Failure mechanisms of bolted connection

Failure mechanisms of a bolted connection

1. Shear failure of bolt: the bolt shears across one plane (single shear) or two planes (double shear). Strength $V_{dsb}=\dfrac{f_{ub}}{\sqrt3\gamma_{mb}}(n_nA_{nb}+n_sA_{sb})$.
2. Bearing failure of bolt/plate: the plate elongates or tears in front of the bolt. $V_{dpb}=2.5k_bdtf_u/\gamma_{mb}$. Prevented by adequate end and pitch distances.
3. Tension failure of bolt: the bolt breaks in the threaded part under direct tension, $T_{db}=T_{nb}/\gamma_{mb}$ with $T_{nb}=0.9f_{ub}A_{nb}\le f_{yb}A_{sb}\gamma_{mb}/\gamma_{m0}$.
4. Tearing of plate at the edge (shear-out): if the end distance is too small, the plate shears out behind the bolt.
5. Tension (net-section) rupture of plate: the plate fails across the net section through the bolt holes, $T_{dn}=0.9A_nf_u/\gamma_{m1}$.
6. Yielding of gross section of the plate: $T_{dg}=A_gf_y/\gamma_{m0}$.
7. Block shear failure: a block of plate tears out along shear and tension planes at the bolt group.
8. Bolt bending (long grip): prevented by limiting the grip to $8d$ (with reduced shear strength when the grip exceeds $5d$).
9. Prying failure: extra tension in bolts due to flexible connected plates.
10. Slip in HSFG joints when the friction is exceeded.

Combined stresses in eccentric connections

• Load in the plane of the bolt group (eccentricity in the plane): bolts get direct shear $P/n$ plus shear due to torsion $T r/\Sigma r^2$; the vector sum of both is the resultant shear on the critical bolt, $R=\sqrt{(F_x)^2+(F_y)^2}$, checked against $V_{db}=\min(V_{dsb},V_{dpb})$.
• Load perpendicular to the plane of the bolt group (bracket on column flange): bolts get direct shear $V=P/n$ and tension due to moment $T=My/\Sigma y^2$. Combined check for bearing-type bolts (IS 800:2007 cl. 10.3.6):

$$\left(\frac{V}{V_{db}}\right)^2+\left(\frac{T}{T_{db}}\right)^2\le1.0$$

For HSFG (friction-type) bolts (cl. 10.4.6) the interaction is $\left(\dfrac{V_{sf}}{V_{df}}\right)^2+\left(\dfrac{T_f}{T_{df}}\right)^2\le1.0$.