Steel Tube: RHS vs CHS vs SHS

Steel tube, also known as hollow sections, are a practical choice for everything from building frames and posts to gates, machinery, rural projects, furniture and architectural work. As they have a hollow interior,  hollow sections provide useful structural performance without the weight of a solid bar.

Edcon Steel’s range of steel RHS (rectangular hollow section), SHS (square hollow section), and CHS (circular hollow section), are cold-formed, electric resistance-welded and manufactured to AS/NZS 1163  for structural and engineering purposes.

When deciding between hollow sections, there is no single “best” steel tube for every project, as the shape changes how the section behaves and how easily it can be fabricated or connected. Deciding which steel hollow section is right for your project depends on what it needs to do.

So let’s dive into steel hollow sections and explore the key considerations when deciding between RHS, CHS, and RHS.

Steel RHS for beams, frames, and directional loads

Steel RHS has a rectangular cross-section, so its depth and width are different, which matters when the section is carrying bending loads. RHS is a popular choice for beams, frames, and supports, as the differences in depth and width allow the section to be selected and oriented for direction bending. That makes RHS a great choice for applications where the load has a clear main direction, or you want a deeper rectangular member without making it equally wide. For example, a steel beam supporting a roof may bend downwards under the weight of the roof and anything placed on it. RHS can be positioned with its deeper side vertical, it can better resist bending. 

However, orientation is very important. Turning the same RHS through 90 degrees changes which principal axis is resisting the load. So, for anything structural, do not choose or rotate RHS simply because it looks strong enough. The nominated size, orientation, restraint and connection detail should match the engineer’s design.

Edcon Steel stocks structural RHS in a range of dimensions and wall thicknesses, with mill finish, primed and galvanised options available across the broader RHS range. 

Steel SHS for balanced frames, posts and fabrication

Steel SHS has equal outside dimensions on all four sides, which means it has equal geometric properties about its main principal axes This means SHS has the same strength on all sides, and can therefore handle forces from different directions. 

The clean, symmetrical appearance also makes SHS useful where the steel remains visible.making it a popular choice for posts, columns, welded frames, equipment supports, gates, furniture and general fabrication. You still get the fabrication advantages of flat surfaces, but without having to decide which of two unequal side dimensions is the “deep” side.

However, it’s important that you don’t assume that SHS is suitable for a particular load just because the outside dimension is large. Wall thickness and grade are also fundamental to its structural properties, and Edcon Steel’s SHS range includes multiple combinations of section size and thickness for different requirements.

Steel CHS for round profiles and multi-directional performance

Steel CHS is circular, so its geometry does not have a strong and weak principal direction in the way an RHS does. That makes a circular hollow section particularly useful where the direction of bending may vary. In fact, CHS is the most structurally efficient profile for resisting torsion (i.e. twisting force), making them perfect for eccentric (off-centre) loads, such as perimeter columns supporting curved roofs or cantilevered walkways. The actual torsional capacity still depends on the dimensions, wall thickness, steel grade and loading, so the shape alone does not determine capacity. 

The circular, smooth finish, can also be an advantage where appearance or handling is important. This aesthetic appeal makes CHS a popular choice for visible applications, like posts, columns, bracing, and handrails.

It is also worth distinguishing structural CHS from ordinary pipe. Products that look similar can be manufactured to different standards and specified differently. AS/NZS 1163 covers structural steel hollow sections,, while AS 1074 covers steel tube for ordinary service. For load-bearing work, confirm the required grade and standard rather than substituting a similar-looking pipe. 

Key Considerations When Choosing between RHS, CHS, and SHS

When choosing between RHS, SHS, and CHS, profile is only part of the decision. Practical differences between each of the hollow sections are just as important, as the flat faces on RHS and SHS make it straightforward to position plates, brackets, cladding, and other components, while the smooth round profile of CHS means attaching flat components may require more thought in the connection detail. 

Size, wall thickness, steel grade, span, loading, connections and restraint are also incredibly important for structural applications, so here’s some things to consider: 

Consider the load direction: For bending mainly in one plane, steel RHS can make efficient use of a deeper rectangular section. Where similar behaviour is wanted about two principal axes, SHS may be simpler. Where the direction varies around the section, CHS has circular symmetry. 

Check size, thickness and grade together: Two tubes with similar outside dimensions can have very different properties if their wall thicknesses or steel grades differ. AS/NZS 1163 includes structural hollow-section strength grades, and Edcon stocks hollow sections in multiple sizes and specifications. 

Think about the connections: RHS and SHS provide flat faces that can make brackets, plates, bolted fittings and welded frames easier to lay out. CHS can be an excellent structural choice, but curved-to-flat or tube-to-tube joints often need more careful detailing. 

Choose the finish for the environment: Edcon’s range of RHS, CHS, and SHS includes mild steel, painted or primed tube, pre-galvanised and galvanised options, as well as stainless steel tube for selected applications. The right corrosion protection depends on whether the steel will be indoors, outdoors, exposed to moisture or used in a more demanding environment. 

Compare the complete job cost, not only the price per metre: Section size, thickness, required cuts, fabrication, coating, freight and installation can all affect the final result. Edcon’s custom cutting service means you only pay for what you actually need.

Edcon Steel stocks a comprehensive range of hollow sections, which can be ordered online and cut to length, with delivery available Australia-wide, or pickup available from Edcon Steel stores in Brookvale, Blacktown, Revesby, Bathurst or Orange.

Important Safety & Specification Disclaimer

This article is intended as a general guide only and should not be relied upon as engineering, design, safety or compliance advice. Steel hollow section product requirements can vary significantly depending on the application, loads, environment and installation method, so always check relevant Australian Standards, building codes and workplace safety requirements, and consult a qualified engineer, builder or other appropriate professional where required before specifying, fabricating or installing these products.