Box Column or Double IPE Column? A Practical Comparison for Steel Frames

In small and mid-rise steel-framed buildings, two column types come up again and again: the box column (a closed square or rectangular section) and the double I column, built up from two I-beams joined by plates or batten strips. This guide compares them from the fabrication and procurement side, so that conversations with the structural engineer and material orders are more precise. The final choice of column type and size always rests with the structural engineer.

The two options

A box column is a closed section. It can be a mill-made hollow section such as the square hollow section (SHS) or rectangular hollow section (RHS) in the Ahan Asa catalog, supplied to EN 10219-2 in grade S235JRH, or a built-up "box" welded from four heavy plates such as S235JR hot-rolled plate.

A double I column uses two IPE beams (sometimes IPN) set at a fixed spacing and welded together with continuous plates or spaced battens. For the difference between the two beam ranges, see IPE vs IPN beams.

Section behaviour: weak axis and torsion

A single I-section has a strong and a weak axis. Doubling the beams and spacing them apart offsets part of this, but the column's behaviour also depends on how the two legs are tied together.

According to a technical article by the Steel Tube Institute, hollow sections are more than 200 times stronger than open sections of similar weight in resisting torsion, and because they have no weak axis, tall columns usually need less bracing; the article recommends them for corner columns where strength about both axes matters. The manufacturer Atlas Tube claims, in promotional material, that an HSS column has a smaller footprint than a wide-flange shape of equal axial capacity and is efficient in biaxial bending. These are general properties of the section, not the outcome of a specific building design.

Beam-to-column connections

• Double I column: flanges and the space between the legs are open to the welder, so seats, connection plates and stiffeners go on accessible faces and welds are easy to inspect visually.
• Box column: once closed, the inside cannot be reached. Any internal plates that moment connections may require must be placed before the last face is closed or handled with special details. The Steel Tube Institute recommends specifying a shear tab on the column face rather than a through plate as the more economical choice, and Atlas Tube mentions blind bolts for connecting to closed sections.

Fabrication, coating and corrosion

Atlas Tube states that a hollow section has a smaller perimeter and surface area than an open section of equal capacity, so it needs less material for coating or fireproofing, and that with no re-entrant corners coating is simpler to apply, with a more consistent thickness at the corners. On the other hand, water must be kept out of a closed column during construction and its ends sealed properly. For hot-dip galvanized members, the SN50 guidance note requires vent and drain holes near each end, diagonally opposite, and forbids fully sealed internal chambers in a galvanized fabrication.

What to order

• Mill-made box columns: outside dimensions, wall thickness, length and quantity from the drawings, from the hollow sections category.
• Built-up plate boxes: a plate list by thickness and width of each face and column length, with cutting waste.
• Double I columns: the number of beams plus battens or plates and base plates.
• On delivery, check the mill certificate and the grade specified on the drawings, and accept substitutions only with the structural engineer's written approval.

Summary

Both column types are well established. The closed section is efficient in torsion and biaxial loading and easier to coat, but its interior is inaccessible and connection details must be solved in advance. The double I column is simpler to connect and inspect but needs more welding and fabrication accuracy. Once the drawings are final, you can contact Ahan Asa to prepare the material list and request a quotation.