tank base thickness

Discussion in 'General Discussions and Advice' started by Neil H, 14 Aug 2009.

  1. Neil H

    Neil H Moderator MASA Contributor

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    Hi Hennie,

    Could you give me some sort of indication as to why we double up on the base thickness of a tank?

    My gut feel is that this is because we pile a whole bunch of rock on the bottom of the tank and the extra sheet helps if there is a rock fall of some sort??? given these sheets are usually joined with silicone, is there additional strength in the double base??
     
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  3. Reef Maniac

    Reef Maniac MASA Contributor

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    Hi Neil,

    As far as I understand this, there are three reasons:

    1. Many (most?) tanks are placed on a stand consisting of only a "frame" of angle iron or square tubing, and the whole tank's weight is supported on this thin "rim" around the outer edge of the tank. The thicker bottom glass is designed to be strong enough to support the whole weight of the tank, water and rocks on this thin edge, spanning the open space between the front and back panes. Many tanks (especially in the USA) are also designed with a "floating" bottom, where the side panes protrude past the bottom pane by a few mm's, and the bottom pane must thus span (carry all the weight) across the tank width.
    2. There is a real risk of applying a point load on the bottom pane if/when a rock "sinks" through the sand substrate, or even worse, if a tank is set up "bare bottom".
    3. The combined weight of the water, substrate and rock exert the greatest pressure (load) in the direction of gravity - i.e. down. This vertical load is normally substantially higher than the horizontal load induced by the water (only) on the side pains of the tank, resulting in a greater deflection of the bottom pane if it is of the same thickness as the side pains.
    IMHO one can reduce the bottom pane to the same thickness as the side pains IF the bottom pane is UNIFORMLY supported over it's total area by a base (stand) which has less potential deflection than the glass in question - something like a solid concrete slab of sufficient thickness.

    Actually, the base should be thicker than the sides, but not necessarily double the thickness. One can get an indication of what is required by playing around with the Glass Thickness calculator. The extra thickness should, ideally, be of a solid (monolithic) single pane of thicker glass, not a "laminate" of two thinner pieces. As posted on a previous thread, laminated glass tend to slide along the laminate material, under sustained pressure. The laminate can also fail due to moisture ingress.

    Hennie
     
  4. Nemos Janitor

    Nemos Janitor

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    Just adding to hennie explanation two other important points.

    1) A double base is normally used in larger tanks. So a tank of 1800mm x 600mm x 600mm will have a "first" base of 1800mm x 600mm. the second base will be smaller. 1778mm x 578mm. So when the side panels are siliconed to the base a better seal is done.

    2) normally the second base is made up of smaller (off cuts) and siliconed to the first base. The reason for this is if a rock does bash the base and cause a crack or there is a stress crack due to the tank not been level then only that pain is damaged and the crack does not run the length of the tank to one of the side panel seals.
     
  5. Reef Maniac

    Reef Maniac MASA Contributor

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    Agreed - this is what I consider to be part of the "Euro-bracing", which should ideally by installed both top and bottom of the tank. This does make for a larger joint area, and is a very good practice.

    Hennie
     
  6. Neil H

    Neil H Thread Starter Moderator MASA Contributor

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    thanks for the awesome info gents
     
  7. Sentari

    Sentari

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    Hennie i have been using your calculator but i would also just like to find out if my tank is okay. It seems like the tank is fine.

    Currently my tank is 1200 x 450 x 450

    Euro bracing at the top and at the bottom with a centre brace.

    My glass thickness is 5mm. Yes i know i'm pushing it but this was lanzo's previous tank and i have modified the hell out of it.

    The tank is full and everything is fine. I would just like to find out if everything would be okay with the tank in the future. I am also adding a lighting unit which will be resting on 4 corners.

    If you want to see what my tank looks like check my thread below.
     
  8. Sentari

    Sentari

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    PS. Sorry if i hijacked the thread!
     
  9. Reef Maniac

    Reef Maniac MASA Contributor

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    My previous 1.5m tank had 6mm glass, and was fine for nearly two years before it failed disastrously one Saturday morning, dumping about 500 liters of water into my lounge within about 5 seconds... It too had Euro bracing...

    [​IMG]

    Hennie
     
  10. SchyffS

    SchyffS Reef Aquarist

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    A agree with this.
    From a technical perspective, try this test to understand how your glass would react to pressure. Take a ruler (ordinary plastic) and hold it on each end so that it lays on its flat side facing down. Now bend it downwards.
    Now turn the ruler so that you hold each end with the flat side facing you,, now bend it downwards.

    Also have a read on the info about ensuring a better seal and join for your tank.
    2006 Reef 7
     
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  11. Reef Maniac

    Reef Maniac MASA Contributor

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    Good link there :thumbup:

    Hennie
     
  12. riyadhessa

    riyadhessa

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    Awesome link...shot
     
  13. Neil H

    Neil H Thread Starter Moderator MASA Contributor

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    my word that is a nasty pic !
     
  14. SchyffS

    SchyffS Reef Aquarist

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    Im glad you like, one day when my ship sales in im gonna build a reef just like this one ;)
     
  15. SchyffS

    SchyffS Reef Aquarist

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    This link is has the tendency to keep you reading, and when you'ved read it all you gonna read it again....:lol:
     
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