Strengthening a wood beam with steel?

[Mechanimal]

Hi,

I'm looking to modify a beam in my basement. Currently joists are connected to a beam that is 2x 2x8, below that there are 3x 2x8 that support this upper section. I would like to remove the 3x 2x8 piece and modify the 2x 2x8 with the addition of a 2x8 and C7x9.8, This assembly would be through bolted with 1/2" bolts along it's length. The advantage of this design is that it would be flush and I would get maximum height in my basement. Are there any drawbacks to this method? See attached.

 

[IsaacStructural]

A few problems/issues to resolve.

1. Stiffness. You'll need to verify compatibility of deflections if you want this to actually work compositely, or else rely solely on the strength of the steel channel.

2. Load path. This is always an issue with this sort of work. The existing framing is already loaded, so adding new members to the side will have almost zero effect, save for adding extra dead load to the members. To get the load into the new framing you need to jack up the flooring, install the reinforcing, and then release the jacked flooring. Be careful with this process as you can damage the structure and finishes by over jacking. This is common procedure for leveling a sagging wood floor.

3. Torsion, hard to tell exactly how this all comes together, but a channel loading all from one side like that is not a very torsionally strong shape.

How about using engineered lumber? would a double or triple LVL provide the capacity you need? these are easier to frame than adding the channel, and you could remove all of the existing 2x8s and swap these in place.

Is there any connection between the (2)2x8s above and the (3)2x8s below? From you description it sounds like the lower 3 are carrying all the load anyhow, in which case LVLs would be in improvement.

M.S. Structural Engineering
Licensed Structural Engineer and Licensed Professional Engineer (Illinois)

 

[structSU10]

You will need to shore the existing joists, and would likely want to jack them up to remove deflection. From there I would follower Isaac, by trying to use LVL's or the like first, with new seat connection on the side. If that cannot handle the load, a steel beam with a nailer on top, and hangers off the side, would probably be the next option. Compatibility of deformations is very important in this suituation, since steel is much stiffer than wood, and unless you could put steel on both sides, it seems like a bad sitation.

 

[Mechanimal]

Thanks for the responses!

I have attached another sketch regarding the arrangement. IsaacStructural I believe you are correct, see sketch. The 3x 2x8 carry the bulk of the joist loads, while the 2x 2x8 carry some floor load and the wall above it. The wall above it is an internal wall which isn't load bearing but has plaster etc. so it can't take a lot of movement. My main issue is deflection and not excessive stress in the members if I remove the 3x 2x8. LVLs are slightly stiffer than SPF, is there another reason why you recommend them? Removing the existing 2x 2x8 and replacing with LVL can't easily be done because of the existing wall above and replacing the bottom 3x 2x8 with LVL doesn't really help out my head room issue.

I could try a flitch plate arrangement by adding PL.1/2" and then another 2x8 to the existing 2x 2x8 section but I wonder if stability would be the issue again.

Are there any other options?

 

[msquared48]

If you have a flat plate on top of the (3)2X8 beam as shown, you could shore the floor, remove the plate and (3)2X8's, and replace the (3)2X8/s with (3)2X10's with about the same height. Or you could install a Glu-lam or LVL beam.

You need to check the deflection too, obviously.

Mike McCann
MMC Engineering

 

[dhengr]

I’d jack up the 3-2x8's to take the load of the 2-2x8's and then remove the 2-2x8's. You haven’t mentioned how the existing jsts. are attached to the 2-2x8's, probably with jst. hangers? With some care the jst. hangers might be saved and salvaged. Peel the right most 2x8 off first and maybe you can get at the jst. hanger nails and drive them back out without yanking on and bending the jst. hangers. Replace the 2-2x8's with properly sized and number of LVL’s, jacked up under the subfloor and wall. Reinstall the jst. hangers and drive some diag. screws up into the wall bottom plate. Remove the 3-2x8's. Of course, all of this has to be properly sized.

 

[BAretired]

The joists are probably end nailed through the first 2x8. If so there would be no joist hangers. The joists are only six feet long, so the tributary width of floor carried by the beam is only about three feet.

It might be simpler to jack both beams, cut off the joist ends to receive a new beam, then fit a new beam between the joist ends and the 2-2x8 beam, then add flush face joist hangers to the new beam and then drill and screw through the 2-2x8 into the new beam to force them to act in unison. Finally, remove the jacks and the lower beam.









BA