Structural steel tubing is a category of cold-formed steel members with a hollow cross-section, manufactured to specific standards for use in load-bearing structures. It is formally known as HSS (Hollow Structural Sections) and comes in three primary shapes: square (HSS), rectangular (HSS), and round (HSS).The key characteristics of structural pipes are that it is engineered not for transporting fluids (like pipe), but for its strength-to-weight ratio, efficiency in carrying multi-directional loads, and clean aesthetic appearance.
What is the difference between structural steel and normal steel?
The terms are a bit informal, but the key difference lies in their intended purpose, chemical composition, and mechanical properties.
Normal Steel : This typically refers to a general-purpose carbon steel. It is versatile and used for a wide range of applications from brackets and frames to machinery parts where complex stresses are not the primary concern.
Structural Steel : This is a category of steel specifically designed for load-bearing structures in buildings, bridges, and towers. While strength is crucial, it must also have other engineered properties:
- Higher Ductility: It must be able to bend and deform significantly before failing (brittle fracture is catastrophic in structures).
- Weldability: It must be formulated to be easily and reliably welded without becoming brittle in the heat-affected zone next to the weld.
- Toughness: Especially in cold environments, it must resist fracturing upon impact.
- Consistent Properties: It is produced to much stricter chemical and mechanical tolerances to ensure predictable performance under load.
What tubing is normally used for structural applications?
The pipes commonly used for structural applications are manufactured according to ASTM A500 standard, which is a standard specification for circular, square, and rectangular cold-formed welded and seamless carbon steel structural pipes
Characteristics of ASTM A500 standard:
- Optimized for Structure: It's specifically designed for load-bearing applications, with mechanical properties focused on yield strength, tensile strength, and ductility.
- Cost-Effective: Its manufacturing process makes it the most economical choice for structural projects.
- Excellent Strength-to-Weight Ratio: The hollow section provides immense strength and stiffness while minimizing weight.
- Weldability: The chemical composition is controlled to ensure it can be easily and reliably welded.
- Grades: It comes in several grades, with A500 Grade B and A500 Grade C being the most common. Grade C has a slightly higher yield strength.
Is Schedule 40 Pipe Structural?
Not by default. Schedule 40 is a wall thickness designation for pipe manufactured to pressure standards like ASTM A53.
ASTM A53 Pipe: Designed to hold pressure. Its properties and testing are focused on containing fluids without leaking.
ASTM A500 HSS: Designed to carry structural loads. Its properties are focused on strength, stiffness, and ductility.
Can Schedule 40 A53 pipe be used in a structural application?
Yes, it is often used for simple applications like fence posts, handrails, or non-critical supports. However, for any engineered, load-bearing frame in a building or bridge, an engineer will specify A500 HSS because its properties are guaranteed, predictable, and optimized for that purpose.
Is Structural Pipe Seamless?
Structural pipe (more accurately called Hollow Structural Sections or HSS) can be either seamless or welded, but the vast majority used in construction is welded.
While seamless structural tubing exists, over 95% of the structural tubing (HSS) used in buildings, bridges, and frames is welded, not seamless. The welding process used is so advanced that the seam is as strong as the parent metal, making it perfectly suitable and cost-effective for almost all structural applications.
Key Takeaway: The most important factor isn't whether the tube has a seam, but whether it is manufactured to a structural standard, primarily ASTM A500.
What is Structural Pipe Used For?
Structural tubing is ubiquitous in modern construction due to its efficiency and clean lines.
- Building Frames: As columns and beams in commercial buildings.
- Trusses: The members of roof and bridge trusses.
- Space Frames & Domes: Complex, long-span structures like those in airports and arenas.
- Bridges: Particularly pedestrian and architectural bridges.
- Architectural Elements: Exposed columns, stairs, handrails, canopies, and sculpture.
- Industrial Applications: Support frames for equipment, mezzanines, and storage systems.
- Vehicle Frames: Roll cages in race cars and frames for trucks and buses.
