Beam Splice Connection Design Theory (EN 1993-1-8)
The theory behind this beam splice calculator: how a splice that gives continuity between two in-line beams (flange cover plates and/or full-strength butt welds + a bolted web cover plate) is verified to Eurocode 3 (EN 1993-1-8) with SCI P358/P398. We cover the distribution of the moment between flange and web by the I_w/I_y ratio, the preloaded (HSFG) web bolts (slip resistance + combined bearing with the bolt-group eccentricity), the tension flange and cover plate, the web cover plate (shear and bending) and the beam web.
A beam splice is the connection that gives continuity between two in-line beams - it transfers the bending moment, shear and any axial force across the joint. The flanges (cover plates and/or full-strength butt welds) carry the tension and compression from the moment, while a bolted web cover plate carries the shear, its share of the moment and the axial force. This page explains the mechanics and every formula behind the checks this calculator performs to Eurocode 3 (EN 1993-1-8) with SCI Publications P358 and P398.
A beam splice: flange cover plates / butt welds carry the moment couple, a bolted web cover plate carries the shear and the web's share of the moment (about the bolt group).
The verification framework
Every link in the load path is verified - the force distribution, the (preloaded) web bolts, the flange bolts, the tension flange and cover plate, the web cover plate and the beam web - with the utilisation kept at or below 1.0.
Check
Governing equation
Reference
Force distribution
Ff,M=(1−Iw/Iy)hb−tfMEd
SCI P398
Web bolt slip
Fs,Rd=γM3ksnμFp,C
EN 1993-1-8 T3.6/3.7
Web bolt bearing
Fb,verFz+Fb,horFx≤1
EN 1993-1-8 T3.4
Tension flange
Ff,Rd=min(γM0Agfy;γM20.9Anetfu)
EN 1993-1-1
Web cover plate
Vwp,Rd,Mc,wp,Rd=γM0Wwp(1−ρ)fy
SCI P358
Distribution of internal forces
For a splice in a flexural member the moment is shared between the flanges and the web in proportion to their second moments of area. The flange force from the moment is
Ff,M=(1−IyIw)hb−tfMEd,Mw,M=IyIwMEd
where Iw is the second moment of the web alone and Iy that of the whole section. The web bolt group also carries an eccentricity momentMecc=VEdecc because it sits a distance from the splice centre-line, plus the vertical shear VEd and the web's share of any axial force.
Web bolts - slip resistance + bearing
A splice that combines welding and bolting uses preloaded (HSFG) bolts (class 8.8 or above) so the joint is slip-resistant and rigid (SS EN 1993-1-8 §3.9). Each bolt is checked for the resultant force from the vertical shear plus the bolt-group moment (Mw,M+Mecc):
with the bolt-group moment resolved through the polar term Ibolts=∑(xi2+zi2). The bolts are also checked for bearing on the web cover plate and the beam web, combining the vertical and horizontal components.
Flanges and cover plates
A welded flange uses a full-strength butt weld, so only the tension flange section needs checking; a bolted flange adds a cover plate with its own bolts. The tension flange (or its cover plate) is checked for gross-section yield Fpl,Rd=Agfy/γM0 and net-section rupture Fu,Rd=0.9Anetfu/γM2, the smaller of which must exceed the flange force Ff,M. A compression cover plate is also checked for local buckling between bolt rows if p1/tfp>9ε.
Web cover plate and beam web
The web cover plate is verified for gross- and net-section shear and for bending under the web moment (Mw,M+Mecc):
Mc,wp,Rd=γM0Wwp(1−ρ)fy,wp,Wwp=6twphwp2
where ρ is a shear-bending reduction applied only when the shear exceeds half the web-cover shear resistance. Finally the spliced beam web itself is checked for gross/net shear.
Detailing notes
use preloaded HSFG bolts (8.8+) for any welded-and-bolted (hybrid) splice;
for a hybrid connection, final tightening of the bolts is done after the welding (SS EN 1993-1-8 §3.9.3);
full-strength butt welds on a flange remove the flange-bolt and cover-plate checks for that flange;
edge and end distances and bolt pitch follow the usual EN 1993-1-8 limits.
Frequently asked questions
A beam splice is the connection that joins two in-line beams to give continuity, transferring the bending moment, shear and any axial force across the joint. It is typically made with flange cover plates and a web cover plate (a bolted cover-plate splice), with full-strength butt welds and/or bolts. Splices are used where a beam is longer than the available rolled length, or to break a member down for transport and erection.
To Eurocode 3 (EN 1993-1-8) with SCI P358/P398, the moment is first distributed between the flanges and the web in proportion to their second moments of area. Then every component is verified: the (preloaded) web bolts for slip resistance and combined bearing, the flange bolts, the tension flange and cover plate (gross yield + net rupture), the web cover plate (shear + bending), and the spliced beam web. Each design resistance must be at least the design action.
The proportion of moment carried by the web depends on its second moment of area relative to the whole section: M_w,M = (I_w / I_y) M_Ed, and the remainder is carried by the flanges as a couple, F_f,M = (1 - I_w/I_y) M_Ed / (h_b - t_f). The web cover plate and its bolt group therefore carry M_w,M plus an eccentricity moment M_ecc = V_Ed e, because the bolt group sits a distance from the splice centre-line.
When a splice combines welding and bolting, or where slip must be avoided for stiffness, EN 1993-1-8 §3.9 requires preloaded high-strength friction-grip (HSFG) bolts of class 8.8 or above. The connection then resists load by friction (slip resistance F_s,Rd = k_s n mu / gamma_M3 x F_p,C, with F_p,C = 0.7 f_ub A_s) rather than by bolts bearing and slipping into contact, keeping the joint rigid. For a hybrid weld-and-bolt splice the bolts are finally tightened after the welding is complete.
In a bolted cover-plate splice, plates are bolted across the flanges and web to transfer the forces - it is fully site-boltable and easy to inspect. In a welded splice the flanges are joined by full-strength butt welds (so those flanges need no cover plate or flange bolts) while the web is usually still bolted with a cover plate. Hybrid splices weld one or both flanges and bolt the web; this calculator lets you set each flange to welded or bolted.
Ready to check your splice? Run the full EN 1993-1-8 / SCI P358 verification for a bolted or welded beam splice in 3D, with step-by-step derivations for every check.
