Steel is everywhere in construction, to the beams holding roofs up to the sceletons of entire buildings, down to the very tools you use. Steel isn’t just one thing though—there are many different kinds of steel and different steel shapes, each with its own purpose and use. Learn more about the different kinds of structural steel how it’s used in construction.
What is structural steel?
Structural steel is metal used in construction materials. Fundamentally, it is defined as steel optimized for use in building construction—differentiated from a steel grade one might use to engineer tools, or stainless steel popularly used in kitchen surfaces and appliances.
Structural steel is generally a carbon steel, meaning it has a chemical composition containing both iron and carbon. Structural steel is any category of steel with a carbon content of up to 2.1% of its total weight. The higher the carbon content, the higher a piece of steel’s yield strength—meaning it is less ductile, or less likely to bend or warp when pressure is applied.
How does carbon content affect steel?
One might think steel used in construction should have a relatively high carbon content because it is less likely to bend under pressure. However, low-carbon steel, also known as “mild steel,” is actually the most commonly used type of steel in building materials. It typically contains anywhere from 0.04% to 0.3% carbon content, rendering it strong yet ductile. Steel buildings, especially tall steel buildings, must be strong, but also somewhat flexible. Overly rigid buildings cannot accommodate natural shiftings in the earth, which can be caused by neighboring construction or even earthquakes, nor can they bend with high winds. For this reason, mid- to high-carbon steels, with carbon content ranging from 0.31 to 1.5%, while technically considered structural steel, are generally reserved for mechanical engineering and toolmaking purposes.
Other grades of structural steel might contain other alloying elements, such as tungsten, zirconium, cobalt, or nickel.
What are the different steel grades?
Below are grades of steel commonly used in the construction industry:
- Carbon steels. Structural steel is designated carbon steel when no other alloying element is added, copper content does not exceed 0.4 to 0.6%, manganese does not exceed 1.6%, and silicone does not exceed 0.6%. It is commonly used in structural pipe and tubing.
- High-strength, low-alloy steels. This steel grade is designed to optimize mechanical properties and corrosion resistance. They contain manganese levels up to 2%. Trace amounts of chromium, nickel, molybdenum, nitrogen, vanadium, niobium, and titanium may be used to alter the properties. These are mainly used in structural shapes and steel plates.
- Forged steels. Forging is the process of shaping metal while still in a solid state. This is done by applying force or heat to steel ingots or billets. The process produces a uniform grain structure to the steel, which upgrades integrity by removing voids and gas bubbles, and increases overall strength.
- Quenched and tempered alloy steels. Quenching and tempering are processes that strengthen structural steel by heating it while simultaneously cooling in water, oil, forced air, or nitrogen. It creates a tougher, less brittle, higher-strength structural steel.
What are the different shapes of structural steel?
Below are types of structural steel sections commonly used in the construction industry: