Cantilevered LVL Ridge Bracing 1

[XR250]

This is a 32 ft. long ridge, 24" LVL beam with a 10 ft. cantilever. Would you consider the bottom "flange" of the LVL braced by the rafters? I am more interested in the negative moment introduced by the cantilever gravity loads rafter than uplift of the ridge as we are not in a high wind area.

 

[EngDM]

Honestly, I probably would consider it braced. When the wood beam buckles, it's not like steel where the bottom flange can buckle independant of the rest of the section; it would all have some movement or rotation to it, and since you are restraining over half of the section from moving I'd be inclined to consider it braced. My only thought would be what % of beam depth do your joists have to be to consider this as braced; what sort of rationale you can come up with or technical document reference. For instance your same scenario but the joists are 2x6 or 2x4 for whatever reason, is this also considered braced.

 

[TRAK.Structural]

I downloaded this paper from a previous thread on the forum. There is a paragraph at the end that basically says if the beam is braced anywhere from mid-depth to the extreme compression fiber that it is likely effective. The farther away from the compression zone that the brace is the stiffer it needs to be.

 

[XR250]

Makes sense - thanks!

 

[phamENG]

Depends on how you're connection those I-joists. Top flange hangers? Probably not. Is this going to be exposed? Simpson makes a strap for this exact situation to brace the bottom of the beam. Well...not this exact situation...it's more for uplift on deep roof beams....but same basic idea.

 

[XR250]

Depends on how you're connection those I-joists. Top flange hangers? Probably not. Is this going to be exposed? Simpson makes a strap for this exact situation to brace the bottom of the beam. Well...not this exact situation...it's more for uplift on deep roof beams....but same basic idea.

Face mount hangers most likely - LSSUI. I really hate using I-joists in a roof due to all those pesky web stiffeners top and bottom.

 

[KootK]

Definitely braced for me. Even if the thing would have to roll to close a 1/4" gap at the hanger, I don't see that being a frequent occurrence.

If the setup will be drywalled, odds are the drywall itself would close any compression gap anyhow.

Lastly, even though we don't treat a multi-ply wood beam as a composite section for many purposes, it surely is a substantially composite section for the low torsional stresses required to develop LTB stability. If a beam of these proportions has rotational restraint at the ends, in my heart I feel that it would pretty hard to uplift buckle it even if you only had continuous restraint at the top. Such a setup really takes all of the "lateral" out of LTB and turns it into constrained axis torsional buckling with a commensurately higher capacity.

 

[jerseyshore]

I downloaded this paper from a previous thread on the forum. There is a paragraph at the end that basically says if the beam is braced anywhere from mid-depth to the extreme compression fiber that it is likely effective. The farther away from the compression zone that the brace is the stiffer it needs to be.

Good reference.

I've always used the "does it look right" method of engineering on a lot of these deep ridge beams. A lot of retrofit projects have 2x4 or 2x6 RR's so a deep LVL ridge definitely needs additional braces.

This one looks pretty good as long as it has face-mount hangers.