Mobile Crane Load Combinations per GB/T 22437.2-2010
GB/T 22437.2-2010 "Cranes — Loads and Load Combinations — Part 2: Mobile Cranes" is the foundational load-analysis standard for the structural design of mobile cranes. The standard specifies the various loads and their combinations to be considered in the design calculations of mobile cranes, including truck cranes, crawler cranes, and all-terrain cranes, and is identical to ISO 8686-2:2004 (IDT). Correct application of load combinations is essential to ensuring both the structural safety and cost-effectiveness of mobile cranes.
GB/T 22437.2-2010 is Part 2 of the crane loads and load combinations series, establishing load classification and combination rules tailored to the load characteristics of mobile cranes. Mobile cranes present unique load cases—such as outrigger reactions and jib deflection—that make their combination calculations more complex than those for general-purpose cranes. This article provides a systematic interpretation of the standard.
Scope and Application of the Standard
GB/T 22437.2-2010 is Part 2 of the crane loads and load combinations series, developed specifically for the structural design load calculations of mobile cranes, including truck cranes, crawler cranes, all-terrain cranes, rough-terrain cranes, and telescopic-boom crawler cranes. The standard identifies the various load types a mobile crane may experience over its design life, specifies the combination factors and methods for different operating conditions, and provides a unified load basis for the strength, stiffness, and stability calculations of structural components. It applies to mobile cranes with a rated lifting capacity of not less than 1 t and, together with GB/T 22437.1 (general principles) and GB/T 3811 Crane Design Standard, forms a complete load system for crane structural design.
Load Classification System for Mobile Cranes
The standard classifies the loads acting on a mobile crane into the following categories:
Main loads (P) — including the lifting load (rated lifting capacity, weight of the lifting spreader, suspended wire rope mass, etc.), dead weight (mass of the crane structure, mechanisms, counterweight, operator cab, and attachments), hoisting impact load (additional vertical dynamic action on the structure during starting and braking of the hoisting mechanism), and fixed loads in the non-working condition (such as counterweight and ballast).
Additional loads (A) — including wind load (for both working-state and storm conditions), temperature load (thermal stress in the steel structure due to ambient temperature differences; to be considered when the temperature difference between structural components exceeds 25°C), snow and ice load (for cranes operating in regions where icing may occur), and slope load (load components resulting from the crane standing or working on uneven ground).
Special loads (S) — including test loads (1.25 times the rated load for the static load test and 1.1 times the rated load for the dynamic load test), buffer collision loads, erection and dismantling loads (loads generated during crane assembly and disassembly), and transport loads (inertia forces and vibration experienced during crane transportation).
Dynamic and impact allowances — Given the frequent changes in operating state and the frequent hoisting and luffing actions of mobile cranes, the standard provides specific values for the hoisting dynamic coefficient (φ₂ = 1.0–1.4, selected according to the hoisting speed grade), the travel impact allowance (φ₃ = 1.0–1.4, selected according to the travel surface class and travel speed), and the luffing dynamic coefficient.
Graded by lifting speed
Selected by surface class
Storm condition per region
Dynamic: 1.10 × rated
≤5° for transport
Load Combination Types and Load Cases
The standard defines three basic operating conditions for mobile cranes and their corresponding load combinations:
Load case A — Normal working condition (no wind): Load combination P, comprising the dead weight and lifting load under steady motion, plus inertia loads with starting and braking dynamic coefficients. This case is used for the structural strength verification of mobile cranes in the non-working condition (stationary) or under light wind conditions. The safety factor is taken as n ≥ 1.22 (relative to yield strength).
Load case B — Working condition with wind: Load combination P + A, superimposing the working-state wind load on the main loads. The allowable working wind speed for mobile cranes is generally Force 7 (17 m/s) or below; operations shall be stopped and the boom retracted when this speed is exceeded. This is the most common load state for mobile cranes and is used for the strength calculation of main structural components such as the jib system, slewing bearing, outriggers, and undercarriage. The safety factor is taken as n ≥ 1.22.
