NCCCO - National Commission for the Certification of Crane Operators Ground Bearing Pressure and Outrigger Setup 1

Question 1

A mobile crane has a maximum single-outrigger load of 85,000 pounds. The outrigger float measures 14 inches by 14 inches. What is the ground bearing pressure under that float?

Accepted Answer

Approximately 434 psi

Answer

Approximately 217 psi

Answer

Approximately 868 psi

Answer

Approximately 6,071 psi

Question 2

A geotechnical report lists the allowable soil bearing capacity as 2,880 pounds per square foot (psf). What is this value expressed in pounds per square inch (psi)?

Accepted Answer

20 psi

Answer

288 psi

Answer

240 psi

Answer

2.88 psi

Question 3

An outrigger exerts a downward load of 72,000 pounds. The allowable soil bearing pressure at the site is 24 psi. What is the minimum outrigger mat area required to keep ground pressure within safe limits?

Accepted Answer

3,000 square inches

Answer

1,728 square inches

Answer

6,000 square inches

Answer

1,500 square inches

Question 4

Per ASME B30.5, what is the maximum out-of-level condition permitted for a mobile crane before a lifting operation begins?

Accepted Answer

1% of grade (approximately 0.57°)

Answer

2% of grade (approximately 1.15°)

Answer

5% of grade (approximately 2.86°)

Answer

0.25% of grade (approximately 0.14°)

Question 5

Due to a congested job site, a mobile crane cannot extend its outriggers to full width and must operate with outriggers at the mid-span extension position. What is the correct procedure?

Accepted Answer

Use the manufacturer's load chart for the mid-span (intermediate) outrigger extension setting

Answer

Reduce all load chart capacities by a flat 25% regardless of the chart

Answer

Operate only over the front of the crane where capacity is highest

Answer

Full outrigger extension is mandatory — no lift may be made at partial extension

Question 6

When placing timber cribbing beneath an outrigger pad, which characteristic of the cribbing is MOST critical for safe load distribution?

Accepted Answer

Sufficient total bearing area and structural capacity to spread the load without crushing or buckling

Answer

The cribbing must be painted or coated to resist moisture absorption

Answer

Individual timbers must be oriented with grain running vertically

Answer

Cribbing height must not exceed 6 inches to maintain stability