Elevated Tank Support - API 650 App E or ASCE 7-05 Chapter 15

[SteveGregory]

API 650 Appendix E Seismic Design seems to be devoted to flat bottom tanks supported at grade. Should I be using ASCE 7-05 Eq. 15.4-5 to generate the seismic shear load to design the tank support structure and foundation.

The tank is 21' in diameter and 20' high and it is supported on a steel grillage about 6' above grade. The steel is supported on a series of concrete walls and footings.

 

[JStephen]

The API-650 standard design assumes that the tank is "rigid" with zero period for the impulsive forces. For an elevated tank, this would likely not be the case. If you could evaluate the fundamental period and show that it was still very small, it might be reasonable to still use the API-650 approach. Otherwise, consider an approach allowing for the added flexibility.

 

[MJCronin]

Steve,

IMHO, you have just crossed into an area where a specialist may be required to perform a more detailed seismic analysis.

There are plenty of engineering consulting firms with lots of detailed analysis tools and experience in the nuclear power industry that can help you.

regards

 

[SteveGregory]

Should the tank vendor supply the support reactions for all of the load cases which should include the seismic base shear?

 

[JStephen]

I think in a situation like that, the design of the support structure and of the tank itself would need to be considered together.

 

[SteveGregory]

In this case, an existing tank is being replaced with a new one. I am evaluating the old foundation to determine if it needs reinforcing or supplementing to bring it up to the current code.