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Truck Crane Systems & Outriggers

2 hours

Learning Objectives

  • •Identify the major components of a truck crane with friction winch drum
  • •Explain the function and operation of outriggers and why full extension is the default requirement
  • •Describe the stability advantages and limitations of outriggers compared to on-rubber operation
  • •Identify the safety devices required on truck cranes under OSHA 1926.1415 and 1926.1416

Topics Covered

  • •Carrier (lower works): the truck chassis with power train, axles, and steering — designed for highway travel
  • •Upperstructure (superstructure): the revolving crane body with boom, drums, engine, and cab mounted on the carrier via slew ring
  • •Slew ring: large ring bearing allowing the superstructure to rotate on the carrier for 360° operation
  • •Friction hoist drums: main hoist and auxiliary (whip line) drums; mechanical friction clutch and band brake engagement
  • •Lattice boom sections: boom butt, standard inserts, and boom top — same assembly concept as crawler crane
  • •Jib (fly): an extension section pinned to the boom top to increase reach; rated separately on the load chart
  • •Outrigger beams: extendable horizontal beams that deploy from the carrier sides perpendicular to the crane centerline
  • •Outrigger jacks: vertical hydraulic cylinders at the end of each beam that lift the carrier off the tires
  • •Fully extended vs. partially extended outrigger configurations: load chart shows different capacities for each
  • •OSHA 1926.1415: required safety devices — crane level indicator, boom stops, jib stops, foot pedal brake locks, horn
  • •OSHA 1926.1416: required operational aids — boom angle/radius indicator, load moment indicator (LMI) for cranes >6,000 lb rated capacity manufactured post-March 2003, anti-two-block device for lattice boom cranes manufactured after November 8, 2011
  • •Load moment indicator (LMI): monitors the relationship between the suspended load and the crane's rated capacity; warns operator as capacity is approached
  • •Swing lock: locks the superstructure from rotating — must be engaged when traveling; must be released before lifting
  • •Outrigger float pads and cribbing: blocking placed under outrigger feet to distribute point loads across soil

Resources

OSHA 1926.1415 — Safety devices

osha

Required

OSHA 1926.1416 — Operational aids

osha

Required

Self-Check Questions

Question 1: Before operating a truck crane, the operator discovers the boom stops are inoperable. What must happen?

  1. A. The operator may proceed if a spotter watches the boom angle
  2. B. The LMI can substitute for boom stops
  3. C. Operations must stop and the crane must be taken out of service until boom stops are repaired(correct)
  4. D. The operator may use the boom angle indicator as an alternative
Show Explanation

Explanation:

OSHA 1926.1415 requires all listed safety devices to be in proper working order before operations begin. Boom stops prevent the boom from over-topping, which can cause a catastrophic boom collapse. No alternative measure is permitted — the crane must be repaired first.

Question 2: A truck crane's load chart shows 18 tons on outriggers fully extended and 9 tons on outriggers at mid-extension. You set the outriggers at mid-extension. What is your maximum rated lift?

  1. A. 18 tons, because the boom length determines the rating
  2. B. 13.5 tons, the average of the two ratings
  3. C. 9 tons — you must use the rating for your actual configuration(correct)
  4. D. 18 tons if you use a tag line to keep the load centered
Show Explanation

Explanation:

You must use the load chart column that matches your actual configuration. Mid-extension outriggers provide less overturning resistance than fully extended outriggers. Lifting 18 tons on mid-extended outriggers would be an overload of the configuration actually in use.

Question 3: What is the primary purpose of the load moment indicator (LMI) on a crane?

  1. A. It automatically stops the crane if the load exceeds rated capacity
  2. B. It monitors the relationship between the lifted load and rated capacity and alerts the operator as limits are approached(correct)
  3. C. It measures the exact weight of the load in pounds
  4. D. It controls the speed of load lowering to prevent two-blocking
Show Explanation

Explanation:

The LMI (or load moment limiter in its limiting version) monitors load moment — the product of the load and radius — and compares it to the rated capacity curve. It warns the operator as capacity is approached. Some limiters also shut off hoist and boom functions at rated capacity, but the fundamental purpose is monitoring and warning.

Question 4: When must the swing lock on a truck crane be engaged?

  1. A. Only when the crane is parked overnight
  2. B. Whenever the crane is traveling on a road or job site(correct)
  3. C. Only when the boom is fully retracted
  4. D. Whenever wind speed exceeds 20 mph
Show Explanation

Explanation:

The swing lock locks the superstructure from rotating relative to the carrier. It must be engaged whenever the crane travels — on public roads or on a job site — to prevent the boom from swinging and destabilizing the machine. Always verify it is released before any lifting operation begins.

Question 5: Under OSHA 1926.1416, lattice-boom cranes manufactured after November 8, 2011 must be equipped with what device?

  1. A. A load weighing device that displays the load in pounds
  2. B. An automatic anti-two-block device at all points where two-blocking could occur(correct)
  3. C. A digital boom angle display readable at 50 feet
  4. D. A wind speed monitor that shuts down operation above 25 mph
Show Explanation

Explanation:

OSHA 1926.1416 requires lattice-boom cranes manufactured after November 8, 2011 to have an automatic device that prevents damage from two-blocking at all potential two-block points. For older equipment, alternative measures such as marking the hoist line and using a spotter are permitted.

Question 6: Outrigger pads and cribbing are used under outrigger floats for which primary purpose?

  1. A. To protect the outrigger jacks from hydraulic oil leaks
  2. B. To distribute the concentrated outrigger point load over a larger soil area, reducing ground bearing pressure(correct)
  3. C. To prevent the outriggers from sinking during travel
  4. D. To level the crane when the ground is slightly sloped
Show Explanation

Explanation:

Each outrigger concentrates the entire supported crane corner load through a relatively small float contact area. Pads and cribbing increase the contact area under that float, spreading the force over more soil and reducing the pounds-per-square-foot ground bearing pressure to a level the soil can safely support.

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