Unit 5.1 Riveted joints

Riveted joints
• The rivets are used to make permanent fastening between the
plates such as in structural work ship buildings, bridges, tanks and
boiler shells.
• A rivet is a short cylindrical bar with a head integral to it. The
cylindrical portion of the rivet is called shank or body and lower
portion of shank is known as tail.
• Types of riveted joints:
1. Lap joint
2. Butt joint
1Unit V Riveted Joint10/24/2019

following are the types of riveted joints
depending upon the number of rows of
the rivets.
1. Single riveted joints
2. Double riveted joints

1. Lap joint
• A joint in which one plate overlaps the other and the two
are then riveted together.

2. Butt Joint
• In butt joint the main plates are kept in alignment butting (i.e.
touching each other) and a cover plate either on one side or on
both sides of the main plates. The cover plate is then riveted
together with the main plates.
• The butt joints are of following types:-
(a) Single strap butt joint -In 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.
(a) Double strap butt joint -In a double strap butt joint the edges of the
plates butt against each other and two cover plates are placed on
both sides of the main plates and then riveted together.

Types of riveted joints

Important terms used in riveted joints
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 denoted by p.
2) Back pitch: It is the perpendicular distance between
the centre lines of the successive rows of rivets. It is
denoted by pb.
3) Diagonal pitch: It is the distance between the centers
of the rivets in adjacent rows of zig-zag riveted joint. It
is denoted by pd.
4) Margin or Marginal pitch: It is the distance between
the centers of rivet hole to the nearest edge of the
plate. It is denoted by m.

Failure of riveted joint
(1) Tearing of the plate on edge -This can be avoided by
keeping the margin m=1.5d. Where d is the diameter
of the rivet hole.
(2) Tearing of the plate across a row of rivets

Cont..
• The resistance offered by the plate against tearing is
known as tearing strength or tearing value of the plate.
• Let
p= pitch of the rivet
d= diameter of the rivet hole
t= thickness of the plate
ft= permissible tensile stress for the plate material.
The tensile area per meter length
At= (p-d) t
Tearing resistance or pull required to tear off the plate /
pitch length.
Pt= At.ft = (p-d) t. ft

Cont..
3. Shearing of the rivets:
The plates which are connected by the rivets exerts tensile stress on
the rivets and the rivets are unable to resist the stress, they are
sheared off.
The resistance offered by a rivet to be sheared off is known as shearing
resistance or shearing strength or shearing value of the rivet.

Cont…
• Let Ps = safe permissible shear stress for the rivet material
n= number of rivets per pitch length
Shear area As= (in single shear)
= (in double shear)
= (in double shear according to Indian boiler regulation)
Shear resistance or pull required to shear off the rivet / pitch length-
(in single shear)
(in double shear)
(in double shear according to Indian boiler regulation)
2
4
d

2
2
4
d


2
1.875
4
d


2
4
s sP n d f

  
2
2
4
s sP n d f

   
2
1.875
4
s sP n d f

   

Cont…
4. Crushing of the plate or rivets
• The resistance offered by a rivet to be crushed is known as crushing
resistance or crushing value or bearing value of the rivet.
• Let σc= safe permissible value of the crushing stress for the rivet or
plate material.
n = number of rivets per pitch length under crushing.
Crushing area Ac= d . T
Total crushing area = n. d. t
And crushing resistance
Pc = n. d. t. σc

Strength of riveted joint
• The strength of a joint may be defined as the maximum
force, which it can transmit without causing it to fail.
• Least of Pt, Ps and Pc is taken as strength of riveted joint.
Efficiency of a riveted 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.
• strength of riveted joint =Least of Pt, Ps and Pc
• Strength of un-riveted or solid plate per pitch length
P= p x t x σt
,
. .
t s c
t
least of P P and P
p t




Problem.1 Find the efficiency of the following riveted joint:-
(i) Single riveted lap joint of 6 mm plates with 20 mm
diameter rivets having a pitch of 50 mm.
(ii) Double riveted lap joint of 6 mm plates with 20 mm
diameter rivets having a pitch of 65 mm. Assume
Permissible tensile stress in plate = 120 MPa
Permissible shearing stress in rivets = 90 MPa
Permissible crushing stress in rivets = 180 MPa

Problem.2 Find the efficiency of the Single riveted lap joint of
6 mm plates with 20 mm diameter rivets having a pitch of 50
mm. the permissible stresses are:-
Tensile stress in plate = 100 MPa
Shearing Stress in rivets= 80 MPa
Crushing stress in rivets = 160 MPa
(Nov- Dec 2011, Nov-Dec 2013)
14Unit V Riveted Joint
Problem. 3 A double riveted double cover butt joint in plates 20
mm thick is made with 25 mm diameter rivets at 100 mm pitch.
The permissible stresses are
σt=120 MPa,
ζ= 100 MPa and
σc= 150 Mpa
Find the efficiency of the joint. April May- 2010
10/24/2019

Unit V Riveted Joint 15
Problem 4 A triple riveted joint is to be made between 6.5
mm plates. The allowable stresses ft= 35 N/mm2, fs=
29N/mm2, and fc =52.5 N/mm2. Calculate the rivet
diameter, rivet pitch, and back pitch. Zig-Zag riveting is
to be used. Indicate how the joint will fail.
April May 2012
10/24/2019

Design of Boiler Joints
• Boiler has two types of rivet joints:-
(1) Longitudinal (2) Circumferential
(1) Longitudinal:- it is used to join the ends of plate to get
the required diameter of a boiler. For this purpose butt
joint with two cover plates is used.
(1) Circumferential:- it is used to get the required length of
the boiler. For this purpose a lap joint with one ring
overlapping the other.

