Backyard Aquaponics
A place to discuss aquaponics

It's just like forming for concrete. If you have a square corner with a lot of load, you have to reinforce it. Consider using steel strapping or 'L' braces.

We will all know soon enough. I began construction on a 30 cm x 30 cm by 2.8m grow bed. will be 1.5 cm thick. The bottom will be a bit thicker though.

i think one of the problems with the square is if you measure the distance diagonally out from the inside to the outside on the corner it is thicker than the depth of the side. I THINK expansion / contraction issues make this area prone to cracking which is not good for water holding vessels.

C1 Where are you?

Well obviously you guys just need to find out about and use fiber glass

All of the above...
shrinkage cracking, stress concentration at corners, high bending moment at the corners...concrete is not very flexible so it can't deal with corners very well. I'd suggest putting extra reinforcement around the corners, doing what you can to round the corners off and being prepared to do some patching or sealing.

But I'm a footings guy, and barely even one of those...someone else might have better advice.

I think 'we' maybe are missing the point of what dt is trying to do.

From memory, this is the project in El Salvadore to build tilapia/tomato AP systems for local farmers to break out of the poverty cycle. I believe that this project is running mostly with locally available materials.

So whilst fibreglass would be nice, it is probably not readily available, nor within the acceptable budget.

So is there anyone on the group who can advise how best to achieve this goal?

Regards

gg

True in DT case GG.... but this is Nico's raised beds on stands idea that we're critiquing......

Good answer steve!!
My uncle had a ferro boat, and big(in my circles anyway, 60' was big about 30 years ago), he built it himself and I went on it so I know it works.

If the water pressure is less strong than the impermiability of the ferro there is only the construction and design/engineering to consider.

Once this is done I have no doubt the structure will hold water.

The things I would consider are the possible damage the GB [s]would[/s] may get in the future with regard to the harvest, nearby ppl traffic and that the product is very rigid not unlike fibreglass.
...happens to be why I like the idea of poly.

The process of constructing poly Tanks and GBs out of recycled waste material and a societys normal production of excess of waste material seems the way I would like try to go...IMHPO.

In saying all that. many tanks are ferro and they are made using what material is readily available and more likely less expensive.

corners in concrete are fine unders LAB conditions, but these condition rarely exsist in the work place.

Many 'glues' aka joint sealants have been technologized to perform under extreme conditions.
It is good to use the unique charictoristics(sp?) such as shrinkage to ones advantage for gluing.

C1

I hope you are taking lots of pictures of the process!


Thanks for your input everyone! I guess I'll have to put some brasses allong the long sides and add some extra support in the corners.

On the other hand, I probably won't be using this design at all. My biggest concern is costs, so I'm now thinking about just digging some holes and lining them with EPDM.

My other concern would be the overall weight on the timber legs - there is going to be near on 3 ton of gravel in the GB...not to mention the water on a flood, think I would be looking for a more substantial stand (with lots of supports)

yes Ell no one thing but the combination of factors.
Think you might need to treat it like an aquarium

C1, when you say water pressure do you mean pressure as in PSI or as in osmotic pressure?

No I agree, from an engineering point of view, it is imperative that stress concentrations are removed or at least reduced. A square outside is ok, but rounding the corners on the inside is important. (make it look sort of like a bath) also the weight some1 brought up is going to be critical. I do hope support under the base is significant.

Concrete compresses like a champion, but under tension just breaks apart. So a small span between supports is preferred, then the bottom can be rather thin. I think 10mm on the bottom, if supported well will hold the gravel.

The issue is the walls, and the total weight on the legs.

If square, and unbraced, the walls will imho fall off as soon as water is added. If the belly is not supported, it will crack. the legs will be ok, if maybe 6 per growbed, 4 may be enough, out of 70*35 timber. I have almost a tonne sitting on only 4 legs which are slightly smaller.

both steve. and
permiablity(sp?)
flexurial and
modulus strength.