NCCCO Principles of Crane Stability and Structural Integrity 2

Question 1

What is the 'tipping axis' of a mobile crane on outriggers?

Accepted Answer

The line connecting the outrigger pad closest to the load and the adjacent outrigger pad

Answer

The tipping axis is the line between the two outrigger pads on the load side. If the load moment (load × radius) exceeds the resisting moment about this axis, the crane will tip.

Question 2

What factor has the greatest effect on crane stability?

Accepted Answer

The operating radius — the horizontal distance from the center of rotation to the load

Answer

Operating radius is the single greatest factor because capacity decreases rapidly as radius increases. A small increase in radius can cause a large decrease in available capacity.

Question 3

What happens to crane stability when the crane is not level?

Accepted Answer

The crane becomes less stable because the effective tipping axis shifts, and the load effectively moves to a greater radius

Answer

An unlevel crane shifts the center of gravity away from center, effectively increasing the radius on the downhill side and reducing the resisting moment. Load charts assume a level crane.

Question 4

What is 'structural failure' in a crane and how does it differ from a stability failure?

Accepted Answer

Structural failure is when a component (boom, pin, wire rope) breaks; stability failure is when the crane tips over

Answer

Structural failure involves component breakage (boom buckling, pin shearing, rope breaking). Stability failure involves the crane tipping over. Both are prevented by staying within load chart ratings.

Question 5

How does the weight of the boom itself affect crane stability?

Accepted Answer

The boom's weight creates a tipping moment that increases with boom length and angle, reducing available capacity for the load

Answer

The boom itself has weight that creates a moment about the tipping axis. Longer booms weigh more and create a greater tipping moment, which is why capacity decreases with longer boom configurations.

NCCCO (National Commission for the Certification of Crane Operators) Practice Test

NCCCO (National Commission for the Certification of Crane Operators) Practice Test

NCCCO Principles of Crane Stability and Structural Integrity 2