Q355B Lattice Column Built Up Column for Heavy Industrial Plant with Up to 30m Height

A lattice column places steel where it works and leaves the middle empty. Two or four legs carry the axial load at the corners of a large section, while lacing or batten plates hold them together. The result is a column with the bending stiffness of a much deeper solid member, at a fraction of the weight.

Bending capacity depends on how far the material sits from the neutral axis, not on how much material there is. A solid web column of the same overall depth would carry the same moment, but most of its web would be doing very little.

The void does three more things:

• It lets services pass through the column — cable trays, pipework, compressed air — without boxing out.
• It reduces the surface area that needs painting or fire protection.
• It lets the column be shipped as separate legs and lacing instead of one welded box that eats container space.

• Legs (main members). Rolled H-sections, channels or welded boxes, sized for the axial load and for the slenderness of a single leg.
• Lacing bars (laced column). Flat or angle bars on both faces, set diagonally. Typically at 40° to 70° to the column axis, in a single or double system.
• Batten plates (battened column). Flat plates on both faces, parallel to each other. Cheaper to make than lacing, less efficient in shear, and it needs end battens.
• Diaphragms. Plates or frames at the ends and at intermediate points, tying the legs together and keeping the section square in plan.

Lacing is not a connector. Once the column bends, the legs try to move relative to each other, and the lacing resists that movement. The shear in the lacing comes from the column shear plus the shear from any imperfection, and it is the reason a laced column is designed as a system rather than as separate members.

That is also why a battened column and a laced column of the same overall size are not interchangeable. The battened version relies on frame action between the battens, so the battens and their connections see larger local forces.

A built-up column has two slenderness values that matter: the whole member about each axis, and a single leg between points of connection. The second one is easy to forget and expensive to get wrong — a leg that is too slender buckles locally, and the column fails well below its calculated capacity.

In Chinese practice the design uses an equivalent slenderness that combines the two. EN 1993-1-1 handles built-up members in its own clause and applies an imperfection of L/500 instead of the L/200 used for a solid member. AISC 360 has its own provisions. The three codes agree on the principle and differ in the arithmetic, which is why the standard has to be named before the column is sized.

Four things decide whether a lattice column arrives straight and fits on site.

• Jig assembly. Legs are set in a jig at the correct spacing and square, then lacing is fitted to the jigged assembly. Building it freehand and pulling it straight afterwards leaves residual stress in every weld.
• Welding sequence. Symmetrical, balanced, back-step where the lacing meets the leg. Lacing is thin relative to the leg, so the heat goes in low and fast to avoid curling the bar.
• Straightness. Checked against the execution standard named on the drawing — EN 1090-2 or GB 50205 — not against what the workshop is used to.
• End bearing. The base and cap plates are machined or milled flat after welding. A column that bears on a plate with a gap shims itself under load, and the load path moves.

A 12 m lattice column at 1.2 m centres occupies the volume of a small room. Shipped assembled, one column can take the space of six tonnes of ordinary beams.

The normal route is to send the legs as bundles and the lacing as a separate crate, with a match-marked erection drawing. Site assembly is bolted where the design allows, or welded under the same procedure used in the factory. Both are cheaper than paying for air.

For a primary member we issue the material certificates to EN 10204 3.1, the dimensional record, the straightness record and the weld inspection report. Where the column is fatigue-loaded or part of a crane structure, ultrasonic testing on the leg-to-batten and leg-to-diaphragm welds is specified at enquiry stage.

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