NCCCO Ground Bearing Pressure and Outrigger Setup 2

Question 1

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)?

Accepted Answer

50 psi

Answer

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.

Question 2

Why must outrigger pads be used on outriggers even when working on concrete surfaces?

Accepted Answer

To spread the point load over a larger area and reduce pressure on the concrete and underlying soil

Answer

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.

Question 3

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?

Accepted Answer

Stop the lift immediately and add more cribbing or a larger pad to distribute the load

Answer

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.

Question 4

What is the primary purpose of extending outriggers to their full width before making a lift?

Accepted Answer

To maximize the crane's tipping fulcrum distance and increase rated lifting capacity

Answer

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.

Question 5

What does the term 'soil bearing capacity' refer to in the context of crane setup?

Accepted Answer

The maximum load per unit area that a soil can safely support without excessive settlement or shear failure

Answer

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.

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

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

NCCCO Ground Bearing Pressure and Outrigger Setup 2