TU Graz/ Research/ Fields of Expertise/

Timber in Building Construction – Nature Meets High Tech

Timber is an ingenious building material that is gaining increasing significance: it is renewable, sustainably cultivable and preserves the environment due to its ability to store CO2. New technological developments and construction techniques pave the way to innovative timber building designs such as higher buildings with ten storeys and more. Researchers in the Sustainable Systems Field of Expertise develop and improve the so-called cross-laminated timber (CLT) construction technique for solid timber construction. Developed by the Institute of Timber Engineering and Wood Technology of TU Graz, in co-operation with the holz.bau forschungs gmbh Competence Centre, this innovative cross-laminated timber comprises several layers of solid timber glued together crosswise measuring a length of up to 20 metres, a width of 4 metres and any desired thickness depending on the number of layers used. These solid timber elements are particularly stable and load bearing, and they are easy to process, shape and even curve using modern manufacturing technologies. Buildings made of CLT are environmentally friendly and sustainable. Since almost half of Austria’s state territory and even two-thirds of the Province of Styria are forested, timber plays a key role in regional and national economy.

Timber as a Past, Present and Future Building Material

How can a renewable material such as timber best meet the requirements of resource-saving and environmentally friendly construction techniques? One solution lies in the use of cross-laminated timber. Internationally known as Cross Laminated Timber (CLT), this revolutionary construction material was developed around 25 years ago by leading researchers from the Institute of Timber Engineering and Wood Technology at TU Graz together with holz.bau forschungs gmbh Competence Centre. It consists of several layers of solid timber, which are glued together cross-wise, mostly using conifers such as spruce, larch or pine, but also deciduous species such as birch, ash and beech. These layers of wood are processed to form solid timber elements of up to 20 metres in length and 4 metres in width, while the number of layers used determines their thickness. In recent years, CLT has meanwhile developed from a niche product into an internationally much sought after and industrially manufactured product. As a result, it is now possible to construct multi-storey buildings in addition to single-family /multi-family dwellings and buildings for commercial and industrial use. According to Gerhard Schickhofer, Head of the Institute of Timber Engineering and Wood Technology, this solid timber building technique is in great demand all over the world: These cross-wise bonded solid timber elements can be used for buildings of up to ten storeys, like the one in Melbourne, Australia. In Vienna, even a 24-floor building is currently in the planning stage. We are talking about timber buildings in really large cities, cities that are already prioritising this construction technique.

Source: holz.bau forschungs gmbh

Solid timber elements are manufactured from layers of wood that are glued together orthogonally, allowing spaces for windows and doors to be cut out easily.

Source: Schickhofer
Gerhard Schickhofer, Head of the Institute of Timber Engineering and Wood Technology

An ever-increasing number of buildings in urban areas is being built with cross-laminated timber: hotels, schools, offices and multi-storey residential housing. Building with this fabulous product has great potential!

Source: holz.bau forschungs gmbh

The production of large span wall, roof and ceiling components allows for a very high level of prefabrication. Loadbearing structures can be erected in a very short time. 

 

Further Information

Head of the Institute of Timber Engineering and Wood Technology
Inffeldgasse 24/I
8010 Graz, Austria 
www.lignum.tugraz.at

Gerhard SCHICKHOFER
Univ.-Prof. Dipl.-Ing. Dr.techn.
Head
Phone: +43 316 873 4600
gerhard.schickhofer@tugraz.at

holz.bau forschungs gmbh
Inffeldgasse 24/I
8010 Graz, Austria

Manfred AUGUSTIN
Dipl.-Ing.
Managing director
Phone: +43 316 873 4604
manfred.augustinnoSpam@tugraz.at 
www.holzbauforschung.at

Source: holz.bau forschungs gmbh

Cross Laminated Timber Offers a Host of Convincing Advantages

Buildings made from cross laminated timber are climate-friendly, sustainable and economical. CLT offers a whole host of other advantages, too:

  • Although the primary material used was originally lumber of inferior quality, the boards were derived from the outer parts of the trunk, which are especially strong and stiff and particularly well suited for processing. Meanwhile, due to increased demand, so-called centre boards are chiefly used.
  • These solid timber elements are particularly stable due to the fact that their layers are glued together longitudinally and transversely. As a result, they undergo no normal changes in dimension due to humidity fluctuation, which is otherwise typical for wood.
  • Industrial robots can easily manufacture cross-laminated timber into practically any desired configuration – even curved CLT elements.
  • CLT is a construction material that is easy to handle and assemble.
  • Buildings made of CLT are extremely earthquake-resistant.
  • Buildings made of CLT are erected very quickly; it is also possible to manufacture module-like room cells in a simple process.
  • Buildings made of CLT are characterised by slender wall constructions, high loadbearing capacity and excellent fire resistance and sound insulation properties.
  • Solid timber walls are equally suitable for temporary buildings to provide flexible living possibilities for limited periods of use. They are of considerably higher quality than, and similarly economical as, for example, steel containers, providing they are planned and constructed accordingly.
  • Building products made of timber are recyclable after use.

Lots of convincing reasons, therefore, why Japan, for instance, has decided to realise solid timber construction using cross-laminated timber on a comprehensive scale and to co-operate closely with researchers from TU Graz!

