Platforms on Umbrella Roof Tanks

[LeonEarle]

Does anyone know of a good reference source for formula to determine effect of installing eccentrically loacted roof top platforms on Umbrella or Dome roofs?

 

[JoeTank]

Don't woryy about the "ecccentric" loads on the roof. It's the concentrated reactions that will give you fits. Thin shells don't like concentrated loads, so you have to consider the local bending stress and instability concerns. And unfortunately, I am now aware of any valid procedures that are in the public domain. The tank construction firms with engineering departments have figured this problem out, but they don't often share. Likewise, there are a limited number of consultants that specialize in tank design that may be able to assist you.

Joe Tank

 

[MJCronin]

Leon,

It is not clear what you mean y "eccentrically"...

 

[LeonEarle]

We have an 87' diameter tank with an umbrella roof. The roof radius is 70'. On the roof, the client desires to place a 10' x 10' platform adjacent to the stair top platform. As a result, the platform will not be at the apex of the roof, but over just two formed plates. Typically, we would bridge under the platform and support in line with the shell. I am looking for a resource that would provide guidance on how to evaluate the concentrated loads from the platform if we were to suppord directly from the roof.

 

[JStephen]

Eccentric placement shouldn't be any problem there.

WRC 107 has the kind of load cases you need, but I'm not sure if it applies to a sphere that thin.

You might also check some of the approaches to loading on cylinders.