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 rated capacity safety factor for most mobile cranes as it relates to tipping load?
Answer: 75% of tipping load
ASME B30.5 requires mobile crane rated capacities to be a maximum of 75% of the load that would cause tipping, providing a 25% stability safety margin.
What is the primary structural failure mode of a lattice boom under excessive compressive loading?
Answer: Buckling of chord members or lacing
Lattice boom chord members and lacing elements are primarily in compression; excessive loading causes buckling, a sudden and catastrophic failure mode where the member deflects laterally and collapses.
How does dynamic loading during crane operations affect the required safety factors?
Answer: Dynamic loads effectively reduce the safety margin because they add to static loads
Dynamic loads from hoisting, braking, and swing add to static load weight, effectively consuming part of the safety factor and leaving less margin until the actual failure load is reached.
What is the purpose of the load moment indicator (LMI) on a crane?
Answer: To monitor the relationship between load moment and rated capacity and warn the operator before limits are exceeded
The LMI continuously monitors boom angle, radius, load weight, and configuration to calculate the current load moment and compare it to rated capacity, alerting the operator as limits are approached.
What structural inspection should be performed on a lattice boom that has been subjected to an overload event?
Answer: Complete inspection by a qualified person including all chord members, lacings, pins, and welds for deformation, cracking, and buckling
Any overload event requires a thorough engineering inspection of all structural components for permanent deformation, cracking, and incipient buckling before the crane returns to service.
What is the relationship between center of gravity (CG) position and crane stability?
Answer: The crane is stable as long as the combined CG of crane and load falls within the tipping line boundary
A crane remains stable as long as the combined center of gravity (machine plus load) falls within the support polygon defined by the tipping lines; when the CG crosses a tipping line, the crane tips.