A gantry crane is specified by five hard parameters — rated load (t), span (m), lifting height (m), travel length (m) and FEM/ISO duty group — and selection starts with locking the load chart before any structural or vendor decision is taken [S3].
The equipment family splits into single-girder (typically 1–20 t, span up to ~30 m), double-girder (5–500 t, span up to ~50 m), semi-gantry (one leg on a runway, one on the floor) and portable/ aluminium gantry (0.5–10 t, fully relocatable) — each matches a different site constraint [S3][S5]. Container-handling gantry cranes (STS/RTG-class) shown on shipyard catalogues open at 30 t under-hook and run super-post-Panamax in port use [S5].
Rated Load and Load-Chart Discipline
Rated load is the maximum SWL the crane can lift at any hook position across the full span — capacity at mid-span equals 100% of nameplate, while capacity at the ends of the travel typically remains 100% but the trolley radius into the corners of the working envelope reduces it on rubber-tyred units [S3].
The hoist is the thermal bottleneck: standard CD1/MD1 wire-rope electric hoists are rated to 60 °C, while metallurgical-grade YZ冶金 hoist motors are wound for continuous operation up to 80 °C ambient with H-class insulation [S4].
Span, Lifting Height and Clearances
Span is the centre-to-centre distance between the two gantry rails measured along the cross-travel direction; the standard envelope is 18 m, 22 m, 26 m, 30 m and 35 m for general industry, with each step adding roughly 8–12% to the steelwork mass [S3].
Lifting height is measured hook-up to floor with the hook at top of travel, and must include the headroom above the highest obstruction plus 0.5 m safety clearance for hook block swing. On outdoor sites add 0.2–0.5 m extra to the calculated height for beam deflection under full load — a 30 m single-girder span will typically deflect 1/750 to 1/1000 of span at nameplate, which translates to 30–40 mm of sag that the hook has to clear [S3].
Duty Class and FEM/ISO Group Mapping
Under-specifying the duty group by one FEM class typically halves gearbox and motor life, and is the single most common root cause of premature bearing failure on the long-travel wheels. Crane class, ambient temperature and atmospheric corrosivity feed jointly into the structural design — for example, a crane in a coastal yard must drop one FEM group (e.g. A5 → A4) when salt-spray exposure is high unless the structure is galvanised [S3][S4].
Power Supply, Travel Length and Wheel Load
Power supply options split into cable reel (≤200 m travel, low cost), busbar (longer runs, cleaner signal), and festoon (light-duty, ≤100 m); high-temperature foundries add heat-resistant cable sheathing rated to 80 °C minimum [S4].
Travel length drives the maximum wheel load that the rails or ground must carry — a 50 t single-girder crane on 22 m span with 4 wheels per side delivers about 145 kN per wheel, which dictates the rail section (typically P43 or QU70) and the runway beam sizing. For higher capacity moves the comparative logic across crane families is laid out in Truck Crane Selection: Capacity, Boom and Chassis Criteria, which contrasts boom reach and chassis mobility against the fixed-rail envelope of a gantry.
Options and Special Environment Build
Standard outdoor build adds a weathertight operator's cabin, rail sweeps and lightning protection; the open-yard tropical package adds canopy over the hoist, IP55 motors and corrosion-resistant paint (C4-M per ISO 12944) [S4].
A complete gantry crane specification is meaningless without these environment-driven options, which can swing vendor price 20–35% from the bare structure. When the duty calls for mobility rather than a fixed runway, the comparison with self-propelled lifts is mapped in Skid Steer Loader Sizing and Selection: ROC, Power and Hydraulic Bands, which sizes engine, hydraulic flow and ROC for site-prep work around the gantry foundations.
Sourcing Logic and Vendor Cluster
The 2026 supplier base for gantry cranes is concentrated in Henan (Nucleon, Weihua, Haitai) for general-industry and shipyard units, Jiangsu/Shanghai for port and STS-class container gantries, and the Korean/EU cluster (Hyundai Samho, Liebherr, Konecranes) for super-post-Panamax ship-to-shore cranes [S5].
For light- and mid-capacity indoor gantries (≤10 t) the mobile crane form factor often competes head-to-head on flexibility, but loses on energy per lift and on repeatability of hook position. Across heavier site moves the crawler crane family takes over once spans exceed the rail envelope, and the crane scale is the standard instrument for verifying that the installed unit is delivering its rated SWL after commissioning. For an adjacent fixed-path material-handling comparison, the storage-yard logic is laid out in Skid Steer Loader Spec Bands for Power Generation Sites, which maps ROC and hydraulic flow against yard-cycle work that often runs parallel to a gantry installation.
Closing signal: request the FEM group letter (e.g. A5) and the full load-chart PDF with end-car and corner capacities before signing a gantry-crane PO, and confirm that the hoist is derated to the actual ambient — these two documents are the leading indicators of a 20-year service life on a well-specified unit [S3][S4].