Torsion in Wood Members

[Charred]

I recently designed a simple wood framed square building that is going to be used for retail space. Therefore, the front of the building has a lot of large openings for store fronts (span = 20' and roof trusses bear on store front wall). I used steel tubes for my beams and columns at the store front because there is ~10' of brick above the openings and the induced torsion from the brick would cause a wood beam to fail.

Now the same owner/architect wants to build the same building in a different location, but is using thin brick on the store front side to hopefully eliminate the need for the steel beams and columns. They would like to use an LVL with an angle bolted to the face to carry the brick. Has anybody ran into this situation before? I can't seem to find any references for this that provide much help. Also, let's say the wood beam CAN resist the additional torsional load, how would the connection at the wood beam to wood column be without having to use steel plates to resist the end torsion reactions that would induce a moment into the column? I have spoken with other structural engineers and it seems this is mostly avoided - but I tend to question why more than accepting it.

 

[XR250]

I thought thin brick was an adhered product that did not require lintels?

 

[Charred]

You are correct, I misspoke there. That is the option I gave them to eliminate the steel.

 

[jayrod12]

I would not be supporting 10' of standard brick on a wood lintel over a 20' load bearing span.

If it were thin brick veneer then sure, but not standard brick.

 

[XR250]

I agree with jayrod. It is done commonly on houses in our area by other engineers but I won't. Seems the brick acts as a deep beam so failures appear to be less than they should.

 

[jayrod12]

It's done around here sometimes too. Hell it's done on my house. And I'm not ripping off the brick just to fix it.It's worked for 58 years without an issue spanning a 9ft window. But there's only like 18" of brick above the window.

 

[KootK]

With sheathing behind the angle that grabs the studs above, there's a load path available to turn the beam torsion into stud bending and eliminate the need for beam end twist resistance. Still pretty dodgy though. And sensitive to plate shrinkage.

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.

 

[jayrod12]

It's better than no load path I guess, but then you've got quite a bit of lateral load at the lintel as well. So instead of torsion it's bi-axial bending, but that at least is calculable.

 

[KootK]

Yeah, the most advantageous approach sort of depends on the height of the stud work above. For those with a taste for danger, the shelf angle itself can be sometimes be effectively used to resist/reduce the would be biaxial load. Diggin' deep.

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.

 

[XR250]

Of course there is always the issue of putting a hanging load on the bottom 1/3 of an LVL - not recommended. Time to get some straps welded to the lintel.

 

[JoshPlumSE]

Obviously, you can check the beam for torsional shear stresses to see if it is sufficient. Similarly you can check to see how much it rotates to see if that could cause serviceability issues. So, that part is certainly do-able.

What I don't like is the connections. I'm not confident in my ability to detail out a wood connection that will be appropriate for transmitting that torsion in the the column. I'm sure it can be done, but it's definitely out of my comfort zone.

 

[msquared48]

Just eliminate the problem by hiring an artist to paint the bricks onto the exterior sheathing. Problem solved.

Mike McCann, PE, SE (WA)

 

[dhengr]

Charred:
Masonry supported on wood framing has generally been frowned on in the past, for a number of reasons, although I believe the IBC now allows it under certain conditions. Almost any masonry system is much stiffer than a wood lintel beam or wood back-up framing, so it will tend to try to take the load, until it starts to crack significantly, due to lintel beam deflection, etc. Obviously, thin brick veneers are lighter than a full brick veneer, but they are no less stiff for their min. thickness. I have seen these crack badly and buckle/peel/crumble right off the face of buildings where support members were too flexible for the brick veneer or where the whole building was so flexible that the thin brick tried to act as a structural shear panel.