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Column Splice Connection Design Theory (EN 1993-1-8)

The theory behind this column splice calculator: how a bolted cover-plate joint giving continuity between two columns is verified to Eurocode 3 (EN 1993-1-8) with SCI P358 §6. We cover the bearing and non-bearing types, the net-tension test (M_Ed vs N_Ed,G·h/2), the flange cover plates and their bolt group (with the packing and long-joint reductions and the γM2,net = 1.1 distinction), the division plate for different serial sizes, the 25% minimum-resistance rule and the structural-integrity tie.

🔗Open the interactive column splice calculator→

A column splice is the bolted cover-plate connection that gives continuity between two columns - usually placed just above a floor level to suit fabrication, transport and erection lengths. It holds the upper and lower shafts in line and transfers the axial force (almost always compression), the moment from any eccentricity, and the structural-integrity tie force. This page explains the mechanics and every formula behind the checks this calculator performs to Eurocode 3 (EN 1993-1-8) with SCI Publication P358 §6.

upper columnlower columndivision plate

A column splice: flange cover plates bolted across both shafts, a division plate transferring compression in bearing where the serial sizes differ.

Bearing vs non-bearing

There are two types. In a bearing splice the column ends are prepared (saw-cut square) so the compression transfers in direct bearing - through a division plate where the upper and lower serial sizes differ. The cover plates then only need to carry any net tension (from the moment), plus hold the shaft in line and provide the tie. This is the simpler, more economical and most common type. In a non-bearing splice there is a physical gap and the cover plates and bolts carry the full axial force and moment - checked for compression (with flange-plate buckling) and tension.

The verification framework (bearing type)

CheckGoverning equationReference
Net-tension testMEd>NEd,G h2⇒NEd=MEdh−NEd,G2M_{Ed} > \dfrac{N_{Ed,G}\,h}{2} \Rightarrow N_{Ed} = \dfrac{M_{Ed}}{h} - \dfrac{N_{Ed,G}}{2}SCI P358 Ck2
Flange cover plateNt,Rd=min⁡(Npl,Rd; Nu,Rd; Nbt,Rd)N_{t,Rd} = \min(N_{pl,Rd};\ N_{u,Rd};\ N_{bt,Rd})SCI P358 Ck3
Flange bolt groupFRd,fp=n min⁡(βpβLFFv,Rd; Fb,Rd)F_{Rd,fp} = n\,\min(\beta_p\beta_{LF}F_{v,Rd};\ F_{b,Rd})SCI P358 Ck4
Minimum resistance0.25NEd≤NRd=2AfpfyγM00.25 N_{Ed} \le N_{Rd} = \dfrac{2 A_{fp} f_y}{\gamma_{M0}}SCI P358 Ck5
TyingNEd=NEd,u2N_{Ed} = \dfrac{N_{Ed,u}}{2}SCI P358 Ck6

Does net tension develop?

The key question for a bearing splice is whether the moment overcomes the permanent compression and opens a net tension across a flange. Net tension develops only if

MEd>NEd,G h2M_{Ed} > \dfrac{N_{Ed,G}\,h}{2}

where NEd,GN_{Ed,G} is the axial force from permanent actions and hh is (conservatively) the depth of the smaller column. If it does, the flange cover plates and their bolts must carry the tension NEd=MEd/h−NEd,G/2N_{Ed} = M_{Ed}/h - N_{Ed,G}/2. Where this tension stresses the upper column flange above 10% of its design strength, preloaded bolts are required; otherwise ordinary bolts in clearance holes suffice.

Flange cover plates and bolts

When tension acts, the flange cover plate is checked for gross-section yield, net-section rupture and block tearing (the net-section terms use γM2,net=1.1\gamma_{M2,net} = 1.1, not the bolt factor), and the bolt group for shear and bearing with the packing reduction βp=9d/(8d+3tpa)\beta_p = 9d/(8d + 3t_{pa}) and, for long joints, βLF\beta_{LF}.

Minimum resistance - the 25% rule

Even with no net tension, EN 1993-1-8 §6.2.7.1(14) requires the splice material (plates and bolts) to transmit at least 25% of the maximum compression in the column, holding the shaft in line:

0.25NEd≤NRd=2Afpfy,fpγM0and0.25NEd≤2FRd,fp0.25 N_{Ed} \le N_{Rd} = \dfrac{2 A_{fp} f_{y,fp}}{\gamma_{M0}} \quad\text{and}\quad 0.25 N_{Ed} \le 2 F_{Rd,fp}

Different serial sizes - the division plate

When the upper and lower columns differ, a horizontal division plate transfers the bearing (spreading the load at 45 degrees) and packs make up the offset between the flange faces. The division plate thickness is at least

tdp≥(hlc−2tf,lc)−(huc−2tf,uc)2t_{dp} \ge \dfrac{(h_{lc} - 2t_{f,lc}) - (h_{uc} - 2t_{f,uc})}{2}

Non-bearing and tying

Frequently asked questions

A column splice is the bolted cover-plate connection that joins two columns to give continuity, usually placed just above a floor level. It holds the upper and lower shafts in line and transfers the axial force (almost always compression), the moment from any eccentricity and the structural-integrity tie force. Splices break a multi-storey column into convenient lengths for fabrication, transport and erection.

In a bearing splice the column ends are prepared (saw-cut square) so the compression transfers in direct bearing - through a division plate where the upper and lower serial sizes differ. The cover plates only carry any net tension plus hold the shaft in line; it is the simpler and most common type. In a non-bearing splice there is a physical gap and the cover plates and bolts carry the full axial force and moment, so they are checked for compression (with flange-plate buckling) as well as tension.

To Eurocode 3 (EN 1993-1-8) with SCI P358 §6: first test whether the moment develops net tension (it does if M_Ed > N_Ed,G·h/2). If so, the flange cover plates are checked for gross yield, net rupture and block tearing, and their bolt group for shear and bearing (with the packing factor βp and long-joint factor βLF). Always, the splice must transmit at least 25% of the column compression (the minimum-resistance rule), and where structural integrity applies, the checks are repeated for the tie force.

Net tension develops in a flange of a bearing splice only when the moment overcomes the permanent compression, i.e. when M_Ed > N_Ed,G·h/2 (h is conservatively the depth of the smaller column). The flange cover plates and bolts then carry N_Ed = M_Ed/h − N_Ed,G/2. If this tension stresses the upper column flange above 10% of its design strength, preloaded (HSFG) bolts must be used; otherwise ordinary bolts in clearance holes are adequate.

When the upper and lower columns are different serial sizes, a horizontal division plate is placed between the prepared ends to transfer the bearing - the compression spreads through it at about 45 degrees onto the larger lower section. Packs make up the offset between the flange faces so the cover plates can run flush. The division plate thickness is at least [(h_lc − 2t_f,lc) − (h_uc − 2t_f,uc)] / 2.

Ready to check your splice? Run the full EN 1993-1-8 / SCI P358 verification for a bearing or non-bearing column splice in 3D, with step-by-step derivations for every check.

🔗Open the interactive column splice calculator→
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