This standard provides criteria for the earthquake-resistant design of elevated and ground-supported liquid retaining tanks. It utilizes a two-degree-of-freedom spring-mass model to calculate the impulsive (liquid moving with tank) and convective (sloshing) hydrodynamic effects during seismic events.
Specifies criteria for the earthquake resistant design of elevated and ground-supported liquid retaining tanks.
Quick Reference Values
Damping for convective (sloshing) mode0.5%
Damping for impulsive mode (concrete tanks)5%
Damping for impulsive mode (steel tanks)2%
Importance Factor (I) for drinking water/firefighting tanks1.5
Importance Factor (I) for other liquid tanks1.0
Response Reduction Factor (R) for RC SMRF elevated tanks2.5
Key Formulas
V = sqrt(Vi^2 + Vc^2) — Total design base shear combined using SRSS
Ah = (Z/2) * (I/R) * (Sa/g) — Design horizontal seismic coefficient
dmax = (Ah)c * R * Rc — Maximum sloshing wave height
Practical Notes
Base shear and moment must be calculated separately for impulsive and convective modes, then combined using the SRSS method.
Ensure adequate freeboard is provided based on the calculated maximum sloshing wave height to prevent uplift or damage to the tank roof.
The convective (sloshing) mass always has a very low damping ratio (0.5%), requiring specific spectral acceleration values.