A simplified procedure for seismic evaluation of large vertical tanks

Large vertical tanks are an important component of the safe shutdown systems in nuclear power plants (NPP). In most plants these tanks were designed for seismic loads based on a procedure that assumes that the tank fluid system is rigid. Earthquake experience and more recent experimental and analytical studies have indicated that the frequency of the impulsive mode of a typical tank containing fluid lies in the amplified range of a typical earthquake response spectrum leading to a much greater seismic response than previously thought. A simplified procedure for seismic evaluation of large anchored flat bottom vertical tanks has been developed and is presented. The procedure accounts for both, the amplified response of the impulsive mode of the tank fluid interaction, and the inelastic stretching of bolts until compressive stress in tank wall reaches buckling capacity