Drag loads on corrugated metal roofing and siding 1

[PostFrameSE]

Is there a way know how much load should be applied to parallel-to-wind surfaces of a building system when the cladding is corrugated metal? My question specifically relates to wind acting parallel with the ridge of a building. The load has to be more than the wind pressure acting on the cross-sectional width of the building I believe, but not sure how to consider that. Does anybody know how something like that can be figured? Is it some "surface roughness" characteristics that can or should be considered? Is there a ratio of cross-sectional endwall area to length of building that could be utilized?

And then................what if the sidewalls of the building are open? How does wing load hitting the webs and chords of trusses impact the overall lateral loading on a building? To sum up the surface area of every truss in the building and apply load over that area seems overkill as no doubt there would be lots of turbulence created as wind would rush through the trusses. Not sure how to think about that either.

Any thoughts would be appreciated.

 

[Guastavino]

I've never heard of an increase for corrugated roof surfaces. I personally wouldn't sweat that too much. As for the open end walls. I would consider something reasonable. I think the last one that I did, I just assumed it was "closed" for the design. That also gave the owner flexibility should they want to close the thing in one day.

With that said, I don't know of a code-prescribed way to calculate the added effect you could have from wind coming in at an upward angle and hitting more than one roof beam. I think letter of the law you could just do projected area. But I wouldn't do that. I'd look at the loads and use judgment based on what the calculated load is for one projected surface, and then the whole surface assuming it was closed off. Based on those numbers, I'd start to see where I was at and make an assumption at that point.

One other thing is you could contact your local PEMB engineer. THey do open buildings all the time and might have insight into their industry standards.

 

[KootK]

I've participated in a similar discussion here in the past. Apparently, Australia has a provision for wind drag on parallel surfaces which makes a ton of sense to me. In the past I've pretended that parallel to wind surfaces were pitched at 15 degrees in order work out poor man's version of a drag load.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[ajh1]

MBMA has commissioned research on the issue of wind load on frames of a building with roof panels only. The attached provisions from the MBMA Design Manual show the equations. An attempt was made to get this included into the ASCE7-16 standard but did not succeed. I think the basic issue was lack of time from presentation until ballot closure and it will be taken up again for the next edition. While ASCE7 currently has provisions for open building winds on roof surfaces there is nothing in ASCE for the lateral forces. Unless you have a very long building, the assumption of fully sheeted endwalls as an option is generally pretty reasonable.

 

[thaidavid40]

@KootK,
Thanks for the lead on how the Australian code handles wind frictional forces.
Dave

Thaidavid

 

[Trenno]

KootK: Correct, Australia has all things that are good.

OP - I'll scan the relevant page from our portal frame bible in the morning for your reference.

 

[Trenno]

See below. However in the worked solution in the textbook, the frictional drag forces make up just over 7% of the total lateral force at the ridgeline... therefore I wouldn't worry too much, unless you have a really long building or massively ribbed cladding.