How much concrete footer do I need for a given wind load?

This structure will hopefully be installed in the fall. the biggest wind load would be on the south North side which is about 65' long and 10.5' tall. made of treated plywood probably 5/8" thickness.
Will be in Orlando Florida, must be designed for 3 second wind load of 110mph winds.

how much concrete do I need to pour? Maybe I just have to ask my local building codes people?

Here is a photo.solararray.jpg

Comments

  • CariboocootCariboocoot Posts: 17,615Banned
    Re: How much concrete footer do I need for a given wind load?

    You absolutely have to talk with the local inspector. Ultimately that is who will say "yea" or "nay" to your plan. Even if you have a certified engineer design the foundation the inspector has the final say. Asking him/her is the fastest way to get the 100% correct answer for your area. They will probably also give you specs for hurricane ties as well.
  • BB.BB. Posts: 24,570Super Moderators admin
    Re: How much concrete footer do I need for a given wind load?

    I don't know--but you may also run into problems if the "roof" (panels) are less than ~8' off the ground (or whatever the exact code is) because of the possibility of somebody standing in wet grass and touching a "defective" panel (rated up to 600 VDC above ground). Unless you put a locked fence around the structure (which you would not want to do--I presume).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • rollandelliottrollandelliott Posts: 755Solar Expert
    Re: How much concrete footer do I need for a given wind load?

    OK, thanks I just wrote an email to the permit dept.
  • rollandelliottrollandelliott Posts: 755Solar Expert
    Re: How much concrete footer do I need for a given wind load?

    Well the building codes dept did NOT respond to my email and instead said it would be easier to call me and answer my questions which I thougth was lame.

    Conversation went like this:
    ME: Is a fence is required around the PV?
    HIM: Yes due to high voltage
    ME:how tall does it need to be?
    HIM:It can't be over 6 feet.
    ME: OK, but that' not really what I asked what is the minimum height it needs to be.
    HIM: Typically 4 feet, but with such high voltage you should probably make it 6.
    ME: What do you mean "probably?" I don't want to make a six foot tall fence and then find out it needs to be a different height.
    HIM: Well we've never had anyone make such a big solar PV system so you'd have to submit plans first and get them approved.

    Any other question I asked him about wind loads was basically a useless response like I'd have to get a professional engineer to submit wind load requirements.

    Even a simple question like what type of conduit is required? got me an answer like look it up in the NEC book, I'd hate to misinform you.

    The problem is hiring an engineer is not really economically viable, I might as well buy a unirac system that is already tested.

    I'll probably try to build a shed and then just mount the units on top of it. He seemed to think that was fine and would avoid the whole wind load issue, didn't really make sense to me since there are still wind loads on the panels, just not as much.

    Only problem is I"ll have to call it Solar PV mounting structure since the HOA doesn't allow sheds.

    I wish I could just over engineer the thing instead of having to pay someone to do a bunch of white collar desing work to tell me that I can get away with the lightest metal possible.
  • CariboocootCariboocoot Posts: 17,615Banned
    Re: How much concrete footer do I need for a given wind load?

    Thank you for once again making me ever so glad I no longer have to deal with such people!

    You might also notice that's another reason why we don't hand out building code advice around here; what's right for one locale is not right for another, and even one that is can be wrong if the half-wit bureaucrat in charge says so.

    Mock conversation with Building Inspector:
    RE: Are you a blinking idiot?
    BI: No. Yes. Maybe. It all depends. You'd better get a professional psychiatrist to assess that.
  • westbranchwestbranch Posts: 4,114Solar Expert ✭✭✭✭
    Re: How much concrete footer do I need for a given wind load?

    Hi RE, I see you did not ask the concrete question..
    IMHO, yes the inspectors are quite vague at times but they normally do concede/defer to a P.Eng. especially to plans with a stamp/seal on them. The seal transfers the legal responsibility to the PE.
    You being in a HIGH wind area , to me, would make it worthwhile, especially to meet that "must be designed for 3 second wind load of 110mph winds" requirement.

    ej
     
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  • Solar GuppySolar Guppy Posts: 1,959Solar Expert
    Re: How much concrete footer do I need for a given wind load?

    You are required to have plans stamped by a state licensed professional engineer. This isn't a DIY calculation that this website or the building department would provide.

    This is no code requirements for fencing of ground mounted PV in the State of Florida, and in my county there is no local requirement either.

    You have to find a PE, and submit plans.

    For a roof mount system, it cost me and people I have referred about 250.00 for the review and approved/stamped plans that in my case I did in MS-Paint. For your building it will be allot more as you now have a structure that must be reviewed to meet hurricane codes on top of whatever is need for the PV support and uplift requirements, detailed blue prints will be required for construction which for the permit will require the PE signoff.
  • rollandelliottrollandelliott Posts: 755Solar Expert
    Re: How much concrete footer do I need for a given wind load?

    thanks solar guppy! you're right, which is why I'm looking to purchase a solar carport that is preengineered with drawings/windload calcs, etc, which I can buy and DIY install.

    It will cost more than the aluminum structure I was going to build which was wayy over engineered with solid 1.5" square posts, but less than having to hire a PE and get them to approved my custom design.

    Peace, Rolland
  • Solar GuppySolar Guppy Posts: 1,959Solar Expert
    Re: How much concrete footer do I need for a given wind load?

    You'll need a Florida PE no mater what ... There is no short cuts for this
  • bluetickbluetick Posts: 19Registered Users
    Re: How much concrete footer do I need for a given wind load?