Application-oriented Research

In order to exploit maximum technical potential of the solid timber construction technique, researchers from both Graz research institutions are refining the CLT method even further. With a focus on application-oriented research, but also including basic research projects, they:

  • develop complete construction kits and/or components that are delivered in a prefabricated state and connected either at the factory or on-site using innovative joining techniques such as self-tapping wood screws or system connectors.
  • develop combined products based on CLT and other timber materials, or building components consisting of high-performance timber hybrids (e.g. timber-steel or timber-concrete structures) for new application areas such as large span floor, wall and roof elements.
  • optimise the production of panels, e.g. the gluing process, and test the practicability of alternative wood species in a variety of combinations, for instance, deciduous species such as birch or beech.
  • test the loadbearing, deformability and vibration behaviour and structural properties of the elements.
  • strive to research and develop novel joining techniques such as gluing metal and/or wooden materials into CLT elements or bonding construction components with even greater dimensions, e.g. by means of screw-press adhesion. 
Source: holz. bau forschungs gmbh

CLT panel made from birch in a bending test

Source: holz.bau forschungs gmbh

Testing of loadbearing, deformability and vibration behaviour and the structural parameters of cross-laminated timber elements and alternative wood species. The above photo, for example, shows a point-loaded CLT panel measuring 2.5 x 4 metres in a test.

Source: holz.bau forschungs gmbh

Cyclic testing of a CLT wall connection

Source: holz.bau forschungs gmbh

Ascertaining vibration parameters of CLT panels in the lab

Source: holz.bau forschungs gmbh

Our Leading Concept Is: Construction System = Element + Joining Technique

One of the building industry’s key future requirements will be to develop cost-efficient and affordable buildings. This could be implemented, for instance, by providing the highest possible degree of prefabrication at the factory in combination with defining clearly structured construction systems, for which CLT is particularly well suited.

The current research programme in the frame of the FFG-COMET K project focus_solid_timber-solutions (focus_sts), which is led by a consortium (hbf), is subdivided into three areas based on the following leading concept:

Construction system (or components) =
element + joining technique

AREA 1

Development of components or systems for roofs, floors (ribbed floors and hybrid structures) and walls as well as stiffening and stabilising systems consisting of cross-laminated timber:
In the process, the vibration behaviour of CLT flooring systems is tested in the lab. Target-oriented leading details are derived from these findings to help standardise the construction technique, for example, in order to meet requirements of proper construction such as piping and HVACR. Implementation of a user-friendly and dynamically serviceable Wikipedia System for CLT and programming of a free CLT measuring programme (CLTdesigner) are already in the pipeline. 

AREA 2

Questions relating to (further) product development, testing procedures and calculation of CLT:
 resource-saving CLT production and characteristic rolling shear properties of CLT are in focus. Production of CLT from various deciduous species, e.g. birch, was investigated and successfully validated. Additional research was done on CLT shear parameters. The Formulation of Loadbearing Models work programme involves investigation into combined stresses as well as stability behaviour (buckling, bending and warping) of CLT components. Topics concerned with local load transmission in walls and floors, and mechanical description of the load-carrying behaviour of ribbed base plates (combination of CLT and laminated timber) have already been completed. One special highlight was to test point-supported CLT floors in standard dimensions as well as perform the respective structural modelling. 

AREA 3

Research and development of joining techniques (VT):
This involves investigating joining techniques in general and specifically for CLT. CLT is excellently suited for use under dynamic stress forces (e.g. earthquakes, see photo 4). Since modern and efficient timber construction would be inconceivable without fully threaded screws, a number of tests were carried out to that extent: single and group testing of lateral and narrow surfaces, block shears, fatigue behaviour, hydrogen embrittlement, combined pull-out and shear loads and development of a micrometer screw gauge, amongst many other things. Besides developing system connectors and designing a monitoring system, screw press adhesion is of great relevance for the future of the product CLT as a construction system. Researchers with special interest in cost efficient construction techniques are investigating possibilities of gluing in steel sheets and timber materials at the factory and then joining the components, for instance, just like steel connections.

Collaboration for Success

In order to achieve specific research targets, engineers and scientists from the Institute of Timber Engineering and Wood Technology at TU Graz collaborate with holz.bau forschungs gmbh Competence Centre in the Sustainable Systems Field of Expertise at TU Graz, and internationally with numerous other research institutions.

 

Selected National Cooperation Partners

  • HCS - Wood Cluster Styria, Graz 
  • Holzforschung Austria, Vienna (fully-owned subsidiary of the Austrian Society for Wood Research)
  • Ingenieurholzbauverband, Graz (Association of Structural Timber Engineers)
  • Institute of Building Construction, TU Graz
  • Institute of Materials Science and Welding, TU Graz
  • Institute of Automation and Control, TU Graz
  • Laboratory for Structural Engineering, TU Graz
  • pro:holz Austria, Vienna
  • pro:holz Styria GmbH, Graz 

Selected International Cooperation Partners

  • ETH Zurich, Switzerland
  • Japan Cross Laminated Timber Association
  • Karlsruhe Institute of Technology (KIT), Germany
  • Technische Universität München (TUM), Germany
  • University of British Columbia, Canada