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Hi I would like to make a fish tank stand like the one in the photo. I have been scouring the internet for an answer to how thick the material I select should be, in either SHS or RHS. I was thinking of purchasing 40mmx40mm but have not been able to find out what thickness I should go for. The fish tank that will sit on top of the frame, is 1800mmx700mm and 590mm high. It will hold about 745 litres of water when full. I intend on placing a sump tank in the bottom section (but not sure if that will effect the choice of the thickness of material or not). The height of the stand will be about 750mm. I appreciate your help. Thank you.enter image description here

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    $\begingroup$ If you have the tank manufactured you can inquire about the support requirements, that will then guide you how much the stand is allowed to deflect under load $\endgroup$ Commented Jan 19, 2023 at 13:36
  • $\begingroup$ Thank you. I made the tank myself using 12mm glass. $\endgroup$ Commented Jan 19, 2023 at 19:13

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There are several modes of failure for such a design but the two main ones you need to consider are:

  1. Bending failure or over deflection of the top two 1800mm beams. While the glass tank will distribute some of its load to the columns, there may be too much deflection in the middle causing the tank to crack and fail as blacksmith37 and ratchet freak have mentioned. One way to reduce this is to use a 3mm rubber liner between the steel and glass tank that will help distribute the load and reduce pressure points. If you don't have an engineer review the structure you want to oversize the member to reduce the risk. For example a 40mmx80mmx4mm wall beam gives you 4x the strength of a 40x40x4mm when oriented with the 80mm vertical. If you want it to look more trim, or weigh less, hire a licensed mechanical engineer in your jurisdiction to draw it up for you with a weld specification. It would be less than an hour of work and would save you money in the long run if you send it to a fabrication shop.
  2. Moment(rotational) failure at the welded joints. Visualize it tipping over as if the tank were set on two dominoes. Or if it rotated on the columns like DNA. While good steel welds at 40mm are probably strong enough for this application, gussets and cross bracing give a lot of insurance. I would recommend a minimum wall thickness of 4mm as thinner walls are more difficult to weld. If you have less than 100 hours of welding experience I would recommend hiring an experienced welder or weld shop to fab the unit for you. Since this is not a structural application requiring a licensed engineer the fab shop can also review your design and help you make sure it works based on their experience of building may similar structures, but plan on it being very overbuilt and heavy in that case.

Remember the weight of the tank is substantial and you don't want to risk crushing yourself or others. If the glass is not tempered, also consider the risk of a partial failure dislodging sharp sheets of glass. Steel is a good material choice for this application since it is very strong and easy to work with; just ensure that it is properly painted or powder coated to be protected from corrosion.

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Have you done something like this before ? You have a weight of about 2000 pounds, not trivial. The aquarium glass provides stiffness itself . But for support the steel stand must not deflect much as the glass has very little deflection. I would plan on a vertical center leg in the center of each 6 ft. side. In the US, steel channel stock is available under names like "Unistrut". They provide much information on strength , etc, on the net. I think you will find Unistrut more available than square tubing. I have a couple pieces of Unistrut as the main strength for an 8 ft. long foot bridge over a pond . Not near the load of your tank but it likely had easily carried dynamic loads up to 600 lb. The various aquarium stands I have built have all been wood ( up to 6 ft. long, 1400lb.). If you are planning to weld ; that is a whole other technology. I suggest looking at the Unistrut information.

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  • $\begingroup$ and putting cross members between the top rails to support the center of the bottom glass is a good idea. $\endgroup$ Commented Jan 20, 2023 at 12:06

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