Understanding GB/T 36033-2018 Crane Stability Requirements
GB/T 36033-2018, "Cranes — Stability Requirements — General Principles," is the governing standard for anti-overturning stability verification of cranes. The standard defines the basic stability requirements, calculation principles, load cases, and acceptance criteria applicable to all crane types, and is equivalent to ISO 12210-1:2005 (MOD). It applies to the design verification of stability for overhead, gantry, tower, mobile, and portal cranes.
GB/T 36033-2018 establishes the general stability requirements for cranes, specifying the calculation methods and verification conditions for anti-overturning stability across all crane types. Stability is a core safety indicator in overall crane design, directly governing the machine's resistance to overturning under both rated operating conditions and non-working states.
Basic Principles of Stability Calculation
GB/T 36033-2018 specifies that the fundamental principle of crane stability calculation is the equilibrium between the overturning moment (Moverturning) and the stabilizing moment (Mstabilizing) under all applied loads. The stability acceptance criterion is that the ratio of stabilizing moment to overturning moment — defined as the stability factor K — must not be less than the required safety factor. The stability factor is calculated as K = Mstabilizing / Moverturning ≥ Kmin, where Kmin is the minimum stability factor, ranging from 1.25 to 1.5 depending on the load case. The stabilizing moment is generated by the crane's dead weight (including counterweights and ballast) acting about the tipping edge, while the overturning moment results from the lifting load, wind load, inertia load, and slope load acting about the same edge. Calculations must consider the crane's most critical overturning condition — that is, the most unfavorable load combination and overturning direction. The standard classifies crane instability into two types: complete overturning (the entire crane rotating about the tipping edge) and local instability (such as one outrigger lifting off the ground or tower mast buckling). For overhead and gantry cranes, stability verification covers both the direction of bridge travel (along the crane rail) and the transverse direction (perpendicular to the rail).
Load Cases and Combinations
The standard defines the following stability verification load cases: Load Case 1 — Working condition without wind (normal operation): applied loads include dead weight, rated lifting load, and inertia loads (vertical inertia force from hoisting mechanism start/stop and horizontal inertia force from travel mechanism start/stop). Minimum stability factor Kmin = 1.5. Load Case 2 — Working condition with wind (normal operation under wind): applied loads include dead weight, rated lifting load, inertia loads, and wind load (working-state wind pressure of 250 Pa, corresponding to Beaufort scale 7 at 20 m/s). Minimum stability factor Kmin = 1.33. Load Case 3 — Non-working condition with wind (parked crane subjected to maximum wind load): applied loads include dead weight and non-working wind load (800 Pa wind pressure for inland regions, corresponding to 36 m/s; 1,500 Pa for coastal regions, corresponding to 50 m/s). Minimum stability factor Kmin = 1.25. Load Case 4 — Erection/dismantling condition: applied loads are determined by the erection plan; minimum stability factor Kmin = 1.25. The standard further requires that for cranes handling molten metal, the stability factor for all load cases must be increased by 10% (i.e., multiplied by a factor of 1.1).
Determination of the Tipping Edge
The standard provides detailed methods for determining the tipping edge for each crane type: Overhead cranes — the tipping edge is the contact line between the crane bridge wheels and the crane rail. For a four-point (four-wheel) overhead crane, the tipping edge is the wheel axle line on the side being lifted (i.e., the line connecting the two wheels on the same side). Because overhead cranes are constrained by the rails inside a factory building, complete overturning is generally not expected under normal conditions — however, research indicates that overturning remains possible under extreme wind events (e.g., rail displacement caused by building collapse) or seismic action, and manufacturers should provide wind stability data to users. Gantry cranes — the tipping edge in the direction of bridge travel is the line connecting the travel wheels on one side of the portal frame; the transverse tipping edge is the line connecting the walkway guardrail and the outrigger leg on the main girder side (the tipping fulcrum being the bottom of the cross beam or outrigger leg). For outdoor gantry cranes, wind load creates two distinct safety concerns — overturning and sliding. Overturning is governed by the stability factor, while sliding is controlled by rail clamps or anchor devices. Tower cranes — the tipping edge is the line along the edge of the concrete foundation or the line connecting the bottom of the outrigger legs where the tower mast connects to the foundation. Stability is the most critical safety parameter in tower crane design — because of their high center of gravity and large wind-exposed area, tower cranes are the crane type most susceptible to overturning accidents. Kelude strictly implements GB/T 36033 stability verification in the design of overhead and gantry cranes.
