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I have a customer that will be installing a billboard I made. He wants a recommendation on the number of poles required. They will be treated 6x6's. The sign is 8' high by 16' wide, 3 to 4 feet above the ground in a "V" shape. The spread on the "V" will be 6 to 8 feet so the two sides can be braced to each other. I know the rule of thumb of 1/3 below ground - 2/3 above for pole depth, but how many poles would be needed to carry the normal 100 mph wind load? My customer is thinking 3 per side, I'm thinking 5, 9 total with both sides sharing the pole at the point of the "V".
The sign has the 4x8 alumalite panels running horizontal, so I'm figuring 3 rows of 2x6's and verticle 2x6's on the outside and center poles so that the alumalite can be attached anywhere around the perimter of all 8 sheets.
-------------------- Dave Sherby "Sandman" SherWood Sign & Graphic Design Crystal Falls, MI 49920 906-875-6201 sherwoodsign@sbcglobal.net Posts: 5396 | From: Crystal Falls, MI USA | Registered: Apr 1999
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Not sure of the math that goes into wind velocity here but couldn't you make the panels vertical and run a pole every 4 feet? Seems like it might be sturdier to me. But what do I know? I use brushes not hammers...LOL!
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Dave, If both sides are 16 feet each in width, 9 or one every 4 feet should be sufficient. I would run 2x4 or 2x6 perlins (horizontals) across about 16 to 24 inches apart. Making sure on hit of the horizotal seams. I wouldn't worry about the vertical seams with aluminum, because they will not warp. I would suggest the use of a little larger than average head on the screws or use several. Aluminum needs a lot of attachment in the winds. Jack
-------------------- "Don't change horses in midstream, unless you spot one with longer legs" bronzeo oti Jack Davis 1410 Main St Joplin, MO 64801 www.imagemakerart.com jack@imagemakerart.com Posts: 1549 | From: Joplin, MO | Registered: Mar 2000
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I would use 5- 6x6s as long as they are placed in concrete. If not you should put a tie down cable on a 45deg.to a concrete base in the middle of the v.
-------------------- Randall Campbell Randy's Graphics, 420 Fairfield N. Hamilton Ontario Canada Posts: 2857 | From: Hamilton Ontario Canada | Registered: Jan 2002
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My mantra here in my shop is "Plan for the worst; hope for the best."
Dave, Go with the five per side. If you don't, as sure as shoot'n, you'll have a windstorm the next day, the signs will be blown over, and your client will blame you for it and for the little dog down the street that got run over.
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Thanks for the replys. I felt I was on the right track with 5 per side. I was going to make the sign with the panels veticle, but switching to horizontal made it possible to keep all vinyl off the seams except for the edge print, (big full color paint can) which would have had 2 seams through the graphic (verticle) instead of one (horizontal).
-------------------- Dave Sherby "Sandman" SherWood Sign & Graphic Design Crystal Falls, MI 49920 906-875-6201 sherwoodsign@sbcglobal.net Posts: 5396 | From: Crystal Falls, MI USA | Registered: Apr 1999
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-------------------- Jeff Vrstal Main Street Signs 157 E. Main Street Evansville, WI 53536 1-608-882-0322 Posts: 670 | From: Evansville, Wisconsin | Registered: Sep 2001
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It actually depends on the soil compaction and the type poles you intend to use Dave. Poles is a realative term used to describe anyhting from a 4x4 post to treated telephone type pole to a steel beam. The soil you intend to put these "poles" into is altogether another story, is it loose sand/hard clay/mud on a creek or close to swampy wetland area? I personally would use 6" treated telephone type poles 2 to a side here in the red clay of the Carolina's. As for wind load specs, the substrate will tear up at those wind loads no matter what you nail or fasten it to if it is only a wood frame behind it.What has to withstand those windloads the structure itself or the panels attached to it? I personally don't think alumilite would stand up to a windload like that unless it has been glued to a heavier base material covering the whole area of the panel.
I say this with 20+ years of billboard experience and doing hurricane repairs several times in the past.Most people will not pay for the type structure that will withstand these types of windloads as they very quickly become cost prohibitive. If it is a prerequisite to obtain the job then I personally would suggest a steel structure with steel panels.
-------------------- fly low...timi/NC is, Tim Barrow Barrow Art Signs Winston-Salem,NC Posts: 2224 | From: Winston-Salem,NC,USA | Registered: Nov 1998
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Laminators claims 120+ mph windload on their 6mm Alumalite panel and 140+ mph on the 10 mil panel when supported on all four edges. The code for signs in our area calls for 90 mph windload tolerance.
