Understanding Structural Steel

The Versatility and Strength of Structural Steel, From the skyscrapers that define our city skylines to the homes we live in and the roads we travel, structural steel plays a pivotal role in modern construction. It combines strength, versatility, and economic efficiency, making it an essential material in various construction projects.

In this article, we delve into the world of structural steel, exploring its composition, characteristics, and diverse applications. For more detailed information on specific grades, you can visit the Steel Friend's high-strength low-alloy structural steel plate page.

Understanding Structural Steel

Structural steel is a category of steel that adheres to specific standards regarding composition and dimensional tolerances. These standards are regulated by various bodies across the globe. In the United States, ASTM International is the primary authority, while Canada and Europe have their own respective standards.

Structural Steel Suppliers

Steel Friend supplies steel plates that meet CSA G40.21 and EN standards, but this article will focus primarily on ASTM standards. Among the numerous grades of structural steel, ASTM A36 and ASTM A572 are the most prevalent. These grades are extensively used to construct the frames of buildings and bridges, as well as in:

  • Construction equipment
  • Freight cars
  • Machinery
  • Truck parts
  • Transmission towers
  • Crane booms
  • Truck frames

According to the American Institute of Steel Construction, structural steel accounts for 47% of all construction materials, underscoring its significance in the built environment.

Production and Testing of Structural Steel

To appreciate the uniqueness of structural steel, it is crucial to understand its production process. Steel can be manufactured either from recycled materials or from raw materials. The recycling process involves melting down existing steel and refining it to meet specific standards, while producing steel from raw materials is a more intricate process.

Steel is essentially an alloy of iron and carbon. Iron is derived from iron ore, primarily from taconite in Minnesota. The extraction process involves grinding the taconite into a sandy consistency and using magnets to separate iron ore (magnetite) from other minerals.

Iron alone is relatively soft, but the addition of carbon transforms it into a much stronger material. The most common method of creating an iron-carbon alloy involves mixing coke, a carbon-rich form of coal, with iron ore and heating the mixture until the coke ignites. This process, known as reduction, results in a material with approximately 4% carbon. Further heating and cooling processes reduce the carbon content, ultimately producing steel with a carbon content below 2.1%.

For structural steel, the carbon content is further reduced to 0.05-0.25%. The resulting material boasts a high strength-to-weight ratio, is 100% recyclable, and is economically priced. Various grades of structural steel, each with a slightly different composition, are produced to meet the needs of different projects.

Composition of Structural Steel

Here is a comparison of the composition of two popular grades of structural steel: ASTM A36 and ASTM A572. Additional processing or the inclusion of other alloys can further modify these grades.

GradeCarbonManganesePhosphorus MaxSulfur MaxSilicon
A360.25-0.29%0.80-1.20%0.030%0.030%0.15-0.40%
A5720.21-0.26%1.35-1.65%0.030%0.030%0.15-0.40%
A514*0.10-0.21%0.40-1.50%--0.15-0.80%

*A514 also contains chromium, molybdenum, titanium, vanadium, and boron.

The primary difference between structural and non-structural steel lies in the presence of additional alloys that enhance hardness but also increase brittleness. These alloys can make the steel unsuitable for structural applications if not balanced correctly.

Yield and Tensile Strength

Beyond chemical composition, yield and tensile strengths are crucial factors in determining steel grades and their applications. Yield strength is the maximum stress at which a material will deform permanently, while tensile strength is the point at which the material will break.

In practical terms, yield strength is like the point at which a diving board bends but doesn't break. If the board bends and doesn't return to its original shape, it has reached its yield point. Tensile strength would be the point where the board snaps.

Elongation, the percentage increase in length before breaking, measures a material's ductility. This is crucial in applications requiring the material to stretch under stress.

Here are the yield and tensile strengths for three common structural steel grades:

GradeYield PointTensile Point
A3636 KSI58-80 KSI
A572-5050 KSI65 KSI
A51490-100 KSI*100-130 KSI*

*Dependent on thickness.

These metrics are essential for engineers when planning the materials for a project.

Charpy Impact Test

The Charpy impact test, developed by Georges Charpy, measures the amount of energy a steel sample can absorb before fracturing. This test is crucial for structural steel used in environments with varying temperatures. The test involves striking a small steel sample, called a coupon, with a heavy hammer pendulum and recording the absorbed energy.

Charpy tests are common in structural steel projects, especially for materials used in cold environments, ensuring the steel's toughness under extreme conditions.

Structural Steel in Building Construction

Structural Steel in Building Construction

When selecting materials for building construction, engineers prioritize strength and constructability. Structural steel, with its high tensile strength, machinability, and ductility, is a preferred choice for commercial and industrial buildings.

Skyscrapers often rely on structural steel due to its strength and relatively lighter weight compared to materials like concrete. Structural sections and reinforcing bars are two common applications in building construction, accounting for 25% and 44% of the steel used, respectively.

In earthquake-prone areas, structural steel's ductility allows buildings to absorb and dissipate seismic energy, reducing the risk of catastrophic damage. The high tensile points and presence of strengthening alloys in grades like A36 and A572 ensure the material's suitability for such demanding applications.


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