If the connected plates are made of high strength steel then failure of bolt can take place by bearing of the plates on the bolts. If the plate material is weaker than the bolt material, then failure will occur by bearing of the bolt on the plate and the hole will elongate.

**Bearing failure**

If the connected plates are made
of high strength steel then failure of bolt can take place by bearing of the
plates on the bolts. If the plate material is weaker than the bolt material,
then failure will occur by bearing of the bolt on the plate and the hole will
elongate. The beating area is given by the nominal diameter of the bolt times
the combined thickness of the plates bearing in any direction. A bolt bearing
on any plate subjected to a factored shear force (Vsb) shall satisfy as Vsb < = Vdb per cl. 10.3.2 of IS 800:2007,
where as Vdb = Vdpb = Vnpb/?mb given by cl. 10.3.4 of the code where, ?mb = 1.25
and V_{npb} = bearing strength of a bolt, calculated as V_{npb}
= 2.5k_{b}dtf_{u} where f_{u} = smaller of the ultimate
tensile stress of the bolt and the ultimate tensile stress of the plate, d =
nominal diameter of the bolt, t = summation of the thicknesses of the connected
plates experiencing bearing stress in the same direction and k_{b} is
smaller of e/3d_{0}, p/3d_{0}-0.25, f_{ub}/f_{u},
1.0 where e, p = end and pitch distances of the fastener along bearing
direction; d_{0} = diameter of the hole; f_{ub}, f_{u}
= Ultimate tensile stress of the bolt and the ultimate tensile stress of the
plate, respectively.

The underlying assumption behind
the design of bolted connections, namely that all bolts carry equal load is not
true in some cases. In long joints, the bolts farther away from the centre of
the joint will carry more load than the bolts located close to the centre.
Therefore, for joints having more than two bolts on either side of the building
connection with the distance between the first and the last bolt exceeding 15d
in the direction of load, the nominal shear capacity Vns, shall be reduced by
the factor, ?lj, given by (Cl.10.3.2.1) ?_{lj}
=
1.075 - l_{j} / (200 d) but 0.75 < ?_{lj}
<
1.0 where, d= nominal diameter of the bolt Similarly, if
the grip length exceeds five times the nominal diameter, the strength is
reduced as specified in IS 800. In multi-bolt connections, due to hole
mismatch, all the bolts may not carry the same load. However, under ultimate
load, due to high bearing ductility of the plates considerable redistribution
of the load is possible and so the assumption that all bolts carry equal load
may be considered valid.

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civil : Design Of Steel Structures : Bearing failure of Bolts |

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