Hydrodynamic force on internal walls for global stability

[StrucutreDr]

I am designing de-silting chamber. There are two divide walls in the chamber, making three bays, independent of each other. I want to evaluate the factor of safety against sliding for the chamber. The critical case is the tank full of water and earthquake. The question is that, to determine the total sliding force, should the hydrodynamic force be considered on exterior wall and the two interior walls?

 

[StrucutreDr]

Or the base shear be determined considering the hydrodynamic force on exterior wall only?
The other option is to determine the total base shear considering the total impulsive force of water in the tank.
Which option should be adopted for the design?

 

[briancpotter]

During an earthquake, the entire structure will vibrate back and forth, so the hydrodynamic forces on the walls will all be acting simultaneously. To consider sliding you need to consider the forces on all the walls in a given orientation, for both x and y directions.

However, due to friction resistance, the worst sliding case may not actually be the maximum load case. You'll need to consider all possible tank fill configurations, and the force and sliding resistance for each of them.

Brian C Potter, PE

http://simplesupports.wordpress.com

 

[StrucutreDr]

Thanks, Mr. briancpotter,
One more question. If I consider the entire water volume as "impulsive mass" (without considering convective mass), and simply determine the "base shear" = total weight x OBE (0.24g). Is this be the same as if using the westergaard hydrodynamic pressure to determine the base shear.
Let me put this question in another way. Consider a water tank with no internal walls. The hydrodynamic force will be acting on one wall. We also calculate the base shear considering complete weight of water in the tank. No if the same tank is divided into three part (two internal walls), the hydrodynamic force will act on three walls (3 times than for the tank without internal walls). While the base shear considering the weight of water in the tank remains the same.

One additional question. Should we use the Wastergaard formula for hydrodynamic force or the 350.3 for the seismic analysis of tank?

 

[briancpotter]

The hydrodynamic force is a function of the length of a cell being designed for. So adding internal walls puts a force on each of them, but each individual force will be less since your cell length is now only a portion of the total length.

I'm unfamiliar with the westergaard method. I've always designed using the method spelled out in ACI 350.3.

Brian C Potter, PE

http://simplesupports.wordpress.com