Whenever possible, avoid drilling vertical holes through LVL beams unless the beam width is at least 89 mm (3.5 in.). Prior to drilling any vertical holes, an engineer or architect qualified in wood design should be consulted. Use a drill guide to minimize ‘wandering’ of the bit as it passes through knots or material of varying density and to ensure a true alignment of the hole through the depth of the beam. The vertical hole should be centered in the beam width.
As a rule of thumb, vertical holes drilled through the depth of an LVL beam cause a reduction in the capacity at that location directly proportional to the ratio of 1.5 times the diameter of the hole to the width of the beam. For example, a 13-mm hole drilled in an 89-mm wide LVL beam would reduce the beam capacity at that section by approximately 22 percent ([13[1.5]/89).
Holes for support of suspended equipment
Heavy equipment or piping suspended from LVL beams should be attached such that the load is applied to the top of the beam to avoid inducing tension perpendicular-to-grain stresses. Any horizontal holes required for support of significant weight, such as suspended heating and cooling units or main water lines, should be located above the neutral axis of the beam and in a zone stressed to less than 50 percent of the allowable bending stress. The beam capacity should be checked for all such loads to ensure proper performance.
Protection of field-cut notches and holes for LVL and glulam
Frequently, LVL and glulam beams are provided from the manufacturer with the ends sealed by a protective coating. This sealer is applied to the end grain of the LVL and glulam beams to retard the migration of moisture in and out of the beam ends during transit and jobsite storage. Field cutting a notch in the end of a beam can change the moisture-absorption characteristics of the LVL/beam at the notch location. This can result in seasoning checks or localized splitting developing at the root of the notch. To minimize this possibility, all notches should be sealed immediately after cutting using a water-repellent sealer. Sealing other field-cut locations as well as field-drilled holes is also recommended. These sealers can be applied with a brush, swab, roller, or spray gun. Find additional resources for free download at www.apawood.org.
Borjen “BJ” Yeh, PhD, PE, is technical services director for APA – The Engineered Wood Association. He has been with APA for 30 years. Yeh earned his M.S. at Iowa State University and PhD at University of California, Berkeley. He can be reached at firstname.lastname@example.org.