Monocoque

Monocoque is a one-piece structure which defines the overall shape of the car. While ladder, tubular space frame and backbone chassis provides only the stress members and need to build the body around them,  monocoque chassis is already incoporated with the body in a single piece



In fact, the "one-piece" chassis is actually made by welding several pieces together. The floorpan, which is the largest piece, and other pieces are press-made by big stamping machines. They are spot welded together by robot arms (some even use laser welding) in a stream production line. The whole process just takes minutes. After that, some accessories like doors, bonnet, boot lid, side panels and roof are added.
Monocoque chassis also benefit crash protection. Because it uses a lot of metal, crumple zone can be built into the structure.
reference:www.autozine.org