Holes drilled in bottom chord of truss 1

[CANeng11]

An electrician drilled 3/4" holes through a 4 ply 2x10 bottom chord of a wood truss and the builder is asking for a repair detail. See the attached pictures. I believe the truss manufacturer is telling them they will need to replace the truss, but they are asking for alternative solutions since this would be very difficult to replace. Any input would be appreciated. I have requested the truss designs from the manufacturer.

 

[SteelPE]

Would be odd for the electrician to drill holes in the web.... where would the wires be going. I initially thought they are Timberlok screws but I may be wrong.

 

[IRstuff]

They appear to be the same color screws in the first image from the PDF. They're Torx head. The screw directly up from the middle of the image shows the indent of the Torx socket

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[IRstuff]

Different things. The first image in the PDF shows both the holes drilled for the wires and the screws:

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[IRstuff]

I actually had the exact same problem a couple of weeks ago.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[phamENG]

Ok, good...don't need glasses just yet...

 

[BridgeSmith]

If wood was a homogeneous material (which it most definitely not), the reduction in axial tension capacity from the holes would be 8%. The reduction in bending capacity would be well under 1%.

If the the truss manufacturer didn't allow for those small reductions in the design, they're cutting it way too close. If they choose to be a hardass about it and won't approve a 3/4" hole in a 9 1/2" deep member (which I believe is fairly common), I wouldn't expect them to be in business for very long, because no one will want to work with them.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[IRstuff]

Hah, I actually agree ;-)

Especially since this is a new fab, and the architect would have designed the trusses and located outlets, can lights, etc., knowing that the builder was going to have to go through trusses or joists to run the power, cable, etc., to supply the outlets, can lights, etc.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[dhengr]

Mas745:
Actually, I would give those electricians high marks for their thoughtfulness and workmanship, from what I can see. The .75” holes are not larger than needed, they are generally in line with the structural screws the truss manuf’er. installed, there are not seven oversized holes randomly chopped, one for each wire. I wouldn’t expect what I see to do any serious harm to the truss in terms of lost net area or horiz. shear area. I would show your photos to the truss guys, and I’ll bet they won’t give you any trouble for what you show. This assumes that someone didn’t use a chain saw on the truss someplace else for a waste line or a heating duct.

The bigger question is…, why didn’t you see the truss package during the shop drawing process, or was the builder acting as his own engineer until he got his watch-a-call-it in the ringer, and now he needs serious help. And, he wants you to act as the insurer of last resort for a pittance fee and to fix his mix-up with the truss guys. Charge him plenty, to cover your insur. premium. That looks like what he is hiring you for. Look to see that the builder has all the supports properly located and fitted under that girder truss, and that they are aligned and properly blocked from fl. to fl.

BA…, I thought the same thing when I first looked at the photos, what are all those symmetrical holes in the truss members? Those are long structural screws, most likely installed by the truss manuf’er. to hold everything together. The builder wouldn’t likely spend his own money to do that. That’s one of those bonus room truss arrangements, and then 4 of them are ganged together into a girder truss at the juncture of several roofs and a mess of framing below. Their software says it works, but nobody can really tell you what the loads or stresses are at any location, with a good degree of certainty. That truss and framing in your photo looks kinda like a botched abortion.

 

[BAretired]

My mistake. I was interpreting the screw heads to be holes. In that case, there is only one 3/4" hole smack in the middle of the bottom chord. I would be surprised to learn that the strength of the truss is affected in the least, but again, it should be the responsibility of the truss fabricator to confirm that. If he refuses, the design of the girder truss becomes the responsibility of the EOR.

BA

 

[IRstuff]

Slightly off topic; are the mending plates in the 3rd picture actually doing anything? They're not supposed to be for structural use, so why are they there?

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[BAretired]

The plates are not mending plates; they are truss plates, usually 16 or 20 gauge with teeth which are pressed into each side of each ply. A four ply truss would have eight truss plates in each location.

BA

 

[oldrunner]

I don't know what the plates are actually doing as well as I don't know what manufacturer made these trusses. The best resource that I can think of right now is reviewing the Truss Plate Institute codes (TPI). There is probably a section in there the will address holes for wires and piping ducts. The IBC used to reference the TPI codes. I don't think that that particular hole is an issue. I'm use to complete detailing of each truss as well as pages of details (many not even for this project) and notes. I am also aware that some of these truss companies are franchises for Mitek or another metal plate manufacturer. There use to be a Truss forum maintained by a very good truss engineer here on Eng-Tips. I talk to the fellow who maintained that forum once in a while, but I think he has gone sailing.

 

[r13]

Truss/wood connection plate - the most money saver invention in the 20th century, I believe.

 

[oldrunner]

YES!! But it's difficult to do your own analysis - especially for the plates as much of the values are obtained by testing. I hadn't checked any shop drawings for some time and then received a set to be checked and was amazed as to how far the industry had come along. They still had the submittal pages with small letters - which made one very careful to read everything. The biggest issue sometimes checking the original input to the computer program in comparison to the archtect's or civil engineer's plans.

 

[IFRs]

Could the electrician pull his/her wires out, reinforce the openings both sides with some of these (or longer) truss plates with a 3/4" hole for the wires, then feed his/her wires back through? Possible also put truss plates across the top and bottom of the built-up chord member centered on his/her holes?