Author Topic: He Ain't Heavy He's My Fishtank (Read 17670 times) 5 replies

MarquisMirage · « **on:** January 05, 2017, 07:32:57 PM »

Can someone check the maths on this for me?

I read that UK houses have a standard of joists that have to support a minimum of 1.5 kN m/s squared for spread loads or 1.5 kN point load.

Assuming a full aquarium system can support 615 l water then that is around 615 kg of water mass. I'll add a further 385 kg for cabinet, glass, and rock/substrate mass. I'll go off a mass of 1000 kg for the aquarium overall. 1 N is 1 kg m/s squared. So 1 kg of force on Earth is approximately 9.8 N because of gravity. 1000 kg mass would be approximately 9800 N or 9.8 kN.

Up to that point I think the maths is acceptable. Now's the confusing part.

The cabinet has twelve legs. Does that mean it has twelve load points? If that's the case 9.8 kN/12 is 0.82 kN per load point and within the limits. Or do I need to work out the m squared the cabinet covers and divide by that? In the second scenario it's way over. But then again in that second scenario my fridge freezer is too heavy. It's a bit confusing.

Littlefish · « **Reply #1 on:** January 05, 2017, 07:55:07 PM »

I'll leave the maths to a grown up - all I can say is that my tank contains 400L of water, plus substrate & decor, plus cabinet and filter. The cabinet has 6 legs, is approx. 5ft x 2ft, and the floor hasn't collapsed yet.
I hope that helps.

fcmf · « **Reply #2 on:** January 05, 2017, 08:03:14 PM »

I've spoken to an architect to get their perspective on this.

Apparently it's not as straightforward as this - any weight / point load on a joist has a 'spread' at a 45' angle from it, like a triangle, and there's consequently a circumference of effect around the weight of something such as a tank or a fridge. Additionally, joists vary in different sizes and makes and types. In fact, there are many, many factors in the equation.

If the tank were to be on a ground floor of a building with concrete, then it's much more likely to be able to support the weight than if it were on a timber floor and/or an upper floor in the house or a block of flats. It also depends on when the house/building was made ie in what era as building regulations were very different or in fact non-existent pre-1980s. However, with a tank of that weight, the architect very much recommends getting a structural engineer to assess the situation.

Hope this is at least somewhat helpful.

Andy The Minion · « **Reply #3 on:** January 05, 2017, 10:05:01 PM »

@marquismirage
I think you have a typo in your units, more likely it is kN/m² unless the tank is in free fall from a great height

There are two things to consider, the amount of weight the joist can hold and then secondly if the load is on legs how much load the floor itself has to withstand, hence the two figures.
On the positive side the 1000kg tank feels to be a bit of an overestimate, firstly the substrate and rocks displace water so its not the sum of the two, you can subtract the weight of their volume in water from the total. The sump will also not be full of water when running, perhaps only 30-50% will be water or you will have a flood when the tank syphons back. The tank and cabinet will be heavy but perhaps 100kg so maybe 700kg ish and that would probably be a bit of an over estimate still.
I AM NOT AN ARCHITECT OR STRUCTURAL ENGINEER and each house is different, so don't take this as a full answer but...
700kg is 6900Newton, 6.9kN and its spread over the footprint of the tank say 60 x 150cm which is 0.9m² giving 8.2kN/m². This would be very bad if it were on one joist but you would put the tank 90° across the run of the joists so its weight is taken by probably 3 or 4 joists, 175-230kg per joist. This is still high but starting to sound more reasonable at least.
The other very important thing is where the load is on the joists length. If its in the middle this would increase the forces and again very bad but again the tank should be as close to the supported ends as possible so more of the weight is taken by the supporting wall.
The other point load figure - you have twelve legs so that is 58kg per leg, if the legs are small you can put them on blocks to spread the weight if needed.

So, you definitely still need to get qualified advice but, with care and proper calculation I think it is within the realm of possibilities.
I have my tank (in a bungalow) on a wooden floor and went through the same thought process. I have been under the floor and checked the joist span, their dimensions and where to put the tank so it is across the maximum number of joists and above a supporting wall. I then added additional 4 2"x4" vertical supports in front of the tank. No problems ....so far!

ColinB · « **Reply #4 on:** January 06, 2017, 07:33:42 AM »

Ther's a lot of imponderables to ponder on this one... but Andy has the main ones.

Will the tank be against a supporting wall where the joists will be at their strongest?
BUT.... this is only the case if your tank is perpendicular to the joist direction so it's not running along the length of just one (or two) joists. The joists run at right-angle to the floorboards so you can easily tell in which direction they're heading.

Have the floorboards been lifted at any time under where the tank is going? If so then the tongue-and-groove will have been cut through and the floorboards won't be coupled together and as strong.

Try putting a table where the tank will go with a large container of water on it. Then walk/stomp/jump around and see how much the water surface sloshes about. This will give you a starting point on the strength of the flooring.

MarquisMirage · « **Reply #5 on:** January 08, 2017, 09:25:56 PM »

Plenty of information that got me thinking. I'll get a structural engineer to take a look before I order a tank and prepare myself to go smaller.

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He Ain't Heavy He's My Fishtank

He Ain't Heavy He's My Fishtank

Author Topic: He Ain't Heavy He's My Fishtank (Read 17670 times) 5 replies

MarquisMirage

He Ain't Heavy He's My Fishtank

Littlefish

Re: He Ain't Heavy He's My Fishtank

fcmf

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Andy The Minion

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ColinB

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MarquisMirage

Re: He Ain't Heavy He's My Fishtank

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