Cranes, defined as mounted mechanical instruments used to transfer small and medium-sized loads over a short distance, come in a variety of designs including the bridge crane and the gantry crane. Cranes whether fixed or mobile are driven manually or by power.
The bridge mounted crane is one of the versatile fleet of cranes that cannot be modeled as an industrial vehicle, the other is the gantry crane (also referred to as overhead traveling bridge cranes). The bridge crane is composed of a beam that bridges a bay (wall to wall) that moves on two tracks mounted on either wall.
A hoist and trolley, which traverses across the bridge, provides a total of three axes of motion. The hoist moves the load up and down, the trolley moves the load right and left, and the bridge of the crane moves the load forward and backward.
The dimensions of a generic bridge crane could include the following: Trolley designed for the maximum cross slope of 1%, End trucks designed for the maximum longitudinal slope of 3%, NEMA 4 weatherproofing, Cold weather protection, emergency brakes that will stop the crane in 12′ and act as a hold-down (brake sufficient for a 50 MPH wind velocity), completely bolted construction to facilitate erection as well as disassembly for easy relocation, radio remote controls and a full-length catwalk with access ladder on 1 leg.
New and used bridge cranes (which are becoming increasingly popular as a cost-effective option) represent a noteworthy class of cranes that function with a pulley system suspended from a trolley that travels on tracks that run along either one or two beams that lie horizontal to one another.