Practical question for mechanical/Civil engineers

[cyrille de brébisson]

Hello,

I find myself faced with a mechanical problem at home that I am unsure how to resolve and since I am pretty sure that some of you can solve stuff like that in your sleep, decided to post it here. Thanks for your help in advance.

Basically, I am trying to calculate the point of maximum deflection on a board set vertically and used to hold concrete in place while it is being poured in a vertical shaft.

Imagine a 'U' channel, but set vertically, 20cm*20cm by 3meters high. 3 sides are already enclosed in concrete, but the last one is 'open'. My plan is to place a board to 'close' the open face, fix it on top, bottom and brace it, if possible at the point of maximum pressure, which I imagine is NOT going to be the middle!

I would also like to get an idea as to how much pressure will be there.

Thanks,
Cyrille

ps: My thinking was that the point of maximum deflection would be at the point where 1/2 of the maximum pressure is exerted.
Assuming that the pressure at any 'height', h is proportional to the sum of the weight of the concrete above it, it means that the pressure at h i sum(0 to h, of p*h), ie p/2*h² where p is a constant based on concrete weight (2.4t/m^3) and how much of that weight actually does act to press.
so, pressure at the bottom is p/2*9=4.5p.
1/2 of this is 2.25p.
h where 1/2 the pressure is exerted would then be sqrt(2.25*2/p) around 2.1meter down from the top...

Am I any close to the solution of just blowing bubbles?