The first step in the making of a concrete building is its design. Designers take into consideration how the characteristics of concrete, including its weight, strength and stability, will affect their design. This is important because the concrete walls and floors become the structure of the building. In a skyscraper, the concrete must be able to withstand the weight of many floors.
Concrete buildings are made with metal forms, which hold the concrete in place while it cures. Typically, the forms are set into place and then braced. Rebar, grooved steel rods of various thicknesses, are placed inside the forms to reinforce the concrete. Some buildings are constructed of poured concrete pillars and floors, with other materials used to construct the walls.
Concrete is poured into the forms by large trucks. Some have booms that pump the concrete up from the truck container and deposit it into the forms. The foundation and the floor of the concrete building are poured first. Utility pipes are pre-installed before the concrete is poured. Once the floor and foundation have cured, the walls and pillars can be poured. Rebar from the floor is tied to the rebar set in the wall forms. Concrete buildings can be constructed level by level in this fashion.