Pole Barn Lateral Bracing

[PSUengineer1]

approx. 60'x128' pole barn.
No shear walls.
Exposed fastener metal roof and siding.
Each frame in short direction receives full lateral wind load based on tributary area.
The endwall posts (6x6) have moved significantly under approx. 60 mph winds (see pics).

Please share detailing information on lateral bracing of endwall posts. My thought is that endwall posts are not adequately braced at top based on photographs.

Please share comments, thoughts, smart remarks

Additionally, if you have a copy of Post-Frame Building Design Manual, National Frame Builders Association can you please share?

 

[msquared48]

Ple3ase excuse my French, but for only a 60 mph wind, the designer of this pole structure did not detail properly or know what the hell they were doing. I would guess that it was an off-the-shelf design, not rated for the prescribed wind loads in the area in which it was constructed - and no one picked it up. Seen that too many times.

The endwall 6x6's needed kickers back to the roof and a substantial roof diaphragm using structural sheathing for a building this size.

If I were you, I would strip off the metal sheathing on the roof and appropriate side walls, add structural sheathing on the roof, and create plywood shearwalls, in addition to adding kickers at the end walls.

The 6X6's look small for what looks like a 12 to 14 foot eave with the bay spacing seen.

I'll step down now, but this kind of crap makes me mad.

Mike McCann
MMC Engineering

 

[Archie264]

I think the way pole barns work is that the poles are embedded into the ground giving them some degree of fixity. If that's the case here give some consideration and lateral capacity to the vertical members for that, if it appears to be done correctly. That said, I'd pay attention to what msquared wrote.

And a general question for the gallery: should the bottom chord's of those trusses be braced to each other?

 

[msquared48]

@ Archie... YES!!!!!!!!!!!!!!!!!!!!!

Mike McCann
MMC Engineering

 

[BAretired]

I think I would be inclined to walk away from that structure, but it may be possible to add shear walls on the interior without stripping the existing metal siding and to add sufficient bracing to the roof to enable it to span 128' as a horizontal truss without removing the roof deck.

The posts and girts will likely need to be beefed up and the trusses should be checked for wind and gravity load. Trusses will require additional bracing, particularly for uplift.

Nice looking boats, though.

BA

 

[Archie264]

Actually, I'm thinking the span might be the 60' dimension. Still quite long, of course. Correct me if I'm wrong.

 

[BAretired]

The existing trusses span 60' but the span of the horizontal truss or roof diaphragm carrying wind load is 128' between end walls. I don't think frame action will be sufficient to carry lateral forces.

BA

 

[JedClampett]

I thought the Southern Pine Association had a pole building manual, but I found this while looking for it.

 

[JAE]

We've had numerous would-be clients come to us over the years and ask us to review, sign and seal wood pole barns. The manufacturer usually tries to build these things out in the country (think barns - farms) and occasionally they try to build one within a city where the building department demands and engineer seal.

The problem we've found is that the pole barns typically do NOT meet the IBC or the standard load/stress requirements of the materials. In other words, we could never get them to "work". Thus we told them we couldn't sign their design.

 

[Jerehmy]

it does have shear walls and a diaphragm, they're just not very strong. For 29 gauge, the ultimate shear is around 250-300plf.

With light gauge siding like this they assume some of the load is carried by the siding and some by the posts.

http://www.nfba.org/Resources/content/dafi.html

NFBA took down their design manual because I can't seem to find it anywhere :\.

I'm trying to wrap my head around why it failed in the direction where it should be the strongest against wind. It looks as if the roof diaphragm had no way to transmit the load to the top of the long shear walls. So the force went to the top of the columns at the end walls and the connection wasn't sufficient.

 

[msquared48]

"For 29 gauge, the ultimate shear is around 250-300plf." Sheet metal this light I wpuld never use as a shear wall material, and these manufacturers are constantly relying on it. Obviously, the deflection allowed by the system is way too much and it failed.

What is the design wind speed for the area? Got to be greater than 60...


Mike McCann
MMC Engineering

 

[Jerehmy]

We recently did a pole barn. The client wanted us to do it instead of a manufacturer that does it everyday (wanted to keep the money in the area, cool). Anyways, our cost estimate was double what they put into it. I'm like, I'd LOVE to see their calculations because I have no idea how they picked some of the sizes they did for the building with no interior walls.

I don't see a problem relying on the light gauge it if its used right, and they test actual wall assemblies to determine its capacity which I think is pretty accurate test. But a 128 foot long structure with no interior shear walls is pretty ridiculous to only rely on light gauge metal.

It's hard to tell from the picture but I just don't see where the wind load in the roof diaphragm can be transmitted to the top of the 128' long shear walls. Obviously in the short direction the gable end truss is able to take it to the top of the wall.

And from the 2003 IBC the lowest wind speed I see is 85 mph. Maybe he meant the damage was done after a 60mph wind storm?

 

[PSUengineer1]

@Jerehmy: yes, the damage was done after a storm w/ approximate 60 mph winds

 

[DaveAtkins]

I think everyone is rushing to judgment. Many buildings of this type have been built over the years and perform quite well. NFBA has done extensive testing of diaphragms and shear walls with light gauge steel roofing/siding and wood framing. Of course, the calculations should be able to prove the structure is safe and serviceable.

I think something else is going on--I don't blame the steel roofing/siding.

DaveAtkins

 

[Splitrings]

NRAES-1 "Post Frame Building Handbook"
ASABE EP486 "Shallow Post Foundation Design"

Here are a couple of references to start with. The only way to brace the top of the end wall is through a ceiling/roof diaphragm or bottom cord lateral and diagonal bracing. My guess is the loads are such that you couldn't get enough fasteners into the bracing members. Its appears pretty likely this is not an engineered structure. I doubt this structure could be retrofitted as a pole building. My guess is a shear walls and ceiling/roof diaphragm will be more economical.

 

[oldestguy]

If you have any Amish in your area, I'd bet they will come up with an idea to get tho end wall forces into the side walls. In our area they pretty much only build barns this way and none have failed to my knowledge.

 

[RFreund]

I would also verify how the 60mph wind was determined i.e. fast mile, 3 sec gust, etc. The current code uses 3-sec gust but weather reports may not use this.

EIT

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