BIZOMAT MAKEOS · Mechanics
Crane Load Swing Check (Pendulum Period, Swing, Rope Tension)
If the trolley stops suddenly, how far will this hanging load swing, how long is each swing, and how much extra pull does the swing put on the rope?
Check of a load hanging from a crane trolley or hoist that stops abruptly from its travel speed: pendulum period for the rope length corrected for amplitude (as the pendulum period tool), the swing angle and horizontal swing from the kinetic energy of the load, the rope tension at the bottom of the swing including the centripetal force, the largest travel speed for your swing clearance, and checks against the clearance and the rated load.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Load mass | kg | Mass of the hanging load including the hook block below the sheave. |
| Rope length to the load centre of gravity | m | Length from the trolley sheave to the load’s centre of gravity. |
| Travel speed | m/s | Trolley or bridge travel speed when it stops. |
| Swing clearance available | m | Horizontal distance the load may swing before it hits something. |
| Rated load of the crane and rigging | kN | Rated load of the crane, hoist or rigging in force units. |
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: Load mass
- What it is
- The mass of everything hanging below the trolley sheave: the load plus the hook block, slings and lifting gear.
- Units and format
- Enter a number in kg: kilograms. The form accepts 0.000001 kg to 10000000 kg. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2000 kg as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Rope tension rises in proportion to mass; the swing itself does not depend on mass.
- Get it right
- This is mass in kilograms, not a force.
What this means: Rope length to the load centre of gravity
- What it is
- The length of the pendulum: from the trolley sheave or suspension point down to the centre of gravity of the hanging load.
- Units and format
- Enter a number in m: metres. The form accepts 0.1 m to 500 m. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 6 m as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A longer rope gives a slower swing period; for a given speed it lowers the swing angle and the extra rope tension.
- Get it right
- Measure to the load’s centre of gravity, not to the hook.
What this means: Travel speed
- What it is
- The speed of the trolley or bridge travel at the moment it stops; the load keeps moving at this speed and swings.
- Units and format
- Enter a number in m/s: metres per second. The form accepts 0 m/s to 20 m/s. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.5 m/s as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The rise of the load grows with the square of the speed, so swing increases quickly with speed.
- Get it right
- Use the actual travel speed in metres per second; convert from metres per minute by dividing by 60.
What this means: Swing clearance available
- What it is
- The horizontal distance the load can swing from its hanging position before it would strike a person, structure or another load.
- Units and format
- Enter a number in m: metres. The form accepts 0.000001 m to 100 m. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.5 m as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Measure from the load’s nearest edge to the obstruction, not from its centre.
What this means: Rated load of the crane and rigging
- What it is
- The rated load of the weakest part of the crane and rigging (hoist, rope, slings, shackles), expressed as a force, from the rating plates and rigging certificates.
- Units and format
- Enter a number in kN: kilonewtons (1 kN = 1000 N). The form accepts 0.000001 kN to 1000000 kN. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 25 kN as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- This is in kilonewtons; a rating in tonnes must be converted (1 t of mass weighs 9.80665 kN).
Method and formulas
- Period T = 2π √(L ÷ g), corrected by (1 + θ² ÷ 16) for amplitude (as the pendulum period tool).
- Rise of the load h = v² ÷ 2g; swing angle θ = cos⁻¹(1 − h ÷ L); horizontal swing = L sin θ.
- Rope tension at the bottom = m g + m v² ÷ L; largest speed for clearance c = √[2g L (1 − cos(sin⁻¹(c ÷ L)))].
- Example: stopping from 0.5 m/s swings the load 0.39089 m (3.7354°) every 4.916 s; keep travel below 0.63978 m/s for 0.5 m clearance.
Limitations
- Abrupt stop of the trolley; gradual braking reduces the swing.
- Point load on a single fall; long loads also rotate.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Set a travel speed limit near obstructions
- Explain load swing to crane operators
- Check the dynamic rope load from swinging
Who it is for
- Lifting supervisors
- Crane engineers
- Riggers
What you get
- Period and swing angle
- Horizontal swing and rope tension
- Largest travel speed for the clearance
Interpreting the result
- Swing grows with speed and with the square root of rope length: slow down and shorten the drop near obstructions.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 173–174. Topic reference; no source tables or recommended settings are reproduced.
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Open the Crane Load Swing Check (Pendulum Period, Swing, Rope Tension) calculator