A crane load chart tells operators how much weight a crane can lift safely in a specific setup. This matters because a crane can tip or suffer structural damage if the load creates too much turning effect around the crane’s center of rotation. The main idea is simple: the farther the load is from the crane, the less the crane can safely lift.
Load charts turn this idea into numbers that crews use before every lift.
The key quantity is load moment, which depends on both the load weight and the horizontal distance from the crane’s center of rotation to the load. A longer boom angle or larger working radius usually increases that distance, which reduces the safe capacity. Load charts list capacities for different boom lengths, boom angles, radii, counterweight setups, and outrigger positions.
Reading the chart correctly helps workers choose a safe radius, rigging plan, and crane configuration before the load leaves the ground.
Key Facts
- Load moment = load weight x working radius
- A crane’s safe lifting capacity decreases as working radius increases.
- Working radius is measured horizontally from the crane’s center of rotation to the load hook.
- Capacity values depend on boom length, boom angle, counterweight, outriggers, and ground conditions.
- If a load weighs 5000 kg at a 6 m radius, its moment is 5000 kg x 6 m = 30000 kg m.
- Never interpolate casually between chart values unless the crane manufacturer’s instructions allow it.
Vocabulary
- Load chart
- A table or diagram that lists the maximum safe lifting capacity of a crane for specific configurations and working radii.
- Working radius
- The horizontal distance from the crane’s center of rotation to the vertical line through the load hook.
- Load moment
- The turning effect caused by a load, equal to the load weight multiplied by its working radius.
- Boom
- The long crane arm that supports the hoist line and reaches outward and upward to lift a load.
- Outriggers
- Extendable supports that widen the crane’s base and improve stability during lifting.
Common Mistakes to Avoid
- Using the load weight alone, which is wrong because safety also depends on how far the load is from the crane’s center of rotation.
- Measuring radius along the boom, which is wrong because the load chart uses horizontal working radius, not slanted boom length.
- Ignoring the crane setup, which is wrong because capacity changes with outrigger position, counterweight, boom length, and other configuration details.
- Assuming a nearby chart value is close enough, which is wrong because small increases in radius can sharply reduce safe lifting capacity.
Practice Questions
- 1 A crane lifts a 4000 kg load at a working radius of 8 m. What is the load moment in kg m?
- 2 A load chart says a crane can lift 7200 kg at 5 m, 5200 kg at 7 m, and 3900 kg at 9 m. Can it safely lift a 5000 kg load at a 7 m radius according to the chart?
- 3 A crew can place the same load either 4 m or 10 m from the crane’s center of rotation. Explain which position is safer for the crane and why.