Understanding GB/T 22437.1-2008 Crane Loads and Combinations

GB/T 22437.1-2008 is the equivalent adoption of ISO 8686-1:1989 and serves as the dedicated methodology standard for crane load calculation. During the design phase, cranes must be evaluated against the full range of loads they may experience over their service life, with structural strength and stability verification carried out under the most unfavorable load combinations. The standard applies to load calculation for all crane types and specifies the load value determination methods and combination factors for dead load, lifting load, inertia load, wind load, temperature load, and special loads.

Load Classification System

The standard divides all crane loads into three major categories. Regular loads (Class I) — loads that occur frequently during normal crane operation, including dead load (self-weight of structure and equipment), rated lifting load (maximum lifting capacity including the lifting spreader weight), start/braking inertia loads (acceleration loads from the hoisting mechanism and horizontal inertia forces from travel mechanism acceleration/deceleration), working-state wind load (calculated per local wind pressure zones and height coefficients), and skewing lateral forces (horizontal guide forces generated when the crane bridge travels with skew). Irregular loads (Class II) — loads that may occur under abnormal operating conditions, including non-working condition wind load (calculated for a 50-year return period maximum wind speed), unexpected shutdown loads, test loads, and temperature loads. Special loads (Class III) — loads that occur rarely but with severe consequences, including seismic loads, collision loads, and process-specific special loads.

Each load category uses different partial load factors, reflecting the influence of load occurrence probability and duration on structural safety. Class I loads use partial factors of 1.0–1.3 (1.0 for fatigue calculation), Class II loads use 1.0–1.1, and Class III loads use 1.0. A larger partial load factor indicates greater load unpredictability and higher safety redundancy requirements. The standard emphasizes that design personnel must correctly identify the load category during calculation — Class II loads must not be reclassified as Class I to reduce safety requirements, nor should Class I loads be treated as Class II, which would lead to overly conservative and wasteful design.

Load Combination Rules

Load combination is the core content of the standard. The standard specifies three load combination cases — A, B, and C: Combination A — working condition without wind (used for fatigue strength calculation and motor power verification), comprising dead load + lifting load + inertia load + skewing lateral force, with a safety factor of 1.50 (fatigue) / 1.25 (local fatigue). Combination B — working condition with wind (used for static strength calculation), adding the working-state wind load to Combination A, with a safety factor of 1.34. Combination C — non-working condition (used for anti-overturning stability and wind safety verification), comprising dead load + non-working condition wind load or other special loads, with a safety factor of 1.15.

Specific load value determination rules within each combination: dead load is calculated from the actual weight of the structure; lifting load includes the rated lifting capacity plus the weight of the lifting spreader assembly, multiplied by the dynamic load factor φ2 (1.0–1.2); the lifting-off-ground impact allowance φ1 is taken as 1.1–1.3. Inertia loads are calculated from the acceleration/deceleration rates and moving masses of each mechanism: the inertia force of the hoisting mechanism is φ5 × lifting load (φ5 being the variable-speed drive dynamic load factor), while the inertia force of the travel mechanism is travel mass × travel acceleration. Wind loads are calculated per the wind pressure zone map and height coefficients in Appendix A of the GB/T 3811 Crane Design Standard. Skewing lateral forces are calculated using the empirical formula F = λ × ΣP (where λ is the lateral force coefficient and ΣP is the total wheel load). Design personnel should select the most unfavorable load combination based on the crane's actual service conditions.

Dynamic Load Factors: Values and Applicable Conditions

The dynamic load factors (φ coefficients) specified in the standard are critical parameters in load calculation. Correctly understanding and selecting these factors is essential for design accuracy. φ1 — the hoisting-off-ground dynamic factor (1.1–1.3): when a load is rapidly lifted from the ground, the elasticity of the hoisting rope amplifies the dynamic load at the moment of lift-off. The factor value depends on lifting speed and wire rope stiffness. φ2 — the hoisting impact factor (1.0–1.2): accounts for impact during starting and stopping of the hoisting mechanism. φ3 — the sudden unloading factor (1.5–2.0): reflects extreme conditions where the load is accidentally released, such as partial wire rope breakage or load detachment from the hook. φ4 — the travel impact factor: depends on rail joint conditions and travel speed; for butt-jointed rails, values range from 1.1 to 1.3. φ5 — the variable-speed drive dynamic factor: used for calculating inertia forces during starting and braking of the hoisting mechanism. φ6 — the test load dynamic factor (1.0–1.1): applied in load calculations for the dynamic load test.

Selection of dynamic load factors should be determined by combining the crane's service conditions, work duty classification, and load characteristics. For example, ladle cranes have a higher probability of sudden unloading than standard cranes, so φ3 should be taken at the higher end of its range. Harbor cranes, which operate frequently and encounter numerous rail joints, should use the upper limit for φ4. For cranes in work duty classes A7 through A8, the dynamic load factors should be approximately 10%–15% more conservative than those for classes A1 through A3. The standard also emphasizes that multiple dynamic load factors should not all be taken at their maximum values simultaneously; instead, a reasonable combination should be selected based on actual service conditions. Kelude Heavy Industry strictly follows the standard when selecting dynamic load factors in design calculations and verifies each factor against the user's actual operating conditions.

Load Combination Cases and Coefficient Comparison Table

The comparison table below summarizes the loads included, safety factors, and applicable calculation types for three load combination cases. Design personnel should select the appropriate case based on the crane's actual work duty classification and operating environment.

Wind Load Calculation Methods

Wind load is a critical environmental load in crane design calculations. The standard specifies that wind load shall be calculated per the method in GB/T 3811 Crane Design Standard, Appendix A: working-state wind pressure is taken as 150–250 Pa (depending on the regional wind pressure zone), while non-working-condition wind pressure is based on the local 50-year return period maximum wind speed. The wind load formula is Fw = Cw × p × A, where Cw is the wind force coefficient (depending on structural shape and wind shielding reduction), p is the wind pressure, and A is the projected windward area of the structure. For lattice structures, the windward area must be calculated using the wind shielding reduction factor. The standard also requires that gust effects be considered in non-working-condition calculations — a gust response factor β of 1.6–2.0 is applied to account for the amplifying effect of wind turbulence on the structure. Tall structures such as Tower Cranes exhibit more pronounced gust response and should use higher values within this range. Wind pressure in coastal and open terrain areas is approximately 15%–25% higher than in urban inland areas; the design must be based on the wind pressure zone at the crane's actual installation position.

The standard also emphasizes special handling of several wind load calculation scenarios: for non-working conditions, the crane's windward area should be calculated for the most unfavorable direction, including the projected area of the slewing portion at different Slewing angles. For cranes with slewing capability, the Hook and Trolley should be positioned to minimize wind load in non-working conditions — typically, the Trolley is moved close to the Tower mast and the Hook is raised to its highest position. The clamping force or anchoring force of anti-wind safety devices (Rail clamp, Anchor device, Windproof Cable, etc.) shall be calculated at 1.25 times the non-working-condition wind load to ensure the crane will not slide or overturn under extreme wind speeds.

FAQ: Wind Load & Load Combination Essentials