steel
A load-bearing skeletal frame made of steel members, including their structural connecting elements.
A steel frame is a skeletal structure made of steel members and their connecting elements.
Steel is a common framing material for office and commercial buildings of various sizes. It is not common in residential architecture, though it occurs sometimes.
A steel framework is occasionally built in combination with other materials, such as reinforced concrete. For example, the lower floors of a building may be concrete while the upper floors or the roof structure are built of steel. In these cases, steel may be assigned as a frame material. However, when steel acts in tandem with reinforced concrete or masonry (generally at the same levels of a structure), it should be classified as a composite frame.