Under ground circular chamber

[sidnum]

Hi there,

I am trying to figure out the effect of a point load on and under ground circular concrete chamber.
I began by looking at hoop stresses etc and thought that the earth load will cause the chamber to go into hoop compression. But I don't think a point load will cause pure compression throughout the chamber. Perhaps looking at it like an arch? If anyone has any usefull formulae for working out moments for this scenario, would be great.
The chamber could be assumed to either fixed or pinned at the base and top, depending on formulae. The support conditon can be detailed later when looking at rebar.
Many thanks

 

[BAretired]

Depends on where the concentrated load is acting. Provide a sketch showing dimensions of chamber and location of load.

BA

 

[dicksewerrat]

How do you get a point load on buried chamber? What is the orientation of this chamber?

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[JStephen]

One approach you might look at is to refer to Roark's Formulas for Stress and Strain. He includes load cases for circular rings with various types of loading in the plane of the ring. You can quite likely assume some arbitrary width of the chamber to be your ring, and superimpose the load cases to find moments or compressive forces around the ring. This approach should be conservative, but if it shows the chamber is okay, it is probably the simplest.

There is design information available for radial loads on cylinders, specifically radial nozzles on pressure vessels. It may be difficult to apply to your case, though, due to the thickness of the wall (may run out of the charts). WRC-107 was the standard source for this type of design, although it was recently pointed out that there is now a replacement standard. You would need to assume loading over a square or circular area rather than a "point".