Load case C — Storm, non-working condition: Load combination P + storm A, used to verify the crane's ability to withstand storms in the non-working condition (with the boom retracted and the crane properly secured). The storm wind speed is determined by the crane's operating region, generally calculated as the maximum wind speed with a 50-year return period for the local area. Under storm conditions, recoverable elastic deformation of structural components is permitted, but permanent deformation or loss of stability is not. The safety factor is taken as n ≥ 1.10 (relative to yield strength).
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| Crane Type | Typical Capacity Range | Common Applications |
| Single-Girder Overhead Crane | 1 – 20 tons | Workshops, maintenance bays, light assembly |
| Double-Girder Overhead Crane | 5 – 150 tons | Heavy fabrication, steel yards, power plants |
| Gantry Crane | 5 – 300 tons | Outdoor yards, precast concrete, shipyards |
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Q: What is the typical lead time for a standard overhead crane?
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| operating conditions | load groupcomplete | wind loadconditions | Safety factor | applicableverification |
|---|---|---|---|---|
| A | normal no-wind | P(main loads) | normal no-wind | n≥1.22 | static parking/light breeze |
| B | working with wind | P+A(includingwind load) | ≤7class(17m/s) | n≥1.22 | Boom/Slewing/Outrigger |
| C | storm non-working | P+storm A | per50return period of X years | n≥1.10 | Anti-overturning/anti-instability |
| special | Test | P×Test Coefficient | ≤5wind class | n≥1.05 | Type Test |
Special Load Cases for Mobile Cranes
Compared to overhead bridge cranes, mobile cranes are subject to a wider range of load cases that must be carefully evaluated during design and selection.
Outrigger Reaction Load Case — Mobile cranes transfer their dead weight and the working load to the ground through outriggers. Outrigger reaction calculations must account for load position changes during slewing and hoisting operations. The most unfavorable outrigger position is used to determine the maximum outrigger pressure, which then drives the structural and hydraulic system strength design. The standard specifies the load combination factors to be applied when calculating outrigger reactions.
Overturning Moment Load Case — This is the most critical load combination for mobile cranes. The ratio between the load moment and the stabilizing moment from the crane's dead weight determines the crane's anti-overturning capability. The standard requires that, under load cases A and B, the stabilizing moment must exceed the overturning moment by a factor of 1.25 (excluding ballast) or 1.15 (including ballast). For crawler cranes, the effect of ground bearing pressure on stability must also be considered.
Telescopic Boom Deflection Load — The extending sections of a mobile crane boom undergo flexural deformation under load, causing the hoisted load to deviate from the boom centerline and generating an additional deflection moment. The standard requires that the horizontal deflection at the boom tip be included in the load combination calculation, typically taken as 1% to 2% of the boom length.
Transport and Travel Loads — Mobile cranes in travel mode are subjected to vibration and impact loads induced by road surface irregularities. The standard specifies a travel impact allowance of 1.3 to 1.5, depending on road surface grade. For tyre cranes, the vibration-damping effect of the tyres must also be taken into account. At Kelude Heavy Industry, load spectrum files are compiled for mobile crane structural design in strict accordance with ISO 4301, and finite element analysis verification is performed for every load case before the structural configuration is finalized.
Mobile Crane Load Combination Comparison Table
The comparison table below summarizes the core parameters for mobile crane load combinations, for reference by selection and operation personnel.
| Load combination | Loadfactor | Coefficientvalue | applicable working conditions |
|---|---|---|---|
| combinationⅠ | Dead Weight+rated load+wind load | φ=1.0 | normal operation |
| combinationⅡ | Dead Weight+test load+wind load | φ=1.25 | Type Test |
| combinationⅢ | Dead Weight+wind load(working condition) | regional wind pressure | working condition |
| combinationⅣ | Dead Weight+wind load(non-working condition) | per50return period of X years | non-working condition |
