Sign Industry Wind Load Charts, Sign Section Modulus Charts

The size of the signs that you are contemplating normally always require a structural engineer. For you edificaton, the wind loading is determined by ASCE 7. There are many factors that must be considered, such as topography, nominal predicted and historical wind data, drag coefficient, etc... It is best that you do not get involved with making recommendations or specifications for liability reasons. Leave it up to the engineer.

Thanks for your input, but that is my job. I am an engineer but not specialized and registered in this exact area of expertise. I will continue to make those recommendations because that is what I'm paid to do. When I get it as close as I can get it, we estimate the job, tell the customer what it will cost and when it's sold I pass it off to my sign engineers to verify and certify. They charge an additional fee that would be an unneeded cost if the job does not get sold.

I'm familiar with topography, wind data, drag coefficients, etc... again, that's my job. I'm also familiar with and own ASCE. But it does not have the specific charts I'm asking about, in the specific format that I'm asking for. And I don't have the time to run all the calculations myself in each individual case.

Something I learned long ago ... A goodly portion of an efficient engineer's skill comes not from necessarily knowing every single formula ever devised ... but in knowing where to look to find the answer that has already been calculated. It's not necessary to re-invent, or even to re-build a wheel every time ... when you can go buy one that someone else has already built.

I'm just looking for a section modulus chart from the sign industry that goes beyond 300 sq. foot signs.

I concur with not reinventing the wheel. Yes, I understand that it is your job. I was once the junior engineer trying to be as fast as I can, and still use charts. But, most of use use computer programs to do the work. You will find it faster to use the programs to do the calculations for you, then spot checking the results. You might feel that the primary concern of your PE is speed, but our primary concern is liability. Charts help us to be expedient, but be conscious of how the charts are generated and to what extent they are useful. Extrapolation is often done, but when your structure gets much larger than values on the charts critical errors often occur as you know. Most wind load charts were generated from empirical data acquire through scale wind tunnel testing. I believe that the charts you are using asume that the effects of torsional and periodic deflections (swaying) are minimal, but the size that you want charts for would be effected by turbulent air flow and oscillating deflections, which could lead to failure unless compensated for, especially if slender columns are used. Laminar flow is normally assumed with charts, hence ASCE 7 recommends that wind tunnel tests be performed when laminar flow cannot be assumed.

There are many computer analysis programs for structures. I'm not aware of any specifically for signs but, you might try ETABS or SAP as they are relatively inexpensive.

My size recommendations are for estimating job costs in order to make a bid. That is done before my drawings are sent to our sign engineers who are sub-contracted Civil Engineers. I'm a Mechanical Engineer, with 20 years of machine design background. I'm not a C.E. or S.E.

If we end up getting the job, the drawings are sent to a C.E. to verify and/or change if needed. The liability is his, after he checks my design and makes any adjustments, if adjustments are necessary. The final design is fully calculated using the appropriate engineering software. By the C.E.

The purpose of my designs are to come as close as possible to what the C.E. will specify in the end ... so he'll have to make as few adjustments as possible after he gets his hands on it. And also to suggest the most economical design, which isn't always the primary concern of the C.E. They will obviously up-size any structural members if needed, as they are liable. But rarely will they down-size members, to save costs, even if it is safe and proper to do so. I don't need any over-built structures. Efficiency and Value Engineering are obviously important.

I just need the charts.

Sorry, that I can't be of more help. I fully understand your situation. Estimating and bidding is not my favorite task, especially spending many long nights trying to get bids out. Lucky, we didn't lose money on a project, just wasted time, and many lost leaders.

I agree with you about value engineering. It is a tacit function of the design process, but I feel it should be an integral step of the design process. Presently, only the Fed's require it for all design projects.

Hope you find the information that you need.

I was also a junior engineer responsible for the erection of overly tall masts. We extrapolated the charts and everyone agreed on the section sizes etc. Including experienced structural and civil engineers.

In steady state wind they oscillated wildly and had to be taken down. We got sued and lost.

In the legal process, we learnt alot about this type of structure. Namely that charts do not go above a certain level because there are too many imponderables that are unique to each situation. The codes do not always cover these types of situations; hence no charts.

Legally we are all bound to do what a "suitably competent engineer would do". This implies that you should seek expert advice on tall masts.

Although you might think it is a matter of upsizing the sections it can turn out to involve quite a few complicated matters: galloping in steady state winds leading to fatigue calculations which may show the structure as designed to be unworkable (this happens occasionally) or the design becomes too expensive for the bid that you made (at this point short-cuts are inevitably made, that's life I'm afraid).

If you are still stubborn enough to continue with your idea of getting bigger charts, I wish you much luck. Because you will have to have some luck. Generally, competent engineers do not rely on luck.