What is the key difference in the lifting mechanism between a bridge crane and a gantry crane?

The key difference in the lifting mechanism between a bridge crane and a gantry crane lies in how the crane's structure is supported. A bridge crane is supported by runways that are typically attached to the building's structure, meaning the crane travels along elevated rails fixed to the building's columns or roof supports. This allows the crane to cover the entire span of the building or a specific bay within the building. A gantry crane, in contrast, is supported by its own legs that travel on rails at floor level or ground level. This means the gantry crane does not rely on the building's structure for support, making it suitable for outdoor applications or areas where the building structure cannot support a bridge crane. The lifting mechanism itself, usually a hoist, is suspended from a trolley that moves along the bridge or gantry beam in both crane types, but the fundamental difference is in the support system, with bridge cranes being building-supported and gantry cranes being self-supported.