Cracked Wood Floor Joist

[gte447f]

See the attached images. I came across this cracked floor joist in a the crawl space of a single family residential building. It's the joist just to the left of the HVAC duct and just to the right of the plugged foundation vent. Any ideas what has caused the crack?

This is the only joist that exhibited cracking like this, so maybe it's a one-off, something simple like it was damaged during construction (40 years old).

Is it a typical shear parallel to grain failure? If so, why just this one joist under normal service loads?

There is some relative lateral displacement of the sections above and below the crack and in one of the photos you can see that the joist looks to be leaning over. So is the crack resulted from rollover at the end of the joist? Maybe the joist isn't fastened to the band joist to prevent rollover, but the top edge is being restrained from rolling over by connection to the floor sheathing?

 

[bones206]

Maybe the HVAC guy beat it over with a hammer to fit the duct boot.

 

[gte447f]

bones206, something like that is certainly possible I guess. I wish I had looked more closely for hammer marks or something while I was there. I didn't really think much about this joist at the time, because there were other more severe issues with rotted framing at other locations in the building. Now, I'm mainly just curious.

 

[phamENG]

bones read my mind. Given all the ways that joist is (or at least should be) constrained, I've never been able to come up with a better explanation for that type of failure than some sort of isolated impact.

 

[bones206]

I see what could be hammer marks in the 4th photo. Near the bottom edge of the joist. I know I've split lumber doing that exact thing many times.

 

[SWComposites]

In first and last photos looks like there is bearing crushing in the cracked joist where it rests on the sill plate.

What is directly above this joist on the floor above?

 

[JoshPlumSE]

In first and last photos looks like there is bearing crushing in the cracked joist where it rests on the sill plate.

Good eye! I didn't notice that until you pointed it out.

Is it a typical shear parallel to grain failure? If so, why just this one joist under normal service loads?

Normal.... Nothing looks normal about this joist to me. LOL. To me, it looks like crack propagation that started as normal minor checking at a growth mark. Not sure what could have caused it to propagate so much. Something related to construction or the duct seems the most rational explanation. But, I don't know if we're ever going to conclusively say that.

 

[SWComposites]

There is a gap in the block wall under the adjacent joist. Could the cracked joist have been overloaded somehow?

 

[lexpatrie]

This kind of looks like some kind of twisting, on the right side of the joist, there's a "flake" up toward the top, like maybe it got hammered from that side and there's a face nail from the skirt board into the joist that was close to the edge and hence it split. On the other side, it looks like the opposite happened on the other side, the "flake" is on the lower side, but it's much larger....

Put tape measures in your photos, people!