Steel Vertical Wet-Well Design

[Kris the Engineer]

I have a project for a temporary sewer wet-well. The bottom portion of the wet-well that is below the ground water table will be cast in place concrete and I designed that portion using RISA-3D. The owner is trying to save some money since this is a temporary well and wants to use a steel sewer pipe for the upper portion of the well. I am trying to determine how to analyze the pipe but the only guides I can find is for the design of a horizontal pipe.

Has anyone designed a vertical steel shaft and if so what design guide did you use or how did you design it? Everything I am seeing accounts for a high soil load on top of the pipe with a passive load on the bottom which is not the case i will have as it will have the same soil pressure around the entire ring.

Thanks is advance!

 

[JStephen]

Roark's Formulas For Stress and Strain includes equations for elastic buckling of cylinders from external pressure.
A more conservative approach is to use the ASME Boiler and Pressure Vessel Code.
I've not seen any data on corrugated-type pipe, and the manufacturers might be able to help on it.

 

[JoelTXCive]

I have not designed one like this, but my gut says you are going to end up with a very conservative design.

A steel pipe can handle 50psi internal pressure no problem; and 50psi translates into 7200 psf.

I think you can argue that the steel pipe is equally strong in uniformly applied compression, if not stronger. (hopefully Roark agrees)

Lets say you had a 10ft deep wet well and soil with an equivalent fluid pressure of 100psf.......You would only be at 1000psf external pressure.

The connection between the upper and lower region of the wet well warrants further discussion and analysis, but the pipe itself should be no problem.

 

[Ron]

I have designed many steel wet wells. Using a pipe will not be an issue. Most of the ones I have done varied from 4' to 8' in diameter and were fabricated from mild steel plate.

 

[Kris the Engineer]

Jstephen, thanks for the information about the Roark's Formulas. I had never heard about that before.

Ron - What do you use to analyze the pipe to determine the thickness needed? I am not finding any equations or formulas for this type of use for a pipe.

 

[dhengr]

Kris the Engineer:
This is nothing more than a shallow steel pipe caisson, more or less. And, there is considerable material out there on the design of these, in the structural, civil, dock and harbor works and foundation literature.