Jib capacity increases as the angle decreases: True or False?

Jib capacity increases as the angle decreases: True or False?

• A. False
• B. True
• C. Depends on load
• D. Cannot be determined

Answer: (A)

The amount you can lift from a jib crane is governed by the tipping moment created by the load about the crane base. When the jib is closer to the horizontal (a smaller angle from the horizontal), the load sits farther out, increasing the horizontal distance to the base and thus increasing the tipping moment for the same weight. That larger moment reduces the safe load capacity. Conversely, when the jib is steeper (a larger angle from the horizontal), the load’s moment arm is shorter, the tipping moment is smaller, and more load can be handled safely. So capacity does not increase as the angle decreases; it actually decreases.

The amount you can lift from a jib crane is governed by the tipping moment created by the load about the crane base. When the jib is closer to the horizontal (a smaller angle from the horizontal), the load sits farther out, increasing the horizontal distance to the base and thus increasing the tipping moment for the same weight. That larger moment reduces the safe load capacity. Conversely, when the jib is steeper (a larger angle from the horizontal), the load’s moment arm is shorter, the tipping moment is smaller, and more load can be handled safely. So capacity does not increase as the angle decreases; it actually decreases.