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.

 

[xyz1100]

Another photo

 

[msquared48]

No worries.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[Ron]

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.

 

[beton1]

Another vote: don't worry.

 

[dik]

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

 

[dik]

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

 

[Ron]

dik...good points. Thanks.

 

[hokie66]

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.

 

[xyz1100]

Thank you all for your answers.


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

 

[dik]

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

 

[RHTPE]

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

 

[RHTPE]

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

 

[ajk1]

I share your concersna about lag screwing or bolting.

 

[woodman88]

Per the WWPA Western Lumber Grading Rules 2011 (I got for $8 at

http://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.

 

[RHTPE]

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

 

[woodman88]

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.

 

[RHTPE]

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 -

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

 

[woodman88]

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.

 

[edstimator]

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.