Beam Splice Connection Calculator

What it checks

A beam splice joins two lengths of beam so the connection transmits the moment, shear and any axial force across the joint. This calculator follows EN 1993-1-8 and SCI P358: it distributes the internal forces between the flange and web cover plates, then checks the web bolts for slip and bearing, the flange bolts, the tension flange and its cover plate, the web cover plate in shear and bending, and the beam web itself.

The force distribution is the part that catches people out. The flanges take the moment as a couple, the web takes the shear - but the web bolt group also picks up a moment from the eccentricity between the bolt group centroid and the splice centreline, and that eccentricity moment is often what sizes the web bolts.

Slip resistance governs a preloaded splice

Running the tool on its defaults - a 533 x 210 S355 beam, welded top flange and bolted bottom flange, M20 grade 8.8 preloaded bolts, mu = 0.5 - gives:

Web bolts, slip resistance

36.69 / 54.88 kN, utilisation 0.669 - GOVERNS

Web bolts, bearing

utilisation 0.264

Web cover plate, bending

28.78 / 137.46 kNm, utilisation 0.209

Tension flange

156.0 / 909.8 kN, utilisation 0.172

Web cover plate, shear

100 / 852.1 kN, utilisation 0.117

Beam web, shear

100 / 947.0 kN, utilisation 0.106

Flange bolts

19.5 / 237.6 kN, utilisation 0.082

Flange force from moment

156.0 kN

Web bolt eccentricity moment

9.50 kNm

Slip governs at 0.669, well clear of everything else - and it governs at less than half the bearing utilisation of the same bolts. That is the defining characteristic of a preloaded splice: the connection is designed not to move, and the friction grip runs out long before the bolts run out of shear or bearing capacity.

The practical consequence is that slip resistance depends on the friction surface, not on bolt strength. A surface treatment that delivers mu = 0.5 rather than 0.3 buys 67 per cent more capacity on the governing check, whereas upgrading the bolt grade changes nothing at all.

The eccentricity moment on the web bolts

The web bolt group sits to one side of the splice centreline, so the shear passing through it also applies a moment equal to the shear times that lever arm - 9.50 kNm in the example above. That moment is resisted by the bolt group as a polar distribution, adding a component to the outermost bolts that the vertical shear alone would not produce.

The tool reports both the direct shear and the eccentricity contribution, and the polar second moment of the bolt group that resolves them. Making the web bolt group taller reduces the force on each bolt from the moment, which is usually a better move than adding a column of bolts further from the centreline.

Formula reference

Slip resistance, preloaded

$F_{s,Rd} = \dfrac{k_s\,n\,\mu}{\gamma_{M3}}\,F_{p,C}$

Preload force

$F_{p,C} = 0.7\,f_{ub}\,A_s$

Flange force from moment

$F_f = \dfrac{M_{Ed}}{h - t_f}$

Web bolt eccentricity moment

$M_{ecc} = V_{Ed}\,e$

Polar second moment of the bolt group

$I_p = \sum (x_i^{2} + y_i^{2})$

Bolt force from moment

$F_{M,i} = \dfrac{M\,r_i}{I_p}$

Cover plate bending

$M_{Rd} = \dfrac{W_{pl}\,f_y}{\gamma_{M0}}$

Assumptions and limits

Slip resistance assumes the declared friction surface class is actually achieved on site. Class A needs blasted, uncontaminated faying surfaces - paint, primer, oil or mill scale void the assumption entirely, and no calculation recovers it. The preload itself depends on controlled tightening, so the specification and the inspection regime are part of the design, not an afterthought.

The tool checks the splice components. It does not check the beam as a member either side of the joint, and it assumes the splice is located where the design forces you enter actually occur - placing a splice near a point of contraflexure is a design decision that changes the forces, not something the tool optimises for you.

Static persistent design situation. Fatigue - which is a common reason to preload in the first place - fire and seismic detailing are outside the scope.

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