Anti-Overturning Measures
The standard recommends the following measures to improve crane stability: Increase dead weight — add counterweights at the crane base or counterweight position to increase the stabilizing moment. For tower cranes, properly sizing and positioning the ballast is the fundamental means of ensuring stability. Reduce wind-exposed area — optimize the crane's structural profile (using streamlined or open-lattice designs) to reduce wind load forces. Widen outrigger spacing — for mobile cranes, increasing the transverse and longitudinal outrigger span significantly improves the transverse stability factor (a 10% increase in outrigger span can yield approximately a 15% increase in the stability factor). Install anti-overturning devices — fit anti-overturning hooks (anti-derailment devices) on both sides of rail-mounted cranes so that wheels cannot lift off the rail even under extreme wind loads. Strengthen the foundation — the foundation dimensions and depth of tower cranes must be verified against the bearing capacity of foundation to ensure the foundation itself cannot overturn under the overturning moment. Operational precautions — strictly prohibit overload operation; avoid sudden starts and hard braking during operation (inertia loads increase the overturning moment); after work, slew the boom to face the wind direction and release the slewing brake (allowing the boom to weathervane freely reduces wind load); and take pre-emptive anchoring measures when a storm warning is issued.
| operating conditions | Kmin | Included Load | Verification Purpose |
|---|---|---|---|
| No-Wind Operation | 1.5 | Dead Weight+Rated+Inertia | Normal Operating Safety |
| Windy Operation | 1.33 | Dead Weight+Rated+Inertia+wind load | Windyoperating conditions Safety |
| non-working condition | 1.25 | Dead Weight+Extremewind load | Maximum Wind Resistance Capacity |
| erection and dismantling | 1.25 | Dead Weight+installation Load | Construction Process Safety |
FAQ: Crane Stability Essentials
Q: What are the basic principles behind crane stability verification?
A: Crane stability is governed by the principle of moment balance: the stabilizing moment (generated by the crane's dead weight) must exceed the overturning moment (caused by the suspended load and wind load). The stability factor K is calculated as stabilizing moment ÷ overturning moment. Standards require K ≥ 1.15 in working condition and K ≥ 1.25 in non-working condition (based on regional maximum wind speed). For mobile cranes, outrigger support conditions and ground load-bearing capacity must also be considered. Stability verification should use the most unfavorable load combination — maximum lifting capacity + maximum working radius + working wind load.
Q: Which factors affect a crane's anti-overturning stability?
A: The key factors are: 1) Crane dead weight and center of gravity position — greater dead weight and a lower center of gravity improve stability; 2) Lifting capacity and working radius — larger loads and greater radii increase the overturning moment; 3) Wind load — wind pressure is proportional to the square of wind speed, and in strong winds can account for 30%–50% of the overturning moment; 4) Rail inclination — both longitudinal and transverse slopes on crane rails reduce the effective stabilizing moment; 5) Foundation load-bearing capacity — ground settlement or deformation can cause the crane to tilt. Standards require all these factors to be fully considered in stability calculations.
Q: What special stability requirements apply to tower cranes?
A: Tower cranes demand stricter stability measures due to their high center of gravity and large wind-exposed area: 1) Ballast and counterweight must be installed per the operation manual — insufficient ballast is a leading cause of tower crane overturning; 2) In non-working condition, the boom must be free to slew (weathervane with the wind) to reduce wind load; 3) For rail-mounted tower cranes, the rail foundation must meet load-bearing requirements, with crane mat and rail slopes ≤ 1/1000; 4) For tied tower cranes, the spacing between anchorage devices and their load-bearing capacity must comply with design requirements. Kelude Heavy Industry supplies a complete stability calculation report with every tower crane at the factory.
Q: What warning signs indicate insufficient crane stability?
A: Early warning signals of inadequate stability include: 1) Abnormal inclination of the whole machine — stop operation and check foundation and rail levelness; 2) Crane wheels (or outriggers) lifting off the ground — a direct sign of critically insufficient stability; 3) Frequent alarms from the load moment limiter (LML) — indicates the operating condition is approaching or has reached the stability limit; 4) Noticeably increased sway of the entire machine in high winds — slew the boom downwind promptly to reduce wind load; 5) Visible settlement or cracking of the rail foundation — halt operations immediately and reinforce the foundation.
