Cross-laminated timber
Cross-laminated timber (CLT) is a subcategory of engineered wood panel product made from gluing together at least three layers of solid-sawn lumber at angles to each other.
Regular timber is an anisotropic material, meaning that the physical properties change depending on the direction at which the force is applied.
[5][6] Significant developments were then made in Austria when Gerhard Schickhofer presented his PhD thesis research on CLT in 1994.
At the same time, the first press system, utilizing water-based pressure, came on the market enabling Schickhofer and his team to think beyond the capabilities originally thought possible for CLT.
A period of substantial growth in production and projects soon followed in Germany and other European countries as a push for green buildings became more prominent.
In the through-feed process extruder heads distribute parallel threads of adhesive along the piece of lumber in an airtight system to avoid air gaps in the glue that could affect bonding strength.
To avoid additional manufacturing costs, adhesive is typically only applied to the top and bottom faces of the lumber, but edge-gluing can be done if necessary.
[1] Panel lay-up is performed next and involves laying the individual pieces of lumber together in preparation for assembly pressing.
Vacuum pressing generates a pressure of approximately 14.5 pounds per square inch (0.100 MPa), which is not always enough to address the warping potential or surface irregularities.
[14] A hydraulic press on the other hand, generates a greater pressure, ranging from 40 to 80 pounds per square inch (280–550 kPa), and applies it to specific faces of the panel.
The CLT panels are then moved to a multi-axis numerically controlled machine that makes precision cuts for doors, windows, splices, and connections.
To meet the requirements of ANSI/APA PRG 320 and ensure that the correct product has been specified, delivered, and installed, CLT panels must be marked to identify a variety of information.
This includes the grade, thickness, mill name, agency name or logo, ANSI/APA PRG 320 symbol, manufacturer designations, and a top stamp if it is a custom panel.
In September 2016 the world's first timber mega-tube structure was built at the Chelsea College of Arts in London, using hardwood CLT panels.
The structure is a curved tube in a shape of a smile touching the floor at its centre and has a maximum capacity of 60 people.
Originally proposed in 2020 by Paul Cocksedge, this bridge will cross the Liesbeek River in Cape Town, South Africa.
In order to help protect the CLT from the rain while keeping it exposed, a façade made from overlapping glass panels will be installed.
[35] Open Platform and JAJA Architects won a design competition in 2020 for their plans to create a Park n’ Play garage in Aarhus, Denmark.
The village was designed as a number of stacked studio apartment modules by London architects WilkinsonEyre, and modeled after Montreal's Habitat 67.
Mechanical properties, particularly compressive strength, are key factors to consider when designing and constructing CLT panels.
[41] To achieve optimal mechanical properties, it is important to carefully consider both the number of layers and the geometry of openings when designing and constructing CLT panels.
Studies have shown that CLT has good seismic performance due to its high stiffness and strength, as well as its ductility and energy dissipation capacity.
CLT production is also eco-friendly, generating fewer greenhouse gas emissions and using less energy than traditional materials like concrete and steel.
Finally, CLT is durable and long-lasting, with a projected lifespan of over 100 years, making it a promising option for sustainable construction.
Additionally, the connection between different layers cannot always be fully bonded, and the moisture content of the wood will change over time.
Furthermore, the impact of different opening shapes on CLT strength requires further investigation, and boundary conditions are not always simply supported.
