Pipe Truss Connection Specifications — The Weld Is the Design
A pipe truss is a set of tubes whose entire load path lives in its connections. The K-joint at every chord-to-web intersection must deliver the forces the analysis calculated, or the truss is a sculpture with a load rating. We design, fabricate and inspect tubular connections to EN 1993-1-8 and GB 50017 — with a shop-floor quality regime that treats every weld as a structural member in its own right. This page sets out the joint types, geometric rules, weld specifications and inspection plan behind our planar and spatial pipe trusses.
K, T, Y and KT: Which Connection Goes Where
T and Y joints connect a web member square onto, or at an angle to, the chord face. They occur at truss ends, supports and localised load points, and their governing limit states are chord-face punching shear, chord wall local yielding and (for wide gaps) local buckling.
K and N joints are the workhorse of planar trusses — two web members meeting the chord from opposite sides, either with a gap (K-gap) or overlapping (K-overlap). The gap geometry controls the force transfer mechanism: a small gap (< gmin) produces high local stresses at the chord wall; a large gap pushes the joint into chord-face shear. We set web member angles between 30° and 60° as a design rule, and lock the gap to the EN 1993-1-8 range 0.5(1-β)d0 ≤ g ≤ 1.5(1-β)d0 — the limits that keep the joint in the calculable regime.
KT joints bring three web members to one chord face, common in spatial truss nodes and Vierendeel transfer levels. KT geometry multiplies the intersection complexity, and we detail them with a clear gap policy so the three members do not crowd into a zone the analysis assumed free of interaction.
For spatial (non-planar) trusses, the connections are modelled and detailed in true 3D — the web members meet the chord at compound angles, and the weld profile is set from the actual dihedral angles rather than the flat projection. Our multi-tube welded joints at Xuzhou East High-Speed Rail Station and the curved-box truss programme are built from these spatial connection details.
Welded Tubular Connection — Standard Parameters
| Parameter | Typical Range | Standard / Note |
|---|---|---|
| Chord member | Φ219 – Φ900 mm × 8-30 mm wall | Q355B/Q390B/Q420B; D/t ≤ 50 for weldability control |
| Web member | Φ76 – Φ480 mm × 4-16 mm wall | β = d1/d0 checked per joint class |
| Joint angle | 30° – 60° web-to-chord | θ ≥ 30° rule per EN 1993-1-8 §7.1 |
| Gap (K/N joints) | 0.5(1-β)d0 ≤ g ≤ 1.5(1-β)d0 | Gap > 0 avoids weld nesting; overlap K detailed separately |
| Weld type | Full-penetration or fillet per force transfer | Full-penetration for tension-critical joints; fillet sized to tube shear |
| Weld profile | Mitre / saddle profile developed from intersection line | CNC pipe profiling; bevel angle 35-60°, root face 1-3 mm |
| NDT | 100% visual; UT per ISO 17640 Level B on tension welds; MT on demand | Records per member ID in the weld map |
| Corrosion protection | HDG 85-120 µm or coating system per ISO 12944 | Internal voids sealed after galvanizing where specified |
Design per EN 1993-1-8 Chapter 7 (hollow section joints) with GB 50017 column for domestic projects; capacities include chord-face yield, punching shear and the web member local buckling check.
How Connection Quality Is Enforced in the Shop
- CNC tube profiling: member ends are cut and bevelled by computer-controlled profile machines from the CAD-developed intersection line — the fit-up gap at the joint face is a machined dimension, not a fitters' achievement.
- Optional pre-assembly: critical joints are dry-assembled and checked for gap and fit before final welding; large trusses are trial-erected in the yard to verify the whole truss geometry.
- Qualified welding: WPS per ISO 15614 for the tube-wall/thickness ranges used, welders qualified per ISO 9606, with process monitoring for the multi-pass fills.
- Weld map traceability: every connection carries its weld map marking; weld numbers, welders' stamps, NDT results and coating records link back to the shop drawing.
- Geometry verification: truss camber and member positions checked against the fabrication drawing after welding, with distortion corrected before coating — the truss ships as-designed.
Connections Proven in the Field
The connection discipline on this page is not theoretical — it is the detail set behind structures our clients see and use:
- Xuzhou East High-Speed Rail Station: curved multi-tube welded pipe trusses for the platform canopy — precision-bent large-diameter tubes with complex spatial K/KT joints at every node.
- Daqing West Railway Station: long-span pipe truss roofs where winter fatigue and low-temperature toughness governed the connection steel and weld metal selection.
- Frankfurt Air-Rail Center (Europe project): EN 1090-2 execution with fatigue-aware weld dressing — the detail categories of the rail-traffic loading satisfied by shop-controlled joint profiles.
- Indonesia Jinrui complex: H-steel and pipe truss frames across 90+ structures on a 250,000 m² programme — connection standardisation at industrial volume without losing the per-joint check.
Request a Connection Design for Your Truss
Send us your truss geometry, member forces and reference code. We return joint classification, weld specifications, NDT scope and a fabrication drawing review — the weld designed before the steel is cut.
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