Riveted Joints
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285
3. Rivet heads for boiler work (from 12 mm to 48 mm diameter, as shown in Fig. 9.5, according to
IS : 1928 – 1961 (Reaffirmed 1996).
Fig. 9.5. Rivet heads for boiler work.
The snap heads are usually employed for structural work and machine riveting. The counter
sunk heads are mainly used for ship building where flush surfaces are necessary. The conical heads
(also known as conoidal heads) are mainly used in case of hand hammering. The pan heads have
maximum strength, but these are difficult to shape.
9.79.7
9.79.7
9.7
TT
TT
T
ypes of Rivypes of Riv
ypes of Rivypes of Riv
ypes of Riv
eted Jointseted Joints
eted Jointseted Joints
eted Joints
Following are the two types of riveted joints, depending upon the way in which the plates are
connected.
1. Lap joint, and 2. Butt joint.
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9.89.8
9.89.8
9.8
Lap JointLap Joint
Lap JointLap Joint
Lap Joint
A lap joint is that in which one plate overlaps the other
and the two plates are then riveted together.
9.99.9
9.99.9
9.9
Butt JointButt Joint
Butt JointButt Joint
Butt Joint
A butt joint is that in which the main plates are kept in
alignment butting (i.e. touching) each other and a cover plate
(i.e. strap) is placed either on one side or on both sides of the
main plates. The cover plate is then riveted together with the
main plates. Butt joints are of the following two types :
1. Single strap butt joint, and 2. Double strap butt
joint.
In a single strap butt joint, the edges of the main plates
butt against each other and only one cover plate is placed on
one side of the main plates and then riveted together.
In a double strap butt joint, the edges of the main plates
butt against each other and two cover plates are placed on
both sides of the main plates and then riveted together.
In addition to the above, following are the types of riv-
eted joints depending upon the number of rows of the rivets.
1. Single riveted joint, and 2. Double riveted joint.
A single riveted joint is that in which there is a single row of rivets in a lap joint as shown in
Fig. 9.6 (a) and there is a single row of rivets on each side in a butt joint as shown in Fig. 9.8.
A double riveted joint is that in which there are two rows of rivets in a lap joint as shown in
Fig. 9.6 (b) and (c) and there are two rows of rivets on each side in a butt joint as shown in Fig. 9.9.
X
X
X
X
Y
Y
p
p
b
p
d
m
( ) Single riveted lap joint.a
( ) Double riveted lap joint
(Chain riveting).
b ( ) Double riveted lap
joint (Zig-zag riveting).
c
Fig. 9.6. Single and double riveted lap joints.
Similarly the joints may be triple riveted or quadruple riveted.
Notes : 1. When the rivets in the various rows are opposite to each other, as shown in Fig. 9.6 (b), then the joint
is said to be chain riveted. On the other hand, if the rivets in the adjacent rows are staggered in such a way that
Riveted Joints
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287
every rivet is in the middle of the two rivets of the opposite row as shown in Fig. 9.6 (c), then the joint is said to
be zig-zag riveted.
2. Since the plates overlap in lap joints, therefore the force P, P acting on the plates [See Fig. 9.15 (a)] are
not in the same straight line but they are at a distance equal to the thickness of the plate. These forces will form
a couple which may bend the joint. Hence the lap joints may be used only where small loads are to be transmit-
ted. On the other hand, the forces P, P in a butt joint [See Fig. 9.15 (b)] act in the same straight line, therefore
there will be no couple. Hence the butt joints are used where heavy loads are to be transmitted.
( ) Chain riveting.a ( ) Zig-zag riveting.b
X
X
Y
Y
mm
m
p
d
Fig. 9.7. Triple riveted lap joint.
t
t
1
XX
t
2
Fig. 9.8. Single riveted double strap butt joint.
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p
b
.
X
Z
X
Z
( ) Chain riveting.a ( ) Zig-zag riveting.b
p
b
Fig. 9.9. Double riveted double strap (equal) butt joints.
X
X
p
Fig. 9.10. Double riveted double strap (unequal) butt joint with zig-zag riveting.
9.109.10
9.109.10
9.10
ImporImpor
ImporImpor
Impor
tant tant
tant tant
tant
TT
TT
T
erer
erer
er
ms Used in Rivms Used in Riv
ms Used in Rivms Used in Riv
ms Used in Riv
eted Jointseted Joints
eted Jointseted Joints
eted Joints
The following terms in connection with the riveted joints are important from the subject point
of view :
1. Pitch. It is the distance from the centre of one rivet to the centre of the next rivet measured
parallel to the seam as shown in Fig. 9.6. It is usually denoted by p.
