Column Splice Connection Calculator

What it checks

A column splice joins two column lengths, typically just above a floor level. This calculator follows EN 1993-1-8 and SCI P358 for both bearing and non-bearing splices: it determines whether net tension develops across the joint, then checks the flange cover plates and their bolts, the compression path, the web cover plates and bolts, the minimum-resistance requirement and the tying resistance for robustness.

The critical question it answers first is whether the splice ever goes into net tension. In a bearing splice the two column ends bear directly on each other, so compression passes through the contact rather than through the cover plates - and if the axial load is large enough relative to the moment, no part of the section ever goes into tension at all.

When no tension develops, the 25 per cent rule governs

Running the tool on its defaults - a 305 x 305 S355 column, external bearing splice with 12 mm S275 cover plates and M20 bolts - gives:

Net tension develops?

No

Moment at which tension would start

235.9 kNm

Net tension force

0 kN

Minimum-resistance bolt group

800 / 1129.0 kN, utilisation 0.709 - GOVERNS

Minimum-resistance cover plates

800 / 1980.0 kN, utilisation 0.404

Flange cover tension

0 kN - not engaged

Lever arm between flanges

314.5 mm

Because no net tension develops, every tension-related check returns zero and would pass trivially. The splice is instead governed by the minimum-resistance requirement - the code rule that a splice must be able to carry a defined fraction of the member capacity regardless of the calculated forces, which the tool evaluates at 800 kN against a bolt group resistance of 1129 kN.

This is the single most misunderstood aspect of column splice design. A designer who checks only the applied forces will size the splice far too lightly, because in a well-loaded column those forces are often zero across the cover plates. The splice still has to exist and still has to be substantial - the rule exists so a column is not left with a joint that has no reserve against the unforeseen.

Bearing versus non-bearing

In a bearing splice the column ends are prepared so they make contact and compression passes directly across the joint. The cover plates then carry only tension, shear and the minimum-resistance requirement. In a non-bearing splice - where the ends are not prepared to bear - the cover plates must carry the full compression as well, which makes them substantially heavier.

The tool asks which type you have because it changes the whole load path, not just a factor. Bearing requires the ends to be sawn or machined flat within a tolerance and erected in contact, which is a fabrication and site requirement, not something the calculation can assume for you.

Formula reference

Moment at first tension

$M_{no\,tension} = N_{Ed}\,\dfrac{h}{2}$

Net-section tension

$N_{u,Rd} = \dfrac{0.9\,A_{net}\,f_u}{\gamma_{M2,net}}$

Gross-section tension

$N_{pl,Rd} = \dfrac{A\,f_y}{\gamma_{M0}}$

Minimum-resistance demand

$N_{\min} = 0.25\,N_{Ed}$

Bolt shear

$F_{v,Rd} = \dfrac{\alpha_v f_{ub} A_s}{\gamma_{M2}}$

Bearing

$F_{b,Rd} = \dfrac{k_1 \alpha_b f_u d t}{\gamma_{M2}}$

Note gamma_M2,net = 1.1 rather than 1.25 for the net-section tension check - a distinct partial factor that is easy to get wrong and was corrected during verification against SCI P358.

Assumptions and limits

A bearing splice assumes the column ends genuinely bear. That requires the ends to be prepared flat within tolerance and erected in contact - if a gap remains, or if packing is used carelessly, the compression path does not exist and the splice behaves as a non-bearing one it was never designed to be.

The tool checks the splice, not the column. Column buckling either side of the joint, the effective length implied by the splice location, and the frame stability that depends on it are separate design questions. Splice location is usually a few hundred millimetres above a floor for access, which is a practical choice that also keeps the moment low.

Tying resistance for structural robustness is checked as a separate requirement with its own load case, and it can govern the detail in a building where accidental-action design applies. Fatigue, fire and seismic detailing are outside the scope.

FAQ