large checks in doug fir columns

[SLTA]

I've looked through the archives, but didn't find anything talking about checks this large. I'm looking at large doug fir timber columns and beams (12x14 or so), about 7 years old. Construction pics show that they were straight with no checks at all when installed, so they must have been wet when milled and installed. Now, one column has a 3/4" wide by about 5" deep check on one side and a corresponding 1/4" wide check on the other (directly opposite, but I can't tell if it goes fully through).

(upper part of col check)

(lower part of col check)

These checks seem larger than the "no big deal" variety, although the timber system is largely just decorative. I'm thinking of lag screws to pull the column together or at least stop further separation, if possible. Of course it's also a $3million house so it has to look acceptable aesthetically.

The beam above it has twisted so much that it is off its seat on the lower beam, and has cracked a portion of the beam off from pressure.

(side view of beam and top of column)

(backside view of end of beam, showing crack and rotation on beam seat)

I'm thinking of shimming it with hardwood to get the pressure off the cracked portion.

Does this sound reasonable? Any other ideas? And thanks!

Please remember: we're not all guys!

 

[dhengr]

SLTA ( we're not all guys )
There seem to be several funny things going on in your pictures. Is the column on the interior? It seems to show that there might be 2x laminations on the left face and about where the check occurs. The check actually approx. follows the glue line, but deviates because sometimes the glue line is stronger than the adjacent wood. I can’t point to an exact para. or sentence, but I think if you look at the grading rules, the codes and timber design texts you will find that they do recognize that that kind of checking can/does occur on large timber members and they account for some of that potential in their grading and allowable stress values. It has surprisingly little affect on the member strength as long as check is relatively parallel to the long axis (the grain) of the member. The exception is if the split/check slopes out to an outside face of the member, which has a weakening effect. In the column, that vert split is akin to a horiz. check or split in a beam, and there we know that as a potential horiz. shear problem.

The beam photos show a real horiz. shear crack, at a reentrant corner, in a high (large) notch in a beam which does appear to be a solid timber member. This member also shows some typical checking, just below the reentrant corner, and it also appears to be an exterior detail. Take a look in the NDS and a good wood design textbook about what they have to say about the problems with notching beams in high shear areas or on tension faces.

Generally, I think your idea of long lag screws (maybe through bolts), some clamps to assist in their installation, and some good waterproof glue in the cracks are about the right approach. Then, instructions to watch and see that this fix settles the problem down, and the cracks don’t grow any further. If the lags and a washer plate end up exposed, I’ve beat the plates a bit with a ball pein hammer, painted them flat black, and sold them as wrought iron hardware. You put a matching fake one on the other end to make it look right. Your idea of hardwood shims for the beam seat sounds about right, and you might put a couple long lags or through bolts up through the whole beam just to protect that reentrant notch corner.

Later addition....
The crack at the beam notch looks fairly new. I’d investigate a bit what caused, or what allowed that beam to roll/twist that way. The beam doesn’t appear to have any lateral support below the bearing notch level. And, if that is an exterior detail/corner, I’d try to do something to divert water from the above corner away from that nasty (messed up) detail of beams, notches and column end grain.

 

[SLTA]

This is all interior, yes. The cols and beams are single members. The photos might be throwing you off, as they show a chamfered edge on the col and the beam (see 3rd photo for what I mean).

That shear crack in the 3rd pic is the same as the piece breaking off in the 4th pic. It's crushing it while the rest of the beam twists on itself.

Please remember: we're not all guys!

 

[mike20793]

How is the beam loaded? Are there members framing into the side of it? I agree with dhengr that the crack at the notched beam end could be a problem. It looks more like cross grain tension caused by the corner binding up on the seat under torsion rather than crushing. Either way, now that the split has propagated into the beam notch, it now has to be mitigated and possibly strengthened, depending on the loads. There should have been some mechanical restraint in the seat, rather than just leaving it up there to bear on it's own. Based on the amount of pith in the member that we can see the end grain, it wouldn't surprise me if it was a twisting due to shrinkage issue.

