Construction crane which rises hundreds of meters into the sky is one of the most noticeable equipment at major construction sites. It’s used for lifting heavy building materials, such as steel and concrete vertically or moving them horizontally in the construction of tall buildings.
Tower crane, one type of fixed crane, consists of concrete slab, mast, slewing unit, long horizontal jib, shorter counter-jib, and the operator's cab. The base is bolted to the concrete slab to fix the construction crane on the ground and attached to the mast which determines the height of the construction crane. Then the mast is connected to the slewing unit which is the gear and motor to rotate the machine. And the long horizontal jib (working arm) is mounted on the slewing unit to carry the load and move it from and to the crane center. On its opposite side is the shorter counter-jib that functions a counterweight to prevent the machine from toppling over. The operator's cab is also located on the slewing unit for the operator to control the machine.
The horizontal jib and the counter-jib must achieve balance all the time to prevent the construction crane from falling over. When the hook on the jib is moving away from the mast, the counter-weight on the counter-jib must run out too to keep the balance.