Page 50 - Built Expressions - Online Construction Magazine - November 2014 Issue

Cover Feature A luffng jib does not use a trolley like a conventional tower crane, but rather raises or lowers the jib as needed for lifts closer to the tower. Because of the added complexity, luffng cranes are more expensive, and only used when needed. • Brief Description- Tower crane is the only type of crane specially designed for buildings and other high rise structures. They can distribute material for whole plan area of a tall structure. Tower cranes can be ftted with a derricking jib or horizontal jib with traversing trolley. A derricking jib is necessary if required to be raised to clear obstructions. A horizontal jib is easier to operate, is faster and has lower power consumption. Tower cranes can be rail mounted but require properly laid level track; the travel is also electrically operated. Other options include In case of high rise buildings, fxed base tower crane or climbing The type and number of cranes tower cranes when attached in to be used will depend on the plan, multi-stage pumps are also the height to be frame work of the size and shape and the height of used. There are many projects building. In such cases the designer the building and the access spaces where the concrete pump of the building should permit around it. Where the tower crane is attachment with resultant loads, at located outside a high rise structure, is directly placed below appropriate points. With winches it is often have to be tied to the the batching plant and the of higher capacity, the maximum structure at intervals to stabilize the height of the attached crane can be mast. The structure assists in taking concrete pipe line is connected increased. up the reaction at a certain points, to the location of pour. Site conditions regulate the height in which case the structure has to be of the unattached crane depending designed for the stresses generated Capacities of these pumps vary upon exposure to high winds etc. by the anchors. in terms of their delivery. The fxed base may involve substantial Mobile tower cranes are area and depth of concrete. Cabins subdivided with respect to their are usually on top of the mast running year into rail mounted, and jib slews either with the mast or truck, wheeled and crawler cranes. Climbing tower cranes are usually around the mast. Control is usually by Most widely are rail mounted cranes, used in the construction of multi- the operator; remote control is they are simple in service and ensure storied and high rise buildings. also possible. The cranes are usually a high safety. Cranes employed in Where access around the site is electrically operated. construction have a lifting capacity restricted, a tower cranes might be of 3 to 25 tonnes and a maximum used internally by leaving out t h e • Choosing the right type of Tower swinging radius is 90m. Separate foor panels or making use of the lift Crane- Tower cranes feature a high motors are used for hoisting, shaft or stair well. Thus it is possible manoeuvrability, a large space below travelling, luffng, traversing etc. to operate from a more central point the crane and high arrangement of Stationery Cranes are mounted on in the structure and make most use the boom which can pass over the a foundation and they serve the of its reach. Alternatively, a climbing erected structures. construction site from one point. crane may be more economical. PG 50 Built Expressions Vol: 3 Issue: 11 November 2014