Calculating Wind Load on Banner 1

[STR-DB]

Hi,

I have a banner 17'x4' that will span from building to building 16ft above a street. I have seen a couple posts on this, but nothing super clear. How should I go about calculating the wind load on the banner as I don't believe it can be considered a sign as the cupping action of the banner when force is applied will cause the load to be greater than a solid sign. I am looking at ASCE 7-05.

Any insight would be greatly appreciated!

Thanks,
EIT

 

[SlideRuleEra]

See Page 9, "Flag Load", of ANSI/NAAMM FP1001 "Guide Specification for Design of Metal Flagpoles".

http://www.SlideRuleEra.net

 

[STR-DB]

Thanks! But, wouldn't the load of a banner supported on both sides be greater than that of a flag just supported by pole?

 

[rb1957]

why would the airload on a flexible banner be more than the load on a equivalent rigid sign ?

Sure there may be lateral loads (as the banner develops membrane loads).

Will the be cuts in the banner (this is typical, no?) ?

another day in paradise, or is paradise one day closer ?

 

[STR-DB]

My thinking was that the curved surface will make it more difficult for air to move around the banner. Similar to a parachute.

Yes, there will be slits that supposedly take 25% of load, but from what I see online 10-15% is more realistic.

 

[SlideRuleEra]

STR-DB - Sorry, I failed to read your post correctly.

You can establish an upper bound by using the basic wind load equation:

Wind Pressure per Square Foot = (0.00256) x (Wind Speed in mph)^2

http://www.SlideRuleEra.net

 

[rb1957]

I think you only need p*A.

If you could I'd design the supports so that the banner would tear before overloading the supports.

In the absence of much thought and knowledge, if you know banner material E, you can calc (roughly) the stress in the banner (across the short side, I'd use hoop stress, guess a CL deflection, that defines a radius, then hoop stress, then strain, then iterate so the length of the stained material equals the arc length). Now this'll change the projected area of the banner, but I'd conservatively neglect this. How do the long sides deflect ? … not a clue !

another day in paradise, or is paradise one day closer ?

 

[Aesur]

Do not many larger banners have relief cuts in them to allow the wind to pass through to negate these effects?

 

[r13]

It is reasonable to use wind load on signs, as the flexible nature of the banner material actually will dampen the effect of the wind. rb is correct, it is rather more critical on hanging material, which is like catenary subjects to dynamic loadings. Also, Aesur has a good practical point to reduce the wind effect.

 

[STR-DB]

Thanks for the responses guys!

Yes, so as of now I am using the wind load on a sign and calculating the pull-out tension on the anchors using Roark's cable equations. And the banner will have slits