IS 1893 Part 2 Learning Page
Ground-supported vs elevated vs buried / partially buried tanksGround-Supported vs Elevated Tanks in IS 1893 Part 2
This page explains why tank support condition changes the whole earthquake problem. Ground-supported tanks are mainly shell-base-foundation systems. Elevated tanks are container-plus-staging systems with inverted-pendulum behaviour. Buried or partially buried tanks bring soil and dynamic earth pressure into the picture.
What students should understand first
Ground-supported
Dominant story: hydrodynamic pressure, shell and base stresses, overturning, anchorage, and possible uplift or rocking.
Elevated
Dominant story: staging stiffness, sway, P-Δ, ductility, and inverted-pendulum behaviour.
Buried / partially buried
Dominant story: liquid effects remain, but dynamic earth pressure must also be included.
Why these tank types respond differently
The liquid is common. The support condition changes the force path, time period, and what actually governs the design.
Ground-supported
Support is direct. Earthquake demand flows rapidly into the wall, base slab, anchorage, and foundation.
Elevated
The supporting shaft or frame becomes a major dynamic participant. Staging flexibility reshapes the impulsive response.
Buried / partially buried
Soil restraint and dynamic earth pressure join the liquid-side demand. Burial changes the problem, but does not erase hydrodynamic action.
Impulsive and convective response
Impulsive component
This is the part of the liquid that moves more or less with the container. It usually drives wall force, base shear, overturning, and staging demand.
Convective component
This is the sloshing component. It often has a longer period and lower damping, so it matters for freeboard, sloshing height, and some force components.
V = √(V_i² + V_c²)
Ground-supported vs elevated vs buried / partially buried
| Aspect | Ground-supported tank | Elevated tank | Buried / partially buried tank |
|---|---|---|---|
| Main dynamic identity | Container directly on base and foundation | Container plus flexible shaft / frame staging | Container interacting with surrounding soil |
| Dominant physical idea | Wall-base interaction, overturning, uplift, anchorage | Inverted-pendulum sway and staging flexibility | Liquid effects plus dynamic earth pressure |
| What usually governs | Impulsive force, local wall pressure, base moment, anchorage | Staging shear, moment, drift, ductility, P-Δ | Wall demand from both liquid and soil sides |
| Student warning | Do not ignore rocking in unanchored tanks | Do not model it like a ground tank placed high up | Do not use earth pressure to reduce liquid dynamic effects |
| Useful memory phrase | “Base-and-shell problem” | “Mass-on-flexible-support problem” | “Liquid-plus-soil interaction problem” |
Tank seismic snapshot calculator
This tool is educational. It uses the amended R-values and minimum impulsive coefficient floor. Effective masses and lever arms must be supplied by the user from the spring-mass idealization of the actual tank.
Is this code appropriate for deployment?
Yes, structurally
This widget is dependency-free, responsive, and namespaced so it is much safer inside WordPress than a second full HTML document pasted into page content.
Main caveat
If your WordPress setup strips inline <script> tags, the page design will still appear but the calculator will not run. In that case move the JavaScript into an enqueued theme or plugin file.
Best deployment route
Use an administrator-level Custom HTML block if scripts are preserved. For the most reliable deployment, keep HTML in the page and enqueue JS/CSS from the theme or a snippets/plugin workflow.
Code points used in this page
From IS 1893 (Part 2): 2014
- Scope covers ground-supported liquid retaining tanks and elevated tanks on staging, with guidance also provided for buried tanks.
- Ground-supported tanks use a spring-mass idealization with impulsive and convective components.
- Elevated tanks are treated as inverted-pendulum type structures supported on shaft or frame staging.
- Buried tank design must consider dynamic earth pressure in addition to liquid effects.
From Amendment No. 1 (March 2022)
- Updated R-values for elevated tanks and ground-supported tanks.
- Underground RC and steel tanks use R = 3.0.
- For partially buried tanks, R may be interpolated between ground-supported and underground values based on embedment depth.
- The horizontal impulsive coefficient Ah,i has a minimum floor by seismic zone.
