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Holes in Bottom Chord

Holes in Bottom Chord

Holes in Bottom Chord

(OP)
How do you generally handle holes drilled through tension chords by a contractor... I have a series of trusses that the electrical contractor has drilled a series of 5/8" holes through a 3-1/2" (2x4)...

Do you just consider the reduced area or do you check the moment caused by the change in centroid?  Does anyone have a reference to this problem; it should be fairly common.

Dik

RE: Holes in Bottom Chord

I recalculate the moment of inertia.  Then recheck the moment and shear.  I check the tension for reduced area.  

RE: Holes in Bottom Chord

(OP)
You include for the moment due to the 'new' eccentric loading?

thanks Dik

RE: Holes in Bottom Chord

I just recalculate the bending stress on the new cross section (new I value).  The neutral axis of the cross section may or may not change depending on the location of the hole.  If by "new eccentric loading" you are referring to the fact that the neutral axis shifts, then, yes, I include for that.  Hope that helps.  

RE: Holes in Bottom Chord

(OP)
Thanks... Dik

RE: Holes in Bottom Chord

Aso, depending on the plate manufacturer, the truss software can account for holes taken out of tension members (for bolts.)  The software does assume the hole be centered in the web or chord.  

woodengineer

RE: Holes in Bottom Chord

(OP)
I'm trying to find out the location of the holes... holes were installed by an electrician after production... if the holes are centred, which I hope, then the truss is OK.  The truss chord was originally stressed to approx 65%...

I was wondering if the location was usually considered, or if any stress overage was considered to redistribute at limit loading... assuming that there are no knots at the hole location if it's not centred.

Dik

RE: Holes in Bottom Chord

We take a 9% reduction in a girder capacity due to normal bolt holes. Any other holes are treated on a case by case basis.

RE: Holes in Bottom Chord

(OP)
Thanks Trussme68... That's for bolting multiple Girder Trusses together?  What bolt size? 1/2"dia?  2x4 chord members...

Dik

RE: Holes in Bottom Chord

1/2" bolts are usually 24" on center in carrying members only. 2x6 or larger members. 2x4 members have to be engineered case by case. I have done it, but just don't like it. Simpson SDS screws work just as good as the 1/2 bolts and save time and labor.

RE: Holes in Bottom Chord

Also with SDS or WS screw, it is not necessary to take a net section reduction or consider group action factor.

woodengineer

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