SPECIFYING AN OVERHEAD CRANE

Specifying an overhead crane. This is generally structural layout where overhead crane is located in building.

BASIC CRANE COMPONENTS

To help you and the reader better understand names and expressions used throughout this course, find below is a diagram of basic crane components.

1) Bridge - The main traveling structure of the crane which spans the width of the bay and travels in a direction parallel to the runway. The bridge consists of two end trucks and one or two bridge girders depending on the equipment type. The bridge also supports the trolley and hoisting mechanism for up and down lifting of load.

2) End trucks - Located on either side of the bridge, the end trucks house the wheels on which the entire crane travels. It is an assembly consisting of structural members, wheels, bearings, axles, etc., which supports the bridge girder(s) or the trolley cross member(s).

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

4) Runway - The rails, beams, brackets and framework on which the crane operates.

5) Runway Rail - The rail supported by the runway beams on which the crane travels.

6) Hoist - The hoist mechanism is a unit consisting of a motor drive, coupling, brakes, gearing, drum, ropes, and load block designed to raise, hold and lower the maximum rated load. Hoist mechanism is mounted to the trolley.

7) Trolley - The unit carrying the hoisting mechanism which travels on the bridge rails in a direction at right angles to the crane runway. Trolley frame is the basic structure of the trolley on which are mounted the hoisting and traversing mechanisms.

8) Bumper (Buffer) - An energy absorbing device for reducing impact when a moving crane or trolley reaches the end of its permitted travel, or when two moving cranes or trolleys come into contact. This device may be attached to the bridge, trolley or runway stop.

EOT CRANE CONFIGURATION

Today's post is to know electric overhead travelling crane configuration.

1) Under Running (U/R)
2) Top Running (T/R)

Under running cranes

Under Running or under slung cranes are distinguished by the fact that they are supported from the roof structure and run on the bottom flange of runway girders. Under running cranes are typically available in standard capacities up to 10 tons (special configurations up to 25 tons and over 90 ft spans). Under hung cranes offer excellent side approaches, close headroom and can be supported on runways hung from existing building members if adequate.

The Under Running Crane offers the following advantages:

o Very small trolley approach dimensions meaning maximum utilization of the building's width and height.
o The possibility of using the existing ceiling girder for securing the crane track.

Following are some limitations to Under Running Cranes:-

o Hook Height - Due to Location of the runway beams, Hook Height is reduced
o Roof Load - The load being applied to the roof is greater than that of a top running crane
o Lower Flange Loading of runway beams require careful sizing otherwise, you can "peel" the flanges off the beam

Top Running Cranes

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. Top Running Cranes are the most common form of crane design where the crane loads are transmitted to the building columns or free standing structure. These cranes have an advantage of minimum headroom / maximum height of lift.