Wind Loading on Open Arch Structure 1

[IslandEngineer]

I have two 42 ft wide x 18 ft high x 40 ft long arch structures similar to a WWII "qunset hut" building. Both are supported along the sides only (not the ends) on walls 9 ft high. The structures consist of a series of light weight steel arches on 4 ft centers with a fabric cover. Both ends are open on one arch structure; one end is open and one end is closed on the other. The wind zone is 85 mph with B exposure. There are work areas under each structure so I cannot consider it storage; must consider it a manufacturing area. Can anyone guide me to a method of calculating the wind lateral loading (about each axis) and uplift for such a light weight, open end, arch type structure?

Thanks,
IslandEngineer

 

[paddingtongreen]

Where are you?, what codes apply?

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[rowingengineer]

while deciding on the code ect, is the fabric attached to your frame, or does the frame just hold it up?

An expert is a man who has made all the mistakes which can be made in a very narrow field

 

[zcp]

A sketch or a picture might help as well.

ZCP

http://www.phoenix-engineer.com

 

[IslandEngineer]

Q - Where are you? What codes apply?
A - Whidbey Island N of Seattle in Washington State. Code is 2006 IBC.

Q "...is the fabric attached to your frame, or does the frame just hold it up?"
A - Arch frames just hold the fabric up. Fabric is pulled over frames after frames erected.

Arch building website attached.

 

[AggieYank]

That fabric is tensioned. This tension will impose loads on your steel.

The wind loads you design for need to match what will actually happen in the field. You need to confidently determine what those loads might be. If you aren't comfortable or don't have an experienced person you can work with in determining wind loads, you shouldn't do this work.

Carefully consider the effect and drainage of rain and snow on the structure.

In addition, the manual shows cables, that are tensioned after installation. Make sure you understand the method of tensioning, the reliability of maintaining tension, and the effect of having undertensioned cables.

I also see the fabric is cut the the installation crew during install. !!!!! Are you responsible for the fabric? Are you comfortable with the fabric? If some portion of fabric fails at any point in the future, what happens to the steel?

 

[IslandEngineer]

Thanks AggieYank for your concern. The arch structure is purchased by others and the manufacturer does not provide reaction loads. My job is to provide a support & foundation for the structure. My request is to find a method of calculating the wind lateral loading (about each axis) and uplift for such a light weight, open end, arch type structure so that I might adequately design the foundation and support. I have done many wind loading analyses but not on this type of arch structure. Any suggestion on where I can find a wind loading procedure for an open end arch type structure?

Island Engineer

 

[AggieYank]

ASCE 7 is where to find wind loads for various structures.

There is something to be said for providing a reasonable product at a good price. However, in the case of your situation: The company that provides the structure should be giving you reaction loads to design for. They should not just be giving you a manual for the structure "so you can figure it out". I mean zero offense by this, but there's the potential that even if you get the loadings correct, the cable forces and fabric tensions might mean your analysis is somewhere between partially and significantly incorrect.

Its a classic case where an engineer will "go conservative" for an unknown situation, ending up costing more money but not necessarily ensuring the design is correct.

I'd inform the owner of the structure of your concerns, let them know you'll have to be "very" conservative for foundation design (which will cost them money!), and that the owner's best interests are served by having the company that provides the structure provide reaction loads.

Either way, good luck.

 

[JedClampett]

You might be interested in this. At least if you do it the same way as them, they won't gig you if it falls down!

http://www.bfrl.nist.gov/investigations/pubs/NISTIR7661_January 2010.pdf

 

[IslandEngineer]

Thanks Jed for the write-up on the Dallas Cowboy Practice Facility collapse.

And Thanks AggieYank for the thoughts and advice.

I plan to use ASCE 7-05 as the basis for the foundation design, specifically, Figure 6-8.

As AggieYank noted, the manufacturer of these arch buildings should be providing reaction loads, yet they do not. To provide an adequate foundation and support, I plan to use loads developed from a conservative calc sequence with ASCE 7-05 as my guide.

The arch structure itself is and will remain beyond my scope of work.

Any other thoughts or advice are surely welcomed.

Regards,
IslandEngineer

 

[JAE]

I didn't think the IBC (i.e. ASCE 7) still has 85 mph wind. Isn't it all at least 90 in the US, with higher zones near the coastlines?

 

[IslandEngineer]

JAE, in ASCE 7-05, Figure 6-1 (pg 33) reflects 85 mph 3 sec gust wind speed; that 85 mph wind speed is converted to pressures in Fig 6-2 (pg 38) and our local building juridictions have adopted the 85 mph basic. We are using the 2006 IBC; the 2009 IBC does not become active for our jurisdictions until July of 2010, yet there will be no change that I see because the 2009 IBC refers to the same edition of ASCE 7 (ASCE 7-05) currently being used.

Of interest, to use ASCE 7-05 I need to establish building type. It appears to me that an open end arch type structure like this (42 ft wide x 18 ft high) is a "Low-Rise" (< 60 ft) Partially Enclosed Building(can't be an "Open" building - the two side walls have no openings - only the ends). Using the building type, I can crank through ASCE 7-05 Wind Load - Method 2 (section 6.5 (page 24)) to get the wind loads.

Thanks,
IslandEngineer

 

[Berkmire]

(I know this is probably after the fact, but someone else may be in a similar situation.)

Here in Vermont snow loading for this type of a structure can control the foundation design, or a wind and snow combination.

I suggest you look closely at the connection of the fabric tie downs to the foundation posts. The ones specified by the manufacturer have been woefully inadequate in some cases.

Finally, if the manufacturer can't or won't give you reaction then you are better off to steer clear entirely. The arch action from those pre-engineered trusses produces sizable thrusts that you aren't going to be able to reliably predict without a full analysis of the trusses - preferably with your wall properties included as the stiffness of your walls will effect the reactions.