KEVOS® MAKEOS · Mechanics
Portable Gantry Crane Check (Beam Stress and Deflection, A-Frame Leg Buckling, Wheel Load)
For a portable A-frame gantry with an I-beam and splayed legs, are the beam stress and deflection within limits, will the legs buckle, and what does each castor carry?
Check of a portable gantry crane: the section properties of the I-beam (as the section shapes tool), the bending moment, stress and deflection with the load at mid-span (as the beam cases tool for a central point load), the end reaction with the load at one end, the axial force in each splayed leg and its buckling capacity and safety factor (as the column buckling tool for a tubular leg), and the load on each castor, against your allowables.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Load including hoist and trolley | N | Rated load plus hoist, trolley and an allowance for dynamic effects. |
| Beam span between leg centres | mm | Span of the beam between the centres of the two A-frames. |
| Beam (I) | ||
| Overall depth | mm | Beam depth. |
| Flange width | mm | Flange width. |
| Flange thickness | mm | Flange thickness. |
| Web thickness | mm | Web thickness. |
| Modulus of elasticity | GPa | Modulus of elasticity. |
| Allowable bending stress | MPa | Allowable bending stress for the beam. |
| Deflection limit (span ÷) | Largest deflection as a fraction of the span. | |
| Legs (two per end) | ||
| Leg vertical height | mm | Vertical height of each leg. |
| Leg splay from vertical | ° | Angle of each leg from vertical in the A-frame. |
| Leg tube outside diameter | mm | Outside diameter of each leg tube. |
| Leg wall thickness | mm | Wall thickness of each leg. |
| Leg yield strength | MPa | Yield strength of the leg. |
| Leg effective length factor | Effective length factor for the leg ends. | |
| Required buckling safety factor | Safety factor against leg buckling you need. | |
| Castor rating | N | Load rating of each castor (one under each leg). |
Method and formulas
- A, I and Z of the I-beam (as the section shapes tool); M = W L ÷ 4 and deflection W L³ ÷ 48EI at mid-span (as the beam cases tool).
- Load at one end: end reaction = W; leg force = W ÷ (2 cos β); leg length = height ÷ cos β; buckling as the column buckling tool.
- Castor load = W ÷ 2 (two legs at the loaded end).
- Example: beam at 37.505 MPa and 1.6669 mm; legs carry 10,353 N each with a factor of 20.817.
Limitations
- Self-weight of beam and frames left out; add it to the load for long or heavy gantries.
- In-plane loads only; side loads from moving or pulling the gantry need bracing checks.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check a workshop gantry for a heavier hoist
- Size the beam and legs of a new gantry
- Check castor ratings for a gantry
Who it is for
- Design engineers
- Maintenance engineers
- Fabricators
What you get
- Beam section, stress and deflection
- Leg force and buckling
- Castor load
Interpreting the result
- Widening the leg splay makes the gantry steadier but raises the leg force and length.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 234–246, 257–277, 281–287. Topic reference; no source tables or recommended settings are reproduced.
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