Question

By now, you should have listened to the audio lecture, read the chapter, and taken the self-assessment and quiz. For this discussion activity, I want you to respond to the following question in the Discussion area in this learning module.

• Tower cranes have tall vertical, latticed masts or towers and horizontal booms called "jibs". There are several different types of jibs available for tower cranes. List at least three jibs and briefly describe each jib type.

Answer 1

There are different types of tower crane jibs available for various purposes namely- Luffing jib, fixed luffing jib, flat top jib, articulated jib, rear pivoted jib, Saddle jibs, A- frame jib etc..

The following are some of the types:

1. Luffing jib:-

• These are adaptable tower cranes which can be used particularly on congested working spaces.
• Luffing jib is capable to lower or rise with small slewing radius.
• Tower cranes with luffing jibs are mainly used in larger projects where high lifting capacities are required with high accuracy and safety is considered.
• One of the adavantage of tower cranes with luffing jibs are it can used with varying slewing radius, this does not create any accidental crash with other cranes on working site.

2. Rear pivoted luffing jib:

• In this type, the jib pivot is loacted towards the rear of the top of tower and the hook is supported by hoist rope,
• This jib has a smaller hook radius compared to normal luffing jib.

3. Fixed Luffing jibs:

• These jibs are mounted on pivots at jib foot. In some of the fixed jibs, the hook radius is altered by moving saddle along the jib. Otherwise saddles are fixed in jib head and hook radius is also kept fixed.

4. Saddle Jibs:-

• These are supported by pendants in horizontal position and hook is suspended from trolley along with jib.
• These jibs can handle loads very closer to the crane tower since it has smaller minimum operating radius. Another adavntage is it is cheaper, easier to erect and dismantle comparred to normal luffing jib.

5. Flat top jib:-

• Tower cranes with flat top jib are generally in sites with higher height restrictions.
• One of the advanatge of cranes with flat top jibs -Capable to dismantle in air, thus it is suitable projects like power plants, cooling towers, bridges etc.