wood post splits 6

[xyz1100]

I have designed a wood garage. When I did the pre-final inspection, I found there were several cracks (or check, or splits) on the 4x6 post. The 4x6 post should be D/F.L., grade No.1. The crack width is 3/16 inch. I am not sure the cracks are due to nailing or shrinkage. My question is if this 4x6 post acceptable? Is there any structual consern? Now it is okay, but will it gets worse later?

There are three 6x6 post. One post is okay. One has a small crack originated from nailing. The 3 rd 6x6 has several cracks too. The cracks are starts from the toe nails at bottom. The max. crack width is about 1/16 inch.

I attached the photos for the 4x6 post. Your help is appreciated.

 

[woodman88]

edstimator:
“A beam that is being graded is having a snapshot in time taken of it.”
“The lumber is graded within minutes of being sawn in some cases but ceartainly before it is totally dry.”
These may be true of the grading of the lumber. But, the design values of lumber is based on the in-grade testing and I find it hard to believe that the testing of these pieces occurred at the same time as the grading. So (IMHO) the design values are not based on a “snapshot in time” of the lumber.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[RHTPE]

The goal of this forum, as I see it, is to provide additional insight to those who may post regarding a particular problem or challenge that they may have. A statement that has been in the NDS as far back as 1968 says "In calculating design values, the natural gain in strength and stiffness that occurs as lumber dries has been taken into consideration as well as the reduction in size that occurs when unseasoned lumber shrinks. The gain in load carrying capacity due to increased strength and stiffness resulting from drying more than offsets the design effect of size reduction due to shrinkage."

So, clearly those involved in In-Grade, their predecessors, as well as those involved in the publishing of wood design values recognize that wood continues to lose moisture and shrink. Since it is not an isotropic material, its shrinkage varies in 3 dimensions, and cracks, checks, shakes and/or splits manifest themselves in a variety of ways.

Over the last 4 decades the horizontal shear stress value for Hem-Fir WWPA #1 has gone from 100 psi to 75 psi and now 150 psi. Compression parallel to the grain from 1,050 psi to 1,000 psi to 1,350 psi. Some issues of the NDS between 1971 and 2005 caused great concern in my industry when they were released, as design values seem to plummet. The In-Grade testing proved to be the best thing that could have happened to design values, as it restored many species to their former levels or beyond. It also made the design process a bit more complicated by adding a number of adjustment factors. Saw timber has declined in quality yet from a 40 year perspective the design values seem to stay relatively consistent.

My main point - I have seen large timbers used in homes, barns and mills with splits or checks much wider (in proportion to member size) than those in the OP's pictures. These timbers are much older than anyone following this forum and have certainly reached equilibrium with their environment with regard to moisture content. Yet they continue to perform flawlessly.

I agree that a split or check going completely thru a member deserves further consideration with regard to its intended function. If it's a column, perhaps it should be checked as a spaced column. If it's a beam, perhaps it should be checked as if it were 2 stacked (or side-by-side) beams. However, if the check or split is simply a natural result of moisture loss and does not go completely thru the member for a substantial portion of its length, then I would be comfortable saying it were okay. It is an aspect of wood construction that adds to the character of the structural material. The bottom line is that it becomes a judgement call on the part of the design engineer who knows the anticipated loading.

All of that said, I would not advocate any attempt to close or restrain the crack by thru-bolting, as I explained previously. It will simply be a feel-good measure that may actually cause more harm than the little (if any) good that it might do.


Ralph
Structures Consulting
Northeast USA

 

[edstimator]

woodman, the point that I was making was in response to someones suggestion that there had been an error in the grading and I feel that the machine that did the grading was imho operational and within specs but that the crack that finally presented itself was not there at the time of grading inspection so obviously no "mistake " was made.
If your point is that a piece of lumber can degrade to a point that is a departure from the specs that a non degraded piece should be you are of course correct. But I think you are kinda overstating the obvious.
My assertion that a post that exhibits a clean lateral split is structurally sound is an assertion that I cannot back up with calcs but if someone else has done tests on a similar piece of lumber in similar shape i would take his word for it.

 

[btrueblood]

Wouldn't you need to know if the post is nearer to its buckling limit vs. compression strength limit? A cracked/split post won't have the same moment of inertia as a solid (unsplit) post.

 

[woodman88]

RHTPE regarding your quotes
1) The NDS "In calculating design values, the natural gain in strength and stiffness that occurs as lumber dries has been taken into consideration as well as the reduction in size that occurs when unseasoned lumber shrinks. The gain in load carrying capacity due to increased strength and stiffness resulting from drying more than offsets the design effect of size reduction due to shrinkage." does not mention that surface checks will or should occur with lumber drying.
The 2001 NDS (and back to the 1944 edition) states Section 1.2.1 "The quality of wood products and fasteners, and the design of load-supporting members and connections shall conform to the standards specified herein." To me this means that the lumber, in-place, must meet the grading requirements. So unless someone so can quote me a section of a standard that states the lumber, in-place, is allowed to have degraded to a lower grade and still be used at the original stamp grade, I will require any such member to be repaired or replaced.
I also apply this to the "In-Grade, their predecessors" comment you made.

2) As for the increases you state "...100 psi to 75 psi and now 150 ..." and "...1,050 psi to 1,000 psi to 1,350 psi..."
Check out this link

http://www.awc.org/HelpOutreach/faq/FAQfiles/In-Grade_Testing.html

which states "Note that concurrent with development of new design values in the 1991 NDS, behavioral equations for column, beam, and beam-column design also changed as a result of the In-Grade Testing program. Therefore, an advisory was issued with the 1991 NDS indicating that new design values were to be used simultaneously with new design equations and pre-1991 design values be used with pre-1991 design equations." So the design values cannot be compared by themselves.
3) As for your "My main point - I have seen large timbers..." and "...are much older than anyone..." you have no idea; 1) If originally it was over-designed. and 2) How many of the buildings and timbers from that time failed or would of failed if they had not been torn down.
The statement that this old piece of lumber is still good so what the problem with this good piece? Does not fit my idea of good engineering judgment.

edstimator - thank you, I would much rather overstate than understate the obvious.

P.S. The link to the WWPA has been changed to

http://www2.wwpa.org

and price for the rules have increased to $20.00.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[RHTPE]

woodsman, Obviously we are not going to completely agree on our approach to the design of wood members. I believe that the grading is done as edstimator has stated. Each piece of lumber will continue to lose moisture and volume changes will occur after grading. The volume change will affect the number of checks, splits and shakes that are visible. I further believe that, for the most part, the subsequent change in visible appearance, from a grade evaluation perspective, is not likely to adversely affect the member's strength.

Now, that said, there will always be a piece or two that degrades badly (i.e. the spruce that I worked with) and will really require a careful evaluation of its condition and its appropriateness for it specific use. I will continue to maintain that a partial depth check, occurring between knot groups, will not adversely affect the strength of a member. This is, after all, what engineering judgement is all about.

With regard to my comments about the various issue dates of the NDS and the wood design values, I was simply trying to note that allowable design values have kinda jumped all over the place over time. While I did not state it, I would not condone intermixing design methodology from one NDS issue year with design values from another.

Perhaps we have hijacked this thread long enough to finally declare a truce on the difference of opinion?


Ralph
Structures Consulting
Northeast USA

 

[woodman88]

xyz1100, My opinion is that, if you are concern about checks in the posts, you should look in the WWPA Western Lumber Grading Rules 2011 (I have given some of the information above) for what is allowed for the grade you have specified. As for the opinions of others, you should look at the sources they give for their opinions before making up your own opinion on this matter.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.