new wood beam directly below an existing wood beam, for additional capacity 1

[SLTA]

I have a client who wants to take out a steel post in his basement, to open up the room. The existing beam doesn't work for that new length. I've recommended removing the existing (2) 2x10 and installing new LVLs of the same depth, which would allow a simple bearing support on the unreinforced CMU wall for the new beam. He really wants the beam dropped below, because his mason says it would be easier to install. I'm concerned about load transfer between the new and old beams as well as stability of the compression side of the new beam. I'm thinking of recommending that he connect the new beam to the old with metal nailer plates and connect the joists to the existing beam with joist hangers as the ledger would be compromised by the plates. Is there anything else I should add or think about?

Please remember: we're not all guys!

 

[TehMightyEngineer]

Shear flow; it's your friend.

Maine Professional and Structural Engineer.
(Just passed the 16-hour SE exam, woohoo!)

 

[JAE]

Once load is transferred you will have a one-time instantaneous deflection as the load it converted to the longer span.

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[chamokinawan]

I think it would be easier to sandwich the LVL's to the existing beam, but just design the LVL's to take the full load.

 

[KootK]

I'd omit the new joist hangers and leave the ledger condition alone. Presumably the bottom of the existing beam Is laterally braced by the joists framing in. If that's true then toe nailing the top of the new beam to the underside of the existing beam should be sufficient to brace the new beam. Omitting the side plate will also allow you to use a new beam wider than the existing one if you care to. Any composite behaviour between the two beams is a bonus but I wouldn't count on it. Do you know if the upper beam is two simple spans or a two span continuous?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Splitrings]

Have you check the deflection in the existing double 2x10's? You may have to jack the existing bean in places to apply the new LVL's to each side.

To place the new LVL under the existing will be difficult if there is any deflection in the existing member. There will be no way to jack unless you place temporary members on each side of the existing beam. The temporary members will have to be stiff enough to transfer the jacking force to a sufficient number of floor joists.

 

[XR250]

As KootK says, just toenail it an be done with it.

 

[Archie264]

I guess I'm missing something...unless you sandwich the existing 2x10's with the new lvl's as chamokinawan suggested then you're going to have to shore the existing joists to remove the post. Since that has to be done anyway it should be easy to remove the existing 2x10's and replace them with the new lvl's. In fact, that seems easier to me than installing it under the existing beam but, like I said, maybe I'm missing something. In any case don't let a lazy mason dictate the design.

 

[dhengr]

SLTA:
Since the masonry contractor is so damn smart, I can’t help but wonder why they are wasting all that money on engineering. Why doesn’t he just design the beam the easiest way possible, and figure out how to install it the easiest way possible, and figure out how to provide bearing for the new beam the easiest way possible, and be done with it. Why should they involve you at all, except as an insurer of last resort, for a dumb condition. Usually, people are fighting for head room in a bsmt. and don’t want a dropped beam, even if it does save the mason a buck or two. How is he going to cut in bearing spaces in the conc. blk. walls for the new beams, below the existing beam, any easier than he would cut them in along side the existing pockets? I’d shore the existing joist, just to start lifting them of the ledger, to unload the existing 2x10 beam. Remove the ledgers, and cut the joists shorter by the width of an LVL, slide the LVL’s up into place, screw them to the existing 2x10 beam, apply joist hangers to support the joists. Maybe not quicker and cheaper than the mason would do it, but a much better solution and finished product.