An HSS column is a structural steel column made from Hollow Structural Sections, which are high-strength welded steel tubes with a hollow center. They come in three shapes: square, rectangular, and round. You’ll find them supporting buildings, bridges, canopies, and exposed architectural frameworks where both strength and appearance matter.
Shape, Size, and Why They’re Hollow
The “hollow” part is the defining feature. Unlike traditional wide-flange steel beams (the I-shaped ones you’ve probably seen on construction sites), HSS columns are closed tubes. That closed shape gives them excellent resistance to twisting forces and makes them efficient at carrying compressive loads, which is exactly what a column needs to do. The hollow core also means less steel is used per unit of strength, making HSS one of the most economical structural members available.
Square and rectangular HSS columns are popular because their flat faces simplify connections to other structural members. Round HSS columns offer the best resistance to buckling in all directions and are a common choice for exposed architectural applications, highway signs, and pipe structures. Sizes range widely, with perimeters up to 88 inches and wall thicknesses up to 1 inch.
How HSS Columns Are Made
Most HSS columns are manufactured using electric resistance welding, or ERW. A flat sheet of steel is cold-formed into a tube shape, then a high-frequency electric current heats the edges until they fuse together without any filler material. This creates a longitudinal seam running the length of the tube. The process is relatively simple and keeps costs low compared to alternatives.
Seamless HSS exists as well, though it’s less common for structural columns. Seamless tubes start as a solid steel billet that’s heated, pierced through the center with a bullet-shaped tool, and rolled into a hollow cylinder. Because there’s no weld seam, seamless tubes handle higher internal pressures (roughly 20% more than ERW) and resist certain types of corrosion better. For most building columns, though, ERW is the standard choice.
Steel Grades and Specifications
The most widely used specification for HSS columns is ASTM A500, with Grade C being the current default in structural design. Grade C steel has a minimum yield strength of 50,000 psi and a minimum tensile strength of 62,000 psi. In practical terms, yield strength is the point at which the steel permanently deforms, so higher numbers mean the column can carry more load before any damage occurs.
A newer specification, ASTM A1085, is gaining traction because it tightens the manufacturing tolerances significantly. Under A500, the actual wall thickness of a tube can vary enough that engineers have to design conservatively, assuming the walls might be thinner than listed. A1085 limits the wall thickness tolerance to just 5% below the stated value and the mass tolerance to 3.5% below nominal. That means engineers can use the full listed thickness in their calculations, which translates to more efficient designs and, in some cases, lighter or smaller columns for the same load.
Filling HSS Columns With Concrete
One of the most practical advantages of a hollow column is that you can fill it with concrete. This creates a composite member where the steel tube acts as permanent formwork and the concrete core dramatically increases the column’s load-carrying capacity. The steel confines the concrete, preventing it from cracking outward, while the concrete prevents the steel walls from buckling inward. Each material compensates for the other’s weakness.
Concrete fill also provides fire resistance. An unfilled steel column loses strength quickly in a fire because steel conducts heat efficiently. A concrete-filled HSS column can achieve fire endurance ratings of up to 3 hours, depending on the column size, concrete strength, load level, and whether reinforcing bars are added inside the concrete. This can eliminate or reduce the need for spray-on fireproofing, which saves money and preserves the column’s clean appearance.
Connection Methods
Connecting other structural members to an HSS column is slightly more involved than connecting to a traditional I-beam, mainly because the hollow interior complicates bolting. Welding is the most common approach. Plates, brackets, or other connection hardware are typically shop-welded to the HSS column before it arrives on site, so field crews can bolt beams and braces to those pre-attached plates without needing to weld at height.
When bolting directly to HSS is necessary, several options exist. Conventional bolts work near the open ends of the tube or when access holes are cut into the wall. Through-bolts pass completely through both walls of the tube. Blind bolts are specialty fasteners designed to be installed from one side when you can’t reach inside the tube. Flow-drilled bolts use friction heat to form a small collar of steel around the hole, creating threads directly in the tube wall without a separate nut on the inside.
Architectural and Visual Appeal
HSS columns are a favorite for architecturally exposed structural steel, where the structure is left visible as a design element rather than hidden behind drywall or cladding. The smooth, consistent surface of an HSS tube closely resembles a hot-rolled shape and takes paint or other finishes well. Round columns in particular create a sleek, modern look that wide-flange shapes can’t match.
When HSS is specified for exposed applications, manufacturers handle and store the material more carefully to prevent surface damage. This matters because scratches, dents, or rust staining that would be invisible behind a wall become obvious on an exposed column. Mechanical-grade pipe, which might look similar at first glance, typically has a rougher “orange peel” texture and isn’t suitable as a substitute in visible applications.
Where HSS Columns Are Used
HSS columns show up across a wide range of structures. In commercial buildings, they’re common in lobbies, atriums, and open-plan spaces where architects want slender, unobtrusive columns. Parking garages use them because the closed shape resists corrosion better than open shapes that trap moisture. In industrial settings, they support mezzanines, conveyor systems, and equipment platforms.
For seismic design, HSS columns can be used in lateral force-resisting systems, though the requirements become more stringent. The AISC Seismic Provisions (AISC 341) specify additional detailing and connection requirements for steel members in high-seismic zones. The closed shape of HSS performs well under the cyclic loading that earthquakes produce, but the wall thickness and width-to-thickness ratios must meet tighter limits to prevent local buckling during repeated load reversals.