This probably is a very easy question for all the civil engineers, but an interesting one nonetheless. Starting with the “reinforcing steel” or “steel reinforcement,” this type can typically be seen in the steel reinforcing bars (rebar), welded wire fabric (WWF) or welded wire mesh (WWM). This type is used to strengthen/reinforce concrete and masonry structural elements. When used compositely with the concrete or masonry, it provides tensile strength complimenting the compressive strength furnished by the concrete or masonry.
Structural steel is used in steel framed buildings that are built on steel columns, beams, braces, plates, and other elements. The applications include wide flange sections, angles, channels, tubes, pipes, bars, etc. and other structural elements built using multiple sections. Structural steel elements are also used along with wood or concrete buildings in certain applications and are the main building component used with reinforced concrete.
Unlike steel reinforcements that come in solid and circular shapes, structural steel sections come in different shapes and sizes, like the I shape, H shape, C shape, circular, square, rectangular hollow sections, etc. These shapes allow the sections to resist compression, bending tension, shear or a combination of these forces.
N W, on Quora, a self-claimed licensed structural engineer and civil engineer has another interesting perspective to add,
“There are situations when steel reinforcement may be combined with structural steel elements, such as a common connection that I detail in structures is a column for a structural steel frame embedded in a concrete foundation with rebar welded to the column and extending out into the foundation for shear and moment transfer; or a column baseplate with rebar welded to the baseplate to transfer shear loads into the foundation/slab. These are just a few of examples of the many different applications”
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