Artificial stone made of a mixture of cement, aggregate (hard material), and water. In addition to its potential for immense compressive strength and its ability, when poured, to adapt to virtually any form, concrete is fire-resistant and has become one of the most common building materials in the world. The binder usually used today is portland cement. The aggregate is usually sand and gravel. Additives called admixtures may be used to accelerate the curing (hardening) process in low temperature conditions. Other admixtures trap air in the concrete or slow shrinkage and increase strength.

The entity contractually responsible for delivering project design and construction. The Design-Builder can assume several organizational structures, the four most common being a firm that possesses both design and construction resources in-house; a joint venture between designer and contractor; a contractor-led team with the designer in a subcontractor role; and a design-led team with the contractor in a subcontractor role.

Steel frame usually refers to a building technique with a “skeleton frame” of vertical steel columns and horizontal I-beams, constructed in a rectangular grid to support the floors, roof and walls of a building which are attached to the frame.  The development of this technique made the construction of the skyscraper possible.