how is a tall crane constructed? how can they put the crane on top of its tall body frame?
They first construct the top of crane on the ground with help from other mobile cranes. This includes the long horizontal part with the operator's cab, and the concrete counterweight. this is then placed on a climber, with which the crane kind of builds and climbs itself to the necessary height. Every vertical section of the crane is placed in the climber. When the piece is in place, the climber climbs to the top of piece from where the next vertical piece is placed and so on. You can see how a crane is constructed in the website I've cited below:
