Few questions regarding Single Mast Sign Structures

Question

Few questions regarding Single Mast Sign Structures

buening (Structural)

(OP)

7 Mar 07 12:50

We were just hired to design a few sign structures for a new Gas Station and Truck Stop. One sign is 70' tall and the other is 30' tall. They want them to be a single mast sign. I've done sign designs in the past using masonry but none with round steel (or maybe aluminum?). The AISC manual lists HSS up to 20" diameter, and i am well aware that the 70' structure will need a larger diameter than that. Are there any other sources for tables on larger size round sections (to choose a shape), or do i just specify the diameter and wall thickness on the plans? Would you think using a stepped/telescoping mast be more cost effective, or would the special manufacturing costs outweigh the steel weight savings? I plan on doing the design by hand and checking it with Staad, but are there any freeware spreadsheets out there that i can use to verify my results? I plan on using a spread footing to support the signs and the sign will be welded to a base plate with anchor bolts into the foundation. I found a few topics using the search feature, but none were specific to my questions. FYI, the square footage of the sign is 441sf for the 70' (not including mast) and 150sf for the 30' sign, so there is a decent amount of area for wind loading on these two signs. Thanks for all the help!

JStephen (Mechanical) · Answer 1 · 2007-03-07 13:25:28

For larger diameters, just calculate section properties. On stepped vs straight, check with a manufacturer that does the kind of work.

I'm not sure how Staad would really help on that kind of a problem.

Check if vibration, fatigue, or torsional loading might control the design.

oldrunner (Structural) · Answer 2 · 2007-03-07 14:17:21

Design your columns per the "Standard Specifications for Structural Supports for Highway Signs, Luminaries and Traffic Signals" published by AASHTO.

miecz (Structural) · Answer 3 · 2007-03-07 16:07:10

Florida DOT has some software available on their web site.

I would forget aluminum. Previous threads on this subject have focused on fatigue at the base connection. I would think aluminum would exacerbate this problem.

csd72 (Structural) · Answer 4 · 2007-03-09 11:06:19

We design signs with poles up to about 7' diameter. There are a few companies that custom roll these to order from A36 plate.

Dont forget to apply the Q factor from the code when calculating bending capacity.

I would only telescope it if you have to put a splice in anyhow due to transport/availability.

civilperson (Structural) · Answer 5 · 2007-03-09 11:24:42

Spread footing is inefficient for horizontal loads, (wind and seismic that produce moment). Consider drilled shaft for minimizing cost. Valmont will give you a complete design and manufactured pole for any specified loading. (Very competetive and proven in thousands of applications).

buening (Structural) · Answer 6 · 2007-03-09 11:29:37

Civilperson,
I was actually looking into Valmont's website. I will be checking on the sign company to see if they have the equipment for drilled shafts. I have used them in the past for signs, but the client requested spread footings. I also think a tapered or stepped pole would be more cost effective a sign this size. Just want to thank everyone for their informative replies and i appreciate all the help!

oldrunner (Structural) · Answer 7 · 2007-03-09 11:53:40

We assume you have a geotechical report for the project site. What is their recommendation? Yes, you can do a spread footing, but they take up real estate. We did one about 50'+ square for a 426' flag pole because there was ground water problems. What kind of wind speed and site exposure will you have to design to?

We've done both step tapered and tapered poles. US Flag in Beaumont is another source as a supplier.

http://usflag.com/

buening (Structural) · Answer 8 · 2007-03-09 20:24:35

Yeah i have a full geotech report and the allowable bearing is 2tsf. Rough preliminary calcs show a 12'x12' slab. Design wind speed is 30psf (located in central illinois). The client just called and said he just needs a section modulus and a foundation design so i guess they don't want the tapered poles.

mrMikee (Structural) · Answer 9 · 2007-03-13 20:21:51

While not exactly a design spec for signs you might find it interesting to check out the following manual for monopoles.

http://www.risatech.com/products/dnloads/risatower/Technical_Manual_1.pdf

Regards,
-Mike

epr (Structural) · Answer 10 · 2007-03-17 13:29:26

I recommend that you contact a company that manufactures single pole signs almost exclusively.  They've got the design and the details down to a science, and the sign fabrication would likely be more economical.

And yes, I agree with Civilperson, a drilled foundation is usually the better alternative, depending on soil conditions.

Try the following, both of whom I have personally worked with on sign projects.

Productivity, Inc.  (800) 428-6999

All Steel Structures, Inc.  (800) 621-1759

mohsenaa (Structural) · Answer 11 · 2007-04-01 15:44:55

are you still working in this job
UBC has a design footing for this application

buening (Structural) · Answer 12 · 2007-04-01 17:15:36

It is still in the bidding process but if our client gets the job then we will be doing the design. Thanks for the heads up!

kbarnett (Structural) · Answer 13 · 2007-04-03 17:03:16

When you say they don't want tapered because they just want section modulus, I think you may be making an assumption. The base plate and foundation are commonly sized to the maximum allowable moment of the pole, and sometimes the yield moment, depending on the code and jurisdiction. On a tapered pole, that would be the properties at the base, where the maximum moment is at. A tapered pole just reduces the cross section nearer the top to save material (and cost), where the moment is not as great.

buening (Structural) · Answer 14 · 2007-04-03 17:19:14

Yeah i guess that isn't a good assumption. The section modulus i would provide would be at the base and they can us a tapered/step type pole as long as the section properties of the base match my values. Guess i should watch my assumptions LOL.

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Few questions regarding Single Mast Sign Structures