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RE: Barn Structure

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Jim is correct about the pole building structure. Many state agricultural
agencies provide plans for farm buildings designed. These designs use
reduced loads for farm buildings per applicable codes.
The pole building do not use a diaphragm or bracing. The lateral loads are
resisted by flexure through the post. Embedment was calculated using ENR
Equation or rules of thumb.
A 50-year old pole structure may have rotten post below grade.

-----Original Message-----
From: Jim Persing [mailto:jpersing(--nospam--at)FHOARCH.COM]
Sent: Tuesday, October 07, 2003 4:03 PM
To: seaint(--nospam--at)
Subject: RE: Barn Structure

This sounds like it might be a "pole building".  There is a lot of
information out there for these types of structures, much of it seemingly
questionable in the terms of what we consider "normal" structural
engineering.  There are even magazine publications that are dedicated almost
exclusively to these structures.  If you do a search for them and still
can't find any info let me know and I can dig up some old information for
Jim Persing, PE

-----Original Message-----
From: Gerard Madden, SE [mailto:gmadden(--nospam--at)]
Sent: Tuesday, October 07, 2003 2:58 PM
To: seaint(--nospam--at)
Subject: Barn Structure

I am working on a Barn Structure that was built in the late 50's. 


The roof structure is simple gable shape with corrugated metal roofing over
2x4 sub-purlins that sit on 2x8 scissor trussed rafters every 10 feet o.c.
with collar-tied rafters in between (5 feet away). There are 6x posts every
10 feet in the long direction of the building. End bays are 10 feet wide
(wall to post), center bay is 25 feet wide (post to post).


The owner wants to convert the barn into a storage area. The dirt floor will
have a new concrete slab. The owner wants insulation and humidity control
and therefore needs to insulate the roof and walls.


I have checked the roof structure and it doesn't work (by calculation) for
existing gravity loads when considering roof live load. The other main
problem I can see is wind load in perpendicular to the long direction of the
building. There doesn't appear to be a real diaphragm, only the corrugated
metal roof fastened to the 2x4's. They sit on top of the trussed rafters and
there is no blocking at the eave.


The problem is the owner wants it to look as is - worn and old from the
inside looking up. Another problem is the exterior look must be the same as
it is now (exterior walls have vertical boards and the metal roof is painted


The architect is considering a foam roofing/insulation over the existing
metal roof, with a new metal roof over the foam. My concerns are pretty
obvious: weight of the new roofing material and creating a diaphragm.
Screwing through foam and existing metal to create a diaphragm seems kinda
iffy (engineering term).


Can others share how they have approached these problems? I was thinking
some sort of diagonal braces in plane with the diaphragm, either blocking or
some kind of rod system. For the gravity, I'm hand strung with the
requirement to maintain the look (exposed old looking lumber). If I
strengthen rafters with new wood, it won't look so old anymore... It's the
live load requirement that kills it, because the dead load is very small
(existing) and probably no more than 4 to 5 psf with the new roof.


Also, if anyone can point me to some design criteria for agricultural
buildings (i.e. historic barns, although this isn't considered historic)
that I can use a basis for my concerns. I'd like to have something to back
me up if I have to break the bad news to the owner.


Comment appreciated in advance.







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