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A hollow structural section (HSS) is a type of metal profile with a hollow cross section. The term is used predominantly in the United States, or other countries which follow US construction or engineering terminology.

HSS members can be circular, square, or rectangular sections, although other shapes such as elliptical are also available. HSS is only composed of structural steel per code.

HSS is sometimes mistakenly referenced as hollow structural steel. Rectangular and square HSS are also commonly called tube steel or box section. Circular HSS are sometimes mistakenly called steel pipe, although true steel pipe is actually dimensioned and classed differently from HSS. (HSS dimensions are based on exterior dimensions of the profile; pipes are also manufactured to an exterior tolerance, albeit to a different standard.) The corners of HSS are heavily rounded, having a radius which is approximately twice the wall thickness. The wall thickness is uniform around the section.

In the UK, or other countries which follow British construction or engineering terminology, the term HSS is not used. Rather, the three basic shapes are referenced as CHS, SHS, and RHS, being circular, square, and rectangular hollow sections. Typically, these designations will also relate to metric sizes, thus the dimensions and tolerances differ slightly from HSS.

HSS, especially rectangular sections, are commonly used in welded steel frames where members experience loading in multiple directions. Square and circular HSS have very efficient shapes for this multiple-axis loading as they have uniform geometry along two or more cross-sectional axes, and thus uniform strength characteristics. This makes them good choices for columns. They also have excellent resistance to torsion.

HSS can also be used as beams, although wide flange or I-beam shapes are in many cases a more efficient structural shape for this application. However, the HSS has superior resistance to lateral torsional buckling.

The flat square surfaces of rectangular HSS can ease construction, and they are sometimes preferred for architectural aesthetics in exposed structures, although elliptical HSS are becoming more popular in exposed structures for the same aesthetic reasons.

In the recent past, HSS was commonly available in mild steel, such as A500 grade B. Today, HSS is commonly available in mild steel, A500 grade C. Other steel grades available for HSS are A847 (weathering steel), A1065 (large sections up to 50 inch sq made with SAW process), and recently approved A1085 (higher strength, tighter tolerances than A500).

Square HSS is made the same way as pipe. During the manufacturing process flat steel plate is gradually changed in shape to become round where the edges are presented ready to weld. The edges are then welded together to form the mother tube. During the manufacturing process the mother tube goes through a series of shaping stands which form the round HSS (mother tube) into the final square or rectangular shape. Most American manufacturers adhere to the ASTM A500 or newly adopted ASTM A1085 standards, while Canadian manufacturers follow both ASTM A500 and CSA G40.21. European hollow sections are generally in accordance with the EN 10210 standard.

HSS is often filled with concrete to improve fire rating, as well as robustness. When this is done, the product is referred to as a Lally column after its inventor John Lally of Waltham, Massachusetts. (The pronunciation is often corrupted to lolly column.) For example, barriers around parking areas (bollards) made of HSS are often filled, to at least bumper height, with concrete. This is an inexpensive (when replacement costs are factored in) way of adding compressive strength to the bollard, which can help prevent unsightly local denting, though it does not generally significantly increase the overall structural properties of the bollard.

CHS – Circular Hollow Sections: For Aesthetics and Strength

Circular hollow sections (CHS) was the first form of hollow section. Commonly used in a wide range of structural, mechanical and construction areas.

From an architectural perspective the constant clean lines provide a very smooth surface appearance which is often employed in many high-profile applications. The lack of protruding edges on these fully closed sections assists in reducing the effects of exposure to the elements and also in increased cleanliness from dust and other material build-up.


RHS – Rectangular Hollow Sections: For Economy and Strength

Rectangular hollow sections (RHS) is a popular choice for mechanical, structural and construction applications. This is due to the flat surface resulting in a structural solution that is more economical for joining and various other types of fabrication works.

Due to the rectangular shape of this type of hollow section, when joining to other flat surfaces sections only need to be straight cut. RHS requires minimal edge preparation for welding or joining.

RHS can also be used for architectural aesthetics due to possessing clean lines alongside structural strength.


SHS – Square Hollow Sections: For Symmetry, Balance Strength and Aesthetics

Square hollow sections (SHS) is another popular type of structural steel tube that’s kind of a middle-man between RHS and CHS in terms of attributes, appearance and structural behavior.

SHS features a flat surface that’s also economical for joining and welding, with clean lines and minimal edge preparation required.

SHS also features attributes of CHS, with its symmetrical appearance, formed in equal-sided square hollow sections – as opposed to circular sections.

SHS provides an ideal balance between strength, functionality and aesthetic appearance for a multitude of applications that require all three aspects.



ASTM A312: TP304, TP304L, TP316, TP316L

EN 10210:S235JRH,S355J2H,S355NH

EN 10219:S235-S550

ASTM A500:Gr.b

ASTM A501:Gr.b

Steel hollow sections are one of the most versatile and efficient forms for construction and mechanical applications. Some of the strongest and most impressive structures today would not have been possible without hollow sections.

We are structural hollow section specialists and hold an extensive range of stock and the widest range of sizes, all from quality assured sources, including:

Structural hollow sections in grades S235, S355 & S420 amongst others.

En10210 – hot finished

En10219 – cold formed

Standard lengths range from 6 metres to 18 metres

Comprehensive stocks of 3CR12 utility stainless and gas list tubes


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