Load Charts & Hydraulic Cranes
2 hours
Learning Objectives
- •Explain the four variables in every crane load chart: boom length, load radius, configuration (on outriggers vs. on tires), and direction of lift
- •Identify how outrigger position affects rated capacity on a telescoping-boom crane
- •Describe the difference between a rated capacity and gross capacity, and why you must never exceed the chart
- •Apply a sample load chart to determine whether a given lift is within capacity
Topics Covered
- •Load chart basics: the legal document that defines maximum allowable loads for every crane configuration
- •Four key variables: boom length, load radius (horizontal distance from center pin to load), load angle, and configuration
- •Configuration column: on outriggers fully extended vs. outriggers mid-extended vs. on tires (rubber)
- •Why on-rubber capacity is drastically lower than on-outrigger capacity
- •How to calculate working radius: measure from center of rotation to center of hook (not boom tip)
- •Deductions from gross capacity: block weight, hook weight, slings, rigging hardware — all reduce net capacity
- •Percentage-of-capacity warnings: OSHA 1926.1417 requires brake test when lifting at 90% or more of line pull
- •Manufacturer's load chart must be present in the cab at all times (OSHA 1926.1417)
- •Electronic vs. paper load charts: if electronic system fails, cease operations until restored
- •Interpolating between chart entries: always use the more conservative (lower) value
- •Why exceeding the load chart by even 1% can trigger a tip-over — crane stability margins are not generous
Resources
Self-Check Questions
Question 1: A load chart shows a capacity of 18,000 lbs at 30-foot radius on outriggers fully extended. Your rigging hardware (hook block, wire rope, slings) weighs 800 lbs. What is your maximum net load?
- A. 18,000 lbs
- B. 17,200 lbs(correct)
- C. 18,800 lbs
- D. 16,200 lbs
Show Explanation
Explanation:
The load chart gross capacity of 18,000 lbs includes everything on the hook — rigging and the load itself. Subtract the 800 lb rigging weight to get a net load capacity of 17,200 lbs. Never confuse gross chart capacity with net lifting capacity.
Question 2: Your boom is at 50-foot length. The load chart shows 12,000 lbs capacity at 20-foot radius and 9,000 lbs at 25-foot radius. Your estimated working radius is 22 feet. What rated capacity should you use?
- A. 12,000 lbs — use the nearest chart entry
- B. 10,500 lbs — interpolate midway between the two values
- C. 9,000 lbs — always use the more conservative (lower) value when interpolating(correct)
- D. 11,000 lbs — interpolate at the appropriate proportion
Show Explanation
Explanation:
When your working radius falls between two load chart entries, always use the lower (more conservative) capacity value. Interpolating may feel precise, but crane stability does not follow a perfectly linear curve — the conservative value protects you.
Question 3: Under OSHA 1926.1417, what must the operator do before picking up a load that is 90% or more of the maximum line pull rating?
- A. Notify the site superintendent
- B. Test the brakes by lifting the load slightly and applying the brakes before proceeding(correct)
- C. Extend the outriggers an additional six inches for safety margin
- D. No special procedure is required below 100% of rated capacity
Show Explanation
Explanation:
OSHA 1926.1417 requires a brake test — lift the load just off the ground, hold it, apply the brakes, and verify they hold before continuing the lift. This check ensures the brake system can control the load before you are committed to a full lift.
Question 4: Why does the on-rubber (on-tires) capacity column show significantly lower rated capacities than the on-outriggers column?
- A. Tires are more expensive to replace, so manufacturers reduce ratings to limit tire stress
- B. On rubber, the crane's stability footprint is limited to the tire contact area; outriggers create a much wider, more stable base(correct)
- C. OSHA requires a 50% reduction for all on-rubber lifts regardless of stability
- D. The hydraulic pump output is reduced when traveling on tires
Show Explanation
Explanation:
Crane stability is determined by the relationship between the load moment and the overturning moment. Outriggers extend the machine's footprint dramatically, increasing resistance to tip-over. On rubber, only the tire stance width resists tipping — a much narrower footprint, hence much lower rated capacities.
Question 5: The crane's electronic load management system fails in the middle of a lift sequence. What must the operator do according to OSHA 1926.1417?
- A. Continue operating carefully using memory of prior lifts and visual estimates
- B. Continue if a competent person visually monitors the lift
- C. Cease operations requiring the failed load information until the system is restored(correct)
- D. Switch to a hand-held calculator and the paper backup chart
Show Explanation
Explanation:
OSHA 1926.1417 states that if electronic load information systems fail, the operator must cease the operations requiring that information until the system is restored. A paper chart is acceptable as an alternative only if it is in the cab and covers the specific configuration — not all cranes carry complete paper backups.
Question 6: When measuring working radius for load chart lookup, where does the measurement begin?
- A. From the front face of the boom at ground level
- B. From the center of the boom tip sheave
- C. From the center of the crane's rotation (center pin) to the center of the hook(correct)
- D. From the front outrigger pad to the center of the hook
Show Explanation
Explanation:
Working radius is always measured horizontally from the center of the crane's rotation (the king pin or slew center) to the point directly below the hook — not from the boom tip, not from the front of the machine. An error of even two feet in radius can place you in a lower capacity column.