beam deflection question
beam deflection question
(OP)
Hi guys,
I have a situation where the contractor needs a beam sized and only has so much headroom to work with. I've sized the beam that fits and it is more than adequate in shear, moment, bearing length, ect.. but the beam is slightly over on deflection (0.55" allowable and 0.61" actual) The beam will be exposed (glu lam) thus no one is worried about cracked drywall. If we size up to the beam that meets deflection limits he looses his headroom and we have to go to a steel beam which would be a lot more work. I'm thinking 1/16" over on deflection things will be just fine, do you all agree?
And for future situations, I wonder if it is negligent to undersize beams with respect to deflection when space is tight. Even if the beam did deflect the allowable 0.55" there would still be cracked drywall in a drywall situation. I guess I am assuming I am still within the elastic limits when I go over the allowable deflection.
The beam is a roof beam, not a floor beam which might create more bounciness..
Your thougths are appreciated.
Thanks,
I have a situation where the contractor needs a beam sized and only has so much headroom to work with. I've sized the beam that fits and it is more than adequate in shear, moment, bearing length, ect.. but the beam is slightly over on deflection (0.55" allowable and 0.61" actual) The beam will be exposed (glu lam) thus no one is worried about cracked drywall. If we size up to the beam that meets deflection limits he looses his headroom and we have to go to a steel beam which would be a lot more work. I'm thinking 1/16" over on deflection things will be just fine, do you all agree?
And for future situations, I wonder if it is negligent to undersize beams with respect to deflection when space is tight. Even if the beam did deflect the allowable 0.55" there would still be cracked drywall in a drywall situation. I guess I am assuming I am still within the elastic limits when I go over the allowable deflection.
The beam is a roof beam, not a floor beam which might create more bounciness..
Your thougths are appreciated.
Thanks,






RE: beam deflection question
I am not a structural engineer but is it possible you could
weld a plate to the beam to strengthen it and bring the deflection down.
Regards
desertfox
RE: beam deflection question
RE: beam deflection question
Is there a typical textbook fixed end condition in wood construction? I always picture a concrete beam pocket for fixed end conditions.
Thanks a ton.
RE: beam deflection question
I have found that any fixity from the weight of floors above is negligible. Can you provide some definate fixity between the beam and the wall studs under to give it some portal frame action?
I would also check this beam for vibration issues.
http://w
RE: beam deflection question
RE: beam deflection question
What are you using for live loads?? Can you get any help form it being highly pitched.
In many applications - I wouldn't worry about it.
RE: beam deflection question
Options:
1. Use a flitch beam comprised of (2)-LVL's on the exterior and a steel plate in the middle.
2. Try a live load reduction based (ASCE 7-05 or IBC) if the situation allow for it.
3. Or like someone else said early, "camber" the beam.
RE: beam deflection question
RE: beam deflection question
The glu lam is a camber beam, still over the allowable deflection. I could reduce snow loads w/ ACE 7-05 if I wanted to but most folks around here don't like it, we had a big snow in '03 that collapsed a lot of roofs.
I think the answer is to give it some fixity with the portal frame action like csd72 talked about, pretty easy to do in this application. I suppose the flitch beam would work as well, I hadn't looked at that yet.
thanks a bunch.
RE: beam deflection question
RE: beam deflection question
If the Architect is worried about the look since it is exposed, just face the parallam with a wood veneer - no worries.
Mike McCann
MMC Engineering
RE: beam deflection question
Mike McCann
MMC Engineering
RE: beam deflection question
RE: beam deflection question
RE: beam deflection question
RE: beam deflection question
If you "heard" it on the internet, it's guilty until proven innocent. - DCS
RE: beam deflection question
If you ran the beam at non-reduced snow and it works for strength considerations, I see no problem taking the allowable reductions to check deflections.
You have considered the most conservative case for life safety.
There are a lot of good options given herein for you to consider.
'03 storm? Colorado front range?
RE: beam deflection question
Wood will creep and "take" a set...