Wood post Cracks 1

[Rsayed PE]

I designed a deck with 8x8 wood posts in Tampa, FL

the posts are 15 ft apart with deck projection of 13.5’ from the house. Those cracks appeared and started to progress in the past 2 month since the GC installed the posts. I know these maybe a normal checking but i needed an opinion. Some of these columns have checkings in both directions. The column per my design is at %50 capacity (Max) The applied ASD axial load is about 11kips for the 11.5’ columns.

Anything I did wrong here ?
Any ideas on how to repair/remediate ?

 

[canwesteng]

I see this all over the internet and have never understood it
How are checks not a structural concern?
Surely they impact both compression and bending capacity, plus have implications for cross-grain loads e.g. screw fixings in tension
I can understand that "some level of checking can usually be accommodated within standard residential design" but that is not the same as "of no concern, structurally"

Some level of checking is baked into the allowable stresses for wood. Would that post be ok if it was sized for select structural? Maybe not. I would probably recommend the owner continue to monitor, but it's likely nothing.

 

[Greenalleycat]

@canwesteng interesting, I have dug up our timber grading standard now and you are right
There is an allowance for checking that varies between different grades of timber...and for 'Building Grade' it is not restricted
To be fair, I'm not sure what "building grade" means as I can't find a definition and it isn't a standard phrase...but I assume that this would apply to deck posts

 

[phamENG]

How are checks not a structural concern?

https://www.structuremag.org/article/seasoning-checks-in-timber/

 

[Ron247]

I think the degree of checking is reflected to some degree in the published design values. Larger lumber tends to have lower allowed stresses.

 

[KootK]

How are checks not a structural concern?

I used to have the same concern. I live in the land of a zillion ski lodges. And when you're a structural engineer sipping hot cocoa in a ski lodge, you can't help but wonder at all of the giant timber beams and columns that are split in half -- or even quarters -- due to checking.

So I looked into it. What I found was the grading rules for timber in North America. And, sure enough, those rules speak to checking and allow a ton of it. Nearly full depth and nearly full length before it's considered a problem. But, yeah, "yes" to your laundry list of concerns.

For many applications, I suppose that it's just down to wood members not needing a ton of longitudinal shear transfer capability relative to allowable shear stresses.

There are two situations that nag at me in particular:

1) Torsion. Sometimes folks try to use wood in torsion. When I imagine the shear flow on a big beam that is effectively split into halves or quarters, I don't like what that implies for torsion. I suspect that this is why most of the standards don't touch wood in torsion (AITC being the exception that I am aware of).

2) Highrise timber columns. In western Canada, we seam bound and determined to push timber until we're building 30 story condos with it. I fear a future where timber columns carry so much axial stress that large columns splitting into two or more independent columns across checks wind up shedding potential energy so fast that collapse results. I feel that this hasn't been the case in the past because, historically, heavy timber columns have tended to be very lightly loaded with axial stress because their proportions have really been chosen based on detailing constraints rather than axial capacity.

 

[Greenalleycat]

Cheers, Pham, a useful read
Basically, it -is- a structural concern, in the sense that it does impact the strength of members
However, for pure checking (no splitting) this is allowed for in the timber grading specifications so the -design- strength is unaffected
Caution should be taken when you have a shear-dominated member or checking near fixings

Presumably a non-checked piece of timber is much better than design value due to the allowance for this?

Edit: @KootK agreed with your concerns, particularly for torsion.
I am surprised that there is no limitation on checking in your or our codes for structural timber
I cannot see how delaminating a quarter of an axially-loaded column or the compresssion side of a beam won't affect strength and stiffness
Small delaminations, sure, but 'no limit' means it could extend down the entire length in theory! All buckling calculations are based off whole section properties....

 

[Ron247]

It appears there is a difference in a check and a split. Splits are all the way through while checks are not. I do agree torsion, end checks and complex loadings should alter the degree of concern.