Glulam timbers vs multi-ply bolted boards

[fastline12]

Working on a design for my own pole barn. Not an area I work in so looking for standards and links to help me along. I am trying to determine structural improvements of a Glulam column for a pole barn vs just multiple timbers bolted together for the main poles.

Right now the design is setup with (4)2x8s on 8ft centers, bolted together on 2ft centers. I am trying to determine if there will be much structural advantage of using the glulam column in this instance. I am VERY concerned, being in tornado alley, about the main poles snapping off which would be next to impossible to repair.

I am also trying to decide on wood species for this. Cost IS a consideration but probably worth a few extra bucks to make sure these poles will out perform the rest of the building by a large margin.

 

[Ron]

If you are trying to design for F5 level tornadoes....you won't get close with what you have or with wood in general. There's a big difference between your code-mandated wind speed (most likely 90mph in your area) and the 250 mph + you might be thinking of.

Go to the local utility company get a real pole! Those work. (but not for F5)

 

[Teguci]

Wood species is a local phenomenon. I'm familiar with Southern Yellow Pine for treated and untreated situations. Lots of flexibility as well. I like Ron's suggestion.

 

[fastline12]

I agree with the utility pole thought and I think that is what started the "pole barn" name but in this situation, square dimension lumber is required.

Local codes is designed around 90mph winds. That design would call for 3ply of 2x6s on 8ft center. There is no WAY I would build to the minimum 90mph specs. I am not trying to get the poles to hold through an F5 but I want to make sure the building skin fails and rips off or even the whole roof before those poles want to let go.

Living in "the zone" I very much realize I can only plan for so much and the rest is out of my hands. I know lots of people say to use I beam iron construction but those will twist up too in a serious nader and all the skin is removed. Wood is ideal here due to the interior build out.

 

[ajh1]

Glulam will tend to give you better allowable strengths than bolted standard lumber, primarily because the wood grades can be tuned to put the best wood where the most stress is located. Glulam also lends itself to eliminating knots, checks, etc. in the wood used.
It's been a long time since I designed in wood, so can't offer any information beyond this.

 

[MiketheEngineer]

How tall are your columns?? and what load is coming off the trusses. That info will dictate what you need.

Glulams are EXPENSIVE. I use multiple 2x6s or 2x8s for 99% of my pole barn designs. Also, using a pneumatic air nailer will give you almost the same performance as bolts and be a lot cheaper and quicker!! You could shoot about 100 nails in the time it would take you to install two bolts. Fire them from both sides of the plies.

 

[fastline12]

Mike, thanks for the reply. The building is not fully designed yet so some loads are not set in stone yet. Since you are familiar, I will share some details. Some might concern you, some might not.

80150x18, 3/12 pitch target (might have to use 4/12) with raised cross chord or scissor for increased head space. the truss will be the mother of all designs for sure. 80ft freespan WITH a more vaulted style truss could get interesting.

26ga metal pba metal, 25psf snow. Depending on what is found in the ground, 5ft will get buries so figure 23ft long columns.

I firmly agree about nailing the columns and planned to just add some bolts for added security but probably shoot 200 nails in each one which should really help with torsional stiffness and load sharing.

QUESIONS - I have two concerns with the post building. One I already mentioned which is the posts breaking off at the ground which is next to impossible to repair. I am not even sure if I designed it to break higher if there is anyway to fix that either...

Second is post protection from rot. ACQ for sure but I have heard that if you pour them in concrete, you will have a problem later. I DON'T want that problem! There is a company making post protectors and I think nothing more than plastic sleeves. I need to figure something out. I will have gutters but...

 

[shobroco]

If you are building a pole barn, you had better be using pressure-treated lumber. These are common agricultural buildings around here (southern Ontario) and posts up to 8x8 x 20' long are commonly stocked, with larger available; I have never seen anyone bolt up 2x lumber into posts. Have a look at these plans, they cover just about everything you'll want in this type of building.

http://www.cps.gov.on.ca/english/frameindex.htm

 

[msquared48]

I wsould use PT Hem-Fir columnsx, solid stick, with failure panels to try to mitigage tornado damage.

Or, You could also design the building so it could be moved from the path of the tornado... No. The tornado will do that.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[BAretired]

Five feet buried in the soil? Is that enough to resist uplift?

BA

 

[fastline12]

msquared - what kind of failure panel are you thinking?

BAretired - this would be 5ft, poured in concrete, with uplift locks on the poles, and a 1M lb 6" floor poured over the top. I have actually seen on picked and and moved in one solid piece but I am hoping my lock system will mitigate that concern.

 

[msquared48]

Basically a failure panel system, similar to what FEMA requires for the foundations of buildings that are in a flood plain. The panel fails allowing the water to flow through, thus reducing the pressurew on the structure.

Considering the suddenness of pressure drop with any tornado, this may not be a realistic or feasible alternative though. I have never tried it, but it seems that if some of the walls and/or roof panels were allowed to quickly fail with a direct hit scenario, maybe the basic frame could be saved, depending on the mass of the debris being tossed around. Just a thought.

I wonder if anyone has tried this concept yet?

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com