Steel Hollow Sections: What are HSS, SHS, RHS, and CHS?

What do HSS, SHS, RHS, and CHS mean?

This is a very technical term. These abbreviations all refer to hollow structural sections, which are widely used in construction, engineering, and manufacturing.

First, let's understand the general term:

HSS - Hollow Structural Sections

HSS is a general term that refers to all hollow steel tubes used in load-bearing structures. It encompasses all of the specific shapes listed below. This term is particularly common in North America, where it is specifically categorized into three types: HSS Square Tube, HSS Rectangle Tube, and HSS Round Tube.

Specific Classifications:

Based on their cross-sectional shape, HSS is primarily categorized into the following three types:

1. SHS - Square Hollow Section

SHS tube refers to hollow structural steel sections (HSS) with a square cross-section.

Features: The four-sided structure of square tubes provides high cross-sectional stability and resistance to deformation when subjected to external forces such as pressure and torque, making them suitable for structural support components. Compared to round tubes, square tubes are more stable in bending and torsion resistance, especially when subjected to vertical loads, where their support capacity is enhanced. Compared to ordinary steel tubes, they are lightweight, making them more suitable for lightweight structures.

Applications: Used in building structures, such as steel columns for residential structures, awning supports, and stair railings. Used in shelving and storage, such as the uprights and crossbeams of heavy-duty racks. Used in furniture and decoration, such as table and chair frames, display racks, and guardrails.

Example SHS tube size: 100mm x 100mm x 6mm SHS (represents a square tube with a side length of 100mm and a wall thickness of 6mm).

2. RHS - Rectangular Hollow Section

RHS tube refers to a hollow structural steel section with a rectangular cross-section.

Features: Rectangular tubes have a higher section modulus along their long sides, resulting in greater bending resistance. It is an ideal material for beams, frames, and trusses because it allows for more efficient material utilization. Rectangular tubes also offer high space efficiency, with a flat profile that fits snugly against walls or flat surfaces, minimizing space savings. Furthermore, they feature two wide flat surfaces, making them ideal for welding, bolting, or connecting with standard connectors.

Applications: Main load-bearing beams, purlins, and curtain wall keels in building structures; machinery frames such as machine tool beds, conveyor equipment supports, and heavy equipment foundations; and chassis and frames for vehicles and ships.

Example RHS tube size: 150mm x 100mm x 8mm RHS (representing a rectangular tube with a long side of 150mm, a short side of 100mm, and a wall thickness of 8mm).

3. CHS - Circular Hollow Section

CHS tube refers to hollow structural steel sections with a circular cross-section, commonly known as round tube.

Features: Of all cross-sections, round tubes have the strongest ability to resist torque. When used to transport fluids, they provide smooth flow without dead spots and low resistance. Round tubes are isotropic, exhibiting identical performance in all directions, allowing for uniform load distribution. They are commonly used in applications subject to pressure and torsional loads, as well as for fluid and gas piping.

Applications: Fluid transport applications such as water, oil, gas, and chemical pipelines (corrosion-resistant); mechanical and automotive transmission components such as drive shafts and rotating shafts; pressure-bearing equipment such as hydraulic and pneumatic cylinders and boiler tubes; and structural applications such as transmission towers and space trusses.

Example CHS tube size: Ø88.9mm x 5mm CHS (indicates a round tube with an outer diameter of 88.9mm and a wall thickness of 5mm).

Manufacturing Standards for Hollow Structural Sections (HSS):

1. American Standards (ASTM)

In the United States, the following standards apply:

1) ASTM A500 - Cold-Formed Welded (carbon steel)
2) ASTM A1085 - An upgraded version of A500, offering atmospheric corrosion resistance (low-alloy steel)
3) ASTM A847 - Excellent atmospheric corrosion resistance (low-alloy steel)

ASTM A500 - Standard Specification for Cold-Formed Welded and Seamless Carbon Steel Structural Tubing in Rounds and Shapes
Features: ASTM A500 is the most commonly used HSS standard in North America. It covers both welded and seamless tubes, as well as round tubes. It is classified by strength into grades A, B, C, and D. Grade B is the most commonly used, offering a good balance of strength and formability.

ASTM A1085 - Standard Specification for Cold-Formed Welded and Seamless High-Strength Low-Alloy Structural Tubing with Improved Atmospheric Corrosion Resistance
Features: An upgraded version of A500, offering higher strength, tighter dimensional tolerances, and improved toughness. It is the preferred choice for high-performance steel structural design.

ASTM A847 - Standard Specification for Cold-Formed Welded and Seamless High-Strength Low-Alloy Structural Tubing with Improved Atmospheric Corrosion Resistance
Features: Excellent weather resistance, forming a dense protective rust layer upon exposure to the atmosphere. Suitable for exposed architectural structures that do not require painting.

2. European Standards (EN)

EN 10219 and EN 10210 are commonly used standards in Europe and its affected regions (such as Australia and the Middle East).

1) EN 10219 Standard - Cold Formed Welding (Non-alloy and Fine Grain Steels)
2) EN 10210 Standard - Hot Finished (Non-alloy and Fine Grain Steels)

EN 10219-1/-2 - Cold Formed Welded Structural Hollow Sections of Non-alloy and Fine Grain Steels
EN 10210-1/-2 - Hot Finished Structural Hollow Sections of Non-alloy and Fine Grain Steels

Features: Separates cold-formed and hot-finished standards. EN 10219 is equivalent to ASTM A500. It specifies chemical composition, mechanical properties, and dimensional tolerances. Hot-finished (hot-rolled or extruded) hollow structural steel pipes typically have more uniform material, thicker walls, and larger corner radii, with properties similar to seamless pipes.

3. Chinese Standards (GB)

In China, the standards followed are:
1) GB/T 6728 Standard - Cold-Formed Hollow Sections for Structural Use (Carbon Steel, Low-Alloy Steel)

Features: This is the core standard for cold-formed welded HSS in China, fully covering shapes such as square, rectangular, and round tubes. It specifies dimensions, shapes, weights, tolerances, and technical requirements.
Grades: Commonly used are Q235 (corresponding to ASTM A36) and Q355 (corresponding to ASTM A572 Gr.50/EN S355).

2) GB/T 8162 Standard - Seamless Steel Tubes for Structural Use (Carbon Steel, Low-Alloy Steel)

Features: Suitable for seamlessly manufacturing round tubes and can also serve as blanks for subsequent cold-drawing into square and rectangular tubes. This standard is used when higher structural performance requirements are required.

How to Choose the Appropriate Standard?

1. Select based on the project location and contract requirements

In North America, ASTM A500 Grade B is the default. In Europe and Commonwealth countries, the default standards are EN 10219 (cold-formed) or EN 10210 (hot-finished).
In China, GB/T 6728 must be followed.

2. Select Based on Application

General building structures: ASTM A500, EN 10219, and GB/T 6728 are sufficient.
High-performance, long-span structures: Consider ASTM A1085 or EN 10210 (hot-finished pipe).
Exposed structures, paint-free: Consider ASTM A847 (weathering steel).
Extremely low-temperature environments: Choose a grade with higher impact toughness requirements.

3. Select Based on Production Process

Cost priority, thin-walled: Choose cold-formed and welded standards (A500, EN 10219, GB/T 6728).

High strength, thick-walled, high-performance: Consider hot-finished (EN 10210) or seamless standards.

Read more: Galvanized Square & Rectangular Tube or Seamless vs. Welded Pipe