Wood - Crushing and Warping in Header

[bookowski]

Wood question here, looking for some input. I've been asked to determine the likely cause of failure of a wood header:
- Header was a (3)-2x10 that was sparsely through bolted
- Header was in a crawlspace and supported a center bearing wall on a two story apt. house.
- The header was supported on steel pipe columns @ 5'-0" o.c., 20'-0" joists on each side of the header were top bearing on the header
- Each pipe column had a 4"x6" bearing plate on top, lag screws through the bearing plate into underside of header

The header was already removed by the time I inspected it so I didn't see the in-situ condition. However, it was still on site and the problems are pretty evident. There is significant warping of the header. The outer plies are curling outward, and the overall 3x header is twisted. There is also crushing failure at all post locations. In some instances there is up to a 3/4" deep pocket in the header where the bearing plate was located.

Based on some rough calcs it seems like this would have seen about 550psi perp to the grain (bearing). That is high, but I doubt this ever saw a design load - especially at every post location over 80ft. of length. Most likely it saw much less than this. Would you expect to see that much crushing at say the... 300psi or 400psi range? (I don't know the species, this is in the Northeast)

I'm also trying to figure out the twisting. Is this likely the result of some differential moisture issue? Green lumber that was bolted together and then warped as it dried? Or is it related to the crushing? Obviously not looking for anything definitive here, just looking for some opinions. See attached pics.

 

[bookowski]

Another picture here (couldn't figure out how to attach two at once...)

 

[MiketheEngineer]

Probably a Fir - Douglas Or Hemlock. Agree with you that does seem strange. Most firs do not curl or twist in moisture although it can happen - esp if green. Might be Southern Pine. Look for a grade stamp. If none found - then you have crappy lumber.

What is the span of the headers and your estimated PLF loading. I can check it real quick.

 

[bookowski]

Posts are at 5'-0", so that's the span and loading is about 2.7klf total load (for just D + L, ignoring snow). The reaction works out to about 13.5k and with the 4x6 bearing plate you get 560psi perp to grain. But again, that would be design load - I'm guessing it never saw anything close to that over the entire length of the building. If you take say 50% live load it's about 400psi. Just crappy lumber?

 

[Michel60]

Good afternoon bookowski,

Maybe the plates were too thin to effectively spread the load? Looks like there is a little bit a a concave surface in the crushed area. Also is there some fire damage to the beam? I see dark patches on the beam in the photos but it's hard to tell if its just moisture or char.

 

[woodman88]

If the moisture content in the lumber exceeded 19% for a extended time period or periods the perp to grain compression would need to be multiplied by 0.67 per the 2001 NDS Table 4A. Which lowers the perp to grain compression of DF-L to 418 psi and HemFir to 271 psi. From the condition of the bolts, nuts and washers in the pictures it might be a possibilty. I would check out the lumber species.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[bookowski]

Thanks woodman, good point. That didn't occur to me and that might have been enough to do it. My guess is that it something like a hem-fir, with the 0.67 factor I guess the crushing is reasonable even under service loads.

 

[oldrunner]

It looks like the header has been wet at some time in the past. What is the snow load at this location? If there had been a very heavy snow load at one time, then the crushing could have happened at that time - remember there is no rebound of lumber from loads perpendicular to the grain. Obviously it was overloaded (maybe just one time) and the wood "brinneled". (Heavy hauling insider joke).

Saw something similar of cripple wall studs crushing into a sill plate. Inspection was done in the summer time - but eventually told that the cabin I was inspecting received about 25 feet snow during the winter.

 

[MiketheEngineer]

Most Firs can't take that Perp load - much less if you need to reduce by a third!! Even SYP would be problematic.

 

[RFreund]

What is all the black/dark color? Is that char or mold?

EIT

http://www.HowToEngineer.com

 

[bookowski]

The black is char, but that was only over a small area and the crushing was at every post location - about a dozen.

Thanks for the input, I think the presence of moisture and the reduction in bearing capacity was the key that I wasn't thinking about.

 

[chicopee]

Nice detective work Bookowski, however, I curious, what replaced the wood header?