wood beam and steel, in plane of joists 1

[SLTA]

I've read the other flitch plate vs channel threads, and that's raised a question for me. I'm renovating an existing deck into party space and have a set depth to work in. The owner is insisting that a column be removed, which means that my span/trib width no longer works for the largest PSL I can use.

My layout requires the top of the beam to be flush with the top of the joists. How does one use channels in this situation, with wood joists framing in at 12" oc into the channels? Or should I just automatically go for a flitch plate instead?

To make matters even more fun, the beam will be exposed continuously to the weather (it's a deck) but covered by decking material above and a gutter system underneath, so it will be hard to do any condition assessments or maintenance.

Thoughts?

 

[dhengr]

Slta:
Channels toe to toe, light cont. weld btwn./on the top toes and the same or stitch welds on the bot. toes. If they weld in the proper sequence they will actually introduce some camber into the final beam, essentially a box beam. Tack them together, then weld the bot. cont. weld first. That will introduce the camber into the whole beam. Weld the top cont. weld with some sequencing and that will take some of the camber out of the whole beam. Drill the webs for bolts and ledgers (2x10's, or whatever) and hang the joist in joist hangers. This could also be weld-on threaded studs. Drill a few drain holes in the bot. of the beam. Maybe end caps, or at least hardware cloth to keep the critters out, but allow inspection. Flash the top of the whole arrangement because you don’t want any water getting in and sitting there, btwn. any of the members of this built-up beam. This flashing can be as simple as some sticky 30# ice and water guard material, hanging an inch or so wider than the ledgers. This protects the ends of the joists too. Cut the existing joists and temp. support them, so you can slide this new beam up into place and install the joist hangers. You could bolt the ledgers on before welding or use some of the new expanding, blind bolts.

 

[SLTA]

dhengr, BRILLIANT.

 

[dhengr]

If they are new joist or there is any chance that they might shrink across the grain, let the steel beam down 1/8 or 1/4" from the top of the joists because it certainly won’t shrink. I’ve seen a hump form in the floor above, right down the length of the beam from this joist shrinkage action. How are you going to support the decking over the stl. beam which will be 7-8" wide, including ledgers?

 

[jdgengineer]

What about using an I-beam and packing the web?

 

[dhengr]

Slta:
I’m always happy to be of help to ‘one of the guys.’

Jdg.... S-shapes drain well, and if you rip a matching slope on the bot. edge of the outer 2x10 pad-out side members, they can bear on the bot. flg. and you don’t need so many through bolts in shear, acting as fairly long cantilevers off the stl. web. The inner pad-out piece, whatever thickness, can be short enough in height to miss the web/flg. fillets. The through bolts primarily hold the whole sandwich together, not carry the joist loads in shear, and as long cantilevers. Drill a few drain holes in the bot. edge of the 2x’s right at the S-shape flg., or just cross cut a few notches in this edge. Still, flash the top, as above, to shed water away from the beam. The wood should all be PT of course.

 

[msquared48]

A lot of field welding guys... but it will work just fine.

I would consider just using a tube section to eliminate the welding though, with the the bolted wood ledgers and vertical offset too.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com