A significant part of the environmental impact of a building is determined from the moment it is built, by the materials chosen to be used. By using wood, a renewable material of choice, this environmental footprint can be reduced. This was explained in a previous blog post, “Building with wood sequesters CO2 for the life of the building, all while the forest grows back and captures even more CO2!”
Propelled by its ecological advantages, but also its aesthetic appeal, wood construction is thriving in Québec and around the world. People are trying to use wood to build as many buildings as possible. In Québec, almost all single-family dwellings are already made up of it. However, the construction system used in these structures, which is called “light-frame construction”, has its limits. Currently, it can only be used for buildings of six storeys or less.
To build higher, or to build industrial, institutional and commercial buildings that will have to meet different needs, other wood-based building systems have to be used. These types of buildings are still often built with steel or concrete, although in many cases wood is a totally suitable material! Other wood-based building systems include post and beam construction and mass timber construction. In the first case, the myriad of studs that make up the walls of the light-frame system are replaced by a reduced number of vertically placed columns or posts that support the beams on which the upper floor or roof rests. In the case of mass timber construction, wood panels are used to form walls and floors, which in turn provide structural resistance themselves. These systems can also be combined and used in hybrid constructions.
Today, there is a wide variety of structural engineering products for construction that are manufactured in Québec. Local companies have developed considerable expertise in this field, successfully designing innovative products for use in buildings of all sizes from the wood harvested in our forests!
Some of the best known are glued-laminated timber (glulam) and cross-laminated timber. The first one is used in the manufacture of posts and beams, while the second one is used in the form of mass panels. Glued-laminated timber consists of wood strands, which are themselves lumber jointed to achieve the desired length with structural adhesives. These strands are then assembled in parallel, again using adhesives, to obtain the final dimension of the structural element. Several large wooden arches are found in the stadiums as the main frame. Cross-laminated timber, commonly referred to as CLT, is ideal for mid-rise buildings. The panels are constructed by stacking several perpendicular layers of lumber.
These engineered products are made from a renewable and natural material, the mechanical properties of which vary greatly from tree to tree.
But how can we guarantee the resistance of such products?
This is where human ingenuity comes into play. This natural variability is taken into account by standards, calculations and mechanical resistance tests. Structural engineering products generally require a prior wood classification from which defects in wood, such as knots and the grain angle, are identified and classified. To be even more precise, its stiffness, which is the force needed to deform the piece of wood, is also measured. Strength testing on a large number of samples directly linked stiffness to resistance. So, based on the established relationships between the defects in the wood, its stiffness and its strength, we can calculate the load that the manufactured product can withstand without having to damage it!
These processes determine which parts can be used and where. Manufacturing standards, based on mechanical tests and calculations, provide some sort of recipes for assembling the different components of the product to achieve the desired resistance. In the factory, quality control tests are carried out at various stages of production to ensure that wood parts meet standards. This will result in products of great strength and safety for the occupants!
The most incredible thing about this is that the manufacturing of these engineering products allows the raw material coming from our forests to be used even more rationally. But this is another story that will be the subject of a future article!