Wind Pressure Calculation for Signage

P=C_f ¹/₂ρu²

where P is the pressure, C_f the drag coefficient, ρ the density of the air and u the speed of the air's hypothetical stagnant streamline.

Thanks for the formula but I think the county wants something a little more concrete like "If the wind is blowing 60mph, will my sign on 4"x4" poles, 1 foot in the ground hold up. Can anyone tell me that?

Thanks!

Debbie

What does the guy painting and installing the sign have to say?

How many poles? What height? How heavy? There are other things to consider besides wind pressure to determine that it will not (prolly) fall over.

Thank you for answering. I am a single lady who owns a small RV park. I am the painter and sign maker. I will get one of the 55+ guys in my park to help me install it. Might need a little help since I weigh 117--but we can do it! I will get back to you on the height, weight and size of poles.

Thanks! Have a wonderful day!

Debbie

Hi Debbie

I can see the problem is not with the sign but with the people allowing you to set it up. Here is what I would do:

1. Build the sign just as your and your helpers imagination would like it to look like.

2. Once it is in the ground (ready mix concrete) about 2 feet and standing there in all its pride, saw it of at about 1 foot above ground.

3. Attach strong hinges to the stumps and the posts.

4. On the opposite side attach these and make it a foldaway sign.

If really strong winds are expected just lay it flat. If you can't get there in time, this is the point were it will brake (Sollbruchstelle, I keep forgetting the English word) and to repair it will be like taking lollies off babies.

If the permission comity has anything to whinge about let them play the big bad wolf. They might be able to blow it over but you will be able to advertise again quicker than they can say regulations.

Don't forget to have a bit of fun as well, Ky.

I like ky's idea, but I'd spring load it so you wouldn't need to run home from the pub and lay the sign down if a sudden wind came up.

Thank you very much. A little over my head but I appreciate the answer!

Debbie

LTS-5 TRev Apx C - TABLE OF CONTENTS

I think you should also consider whether the sign will be attached to the posts at the top and bottom (of the sign), or whether it will be attached at only the top and thus can swing in the wind.

Building codes probably specify the wind pressure for your location, the drag coefficient will also come from tables--"big flat thing!"

Burial depth may also be specified by code, and may depend on the frost depth for your area. One foot sounds too small.

Thank you so much for the answer Lehman! I will talk to the county more. Is your first name Carlton, by any chance?

Debbie

No. Lehman indicates my high school.

I see.

Thanks

Wind pressure or velocity pressure, q_z = 0.00256 k_z (I V)², lb/ft²

For more details, see CR4 Threads:

• Wind Speed to Wind Load, post #5.

• Calculating Wind Resistance, post #2.

Thank you so much everyone for the posts! I will talk more to the county and get back to you.

Happy Day to you!

Debbie

That is what I would do... The red tape involved in such simple matters for owners who prefer for what ever reason to do their own work is always problematic...

Ask them what range of wind speed needs to be accounted for.

In Florida they require a simple wooden storage shed to be engineered to protect against possible hurricanes...

Another possibility is that a local sign maker could help you determine what you need to cut up the red tape.

A REASONABLE FIGURE FOR HIGH SPEED WINDS ON SIGN COULD BE 30 Ib PER SQ FOOT WHICH IS 30*16=480 Ibs PRESSURE AT MIDDLE .AT A HIGHT OF 8 Ft FROM GROUND MIDDLE POINT IS 10 FT FROM GROUND. A WOODEN POLE OF 10 INCHES DIAMETER (MINIMUM) AND 10 Ft HIGH ABOVE GROUND IS RECOMMENDED FOR 4*4 SIGN.I HOPE IT WILL SATISFY YOUR COUNTY AND HELP TO MAKE STRONG ENOUGH SIGN.

The thing about 'CAPS LOCK' is it is internet for YELLING!

And if you YELL, your answer should be correct - not totally ridiculous.

Like 'you need a telephone pole for a 4' sq sign'

more like 1500 lb force at centre, at 60miles per hour winds.

Since you are probably in Florida, the wind code here is usually 120 mph inland and 130 near the coast.

I'd use 10' long 6x6 pressure treated pine from HD or Lowe's and put them 3 feet in the ground with cement around them.

Fasten the sign with five 3/8" galvanized lag bolts, 4" long with galvanized fender washers on each side.

What the County is looking for is a drawing stamped by a certified engineer though, which will cost you about $250-$350 to get them to sign and seal a drawing.

Find someone in your county with a similar sized sign and use their numbers. Since you're drawing your information from an existing sign, approval is practically guaranteed.

It really depends on where you live that determines the Basic Wind Speed in your area. Wind speeds in FL are based on hurricane wind forces, whereas in Iowa or Kansas or Boston they will be quite different.

I'm afraid in order to satisfy the County's sign regulations you'll need to obtain the services of a Licensed & Registered Professional Engineer. It won't cost you too much. They, the County (why isn't your Town involved, or did they pass it off to the County?), need assurances from you that whatever is installed will be safe and not break away and hit someone or cause property damages.

Regardless of where you're located, I strongly feel that burying the posts only 1 foot into the ground (even with concrete placed around the posts) that that construction will be adequate to resist the required Design Wind Forces (by ASCE 7-2010) and will result in the sign's failure, and mostly likely it'll be ripped out of the ground. Likewise, if you're located along the SE seaboard, FL and the Gulf of Mexico, I highly doubt that two 4x4 wood posts are going to be adequately strong enough to resist the Design Wind Speed.

I do applaud you for DIY on this sign project, but you're going to satisfy statutes adopted by the County you live in (and where this sign is to be erected), and possibly the State Building Code (usually governs).

There are some of us in here that could design the sign for you if we knew where you're located (USA?), but even then if we did so your County is going to require that the Professional Engineer be Licensed and Registered in your state, not some other state or country. They will also require from you to produce Permitting Drawings that have a PE's seal and affixed signature. Most state Education Departments that regulate the licensing of PE's are very specific about this....that the PE must be licensed and registered to perform consulting services in that very state.

I hope this points you in the right direction. Good luck with the sign!

Signed, CaptMoosie, NYS PE / PhD

(Civil, Structural & Environmental Engineer)

I can't find it but who suggested to do this?

I strongly feel that burying the posts only 1 foot into the ground....

With your title you should be able to remember

Debbie - as an example of the data she needs in #3

Sounds like I need to talk to the County more. Yes, I may have to hire an engineer. Was hoping this might be easier. I live in Black Canyon City, AZ. We are not incorporated so I deal with Yavapai County.

Thanks so much CaptMoose!

Debbie

It depends from square o the sped of the wind. nothing fancy! You can also stick any number as this idiots never know what they want, just making your life miserable. Try to say if wind 100 mph than pressure would by 150 Tr and that need poles at lest 2X3 or steel pipe 3" . Whatever you tell them they accept without question asked. Indeed this is to cover their ass.

Your local utility commision should have references as to how to calculate the wind force. It is likely that the NESC (National Electric Safety Code) will be referenced. There are several formulas in this book for wind force. They may have one at the local utility commission, or you might ask your local Telephone company, or Power Company if you can look at theirs. The NESC also shows a 3 second max wind map. Make sure you get a current one. Older versions do not have the 3 second max wind maps.