What is a double girder overhead crane?
A double girder overhead crane is an electric overhead travelling (EOT) bridge crane whose bridge is built from two parallel main beams rather than one. The trolley carrying the hoist runs on rails fixed to the top of the two girders, with the hook hanging between and below them. This top-running trolley arrangement is what gives the configuration its defining advantages: more under-hook height, higher achievable capacity, and the ability to carry auxiliary hoists and a maintenance walkway between the beams.
Because the trolley sits on top of the girders instead of hanging beneath a single beam, the crane recovers headroom that a single-girder design loses to the hoist hanging below the flange. That makes the double-girder layout the standard choice once capacity, span or duty cycle climb beyond what a single beam handles economically.
How a double-girder bridge is built
The two main girders are tied together at each end by end-carriages, which carry the travel wheels running along the runway beams on each side of the bay. The hoist crab (trolley) spans the two girders and traverses across the bay on its own rails. Long-travel motion (the whole bridge moving down the runway), cross-travel (the trolley across the bridge) and hoisting (the hook up and down) give the three axes of movement.
Sorian designs, manufactures and installs the bridge structure, end-carriages and crane controls. The hoist and radio remote fitted to the crane are quality components we supply and integrate — selected to suit the duty class and Maximum Rated Capacity (MRC) of the application.
Double girder vs single girder — quick comparison
| Bridge structure | Double-girder: two parallel beams, top-running trolley. Single-girder: one beam, trolley runs on the lower flange. |
| Capacity range | Double-girder: ~5 t to 100 t+ with custom engineering. Single-girder: typically 500 kg to ~20 t. |
| Span range | Double-girder: economical from ~5 m to 35 m+. Single-girder: economical to ~20–22 m before deflection and weight dominate. |
| Hook height (under-hook to runway) | Double-girder: higher — trolley sits between the beams. Single-girder: lower — hoist hangs below the beam. |
| Duty class | Double-girder: comfortable to A6–A8 (high cycle). Single-girder: A2–A5 typical, A6 with care. |
| Auxiliary hoist | Double-girder: readily accommodated on the same trolley. Single-girder: generally not feasible. |
| Maintenance access | Double-girder: a walkway between the beams gives top access to drives, motors and hoist. Single-girder: trolley accessed from below. |
| Relative cost | Double-girder: higher capex (two beams plus crab), but mandatory above ~20 t. Single-girder: typically 20–40% less for capacities under 20 t. |
When a double-girder overhead crane is the right choice
- Capacity over ~20 tonnes — single-girder becomes structurally limited above this.
- Span over ~22 metres — single-girder deflection becomes hard to control.
- High duty class (A5–A8) — twin girders handle high-cycle, near-rated-load work better.
- Maximum hook height required — gaining roughly 0.5–1.5 m of under-hook clearance matters.
- Auxiliary hoist needed — a second, smaller hook for tandem or turning lifts.
- Maintenance walkway wanted — top access to the crab and drives between the beams.
- Heavy industrial environments — steel mills, foundries, port and mining maintenance, paper mills.
Limitations and trade-offs
- Higher cost — two girders plus a top-running crab cost more to fabricate, deliver and install than a single beam.
- Heavier bridge — more steel means higher runway wheel loads, so the runway and supporting structure must be sized for it.
- More building demand — the heavier crane can drive heavier runway beams and columns in the host structure.
- Over-specification risk — for a light, low-duty, short-span application a double-girder is simply more crane than the job needs; a single-girder bridge does the same work for less.
For applications under roughly 20 tonnes at moderate duty and span, a single-girder bridge usually wins on cost without compromising performance. The double-girder advantage shows up once you push capacity, span, duty cycle or hook height.
Standards and design
Sorian designs and manufactures double-girder overhead cranes to AS 1418 (Cranes, hoists and winches), with in-service inspection and maintenance referenced to AS 2550. Capacity is always stated as Maximum Rated Capacity (MRC). Duty class is selected from the expected load spectrum and number of operating cycles so the structure and mechanisms are sized for the working life the application actually demands — not a catalogue default.
Talk to an engineer
Sorian designs, manufactures and installs both single and double-girder EOT bridge cranes, and we'll tell you which configuration suits your bay based on the real numbers. Send through your span, MRC, duty cycle and required hook height and we'll come back with a configuration recommendation.
Frequently asked questions
What is a double girder overhead crane?
A double girder overhead crane is an EOT bridge crane built with two parallel main beams. The trolley and hoist run on rails on top of the two girders, with the hook between them. This top-running layout gives more hook height, higher capacity and higher duty-class capability than a single-girder bridge.
When should I choose a double-girder over a single-girder crane?
Choose double-girder for capacities over roughly 20 tonnes, spans over about 22 metres, high duty classes (A5–A8), where maximum hook height is critical, or where an auxiliary hoist or a maintenance walkway between the beams is needed. Below those thresholds a single-girder bridge usually does the job for less cost.
How much capacity can a double-girder overhead crane handle?
Double-girder configurations typically span from around 5 tonnes up to 100 tonnes and beyond with custom engineering. The exact Maximum Rated Capacity (MRC) depends on span, duty class and runway capability, and is engineered for each application to AS 1418.
Is a double-girder crane more expensive than a single-girder?
Yes. For capacities under about 20 tonnes a single-girder crane is typically 20–40% cheaper because it uses less steel and lighter runway. Above that capacity the single-girder option becomes structurally limited, so for higher capacities double-girder is often the only sensible choice.