BOLTED CONNECTION
INTRODUCTION
• A bolt is a metal pin with a head formed
at one end and shank threaded at the
other in order to receive a nut.
• On the basis of load transfer in
the connection bolts are
classified as:
• (a) Bearing Type
• (b) Friction Grip Type
Types of bearing bolts
• There are two types of bearing type
bolts, namely,
• (i) Unfinished or Black Bolts.
• (ii) Finished or Turned Bolts.
Unfinished or Black Bolts.
• The shanks of black bolts are unfinished,
i.e., rough as obtained at the time of
rolling.
• For black bolts, diameter of bolt hole is
larger and are used in most of the work.
• A black bolt is represented as M16, M20,
etc. which means black bolt of nominal
diameter 16 mm, black bolt of nominal
diameter 20 mm, etc.
Finished or Turned Bolts.
• turned bolts are obtained by
turning hexagonal shank to
circular shape.
• The bolt hole diameter is only 1.5 mm
larger than that of the shank in case of
turned bolt.
• These bolts are used in special jobs like
connecting machine parts subject to
dynamic loadings.
TERMINOLOGY
The following terms used in bolted
connection should be
1. Pitch of the Bolts (p): It is the centre-to-
centre spacing of the bolts in a row,
measured along the direction of load.
2. Gauge Distance (g): It is the distance
between the two consecutive bolts of
adjacent rows and is measured at right
angles to the direction of load.
3. Edge Distance (e): It is the distance of bolt
hole from the adjacent edge of the plate.
Grade Classification of
•
Bolts
The grade classification of bolt is indicative of the
strength of the material of the bolt. The two grades of
bolts commonly used are 4.6 and 8.8.
• For a 4.6 grade 4 indicates that the ultimate
tensile strength of the bolt,
fub = 4 x 100 = 400 N/mm2
and, 0.6 indicates that the yield strength of the
bolt, fyb= 0.6 x Ultimate strength
= 0.6 x 400 = 240 N/ mm2
The yield stress (fyb) and ultimate stress (fub) for the
standard grades of bolts are given in the table
below;
Specification
For connection, see section 10 code IS 800 : 2007.
1. Pitch 'p' shall not be less than 2.5d, where, 'd' is the
nominal diameter of bolt (also see clause 10.2.2 of
code IS 800 : 2007)
2. Pitch 'p' shall not be more than;
a) 16 t or 200 mm whichever is less, in case of tension
members. (Also see clause 10.2.3.2 of code IS 800 :
2007).
b)12 t or 200 mm, whichever is less in case of
compression member where, 't' is the thickness of
thinnest member.
c) In case of staggered pitch, pitch may be increased by
50 percent of values specified above provided gap
distance is less than 75 mm. (See clause 10.2.3.4 of
code IS 800 : 2007).
3.In case of butt joints maximum pitch is to be restricted to
4.5 d for a distance of 1.5 times the width of plate from
the butting surface.
4.The gauge length 'g' should not be more than 100 + 4 t
or 200 mm whichever is less.
5. Minimum edge distance shall not be;
a)Less than 1.7 x hole diameter in case of sheared or
hand flame cut edges.
b)Less than 1.5 x hole diameter in case of rolled, machine
flame cut, sawn and planed edges (See clause 10.2.4.2 of
code IS 800: 2007).
6. Maximum edge distance (e) should not exceed
a) 12tE where, and 't' is thickness of thinner outer plate
(See clause 10.2.4.3 of code IS 800 : 2007).
b)40 + 4 t where, 't' is the thickness of thinner connected
plate, if exposed to corrosive influences.
Types of Bolted Connections
Types of joints may be grouped into the following
two;
a) Lap Joint: It is simplest types of joints. In this,
plates to be connected overlap one another.
b) Butt Joint: In this type of connection, the two main
plates about against each other and the connection is
made by providing a single cover plate connected to
the main plate or by double cover plates, one on
either side connected to the main plates.
Bolted joint
lap Butt
joint joint
