Longitudinal Split in wood

[JKJohn]

Hi All -

I have inspected an attic with wood trusses. It was built 40-years ago. I found numerous number of split members. The members are in both tension members and compression members. I could not identify a pattern. They are random. This image represents the type of cracks I found.

I did a quick analysis of the truss and found it to be fine (4/12 Fink truss spans 28').

What could the cause of suck split be?

Thanks in advance.

 

[jayrod12]

Is it all the way through the section? Cracks and checks are fairly common in lumber. I believe there's guidance in the NDS, sorry I don't know the reference directly, or the lumber grading agencies that discuss amount of allowable checks/cracks.

 

[phamENG]

As long as they aren't more than halfway through the member and not in the vicinity of the truss plates, I wouldn't be all that worried.

 

[Eric C.]

That looks like the tree pith, especially given the knot locations. Do you have a closer view?

 

[jimstructures]

JKJohn,

I agree with Eric C., looks like pith, i.e. the center of the tree. If a crack does not propagate thru the thickness of the member, across the member. It is usually not significant.


Jim

 

[JoshPlumSE]

This is a 4x12, correct? That's a pretty beefy member, so it's not unusual to see significant checks around the middle of the member. It's probably just a differential drying type of action. Make sure it doesn't go all the way through (probably not).

While it looks terrible, checking does NOT affect the flexural strength of a member. It does affect the shear strength. If you look at the 1991 or 1997 NDS there should be a factor to INCREASE the shear strength of beams that do NOT have checks like this. Sort of a backwards way of doing it.

The newer NDS codes, I believe, do NOT have this factor. But, from a first principals standpoint it could still be applied.... Long complicated story about why the codes essentially doubled the shear capacity for all wood beams.

I'm not certain about whether it affects tensile or compressive strength. But, if my memory is correct, I don't think it does. Though intuitively I would think it would affect the tensile strength.

 

[phamENG]

Josh - if that's a 4x12, I'd hate to be the one to handle that roll of tape! I think the OP was saying a 4/12 is the slope of the top chord. Proportions look like a 2x4 to me. Maybe a 2x6.

 

[JoshPlumSE]

You're probably right. The picture does look a little odd to me.

If it's a small member 2x4 2x6 or such, then that type of checking / splits would be pretty odd. And, it does look like lower grade wood. Maybe worth doubling up the members that are split like this, though I don't want to nail into them much in fear that it'll split more. Anyone use adhesives to double up a damaged member like this?

 

[ChorasDen]

I agree about that probably being a 2x4. As far as how this affects the truss, tough to say definitively without more info regarding the stresses in the chord, and the depth of the split.

JoshPlum, if you are trying to justify adding a member alongside, my suggestion would be to use a structural epoxy. My experience in the wood product manufacturing industry is that standard construction adhesive simply is not effective enough on wood to wood connections to develop appropriate load sharing. Not sure I agree that it would be as simple as sistering a new chord alongside this truss chord, however.

 

[msquared48]

If the checking creates two separate members, it is significant as S andI are significantly decreased.

Mike McCann, PE, SE (WA, HI)