A36 Steel is the American Society for Testing and Materials (ASTM) designation for carbon steel. ASTM A36 steel is the most common type of steel used in construction. Its properties allow the steel to be used in many applications, unlike higher-performance alloys.
Steel alloys are composed mostly of iron. However, each alloy has differing amounts of other materials, such as carbon, nickel, manganese, tungsten and molybdenum. The different compositions create different properties among alloys. All steel alloys have a modulus of elasticity, or measurement of stiffness, of 29 million psi. Modulus of elasticity is used to calculate when a piece of steel will deform too much to carry a load safely. Other properties of steel include yield strength, or maximum stress before the steel deforms permanently; allowable bending stress, or stress the steel can safely carry before contorting out of plane; and ultimate limit, or stress at which the steel will completely fail.
ASTM A36 Steel Properties
ASTM A36 has a yield strength of 36,000 psi and an allowable bending stress of 22,000 psi. The properties of ASTM A36 steel allow it to deform steadily as stress is increased beyond its yield strength. This ductility allows buildings to stand long after the limits of a structure have been met in an emergency, allowing the inhabitants to exit safely before collapse. Other high-performance steels, such as bridge strand, are extremely strong but brittle, and there is minimum deformation before the bridge strand breaks violently.
As mentioned, ASTM A36 is the most common type of steel alloy. It is used for most building components, including columns, beams, decking and finish elements. The ductility of ASTM A36 doesn't allow the alloy to be used as cable, and it should not be used as reinforcing bar (rebar). Nevertheless, the majority of other uses are perfect for ASTM A36.
ASTM A36 and other alloys can be formed into various shapes for building construction. These include steel tubes; wide flanges, or W shapes; American Standard I-beams, or S shapes; structural tees, or T shapes; channels, or C shapes; angles, or L shapes; steel plates; and steel bars. Steel tubes are usually used as columns. Wide flanges have a profile that looks like an "I" or "H," and they are used for columns or beams. I-beams should only be used for beams, and T shapes and C shapes can be used as beams or bracing. Angles are usually only used for bracing or finish elements, while steel plates and bars have many uses in construction.
There are many different alloys with varying ASTM designations. Other steel alloys include: ASTM A242, used in marine and humid environments, is a high-strength, corrosion-resistant alloy with a yield strength of 42,000 to 50,000 psi and an allowable bending stress of 25,200 to 30,000 psi; ASTM A441, used in low-tolerance, state-of-the-art structures, such as towers and large telescopes, is a high-strength structural grade with a yield strength of 40,000 to 50,000 psi and an allowable bending stress of 24,000 to 30,000 psi; and ASTM A572 Grade 50, used in large-scale construction, is an extremely strong alloy with a yield strength of 65,000 psi, an allowable bending stress of 39,000 psi and a future as the high-performance replacement of ASTM A36 steel.
Ryan Crooks is a licensed architect with 15 years experience in residential, institutional, healthcare and commercial design. Crooks is also an instructor, teaching architecture to high school and college students. He has written hundreds of articles for various websites.