Space Frame Node Specifications — The Joint Is the Structure
A bolted sphere node connects up to eleven members from nine directions into one hot-dip-galvanised steel ball; a welded hollow ball joint carries it further where loads are heaviest. In a space frame, the node is not a detail — it is the entire argument: every member's force resolves through it, every tolerance error concentrates in it, and every construction saving depends on it. We have manufactured millions of nodes since 1999, and the specification below reflects the limits and locks the quality.
Bolted-Sphere vs Welded-Hollow-Ball: Choosing the Right Joint
Bolted sphere nodes suit the majority of roofs and floors up to roughly 80-100 m span: the structure breaks down into members with pre-tensioned high-strength bolts at each end and screw into a hot-forged steel ball. Site erection becomes a bolting operation — no welding on scaffolding, no fire risk at height, simple inspection of every joint — which is why bolted grids dominate stadium roofs, exhibition halls and industrial canopies where speed and ease of erection decide the programme.
Welded hollow-ball nodes take over where forces grow too large for a bolted connection: heavy industrial roofs, coal-storage domes at 100-229 m span, and structures carrying concentrated equipment loads. The members weld directly to a pressed steel hollow ball, giving a stiffer joint with no bolt slip and higher force capacity — at the cost of site welding and inspection. Our 229 m world-record coal shed and its 100 m+ industrial domes are welded-ball systems.
For both systems, the node is designed and checked to GB 50017 node rules (and cross-checked to the client's reference code where the project requires), and every batch of balls is tested for hardness, chemical composition and weldability before it reaches the nesting table.
Bolted Sphere Node — Standard Parameters
| Parameter | Typical Range | Standard / Note |
|---|---|---|
| Ball diameter | Φ100 – Φ320 mm (bs-100 to bs-320 series) | Machined from forged blanks, BS255 per GB/T 699 |
| Ball material | 45# steel, BS255 ball grade, heat-treated | Surface hardness 260-280 HBW after quenching & tempering |
| Bolt grade | 40Cr (M20-M64), 35CrMo (M64+) | Grade 10.9 high-strength, GB/T 1228-1231 torque control |
| Member connection | Φ48×3.5 to Φ219×20 steel tube | Sleeve + set screw + taper pin, full thread engagement |
| Thread tolerance | 6H/6g threads, 1.25-1.5×d thread length | Threads checked with ring/go gauges batch-wise |
| Member-to-ball fit | Tapered sleeve packs the gap | Min 65% thread engagement per design |
| Corrosion protection | Hot-dip galvanizing 60-85 µm (interior) / 85-120 µm (coastal) | ISO 1461; threads masked & re-cut after galvanizing |
| Erection | Torque wrench, no site welding | Torque values per bolt grade stamped on shop drawing |
Design input per GB 50017-2017 Chapter 12 (node design) and JGJ 7 space grid code; capacities include the bolt-slip and node-rotation limits, not just the member-end resistance.
Welded Hollow-Ball Node — Standard Parameters
| Parameter | Typical Range | Standard / Note |
|---|---|---|
| Ball diameter | Φ200 – Φ1200 mm | Pressed and welded hemispheres, two-piece assembly |
| Wall thickness | 8 – 40 mm | Design-checked for local buckling at the member junction |
| Material | Q355B, Q390B, Q420B steel | Design yield per GB/T 1591; Charpy tested ≤ -20°C where required |
| Member connection | Φ89 to Φ711 tubular members, full-penetration butt weld | Weld QC: visual + UT per ISO 17640 Level B on tension members |
| Eccentricity control | Design eccentricity ≤ 0.25 times ball outer diameter | Per GB 50017 node eccentricity rules |
| Bearing capacity basis | Ball node axial and shear capacity per formula in JGJ 7-2010 | Verified by FEA on high-loaded nodes (>200×10³ kN) |
| Corrosion protection | Hot-dip galvanizing or duplex / intumescent per exposure | ISO 12944 C3/C4/C5 system selection by project site |
The 229 m world-record beam-string coal shed and the 100 m+ industrial domes we have delivered are welded-hollow-ball systems; every node's capacity was FEA-verified at design stage and its weld inspected during fabrication.
What Guarantees a Node Before It Leaves the Factory
- Mill test certificates for every ball blank, bolt lot and tube batch — traceable to the node by heat number.
- Batch hardness and chemical checks on sphere blanks before machining; ball surface defects rejected at nesting inspection.
- Thread verification with ring and plug gauges; bolt lot testing per GB/T 1231 including hardness and wedge-load tensile tests.
- Welded-ball NDT: 100% visual of all welds, UT per ISO 17640 Level B on tension-loaded member welds, with MPC recorded.
- Fit-up trial of node + members for the first structure of every project before bulk shipment — a trial jig that catches geometry errors while they are still cheap.
- Galvanizing thickness reports per ISO 1461 with thickness spot checks at the ball surface and thread re-cut verification.
How We Specify Your Nodes
Send us the roof geometry, loading and span and we return a node specification that matches the real force flow — not a catalogue guess:
- Node force envelope from the grid analysis (axial design force, node displacement) at the worst-loaded nodes.
- Ball size and bolt selection per the governing compression/tension at each node, with the slip and rotation check documented.
- Member-nesting and thread-length drawings released for fabrication review before the first ball is machined.
- Erection method statement covering torque control (bolted system) or site weld QC and inspection (welded system).
- Cross-code options: where the consultant works to Eurocode, AISC or a national code, the node check is translated to the reference code with equivalence notes.
Every node shipped includes its identity marking matching the shop drawing — your erector knows exactly which ball goes in which node, and your inspector can trace any one of them to its steel.
Specify Nodes With the Numbers, Not Guesswork
Send us your grid geometry, loads and span. We return a node specification with ball sizes, bolt grades, capacities and a fabrication drawing review — designed to your code, traceable to its steel.
Email: market@permanentsteelstructure.com | WhatsApp: +86 18621689980 | Phone: +86 516-83269982