The size and location of holes that can be cut in wood beams, whether sawn lumber, glulam or structural composite lumber, have traditionally been very restrictive with few options for designers outside standardized rules in the building code or manufacturer’s literature. This is because the failure modes and stresses at holes are complicated and not well understood. Historically, we have limited hole sizes in Microllam® LVL, Parallam® PSL and 1.3E TimberStrand® LSL to a 2″ diameter round hole for members 7.25″ and deeper. For 1.55E TimberStrand® LSL, a maximum 4 5/8″ diameter hole for members 14″-16″ deep is permitted (see TJ-9000, TJ-9020, TJ-9500, TJ-9505 for additional information).
In contrast, large holes can be cut into the webs of TJI® Joists. For example, a maximum 11¼” hole can be cut in a 14″ deep TJI® Joist. To take advantage of this key feature, changing direction of ducts, adding soffits and complicated coordination with trades is required to avoid interference with rectangular beams. With changing energy codes and the desire to run ducts in conditioned spaces such as the floor cavity, larger beam hole capabilities has become a more frequent request from our customers.
To provide a solution for the changing market needs, we destructively evaluated full scale structural composite lumber beams with round holes of varying sizes to better understand the effects of the holes. As a result of the testing, proprietary design procedures were developed so that multiple round holes up to 2/3 member depth could be located in Microllam® LVL, Parallam® PSL and TimberStrand® LSL with reduced design capacities and limitations on the number and location of holes.
The new round hole capabilities, summarized in the table below, are included in our Javelin®software today and will be available soon in our Forte® single member sizing software. Since these large holes result in reduced capacity, evaluation of any hole condition beyond that shown in our literature is necessary to ensure structural adequacy. It is also important to ensure holes are cut in a quality manner using the appropriate tools (such as a hole saw or router) with no overcuts. If inappropriate tools or methods are used, the beam may be structurally inadequate and require replacement.
-Software Analysis Required-
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