Backyard Aquaponics
A place to discuss aquaponics

I have 4'x4' (1.2 meters) grow trays that I would like to use as grow beds. They are 4' x 4' x7" (1.2m x 1.2m x 18cm) so they would hold about 70 gallons (265 liters) of gravel and water. Would 1" (2.54 cm) square tube (steel) be strong enough to support this kind of weight?

I would think so... We use the same size steel for our outback systems which sound like they have a similar sized bed.

Hey Steve

not an engineer so unable to help with the question but to help the engineers on the forum assist what wall thickness are you looking at using ?

The steel book i have here lists 1.6, 2.0, 2.5 & 3.0 for the 25mm Square section RHS and the wall thickness will also play a big part on strength.

What wall thickness do the stands that you make use earthbound ? That should give a bit of an idea since your store says that yours are designed to support one metric tonne.

Cheers

I have made alot of tiered fish tank stands out of 25mm shs, 2.5mm thick.
They support 4' x 18" x 18" tanks No probs. They hold 250 litres per tank or ~67 gallons

Ok First the maths,

1/2 cube of gravel (blue metal) weighs around 700kg (im taking this from a guy at the gravel yard i stand to be corrected)

so your looking at around 300kg if u use gravel + around 110kg of water so lets say 400kg for good measure.

Now given that the Steel tubing is around 2mm minimum and is welded well , with all the correct bracing etc i would say yes it will do the job..... just.... i wouldnt jump up on the bed and dance... i wouldnt let my kids play near it...... but it will hold it just dont know how long for......

the use of 3mm greatly strengthen things up as the welds will be able to be stonger and it will just have more rigidity....

I'm a Qualified Metal Fabricator and i work with it all day everyday.... and have done so for over 10 years....

Iv Made frames for BYAP Beds from 40x40x2.5 which hold them full of hydroton fine..... no bowing etc, i tested one of these with blue metal and it bowed around 30mm in the bottom.

thats with no leg braces....

On the contrary to that iv build a work table with all the correct braces and engineering out of 40x40x2 and have put over 2 tonnes of sheet steel on it without it moving at all...

so if you can weld, and have got the time to brace it up well using a light guage steel (within reason) will be fine, keep the base legs apart, brace them back to eachother down the bottom and even a diag brace on 2 sides from top to bottom will make sure it will do the job.

just for a note on this forum iv seen someone who had a bed stand drop on them and they got stuck and fairly hurt..... i had a similar thing near happen when i first started out using some old trampoline bases for a stand.... Just be carfull mate

I am well known for overkill on building stuff.....

Thanks for the responses everyone.

eb: do you know how much weight the growbed in the outback system typically holds?

masterspoon: I am not sure about the thickness, I will have to check in the morning.

werdna: very cool set up, I may have to copy that design for a little hatchery I have in mind.

jamey: thanks for the detailed info, I was wondering how everything would be affected if instead of welds I were to use fittings?

I highly do not recommend doing this...... i cant express the need for safety on this matter... expecially if you have children around 10x this.....

Yeah we have them made out of 50x50x5, you can fill them with blue metal and have a party on top of them without any problems... (not that I've really tested the party bit)

I'm not sure how thick our box is on the other steel stands, we have them made for us.. The stands support a bed which I think normally takes 5 bags of clay to fill. We haven't put rock in them, but I don;t think it would be a problem.

thats angle isnt it joel??

in theory RHS is twice as strong as Angle due to it being 2 pieces of angle....

i love the angle frames, but due to no galvinisers here in central vic, its not viable to use pregalv angle due to price is about 3 x times that of black steel.... and freight to melb for frames is just over the top.. this is why i make mine from pre galv RHS 40 x 40 x 2.5.


Steveiscrazy: I think that using connecters on the 1" steel framing wont be sufficient as it will end up with a bit of movement then that will end up in toppleing over and no good will ever come from that.

you would be surprised how much a fab shop would charge to quickly weld up a frame, especially if you can cut it all to size and have it ready to go with a drawing etc. piece of mind may cost a little more but it helps u sleep at night

Yeah, and galv dipping the pre-constructed angle stands isn't exactly cheap I can tell you....

with the price of power and gas etc going up if the carbon pricing comes in they will sky rocket.... galvinisers may shutdown for 2 weeks over xmas, but the dont turn the baths off due to how long it takes to heat them up again....

We send a lot of stuff with the fab place i work at over to the galvz there prices go up every time..... its crazy eh...