Ground Bearing Pressure and Outrigger Setup 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 Ground Bearing Pressure and Outrigger Setup flashcards as text
A crawler crane weighs 200,000 pounds and each track pad has a total ground contact area of 2,000 square inches. What is the ground bearing pressure under each track in pounds per square inch (psi)?
Answer: 50 psi
Ground bearing pressure = Total weight divided by Total contact area. Each track supports 100,000 lbs over 2,000 sq in, so GBP = 100,000 divided by 2,000 = 50 psi per track.
Why must outrigger pads be used on outriggers even when working on concrete surfaces?
Answer: To spread the point load over a larger area and reduce pressure on the concrete and underlying soil
Outrigger pads spread the concentrated point load from the outrigger float over a larger area, reducing pressure per square inch on the concrete slab and the soil below. Concrete slabs can fail if point loads exceed the slab's capacity.
During a pre-lift check, the crane operator observes that one outrigger pad is sinking into soft ground more than the others. What is the appropriate action?
Answer: Stop the lift immediately and add more cribbing or a larger pad to distribute the load
Differential outrigger settlement indicates the ground at that point cannot support the load. The lift must stop immediately and the setup corrected by enlarging the bearing area or improving the ground support before continuing.
What is the primary purpose of extending outriggers to their full width before making a lift?
Answer: To maximize the crane's tipping fulcrum distance and increase rated lifting capacity
Fully extended outriggers widen the crane's support base, pushing the tipping axis farther from the center of gravity, which significantly increases the crane's rated lifting capacity and stability.
What does the term 'soil bearing capacity' refer to in the context of crane setup?
Answer: The maximum load per unit area that a soil can safely support without excessive settlement or shear failure
Soil bearing capacity is the maximum pressure (in psi or psf) that a particular soil type can support without failing. The outrigger ground pressure must not exceed the soil's bearing capacity.
OSHA 29 CFR 1926.1402 requires the ground to be firm, drained, and graded before crane use. What additional requirement is stated for supporting surfaces under outriggers?
Answer: Adequate blocking, cribbing, or pads must be used to prevent settling or shifting of the crane
OSHA 1926.1402 specifically requires adequate blocking, cribbing, or outrigger pads under outrigger floats to prevent the crane from settling or shifting during operations.