Standard sizes have been developed for Canadian glued-laminated timber to allow optimum utilization of lumber which are multiples of the dimensions of the lamstock used for glulam manufacture. Suitable for most applications, standard sizes offer the designer economy and fast delivery. Other non-standard dimensions may be specially ordered at additional cost because of the extra trimming required to produce non-standard sizes.
Standard finished widths of glulam members and common widths of the laminating stock they are made from are given in Table 4 below.
Single widths of stock are used for the complete width dimension for members less than 275mm (10-7/8") wide. However, members wider than 175mm (6-7/8") may consist of two boards laid side by side. All members wider than 275mm (10-7/8") are made from two pieces of lumber placed side by side, with edge joints staggered within the depth of the member.
Members wider than 365mm (14-1/4") are manufactured in 50mm (2") width increments, but will be more expensive than standard widths. Manufacturers should be consulted for advice.
|Table 4: Standard Glulam Widths|
|Initial width of glulam stock||Finished width of glulam stock|
|235 (or 89 + 140)||9-1/4 (or 3-1/2 + 5-1/2)||225 (or 215)||8-7/8 (or 8-1/2)|
|286 (or 89 + 184)||11-1/4 (or 3-1/2 + 7-1/4)||275 (or 265)||10-7/8 (or 10-1/4)|
|140 + 184||5-1/2 + 7-1/4||315||12-1/4|
|140 + 235||5-1/2 + 9-1/4||365||14-1/4|
Standard depths for glulam members range from 114mm (4-1/2") to 2128mm (7') or more in increments of 38mm (1-1/2") and l9mm (3/4").
A member made from 38mm (1-1/2") laminations costs significantly less than an equivalent member made from l9mm (3/4") laminations. However, the l9mm (3/4") laminations allow for a greater amount of curvature than do the 38mm (1-1/2") laminations.
Laminating stock may be end jointed into lengths of up to 40m (130') but the practical limitation may depend on transportation clearance restrictions. Therefore shipping restrictions for a given region should be determined before specifying length, width or shipping height.
For long straight members, glulam is usually manufactured with a built in camber to ensure positive drainage by negating deflection. This ability to provide positive camber is a major advantage of glulam. Recommended cambers are shown in Table 5 below.
|Table 5: Camber Recommendations for Glulam Roof Beams|
|Type of Structure||Recommendation|
|Simple Glulam Roof Beams||Camber equal to deflection due to dead load plus have of live load or 30mm per 10m (1" per 30') of span; where ponding may occur, additional camber is usually provided for roof drainage.|
|Simple Glulam Floor Beams||Camber equal to dead load plus one quarter live load deflection or no camber.|
|Bowstring and Pitched Trusses||Only the bottom chord is cambered. For a continuous glulam bottom chord; camber in bottom chord equal to 20mm per 10m (3/4" in 30') of span.|
|Flat Roof Trusses (Howe and Pratt Roof Trusses)||Camber in top and bottom glulam chords equal to 30mm per 10m (1" in 30') of span.|