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.
|Glued-laminated timber, or glulam, is a timber product manufactured from dimensional lumber, called laminating stock. This laminating stock (lamstock) comes in 2” nominal thickness and standard nominal widths although custom widths are possible ranging from 2” up to 14 ¼” actual widths. The lamstock is joined together end to end, then glued together in laminations using waterproof, state of the art adhesives, creating nearly unbounded possible beam depths and lengths. After a curing process, glulam beams are planed and sanded, then sent to fabrication. Each beam is fabricated to the exacting standards set forth by Timber Systems’ designers.
Glulam is available in several species of wood including southern pine, douglas fir, port orford cedar, and Alaskan yellow cedar. Southern pine species can be preservative pressure treated prior to gluing, which unlike treatment after gluing, allows the treatment to reach the center of the beam for additional weather resistance. Port orford cedar and Alaskan cedar are naturally decay resistant and therefore don’t require preservative treatment. Douglas fir is the exception in glulam. Doug fir cannot be preservative treated without incising (a process that scars the beam with thousands of slit-like holes in the surface), nor is it naturally decay resistant. Topical treatments are available, but not nearly as effective as pressure treatments.
Because of the utilization of lamstock in the manufacture of glulam, larger beams and columns can be created from smaller trees harvested from timber plantations. Many plantations are responsibly managed to ensure our natural wood resources are not depleted.
Glulam can be manufactured to a variety of straight and curved configurations so it offers architects artistic freedom without sacrificing structural requirements. Wood has two times the tensile strength to weight ratio relative to steel. And wood has greater compressive resistance strength than concrete.