I have a quick question, on the media outlet "Sploid" a post recently came out about this interesting flood wall in Austria that keeps water from destroying a community. The wall seems to contain a massive amount of water but the wall itself looks pretty flimsy.
I was wondering if there is a point at which a physicist or engineer, when designing a dam or flood barrier, has to take into account the volume of the water behind the wall.
One of the commenters to the sploid post said:
Because the force on the wall does not depend on the quantity of water behind it but only on the height of the water. The pressure on the wall has a linear distribution.If we consider a piece of wall of unitary length ( 3m of height by 1m of lenght) the pressure goes from 0 kPa (on the top) to 29.4 kPa on the bottom . The critical point would be the base with a bending moment of 44.1 kNm. If the beams are made of steel, which has a breaking tension of 450 N/mm^2, an I-shaped beam with dimension of 16x7.4 cm would be more than enough to hold that water in place. If my calculations are correct they would need to have a wall made of 16x7.4cm beams placed 1 meter apart. This is valid for static water. Dymanics introduce inertia forces but the concept is the same.
His answer is what got me started wondering about this in the first place. If you understand his calculations and agree with them can you explain why they are correct?