Sistering steel channels to wood beam

[reverbz]

Hey Guys,

I am working on a project where I'm considering sistering an existing wood beam with steel channels to help with DEFLECTION.

It seems this is a common solution but I have a couple of concerns:

1. With critical slip(especially if using bolts), don't I need to basically just consider the channels as taking the entire load and deflection or is that overly conservative?

2. I feel like lateral torsional buckling is a concern in the channels and I'm not sure if this has been discussed but would be interested to hear if my worry is misplaced.

Please let me know your experience with this detail. Have you used it alot? Do you feel comfortable with the concerns I mentioned?

Thank you!

 

[Harbringer80]

I've used it. Unless you specify that the framing is to be shored (jacked up) prior to installation the channels will only begin deflecting under any new dead load and live load.

Generally, I've just designed these as back-to-back channels, though I have went the transformed section route for specific cases.

1. Don't use bolts, use lags. You will still experience some slip.
2. If you are concerned either brace the beam or run the calculations for LTB.

 

[KootK]

Some questions:

- what size is the wood member?

- what size are the channels?

- where are the channels vertically relative to the wood?

- do the channels make it out to the bearings or only run partial length?

I often will just use the channels for capacity if they dwarf that of the wood.

I wouldn't normally sweat LTB if the member is simple span and compression edge of the wood member laterally braced. The channels will tend to rotate into one another to some extent owing to the locations of their shear centers.

 

[jerseyshore]

I do this from time to time and agree with the two other posts above. Not too worried about buckling. And I'll always design the channels to take the full load. And designed the bearing supports to receive the channels as well.

It's rare they actually jack and remove stress, that kind of defeats the purpose IMO. Might as well put a new beam in then.

 

[Ron247]

I generally jack them some if reasonably possible, but that is so the fasteners can get some of their slip out of the way when the jack is released.

Also, if you are using bolts, consider the carpenter will use 1/8" over-sized holes in the wood unless you watch them. Wood bits tend to come in 1/8" increments, not 1/16". They have to buy a metal type bit to get the 1/16" oversize hole and many do not want to spend the money. So, if you want to consider the wood joists in your calcs, 1/8" oversize holes may be an issue.