Cracks in Round Log Girder

[PSUengineer1]

A round log girder supporting first floor and visible from the basement is approximately 8-inches wide, 7-inches deep, and spans approximately 12 feet north-south and supports a tributary floor area of 19 feet. The girder supports residential loading of 40 psf live load and 10 psf dead load. The perpendicular 8-inch block basement wall supports the end of the girder and the block was struck by a vehicle about 10 feet away from the log girder. The round log girder is split as seen in the attached photographs. The splits appear recent (exterior wood surface of log girder is darker than interior of split). The lighter color inside the split indicates to me that the splitting could be attributed to the impact. Do you agree?... or do I have other factors to consider in regard to the split?
Thanks.

 

[BAretired]

Doesn't look like a round log. It looks flat on the bottom. Is that a veneer on the bottom which has cracked at right angles to the beam? If not, what is it?

What do you mean when you say it supports a tributary floor area of 19 feet? Do you mean it supports a tributary width of 19 feet? If so, the beam supports a tributary area of 12x19 = 228 square feet.

BA

 

[EngineeringEric]

At first glance it looks like it could be simple timber checking, but i would not rule out structural damage. how would the impact have caused the cracking? are you thinking the impact induced an axial load which then split the log along it's entire length?
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And for future reference, one should not post questions like this online about a possible claim. it isn't too difficult for a lawyer to rip your findings to shreds if you posed questions online. It basically discredits your engineering opinion /judgment in court (I sometimes disagree but this is how it is)

 

[msquared48]

I find it hard to believe that the beam would split longitudinally from a force 10 feet away on a CMU wall. I don't feel that the wall would be strong enough to transmit that much force laterally to the beam. I would also expect to see damage to the end bearing connections and joist to beam connections. The beam just does not seem like the weak link in this scenario.

Mike McCann
MMC Engineering

 

[msquared48]

In looking closely at the pictures, I see both fresh wood exposure and old wood exposure areas. I think this was a pre-existing crack with loose areas that may have been knocked further loose, or removed by the current owner, after the accident. In my opinion, the impact most probably did not cause the crack.

Tell the owner not to go there...

Mike McCann
MMC Engineering

 

[SLTA]

The splitting definitely looks new. I've been in tons of basements and haven't seen checking anywhere near that deep. That cracked bottom in the last picture looks bad, too - perp to the main deep crack.

I'd recommend shoring and replacing, and getting them out of the house. What a pain to deal with. Do they possibly have any basement pictures that you could use for comparison?

And can you draw a picture of where the car hit, and the relationship of the wall to the beam?

 

[Jerehmy]

Did you measure the deflection. Was there any visible sag in the beam. Can you tell how far the crack goes up? Since the cracks are fresh it'll be hard to justify it not being attributed to the wall being crashed into. But more importantly, is it structurally sound and can it be repaired?

Odd crack, I haven't seen a wood beam split like this during my inspections. Let's say the wood beam splits entirely in half. It would have a reduced capacity if it wasn't laterally braced but for all intent and purposed would have the same strength.

Again its hard to say if it was structurally damaged without measuring the infield deflection and comparing to calculated deflection.

Do you have any photos of the beam from further away, like overalls?

 

[SLTA]

If the beam took some of the lateral load, especially at the end, it might be similar to a mid-level shear crack due to bending, except on its side. Not explaining that well, sorry.

 

[BAretired]

Depending on what the OP means by "tributary floor area", the existing beam appears to be severely overstressed in both bending and shear. The existing beam should be replaced or suitably reinforced.

BA

 

[msquared48]

OK. Rethinking this again after looking at pictures 3 and 4, the cracking seen is new. However, there is another scenario here...

As alluded to previously by BA, the structure of the beam seems funny, with a possible veneer. Is it possible that the beam may, in actuality be two beams (or more) side by side that were not stitch-bolted together, and covered by a 2X "veneer" as it were. This could account for the splitting seen - of the veneer only, and non-structural in nature. It would be very likely for two parallel beams to move differentially longitudinally in this manner from the load described.

If this is the case, just stitch-bolt the existing beams together and replace the cracked covering, assuming they are adequate to carry the floor load as BA suggests, and possible roof load depending on the framing above.

Mike McCann
MMC Engineering

 

[RockEngineer]

From the pictures it looks to me like a round log flatted top and bottom which is not unusual for log homes that I work with. Although unusual I have seen a log girder split/check vertically top to bottom along about half it's length in a log home after an earthquake. As Mike said, check for deflection. If it has a reasonable deflection (less than 1/4" under dead load) and the only problem is the longitudinal vertical crack, then stitch bolt the girder so it can't split apart and will continue to act as a single crossection. The only thing I can't assess is the transverse cuts/cracks shown in the pictures. If they are surface only (less than 1/4") I personally wouldn't worry about them. You are the engineer and have to use your judgement based on what you see.

PS. From my calculation with 19 ft tributary width and 12 ft span you have about a 600 psi bending stress in the girder which is acceptable for most woods. My take is you have about a 7"x7" effective crossection of girder. I have about 20 years experience designing and working with log homes. Free advice in the internet is worth every penny you pay.

 

[RockEngineer]

Correction. I hit a wrong key on my calculator. Your log girder is very overstressed if you have a 19 ft tributary width acting on the girder. I knew something didn't seem right.

 

[Compositepro]

The transverse "cracks" appear to be saw cuts which allowed the flats to be made by splitting out the wood between cuts.

 

[racookpe1978]

Rather than looking "down (axially) the length" of the beam, I'd rather look sideways across the beam.

Also, what is the "sag' from end to middle to other end/

If the beam is 'roughly square" but split down the middle - WITHOUT either side of the beam drooping more than the other - then it "might" be better than if one side drooped badly, or if both are sagging. The strength of a beam against the overhead load (the floor above) is primarily in the depth of the beam, but the two sides separately are not as strong than if they were bolted together or as they were originally.

you have several ways of strengthening the beam - you will need them almost certainly.

 

[moltenmetal]

The serrations perpendicular to the grain look like remnants of the flattening process- sawcuts made too deep or perhaps adze or broadaxe strikes that went too deep (if this were a timber from an old barn etc.). The thing is definitely solid wood, not laminated.

 

[oldestguy]

I have a log house made from green pine. It is normal for these logs to shrink perpendicular to the grain. The shrinkage is greatest at the exterior, tapering in to the center. On my log house, those cracks stop at the center of the log and do not extend through. The width shown is normal for some wood. Thus, for a side wall, no problem with air leakage through them. This crack looks typical of this shrinkage and by the shape of things, it looks like the center of the tree is up at the top of this "beam". Likely this was fresh cut log used in the original construction. Since the crack is parallel to the stresses, it is no big deal. It's like two wood beams side by side. No shearing stresses either. Seeing that it is near the furnace, would imply that the heated area has affected the wood. Furnace probably was not installed when house was built. Cracks came after furnace was installed. I'd leave well enough alone.