Hydrostatic Pressure on a curved surface
Hydrostatic Pressure on a curved surface
(OP)
I need a formula to figure the pressure present on a curved form (tank)
the form is a circle 10ft in dia. and 40ft tall. the form is standing vertical on solid concrete. the bottom is flat. the fluid placed in the form has a density of 2.4. there are no additional forces acting on the fluid (only atmospheric, the form has an open top)
I need know the pressure on the form at any point.
Dittowizard@infoave.net
the form is a circle 10ft in dia. and 40ft tall. the form is standing vertical on solid concrete. the bottom is flat. the fluid placed in the form has a density of 2.4. there are no additional forces acting on the fluid (only atmospheric, the form has an open top)
I need know the pressure on the form at any point.
Dittowizard@infoave.net






RE: Hydrostatic Pressure on a curved surface
RE: Hydrostatic Pressure on a curved surface
the weight of the (at max cap)column placed on the base is 471,238 lbs (150lbs/cuft)
the formula given looks to be low. Please verify.
Dittowizard
RE: Hydrostatic Pressure on a curved surface
RE: Hydrostatic Pressure on a curved surface
Maybe someone could do some QA and check this:).
Briansch
RE: Hydrostatic Pressure on a curved surface
Dottowizard - if you're placing a concrete column 40 ft high you can reduce the maximum internal pressure according to ACI formula which accounts for the concrete at the bottom starting to set before you get the full 40 ft placed. Depends on pour rate and temperature.
RE: Hydrostatic Pressure on a curved surface
Dittowizard, what are you building?
RE: Hydrostatic Pressure on a curved surface
RE: Hydrostatic Pressure on a curved surface
Brainsch was correct when he stated,"Are you sure this is not specific gravity in which case the density would be 2.4 * 62.4 pcf (water) = 150 pcf."
krd was correct when he stated,"The question looks like pressure in a pipe, not force on a flat plate."
It looks like Denisty(pcf)*Height(f)=Pressure(psf) is the formula.(?)
Example: a fluid colum with a density of 90(pcf) and 4(f) tall will have an outward pressure on a curved surface at the lowest point of 360(psf)
RE: Hydrostatic Pressure on a curved surface
Having a mechanical background, this is just about all the level of detail I know, but I've watched a couple of these projects in construction.
RE: Hydrostatic Pressure on a curved surface
RE: Hydrostatic Pressure on a curved surface
This thread appears to take the biscuit for the number of confused responses, but maybe that is because Dittowizard initially referred to concrete as a fluid.
(a) You can forget all reference to "density times height" for depths below the point where the fluid concrete has commenced to gain shear strength. Below that point, (which is dependent on the rate of concreting and the concrete mix involved) lateral pressure is less than vertical, and the concrete no longer behaves as a pure fluid.
(b) The curvature of the forms has no practical effect on the lateral pressure on them, but the distance between inner and outer forms may have an effect (due to "arching").
(c) Just design the forms as if they were flat, and use the established equations for pressure on formwork, taking into account the type of cement, additives used, rate of pour (in ft/hour [or m/hr] rise in the forms).
RE: Hydrostatic Pressure on a curved surface
Amen,brother
Brad
RE: Hydrostatic Pressure on a curved surface
The pressure is unit weight times depth measured from the free surface.
The company I work for recently designed a bridge using single concrete column piers (we refer to these as hammerhead piers). The pier columns were seven feet in diameter for the shorter ones and ten feet in diameter for the taller ones. The forms were made of steel and included a number of stiffeners to help them hold their shape when they were being handled. They came in quarters and could be bolted together to permit pour depths of around forty feet. The reason the pours were limited to forty feet is because that is the stock length of a reinforcing bar used for the primary reinforcement. The Contractor set a cage forty feet tall (less the lap requirement) and the form and poured the next lift. I don't know how he sealed the forms at the base, but theoretically you could just clamp the forms tight to the previous hardened concrete.
What is your application?
RE: Hydrostatic Pressure on a curved surface
Further to Austim's post, the main factor governing lateral concrete pressure is your proposed rate of pouring and slump of the concrete. Most commercial formwork systems have a limit of for example 2-3m vertical per hour, for wide elements with limited concrete arching to the formwork.
If you are considering pressure on the formwork, I would suggest using available design tables for a square column of the same cross-sectional area. If you are designing bolted steel formwork, then the "pressures" from those tables can be applied to provide a hoop force to design your bolts.
RE: Hydrostatic Pressure on a curved surface
I needed a formula to find the blowout pressure on the side wall of the tank.
Example: If the walls of the tank were steel and they had a bolted seam. How much pressure would there be trying to pull the seam open or how much (tensile) pressure would placed on the bolts?
Example and question: The tank is 10' Dia or has a Circumference of 31.4' or (considering the lower 1' ring of wall) 31.4 sqft of surface. If the pressure on the walls is [40'(tall)x150pcf(density)=6000psf] 6000(psf)x31.4(sf)=188,400pound of pressure on the seam in the lower 1' of the ring.
??Is this correct??
I hope this will clarify my question.
RE: Hydrostatic Pressure on a curved surface
This IS "pressure in a pipe". Think of it as a vertical cylinder with a east half and a west half. Pressure acts in all directions, so the force pushing on the east half is:
Pressure*Diameter*Height, which is same as force pushing on west half (I hope, or tank would be moving!).
The tank wall area holding the two halves together is:
2*Height*Wall Thickness, so the wall stress is:
S=Press*Dia*Height/(2*Height*Thk) = PD/2t (this cannot be applied to your ENTIRE tank because you have a varying hydrostatic head (P); you could apply it if pressure was due to a gas; read on...).
(Note circumference, or area of the wall, is not a factor - i.e., on either of our halves, the components of the forces acting on our curved wall that are not in a direction of directly east or west, say the north force component, are canceled out by the south force components.)
For you, P varies with depth in tank so the force on the bottom 1 foot of the cylinder where the pressure is ~6000 psf is 6000psf*10'*1'=60,000 lbs, where as on the top 1 foot of the cylinder where the pressure is 0 psf at top and 150 psf at bottom (average =75) is 75psf*10'*1'=750 lbs. As you can see, the required wall thickness will vary with depth; this is why large API tanks are often built with varying wall thicknesses.
For resisting "blowout", you need to substitute in an acceptable "allowable stress" when calculating the required wall thickness. If bolts are involved, they also need to be sized to carry the load.
Remember, thick and strong at the bottom, no problem at the top. Hope this helps.