Arch construction with uniform pressure. Unnatural deformation?

[Nougatti]

Hi there

Got this gate which has

A: 17 mWC of water pressure evenly distributed on its front face.
B: Support and restriction from moving in X- and Y-directions. Restricting from rotation around X- and Y-axis.
C: Support and restriction from moving in Y-direction. Restricting from rotation around X- and Y-axis.
D: Support and restriction from moving in Z-direction.

I other words; the left side is locked in all ways apart from rotation around Z-axis. The right side only locked from moving in the Y-direction.
With pressure applied to the front face, you'd expect the right side to slide further towards the right (X-axis) as the arch is compressed. This is confirmed by the FEM analysis.

The plate behind the arch would be expected to experience pure tensile forces.
Why then, do I experience a large deflection/bending of the back plate in negative Y-direction?

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I am Norwegian.
I design mechanicals for hydroelectric powerplants.
I use NX 8.0.3.4 and ANSYS 15
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Tom you can't knit at these speeds! Nobody can! DON'T BE A GODDAMNED HERO TOM!

 

[dhengr]

Nougatti:
As the arch is loaded, it tends to flatten out and this causes some rotation at the bottom reactions (spring line/tension plate plane) of the arch. This will induce moments into the tension member unless you provide a pinned connection btwn. the arch and the tension plate behind the arch. In the extreme, maybe the tension member should be a number of tie bars/rods with clevises and pins at their ends (at the arch reaction points) and a turnbuckle to help adjust the length of the tension member. This might allow you to adjust the fit-up to the primary support structure better. And, allow you to account for differences in these reaction with depth on the gate.