ISO 8686-4:2005 Gantry Crane Load Combination Guide

Load Classification and Design Values

Permanent loads G (dead weight, fixed equipment, crane rail), variable loads Q (suspended load, wind load, snow load, impact, temperature), and accidental loads A (earthquake, collision). The operation wind pressure is 250 N/m², with a 50-year return period extreme value for out-of-service conditions. The dynamic load factor ranges from 1.1 to 1.3, and the running impact allowance from 1.1 to 1.3. Gantry-specific loads include outrigger skew loads (height difference ≤ S/1000), rail clamping force (10% of wheel load), and horizontal load from load swing (5%–10% of the suspended load).

Load Combination Method

For in-service basic combinations: γG × G + γQ × Q + ψW (γG = 1.2, γQ = 1.5, ψ = 0.6–0.7). For out-of-service conditions: G + Wmax (γG = 1.0, γW = 1.0). For erection: G + Q × 1.3. For accidental conditions: G + A + ψQ (ψ = 0.5). In all combinations, the design stress σd must satisfy σd ≤ fd / γM (steel γM = 1.0–1.1, weld seam γM = 1.15–1.25). The gantry structure is checked for overall stability, and the outriggers for local stability.

Foundation and Crane Rail Inspection

Foundation settlement is measured every six months, with annual settlement limited to ≤5 mm and differential settlement to ≤1/1000. Crane rails undergo monthly inspection, covering wear (≤5 mm), span deviation (±5 mm), and joint gaps (1–2 mm). Bolts are checked for torque monthly, and grounding resistance is verified every six months to stay within ≤4 Ω.

The core of gantry crane structural design lies in accurately determining load effects and establishing rational load combinations for each operating condition. The permanent load G includes the self-weight of the main girder (derived from structural self-weight calculations — steel density 7850 kg/m³, multiplied by the cross-sectional area and length of each component and summed), the self-weight of the trolley and hoisting mechanism (actual weights provided by the manufacturer), the self-weight of the crane rail and its fastenings (calculated as the unit weight of the rail type × length), and the self-weight of the walkway, platform, and electrical equipment. When calculating structural internal forces, the partial safety factor for permanent loads γG is taken as 1.2 (where the load effect is unfavorable to the structure — cases that amplify effects such as mid-span bending moment in the main girder or axial compression in the outriggers) or 1.0 (where the load effect is favorable to the structure — cases that reduce effects such as overturning stability or anchoring reactions).

Wind load calculation under variable loads Q must account for multiple factors. The characteristic value of wind pressure in the working condition is taken as 250 N/m² (corresponding to a wind speed of approximately 20 m/s, Beaufort scale 7–8). For the non-working condition, the wind pressure is based on the extreme wind speed with a 50-year return period for the local area (which can reach up to 1500 N/m² in coastal regions, while inland areas typically range from 500 to 800 N/m²). In the wind load formula Fw = C × q × A, the wind force coefficient C is determined by the cross-sectional shape of the component — 1.3 to 1.6 for box girders (rectangular cross-section), 0.7 to 1.0 for tubular trusses (circular tubes), and 1.0 to 1.3 for outriggers (I-shaped or box-shaped). The windward area A is calculated as the projected area of the actual component profile multiplied by a fill factor of 0.4 to 0.6 (accounting for voids in lattice and truss-type structures). Wind pressure varies with height above ground — increasing by 2% for every 10 m of elevation gain.

FAQ: Gantry Crane Load Design Essentials