Wood Expansion Calculation 1

[Jerehmy]

Does anyone know of a book that gives guidance on factors for wood expansion due to increased moisture content?

I have a claim where the hardwood flooring expanded so much it literally pushed the plywood panels outwards with the stud wall causing damaging the brick veneer.

I need a calculation to verify if this is even possible.

Thanks.

 

[BAretired]

I just had a quick look in this link which appears to address your question:

http://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0CC8QFjAC&url=http://

http://www.crescenthardwood.com/nof...aw37ZzpNyMolYng&bvm=bv.69411363,d.aWw&cad=rja

BA

 

[Hokie93]

I recently ran into a similar question regarding plywood panels and contacted Dr. Frank Woeste at Virginia Tech. He was extremely helpful and responded in a very timely manner. You can find his email address on several articles authored by him that were recently published in STRUCTURE magazine. Lumber shrinkage and swelling is also covered in Woeste's textbook, "Wood Technology in the Design of Structures". The textbook "Design of Wood Structures" by Breyer, et al, discusses moisture content effects in Chapter 4. Both the Woeste and Breyer books reference The Wood Handbook as an authoritative source regarding moisture-induced movement in wood.

 

[msquared48]

"Example 3: Width. Wider pieces of flooring will shrink or expand more than narrow pieces of flooring for a given change in moisture content. As shown in example 1, a plainsawn, ¾” x 2 ¼”, red oak strip will change in width by 0.0332” if the moisture content changes by 4%. If a plainsawn, ¾” x 5”, red oak plank changes in moisture content by 4%, the change in width may be as much as 0.0738”, which is more than twice that found with 2 ¼” wide red oak."

This is a ridiculous statement as the wood expands or contract the same regardless of the width.
Note that (5/2.25)X.0332 = .0738". duh...

Mike McCann
MMC Engineering

 

[TehMightyEngineer]

Nice observation Mike.

Maine EIT, Civil/Structural.

 

[Jerehmy]

BA - Thanks for the article, this will give me an order of magnitude calculation which is exactly what I needed.

Hokie - I have the breyer book and I love it. I really need to get the wood handbook, I'll have to look into it.

 

[Jerehmy]

Jeez the wood handbook is free online. Made my day lol. I've used chapter 5 before but I didn't know the entire book was available online.

 

[dhengr]

Jerehmy:
That could possible happen. I would like to see a section through the bldg. at the floor framing including the exterior wall, with complete details, dimensions, sizes, material types, photos, etc. etc. The wood floors will expand and contract, and as often as not this shows up as floor planks buckling in high moisture periods and cracks opening up during dry periods. There might be something strange about the way these floors were put down, or the way the structure was detailed that needs study. BA’s article looks good and the “Wood Handbook: Wood as an Engineering Material” is a very good all around ref. book.

 

[Jerehmy]

dhengr:

I don't have time at the moment to draw that all up but I can give you an overview of what I found and what happened:

A person who was a friend of the homeowner would periodically check on the house. He found the house saturated water on the first floor with the hardwood flooring buckled at least 8" up. There was at least 10" of water in the basement.

The hardwood flooring was gone but it spanned N/S and the E/W elevation walls were the ones with the most damage. The plywood panels had 3/8" gaps and larger. Also, the panels that seemed to have "pushed out" had nail heads that either popped up or rotated as if the panel WAS indeed pushed out. Nail heads on other panels were perfectly vertical. Also, the rim joist in the basement was pushed outward at the top while the bottom was flush.

The damage to the veneer was a bulge approximately 4-5" above the wall bottom plate. The bulge caused a bed joint crack in the west wall, south wall, and part of the east wall. The north wall was not damaged. There were also numerous step cracks and vertical cracks, all seeming to be fresh as they lacked debris and were crisp.

The house was gutted when we were there besides plywood flooring, studs, exterior wall sheathing (thermosot? idk how to spell it), then brick veneer.

The only other possible explanation would be water buildup in the cavity between the brick veneer and the thermosot. But the bulge occured ABOVE the sill plate, which doesn't make sense. The max water level would be the sill plate. Also, if the water DID freeze behind the brick I'd expect the thermosot to fail before the brick as it seemed very flimsy.

 

[dhengr]

While Mike’s observation is profound, just what you would expect..., if you think a little deeper, the point that was trying to be made is that the wider board will show twice as much movement at each joint; leaving wider gaps in the dry season. Alternatively, you have half as many joints to accommodate any cross grain expansion, when you lay wide boards too tightly. Wider floor boards are more prone to buckling for this reason.

 

[Jerehmy]

Clarification: "But the bulge occurred ABOVE the sill plate wall bottom plate" and "max water level would be the sill plate wall bottom plate"

 

[msquared48]

Well, the only thing I would question is why the force was relieved in two locations - at the wall sill plate, showing up in the brick veneer, and within the flooring itself.

Usually I would expect the force to be relieved by one weak link, not two, as the pressure would continue to be relieved by the first link, not overstressing the second. Am I making sense here?

Mike McCann
MMC Engineering

 

[Jerehmy]

Here's my understanding of what happened: The hardwood flooring pushed the plywood underneath apart and the wall outward. It had to push the wall outward to make room, the plywood pushed apart because it had no choice so I wouldn't say it was a weak link, just evidence of the outward pushing. The same as the rim joist pushed out at the top.

The tenting I'm fairly certain occurred in the northwest portion of the house. This portion did not have plywood pushed apart AND the brick veneer was not damaged at this location.

 

[Jerehmy]

And yes you made sense

 

[msquared48]

dhengr:

Yes, I agree, but if the boards are properly installed, the joints should be tight before any drying. They are supposed to really be hammered tight, and I have done this. Still, joints can open up. The wider boards are just more prone to cupping, which would induce secondary moments on the boards. This is why you use (3)2X4's for stair treads rather than (2)2X6's.

Mike McCann
MMC Engineering