Text 2. Engineered wood

In today’s sustainably built environment engineered wood products play a major role, both in interior and exterior applications. Engineered wood is sometimes referred to as composite, as it is comprised of wood veneers, lumber, panels, fibers or strands bound together with an adhesive to make the end product. Engineered products are also made with shredded wood which is glued together, and can include other plant materials such as rice stalks.

Engineered wood products are produced all over the world, and can be found in use as flooring, structural supports, cladding, and a number of other components of a structure. They offer a high-performance, dimensionally stable and environmentally responsible option for any building project, however large or small, residential or commercial. And structural engineered wood products offer incredible design versatility for architects.

One advantage to engineered wood is that it is very strong and durable, and can be stronger than regular wood of the same size. This can be an advantage when people want to increase the strength of a structure without making it heavy or bulky.

Plywood is sometimes called the original engineered wood. It is made out of thin wooden sheets which are glued together and compressed to create a block of durable wood. Plywood is produced by assembling veneers (thin sheets of wood of uniform thickness) and bonding them together to form a panel. The veneers are usually assembled with the grain direction in one veneer being at right angles to that in the adjacent veneer. To insure a stable balance construction free of warping tendencies, an odd number of veneers is used (e.g. 3-ply, 5-ply and 7-ply). The grain on the face and back veneer is parallel. The crossing of the grain at right angles tends to equalize the strength in all directions and the uniformity increases with the number of plies used.
Glued Laminated Timber, often referred to as Glulam, is an engineered structural wood product, developed in the 1960's. It is produced by bonding together a number of graded, seasoned and mostly finger-jointed laminates with a structural moisture-resistant adhesive to form a solid member. The laminates are bonded together with the grain running essentially parallel. Because the product is made up of many laminates, any strength reducing characteristics (that might affect a piece of solid timber of the same cross section) are not present in a glued laminated product.

Glulam structural members are used as vertical columns or horizontal beams, as well as curved, arched shapes. In fact, glulam is the only engineered wood product that can be produced in curved shapes, offering unlimited design flexibility.

Now, a new development in wood construction called cross-laminated timber (CLT) is making new possibilities available in wood construction.

Cross-laminated timber panels are like massive plywood boards. Instead of shaving a log into a veneer and then gluing it together to make a board, a CLT panel is made from pieces of sawn wood and is several inches thick. Like plywood, alternating layers are laid perpendicular to one another, so that the finished panel is stronger and more dimensionally stable than plain wood would be.

Because the panels are many inches thick, there is an inherent fire resistance to the material. Construction with CLT is also faster and requires fewer workers and lighter equipment, which can make construction more affordable.

Laminated Veneer Lumber (LVL) and Laminated Strand Lumber (LSL) are engineered structural products. They are produced by assembling wood veneers (thin sheets of wood of uniform thickness) or strands and bonding them together with a structural adhesive to form a solid product. The grain direction of each veneer or strand is usually oriented to be parallel with the length of the piece but may be cross-banded for specialty applications. The laminated structure disperses strength and gives LVL and LSL a higher bending strength and stiffness than the equivalent solid timber of the same species.

LVL is typically used in structural applications where the high strength and stiffness, long lengths and large section sizes are advantageous. These applications include floor joists, lintels, purlins, roof truss components, and portal frames.

Some engineered wood products, like oriented strand board (OSB), can use trees from the poplar family, a common but non-structural species. Alternatively, it is also possible to manufacture similar engineered cellulosic products from other lignin-containing materials such as rye straw, wheat straw, rice straw, hemp stalks, or sugar cane residue, in which case they contain no actual wood but rather vegetable fibers.

Дата добавления: 2014-12-23