Glued Laminated (Glulam) Timber Design - Design Practices

An example of a glulam arch
Fig. 1: A glulam arch in the Ontario Art Gallary

Glued Laminated Wood (glulam for short) is a wooden member that consists of numerous laminations of flatwise wood, which have been glued together to form one larger, stronger piece of wood (common bending values for glulams are in the order of 1600-2400 psi compared to 1000 psi for sawn lumber). For example one glulam could start out as a group of douglas-fir larch 2x6's (1.5"x5.5" nom.) which would then be shaven down to get rid of the rounded edges. The finished product would be a 5 1/8" x 22.5" (this would be 15-2x6's stacked and glued together).

Notes on Glulam Design:

  • One may naturally think that the glue would become the weakest element in a glulam when in fact the glue is stronger than the wood. This allows glulams to have bending capacities well above that of sawn lumber
  • Glulams are usually broken up into being either a western species or southern pine.
  • General glulams will be analyzed here, but the thickness and type of the lamination along with the type of glue can greatly vary the strength of a glulam member. Specialty glulams, aka Microlam and Paralam (which are similar to a glulams except veneer strips are used in lieu of lumber) are available for high strength applications and known as laminated veneer lumber. Due to the wide range of allowable forces a glulam may be capable of supporting, most glulams will provide an allowable stress, moment, or force.

Glued Laminated Timber Analysis

Analysing the stress acting on the member can be done from the Structural Analysis section (it is no different than analysing the stress in other types of material). In order to find the allowable stress for a glulam member you will have to go through the Glued Laminated Adjustment Factors section below. Numerous examples on how to calculate out different factors has been provided for completeness.



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