Cranes nowadays are MASSIVE! but something that has been bugging me for ages is how do they get the massive crane bit at the top down once they have finished constructing the skyscraper/building?
After this the crew uses a mobile crane to assemble the jib and the machinery section, and places these horizontal members on an approximately 40 foot mast that consists of two mast sections. The mobile crane then adds the counter weights. The mast which is a large triangulated lattice structure typically 10 feet square then rises from this firm foundation. This triangulated structure gives the mast the strength to remain upright. The tower crane rises to its maximum height by using one mast section at a time, the crew uses a top climber that fits between the slewing unit and the top of the mast. This is done by hanging a weight on the jib to balance the counter weight. The crew then detaches the slewing unit from the top of the mast, this is done by using large hydraulic rams in the top climber to push the slewing unit up to 20 feet. The crane is then used to lift another 20 foot mast section into the gap opened by the climbing frame. Once bolted in place the crane gains a height of 20 feet. This process is reversed once the building is finished and its time to dismantle the crane and as stated earlier a smaller crane is used to dismantle the tower crane except the mast which is dismantled by the crane itself
