Behind every safe and reliable crane structure lies a deep layer of engineering logic — and at the heart of this logic are load group coefficients and hoisting load coefficients. These factors help engineers account for real-world operational conditions when calculating stresses, material fatigue, and safety margins.
Whether you’re designing a portal crane for an open-pit mine or a gantry system in a logistics yard, accurate coefficient application is essential.
What Are Load Group Coefficients (φ)?
A load group coefficient represents the combined effect of dynamic loads acting on a crane based on its duty class and usage frequency. It accounts for:
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Load lifting intensity
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Repetition frequency
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Motion speed (start/stop cycles)
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Shock and impact potential
This coefficient is generally derived from classification systems such as FEM 1.001, DIN 15018, and ISO 4301. It’s applied to the nominal load to obtain the design load.
Example:
If a crane is rated at 20 tons and has φ = 1.3, then:
Design load = 20 × 1.3 = 26 tons
Hoisting Load Coefficients (ψ)
The hoisting load coefficient accounts for the dynamic behavior of the lifting mechanism, including:
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Rope acceleration
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Hook swing
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Drum inertia
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Mechanical elasticity
It reflects how the load behaves during motion, especially under sudden lifting or braking.
In practice:
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ψ values range from 1.05 to 1.6
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Higher values apply to fast-lifting or high-frequency cranes
Combined Use in Crane Calculations
The two coefficients are often multiplied together to calculate the total design force:
Total Load (F) = Nominal Load × φ × ψ
This ensures that:
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Load spikes are absorbed by design
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Fatigue limits are not exceeded
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Welded and bolted joints are safely dimensioned
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Drive systems can withstand long-term operation
Application in Mining Cranes
Mining cranes operate under:
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High vibration
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Uneven loads
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Extended duty cycles
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Harsh terrain and outdoor exposure
A crane lifting ore buckets 16 hours a day at a quarry might require:
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φ = 1.4
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ψ = 1.5
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Total design multiplier: 2.1 — more than double the nominal load
This extra safety margin prevents structural failure, reduces unplanned downtime, and aligns with regulatory expectations.
Tips for Engineers
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Always use manufacturer data or FEM guidelines to determine coefficients
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Perform case-specific coefficient evaluations — don’t generalize
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Factor in environmental dynamics (wind, slope, temperature)
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Document assumptions and coefficients clearly in calculation sheets
Crane safety begins with correct load assumptions. Load group and hoisting load coefficients are more than just numbers — they’re essential tools for bridging the gap between theoretical loads and real-world operational challenges. Especially in mining and heavy industry, accurate coefficient use defines the line between failure and flawless performance.