Definition, Characteristics, and History of CLT
– CLT is a subcategory of engineered wood, made by gluing together at least three layers of solid-sawn lumber.
– Each layer is usually oriented perpendicular to adjacent layers, achieving better structural rigidity.
– CLT is similar to plywood but with thicker laminations.
– CLT was first developed in the 1920s by Frank J. Walsh and Robert L. Watts.
– The first patent resembling CLT was patented in France in 1985.
– CLT production started in Austria in 1998 after gaining approval from government bodies.
– CLT gained momentum in Europe but was slow to take off in North America.
– Austria created the first national CLT guidelines in 2002.
– The International European Technical Assessments (ETA) regulate CLT properties and design since 2006.
– Efforts to standardize CLT in Europe started in 2008.
– The first European product standard for CLT, EN 16351, was approved in 2015.
– CLT was incorporated into the International Building Code and researched for fire safety by the NFPA.
Manufacturing Process and Quality Control of CLT
– The manufacturing process involves nine steps, including lumber selection, planing, and adhesive application.
– Moisture content check and visual grading are performed during primary lumber selection.
– Lumber is grouped based on strength and aesthetic purposes.
– Planing improves the surfaces of the timber to reduce oxidation.
– Adhesive is applied using through-feed or side-by-side nozzle methods.
– Quality control machining ensures desired thickness and precision cuts for doors and windows.
– CLT panels must be marked to identify grade, thickness, manufacturer, and other information.
– Markings should be stamped at intervals of 8 feet or less.
– CLT panels must be protected during shipping to maintain structural integrity.
– CLT must meet the requirements of ANSI/APA PRG 320 for correct specification, delivery, and installation.
Applications and Uses of CLT
– CLT is used in construction for walls, floors, and roofs.
– It is suitable for both residential and commercial buildings.
– CLT offers faster construction times compared to traditional methods.
– It provides excellent thermal and acoustic insulation properties.
– CLT is considered a sustainable and environmentally friendly building material.
Advantages and Challenges of CLT
Advantages:
– Design flexibility: CLT can be used for walls, floors, and roofs, with easily varied panel sizes.
– Environmentally conscious: CLT is renewable, green, and sustainable when sourced from managed forests.
– Carbon capture: CLT sequesters carbon, contributing to reduced net carbon emissions.
– Prefabrication: CLT panels are fully fabricated off-site, enabling quicker construction times.
– Thermal insulation: CLT panels provide air tightness and excellent thermal insulation.
Challenges:
– Costs: Transporting CLT panels across long distances incurs additional upfront costs.
– Limited track record: Lack of knowledge and experience with CLT can make engineers and contractors hesitant to use it.
– Building codes: Codes for mass timber projects are not as developed as those for concrete and steel.
– Integration into industry: It takes time to integrate new practices and results into the building industry.
– Acoustics: CLT alone does not meet sound insulation ratings and requires additional elements.
Specific Applications of CLT (Pavilions, Plyscrapers, Bridges, Parking Structures, Modular Construction)
– Smile, the world’s first timber mega-tube structure, was built using hardwood CLT panels.
– Stadthaus in Hackney, London, was the first building constructed using only CLT framing.
– Forte Living in Melbourne, Australia, became the tallest plyscraper framed with CLT alone.
– Mistissini Bridge in Quebec, Canada, used locally sourced CLT panels and glue-laminated timber girders.
– The Glenwood in Oregon is a CLT parking garage under construction.
– The Dyson Institute Village in England provides on-campus student housing and was built using stacked CLT modules.
– CLT has been identified as suitable for use in modular construction, with examples in Washington and England.
Note: The subtopic regarding the effect of wall openings on wall strength and the assumptions and considerations for further research can be included as additional information within the relevant groups. Source: https://en.wikipedia.org/wiki/Cross-laminated_timber
This article may be too technical for most readers to understand. (April 2023) |
Cross-laminated timber (CLT) is a subcategory of engineered wood with panel product made from gluing together at least three layers of solid-sawn lumber (i.e. lumber cut from a single log). Each layer of boards is usually oriented perpendicular to adjacent layers and glued on the wide faces of each board, usually in a symmetric way so that the outer layers have the same orientation. An odd number of layers is most common, but there are configurations with even numbers as well (which are then arranged to give a symmetric configuration). Regular timber is an anisotropic material, meaning that the physical properties change depending on the direction at which the force is applied. By gluing layers of wood at right angles, the panel is able to achieve better structural rigidity in both directions. It is similar to plywood but with distinctively thicker laminations (or lamellae).
CLT is distinct from glued laminated timber (known as glulam), which is a product with all laminations orientated in the same way.