2. Back pitch. It is the perpendicular distance between the centre lines of the successive rows
as shown in Fig. 9.6. It is usually denoted by p
b
.
3. Diagonal pitch. It is the distance between the centres of the rivets in adjacent rows of zig-zag
riveted joint as shown in Fig. 9.6. It is usually denoted by p
d
.
4. Margin or marginal pitch. It is the distance between the centre of rivet hole to the nearest
edge of the plate as shown in Fig. 9.6. It is usually denoted by m.
Riveted Joints
n
289
X
X
p
Fig. 9.11. Triple riveted double strap (unequal) butt joint.
9.119.11
9.119.11
9.11
Caulking and FulleringCaulking and Fullering
Caulking and FulleringCaulking and Fullering
Caulking and Fullering
In order to make the joints leak proof
or fluid tight in pressure vessels like steam
boilers, air receivers and tanks etc. a process
known as caulking is employed. In this
process, a narrow blunt tool called caulking
tool, about 5 mm thick and 38 mm in
breadth, is used. The edge of the tool is
ground to an angle of 80°. The tool is moved
after each blow along the edge of the plate,
which is planed to a bevel of 75° to 80° to
facilitate the forcing down of edge. It is seen
that the tool burrs down the plate at A in
Fig. 9.12 (a) forming a metal to metal joint.
In actual practice, both the edges at A and
Caulking tool
Caulked rivet
C
A
B
( ) Caulking.a
( ) Fullering.b
80º
Fullering tool
Fig. 9.12. Caulking and fullering.
Caulking process is employed to make the joints leak
proofs or fluid tight in steam boiler.
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B are caulked. The head of the rivets as shown at C are also turned down with a caulking tool to make
a joint steam tight. A great care is taken to prevent injury to the plate below the tool.
A more satisfactory way of making the joints staunch is known as fullering which has largely
superseded caulking. In this case, a fullering tool with a thickness at the end equal to that of the plate
is used in such a way that the greatest pressure due to the blows occur near the joint, giving a clean
finish, with less risk of damaging the plate. A fullering process is shown in Fig. 9.12 (b).
9.129.12
9.129.12
9.12
FF
FF
F
ailurailur
ailurailur
ailur
es of a Rives of a Riv
es of a Rives of a Riv
es of a Riv
eted Jointeted Joint
eted Jointeted Joint
eted Joint
A riveted joint may fail in the following ways :
1. Tearing of the plate at an edge. A joint may fail due to tearing of the plate at an edge as
shown in Fig. 9.13. This can be avoided by keeping the margin, m = 1.5d, where d is the diameter of
the rivet hole.
pd-
d
m
P
P
P
P
p
d
Fig. 9.13. Tearing of the plate at an edge. Fig. 9.14. Tearing of the plate across the
rows of rivets.
2. Tearing of the plate across a row of rivets. Due to the tensile stresses in the main plates, the
main plate or cover plates may tear off across a row of rivets as shown in Fig. 9.14. In such cases, we
consider only one pitch length of the plate, since every rivet is responsible for that much length of the
plate only.
The resistance offered by the plate against tearing is known as tearing resistance or tearing
strength or tearing value of the plate.
Let p = Pitch of the rivets,
d = Diameter of the rivet hole,
t = Thickness of the plate, and
!
t
= Permissible tensile stress for the plate material.
We know that tearing area per pitch length,
A
t
=(p – d) t
∀ Tearing resistance or pull required to tear off the plate per pitch length,
P
t
= A
t
.!
t
= (p – d)t.!
t
When the tearing resistance (P
t
) is greater than the applied load (P) per pitch length, then this
type of failure will not occur.
3. Shearing of the rivets. The plates which are connected by the rivets exert tensile stress on
the rivets, and if the rivets are unable to resist the stress, they are sheared off as shown in Fig. 9.15.
Riveted Joints
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291
It may be noted that the rivets are in *single shear in a lap joint and in a single cover butt joint,
as shown in Fig. 9.15. But the rivets are in double shear in a double cover butt joint as shown in Fig.
9.16. The resistance offered by a rivet to be sheared off is known as shearing resistance or shearing
strength or shearing value of the rivet.
P
P
P
P
( ) Shearing
of
farivet in a lap joint.a
( ) Shearing
of
farivet in
asingleco
ver butt joint.b
Fig. 9.15. Shearing of rivets.
P
P
Fig. 9.16. Shearing off a rivet in double cover butt joint.
Let d = Diameter of the rivet hole,
# = Safe permissible shear stress for the rivet material, and
n = Number of rivets per pitch length.