    This may help point you in the right direction.


    http://signcost.org/winds.html

    HTH

    Square footage of exposed area, height, then shear factor of the uprights, type of soil and a good bit of overbuild. =)
  • bluetickbluetick Posts: 19Registered Users
    Re: How much concrete footer do I need for a given wind load?

    I was playing around with this yesterday, thinking about building a solar tracker.

    I was amazed how much wind load a 12x10 area has.

    But my area is rated at 110 mph.
  • BB.BB. Posts: 24,570Super Moderators admin
    Re: How much concrete footer do I need for a given wind load?

    Even the professionals get it wrong once in a while:

    Large Windmill collapse in NH

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • rollandelliottrollandelliott Posts: 755Solar Expert
    Re: How much concrete footer do I need for a given wind load?

    got a quote back from schletter.us
    standard ground mount was a little less than 3 yd3 of concrete
    However car port design raised that to 10 yd3 of concrete!
  • solarixsolarix Posts: 713Solar Expert
    Re: How much concrete footer do I need for a given wind load?

    Call a steel building company. That industry is very competitive and will willingly whip out at least a modification of their standard building for what you want that is engineered for your location. Buy that or something similar. Pretty hard to beat the cost effectiveness of a steel structure. Your permit people will love it. They don't usually do the foundation design as part of the building design though. But I never heard of a conc. slab getting picked up by a hurricane.
  • icarusicarus Posts: 5,070Super Moderators admin
    Re: How much concrete footer do I need for a given wind load?

    Admittedly coming late to the thread, looking at the OP drawing, personally, I would be way more concerned with the structural elements of the structure than that of the footing. The wind loading of the structure needs to be calculated like any other building, the fact that it has PV on the roof is almost irrelevant OMHO. One does need to calc the wind load on the PV to the structure however.

    Tony
  • rollandelliottrollandelliott Posts: 755Solar Expert
    Re: How much concrete footer do I need for a given wind load?

    I did call a steel building company, I think Arrow? Anyways they said none of their buildings meet florida wind load codes.

    The structure may not have sides after all, trying to work things out with HOA, and local codes people.

    So far schletter's rack system seems the most economical and meets local wind/building codes.
  • Ralph DayRalph Day Posts: 839Solar Expert ✭✭✭
    Re: How much concrete footer do I need for a given wind load?

    On my 10kw ground mounted system (see signature) for 100mph wind load the ballast requirement was 55 pounds per square foot of panel. The ballast weight probably included the weight of steel and concrete (19cu yds of concrete). Not sure what the steel component is or was. For 120mph it would be more than my amount.

    Ralph
  • rollandelliottrollandelliott Posts: 755Solar Expert
    Re: How much concrete footer do I need for a given wind load?

    yeah cement requirements can vary alot, you are a lot further north, maybe a 20 hr drive so your panels look like a 45 degree angle vs maybe a 20 degree angle down in florida, so that is a huge difference there even though both arrays have the same output.
  • Solar GuppySolar Guppy Posts: 1,959Solar Expert
    Re: How much concrete footer do I need for a given wind load?

    Until you have signed plans from a Florida PE approved by the building department you won't know what the final amount of concrete will be. The angle makes little difference to the wind load as its uplift ( Coriolis effect ).

    Due to the cubic nature of wind speed vs energy, the difference from 100 to 120mph is 72% increase and the Ralphs number fall inline with what my PE required
  • Peter_VPeter_V Posts: 213Solar Expert
    Re: How much concrete footer do I need for a given wind load?
    Well the building codes dept did NOT respond to my email and instead said it would be easier to call me and answer my questions which I thougth was lame.

    Conversation went like this:
    ME: Is a fence is required around the PV?
    HIM: Yes due to high voltage
    ME:how tall does it need to be?
    HIM:It can't be over 6 feet.
    ME: OK, but that' not really what I asked what is the minimum height it needs to be.
    HIM: Typically 4 feet, but with such high voltage you should probably make it 6.
    ME: What do you mean "probably?" I don't want to make a six foot tall fence and then find out it needs to be a different height.
    HIM: Well we've never had anyone make such a big solar PV system so you'd have to submit plans first and get them approved.

    Any other question I asked him about wind loads was basically a useless response like I'd have to get a professional engineer to submit wind load requirements.

    You're probably talking to a clerk. All they know is what they've seen before.
    Even if it was an engineer, they don't know everything off the top of their heads.
    If it's something they haven't dealt with before they'll have to look it up.

    Submit your plans, the engineers will look over them and either approve them, or tell you what needs to be changed.

    Once they approve your plans you're good to go, build it like the plans say and everything will be fine.
  • Ralph DayRalph Day Posts: 839Solar Expert ✭✭✭
    Re: How much concrete footer do I need for a given wind load?

    Never in all my years on this forum have I seen Solar Guppy make a boo boo. There's always a first time.:confused:

    "The angle makes little difference to the wind load as its uplift ( Coriolis effect )."

    http://en.wikipedia.org/wiki/Coreolis_effect

    I think what was meant regarding uplift effect of the wind on the array is the Bernoulli effect.

    http://en.wikipedia.org/wiki/Bernoulli%27s_principle

    Only realized this because of ground school many years ago. I like Wikipedia.

    Ralph
  • Solar GuppySolar Guppy Posts: 1,959Solar Expert
    Re: How much concrete footer do I need for a given wind load?

    Up, that's what I meant
  • mike95490mike95490 Posts: 6,298Solar Expert ✭✭✭✭
    Re: How much concrete footer do I need for a given wind load?
    ..... Due to the cubic nature of wind speed vs energy, the difference from 100 to 120mph is 72% increase and the Ralphs number fall inline with what my PE required

    Hmmm... sure that's not Renolds Number ?
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