Not every engineering application calls for a circular tube cross-section. Square and rectangular hollow sections (SHS and RHS) offer flat bearing surfaces, easier connection detailing, and aesthetic advantages that make them the default choice for many structural and architectural applications. Understanding when each section shape delivers the best performance helps you optimise both structural efficiency and fabrication cost.
Round Hollow Sections (CHS)
Circular hollow sections are the most structurally efficient shape for axial compression and torsion. The uniform radius distributes compressive stress evenly around the circumference, and the absence of corners eliminates stress concentration points. CHS columns have the highest compressive capacity per kilogram of steel of any standard section shape, making them the optimal choice for heavily loaded columns, offshore jacket legs, and transmission towers.
CHS also excels in fluid-handling applications where the tube must resist internal pressure. The hoop stress in a circular tube is uniform and equal to PD/2t — the most efficient geometry for pressure containment. For hydraulic cylinders, pneumatic actuators, and pressure vessels, CHS is the only practical choice.
The limitation of CHS is connection complexity. Welding a CHS branch to a CHS chord requires profile-cut (saddle-cut) preparation that is more labor-intensive than the straight mitre cuts used for square and rectangular connections. For heavily braced structures with many joints, the fabrication cost of CHS connections can offset the material savings.
Square Hollow Sections (SHS)
Square hollow sections provide equal bending resistance about both axes, making them the natural choice for columns subjected to biaxial bending or where the load direction is indeterminate. SHS connections are simpler than CHS: flat faces allow straight-cut preparation and fillet-welded joints without the profile cutting that CHS demands.
Architecturally, SHS provides a clean, modern aesthetic for exposed structural elements in commercial buildings, facades, and furniture. The flat faces also simplify the attachment of cladding, handrails, and secondary steelwork using bolted cleats or welded gussets.
SHS is less efficient than CHS for pure axial compression (the corner regions are further from the centroid and contribute less to the section’s second moment of area), but the fabrication cost savings on connections typically compensate for the slightly higher steel weight.
Rectangular Hollow Sections (RHS)
Rectangular hollow sections are the right choice when bending resistance is required primarily about one axis. By orienting the major axis of the RHS in the direction of the primary bending moment, you achieve greater section modulus for the same weight of steel compared to an SHS of equivalent area. This makes RHS the standard section for beams, rafters, and horizontal members in portal frames and trusses.
RHS also provides an efficient cross-section for columns in moment frames where the bending moment from beam connections is predominantly in one direction. The deeper section provides greater stiffness in the critical direction without the weight penalty of a larger SHS.
Selection Guidelines
For columns with dominant axial load: CHS for maximum efficiency, SHS for simpler connections. For beams and members with single-axis bending: RHS oriented with the major axis in the bending direction. For columns with biaxial bending: SHS for equal resistance both ways. For pressurised service: CHS always. For architectural exposure: SHS or RHS for clean lines and flat connection surfaces. For structures with many brace connections: SHS or RHS to minimise fabrication labor.
Global Seamless Supply
Global Seamless manufactures seamless CHS, SHS, and RHS in structural and mechanical grades to ASTM A500, A501, and A519. Cold-formed and hot-finished sections are available across standard size ranges with custom lengths to minimise site cutting waste.
Need structural hollow sections? Submit your section sizes and loading requirements for a quotation.