Principles of Crane Stability and Structural Integrity Flashcards
6 cards from real NCCCO practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Principles of Crane Stability and Structural Integrity flashcards as text
What is the 'moment' in crane stability calculations?
Answer: The product of a force (weight) multiplied by the distance from the tipping axis — measured in foot-pounds
Moment = Force × Distance. The load moment (load weight × radius) must not exceed the resisting moment (counterweight × its distance from the tipping axis) for the crane to remain stable.
What is the purpose of counterweight on a crane?
Answer: To create a resisting moment that balances the load moment and prevents the crane from tipping toward the load
Counterweight creates a stabilizing moment opposite to the load moment. The correct amount is critical — too little reduces capacity, too much wastes energy and stresses the structure.
A crawler crane is operating on a slope. How does this affect the load chart?
Answer: Load chart values decrease because the crane's center of gravity shifts, reducing the effective resisting moment on the downhill side
On a slope, gravity pulls the crane's center of gravity toward the downhill side, reducing the resisting moment in that direction. Most manufacturers require derating or special procedures for sloped operations.
What structural component is most likely to fail in a lattice boom crane when overloaded?
Answer: The boom — specifically the chord members and lacings that can buckle under excessive compressive forces
Lattice boom chords carry compressive loads. When overloaded, these slender members can buckle — a sudden, catastrophic failure that collapses the boom structure.
How does 'freely suspended load' affect stability differently than a load resting on the ground?
Answer: A freely suspended load acts at the boom tip radius, while a load being dragged applies unpredictable horizontal forces that can dramatically reduce stability
Dragging a load adds horizontal forces that create additional tipping moments. A freely suspended load applies force vertically at a known radius, which is predictable and accounted for in the load chart.
What safety factor is built into crane load chart ratings?
Answer: Typically 15-25% safety margin below the actual tipping or failure point
Load charts typically include a 15-25% safety margin below the theoretical tipping or structural failure point. This margin accounts for dynamic loads, measurement uncertainties, and minor field variations.