Vertical hole through glulam beam 2

[galvitarito]

Hi folks -

Had a contractor contact me today looking for me to buy off on him drilling a hole through the bottom of a glulam beam to hang a fan & light fixture from. The beam in question is an 8.75x24 glulam spanning 19ft and supporting an almost 35kip point load from the smaller intersecting glulams above (very high snow load project location).

The contractor says the hole is only 1/2" diameter but I'm skeptical based on what I can see in the photo. I have concerns on this affecting the strength of the beam by reducing cross-section through the tension plies at the most critical point in the beam's span.

What are other's opinions? Are there repair solutions available?

Thank you

 

[jayrod12]

If you analyzed it as an 8" wide beam, what happens?

 

[galvitarito]

Thank you jayrod, that is a helpful insight.

 

[ctopher]

Doesn't the contractor have an engineer they have worked with before that can approve it?

Chris, CSWP
SolidWorks
ctophers home

 

[galvitarito]

@ctopher, it is a residential project and in this area the construction related changes are coordinated with the Engineer of Record.

 

[ChorasDen]

Check out page 6 of AITC's Technical Note 19 (TN-19).

[URL unfurl="true"]https://www.plib.org/staging/wp-content/uploads/2023/06/Technical-Note-19-2023-04-23.pdf[/url]

 

[lexpatrie]

Drill first, ask later. Perfect.

There's always the "I decline" option. This mentality will perpetuate until we start holding the line and saying no to these cowboy approaches.

There's a difference between cutting roof plywood for a vent and drilling a hole through an obvious structural member, particularly when they make mounts for fans and you don't have to drill a hole. This mentality where structure can simply be cut wily nilly for no particular reason...... were they plumbing contractors previously?

 

[hokie66]

Looks like he has used about a 3" hole saw to take out an undetermined depth of the bottom lamination. I would just check the beam to determine if it works with one less lamination.

 

[Celt83]

No one else has mentioned but a lot of glulam beams have specific lumber grades at the outer plys vs the inner plys. So just checking it as reduced depth glulam may not be as simple as suggested.

 

[XR250]

Just like most things residential, deflection likely controlled this design.
I would do the math and see what the stress ends up being.

 

[galvitarito]

Thank you all for the responses - they have given me helpful perspectives of items to be concerned with and potential approaches to analysis.

 

[phamENG]

Celt is on the right track here. Unless you go the reduced section route using the full depth, it's not just a question of reduced depth - it's a question of reduced allowable stresses. There's also a potential for reduced modulus of elasticity depending on the grades of the various plies. This is not as straightforward as it may seem.

 

[lexpatrie]

That is quite a hole. I think you're going to have to "find" your own methodology there. The bottom is typically a tension lamination and has higher stress allowables, this is true, you also have the stress concentration in the bending stress due to the hole, and you're in the location of maximum bending stress (most likely), and given this span and framing, I'd really question if it's "deflection controlled" design.

Is the original EOR available to check this or are you the original EOR and are now "stuck" with this?

Is that hole through the entire beam or is it partial depth? I'm not seeing that clearly stated, but I'm deeply skeptical that it's a 3/4" diameter hole.

 

[Canuck65]

It looks to me like the contractor drilled a large diameter hole in the bottom of the glulam to recess the electrical junction box. My guess would be 4" diameter and 1-1/2" deep. A 1/2" diameter vertical hole was likely drilled full depth for the wire.

A lot of good points brought up above. Indeed it is not as straightforward as it may seem. Reduced section analysis is easy when you have a uniform cross-section, but in this case one does not have a uniform cross-section as the wood grades vary.

One non-technical point to add ... have you reached out to the electrical contractor to get a signed agreement and healthy retainer for the time you are going to spend analyzing their mistake?