Windbreak mesh

[mobe]

I've been asked to calculate an overturning load on a mobile structure that will have windbreak mesh on it. I see it quoted as 50% or 60% reduction. Would this be a reasonable approach to say an overall Cp of 0.5? Has anybody any experience of this or know where there are any actual design references. In this case I would like to see a reduced figure rather than take a conservative view of it with a solidity factor of 1. Thanks Mobe

 

[MacGruber22]

Recently, I have searched for backup data for drag forces on mesh and found nothing too helpful for the cases I have had. I have called the manufactures and they essentially told me that it is the EOR's responsibility to figure it out (jeez). That said, Cp = .5 sounds really low. If the mesh is flexible and is able to "dish", I can't see Cp = 1 even with the proposed reduction of closed area. Frankly, I wouldn't consider anything less than 1.0. I did find a masters thesis on the subject, but I didn't trust it and not sure if I could even relocate it.

Also: Even if you can justify a lower drag coefficient, I would check the wind on ice load combination in ASCE 7 (or similar check in whatever code you are using) considering the mesh as a solid panel, if of course this mobile structure will see ice. I am sure that would govern in most cases.

"It is imperative Cunth doesn't get his hands on those codes."

 

[MikeHalloran]

Any mesh type structure will eventually have a flag attached to it, negating the open area of the mesh.

There was a scary incident with a huge flag on the suspension cables of the Verrazano Narrows Bridge.
They don't attach flags to it anymore.


Mike Halloran
Pembroke Pines, FL, USA

 

[Triangled]

attached was a Florida commissioned study for wind screening RTUs with a metal grating 50% porous

 

[Triangled]

hmmm.. seems my attachment procedure was 100% porous, try this....

 

[dik]

I believe that AASHTO has a wind loading for chainlink fencing of 15 psf...

Dik

 

[JedClampett]

Both the ASHRAE Handbooks and "Handbook of Hydraulic Resistance" 3rd Edition by I.E. Idelchik (looks like there's a free version on-line, but I don't want to encourage that) have examples that can used to calculate Cp for mesh. They're a lot of work, with you having to figuring out wire sizes, open areas, etc. And you'll find the numbers get close to 1.0 pretty easily.
As the others have said, use a solid sheet and make your life easier.

 

[JAE]

nd you'll find the numbers get close to 1.0 pretty easily.

I'd agree with this but I'm not an expert in this by any means.

I once had an aerospace engineer friend of mine tell me that the drag on a typical single engine plane wing was lower than that of the cross-wise wing stabilizing cables used on the old Sopwith camel bi-planes.

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[mobe]

Thanks all & thanks Triangled for the link, most helpful. M.

 

[Triangled]

you bet