Q355B Large Diameter Welded Steel Tube Column CHS for High Rise Steel Frame Building

Large diameter steel tube columns — rolled, welded and concrete-filled. Diameter 400–2,000 mm, wall 8–60 mm, Q355B, supplied as CHS or CFST.

• 400–2,000 mmDiameter range
• 8–60 mmWall thickness
• Q355BSteel grade
• CHS / CFSTSection type

A steel tube column behaves the same in every direction. That single property is why it is used where wind or seismic load can come from anywhere, and why it looks right when the structure is left exposed. Making one is a different problem from making an H-column, and the difference starts at the plate.

A steel tube column has the same second moment of area about every axis through its centre, so it does not have a weak direction. In torsion, a closed section is far stiffer than an open one, which matters on a slender column under eccentric load.

It is also the most efficient shape for a given perimeter, which is why it wins on exposed structures where the surface is the cost.

What it loses is connection simplicity. An H-column takes a bolted end plate, a cleat or a simple seated connection with no fabrication. A tube needs a machined end, a flange ring, or a profiled joint — and that work is where the cost sits.

Large diameter steel tube columns are not bent on a pipe bender. A pipe bender forms small tube; a structural column of 800 mm diameter starts as a flat plate.

1. Plate preparation. Plate is cut to the developed width, with the longitudinal edges bevelled for a full-penetration seam.
2. Rolling. The plate is rolled into a cylinder on a three-roll or four-roll machine, with the ends pre-bent so the seam closes without a flat spot.
3. Longitudinal seam. Submerged arc welding, inside and outside, with the seam rotated to the flat position.
4. Re-rounding. After welding the tube is mechanically re-rounded, because the seam contraction makes it oval.
5. Circumferential splices. Where the column is longer than a plate, sections are joined with a circumferential weld, aligned on a fitting jig.
6. End machining. Both ends are machined square and flat, so the column bears on its base plate across the full section.

Seamless and spiral-welded pipe are the other two sources. Seamless is limited in diameter and wall; spiral pipe is common for piles and less common for architectural columns.

A steel tube column has two failure modes that an H-column does not have in the same way. The first is local buckling: if the wall is thin relative to the diameter, the tube dents before the column as a whole buckles, and the calculated capacity is never reached. The diameter-to-thickness ratio is the number that controls it, and every code sets its own limit.

The second is out-of-roundness. A tube that is oval has a lower section modulus than the nominal section, and the loss is not obvious on site. Both roundness and straightness are measured and reported against the execution standard — EN 1090-2 or GB 50205 — not against what the shop is used to.

A tube-to-tube joint is cut on a profile, not with a square saw. The brace end follows a saddle curve that depends on the diameter ratio and the angle, and it is cut on a CNC pipe profiling machine. A joint cut by hand and dressed with a grinder leaves a gap that no amount of weld will close properly.

Where a beam meets a column, the usual details are a through-plate, an internal ring stiffener, or an external flange ring. Each has a different fatigue behaviour, and the choice is usually made by the designer — but it has to be buildable. An internal ring that cannot be welded from the outside is a design that cannot be fabricated.

Filling the tube with concrete changes three things at once: stiffness goes up, fire resistance improves because the concrete absorbs heat and the steel is protected from within, and the section can be smaller for the same load.

It also adds a site process. The tube needs vent holes at the top and a filling point at the bottom, the concrete has to be pumped or poured without voids, and the mix has to flow — self-compacting concrete is normal. The steel is inspected before filling and not after.

If CFST is intended, say so at enquiry stage. The vent and filling details belong on the fabrication drawing, not on a site instruction.

Longitudinal seams are submerged arc, welded both sides. Circumferential splices are welded with the procedure qualified for the wall thickness, and where the column is a primary member the seam and the splice are ultrasonically tested.

Specify the execution standard, the weld quality level, the NDT percentage and the certificate grade at enquiry stage. A tube column that meets one standard is not automatically acceptable under another, and the argument usually happens after the steel has been painted.

Diameter, not length, usually governs. A steel tube column of 1.5 m travels as break-bulk or on an open-top; a 2 m tube ships on deck with the ends capped. Columns longer than about 12 m are spliced, and the splice position is set by the transport route rather than by the structure.

Site splices are either bolted flange connections or welded. Bolted is faster and needs no site welder; welded is cheaper in steel and needs a qualified procedure on site. Decide before the drawings are issued.

Send these and we return the fabrication drawing, the weight and a quotation.