1.Diameter of the bolts 2.Pitch

**SP ECIFICAT ION
OF BOLTED JOI NTS **

**1. ****Diameter of the bolts**

In
general, a connection with few larger diameter bolts are economical than a
connection with smaller diameter bolts. This is basically because as the number
of bolts increases, the work associated with drilling of holes and
installations of bolts will also
increases. Larger diameter bolts are particularly advantages in the case
of connections where bolt shear governs
the design because the shear strength of bolts varies as the square of bolt
diameter.

**2. Pitch**

Spacing of bolt holes
in ajoint is defined by three parameters namely; pitch, edge distance an end
distance. Pitch is the distance between the centers of two consecutive bolts
measured along a row of bolts. When the bolts are placed staggered, then the
pitch is known as staggered pitch.

**2.1. Minimum pitch**

This is to prevent the
bearing failure of the plate between the two bolts, to permit the efficiency in
installation of bolts by providing sufficient space for tightening of bolts, to
prevent overlapping of washers and to provide adequate resistance to tear out
of bolts.

Minimum Spacing is
specified by IS 800:2007 in cl. 10.2.2. The distance between centre of
fasteners shall not be less than 2.5 times the nominal diameter of the
fastener.

**2.2. Maximum Spacing**

This is to ensure a compact joint reducing the
length of connection and to ensure uniform stress in

bolts

Cl. 10.2.3.1 gives the
maximum distance between the centres of any two adjacent fasteners which shall
not exceed 32t or 300 mm, whichever is less, where t is the thickness of
thinner connected plate. Cl.10.2.3.2 gives the distance between the centres of
two adjacent fasteners (pitch) in a line lying in the direction of stress,
which shall not exceed 16t or 200 mm, whichever is less, in tension members and
12t or 200 mm, whichever is less, in compression members; where t is the
thickness of the thinner plate. In the case of compression members wherein
forces are transferred through butting faces, this distance shall not exceed
4.5 times the diameter of the fasteners for a distance equal to 1.5 times the
width of the member from the butting faces.

Cl. 10.2.3.3 specifies
the distance between the centres of any two consecutive fasteners in a line
adjacent and parallel to an edge of an outside plate shall not exceed 100 mm
plus 4t or 200 mm, whichever is less, in compression and tension members; where
t is the thickness of the thinner outside plate. Cl. 10.2.3.4 deals with the
staggered fasteners. When fasteners are staggered at equal intervals and the
gauge does not exceed 75 mm, the spacing specified in 10.2.3.2 and 10.2.3.3
between centres of fasteners may be increased by 50 percent, subject to the
maximum spacing specified in 10.2.3.1.

**2.3. Edge and End Distances**

Cl. 10.2.4.1 specifies
the way to compute the edge distances in various cases. The edge distance is
the distance at right angles to the direction of stress from the centre of a
hole to the adjacent edge. The end distance is the distance in the direction of
stress from the centre of a hole to the end of the element. In slotted holes,
the edge and end distances should be measured from the edge or end of the
material to the centre of its end radius or the centre line of the slot, whichever
is smaller. In oversize holes, the edge and end distances should be taken as
the distance from the relevant edge/end plus half the diameter of the standard
clearance hole corresponding to the fastener, less the nominal diameter of the
oversize hole.

Cl. 10.2.4.2 gives the
minimum edge distance. The minimum edge and end distances from the centre of
any hole to the nearest edge of a plate shall not be less than 1.7 times the
hole diameter in case of sheared or hand-flame cut edges; and 1.5 times the
hole diameter in case of rolled, machineflame cut, sawn and planed edges.

Cl. 10.2.4.3 specifies
the permissible maximum edge distance. The maximum edge distance to the nearest
line of fasteners from an edge of any un-stiffened part should not exceed 12t?,
where ? = ?(250/f_{y}) and t is the thickness of the thinner outer
plate. This would not apply to fasteners

interconnecting the
components of back to back tension members. Where the members are exposed to
corrosive influences, the maximum edge distance shall not exceed 40 mm plus 4t,
where t is the thickness of thinner connected plate.

**2.4. Tacking Fasteners**

In case of members
covered under 10.2.4.3, when the maximum distance between centres of two
adjacent fasteners as specified in 10.2.4.3 is exceeded, tacking fasteners not
subjected to calculated stress shall be used. Tacking fasteners shall have
spacing in a line not exceeding 32 times the thickness of the thinner outside
plate or 300 mm, whichever is less. Where the plates are exposed to the
weather, the spacing in line shall not exceed 16 times the thickness of the
thinner outside plate or 200 mm, whichever is less. In both cases, the distance
between the lines of fasteners shall not be greater than the respective
pitches. All the requirements specified in 10.2.5.2 shall generally apply to
compression members, subject to the stipulations in Section 7 affecting the
design and construction of compression members. In tension members (see Section
6) composed of two flats, angles, channels or tees in contact back to back or
separated back to back by a distance not exceeding the aggregate thickness of
the connected parts, tacking fasteners with solid distance pieces shall be
provided at a spacing in line not exceeding 1000 mm. For compression members
covered in Section 7, tacking fasteners in a line shall be spaced at a distance
not exceeding 600 mm. These specifications are outlined in Cl. 10.2.5 of IS
800: 2007.

**2.5. Combination of fasteners**

When
different fasteners are used to carry shear loads or when welding and other
types of fasteners are combined together, then one form of the fasteners should
be designed to take up the total load. Nevertheless, if we use HSFG bolts along
with welds and the bolts are tightened after welding is completed, then such
bolts can be used to share the load with the welds.

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civil : Design Of Steel Structures : SP Ecificat Ion Of Bolted Joints |

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