Our soil type is sand, clay, rock combo and has always held poles very tight here, which is why I didn't mention it. Up here in the U.P., steel poles in concrete is typically only used for large electric signs and when the soil is poor.
-------------------- Dave Sherby "Sandman" SherWood Sign & Graphic Design Crystal Falls, MI 49920 906-875-6201 sherwoodsign@sbcglobal.net Posts: 5396 | From: Crystal Falls, MI USA | Registered: Apr 1999
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Dave, someplace in the letterhead archives is a reference to a really good sign installation manual that is sold by SignCraft and/or S/T. Something like Sign Foundation Design. It is fairly easy to read, and I recommend you track it down and get a copy. Even if you never design a foundation, it helps understand what goes into the process.
I suspect Timi knows more about foundations than the rest of us, but here goes.
Wind load in pounds per square foot can be found in lookup tables in design books and building codes. A local inspector can usually tell you what wind load you have to design for.
Let's assume that you need 22 pounds per square foot. Your sign is 8x16 feet on each side, or 128 square feet. You have a wind load of 2816 pounds.
That load can be treated as a point load dead center of the sign. So if you put up one post, it would have to hold 2816 pounds. Two poles would each carry 1408 pounds, and so on. So you need enough poles to carry 2816 pounds without breaking off.
Now you attach the sign with just two screws. Each screw would have to carry 1408 pounds without breaking or tearing out. So you use lots of lag screws with flat washers to spread the load. Divide the load by the number of screws to see the load per screw.
Now you have the soil. For engineering purposes the first foot never counts because it is assumed to be loose soil. If you have Timi's NC red clay all the way to the top, you can count it even though an engineer never will.
Now you have a bending moment in the soil that depends on whether the soil is red clay or beach sand or somewhere in between. So most people wing it with the old 1/3 to 2/3 rule of thumb. There are lookup tables for the various types of soil so that you can calculate the proper depth of the hole.
Like Timi says, the likelihood of your achieving an engineered sign is almost zero since no one will pay you for one.
If something has to fail, the best case in my estimation is for the sign to lean over in the worst case wind - the soil lets go. At least you can straighten it back up. The worst case is for the sign face to let go and start flying around where people can get hurt. If the poles break off at the ground, the sign will probably be heavy enough not to fly off too far.
That's less than a complete story, but you see the fundamentals.
You'll be doing this again in the future, and a good installation book will help you. VIc G
-------------------- Victor Georgiou Danville, CA , USA Posts: 1746 | From: Danville, CA , USA | Registered: Dec 1998
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I don't know about the specs for alumilite personally as I have not used it,but from what I've seen with normal installation precedures for billboards, I personally know 1/2 mdo and steel tiffin panels that the manufacturers spec to withstand windloads at hurricane strength disintigrate.Windloads at those speeds can take steel structures and bend them like abstract pretzels. I'm not speaking from any engineering specifications but just plain ol bad experiences.My point was that a piece of coroplast with aluminum laminated to both sides isn't going to hold up practically(with normal instalation procedures) under those circumstances.Not that I wish to discredit the quality of the substrate but to emphasis the fact that not much will withstand those kind of sustained winds for any length of time.Another point I was trying to make is that if you do the math 5 6"x6" posts is over engineered for that application. We build those type strutures on a regular basis here with mdo and have had no problems.If you do have a storm that bad you want the panels to come down or off before the structure itself fails as it will be easier to replace the panels than the structure itself.If the soil fails odds are you'll have to take the structure apart to repair it properly.As for anyone getting hit by the panels at those windspeeds there is gonna be alot more than those panels flying about to worry about.
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Dave, Run a 2x6 at each horizontal stringer across the open end of the V connecting the 6x6 posts. Lag screw them in place and you'll have a remarkably solid structure.
-------------------- Bill Dirkes Cornhole Art LLC Bellevue, Ky. Goodnight Mrs. Calabash, wherever you are. Posts: 591 | From: Bellevue,Ky. US | Registered: Aug 1999
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Whatever ammount you use (I'd be afraid to suggest something I haven't tried), why don't you use steel? It'd probably be much cheaper & less labor intensive. (At least it is down here. Wood is real expensive)
-------------------- Felix Marcano PuertoRicoSigns.Com Luquillo, PR
Work hard, party like a tourist! Posts: 2274 | From: Luquillo, Puerto Rico, USA | Registered: Nov 2000
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