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Forming a concrete tank with steel removable and non removable sheets...
Hi Victor, I have found an interesting example on the Internet which I wanted to simulate. "We are looking for a structural engineer to calculate the loads on the forming of a vertical concrete cylinder/tank of 12' I.D./14' O.D. x 20' tall. The inner form will be a bladder filled with water during the concrete pour. The outer form will be a cylindrical membrane (flexible) containing the concrete to the round/cylindrical shape until cured. The water within the inside tank will then be pumped out, leaving the bladder bonded to the concrete around the entire interior of the cylinder.
We are looking for the pressure loads on:
-The interior bladder/tank during forming.
-Determination that the water inside the bladder/tank will resist the force of the concrete during the pour until hardened.
-The tensile strength needed for both the inside bladder and outside bladder to withstand both the hydrostatic water and concrete pressures on each bladder form.
-The ideal concrete mix to achieve the desired structural strength of the hardened concrete cylinder.
-The amount of steel mesh that should be placed within the cavity of the inner and outer forms for maximum strength when cured.
-The amount of force the concrete cylinder can withstand when hardened, assuming different amounts of steel mesh being used.
-The ideal rate for the pouring of the concrete, e.g. 1' - 3' per hour."
I did a model in Mecway but the results were far from expected in terms of behavior. I did two walls (one as a shell one as a solid) and connected them by wooden logs, which were connected to steel supports. I can explain all the steps but probably easier will be to supply the lim file.
The biggest worry was applying hydrostatic pressure as it wasn't clear enough what is the method of applying it. Looking at the load arrows it all seems as it should be (pressure gradient increases with depth). I don't know why just one of the supports shows the biggest deflections and why are they so high. I had an example with internal wall thickness of 0,5m to avoid buckling and instability influence as gravity is involved in a slender and quite high wall.
Please have a look at the file and comment as I have done few changes to make the model overstiffen but couldn't overcome the problem.
Cheers,
apadzak
We are looking for the pressure loads on:
-The interior bladder/tank during forming.
-Determination that the water inside the bladder/tank will resist the force of the concrete during the pour until hardened.
-The tensile strength needed for both the inside bladder and outside bladder to withstand both the hydrostatic water and concrete pressures on each bladder form.
-The ideal concrete mix to achieve the desired structural strength of the hardened concrete cylinder.
-The amount of steel mesh that should be placed within the cavity of the inner and outer forms for maximum strength when cured.
-The amount of force the concrete cylinder can withstand when hardened, assuming different amounts of steel mesh being used.
-The ideal rate for the pouring of the concrete, e.g. 1' - 3' per hour."
I did a model in Mecway but the results were far from expected in terms of behavior. I did two walls (one as a shell one as a solid) and connected them by wooden logs, which were connected to steel supports. I can explain all the steps but probably easier will be to supply the lim file.
The biggest worry was applying hydrostatic pressure as it wasn't clear enough what is the method of applying it. Looking at the load arrows it all seems as it should be (pressure gradient increases with depth). I don't know why just one of the supports shows the biggest deflections and why are they so high. I had an example with internal wall thickness of 0,5m to avoid buckling and instability influence as gravity is involved in a slender and quite high wall.
Please have a look at the file and comment as I have done few changes to make the model overstiffen but couldn't overcome the problem.
Cheers,
apadzak
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Comments
The large deflection in the support is because it's made from truss elements which have ball-joints at each node. Change them to beams by selecting the elements then right clicking one of them and choosing Element properties. Uncheck "truss".
I think there should also be rotational constraints on the vertical edges of the shells to enforce mirror symmetry. You already effectively have this on the solid elements by way of displacements over the whole edge surfaces.
If you do the whole thing with solids, it might be an idea to run a nonlinear analysis too. I'm skeptical that there aren't membrane action effects due to the very thin walls. Nonlinear analysis would also detect buckling if you apply a small asymmetry the the loads or geometry to initiate it.
Also, hex8 solid elements are not very good in bending, so results may converge very slowly with mesh refinement. Better to use quadratic elements like hex20.
Merry Christmas.
apadzak