Tank farm is located in seismic zone

[kezen]

Dear members,
Currently I am working on the design of steel storage tank foundation for project in Saudi Arabia. Tank diameter is ranging to 25m to 49m. Mechanical group has firm up anchorage requirement. The tanks require anchorage is supported on concrete ring beam foundation and others which do not require anchorage are proposed on earthen foundation.
Tank farm is located in seismic zone 2A and API 650 is contractual code. Seismic forces have been considered for the design of concrete ring foundation for anchored tanks.
My question is:
1. Should the seismic forces be considered for the calculation of bearing pressure below the earthen tank foundation where tank is directly sitting on the top without any anchorage?
2. Which is governing code for the design of earthen tank foundation considering seismic forces?
Learned members comments and help will be highly appreciated.
Thanks and Regards

 

[Soln]

The required bearing area for the foundation could possibly be governed by the seismic case. In other words, the seismic overturning moment imparts a force to the sub grade that has to be taken into account. Regarding code- I believe ACI 318 will be your guide. I'm not familiar with any standard or code that specifically addresses tank foundations under seismic forces although, Process Industry Practices (PIP STE03020), Guidelines for Tank Foundation Designs, is the closest thing I can think of.

I would appreciate hearing if you find a standard, or guideline that gives you more confidence.