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wood post splits
6

wood post splits

wood post splits

(OP)
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.

 

RE: wood post splits

Not a big deal from load path standpoint.  Looks like your lumber was not correctly graded if sold for No. 1.

If it would make you feel better, put a lag screw perpendicular to the crack every 12 inches top to bottom...to prevent further separation from shrinkage.

You should note that anomalies such as this will cause problems later on when the property is sold.  An inspector will highlight the issue and potentially make a big deal out of it.  Will cost extra to prove him wrong.

If you can push the grading issue, have them change it.

RE: wood post splits

Another vote: don't worry.

RE: wood post splits

The shrinkage cracks are not uncommon for dimensioned lumber although you seem to have a lot of them. I don't know the grading requirements, but there seem to be a lot of knots for #1 D-Fir.

If you lag screw the members, predrill the holes for 3/4 the diametre of the lag screw and if you install it by power drill, tighten the last half an inch by hand and socket set to prevent tearing out the threaded area.

Dik

RE: wood post splits

Forgot to add that if you put lag screws in, use soap for lubricant or, alternatively, consider using through bolts since the cracks seem to overlap a bit.

Dik

RE: wood post splits

dik...good points.  Thanks.

RE: wood post splits

I would want it tied together, and through bolts would be my choice.  Lag screws will hold it like it is, while with through bolts, you can tend to pull it back together.  Depending on the cladding, you may have to countersink.

RE: wood post splits

(OP)
Thank you all for your answers.


This 4x6 will be the garage roll-up door support. Is there anything else I should be concerned?   

RE: wood post splits

keep it off the concrete, since it's D-Fir... it's not likely pressure treated.  Use a Simpson support that will elevate it off the concrete a tad.

Dik

RE: wood post splits


xyz1100  I would also vote "No worry".

Further, I would start any basic timber design class with a similar line that I heard from my prof who taught reinforced concrete design: "Timbers split parallel with the grain as they lose moisture."  The larger the cross-section, the larger (wider) the split could be.  With today's lumber, a high percentage of 6x6 & larger timbers come from the center of the log.  Having sawn a lot of my own timbers, I have consistently seen this phenomenon.

Wood shrinks the most in a direction parallel with the growth rings.  As you move farther out from the "year 1" growth ring, the circumference increases by a factor of pi.  Thus, as the wood loses its moisture, there is more cumulative shrinkage as you move farther from the center of the original log.  The timber has no choice but to split.  If the split is because of this shrinkage, it will not go completely through the timber - it will stop once it nears the center of the rings.  Perfectly normal, and you will find it in any large timber.  At some moisture content the split depth will stabilize.  While its width will vary with seasonal humidity levels (wider in dry, winter weather, smaller in humid summer weather), its depth will remain constant.

I submit that using lag screws or any other means to arrest the split is a bad practice.  While it provides the uninformed with some degree of assurance, it may actually cause the opposite side of the timber to split, thus compounding the problem.  Now the resulting 6x6 timber may effectively become (2) 3x6 (or 2x6 + 4x6, etc.) timbers.  Wood is an organic material and it has unique properties.  This is one of them.

dik is correct - it would be best to keep it off the concrete (though it may be moot at this point in time), particularly in a non-climate-controlled environment.

Ralph
Structures Consulting
Northeast USA

RE: wood post splits


xyz1100 and others following this thread....

As I pondered world problems + other stuff this morning before rising I realized that my post was somewhat incomplete.

First, wood also shrinks in a direction parallel to a radial line through the growth rings.  This may or may not be of a greater magnitude than the circumferential shrinkage - it depends on the growth conditions of the tree that the timber was cut from.  I have seen second-growth Douglas Fir with almost 1" wide annual growth rings.  Probably a tree surrounded by taller growth really trying to reach the sun.

Second. wood shrinks less in the vicinity of knots, as the fibers are denser in that region.  This is why most all splits are not continuous along the entire length of the piece (your 2nd photo).  Note that I didn't say it doesn't split in that region.  Where it splits is a function of the 3-dimensional make-up of the wood, i.e. circumferential shrinkage + radial shrinkage + arrangement of the knots.  It's going to give wherever the highest amount of tension exists resulting from volume change due to the shrinkage.

