Glulam (glued-laminated timber) is a structural timber product manufactured by gluing together individual pieces of dimension lumber under controlled conditions. The attributes of this wood product account for its frequent use as an attractive architectural and structural building material.
In the manufacture of glulam, the wood pieces are end jointed and arranged in horizontal layers or laminations.
Laminating is an effective way of using high strength lumber of limited dimension to manufacture large structural members in many shapes and sizes. Glulam is used for columns and for beams and frequently for curved members loaded in combined bending and compression.
Glulam is manufactured at certified plants where standards governing lumber grading end joining, gluing and finishing are used to control quality. Qualified manufacturers can supply a certificate of conformance for their products upon request.
The lumber used for the manufacture of glulam is a special grade (lamstock) which is purchased directly from lumber mills. It is dried to a maximum moisture content of 15 percent and it is planed to a closer tolerance than that required for dimension lumber.
Canadian glulam is manufactured in three species combinations: Douglas Fir-Larch, Hem-Fir and Spruce-Pine as shown in Table 3.6.
|Table 3.6: Commercial Species for Canadian Glulam|
|Commercial Species Group Designation||Species in Combination||Wood Characteristics|
|Douglas fir, western larch||Woods similar in strength and weight. High degree of hardness and good resistance to decay. Good nail holding, gluing and painting qualities. Colour ranges from reddish-brown to yellowish-white.|
|Hem-Fir||Western hemlock, amabilis fir, Douglas fir||Lightwoods that work easily, take paint well and hold nails well. Good gluing characteristics. Colour range is yellow-brown to white.|
|Spruce-Pine||Spruce (all species except coast sitka spruce), lodgepole pine, jack pine||Woods of similar characteristics, they work easily, take paint easily and hold nails well. Generally white to pale yellow in colour.|
All Canadian glulam is manufactured using waterproof adhesives for end jointing and for face bonding and is therefore suitable for both exterior and interior applications. However, the specified strengths used in design will depend upon whether the service condition is wet or dry.
Glulam is a structural product used for headers, beams, girders, columns, and for heavy trusses. It is often used where the structure of a building is left exposed as an architectural feature.
Glulam can be manufactured to an almost limitless variety of straight and curved configurations (see Figure 3.6 below). It offers the architect artistic freedom without sacrificing structural requirements.
Figure 3.6: Common Glulam Shapes for Large Buildings