Cross laminated timber
Plywood board (also known as Multi-layer solid wood panels , cross-laminated timber , cross-laminated timber , and timber engineering as thick timber hereinafter) is the generic term for used in construction of solid wood panels , which consists of several crosswise flat on each other glued board layers exist. In the case of glued laminated timber , on the other hand, all layers are arranged along the grain.
Using the same principle as with veneer plywood , the cross-wise construction of at least three layers achieves a high level of dimensional stability: each layer of wood prevents the change in the wood moisture content of the adjacent layers in individual boards .
Abbreviations are BSP (wood) (cross laminated timber), KLH (cross laminated timber), CLT or XLAM (cross laminated timber).
Cross laminated timber was developed in Germany and Austria in the early 1990s. The Austrian Gerhard Schickhofer completed his doctoral thesis on this wood product in 1994. In Austria, the first national guidelines on cross laminated timber were published in 2002, based on Schickhofer's research. These national guidelines "solid wood construction" pave the way for the construction of multi-storey buildings in wood construction. Gerhard Schickhofer was awarded the Marcus Wallenberg Prize 2019 for his research on cross laminated timber.
The use of cross-laminated timber in single-family houses and multi-storey residential buildings has been established in Europe since the 2000s. In individual cases, small hotels and kindergartens have also been built. The use of multilayer, solid and storey-high solid wood boards, board slats - and Brettstapel wooden elements previous methods of construction as have been timber frame and Holztafelbau partially replaced.
Properties and qualities
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Cross-laminated timber can be varied greatly in its elastomechanical properties, i.e. in its vibration behavior, through the choice of wood type, wood quality and the thickness of the individual layers. The surface quality of the cross laminated timber panels can also be designed individually. As a rule, the panels are produced in non-visible quality. For panel surfaces in visual quality, the top layer (top layer) must be designed accordingly. Depending on the property, there are top layers in a load-bearing or non-load-bearing design. Plates with three to seven layers and a total thickness of up to about 50 centimeters are common.
The tensile strength of cross-laminated timber panels is around 1.0 kilonewtons per square centimeter, and the flexural strength is slightly higher (approx. 1.1 kilonewtons per square centimeter). The burning rate, which is important for fire protection, is around 0.7 millimeters per minute.
The three-layer board has the largest market share and is offered in many hardware stores. The thickness of the top layer boards is between 4 and 9 mm, the thickness of the middle layer between 4 and 50 mm.
Three-layer panels are used for general carpentry work, but also for load-bearing and stiffening cladding of wall , ceiling and roof panels for wooden houses in panel construction, roof and ceiling panes, ventilated facades and curved surface structures.
Three-layer panels are usually produced as large-format panels with the dimensions 2,050 × 5,000 mm or 2,050 × 2,500 mm. The most common thickness of three-layer panels is 19 mm. 13 and 27 mm are also common, but panels up to 80 mm are also made.
Cross laminated timber is usually produced industrially today. Usually boards made of dry softwood are used as the raw material for the individual layers. These are glued with z. B. formaldehyde-free polyurethane adhesive almost rigidly connected to each other. Alternatively, more flexible mechanical fasteners such as nails or wooden dowels can be used. The typical structure of a cross-laminated timber board is made with board layers or single-layer boards oriented at right angles to one another . It is also possible to align the board layers at an angle of 45 degrees.
The raw material for the production of cross-laminated timber panels are rough-sawn boards. Side goods are mainly processed, i.e. relatively narrow boards from the edge zones of the sawn tree trunk. These qualities are considered inferior wood because of their limited uses, but have the best properties in terms of rigidity and strength.
Requirement for production
Proof of suitability for gluing load-bearing wooden components in accordance with DIN 1052: 2008-12, certificate A, B or C. Certificate from a body notified for monitoring the production of cross-laminated timber .
Cross laminated timber products have gained importance in modern timber construction since the 1990s . In residential construction as well as in municipal and commercial property construction, they are used as static load-bearing elements. Cross laminated timber can not only be used for the construction of external and internal walls as well as roof and ceiling elements, but also for staircases and balcony slabs. Alignment or fitting at the place of use are not necessary. Insulation, cladding and facade elements can easily be attached to the cross laminated timber.
Due to the significantly higher rigidity in contrast to lightweight or frame construction , the number and length of the stiffening wall elements can be reduced. Compared to lightweight wood structures, where fire protection is achieved with planking, cross-laminated timber panels can achieve fire resistance class F90 ("fire-resistant") without additional fire protection panels .
The industrial production of the product has now, after the first pioneering and development phase, assumed an order of magnitude relevant to the Austrian timber industry. In 2008 Austrian companies produced over 100,000 m 3 of cross laminated timber, the capacity is more than 350,000 m 3 . Alongside Austria, Germany is one of the most important cross laminated timber producers. The market for exports within Europe, but also overseas, is correspondingly large and will continue to grow. With regard to climate protection, earthquake safety, prefabrication and series production, there is increasing demand worldwide.
- proHolz Austria : Massiv über Kreuz , in: Schneid , Nr. 31, Vienna, September 2008, ISBN 978-3-902320-60-5 ( details ).
- Steffen Tobisch: Multi-layer solid wood panels - innovative materials with high performance potential . 2007, VDM Verlag Dr. Müller, ISBN 978-3-8364-2659-6
- Gerhard Schickhofer: Rigid and flexible composite with layered, flat wood structures . Graz University of Technology , Graz 2013, ISBN 978-3-85125-268-2 , doi : 10.3217 / 978-3-85125-262-0 .
- Executive Secretary of the Marcus Wallenberg Foundation: Green technology behind high rise wood-based buildings . March 22, 2019.
- Description of the family hotel Weimar which, like the Kindergarten Holzwürmchen, was built in solid wood. In: Architekten-Thueringen.de. Accessed July 2020
- Stacked board and laminated timber - Beyond Blockhaus-Charme , In: BBA-Online.de, November 5, 2002
- Erol Karacabeyli, Brad Douglas, Forest Products Laboratory (US), FPInnovations (Institute), Binational Softwood Lumber Council: CLT handbook: cross-laminated timber ( English ). FPInnovations, Pointe-Claire, Québec 2013, ISBN 9780864885548 , OCLC 820617275 .
- proHolz Austria: Constructive solid wood - data sheet cross laminated timber
- proHolz Austria: Cross-laminated timber - product overview
- ZUSCHNITT 31 "Massiv über Kreuz" (booklet on the topic of cross laminated timber)