Load Charts and Capacity Calculations Flashcards
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Read the first 7 Load Charts and Capacity Calculations flashcards as text
A crane's load chart has a note stating 'capacities based on freely suspended load.' What does this mean for the operator?
Answer: The load must hang free and clear, not be dragged, side-loaded, or restrained by tag lines under tension
Load charts assume the load hangs freely under gravity with no horizontal forces; side loading, dragging, or taut tag lines impose additional forces not accounted for in the rated capacities.
What is the primary purpose of derating factors listed in some load charts for wind conditions?
Answer: Wind creates a horizontal force on the load and boom that increases effective radius and structural stress, reducing safe capacity
Wind exerts a horizontal force on the load and boom, increasing the effective overturning moment and reducing the crane's safe lifting capacity.
A lattice boom crane load chart shows a blank (no value) at a specific boom length and radius combination. What does this mean?
Answer: The combination is not permissible — the crane cannot safely operate at that boom length and radius
A blank cell on a load chart means the crane manufacturer has determined that operating at that configuration is not safe, and no lift may be performed in that configuration.
How does adding a superlift or backhitch attachment typically affect a crane's load chart capacities?
Answer: It increases capacity, especially at longer radii, by providing additional stability and structural support to the boom
A superlift or backhitch counteracts boom bending and tipping moment, allowing the crane to lift heavier loads at radii that would otherwise be limiting.
A crane load chart footnote states 'these ratings apply only when the crane is level within 1% of grade.' The site has a 2% grade. What is the correct action?
Answer: Level the crane using cribbing or grading until it is within the 1% specification before using the load chart
The load chart is only valid under the conditions stated in the footnotes; the crane must be leveled to within specification before the chart capacities apply.
On a hydraulic truck crane load chart, what is typically meant by the notation 'on rubber' in a capacity column?
Answer: The crane is traveling on its tires with outriggers retracted and stowed, using only the tires for support during the lift
'On rubber' means the crane is lifting while supported only by its tires with outriggers not deployed, which significantly reduces rated capacity due to lower stability.
A crane operator needs to make a lift at a 45-foot radius, but the load chart only shows values for 40-foot and 50-foot radii. What is the correct procedure?
Answer: Use the capacity listed for the 50-foot (greater) radius, as it is the more conservative value
When the actual working radius falls between chart values, the operator must use the capacity listed for the next greater (larger) radius, which is the more conservative and safer value.