Hydrostatic pressure pressure

[vomi1]

Hello,

I was asked to analyze a fixture that contains grout material. The fixture is a like a thin open top box has a volume of 79" (height) 72" (width) and 0.9" (depth). One wall is made of 0.5" Lexan plate (E=345ksi, Poisson ration:0.37, Fty=9,000 ksi) and another one is made of aluminum 6061-T6. The grout density is 0.0379 lbf/in3. I use Patran to build a simple FEM model for the Lexan plate and constrained it on 3 sides fixed; top side is free and evaluated to a hydrostatic pressure loading (p=density*79" = 2.997 psi near the bottom, 0.0 near the top). My deflection result in very high and not real, about 79". The von Mises stress is around 10.3 ksi at the base. Roark has the formula to calculate stress but not deflection. I wonder if there is a formula to calculate the deflection for such case. The deflection seem awfully large for a 0.5" plate even with a 1.0". I am very confused. Is hydrostatic pressure realy worst to deflect the plate that much when the depth (the gap of the box) is less than 1.0"?

I appreciate very much for you time and help.

vomi1

 

[BigH]

Sounds like a university homework problem . . . did you mix up your "height" and "depth"?

 

[vomi1]

Hi BigH,

Thank you for your responding. The fixture is like a very large but thin container. Al frames and two flat plates bolted on the side. it is 79" tall, 72" wide, and 0.9" depth (inside gap). The pressure I calculated is from the grout density x fixture height and applied to the plat plate normal to the surface as a function of the height.

Thanks,

Vomi1

 

[dgillette]

Try this:

http://www.usbr.gov/pmts/hydraulics_lab/pubs/EM/EM27.pdf

It may not have the exact hydrostatic (groutostatic?) pressure distribution you want, but it should give you enough information to figure out what's reasonable to expect.

DRG

 

[vomi1]

Thanks DRG! great info.

vomi1

 

[Ron]

The hydrostatic pressure from the grout is a triangular load distribution. For your depth of 79", you would have a resultant load of 150pcf x (79/12) = 987.5 psf acting at 26 inches from the bottom of the box. For a 12" strip of loading, your load would be 987.5 plf acting at 26 inches above the bottom of the box.

That's a reasonably high load for thin plates.

Post a picture of your Von Mises stress distribution.

If you place the grout very slowly, its pressure is reduced as it sets up. When set up, the lateral pressure essentially goes to zero.