Flitch Beam

[KenSchnee]

Hi and thank you in advance for your feedback.

I am working on a site where we have planned on a 20ft flitch beam comprised of 3 1 3/4 x 9 1/4 X 20 LVL and 2 5/8 x 9 1/4 X 20 Steel Plates. While the plans called for 9 1/4 steel plates we were only able to source 9 inch plates. Will this be fine or must the plates match the LVL exactly? If the dont match, what would be the recommend position installation of the plates to the LVL.

 

[dik]

It can work... don't know what's required. Check with the EOR. Can they increase the thickness of the flitch plate by a tad?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Flotsam7018]

The width of the plate just needs to be ripped down from a large piece of plate, there's no reason a 9 1/4" steel plate can't be provided.

 

[KenSchnee]

The steel was already purchased at 9in and pre drilled for flitch beam. Trying to avoid having to go back and repay/reorder the steel. Can I still use the 9 inch?

 

[kipfoot]

Can I still use the 9 inch?

The person who designed it originally will have to tell you. What you're proposing has less capacity than the spec, so if the design was close to using the full capacity it may not work.

 

[jayrod12]

I agree with the others that the original designer would be the one to make that final call.

That being said, I highly doubt that the design was that tight to need the additional 1/4". I'm betting they just made the depth to match and unlikely to need every last 1/16" to work.

Do not take my response as approval, talk to the original designer, I just don't think you need to feel the sky is falling quite yet.

 

[dik]

I suspect that the plate supplier ordered BARplate stock instead of having to cut it out of a bigger plate. Jayrod has the right approach and maybe time to sharpen your pencil. 1/2x9 is plate, not BAR... just checked.
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[XR250]

In 30 years, I have never seen a flitch with anything but round numbers for the plate.
9" plate is standard for 10" nominal flitch beams. Best to install the steel tight to the bottom to add some additional bearing area.

 

[KootK]

1) I believe that it is common to use steel plates that are shorter than the wood members that they reinforce. See the clip below.

2) Unless the beam bears upon a steel support, I believe that it is best to not put the bottom of the steel plate flush with the bottom of the wood members. Two reasons:

a) Where the nature of the wood components is such that shrinkage can be expected to occur, I don't want the steel plate protruding and plowing through the bearing material. This is not much of a concern with LVL given its dimensional stability.

b) This, hopefully, reminds designers that the shear carried within the steel plate usually needs to be transferred out to the wood components prior to making its way to bearing. This often requires concentrated ply fastening at the beam ends.

 

[XR250]

) Where the nature of the wood components is such that shrinkage can be expected to occur, I don't want the steel plate protruding and plowing through the bearing material. This is not much of a concern with LVL given its dimensional stability.

I don't share this concern as it seems to be a self limiting situation.
In the past, where the end reactions are big, I have have specified welded 1/4" bearing plates on the bottom of the steel in which case you would want the steel flushed out with the top.

 

[KootK]

I don't share this concern as it seems to be a self limiting situation.

It would be self limiting in most situations. But why bother to deal with it at all, self limiting or otherwise, if a simple adjustment to the detailing can sort it?

The other area where shrinkage can bite you is with the sheathing, top of bottom. If shrinkage causes the steel to protrude meaningfully, then you've likely withdrawn your sheathing fasteners, at least partially.

 

[XR250]

It would be self limiting in most situations. But why bother to deal with it at all, self limiting or otherwise, if a simple adjustment to the detailing can sort it

I feel like there is benefit to allow the steel to bear as it reduces the burden on the fasteners to transfer the shear back into the wood - which undoubtedly will have some slop. I suppose if the wood was really wet, withdrawing of the fasteners could occur.