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Are My Columns Too Short?

Are My Columns Too Small or Too Short?

We receive and answer lots of questions. Even with a Construction Guide which extends over 500 pages, covering a plethora of topics and how to’s, there is always an unanswered question (sometimes two).

One of our good clients recently sent a query to the Hansen Pole Buildings’ wizardess of all things shipping, Justine, which I share now:

“Hi Justine, I received delivery of the columns for my building on Friday. After inspection, I had 2 questions that I’m hoping you can clarify for me because I don’t know if there is an issue with them. I also want to apologize in advance, because I know these questions are pedantic and probably nothing to worry about, I just want to make sure there’s no problem here since I haven’t been involved with the kind of construction that requires inspections before. 🙂

The building plans seem to have a slightly larger dimension than what was delivered. I’m sure the engineering has allowed enough safety margin that this won’t be a problem, I just don’t know if it’s going to be an issue on an inspection. For example, the corner columns are shown on the blueprints at 5 3/8″ x 4 1/8″ but the columns that were delivered are 5 1/4″ x 4 1/8″. So, you see it’s only 1/8″ on the long dimension of the column, but I don’t know if an inspector will have a problem with that. The same 1/8″ undersize dimension is true on the corner, endwall, sidewall, and shed columns.

I was under the impression that the length of the columns was a minimum length and not a nominal length that might be slightly less than that. It could also be that I have a misunderstanding about how the columns are spec’d. What I found is that the 14′ columns are all actually 14′ 1″, which is great, however all of the 24′ columns are actually only 23′ 10 1/4″ when measured to the shortest of the three laminated boards. They are all right at 24′ when measured to the longest of the laminated boards. This is only a concern of mine because I’m in the process of getting the site leveled out, but I’m currently at about 12″, which is cutting things pretty close on some of the columns. So, I didn’t know if the manufacturer made a mistake or if I just need to correct the way I measure them. My main concern is around ensuring I have full weight bearing on the notched post, which will only happen if I notch them at least 11″ down. I’ve attached a photo to show how I’m measuring them.”
To which our Technical Support Department cheerfully responded:

Thank you very much for sending us your concerns.

#1 You are going to find the dimensional lumber (2×4 through 2×12) provided can vary as much as 1/4″ plus or minus from the anticipated “ideal” dimensions. It is part of the randomness of dealing with an organic product (wood) which has to be milled. It is also why we are only able to use 40% of Pult (the ultimate strength of a material in a wood assembly) when engineering calculations are produced. In looking at the calculations for the long columns in the center of your building, for example, they are stressed to 92% using the “call out” dimensions. Using a Sm (Section modulus – depth of lumber squared x width of lumber divided by 6) of the 1/8″ under size, reduces the actual Sm by 1.64%, which would mean the member would be stressed to 94% under maximum design load.

#2 Column lengths do vary slightly due to the material lost in finger jointing. On the 20′ eave raised center section, with the bottom of the column at 32″ below grade, the amount of column needed would be 22’8″. With a column length of 23’10-1/4″ you could have as much as 13-3/4″ of grade change and still have plenty of column.

If you do happen to have a foot of grade change, it would be my recommendation to have the site brought closer to level before setting columns. Good compactable fill is not inexpensive. Reducing the grade change from 12″ to say four inches, as an example, saves 27 yards of fill across just the footprint of your building.

Please do not hesitate to reach out to this department further with any technical questions.

This entry was posted in Pole Barn Planning, Columns, Lumber, Pole Barn Questions, Pole Barn Design, Building Department and tagged , , , on by .

Glulams vs. Solid Sawn Columns

A Hansen Pole Buildings client recently called his Building Designer Rick. The client was concerned as three ply glulams were provided for his pole building kit package, instead of the 4×6 and 6×6 solid sawn columns which were on his plans.  He is concerned his inspector will give him trouble about this and would like an e-mail stating all is good.

