60 Foot Span Sign

[bigcreek]

Ok a company has contacted me about building a sign for them. Sign building is what I do, but this one brings about ALOT of questions and concerns. They want a steel sign 60' wide x about 8' tall. Normally that wouldn't be a problem IF it were to be mounted in a different manner, such as against a building or some other good support. This sign will be mounted on top of 14' tall posts one on each end, no support in the middle. The bottom of the sign will be flat, the top will have an arch to it. Ive built signs where the ends attach to the top of posts lots of times but usually only around 25' or so wide, or shorter. 60' is a huge span. I would use rectangular tube top and bottom for the horizontal piece and the arch so Id have to roll some tube for the arch but would have to outsource the rolling because my roller isn't big enough to handle the size of tubing Id use. Im not even sure yet what size of tubing would be necessary for a span like that. I would weld vertical pieces of tube from the bottom horizontal tube to the top arched tube making a solid frame, then would cut the sheet metal in 20' sheets on the plaz table and bolt the skin to the frame. Id weld brackets to the frame so the sheet metal would bolt/rivet to it. All I know is that frame will have to be strong to hold up well when winds hit that large surface area because there will be no cutouts from the sheet metal for wind relief.

I know I can get tubing in 40' pieces no problem but 60'? I could weld the tubing together to make it 60' long but do they make tubing in 60' lengths? Then I was thinking about shipping and as far as I know semi trailers are 48' long, do they come any longer? If not I suppose it wouldn't be a problem to double up with a shorter trailer and pull doubles and have that second trailer as a buffer so the sign doesn't overhang off the trailer 12'. I could set it up a couple feet so it wouldn't have any contact with the rear trailer.

Then there is the painting / powder coating part to think about. I would paint the frame and powder coat the rest of it is what I was thinking since the rest would be broken down into small enough sections to fit inside a 20' powder coat booth.

 

[AMCguy]

I don't think the skin should be structural. You need to make the frame a truss and then the skin is just cladding.

 

[tarmy]

Somebody better get a structural engineer...and a soils/ foundation guy...that is going to have a hellava lot of force applied to it via wind...let alone the struture for that span...

I have seen some big foundation ripped out of the ground when the wind load gets on a big surface like that...

 

[lukedwag]

I would consider building it in 2 or 3 pieces. It's a pretty simple task to design it like that and bolt it together. If your nervous about the design have a PE do it for ya. Should only be a days charge.

 

[bigcreek]

I don't think the skin should be structural. You need to make the frame a truss and then the skin is just cladding.

Ya I agree. My thought was not to have the skin structural. The frame would be built like a truss and that part would be structural, the skin would just fasten to it but wouldn't have any structural purpose.

 

[readhead]

Years ago I built signs at Cal Neon in San Diego. Jack in the Box was our customer. We had a standard 75'x10'x8' pole sign that they used at locations by freeways. We built the can like a truss with a roof hatch, ladder and cat walk inside to service the lamps and ballasts. It was all built out of angle and skinned with sheet metal. It was brought out in one piece and set on two very large poles. Considering the wind load I would have an engineer design the foundation, concrete and sign design.

 

[kbs2244]

I agree on the pole foundation concern for wind load.
That bus accident out west where the sign post went 2/3 through the bus shows the kind of strength they engineer into those big, green, signs..
Maybe talk to the local highway department for who does their sign design.

 

[Bill Bowman]

Aren't there "rules", i.e., zoning, etc. that limit the size of the sign face? That seems like it would make quite a great sail if a good wind came along.

 

[bigcreek]

I agree on the pole foundation concern for wind load.
That bus accident out west where the sign post went 2/3 through the bus shows the kind of strength they engineer into those big, green, signs..
Maybe talk to the local highway department for who does their sign design.

Ya thats what I was thinking when I saw that picture, absolutely amazing. It didn't even look like the post had any lean to it afterwards, like it was no worse for the wear and a bus isn't a light vehicle!

 

[bigcreek]

Aren't there "rules", i.e., zoning, etc. that limit the size of the sign face? That seems like it would make quite a great sail if a good wind came along.

Ill build it and ship it but wont travel across the country to install, that is on the customer, as is making sure they are abiding by all zoning regulations. I agree an engineer should make up the design for sign and footings. It is all in writing so it is all in the open as to what they do and don't get and what they are responsible for and what I am responsible for.

 

[txvwnut]

Since it's an arch do it in three pieces with the center piece keystone shaped and bolted together for assembly. But my suggestion should only be followed after you get a full engineering work up for footing size to handle the wind load that will be exerted on it.

You might try to talk them into perf or expanded metal backer with solid letters for the actual signage. The perf should help reduce the wind load.

 

[RPH]

Welded tube is made in a continuous process. I seen them cut it in hundred foot lengths.

 

[bigcreek]

Welded tube is made in a continuous process. I seen them cut it in hundred foot lengths.

Interesting, that's what I was wondering about. Thanks

 

[astroracer]

And, keep in mind, you don't have to "roll the tubing" to follow the shape of the sign. Use the steel skin to make the shape. The inner structure can be designed as square or triangular components to carry the load.
Like everyone else I think the wind load on this thing will be tremendous... You need to talk to the customer about that.
Mark