Chicken Wire Wind Pressure

[WAstruc10]

Is anyone aware of testing done for drag coefficients for chicken wire fencing? ASCE 7 seems to agree with hand calcs based upon Reynold's number, using the width of a single wire and the opacity (% solid area) of the mesh. However, I have been warned by another engineer that it would be typical to take up to 6 times the actual profile area to account for turbulence. Much thanks...

 

[JAE]

I had an old friend of mine once show me a picture of a typical airplane wing cross section as compared to a small dot next to it representing a thick wire. He claimed that the wire produced as much drag as the wing.

We've designed lattice grids in the past where we reasoned that either the owner might someday add a nice banner to it or a large piece of plastic would blow onto it - so we designed it as a solid entity.

Otherwise...would you design for, say, 50% effective area? Just a thought.

 

[WAstruc10]

Thanks JAE. If it were a small fence I would agree with your philosophy, but we've got thousands of square feet of mesh, with severe limitations on the supporting structure, so every tenth of a psf counts.

 

[Lutfi]

There is a manual that is published by the chain link fence institute. It is not chicken wire but the nearest thing that I can think of. The following link will take you to the site and you can download it. It is in PDF format.

http://www.chainlinkinfo.org/fs-architects.html

 

[Ron]

WAstruc10...if latitude available, I would take JAE's approach, but it appears you don't have that latitude.

I would be careful about putting too much emphasis on the turbulence/supplemental drag issue. I believe those were developed with a "steady state" condition, rather than a "gust" condition. For the gust condition, a momentary large lateral deflection might be very acceptable, thus allowing a bit more range in your design.

Further, the importance factor of such a structure need not be very high. In the Florida Building Code, screen enclosures are to be designed for an importance factor of 0.77 (don't ask me why it isn't 0.75 or 0.80!).

 

[VoyageofDiscovery]

Hi WAstruc10,

One should also consider the appropriate radial ice case on the mesh. Total weight will also affect your connections.

Regards

VOD

 

[JedClampett]

Whenever I've had to do a hydraulic loss calculation, I use the Tables in the Back of ASHRAE Fundamentals Books. They tabulate losses for all sorts of cases. For a screen in a duct with 90% free area the drag coefficient is .14

 

[WAstruc10]

Lutfi - we've checked the chainlink fence institute recommendations; appears to match ASCE 7. I wonder if this is based upon testing (?) or more likely they hired a consultant that used the code...