Friday, June 23, 2017

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Bridge Cranes

This web page is intended to give a general understanding of the terminology used in the overhead crane industry. The following explanation of terms should provide you with the information you will need to make an informed decision when purchasing material handling equipment.

You can click on the links to see detailed pictures of the equipment being described. 

Bridge Crane Types

This section specifies the kind of equipment you require. Overhead cranes come in four basic configurations:

Top Running - The crane bridge travels on top of rails mounted on a runway beam supported by either the building columns or columns specifically engineered for the crane.

Under Running - The crane bridge travels on the bottom flange of the runway beam which is usually supported by the roof structure.

Single Girder - The crane consists of two end trucks, a single bridge girder and the trolley hoist unit. The trolley runs on the bottom flange of the bridge girder.

Double Girder - The crane consists of two end trucks, two bridge girders and the trolley hoist unit. The trolley runs on rails on top of the bridge girders.

Bridge Components

Bridge - The main travelling structure of the crane which spans the width of the bay. The bridge consists of two end trucks and one or two bridge girders depending on the Equipment Type. Bridge Crane Component Diagram

End trucks - Located on either side of the span, the end trucks house the wheels on which the entire crane travels. These wheels ride on the runway beam allowing access to the entire length of the bay.

Bridge Girder(s) - The principal horizontal beam of the crane bridge which supports the trolley and is supported by the endtrucks.

Hoist - The hoist is mounted to the trolley and performs the actual lifting function via a hook or lifting attachment. There are two basic types of hoist. Wire Rope Hoists which are very durable and will provide long term, reliable usage. The other type of hoist is the Chain Hoist. These hoists are used for lower capacity, lighter duty applications and for projects in which cost is a primary deciding factor.

Trolley - The trolley carries the hoist across the bay along the bridge girder(s) traversing the span.

RunwayThis is a system of structural steel beams that support the crane. The bridge travels along the runway.

Basic Terminology

Capacity - The maximum weight the crane will be required to lift.

SpanThe horizontal distance between the rails of the runway on which the crane is to travel.

Lift or Hook Height - The required distance from the floor to the crane hook. This dimension is critical in most applications as it determines the height of the runway from the floor and is dependent on the clear inside height of the building.

Bridge, Trolley and Lift Speeds - The rate at which the bridge or trolley travels, or at which the hoist lifts, usually infeet per minute or FPM. You may specify either Single Speed or Two Speed travel/lift or a specific rate of speed, (i.e. 120 & 30 FPM bridge travel). Another option as far a motion speeds are concerned is a Variable Frequency Drive. See the Control section for more information.


Pendant - The pendant gives the operator precise control over the motions of the crane. There are many configurations of pendant depending on the functions of the equipment being controlled. Each push-button on the pendent controls an operating function of the crane. The pendant may be suspended from the Trolley Hoist, requiring the operator to walk with and beside the load, or on a separate sliding track system allowing the operator to move independently of the load.

VFD - A pendant can also be used in conjunction with a Variable Frequency Drive. A VFD is used to vary the frequency of the motors controlling the motions allowing for smooth acceleration and deceleration. The buttons on the pendant operate a VFD unit operated in much the same way as Two Speed control. The first step is held to maintain the current speed while the second step is used for acceleration. Deceleration is achieved by releasing the button entirely. Pressing the button back to the first step will maintain the new slower speed. It should be noted that the deceleration is not achieved through uncontrolled coasting but through a programmable dynamic braking system. The control provided by a VFD allows for a high level of customization.

Radio Control - The radio control performs exactly like the pendant but operates using a radio frequency. The radio control incorporates numerous safety features and allows the operator a greater range of operator motion than a pendant.

Power Supply - The electrical service available in the building for which the crane is being designed (i.e. 460 Volt, 3 phase, 60 Hertz).

Runway - The rails, beams and columns on which the crane operates. The rail, on which the end-trucks run, is fastened to the runway beam. This beam is then supported on columns (Top Running) or from the roof structure (Under Running). The existing building columns can be used or new ones can be supplied with the system. New columns can either be completely Free Standing or Tied Back to the existing building structure for additional lateral support. When designing a runway system that is to use existing building columns, it is important to provide the down shop center to center spacing between them. Conductor supply power to the crane and are mounted on the runway beam.


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