Splice of 18 mm flats with M18 10.9 bolts

Reading of the figure: 4 bolts M18 (class 10.9, $f_{ub}=1000$ N/mm²) on each side of the splice, in two rows of two (gauge 110 mm, edge distances 55 mm, pitch 85 mm, end 45 mm); flats 220×18 mm; two cover plates 8 mm (total 16 mm); double shear; $d_0=20$ mm; $f_y=250$, $f_u=410$.

Plate checks

• Flat (18 mm): $T_{dg}=\dfrac{220\times18\times250}{1.10}=900.0$ kN; $T_{dn}=\dfrac{0.9(220-2\times20)\times18\times410}{1.25}=956.4$ kN
• Covers (2 × 8 = 16 mm): $T_{dg}=800.0$ kN; $T_{dn}=850.2$ kN

(i) Slip permitted at ultimate load (bearing-type)

• Shear (double shear, one plane in thread): $V_{dsb}=\dfrac{1000}{\sqrt3\times1.25}(192+254)\times10^{-3}=206.0$ kN
• Bearing on cover plates (16 mm, thinner than the flats): $k_b=\min(\tfrac{45}{60},\tfrac{85}{60}-0.25,2.44,1)=0.750$; $V_{dpb}=\dfrac{2.5k_bdtf_u}{1.25}=177.1$ kN
• Bolt value $177.1$ kN; four bolts $=708.5$ kN
• Design load $=\min(708.5,\ 900.0,\ 956.4,\ 800.0)=708.5$ kN

(ii) Slip not permitted at ultimate load (slip-critical)

• $F_o=0.7\times1000\times192\times10^{-3}=134.4$ kN
• $V_{nsf}=\dfrac{\mu_fn_eK_hF_o}{\gamma_{mf}}=\dfrac{0.48\times2\times1.0\times134.4}{1.25}=103.2$ kN per bolt ($\mu_f=0.48$, $\gamma_{mf}=1.25$)
• Four bolts: $412.9$ kN
• Design load $=412.9$ kN (slip resistance governs).