Effects of Wind Loading on 40'x20' Banner
Effects of Wind Loading on 40'x20' Banner
(OP)
I am working on the wall anchors for a large 40'w x 20'h banner which is to be suspended from the uppermost wall of an 11 storey building. The wall consist of 4 inch thick precast panels. I am trying to use 5/8" dia. through bolts spaced at 5'-0" on centre (top and bottom of banner).
As I apply my wind loading to the banner, I notice that I should be considering the effect of the resulting tension in the banner which in turn creates large shear loads in the bolts if the banner is tight to the wall (i.e. like pulling on the centre of a tight steel wire between two roof anchors. When there is very little slack in the wire, the resulting loading on the anchors perpendicluar to the applied load are large).
Am I getting to analytical in considering this. Should I just be considering straight pull out resulting from the wind on the specific anchor bolt's tributary area?
Thanks
gmf






RE: Effects of Wind Loading on 40'x20' Banner
RE: Effects of Wind Loading on 40'x20' Banner
If you can keep the cable from sagging and do not preload too high - loads will not be too bad - In other words - more connections
Basic equation:
H = wL^2/8d
H = tension
w = plf on cable
L = span
d = sag
Watch units and good luck
RE: Effects of Wind Loading on 40'x20' Banner
The catenary tensions forces will be the primary load on your anchors in this type of structure. I would expect the shear from this to be roughly 3 or four times the tension.
This is something that I have seen overlooked by many engineers and it is a good thing that you have picked it up.
Look up the catenary formulii in roarks for the typical formulii for a one way cable. You can get a rough estimate of the average loads on each side by equating the deflection at the banner center.
The hardest thing on this will be determining the EA as this information is not usually readily available. I would suggest seeing if you can obtain elongation data from the manufacturer from which you can estimate the EA at the service loads.
Keep in mind that inward pressure will blow the banner into the face of the building and therefore does not normally need to be considered.
The banner also will need to be tensioned to take the kinks out, they never get the size right. Have you allowed for future banner replacement?
RE: Effects of Wind Loading on 40'x20' Banner
csd72 - I have allowed for future banner replacement. In fact, the client wants the ability to replace the banner on a regular basis.
Thanks again, everyone, for the help.
gmf
RE: Effects of Wind Loading on 40'x20' Banner
As csd72 noted, the forces are catenary in nature. The only way to avoid shear forces on the anchors is to provide a compression frame against the wall to resist that component.
RE: Effects of Wind Loading on 40'x20' Banner
I stress again that the fabric manufacturer will definately not get the banner size right and you should allow 3" tolerance to allow for this.