[Kelvin]

The cost difference between steel frame and RC frame is, on average, small. However, regional differences in labour & material often favour one system over the other.

Cost aside, we generally see faster construction times in steel frames. While the steel frame may rise quickly on site, what is not generally known, is that the procurement, fabrication, and delivery of steel may require 6 to 10 months of lead time. Concrete structures can go up without that excessive lead time and essentially start work on "day 1".

Design wise, steel is definitely lighter (not always a good thing) and more flexible. To help counter this inherent flexibilty, designers often couple the frame with concrete or masonry infill panels and/or "cores". Usually this works out well because most codes require some fire separation at the stairwell(s) and block or solid concrete does the job nicely.

Concrete frames really shine in super-slender structures because they can produce a very stiff system even within a small profile. Carnegie Hall Tower is such an example where the tower is 50' wide in the upper portion. Designers rejected a steel frame only because they could not get it to develop sufficient lateral stiffness. The extra mass of concrete structures also produces better damping, meaning that it adsorbs energy quicker and produces better (generally speaking) dynamic performance. This is advantageous when controlling any movements - whether seismic or wind induced.

One should also recognise the newer composite systems (RC is itself a composite system) whereby conventional structural steel sections are either filled or encased with concrete. The overall performance of these types of frames are generally better than either of the constituent parts could offer individually. To take full advantage of these new hybrids we also ofter use "high performance" steels, concretes, polymers, composites, etc.