A tube-on-tube cap plate under BS EN 1993 reuses the identical two-way cantilever-plate method already established for the base plate, mechanically the same bearing problem just applied 'upside down' — a chord bearing down on a column through a plate, instead of a column bearing down on a pedestal.
Every check above runs automatically inside the Structyze HSS Cap Plate Connection module — this particular module is part of the full desktop catalogue rather than the free browser trial, since the trial only carries a curated flagship set. You can still try the free trial modules right now to see the same calculation style in action on RCC Beam, Column, Slab and a handful of others.
The Example We'll Use
- Column tube 150 mm, chord tube width 150 mm (both square SHS)
- Design reaction 100 kN
- Cap plate 220 × 220 × 12 mm (provided), fy = 235 MPa
- Welded connection: cap-to-column and chord-to-plate, both 6 mm, S235
Working Through It
Bearing pressure under the cap plate: w = 100,000/(220×220) ≈ 2.07 MPa. With a square column centred on a square plate, both projections equal 35 mm.
Reusing the base-plate two-way formula: treq = √(2.5(2.07)(35²−0.3×35²)(1.0)/235) ≈ 4.34 mm against the 12 mm provided — utilisation 0.362, wide margin.
Both perimeter welds share identical geometry here (same 150 mm tube, same 6 mm weld), landing at the same comfortable utilisation of 0.191.
What Governs, and Why
Cap plate bending governs at utilisation 0.362 but with wide margin — both perimeter welds run identically at 0.191. All three checks pass comfortably, typical of a lightly-loaded truss-to-column bearing detail.
Where Structyze Takes Over
Every check above runs automatically inside the Structyze HSS Cap Plate Connection module — this particular module is part of the full desktop catalogue rather than the free browser trial, since the trial only carries a curated flagship set. You can still try the free trial modules right now to see the same calculation style in action on RCC Beam, Column, Slab and a handful of others.
For HSS Cap Plate Connection and the rest of the full catalogue — 80+ components across RCC, Steel, Composite, Timber, Masonry and more, across 20+ design codes — buy the full Structyze desktop app or see everything it does on the Software page.
Quick FAQ
Why call this connection 'upside down' relative to a base plate?
A base plate has the column bearing down onto the plate, which in turn bears onto a concrete pedestal below; this cap plate connection instead has a tube chord bearing down onto the plate, which sits atop a tube column below — the load direction and support arrangement are mechanically equivalent, just with a different member playing each role — the reason the identical formula applies unchanged.
What's not checked in this simplified method?
Local crushing or punching of the hollow column's own tube wall under the concentrated cap-plate reaction isn't separately checked here — only the plate's own bending and the two perimeter welds, an assumption reasonable for this lightly-loaded example but worth verifying explicitly for a more heavily loaded connection.
Final Thoughts
Recognising a cap plate connection as a base plate turned upside down is the cleanest way to understand why the identical two-way cantilever formula applies to both without any modification.