18 m Round-Tube Truss HJ-1: φ478 Chords, φ219 Webs, Q235B

English Version

Title: 18 m Round-Tube Truss: φ478×10 Chords, φ219×7 Webs, Q235B Spiral Tube

Overview

A round-tube truss carries long spans without a heavy solid beam. Chords take the tension and compression; the webs split the load into short, predictable diagonal members. Because every member is a tube, the section looks clean and weighs less than a plate girder over the same 18 m.

This member is HJ-1, added to an existing frame. The drawing set covers the plan, the elevation, and section 1-1: a 18,000 mm span, 2,778 mm deep, with φ478×10 chords and φ219×7 webs in Q235B spiral-welded tube.

Geometry (from Drawing)

表格

Section Table (from Drawing)

*kg/m calculated from the tube dimensions at 7,850 kg/m³; the drawing lists sections only.

How the Truss Works

• Chords carry the span. HJL-1 and HJL-2 are the two φ478×10 tubes running the full 18 m. One works in compression, the other in tension; the moment between them sets the 2,778 mm depth.
• Webs split the load. FG-1 verticals and XFG-1 diagonals, both φ219×7, transfer panel loads to the chords. Diagonals carry shear; verticals hold the panel spacing.
• Tube nodes are welded. Tubes meet at welded gusset or directly at the chord; round sections reduce the node surface and wind drag.
• Added to an existing frame. Both ends tie into the existing side-hole haunch; the truss replaces or supplements the original K-type beam above.

Advantages

1. Light for an 18 m span — tube chords and webs use steel where the force is; a solid beam at this span would weigh far more.
2. Open section — no enclosed box to inspect inside; every member is visible and paintable.
3. Round tubes resist wind — circular sections have low drag, which matters for exposed roof and outdoor trusses.
4. Standard spiral tube — φ478×10 and φ219×7 are produced in volume; availability and pricing are predictable.
5. Bolted or welded end connections — the end zone can be bolted to the existing frame, so the retrofit does not require shutting the building down.

Disadvantages / Limitations

1. Node welding is skilled work — round tubes cut to angle and welded to a chord or gusset need qualified welders and fit-up jigs.
2. Hollow tubes need sealing — water and condensation collect inside an open tube; venting and end caps are required.
3. Flexible against a solid girder — a truss deflects more than a plate girder of the same weight; deflection and vibration control matter for live load.
4. Web members carry slenderness limits — φ219×7 diagonals must be checked as tension/compression members; long diagonals buckle if over-compressed.
5. Retrofit load path — an added truss must transfer forces into the existing haunch; the old structure has to be checked for the new load.

Typical Use Cases

1. Existing-frame reinforcement — adding HJ-1-type trusses to strengthen an old roof or platform, as in this drawing.
2. Long-span roof trusses — sheds, warehouses, and canopies over 15–20 m.
3. Platform and gallery spans — walkways, equipment platforms, and pipe racks needing an open truss underneath.
4. Exposed outdoor structures — where wind drag and appearance both count.
5. Bridge and trestle spans — light steel truss between supports.

Fabrication and Erection Notes

• Tube: Q235B spiral-welded; check mill certificate and roundness before cutting.
• Chords: mark panel points from the 11,000 mm middle zone and the two 1,500 mm end segments.
• Node: cut web tubes to the true angle; check fit-up before welding; weld all around at each node.
• Ends: connect to the existing haunch; verify the old column and beam take the new truss reaction before loading.
• Internal protection: seal tube ends, provide vent holes; coat the exterior after fabrication.
• Erection: lift the truss as one piece where weight allows, or erect chords and webs in sequence; brace the truss before releasing the crane.

Bottom Line

An 18 m round-tube truss on Q235B: two φ478×10 chords, φ219×7 verticals and diagonals, 2,778 mm deep, added to an existing frame. It covers the span with a fraction of a solid beam's weight. Get the node fit-up, the tube sealing, and the old-frame load check right, and the truss will carry what it was designed for.

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