Doublegirder

Doublegirder, often written as double girder or double-girder, is a term in structural engineering describing systems that use two parallel girders to carry a load. The two members provide higher lateral stiffness and bending resistance than a single-girder arrangement, enabling greater span lengths and lifting capacities. The concept is widely used in overhead cranes and gantry cranes, as well as in some bridge applications.

In overhead and gantry cranes, the double-girder bridge forms the top structure of the crane. A hoist trolley is suspended between the girders and travels along them, while the entire bridge moves on rails along the runway. There are two common configurations: top-running double-girder cranes, where the hoist trolley runs on the top flanges, and underslung (or bottom-hung) double-girder cranes, where the girders are suspended from the building structure and the hoist operates below the girders. Double-girder cranes are favored for higher duty cycles, long spans, and heavy lifts, but they require more space, are heavier, and cost more than single-girder cranes.

In bridge and industrial structures, a double-girder layout uses two main girders to support a deck or loads transmitted to the supports. These girders are typically steel plate or box girders connected by bracing; the deck can be attached to the bottom flange or expanded between the girders.

In sum, doublegirder denotes a two-girder configuration that increases capacity and stiffness compared with single-girder designs.