Twin-Leg Steel Lattice Column: Φ920×20 Tubes up to 29 m

English Version

Title: Lattice Column, 32 m Tall: Two Φ920×20 Tubes, X-Braced, Q355

Overview

A lattice column  is a built-up column made of two or more slender steel legs tied together by bracing. Instead of one heavy rolled section, it uses separated legs — placed far apart — to get bending stiffness from distance rather than from mass. That makes it the economical choice for tall, heavily loaded columns in large-span workshops and industrial buildings.

This project's column is a twin-leg lattice: two Φ920×20 steel tubes, X-braced along the height, from foundation level −3.150 m to the roof at +29.000 m.

Drawing Data

Why a Lattice Instead of a Solid Column

• Bending stiffness from separation: two legs 500 mm apart have far more bending resistance than one tube of the same total steel area.
• Slender legs are cheap: Φ920 tubes are mill products; a single solid section of the same capacity would be a heavy welded box.
• Height is the driver: at 32 m tall, a solid column would be enormous; the lattice keeps each leg manageable for transport and erection.
• Buckling control: X-bracing between legs stops each leg from buckling independently — the braced pair acts as one column.
• Boxed transition at the base: the BH1400×650×25×30 box ties the two legs into a single base for the foundation connection.

Advantages

1. High capacity for the steel used — separated legs carry big axial load and bending moment with less tonnage than a solid section.
2. Transportable — each Φ920 leg ships as a normal tube length; no oversize loads.
3. Erection-friendly — legs are erected one at a time, then braced; the crane lifts manageable pieces, not a 30 t monolith.
4. Open interior — the space between legs can carry ladders, pipes, and cable trays inside the column.
5. Inspectable — every leg and brace is visible; corrosion and damage are found before they become structural.

Disadvantages / Limitations

1. More fabrication labor — two legs, dozens of braces, many welded or bolted joints; cost per ton is higher than a rolled section.
2. Bracing welds are fatigue points — X-braces get cyclic stress from wind and crane loads; weld details need proper design, not shop improvisation.
3. Larger footprint — the 500 mm leg spacing plus bracing takes floor area that a single column would not.
4. Fire protection is harder — coating two legs and all braces takes more labor and material than one solid column.
5. Connection complexity — base box, cap plate, and beam connections must be coordinated; misalignment at the base box is costly to fix.

​​​​​​​Typical Use Cases

1. Large-span workshop columns — tall columns under long roof spans, where a single section would be too heavy (this drawing).
2. Industrial plants with heavy roof loads — columns carrying roof, equipment, and pipe loads at 20–30 m height.
3. Crane-supporting columns — lattice columns that carry heavy crane girders and dynamic loads.
4. Pre-engineered large buildings — exhibition halls, hangars, and logistic centers with tall clear heights.
5. Retrofit and strengthening — existing columns upgraded by adding a second leg and bracing.

Fabrication and Erection Notes

• Legs: Φ920×20 tube, Q355 — verify wall thickness and mill certificate; measure ovality before fit-up.
• Segmentation: follow the drawing's segment lengths (2,500 / 1,800 / 2,800 / 2,200 / 1,250 / 2,900 / 2,150) for shop assembly and transport.
• Bracing: X-diagonals welded between legs; use full-penetration or fillet welds per drawing; check with UT/MT at critical joints.
• Base box: BH1400×650×25×30 welded box at the bottom; align with the foundation anchor bolts before welding the legs in.
• Erection: erect legs individually, plumb, then install bracing from bottom up; do not release the crane until the first bracing tier is complete.
• Coating: blast and coat each leg and brace before erection; repair weld zones after site welding.

Bottom Line

A 32 m lattice column is how you carry a big roof load without a big solid column: two Φ920×20 tubes, X-braced, boxed at the base, in Q355. It uses distance for stiffness and keeps every piece shippable and liftable. The price is fabrication labor and weld quality — the bracing welds are where this column earns or loses its safety margin.

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