Double Girder Double Cantilever Gantry Crane

In a double cantilever gantry crane the bridge girder is extended outward from both sides of the leg line. The hook can therefore reach lanes on either side of the rail track, making the reach of the single cantilever model symmetrical.

It frees the yard layout

With a single cantilever, which side of the yard will be used is fixed at the outset and cannot be changed once the track is laid. A double cantilever removes that constraint. Where a truck road runs along one side and a storage area along the other, work continues wherever the vehicle pulls up.

That flexibility also cuts the crane's empty return travel: after releasing a load the hook descends at the nearest pick-up point rather than returning to the same end of the track every time. On busy yards the difference shows directly in the daily cycle count.

The load it puts into the structure

Two cantilevers inevitably raise both the moment on the legs and the wheel pressure. With the hook at one cantilever tip, wheel load on the opposite side falls and on the same side rises; this asymmetric distribution governs both rail and ground.

Floor bearing capacity is therefore checked at an earlier stage on double cantilever models, and the fill and foundation detail beneath the rail are sized more carefully than on a single cantilever equivalent. Rated capacity on the cantilevers is set and marked separately from the main span.

Girder and trolley arrangement

The double girder structure carries the trolley on top, so the hook rises to girder level. Girders are fabricated as box sections and the section is usually maintained through the overhang zones, because bending moment there can approach main-span values.

On long spans girder deflection is checked separately: vertical displacement with the hook at the cantilever tip affects the operator's positioning accuracy.

Applications

Plate and profile storage yards, precast concrete plants, scrap and foundry preparation areas, and open storage zones used on both sides.