BIZOMAT MAKEOS · Strength
Tank Stand Leg Check (Full Tank Weight, Load per Leg, Leg Buckling)
For a vertical tank standing on tubular legs, what does it weigh full, how much does each leg carry, and are the legs safe against buckling?
Check of the legs of a vertical cylindrical tank stand: the full volume of the tank (as the tank volume tool), the full weight with the empty tank mass, the load on each leg, the area and least second moment of area of a tubular leg, then the slenderness, Euler or Johnson critical stress and buckling load and the safety factor (as the column buckling tool), against your required factor.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Tank inside diameter | mm | Inside diameter of the tank. |
| Tank shell height (full level) | mm | Height of the cylindrical shell up to the full level. |
| Contents density | kg/m³ | Density of the contents. |
| Empty tank mass | kg | Mass of the empty tank, roof and fittings. |
| Number of legs | legs | Number of legs sharing the load. |
| Legs | ||
| Leg outside diameter | mm | Outside diameter of each tubular leg. |
| Leg wall thickness | mm | Wall thickness of each leg. |
| Unsupported leg length | mm | Length of leg between the base and the first brace or the tank. |
| Effective length factor | Effective length factor for the end fixity (1.2 to 2 for legs fixed at the base with little restraint at the top). | |
| Elastic modulus | GPa | Modulus of elasticity of the leg. |
| Yield strength | MPa | Yield strength of the leg. |
| Required safety factor | Safety factor against buckling you need. | |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Tank inside diameter
- What it is
- The inside diameter of the cylindrical tank shell, which with the full level sets how much liquid the tank holds.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1200 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The contents volume, and so the load on each leg, grows with the square of the diameter.
- Get it right
- Use the inside diameter: the outside diameter overstates the volume by twice the wall thickness.
What this means: Tank shell height (full level)
- What it is
- Height of the cylindrical shell up to the full liquid level. The tool treats the tank as a plain cylinder filled to this height.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1500 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The contents mass rises in direct proportion to this height.
- Get it right
- Use the overflow or highest possible level, not the normal working level, so the leg check covers the worst case.
What this means: Contents density
- What it is
- Mass per cubic metre of the liquid or bulk material the tank holds when full.
- Units and format
- Enter a number in kg/m³: kilograms per cubic metre. The form accepts 0 kg/m³ to 25000 kg/m³. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1000 kg/m³ as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The contents mass, and so the leg load, rises in direct proportion to the density.
- Get it right
- Use the densest product the tank may ever store, from its safety data sheet or supplier data.
What this means: Empty tank mass
- What it is
- The mass of the tank itself with roof, nozzles, ladders and fittings, but no contents. It is added to the contents mass.
- Units and format
- Enter a number in kg: kilograms. The form accepts 0 kg to 10000000 kg. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 250 kg as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Include insulation, agitators and anything else the legs carry.
What this means: Number of legs
- What it is
- How many legs share the weight of the full tank. The tool divides the total weight equally between them.
- Units and format
- Enter a number in legs: legs. The form accepts 3 legs to 24 legs. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 4 legs as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- More legs reduce the load on each leg and raise the safety factor.
- Get it right
- Equal sharing assumes a level base and a stiff tank ring; uneven ground can put more load on some legs.
Legs
What this means: Leg outside diameter
- What it is
- The outside diameter of each tubular leg, which with the wall thickness sets the leg’s area and its resistance to bending.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 5000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 60.3 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- For pipe, use the actual outside diameter from the pipe table, not the nominal pipe size.
What this means: Leg wall thickness
- What it is
- The wall thickness of each tubular leg.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 500 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 3.91 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Use the measured or specified wall, allowing for any corrosion loss you expect over the tank’s life.
What this means: Unsupported leg length
- What it is
- The length of each leg that is free to bow sideways, from the base plate to the first brace or to the tank connection.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1500 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Longer legs are more slender and buckle at a lower load.
- Get it right
- Measure between points that are actually held sideways; a brace that is not fixed does not shorten the length.
What this means: Effective length factor
- What it is
- The multiplier that turns the actual leg length into an effective buckling length, depending on how the ends are held against rotation and sideways movement.
- Units and format
- Enter a plain number with no unit. The form accepts 0.5 to 2.5. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1.2 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger factor raises the slenderness and lowers the buckling load.
- Get it right
- Choose it from a structural design reference for the real end conditions; a leg free to sway at the top needs a large factor.
What this means: Elastic modulus
- What it is
- The elastic modulus (Young’s modulus) of the leg material, which governs buckling of slender legs.
- Units and format
- Enter a number in GPa: gigapascals (1 GPa = 1000 MPa). The form accepts 0.000001 GPa to 1000 GPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 200 GPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Enter it in GPa, not MPa; take it from the material standard or supplier.
What this means: Yield strength
- What it is
- The yield strength of the leg material, used for shorter legs where yielding mixes with buckling.
- Units and format
- Enter a number in MPa: megapascals (1 MPa = 1 N/mm²). The form accepts 0.000001 MPa to 5000 MPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 250 MPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Use the minimum yield strength from the material standard or mill certificate.
What this means: Required safety factor
- What it is
- The lowest ratio of buckling load to load per leg you will accept. Your design code or company rules set it.
- Units and format
- Enter a plain number with no unit. The form accepts 1 to 20. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2.5 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- The tool does not include wind, seismic or impact loads, so set the factor with that in mind or check them separately.
Method and formulas
- Full volume = π D² H ÷ 4 (as the tank volume tool, vertical and full).
- Load per leg = (empty mass + volume × density) g ÷ legs.
- Leg A and I of the tube; slenderness K L ÷ r; Euler above C_c, Johnson below; buckling load = σ_cr A (as the column buckling tool).
- Example: 1,696.5 L full, 4,772.1 N per leg; legs buckle at 128,690 N (factor 26.967).
Limitations
- Concentric vertical load shared equally; wind, seismic and sloshing loads and an uneven base are not included.
- Leg buckling only; leg-to-tank welds and base plates need separate checks.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check legs for a header or rainwater tank
- Size legs for a process tank
- See how longer legs reduce the safety factor
Who it is for
- Design engineers
- Fabricators
- Plant engineers
What you get
- Full volume and weight
- Load per leg
- Leg buckling load and safety factor
Interpreting the result
- Cross-bracing the legs halves their unsupported length and roughly quadruples their Euler buckling load.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 68–69, 281–287. Topic reference; no source tables or recommended settings are reproduced.
Learn the Concepts Behind This Tool
These BIZOMAT Library readings explain the method this tool uses, with worked examples.
Method explained here · BIZOMAT original book
Ends, bracing and effective length
What it covers: How the way a member is held at its ends sets its buckling load: effective length factors, braced and sway frames, and why an unbraced tank stand can buckle under its own contents.
Method explained here · BIZOMAT original book
Pressures in a silo: the Janssen equation
In Bulk Solids Flow by the Numbers
What it covers: Derive the Janssen equation from a slice balance, apply it to Plant C's pellet silo, see how wall friction shifts weight from the floor to the walls, and know what static pressures leave out.
BIZOMAT tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
Open the Tank Stand Leg Check (Full Tank Weight, Load per Leg, Leg Buckling) calculator