IS 800's cap plate connection reuses the identical two-way SP:6 cantilever-plate formula already established for a concrete base plate — the bearing-pressure-under-a-plate mechanics actually don't care whether the pressure comes from a concrete pedestal or a tube column bearing on another tube.
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)
- Factored reaction 100 kN
- Cap plate 220 × 220 × 12 mm (provided), Fy = 250 MPa
- Welded connection: cap-to-column and chord-to-plate, both 6 mm, shop welds, Fu = 410 MPa
Working Through It
Bearing pressure under the cap plate: w = 100,000/(220×220) ≈ 2.066 MPa. With a square column centred on a square plate, both projections coincide at a = b = 35 mm.
Reusing the base-plate two-way formula directly: ts,req = √(2.5(2.066)(35²−0.3×35²)(1.1)/250) ≈ 4.41 mm against the 12 mm provided — utilisation just 0.368, plenty of reserve.
Both perimeter welds — cap-to-column and chord-to-plate. Happen to share identical geometry (same 150 mm tube, same 6 mm weld), so both land at the same comfortable utilisation of 0.210.
What Governs, and Why
Cap plate bending governs at utilisation 0.368, the tightest of the three checks but still with wide margin — both perimeter welds run at the lighter 0.210. All three checks pass with substantial reserve, 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 does this connection reuse the base-plate formula instead of a tube-specific one?
The underlying mechanics — a plate cantilevering (in two directions, per IS 800's SP:6 method) under uniform bearing pressure from whatever sits on top of it — are structurally identical whether that pressure comes from a column bearing on a concrete pedestal or a tube chord bearing on a tube column. Reusing the established formula for a genuinely analogous problem is deliberate, not a shortcut.
What happens for a rectangular (non-square) column tube?
Both the cap-to-column weld perimeter and the plate-bending projections assume a square SHS column with equal projections on all sides; for a rectangular column, the actual perimeter and the two different projections (a and b) both need substituting into the same formulas rather than assuming they coincide.
Final Thoughts
Seeing IS 800's own two-way SP:6 formula applied unchanged to a tube-on-tube cap plate, instead of the wide-flange-on-concrete case it was originally set up for, is a clean demonstration of how far a well-generalised bearing-plate formula can travel.