 

[MikeHalloran]

My expertise extends as far as having rented a few timber framed vacation properties, and spent idle time appreciating the joinery. I have seen videos of log cabins being constructed with the angle bottom notch shown. ... using chainsaws to make the notches and the beveled tenons, and they all fit a _lot_ better than your exemplar. ... which looks like it once fit better.

I'd have to guess that a pretty large moment would be required to rotate the beam in the notch as shown. Can you find witness marks of something being jacked against or impacting the bottom of that beam?


Mike Halloran
Pembroke Pines, FL, USA

 

[Tmoose]

Someday I plan on adding a few keys to a beam that I notched too deeply on the ends, and split from the horizontal shear. So far, For the last couple of decades the thru bolts near the ends have sufficed.

Like this -

https://s-media-cache-ak0.pinimg.com/564x/f3/76/8d/f3768dbaa1604dd44e34c94d00ec2be5.jpg

http://www.ftet.biz/index.php?action=resources.wp01

 

[KootK]

The column checks don't bother me so long as they're not full depth. Every post in every ski lodge in western Canada seems to have that degree of checking and more. And with a gazillion pounds of drift load. Consequences = zilch.

The notched beam is a problem. In order of sexiness:

1) Jack the beam a little and sit it on a nice steel bracket mounted to the side of the column.

2) Reinforce the beam with some of those nifty new timber screws. These guys will even design it for you: Link.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Ron]

SLTA...agree with the "glue, clamp and nail process". If you can't nail and clamp, epoxy injection (just like concrete) works fine. Have used it on deteriorated timber sections and badly checked sections.

 

[SLTA]

Thanks, everyone.

mike20793: It's really lightly loaded, like maybe just a bit more than self-weight and some drywall. The actual structure runs above and spans over it. The whole beam has twisted bigtime (the other end the opposite way).

MikeHalloran: No marks at all of it being knocked into.


Tmoose: that's pretty!

KootK: Glad to hear experience of the great white north. I may add a few screws to the col just because I really can't see if the crack is all the way through, and it looks as if it may be close. I'll definitely work on that beam support.

Ron: Thanks for that! I hadn't even thought of epoxy.

Please remember: we're not all guys!

 

[KootK]

KootK: Glad to hear experience of the great white north. I may add a few screws to the col just because I really can't see if the crack is all the way through, and it looks as if it may be close. I'll definitely work on that beam support.

Among woodies, there is a school of thought that, within reason, the development of checks within timber members serves to relieve internal stresses and thus actually strengthen the afflicted member. I worry that reinforcing/repairing the columns might actually have a negative impact on aesthetics. When you close up / secure the existing checks, the member may seek alternate avenues of relieving internal stresses. In that respect, I'd definitely prefer a gap filling strategy to a gap closing strategy.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[msquared48]

Three Questions:

1. What is supporting the end of the beam"? The third picture seems to suggest nothing unless there is a side notch into the other beam. The fourth picture seems to suggest a vertical notch beam to beam.

2. Does the twisted beam see any torsional forces that might encourage twisting? If not, this is a curing issue and a section cut location in the tree dependent problem. Different areas of the tree warp and twist differently.

3. Were the beams kiln dried or put in wet?

Lastly, since you found big checks, can we get some of the loot?

Mike McCann, PE, SE (WA)

 

[SLTA]

HA! Loot, indeed.

1. The beam is notched into the perpendicular beam. The bottom of the rotated one and the top of the perpendicular one were cut away and they are seated on each other. The last picture shows the other side of the rotated beam wit its bottom cut, sitting (now rotated) on the cut portion of the perp beam. (like an "L" on the perp beam and one side of a "T" on the rotated beam, fitting together.)

2. There are no torsional loads on it. I definitely think it's a curing issue.

3. No idea, but they were installed in late winter/early spring in the mountains, and by the time they were enclosed there were leaves on the trees, so I'd say there was a lot of moisture available to them for a while. Then the A/C was likely kicked on and then winter and very dry air came.

I just had a nice chat with the guys at AITC - they were super helpful. I think I'm going to reseat the beam on some shims to stop the crushing and then put a couple (disguised) crack monitors on the beam seat and the column check, to see if movement continues.

Cheers, y'all!

Please remember: we're not all guys!