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8 foot Aquarium -> sub flooring enhancements

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  1. #1
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    Question 8 foot Aquarium -> sub flooring enhancements

    Hi all! Happy New Year everyone.

    So, my wife wants to get an 8 foot tank, which, deserves some subflooring reinforcement.

    This is a diagram of the tank with the existing subfloor.

    This is relative to the rest of the room (which is open plan)


    Here are some photos of the subfloor on the left side



    on the right side:



    and above



    ---
    Noting that it appears that the existing floor was reinforced with additional joists.

    What are some options?

    some thoughts and questions:
    - just add more joists that are perpendicular to the tank?
    - use a 3m ~150x50mm beam, supporting the existing joists, running parallel to the tank, on the left side?
    - create 3 places of support for this beam (i.e. 3 brick piers, or 3 stirrups)
    - do I need a 300mm deep concrete foundation under the pier?
    - use bricks for the pier? (do I need to use mortar?)
    - use stirrups + vertical 90x45mm under the beam, on top of concrete? (or concrete pavers?) (could sister 2x 90x45 -> 90x90)
    - Alternatively, I could get some adjustable bearer supports, and use the 90x45 to make up the gap (since the klevaklip ones extend to ~265mm)


    I currently have:
    - mixed sized long hard wood beams (~2.5->3.5m, ranging 170 x 50, to 90x40)
    - some h2 mpg10 90x45s (6x 1m)
    - some h2 mpg10 70x35s (3x 2m)
    - ~64 ENF solid bricks
    - ~ 6 concrete blocks
    - ~3 short (65mm or 130mm, I can't recall) pryda stirrups.


    Keen to hear any comments, questions, answers etc.
    Thanks so much!
    Attached Thumbnails Attached Thumbnails screenshot.121.jpg   screenshot.122.jpg   screenshot.129.jpg   screenshot.124.jpg   screenshot.127.jpg  

    screenshot.128.jpg   screenshot.118.jpg   screenshot.125.jpg  
    Last edited by cptcherry; 3rd Jan 2022 at 01:25 PM. Reason: inserted the klevaklip adjustable bearer support option

  2. #2
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    Big tank.
    I'll let the real builders give expert advice but if I was reinforcing the subfloor there I would certainly be using all 6 of the 90*45 shorts, sistered to the existing joists or at the midpoint and supported by the 170mm deep hardwood [ doubled to 170 * 100] as a bearer. Three supporting posts or stumps to suit your soil.
    At least you seem to have reasonable access under the house just there.
    Perhaps also I would use a section of strong solid flooring over the existing T&T floorboards as a footprint
    "A big boy did it and ran away"

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  3. #3
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    Where are the load bearing points of the tank/enclosure?

    Assuming the back and front bear all the weight, and keeping it simple, I'd just add a bearer at the front of the tank

    If 15 average adults could stand safely in the section of the tank, you don't have a lot to worry about

  4. #4
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    You're right in that the bearer is the most important part but what else to do with the joist off-cuts? May as well use them and there is nothing wrong with being stronger than design minimums. Proper stump footings are probably more of an issue
    "A big boy did it and ran away"

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  5. #5
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    Quote Originally Posted by Moondog55 View Post
    You're right in that the bearer is the most important part but what else to do with the joist off-cuts? May as well use them and there is nothing wrong with being stronger than design minimums. Proper stump footings are probably more of an issue
    I can find other uses for the joists - haha.
    But yes, advice on the stump footings would be appreciated.

    Quote Originally Posted by [COLOR=#3E3E3E
    r3nov8or[/COLOR];1134440]
    Where are the load bearing points of the tank/enclosure?

    Assuming the back and front bear all the weight, and keeping it simple, I'd just add a bearer at the front of the tank

    If 15 average adults could stand safely in the section of the tank, you don't have a lot to worry about
    along the back, front, sides and through the middle there are a few pieces (i'll take some photos later).
    I don't think we can compare 15 adults vs a dead weighted tank?

    Quote Originally Posted by Moondog55 View Post
    Big tank.
    I'll let the real builders give expert advice but if I was reinforcing the subfloor there I would certainly be using all 6 of the 90*45 shorts, sistered to the existing joists or at the midpoint and supported by the 170mm deep hardwood [ doubled to 170 * 100] as a bearer. Three supporting posts or stumps to suit your soil.
    At least you seem to have reasonable access under the house just there.
    Perhaps also I would use a section of strong solid flooring over the existing T&T floorboards as a footprint
    Thanks for the suggestion and reconfirming my thoughts.
    The access is tricky (photos were via a selfie stick) - via a 17cm x 53cm gap - pretty stupid.
    I think there is an access point from the backyard, underneath the kitchen which then should come across to the hole on the left, far side of the subfloor pictured.

