concrete and steel stacked
A load-bearing frame of reinforced concrete stacked above or below a steel framework.
Pictured: 900 North Michigan
A concrete and steel stacked structure is a mixed material framework in which a steel frame sits on top of a reinforced concrete frame, or vice-versa.
Unlike other mixed material frames, the two materials do not coexist side-by-side, but are stacked in layers at different floor levels. Despite the intuitive appearance of concrete being far heavier than steel, it is possible to rest a concrete frame on top of a steel frame - so both combinations are feasible and have been employed in tall buildings.
The different frameworks occupy successive levels of the structure. A tandem arrangement instead combines concrete and steel framing elements side by side.