I worked with the wood from a particular spruce tree that I grew up with (We started out about the same height).  It was cut when it was about 24" diameter and had growth in an open field so it had many side branches.  It was milled green, and of course exhibited many knots.  We used a bandsaw mill to cut it, and at the time the blade was getting a bit dull.  The blade would ride up a bit at some of the knots (indicating denser wood with fibers not orthogonal to the plane of the saw blade.  What was most striking was the differential shrinkage of each pience of lumber as it lost moisture over time.  Splits were mainly between knot 'bands' and were substantial - some opening to well over 1/4".

Anyway, as engineers we want it idealize the properties of materials (and structures) into a form that we know to be readily analized.  Wood is obviously not isotropic, so as a particular piece of timber is liberated from a log, it will have properties totally unique unto itself and unlike any other.  It will shrink and split and warp in a totally unique way.
 

Ralph
Structures Consulting
Northeast USA

RE: wood post splits

I share your concersna about lag screwing or bolting.  

RE: wood post splits

Per the WWPA Western Lumber Grading Rules 2011 (I got for $8 at www.wwpa.org), For a 4x6 #1 DF-L
"Checks – Surface checks, not limited. Through checks at ends are limited as splits."
"Shake – if through at the ends, limited as splits. Surface shakes up to 2' long"
"Splits – Equal in length to the width of the piece"

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.

RE: wood post splits


woodman88  Please correct me if my impression is incorrect, but the grading rules apply at the time each piece is graded.  Once incorporated into a structure, environmental factors come into play.  If in a dry environment, wood will continue to lose moisture until it reaches some equilibrium moisture content consistent with its environment.  As it loses moisture it will continue to shrink - checks, shakes and some splits can continue to increase is size.  I suspect what is shown in the OP's 2nd photo is a 'check'.

This web page explains checks & shakes quite well:

http://www.vermonttimberworks.com/home/working_pages/wood_finishes/shake_checking/index.html

 

Ralph
Structures Consulting
Northeast USA

RE: wood post splits

Per the attached website "Great care is taken by lumber mills to package and ship wood to lumber yards. Upon arrival at the yard, lumber should be properly stored and handled to ensure it retains its value, quality and appearance.
Proper storage is primarily a means of protecting the lumber's appearance and of controlling moisture changes in the wood. Good storage practices enhance sales by keeping lumber clean and bright. Proper storage also retains lumber's dimensional stability, which helps prevent twist, cup, warp and other characteristics that can result in degrade or material loss."

From this I would say the lumber should be able to the graded as stamp when placed in use.

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.

RE: wood post splits


Garth  Everything you quote still translates to the lumber's condition on the day it is first put to use.  I maintain that it's the environmental factors than can greatly affect a piece of lumber after it has been in use for some time, and after its moisture content has reached equilibrium with that of its environment.  None of this addresses the OP's original issue -

Quote:

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?

I submit that the post is fine with the checks observed in the photo.
 

Ralph
Structures Consulting
Northeast USA

RE: wood post splits

Ralph Quote "..None of this addresses the OP's original issue..." What part of my quote from the WWPA Western Lumber Grading Rules 2011 of "Checks – Surface checks, not limited. Through checks at ends are limited as splits." did you not understand as applying to the OP? And how can you tell if the checks are not through at the end and extend less than the width of the member from just the pictures uploaded?

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.

RE: wood post splits

As a previously certified lumber inspector I can assue you that you should have no structural issues with a straight grained crack. What you are seeing is the circumfrance of the log as it dries and shrinks it opens up one major crack that if seen in crosssection would resemble the pacman icon. This is natural and other than asthetics does not compromise the integrity of the beam or post in any way because it has not actually cut any fibers.
Once in a while two cracks will occur on the same log and when that happens one should use it with caution as it has become excessive at that point.
A beam that is being graded is having a snapshot in time taken of it. It can only be judged in that one moment and although modern  inspection equipment has advanced light years with modern technology the split lateral to the log that occurs because of shrinking is often missed simply because it hasn't happened yet, not because someone or rather something as in a grading machine miss graded the product. it just hasn't manifested itself because logs are sawn wet. The lumber is graded within minutes of being sawn in some cases but ceartainly before it is totally dry.  

RE: wood post splits

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.

RE: wood post splits


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

RE: wood post splits

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.
 

RE: wood post splits

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.

RE: wood post splits

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 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.

RE: wood post splits


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

RE: wood post splits

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.

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