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Why are there grooves on almost every water tank? Just typing water tank in Google images would reveal what I am talking about. And here is a sample picture!

I think it would mostly be regarding water pressure. Please share your knowledge.

 Sample picture showing grooves on water tank

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  • $\begingroup$ maybe for tying some elastic band to the tanks, like when you want to hold them together or you want to place some pipe on the side of the tank. Just guessing.. $\endgroup$ – AoZora May 15 at 7:42
  • $\begingroup$ Something interesting you might notice (and it relates to the answer) is that typically you see this done for non-carbonated beverages, but for carbonated drinks they often don't bother. $\endgroup$ – JMac May 15 at 11:05
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Of all the reasons I can think of, I came up with two advantages that the grooves may provide.

  1. The grooves increase the distribution of material away from the neutral axis. Therefore they increase the moment of area. An increased moment of area means that the material is more resistant to bending.
    $\sigma_=\frac {My}I$
    It's just like a sheet of paper. If you hold a sheet of paper from an end, it easily bends over. But if you roll it up into a cylinder, then hold it from an end; that should keep it straight like a cylinder.
    But why don't they just bulge the whole think out? (That should provide even more resistance to bending). The answer is that though it does increase the resistance to bending, it also increases the shear stress between adjacent layers. The right balance is obtained by implementing an $I$-beam shape. They make multiple $I$ beam shapes in the form of grooves.
    In short, the grooves increase resistance to bending and decreases shear stress between adjacent layers of the tank.
  2. The grooves provide holding support, allowing for better transportation of the tank.
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    $\begingroup$ The bending force in question comes specially 1) when the tank is subject to negative pressure, that tend to squeeze it 2) when weight is put over it $\endgroup$ – patta May 15 at 10:01

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