![]() Note the horizontal hole should not be drilled in the moment-critical zone, as defined in Figure 3, unless approved by an engineer or architect qualified in engineered timber design. The hole should have a minimum clear distance, as measured from the edge of the hole to the nearest edge of the beam, of four hole diameters to the top or bottom face of the beam and eight hole diameters from the end of the beam. The hole diameter should not exceed 38 mm (1.5 in.) or one-tenth of the beam depth, whichever is smaller, with the exception of 25 mm (1 in.) diameter or smaller holes as noted in the section below. This image illustrates the zones where small horizontal holes are permitted in a uniformly loaded, simply supported beam. These field-drilled horizontal holes should meet the following guidelines. Examples of access holes include those used for the passage of wires, electrical conduit, small-diameter sprinkler pipes, fiber-optic cables, and other small, lightweight materials. The APA – The Engineered Wood Association Technical Note, Effect of Large Diameter Horizontal Holes on the Bending and Shear Properties of Structural Glued Laminated Timber, Form V700, provides additional engineering guidelines where larger horizontal holes than those specified here cannot be avoided.įield-drilled horizontal holes should be used for access only and not as attachment points for brackets or other loadbearing hardware unless specifically designed as such by the engineer or designer. For beams of more complex loading or other than simple spans, similar diagrams may be developed. These non-critical zones are located in portions of the beam stressed to less than 50 percent of design bending stress and less than 50 percent of design shear stress. Figure 3 shows the zones of a uniformly loaded, simply supported beam where the field drilling of holes may be considered. Hence, horizontal holes in glulam timbers are limited in size and location to maintain structural integrity. These effects cause a reduction in the capacity of the beam in the area of the penetration. Like notches, holes in glulam remove wood fiber, thus reducing the net area of the beam at the hole location and introducing stress concentrations.
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