There are situations where architects desire a tension side milling in lumber laminations of glulam beams, glulam planks, or NLT. Doing this is not allowed per NDS or ANSI 117 as the lamination grades are voided. Same is true for NLT lumber laminations which are graded to WWPA or PLIB. That being said, the NDS (2024) Section 3.1.2 "Net Section Area" can mislead some engineers to think you just design for the net section. I've confirmed this is not true with AWC Staff and APA Staff and WWPA Staff. Does anyone have a suggestion on how to approach this issue with a Code Alternative design method, or testing methods to demonstrate safe design? Examples shown below.
That looks pretty interesting. There is a real need. I guess you can always just go conservative and ignore the depth that was cut. 🙄 But if you have a ton of these in a project, that will be a lot of waste and overly conservative.
I dont know, let me post this on X to see if anyone has experience. 🤨
@drammer ?
@ling Thanks for initial thoughts. For a glulam beam (not glulam plank) I can maybe see your logic that if you design the beam for the depth above the notch and you make sure you have the extra tension lams added up into the un-notched areas that may be deemed to work. I don't know what APAs interpretation of this would be regarding design values. The theory out there is that the notch may initiate a failure that could run up into the un-notched portion of the beam. What does your gut say on that one? For the NLT or GLT plank though you are more stuck in my opinion. You are modifying each lamination making each lamination off-grade. I have not seen a technical justification that it is conservative to just use the depth of above the notch. I remember an comment from a seasoned person the AWC Wood Design Standards committee that they have seen tension side notches significantly influence the COV when you test them. COV 30% +. This is a little more to the story and why I'm reaching out for opinions and ideas here on the TEF. @drammer - your thoughts here would be great.
Yeah, @heblomgren for a composite section with different lamination grade, it could be an issue. My gut feeling is that by ignoring ALL wood involved in the notched depth, you have some added conservativeness in there, which might off-set the concern about stress concentration or reduction in lamination strength. But sure this is just a gut feeling and it always depends on how much you route out.
I agree APA would be a good party to address this. Let me forward this discussion to APA to see if they care to respond. @drammer will be a good reference on this too as he tested many glulams, not sure if he did any notched in the beam span direction...
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