API Standards

I´m doing a plastic collapse evaluation as per API 579-1 Appendix B1, and one of the load cases is Earthquake loads. 579 refers to ASCE 7, which for tanks refers to API 650 Appendix E. The approach in 650 is a static equivalent lateral force seismic analysis where you find equivalent lateral forces and moments according to some likely earthquake spectrum. It seems that what you do is apply these at the top of the tank shell, which mimics the overturning and shear behavior, assuming the tank doesnt slide from inertia.