in PSL are clipped veneer elements having a ...
*
Particle board Particle board, also known as chipboard or low-density fiberboard, is an engineered wood product manufactured from wood chips and a synthetic resin or other suitable binder, which is pressed and extruded. Particle board is often confused with ...
*
Plastic composite (disambiguation) Plastic composite may refer to: * Wood-plastic composite * Composite lumber See also * Composite armour * Composite material * Fiber-reinforced composite * Plastic recycling Plastic recycling is the reprocessing of plastic waste into new p ...
* Plywood * Pressed wood *
Timber framing Timber framing (german: Holzfachwerk) and "post-and-beam" construction are traditional methods of building with heavy timbers, creating structures using squared-off and carefully fitted and joined timbers with joints secured by large wooden ...
* Plyscraper * Tretten Bridge collapse (2022)


References


External links


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
{{Wood products Composite materials Engineered wood Timber framing