Sister LVL to bottom chord of truss

[Drasticdesigning]

I am working on a residential project. The owner wants to take down an interior load bearing wall . Above the wall that is to be removed there is a double truss made of 2x6s bottom chord with vertical 2x4 members. There are an additional 10 trusses/girders connected to the bottom chord of the 2x6 double truss.

The owner wants to have the ceiling flush with existing after removing the wall. I have been calculating loads and spans for a new power beam mounted flush with the bottom chord. Its span is 20' and will be bearing on the exterior wall and a newly constructed interior wall.

Project is in south Florida. Live loads are 20 psf for roof and 20 for attic with storage. Dead loads are 15 psf for roof and 10 for ceiling.

The supported framing span of the truss is 30 feet. Per the power beam spec and my calcs, a 5.5" x 16" size is required.

I checked the moment and shear capacity of the beam, and its allowable moment and shear exceeds both. So thats no problem.

In the brochure for the power beam, it mentions how to attach two beams together with thru bolts, 0.5". It also mentions the load being top or side loaded.

I want to thru bolt every 12" thru bottom chord of truss and power beam. I am stuck on how to attach the 16" height power beam to the supporting walls. All connectors are bottom mount. But that would not leave the beam flush with the ceiling. Im thinking installing the beam connector upside down and have it mount to the face of top plate and the beam can bear on the walls top plate.

Sorry if this wordy. Im looking for ideas that will lead me down the right path.

Thanks.

Rich.

 

[jayrod12]

How are you planning on working around the bolts? That would be my biggest concern. I would talk the homeowner into a bulkhead for a dropped beam. Then all the concerns about rotation and fastening issues go away.

 

[Drasticdesigning]

Jayrod12,

I was going to attach a 2x6 notched out for the bolts along the entire bottom chord with truss screws. Then I would attach the .5" dia thru bolts through the bottom chords, 2x6, and new lvl. Bolt spacing at 12" staggered.

Home owner wants the ceiling flush. This would put the new lvl sticking up 10" past the top of the bottom chord.

 

[jayrod12]

Then I'd probably be looking at bracing the top flange of your new lvl to each of those trusses framing into the girder truss. It's going to be a messy install but doable in my eyes.

 

[Drasticdesigning]

Jayrod 12,

Thats interesting. Im imaging two Simpson connectors and a 2x4 from top of lvl to top of each girder trusses.

Any ideas on how to check moment applied and resisting. Maybe possible to reduce the amount of connections needed.

 

[jayrod12]

I'm not 100% sure off the top of my head, but I believe the LVL design values assume lateral bracing for the compression flame at 24" on-centre. Which would mean every truss.

Besides, each truss just feels good. And a lot of residential/wood framing is more what feels/looks good then putting in the minimum amount.

 

[KootK]

- I would consider the power beam LTB braced at each truss web. Any chance it can work like that? Seems like you'd be braced at quarter points-ish. That's not too bad.

- You could fasten a flange to the top of your beam. Not for composite behavior but for beam top lateral bracing. Only needs to span between truss webbing so not too onerous.

- I'm not sure I understand the support difficulties. Can you not taper the beam end and have it sit on the wall plate like the truss does? With an intermediate bearing wall, you can probably do this as two pieces?


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.

 

[Drasticdesigning]

Kootk,

Notching is not an option. The resulting allowable shear stress would be reduced to below required.

I will look into attaching the top of the beam to the truss side chord with 2x4 or bigger. I am unsure of what to install to satisfy LTB connections.

Installing a 2x6 sideways atop the beam and across the length of the beam sounds good. That would be my connection point to the trusses.

The new beam should sit flat atop the existing building walls top plates. Lots of jack studs and connectors throughout.