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    Quote Originally Posted by cptcherry View Post
    ...
    I don't think we can compare 15 adults vs a dead weighted tank?...
    The dead load of the tank will be less of a problem than the live load of equivalent humans

    "+ stand + rocks", ok make it 18 people...

    Asking again, where are the load bearing parts of the tank? Has the stand 4, 6, 8 legs etc?

  7. #7
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    If the tank is to be a permanent fixture just cut the floor out to do the stumps and bearer
    "A big boy did it and ran away"

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  8. #8
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    Quote Originally Posted by r3nov8or View Post
    Where are the load bearing points of the tank/enclosure?...
    This is the main point.
    Is the tank support one of those steel frames with 8 or so legs.
    If so, then all the weight is going through those legs and you will want them over a joist/bearer, not on a floorboard (I have seen a tank leg go through a floorboard, on a mezzanine, it wasn't pretty).
    Or maybe the tank support is a custom cabinet where the weight is distributed across the plinths thereby spreading the weight across the floor.

    So your solution depends ...

  9. #9
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    That was why I suggested using a secondary flooring layer over the existing. Doing so means a better resistance to point load, effectively doubling/tripling the flooring thickness
    "A big boy did it and ran away"

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  10. #10
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    Quote Originally Posted by r3nov8or View Post
    The dead load of the tank will be less of a problem than the live load of equivalent humans

    "+ stand + rocks", ok make it 18 people...

    Asking again, where are the load bearing parts of the tank? Has the stand 4, 6, 8 legs etc?
    We collected the tank and stand last night.
    The contact points on the floor are marked in blue.

    screenshot.134.jpg

    From what I have read, putting a layer of ply etc under the tank only expands the point load by the thickness of the ply. It doesn't distribute it extensively.

    I plan on getting back under the house to measure more precisely the location and dimensions of the joists.

  11. #11
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    Quote Originally Posted by cptcherry View Post

    From what I have read, putting a layer of ply etc under the tank only expands the point load by the thickness of the ply. It doesn't distribute it extensively.

    .
    Do you have any references? I'm interested in learning more.
    "A big boy did it and ran away"

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  12. #12
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    Quote Originally Posted by Moondog55 View Post
    Do you have any references? I'm interested in learning more.
    Not really a reference, but i read it here, https://badmanstropicalfish.com/articles/article28.html under myth #7.
    and, if you think about it, as ply wood, when pressure is applied, as its not very solid, it's going to flex a little and compress, and transfer the compression through to the other side. the area will be larger, but i did read somewhere else that its only about 2x the surface area of the applied force that is transferred through.
    I.e. it won't share the load to the adjacent joist.

  13. #13
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    That makes sense but from an empirical POV I know how much stiffer doubled up flooring thickness is. From you sketch the tank has a large supporting frame and the load seems to be spread over 5 sections so no point load as such?
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  14. #14
    Senior Member ForeverYoung's Avatar
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    Quote Originally Posted by cptcherry View Post
    We collected the tank and stand last night.
    The contact points on the floor are marked in blue.



    ....
    They well maybe the contact points but that doesn't mean that is where the weight is transferred.
    You need to examine the cabinet structure or ask the manufacturer.

  15. #15
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    Quote Originally Posted by ForeverYoung View Post
    They well maybe the contact points but that doesn't mean that is where the weight is transferred.
    You need to examine the cabinet structure or ask the manufacturer.
    Maybe I'm missing something here but I thought that the "blue lines" were intended to be the rails that are in contact with the floor and therefore where the weight is transferred no matter where the supporting legs/posts were located. The discussion is now getting too technical for my own knowledge but good luck with it.
    "A big boy did it and ran away"

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  16. #16
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    Quote Originally Posted by Moondog55 View Post
    Maybe I'm missing something here but I thought that the "blue lines" were intended to be the rails that are in contact with the floor and therefore where the weight is transferred no matter where the supporting legs/posts were located. The discussion is now getting too technical for my own knowledge but good luck with it.
    Imagine kitchen cabinets with legs, that is where the weight is. Add a plinth to hide the gap below the cabinets and the legs - no weight on the plinth.
    Those floor contact points on the cabinet could just be decorative plinths (especially the front one) and the others could just be framing components for the cabinet to keep it square, add shelves ... can't tell from the info provided.

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    Any progress on the tank and subfloor?
    I'm intrigued
    "A big boy did it and ran away"

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  18. #18
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    Cabinetmaker here. Wow. 1.184 tonnes. I second ForeverYoung. How strong are the floorboards? How thick are they? A structural engineer should weigh in, but it'd be wise to widen the weight distribution load with a wide base. Thick gluts and structural plywood won't hurt. Concrete pavers for example 600x600mm can hold 1t, half a car, before cracking. Wood however may not break but will flex. Just some thoughts.

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