We know that shearing area,
A
s
=
4
∃
× d
2
(In single shear)
=2 ×
4
∃
× d
2
(Theoretically, in double shear)
= 1.875 ×
4
∃
× d
2
(In double shear, according to Indian
Boiler Regulations)
∀ Shearing resistance or pull required to shear off the rivet per pitch length,
P
s
= n ×
4
∃
× d
2
× # (In single shear)
= n × 2 ×
4
∃
× d
2
× # (Theoretically, in double shear)
* We have already discussed in Chapter 4 (Art. 4.8) that when the shearing takes place at one cross-section
of the rivet, then the rivets are said to be in single shear. Similarly, when the shearing takes place at two
cross-sections of the rivet, then the rivets are said to be in double shear.
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A Textbook of Machine Design
= n × 1.875 ×
4
∃
× d
2
× # (In double shear, according to Indian
Boiler Regulations)
When the shearing resistance (P
s
) is greater than the applied load (P) per pitch length, then this
type of failure will occur.
4. Crushing of the plate or rivets. Sometimes, the rivets do not actually shear off under the
tensile stress, but are crushed as shown in Fig. 9.17. Due to this, the rivet hole becomes of an oval
shape and hence the joint becomes loose. The failure of rivets in such a manner is also known as
bearing failure. The area which resists this action is the projected area of the hole or rivet on
diametral plane.
The resistance offered by a rivet to be crushed is known as crushing resistance or crushing
strength or bearing value of the rivet.
Let d = Diameter of the rivet hole,
t = Thickness of the plate,
!
c
= Safe permissible crushing stress for the rivet or
plate material, and
n = Number of rivets per pitch length under crushing.
We know that crushing area per rivet (i.e. projected area per rivet),
A
c
= d.t
∀ Total crushing area = n.d.t
and crushing resistance or pull required to crush the rivet
per pitch length,
P
c
= n.d.t.!
c
When the crushing resistance (P
c
) is greater than
the applied load (P) per pitch length, then this type of
failure will occur.
Note : The number of rivets under shear shall be equal to the
number of rivets under crushing.
9.139.13
9.139.13
9.13
StrStr
StrStr
Str
ength of a Rivength of a Riv
ength of a Rivength of a Riv
ength of a Riv
eted Jointseted Joints
eted Jointseted Joints
eted Joints
The strength of a joint may be defined as the maximum force, which it can transmit, without
causing it to fail. We have seen in Art. 9.12 that P
t
, P
s
and P
c
are the pulls required to tear off the plate,
shearing off the rivet and crushing off the rivet. A little consideration will show that if we go on
increasing the pull on a riveted joint, it will fail when the least of these three pulls is reached, because
a higher value of the other pulls will never reach since the joint has failed, either by tearing off the
plate, shearing off the rivet or crushing off the rivet.
If the joint is continuous as in case of boilers, the strength is calculated per pitch length. But if
the joint is small, the strength is calculated for the
whole length of the plate.
9.149.14
9.149.14
9.14
EfEf
EfEf
Ef
ff
ff
f
iciencicienc
iciencicienc
icienc
y of a Rivy of a Riv
y of a Rivy of a Riv
y of a Riv
eted Jointeted Joint
eted Jointeted Joint
eted Joint
The efficiency of a riveted joint is defined as the ratio of the strength of riveted joint to the
strength of the un-riveted or solid plate.
We have already discussed that strength of the riveted joint
= Least of P
t
, P
s
and P
c
Strength of the un-riveted or solid plate per pitch length,
P = p × t × !
t
P
P
Fig. 9.17. Crushing of a rivet.
Riveted Joints
n
293
∀ Efficiency of the riveted joint,
% =
Least of , and
ts c
t
PP P
pt
&&!
where p = Pitch of the rivets,
t = Thickness of the plate, and
!
t
= Permissible tensile stress of the plate material.
Example 9.1. A double riveted lap joint is made between 15 mm thick plates. The rivet diameter
and pitch are 25 mm and 75 mm respectively. If the ultimate stresses are 400 MPa in tension,
320 MPa in shear and 640 MPa in crushing, find the minimum force per pitch which will rupture
the joint.
If the above joint is subjected to a load such that the factor of safety is 4, find out the actual
stresses developed in the plates and the rivets.
