Wind speeds, post sizes and hole size and depth for a 4'x8' panel ground sign

[Billct2]

like unclebun, when I started in this business after high school the guy I worked for did all his post with tamped earth, well rocks & tamped earth. I'd back fill, drop a couple good size rocks in and beat them to death, and repeat the process till the hole was full. I definitely prefer concrete now . Another thing engineers don't seem to get, undisturbed earth is really strong. A narrow hole dug with post hole diggers and filled with concrete is stronger than a wide hole with a sonotube dropped in it.

 

[TimToad]

I just like a happy ending.

Ahh...... how do they check if your hole is deep enough ?? Do they come out and inspect it before you can pour ??

Yes, despite the fact that our town is full of non-compliant, unpermitted signs with very little enforcement, the inspector will actually make us dig the holes, cover them with plywood for safety and then go out and measure them BEFORE we can pour the concrete and set the posts.

To make matters even more ridiculous, the permit cost for this simple double sided 3/4" digital print MDO 4'x8' sign is $507.00.

 

[bannertime]

the permit cost for MDO 4'x8' sign is $507.00.

Hopefully that includes everything right? The extra cost for 6x6 and concrete and the permit? Right? Surely that isn't the price for just the permit!

 

[unclebun]

If they are willing to go back and change things in the online calculator, maybe you can prevail upon them to change the post type to 4"x4" treated yellow pine and find that it's OK.

 

[Gino]

Yes, despite the fact that our town is full of non-compliant, unpermitted signs with very little enforcement, the inspector will actually make us dig the holes, cover them with plywood for safety and then go out and measure them BEFORE we can pour the concrete and set the posts.

To make matters even more ridiculous, the permit cost for this simple double sided 3/4" digital print MDO 4'x8' sign is $507.00.

That's just ridiculous. What if you dig the holes and they don't come out until the end of the day and then it rains the next day ?? Are you supposed to just sit around with your thumbs up your a$$ while they play Mr Inspector ?? I'd make sure they were within earshot while I'm digging and they inspect the hole on the spot.... or I'm going ahead as planned. I ain't gonna leave no 24" x 36" series of holes just covered with a piece of plywood. Any kid could toss that outta the way. You got some real winners out your way..... and I thought it was bad around here. Like a piece of cake compared to your yo-yos and the costs. Then again, you are in California..............................

 

[TimToad]

like unclebun, when I started in this business after high school the guy I worked for did all his post with tamped earth, well rocks & tamped earth. I'd back fill, drop a couple good size rocks in and beat them to death, and repeat the process till the hole was full. I definitely prefer concrete now . Another thing engineers don't seem to get, undisturbed earth is really strong. A narrow hole dug with post hole diggers and filled with concrete is stronger than a wide hole with a sonotube dropped in it.

Absolutely! That was why we originally specced a 4"x4" PT post in a 9"x36" hole. You'd think guys in the planning department would know how strong undisturbed earth is and that the depth of a hole is typically more important than the diameter.

Hopefully that includes everything right? The extra cost for 6x6 and concrete and the permit? Right? Surely that isn't the price for just the permit!

No, that is just the cost of the permit. We've had to add another $500.00 in the posts, far more concrete and labor.

A simple, non-illuminated, double sided MDO digital print went from $1,500 total to now over $2,500.

They are using the same permit cost as if it was an illuminated cabinet sign. Either the planner working on it just got hired or they are partaking of the recreational drug our fine state just legalized last year. Maybe that should be my angle from now on. Just send over a gift box of "enhanced" brownies when we drop off a permit application.

 

[TimToad]

That's just ridiculous. What if you dig the holes and they don't come out until the end of the day and then it rains the next day ?? Are you supposed to just sit around with your thumbs up your a$$ while they play Mr Inspector ?? I'd make sure they were within earshot while I'm digging and they inspect the hole on the spot.... or I'm going ahead as planned. I ain't gonna leave no 24" x 36" series of holes just covered with a piece of plywood. Any kid could toss that outta the way. You got some real winners out your way..... and I thought it was bad around here. Like a piece of cake compared to your yo-yos and the costs. Then again, you are in California..............................

Yeah, its nuts. On one hand, the city council doesn't want them to look anti-business so they don't enforce anything or come down too hard on the scofflaws, but then when someone actually goes through the process they make it as hard and expensive as possible.

In the next city ten minutes to the north, they put every sign through Design Review Committee, then a full building permit process and it can take 2-3 months from start to finish. To get on the agenda for the DRC, every application has to be submitted 2 weeks in advance. We tell all of our clients in that the sign CANNOT be the last thing they prepare for.

The bigger city to the south has a walk up counter, overlays of all the different zoning areas, experienced planners and it's a walk in and walk out with permit process as long as what you've applied for meets code.

 

[Bigdawg]

I just like a happy ending.

Ahh...... how do they check if your hole is deep enough ?? Do they come out and inspect it before you can pour ??

That's what they do down here. You have to have a footer inspection before you can put in the concrete and set the sign. And inspectors are so busy around here that it can take a few days just to get the footer inspection.

 

[Gr8PlaneBrain]

Licensed PE here.
Commercial signage often uses Risk Category II unless it's remote. It rarely hurts to consider higher wind loads.
The wind loads via the ASCE Hazard Tool are a direct reflection of the wind maps in ASCE 7 Chapter 26.
When calculating wind loads, it's the velocity pressure times the signage area.
There are adjustment factors which often compute to around 1. Depending on the location, they can be higher or lower. I always compute a slightly more conservative value, meaning higher wind speeds, larger factors, etc.
For a 4ft x 8ft sign (32 sqft) with a local engineered wind gust speed of ~110 mph, if the factors calculate to 1, the velocity pressure will be ~31 psf, which gives a force of ~992 lbs on the face of the sign. With the top of the sign at 7ft, the center of force is at 5 ft, giving a moment load of 4,960 lb-ft total or 2480 per post.
That would be relatively equivalent to 7ft of a uniform load of 88.6lb per ft.
The stress at the base is 2480*(half the thickness)/(bending moment of inertia). For a 4x4 (3.5x3.5actual), half the thickness is 1.75 in, and the inertia is 12.5 in^4, giving a stress of 347 psi.
Now, you can not use my numbers as PROOF, but yes, a 4x4 should be sufficient in this situation.
Default soils have a 1500 psf bearing capacity and a 100 lb lateral capacity.
At 4950 lb-ft, the concrete needs to counter that moment.
I could calculate that for you also, but I typically charge for that.

 

[JBurton]

Licensed PE here.

Welcome to the forum! Great write up there. Do you provide engineering services to the sign industry in particular, or general engineering?

 

[kcollinsdesign]

My calculations yield about .54 cu. yard of concrete will be needed to meet engineering specs, which would be about .27 cu. yds./hole. A 24" hole 3' deep with a 6x6 post in it would be about that (your engineer is not wrong). That's about 31 60lb. bags of concrete. You'll probably not be able to buy less than one yard of ready-mix (and you'll pay a premium for that short load). Dig the hole deeper if you have no place to put the excess or pay the ready-mix company extra to haul it off. That or buy your guys lunch.