Cranes ....

I saw this humungous cranes in a construction site yesterday evening. Didn't get to see the base where the cranes stood, but I wondered how they would alleviate the crane to a higher level when they are required? Any clues...Err, Cik Alang, u being the so called ENGINEER of the family, don tell me u donno? muakakakakakaka.. Tgh boring..