Laminated veneer lumber (LVL) is fabricated by laminating and gluing multiple veneers together in the same orientation. This enables long elements to be produced that have high strength in one direction.
Laminated strand lumber (LSL) is fabricated from flaked wood strands glued together in large billets. The length is limited only by standard shipping and trucking dimensions. LSL can be used for floors, walls and vertical members where large floor-to-floor heights are required.
Parallel strand lumber (PSL) is fabricated from long strands of veneer pressed and glued into standard dimensions and lengths. It has very consistent properties and high strength.
In North America, glulam has traditionally been made from Douglas fir, SPF (spruce/pine/fir), larch (Larix decidua) or southern yellow pine. However for exterior applications it is now possible to obtain glulam made from Alaskan yellow cedar. In Northern Europe and Russia, red pine (Pinus resinosa) and white spruce are the most common species used for the manufacture of glulam. Lamstock is typically supplied in nominal thicknesses of 25 or 34mm and (according to species and country of origin) widths of 80 to 170mm. Lengths are typically 3 metres or longer, with pieces being finger-jointed and glued together as necessary. The lamstock is kilndried to a moisture content of between 10 and 14%, then end-glued together to attain the required length. The multiple laminations are then face-glued together under pressure in a jig that (if required) gives the final product the desired camber, curvature or taper. Glulams can be fabricated to any length, enabling them to be used for long free spans, or continuous spans over multiple points of support. They can also be used for columns that extend over multiple floors. Glulam beams are normally laid up so that they are in the vertical orientation when loaded (i.e. the load is applied perpendicular to the long face of the laminations). In such cases, the upper and lower laminations may be specified to have a higher strength class than the centre laminations, as these are the parts of the beam where compressive and tensile forces are greatest. Nordic, an engineered wood products manufacturer in northern Quebec makes glue-laminated products using small-dimension square sections cut from the tips of black spruce trees. The sections are then glued together both horizontally and vertically to make glulam beams, columns and panels that have a distinctive checkerboard cross section. This material was used for the columns, beams and floor panels of the six-storey Fondaction CSN Building in Quebec City, designed by GHA – Gilles Huot architecte and completed in 2010 [ill. p. 34]. Glulam can be supplied in a variety of appearance grades for concealed or exposed
28 | PRINCIPLES OF TALL WOOD BUILDINGS