The modern movement, in the period after the First World War, took the steel frame for granted, as an indispensable instrument for achieving freedom and rationality in design. The outburst of building activity after the Second World War helped to perfect and spread the methods of steel frame construction to the most diverse of building types.
Although steel is not the key material we see in brutalist architecture, it is the material often used to reinforce it. It is also used to frame windows or as a support structure.
The image above shows Ludwig Mies van der Rohe. Crown Hall, Illinois Institute of Technology. Chicago, 1952-6. (Steel work in course of erection)