Always happy to oblige Rick and help out a client, this is what I wrote:

“At no extra cost to you, your building columns have been upgraded from solid sawn columns, to glulam columns.

The strength of any member which resists bending, is primarily determined by its fiberstress in bending (known as Fb) multiplied by the section modulus (Sm) of the member.

For information on the solid sawn columns, this makes for good reading: https://www.hansenpolebuildings.com/blog/2014/08/lumber-bending/

The design specifications for the Titan Timbers provided are here: https://www.timber-technologies.com/webfiles/fnitools/documents/column_specs.pdf

With a Fb rating of 1900 psi and a Sm of 19.9, the product of the two is 37,854 in-lb. Compare this to the values of solid sawn timbers and you (or anyone who might question them) can see the huge difference in strength provided by the glulams.”

In a not too distant past life, Dale (one of the owners of Timber Technologies, which manufactures the glu-laminated Titan Timbers) and I worked together for another glu-laminated column fabricator.

Both of us learned plenty from the experience.

In my case, I learned the values of glu-laminated columns other than just the strength (in many cases a three-ply 2×6 glulam will even replace a 6×8 timber!).

They are light weight. I’ve stood 24 foot long 6×6 columns in holes before. Weighing in at well over 200 pounds – it is a task! A triple 2×6 glulam – about ½ the weight!!

Properly fabricated, a glulam columns is going to also be perfectly straight, as well as prone to resist the bane of anyone constructing a pole building – warp and twist!

All-in-all this particular Hansen Pole Building customer got what is known as, “A pretty sweet deal”.

This entry was posted in Lumber, Columns and tagged , , , , on by .

Parallam® Plus PSL

Justine (a Hansen Buildings Project Coordinator) recently needed to order some glu-laminated columns for a pole building kit package. One of our vendors recommended she instead order Parallam® Plus PSL columns instead, insisting they would be as strong as or stronger than glu-lams.

Parallam beamParallam® is the brand name for an engineered wood product developed by Trus Joist MacMillan which is made from veneer strands laid in parallel alignment and bonded with adhesive. It is used for beams, headers, columns, and posts, among other uses.

The rated strength of Parallam®  is greater than the wood from which it is made. This is because knots and other imperfections are removed so strength variability is less than in solid sawn wooden beams.

When I served on the board of directors of the MSRLPC (Machine Stress Rated Lumber Producers Council), we had the opportunity to tour MacMillan’s Parallam® manufacturing plant. Truly an amazing process, as the product is continuously formed – it is extruded, not unlike plastic pipe! This means the maximum length of the beams are limited only by the maximum length capacity of the plant.

The product is produced as a huge rectangular “slab”, which is then cut down to popular sizes – widths of 3½”, 5¼” or 7″ and depths between 9¼” and 18″.

Parallam® Plus PSL columns are typically manufactured in three sizes: 3-1/2” x 5-1/4”, 5-1/4” x 5-1/4” and 7” x 7”. For use as a structural building column, Weyerhauser has simplified product design and specification by grouping the AWPA (American Wood Preservers Association) Use Categories into Service Levels. As such, the Service Level for exposed posts in contact with the ground would be SL 3.

In this application, the Parallam® Plus PSL columns would have a Fb (fiberstress in bending) value of 1344 psi. Multiplying this value by Sm (section modulus of the column) gives a value of 32,413.5.

Most typically, Hansen Buildings utilizes glu-laminated columns as manufactured by companies such as Timber Technologies, LLC, which have a Fb of 1897.5 psi. With a standard 3 ply 2×6 column measuring 4-1/8” x 5-3/8”, Fb x Sm for the glulams equals 37,688.7.

While the Parallam® Plus PSL columns are a great product, the vendor was incorrect in his advice to Justine, as the glu-lam would be over 16% stronger in bending. This is where it pays off to do investigative research on a product, rather than just relying upon what may perhaps be errant information from a vendor.

This entry was posted in Lumber and tagged , , on by .
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