Mobile Crane Assembly and Disassembly Flashcards

A crane's heaviest loaded outrigger reads 210,000 lbs. The geotechnical report lists an allowable soil bearing capacity of 3,500 psf, and the site engineer requires a safety factor of 1.5 applied against that allowable. What is the MINIMUM outrigger pad area required?

Answer: 90 sq ft

When a safety factor of 1.5 is applied to the allowable bearing capacity, the effective design allowable is reduced: 3,500 psf ÷ 1.5 = 2,333 psf. The required pad area is then 210,000 lbs ÷ 2,333 psf ≈ 90 sq ft. Many candidates skip the safety factor step and calculate 210,000 ÷ 3,500 = 60 sq ft, which is the trap answer. Site-specific engineering requirements always take precedence and can increase pad size beyond the raw bearing capacity calculation.

After assembling a telescoping boom crane, the LMI is verified with a calibrated test weight and found to display a reading 12% LOWER than the actual load on the hook. What is the correct course of action?

Answer: Remove the crane from service and recalibrate the LMI to manufacturer specifications before use

An LMI reading 12% BELOW actual load is the more dangerous failure mode — the display will show a safe margin when the crane is already being overloaded. This is not conservative; it allows the operator to unknowingly exceed rated capacity before the alarm triggers. ASME B30.5 requires rated capacity limiters to be calibrated per manufacturer specifications, and a 12% under-read is a disqualifying defect. The crane must be taken out of service for recalibration immediately.

During pre-assembly inspection of a lattice boom section, a technician discovers a 3-inch longitudinal crack in a chord tube at the midpoint of the section — not at a weld. Per ASME B30.5, what is the required action?

Answer: Remove the section from service; it must be repaired by a qualified person before returning to use

ASME B30.5 Section 5-2.4.1 mandates that any cracked structural member be removed from service immediately. There is no provision in B30.5 for continued operation at reduced capacity, periodic monitoring, or crack-length thresholds for structural cracks. The section must be repaired by a qualified person and re-inspected before being returned to service. Operating with a cracked chord tube risks sudden, catastrophic boom collapse.

During lattice boom assembly, workers need to thread the load line through boom-tip sheaves, but the anti-two-block (ATB) device prevents the block from reaching the tip for reeving. A qualified person determines that temporarily deactivating the ATB is necessary. Under OSHA 1926.1416, this deactivation is permissible ONLY when which condition is met?

Answer: No load is on the hook, the operator is specifically informed of the deactivation, and the device is reactivated immediately after reeving is complete

OSHA 1926.1416(d)(1) allows a qualified person to authorize temporary deactivation of a safety device during assembly/disassembly under three conditions: (1) no load is being handled, (2) the operator is informed of the deactivation, and (3) care is taken to ensure safety. A maintenance log entry and owner signature are not required by OSHA. An observer alone does not fulfill the regulatory conditions. The ATB must be reactivated as soon as the task requiring deactivation is finished.

After completing a multi-part line reeving during crane assembly, the operator observes that the load line is crossed at the second sheave, causing the rope to contact itself. What is the correct response before making any picks?

Answer: De-reeve the entire load line and re-reeve correctly before placing any load on the rope

A crossed wire rope at a sheave creates a point of metal-to-metal contact where the rope will abrade against itself under load, causing accelerated wire breakage and unpredictable fatigue failure. No derating, lubrication, or partial fix resolves a fundamentally incorrect reeving path. The entire load line must be de-reeved and re-reeved correctly before the crane is placed in service. Shortcuts that leave the rope crossed can result in a sudden, undetected rope failure during a lift.

A mobile crane's manufacturer specifies a maximum level tolerance of 1.0% for operation at rated capacities. The only viable setup position on site measures a grade of 0.8% confirmed with a digital level. The manufacturer's load chart contains no slope-compensation tables. How should the operator proceed?

Answer: Operate at rated capacities — 0.8% is within the 1.0% manufacturer tolerance and no derating is required

The manufacturer's 1.0% level tolerance is the engineering boundary within which the crane's load charts are fully valid. A measured grade of 0.8% is inside that boundary, meaning rated capacities apply without any derating. The tolerance exists precisely to account for minor grade variations on real job sites. Applying additional derations beyond what the manufacturer specifies is unnecessary and is not required by ASME B30.5 or OSHA when the crane is within its published setup parameters. Only when grade exceeds the tolerance must work stop or special engineering be obtained.