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Crane TypeSingle Girder Overhead Crane
The most economical overhead crane solution at moderate tonnage and moderate span.
Construction
In a single girder crane the bridge consists of a single main girder. It's usually built as a rolled section or a box girder, with end carriages at both ends carrying the wheels and the travel drive.
The hoist unit hangs from a trolley that runs on the girder's bottom flange. This arrangement significantly reduces the crane's total weight — and with it, the wheel loads and the demand placed on the runway and the building.
Strengths and weaknesses
Its strength is economy and adaptability: less steel, a lighter runway, easier installation. When adding a crane to an existing building, single girder is often the only option that can be fitted without reinforcing the structure.
Its weakness is lifting height. Because the trolley sits under the girder, the hook can never rise above the girder's underside level. In buildings with limited headroom, that means long parts can't be lifted.
When it's the right choice
| Criterion | Assessment |
|---|---|
| Tonnage | Efficient for low and moderate tonnage |
| Span | Economical at moderate spans; the section grows fast as span increases |
| Lifting height | Limited by the girder's underside level |
| Wheel load | Low — easy to fit to an existing building |
| Maintenance platform | Generally not practical |
| Auxiliary hook | Not practical |
| Installation time | Short |
| Initial investment | Noticeably lower than double girder |
Technical terms
| Term | What it means |
|---|---|
| Bottom flange | The bottom face of an I- or H-section; the trolley wheels run on it. |
| End carriage | The section at the end of the main girder carrying the wheels and travel drive. |
| Box girder | A girder cross-section welded from four plates, resistant to torsion. |
| Wheel load | The load each wheel transfers to the rail and the structure. |
Frequently asked questions
Up to what tonnage is single girder built?
Capacity alone doesn't set the limit — it's assessed together with span and duty class. Single girder is technically possible at high tonnage, but the section and weight grow quickly, and double girder becomes the more economical choice.
Can I convert it to double girder later?
In practice, no — the bridge, end carriages and trolley are all replaced, and the building loads have to be recalculated. If you expect a future capacity increase, starting with double girder is more economical.
What do I do about a low ceiling?
There are two options: move to double girder to raise the hook, or use a low-headroom (underslung-type) trolley. The decision is made by measuring the column height and the length of the part to be lifted.