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beam deflection in a two story renovation

beam deflection in a two story renovation

(OP)
I would like to get input on what to do about beam deflection for a new 24' beam that will serve as a header for a sliding door on the first floor of a two story renovation project.
My concern is that if the beam is ordered with camber in the beam that they camber will crack the wall and disrupt the doors and windows in the walls above the beam when the beam is raised into position.
If the beam is ordered without the camber (flat) then I have the same concern that when the shoring is removed that the wall will settle into the deflection causing cracks in the wall and the doors and windows in the walls to not function.
The beam is going in an exterior wall carrying roof and floor loads front above.
I would like to find our how other people have handled this situation and what solutions have worked for them.
Thank you

RE: beam deflection in a two story renovation

You can't get rid of deflection through cambering. All it does is allow the beam to be more or less flat after the dead load is applied. It's unlikely that they could camber a beam that short, anyhow.
If you need less deflection, increase the moment of inertia or modulus of elasticity of your member.

RE: beam deflection in a two story renovation

(OP)
Aloha Jed,
Thanks for your response.
The situation that I am dealing with in this renovation is that we need a very shallow beam, something in the neighborhood of a W12x58. We are trying to keep the bean shallow so the doors under it can be as tall as possible.
With the W12x58 the total (live and dead loads) deflection calcs out at .7" which would be a lot of sag for the wall above that it is supporting. I am trying to understand how other people have dealt with this situation in other renovations. I could keep increasing the weight of the beam but even with a W12x136 there is still some deflection. I would like to know how other people deal with that deflection.
Thanks

RE: beam deflection in a two story renovation

It depends on the wall finishes you are supporting. AISC has a design guide #3 which discusses some deflection criteria to consider. If your doors have some sort of deflection head, and you aren't supporting brick you could probably have an L/360 deflection without any real issues.

RE: beam deflection in a two story renovation

Consider transferring out some of the load from the story above so the beam does not see it - as in a 24 foot long header in the story above.

Mike McCann
MMC Engineering

RE: beam deflection in a two story renovation

You could:
- make a rally cool hidden truss in the exterior wall above
- add intermediate beams like M^2 suggests
- Install a deeper beam that will stick above the floor. Lots of reframing, etc.

If the view is more important than the money any of the above are possible. You can't get long openings with shallow headers and no deflection. You can get (2) of the (3), but not all (3).

RE: beam deflection in a two story renovation

I think we should all meet on the jobsite to discuss further smile

Who is bringing the beer?  

RE: beam deflection in a two story renovation

Add posts on each side of the doors(decreasing span), Increase S, Glulam....
Make sure the bottom of the deflected beam and the door frame have clearance.

RE: beam deflection in a two story renovation

Is the beam dropped in your design? Would it be practical to add a ledger to the top of the beam & web stiffener to do a flush beam instead?

RE: beam deflection in a two story renovation

You could also make the beam fixed ended to a post on each side of the doors. The problem with this is that the new posts would carry the load instead of whatever is carrying it under your arrangement.

The idea, whether you camber or not, is to drop the DL onto the beam before you instal the doors, that way you only have LL deflection to worry about.

Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin

RE: beam deflection in a two story renovation

I would bet it is next to impossible to provide a fixed connection for the beam. I doubt the existing structure has the stiffness at the beam supports to provide the rigidity required.

RE: beam deflection in a two story renovation

I did say "to a post at either side", I was thinking of new posts, moment connected to a the new beam. As it is, he is landing the new beam on the masonry.

Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin

RE: beam deflection in a two story renovation

Right, missed that, you're thinking a new moment frame.

It's an option for sure, I just forsee the member size being much too large to be functional. But might be worth checking out.

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