The evaluation of check size in glued laminated timber beams is a process that involves understanding the behavior of wood as it gains or loses moisture in response to changing relative humidity and temperature in the surrounding environment.
Individual laminations in glued laminated timber (glulam) are relatively thin (typically 1-3/8 to 1-1/2 inches) and dry more uniformly. Also, the maximum moisture content of each lamination is limited to 16 percent or less for gluing purposes. As a result, seasoning checks occur less frequently in glulam than in sawn lumber.
It’s crucial to distinguish glulam seasoning checks from delamination, resulting from inadequate glue bonds between laminations. The key to identifying seasoning checks is the presence of torn wood fibers in the separation along the grain. A smooth lamination surface represents delamination without torn wood fibers.
For glulam bending members, the presence of seasoning checks generally affects only the horizontal shear capacity and usually is not significant outside the shear-critical zone. Bending and tensile strengths are virtually unaffected.
Although checking typically has a minimal effect on the strength of glulam members, its presence should be evaluated by a qualified Structural Engineer. This normally involves a field investigation in which detailed measurements are taken, followed by an engineering analysis to determine the structural effects of the checking (if any).