Wind Loading on Camouflage Netting 1

[UKNZEng]

Does anybody know of any tests that have determined the coefficient of drag for camouflage netting?

The only way I can think of making an assessment is to break it down into two parts:
1 - The part of the camouflage that remains perpendicular to the wind at all times. I could assess the drag for of the core fabric netting, something like a chain fence.
2 - The Part of the camouflage that flaps in the wind. I could calculate the drag on a lot of 'little flags'

I could then add these two parts together.

Any better ideas would be helpful.

 

[concretemasonry]

You are splitting hairs based on the theoretical conditions you imposed.

If you have netting, you could get anything in the net and throw all your calculations out the window. When you get wind, you get debris that could be cumulative. Just a ream of paper could double your wind loads.

If you are concerned about the structural support, base your design on the strength the netting can conduct to the structure or what the supplier can provide based on the real conditions it can encounter. A good supplier can tell you the performance of the netting they supply.

If you have a big wind, it will be cheaper to replace the netting than rebuild the supports since the netting will fail first.

Dick

 

[structuresguy]

I agree with Dick here. Limit your design to the capacity of the connection of the netting to the structure. It would be easier to find out the tensile strength of the rope or cable used to connect to the supports, than to figure out the wind load on the netting.

 

[MiketheEngineer]

I generally just figure the netting is "solid" - as mentioned - and go from there. The "flapping" will add little load...

 

[unclesyd]

You will have to get the particular type netting you have as there are many flavors of camo netting available. The military had a least 3 general types with all types of variation on the theme. There was a single ply, double ply, and triple ply made from several different fibers but mainly polyester. The breaking strength goes from around 100 to 5000 lbs.
If can get with your supplier and get his mesh breaking strength values an as stated above and you can design your supports for this value if laced to a strand or if tied off use the breaking strength of the tie rope. As noted above one would normally want the net proper or the ties to fail before the supports.

Any manufacturer should be able to give you the thread and mesh sizes along with the single strand and mesh breaking strengths. If you are lucky they may have some wind resistance numbers.

 

[UKNZEng]

I recieved a sample of the comouflage and it is much more dense than I anticpated. As you say, there are many different types of camo. In the end I figured that it is near solid, or will induce the drag of a near solid membrane anyway, as you also say. I couldn't really ignore the load on the camouflage and let it rip, it would defeat the purpose. Thanks for your help.

We are looking at wrapping a 30 storey building in camouflage as it is being constructed, then when the building is near completion it will be unveiled. It's just a big publicity stunt, but should be a bit of fun!

 

[MiketheEngineer]

MECA Wind has a good software program. I think single user is $150.00

I just assume that the netting is solid. And the breaking strength really does not give you a good idea of when or at what wind speed it will fail. That has a lot to do with the "sag" of the material and how it was installed. Larger sag - higher wind speed. The old suspension bridge cable problem.

One company extolls the virtues of their shrinkwrap by stating it will withstand a 125 mph wind - and it did - damn near wrecking (wrecked some of it) the scaffold on which it was installed.

Monarflex uses small "bungee" cord type attachments that have predictable blowout loads based on the number and type of installation.

Good Luck

 

[cessna98j]

Remember to take catenary effects into account if applicable - they can be pretty significant for wind loading on fabric in such cases.