NCCCO Ground Bearing Pressure and Outrigger Setup 5 — Questions and Answers
Question 1: When a crane is set up on a slope, which outrigger typically carries the greatest load?
- The uphill outrigger on the low side
- The downhill outrigger on the low side (Correct answer)
- All outriggers share equal loads regardless of slope
- The front outrigger regardless of slope direction
Correct answer: The downhill outrigger on the low side
The downhill (low-side) outrigger carries the highest reaction load because the crane's center of gravity shifts toward the lower side on a slope.
Question 2: What is 'mat bearing pressure' in the context of crane setup?
- The pressure exerted on crane tracks by the travel drive motors
- The distributed ground pressure beneath a timber or steel mat used to support outriggers or crawlers (Correct answer)
- The hydraulic pressure in the outrigger extension cylinder
- The surface contact pressure between boom sections
Correct answer: The distributed ground pressure beneath a timber or steel mat used to support outriggers or crawlers
Mat bearing pressure is the load per unit area transmitted to the ground through a mat system used to spread crane outrigger or crawler loads.
Question 3: A crane manufacturer requires outrigger pads to be used whenever the crane is set up on outriggers. An operator decides to skip pads on a paved parking lot. This is:
- Acceptable because pavement is always stronger than soil
- Acceptable if the lift is under 50% of chart capacity
- Unacceptable; manufacturer requirements must be followed regardless of surface type (Correct answer)
- Acceptable with the rigger's verbal approval
Correct answer: Unacceptable; manufacturer requirements must be followed regardless of surface type
Manufacturer requirements for outrigger pads are mandatory; pavement does not exempt operators from following setup specifications.
Question 4: When outrigger beams are extended and the floats are down, what must be confirmed before beginning a lift?
- That the engine is running at full throttle
- That the crane is level within manufacturer's specified tolerance (Correct answer)
- That all workers on site are aware of the boom length
- That the load line is reeved with maximum parts of line
Correct answer: That the crane is level within manufacturer's specified tolerance
The crane must be level within the manufacturer's tolerance (typically ±1%) before lifting, as unlevel conditions shift loads and reduce stability.
Question 5: Which of the following best describes 'outrigger reaction force'?
- The force required to extend the outrigger beam hydraulically
- The downward force transmitted from the crane to the ground through each outrigger (Correct answer)
- The upward force of the ground pushing back on the crane body
- The lateral force generated when the crane slews under load
Correct answer: The downward force transmitted from the crane to the ground through each outrigger
Outrigger reaction force is the vertical downward load each outrigger transmits to the supporting surface, determined by the crane's weight, boom configuration, and lifted load.
Question 6: Why is it important to position outrigger pads under the outrigger float rather than offset to one side?
- Offset pads increase the effective bearing area
- An offset pad creates an eccentric load that can cause the float to tip off the pad under load (Correct answer)
- Offset pads are required by most crane manufacturers
- It only matters when the pad is made of wood, not steel
Correct answer: An offset pad creates an eccentric load that can cause the float to tip off the pad under load
The float must bear directly and evenly on the pad; an offset causes the float edge to dig into the pad or ground, potentially tipping the crane.
Question 7: After a heavy rain, a previously approved crane setup area should be:
- Used immediately since water improves compaction
- Re-evaluated for bearing capacity because saturation significantly reduces soil strength (Correct answer)
- Approved automatically if it passed the original inspection
- Used only if the water has visibly drained from the surface
Correct answer: Re-evaluated for bearing capacity because saturation significantly reduces soil strength
Water saturation dramatically reduces soil bearing capacity, so any previously approved area must be re-inspected and re-evaluated after significant rainfall.
NCCCO Ground Bearing Pressure and Outrigger Setup 5
When a crane is set up on a slope, which outrigger typically carries the greatest load?