Dual Wood Post Bearing - Differential Bearing Issue

[KootK]

THE SITUATION

- One story post.
- Somewhat important support for steel beam.
- Field issue has arrived and this is what arch wants.
- Prefab wall panels. I expect that they'll accomplish the level bearing to begin with.

MY CONCERN

I'm a tad concerned that sole plate shrinkage on the right will be more than on the left and that the beam bearing will seem some differential settlement as a result. Then, maybe, the beam will rotate and cause drywall cracking issues etc. On the other hand, I wouldn't expect the differential bearing settlement to be more than 1/8".

Am I worrying about nothing here? It will come as a surprise to no one that I occasionally struggle to remain "solution focused".

 

[dhengr]

KootK:
Cut the sub-floor away immediately around the right 6x6 post, or maybe stop the sub-fl. at the vert. plane btwn. the conc. wall and the standing 2x rim board/blocking. Then, under the left post and for a stud space or two, use a double bottom sill pl. Still-n-all, the right post is going to take 75% of the beam load. Add a note that the tops of the two post must match +/- in elev. or be shimmed under the beam.

 

[jayrod12]

You could specify that the will plates at the post locations are engineered lumber, therefore subject to significantly less shrinkage.

 

[KootK]

I appreciate the input dhengr but I'm not actually asking for solution strategies here. I'm happy to entertain them for sport but what I'm really asking her is whether or not I have a legitimate problem that needs to be addressed or if I can just let my client do things as they wish. A poll basically. PROBLEM; NO PROBLEM. My gut feel is NO PROBLEM.

 

[Ron247]

When you say "sole plate shrinkage", are you actually talking about crushing/flattening of the sole plate? In just studying your drawing, I see the following:
Having 2 layers of sole plate on the right but 1 layer on the left will probably lead to more "flattening" on the right.
The higher axial in the right post will lead to more Pl/AE on the right also.

The 4.5" sill width on the left will probably increase the flattening on the left since it appears smaller than the right side.

Spitballing ideas:
[ol 1]
[li]Could you use a lower compression perp to grain sill on the left and use 2 layers on the left?[/li]
[li]Use a web stiffener on left side but not right side; This will minimize left flange bending and therefore it may cause it to flatten more also.[/li]
[li]Connect the posts to each other to some degree. Recess some lag screws for example.[/li]
[/ol]

 

[Ron247]

As far as it being a problem. I think it is a minor problem at the most. If this is something the Clients wants, warn him of potential drywall cracks that are not structural in nature and let him have his way.

I see jayrods idea and it sound like a good remedy.

 

[Teguci]

Right post deflects more, load concentrates on left post, top of beam wants to rotate right, a small amount of lateral load is added to the diaphragm (you do have a diaphragm?), left post is eccentrically loaded and buckles out to the left (braced in the other direction?), which redistributes load back onto the right post.

So quick check on diaphragm and post buckling and I'd say good to go. Probably wouldn't even do that but that is an ugly connection and worthy of suspicion.

 

[KootK]

All: if we decide this is a legit problem, I'll just center a single under the column and deal with it a the foundation level. Probably should have mentioned that to begin with.

You could specify that the will plates at the post locations are engineered lumber, therefore subject to significantly less shrinkage.

Thanks for the idea, I'll noodle on that. The only hitch is that, if I start this, I'll either want to do it everywhere or stop it somewhere. And then, where I stop it, do I create an issue there. Probably a lesser issue.

Cut the sub-floor away immediately around the right 6x6 post

I don't see the subfloor being an issue and extending the post kinda messes with the wall penalization. Another thing that I should have mentioned is that the bearing stresses here aren't huge. The steel beam is only really a steel beam because of the combo of limited depth availability and tight deflection.

When you say "sole plate shrinkage", are you actually talking about crushing/flattening of the sole plate?

Exactly, thanks for your input.

Could you use a lower compression perp to grain sill on the left and use 2 layers on the left?

I could but deem this too complex in the field relative to other solutions at my disposal.

Use a web stiffener on left side but not right side; This will minimize left flange bending and therefore it may cause it to flatten more also.

I'd have little faith in this. The steel's just so much stiffer than the wood, even without the stiffener.

left post is eccentrically loaded and buckles out to the left (braced in the other direction?), which redistributes load back onto the right post.

[/quote]

connect the posts to each other to some degree. Recess some lag screws for example.

Was considering this and will do it now. Probably LPT4 or something rather than lags as the two posts will be different panelized walls I believe.

you do have a diaphragm?)

I do. At least is as much as these choppy houses ever do.

 

[TehMightyEngineer]

I'm going to go with not a problem. If you get any differential shrinkage (which I don't expect to be a problem as the difference should be minor) the bearing of the beam on the post should compress more on the un-shrunk side until you get roughly equal load transferred to the posts. In addition, the bolts in the WF bolted connection to the posts should provide some uniformity in the load transferred and prevent rotation of the beam or uneven load distribution.

Ideally the drywaller will also be good enough to avoid putting the edges of the drywall in any areas where movement of the post would cause issues. A good drywaller should know that a post supporting a steel beam will be taking some serious axial load and gap their drywall accordingly.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL, CO) Structural Engineer (IL, HI)

 

[jayrod12]

If it were me in all honesty, I wouldn't of given it two thoughts and just let it go. I was originally under the impression you wanted a fix.

In my mind, with the variability of wood, even within the same species and grade, you could end up with the left sill being at the low end of the perp to grain capacity and both plates on the right at the high end, eliminating the concern altogether. In a worst case scenario it would be the reverse. And in the worst case scenario, what level of crushing are we actually talking about? Probably 1/8" like you indicated, not enough to really bat an eye at if you ask me. I feel with the redundancy and variability in wood, you're KootKing this problem.

 

[gte447f]

On the shrinkage/shortening issue, I lean towards not a problem. I would make sure that both posts are good to go for eccentric loading, including a little extra load capacity in both to account for uncertain/varying load distribution between the posts that might result as the posts find equilibrium during the shrinkage/shortening process.

 

[JoshPlumSE]

A good drywaller should know that a post supporting a steel beam will be taking some serious axial load and gap their drywall accordingly.

I personally have no faith in drywall guys to recognize something like this.....

 

[Tomfh]

Potential problem. Use preshrunk plates. Or alternatively laminate the posts to allow them to bear one side only.

 

[KootK]

If it were me in all honesty, I wouldn't of given it two thoughts and just let it go

That's what I'm taking about.

...you're KootKing this problem

It was only a matter of time before I became my own, unflattering verb. I like it.

 

[KootK]

Potential problem.

Finally... some dissent. Thanks for weighing in Tomfh.

 

[Tomfh]

It could well be nothing, but plates and joists do shrink, and differential shrinkage can cause hassles.

My house had a sheet of dry wall pop off due to plate shrinkage, and a friend of mine had to fix his skirting boards when there was a differential shrinkage issue. The joists shrunk more. Joists are a lot thicker than plates so can cause more issues, but even one plate can shrink enough to crack things if there’s no room to move.

 

[KootK]

Yeah, and it's not as though the monstrously rich are super tolerant with their construction defects.

Regardless, for what it's worth, the decision's been taken and I'm on the do nothing path.

 

[Tomfh]

Report back in 2049 and let us know if it misperformed in any way.

 

[jayrod12]

I also feel that your plate connection to the posts will provide a bit of fixity if the posts end up even nominally fastened together that will help resist any torquing that may present itself.