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KN/m3 - based on a water tank

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  • KN/m3 - based on a water tank

    Hello all,

    I hope you don't mind me asking this question as I'm new to the page, I work for a water tank company who put together tanks in buildings. what I seem to get asked a lot is what is the loadings (KN/m2) upon the tank.. is there a specific formula to use to work this out? (I do have all of the weights for the specific tanks).

    I.e. from my understanding currently/info I current hold :

    Weight of tank 2x2x2m: 600kg
    Weight of water this holds (room temp): 7984.16 kg

    I'm assuming there will also be a gravity force applied however I'm completely new to physics which is why I'm searching for the assistance.

    thank you in advance for any assistance that you guys can provide!.
    Last edited by 09dawsonb; 11-20-2020, 12:37 AM.

  • #2
    Originally posted by 09dawsonb View Post
    Hello all,

    I hope you don't mind me asking this question as I'm new to the page, I work for a water tank company who put together tanks in buildings. what I seem to get asked a lot is what is the loadings (KN/m2) upon the tank.. is there a specific formula to use to work this out? (I do have all of the weights for the specific tanks).

    I.e. from my understanding currently/info I current hold :

    Weight of tank 2x2x2m: 600kg
    Weight of water this holds (room temp): 7984.16 kg

    I'm assuming there will also be a gravity force applied however I'm completely new to physics which is why I'm searching for the assistance.

    thank you in advance for any assistance that you guys can provide!.
    We are here for questions like this

    Gravity varies slightly from pole to equator and with elevation above sea level. Unless very high accuracy is needed for some reason, local gravity is rarely measured for this conversion. People tend to use "standard gravity," 9.80665 m/s, or even round it off to 9.81 m/s. I would also round total weight of tank and water to 8600 kg. The gravitational force acting on a mass is mass times local gravity, and the newton is defined as 1 kgm/s (no scaling factor). For floor loading, you also need to divide by the area the tank occupies (2 m x 2 m)

    8600 kg x 9.81 m/s / 4 m = 21 000 N/m or 21 kN/m.

    This assumes the tank is flat bottomed and the load is spread uniformly over the floor. If the tank has legs, the problem becomes more complex. Most floors are some thin floor material over beams that support the load. The above calculation is adequate for whether the beams can support the load.

    However, if the load is on legs of relatively small area, the flooring material may be damaged. For the calculation, you don't divide by the 4 m total area, but by the area of the "feet" on the end of the legs. Even a skinny supermodel in high heels can exert enormous forces on the flooring material, when the stiletto heel comes down, but she represents no threat to the beam loading. Usually the flooring material has a separate rating from the acceptable beam loading. It may be necessary to have a "foot" of some study material on each leg to spread the load and protect flooring material.

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    • #3
      Thanks for the reply JohnS that information was very useful!, our tanks are built out of 1x1m panels and bolted together.. these can sit on a flat floor (usually a concrete slab) however if this is not "level" within a tolerance of 2mm in any square m or 6mm in 6m we have to position steels below spaced out at every 0.5m c/c (the standard profile of steel we use is 100x50x5mm

      If I'm reading that above correctly would this technically alter the formula above due to the loading now put on the steel rather than the overall flat base... as you described above kind of on high heels haha!!..

      I will try using the formula/calculation you have given me on some different sizes of tanks to see if I get the jist!... thanks again as I said proper beginner to physics but really interested in this kind of thing!

      P.s. I never knew the gravity would be effected by the pole to equator factor... very interesting... but makes sense if you think about it!... our tanks are mostly UK based so shouldn't be a problem
      Last edited by 09dawsonb; 11-20-2020, 08:03 AM.

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      • #4
        You may need a formal opinion from a structural engineer (I am not one), but it should not affect beam loading at all. Concrete is a pretty tough material and those seem like decent "spreaders." I would be more concerned about something like an L-section leg that has a very small floor area.

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        • #5
          Thank you for the feedback, yes we currently do state that everything needs signing off by a structural engineer so will continue to do so. I was more just curious about the formula and work that goes into it!

          thank you again for your input!

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