Solution. Given : t = 15 mm ; d = 25 mm ; p = 75 mm ; !
tu
= 400 MPa = 400 N/mm
2
; #
u
= 320
MPa = 320 N/mm
2
; !
cu
= 640 MPa = 640 N/mm
2
Minimum force per pitch which will rupture the joint
Since the ultimate stresses are given, therefore we shall find the ultimate values of the resistances
of the joint. We know that ultimate tearing resistance of the plate per pitch,
P
tu
=(p – d)t × !
tu
= (75 – 25)15 × 400 = 300 000 N
Ultimate shearing resistance of the rivets per pitch,
P
su
= n ×
4
∃
× d
2
× #
u
= 2 ×
4
∃
(25)
2
320 = 314 200 N (∵ n = 2)
and ultimate crushing resistance of the rivets per pitch,
P
cu
= n × d × t × !
cu
= 2 × 25 × 15 × 640 = 480 000 N
From above we see that the minimum force per pitch which will rupture the joint is 300 000 N
or 300 kN.
Ans.
Actual stresses produced in the plates and rivets
Since the factor of safety is 4, therefore safe load per pitch length of the joint
= 300 000/4 = 75 000 N
Let !
ta
, #
a
and !
ca
be the actual tearing, shearing and crushing stresses produced with a safe
load of 75 000 N in tearing, shearing and crushing.
We know that actual tearing resistance of the plates (P
ta
),
75 000 = ( p – d ) t × !
ta
= (75 – 25)15 × !
ta
= 750 !
ta
∀!
ta
= 75 000 / 750 = 100 N/mm
2
= 100 MPa
Ans.
Actual shearing resistance of the rivets (P
sa
),
75 000 = n ×
4
∃
× d
2
× #
a
= 2 ×
4
∃
(25)
2
#
a
= 982 #
a
∀#
a
= 75000 / 982 = 76.4 N/mm
2
= 76.4 MPa
Ans.
and actual crushing resistance of the rivets (P
ca
),
75 000 = n × d × t × !
ca
= 2 × 25 × 15 × !
ca
= 750 !
ca
∀!
ca
= 75000 / 750 = 100 N/mm
2
= 100 MPa
Ans.
Example 9.2.
Find the efficiency of the following riveted joints :
1. Single riveted lap joint of 6 mm plates with 20 mm diameter rivets having a pitch of 50 mm.
2. Double riveted lap joint of 6 mm plates with 20 mm diameter rivets having a pitch of 65 mm.
Assume
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Permissible tensile stress in plate = 120 MPa
Permissible shearing stress in rivets = 90 MPa
Permissible crushing stress in rivets = 180 MPa
Solution. Given : t = 6 mm ; d = 20 mm ; !
t
= 120 MPa = 120 N/mm
2
; # = 90 MPa = 90 N/mm
2
;
!
c
= 180 MPa = 180 N/mm
2
1. Efficiency of the first joint
Pitch, p = 50 mm (Given)
First of all, let us find the tearing resistance of the plate, shearing and crushing resistances of the
rivets.
(i) Tearing resistance of the plate
We know that the tearing resistance of the plate per pitch length,
P
t
=(p – d ) t × !
t
= (50 – 20) 6 × 120 = 21 600 N
(ii) Shearing resistance of the rivet
Since the joint is a single riveted lap joint, therefore the strength of one rivet in single shear is
taken. We know that shearing resistance of one rivet,
P
s
=
4
∃
× d
2
× # =
4
∃
(20)
2
90 = 28 278 N
(iii) Crushing resistance of the rivet
Since the joint is a single riveted, therefore strength of one rivet is taken. We know that crushing
resistance of one rivet,
P
c
= d × t × !
c
= 20 × 6 × 180 = 21 600 N
∀ Strength of the joint
= Least of P
t
, P
s
and P
c
= 21 600 N
We know that strength of the unriveted or solid plate,
P = p × t × !
t
= 50 × 6 × 120 = 36 000 N
∀ Efficiency of the joint,
% =
Least of , and
ts c
PP P
P
=
21 600
36 000
= 0.60 or 60%
Ans.
2. Efficiency of the second joint
Pitch, p = 65 mm (Given)
(i) Tearing resistance of the plate,
We know that the tearing resistance of the plate per pitch length,
P
t
=(p – d ) t × !
t
= (65 – 20) 6 × 120 = 32 400 N
(ii) Shearing resistance of the rivets
Since the joint is double riveted lap joint, therefore strength of two rivets in single shear is
taken. We know that shearing resistance of the rivets,
P
s
= n ×
4
∃
× d
2
× # = 2 ×
4
∃
(20)
2
90 = 56 556 N
(iii) Crushing resistance of the rivet
Since the joint is double riveted, therefore strength of two rivets is taken. We know that crushing
resistance of rivets,
P
c
= n × d × t × !
c
= 2 × 20 × 6 × 180 = 43 200 N
∀ Strength of the joint
= Least of P
t
, P
s
and P
c
= 32 400 N
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