Assumptions for designing
1. Load on joint is equally shared by all the joints.
2. Tensile stress is equally distribute over the section of
metal between the rivets.
3. Shearing stress in all the rivets is uniform.
4. Crushing stress is uniform.
5. No bending stress in rivets.
6. The rivet fills the hole after it is driven.
7. The holes into which the rivets are driven do not
weaken the member.
8. The friction between the surfaces of the plate is
neglected.

1. Design of longitudinal butt joint for a boiler
1. Thickness of the boiler shell (t):-
(Data Book page 7.126)
mm
Where
P = steam pressure in the boiler
D = internal diameter of the boiler shell
σt = permissible tensile stress
= efficiency of the longitudinal joint. (from Data Book page
no. 7.126)
Note: Thickness of the shell should not be less than 8mm.
1
2. .t l
PD
t
 
 
l

Cont…
2. Diameter of the rivet (d):- when t > 8mm
Otherwise find d by Ps= Pc
3. Pitch of rivets (p):-
Pt= Ps
or pmax= C . t + 41 mm (Least of two value)
Where
C = constant ( from data book for various type of joint)
6d t

4. Distance between the row of rivets (pb):-
pb = 0.33 p + 0.67 d for Zig-Zag riveting
pb = 2 d for chain riveting

Cont…
5. Thickness of butt strap (t1):-
t1= 1.125 t (for single cover)
t1= 0.625 t (for double cover)
For unequal straps
t1= 0.75 t
t2= 0.625 t
6. Margin (m):-
m = 1.5 d

2. Design of circumferential lap joint for a boiler
1. Thickness of the shell (t) and diameter of rivets (d):-
same as for longitudinal joint.
2. Number of rivets (i):-
3. Pitch of rivets (p1):-
Where
= efficiency of circumferential joint (from Data book page 7.127)
4. Number of rows of rivets (rn):-
5. Margin (m) and back pitch (pb) are same as for longitudinal joint.
2
D p
i
d 
 
  
 
1
1
c
p d
p



c
.
( )
n
i p
r
D t



Problem.4 Design a double riveted zig-zag butt joint with
two cover plates for the longitudinal seam of a boiler
shell 1.5 m in diameter subjected to a steam pressure of
0.95 N/mm2. Assume joint efficiency as 75%. The
allowable tensile stress in plate is 90 MPa; compressive
stress 140 MPa; and shear stress in rivet 56 MPa. Make
a check for efficiency.
(April May 2010, April May & Nov-Dec 2013)

Problem.5 Design a double riveted butt joint with two cover
plates for the longitudinal seam of a boiler shell 0.75 m in
diameter to carry a maximum pressure of 1.05 N/mm2.
Assume joint efficiency as 75%. The allowable stresses are
(i) σt = 35 N/mm2
(ii) σc = 52.5 N/mm2
(iii) ζ= 28 N/mm2
Make a check for efficiency. (April May 2011)

Problem. 6 A steam boiler is to be designed for a working
pressure of 2.5 N/mm2 with the inside diameter of 1.6 m.
Give the design calculation for the longitudinal and
circumferential for the following working stress for steel
plates and rivets:
In tension = 75 MPa;
In shear = 60 MPa;
In crushing = 125 MPa.
Assume triple riveted butt joint double strap with unequal
cover plate. (Nov Dec- 2013)

Eccentrically Loaded Riveted Joint:-
Problem. 8 A Bracket attached to a vertical column by
means of four identical rivets is subjected to an eccentric
force of 25 kN as shown in fig. Determine the diameter of
rivets if the permissible shear stress is 60 N/mm2.

Problem. 9 A riveted joint consisting of four identical rivets
is subjected to an eccentric force of 5 kN. Determine the
diameter of rivets if permissible shear stress is 60
N/mm2.

Problem. 10 The bracket as shown in fig is to carry a load
of 45 kN. Determine the size of the rivet if the shear
stress is not to exceed 40 MPa. Assume all rivets of
same size. Nov-Dec 2010

Problem. 11 A bracket is attached to a vertical column by
means of six identical rivets. It is subjected to an
eccentric force of 60 kN at a distance of 200 mm from
the centre of gravity of the column. The maximum
permissible shear stress for the rivets is 150 N/mm2.
(i) Which rivet is subjected to maximum shear force?
(ii) What is magnitude of maximum force?
(iii) Determine the diameter of rivets.

Problem. 12 A bracket is attached to a horizontal column
by means of three identical rives as shown in fig. The
maximum permissible shear stress is 60 N/mm2. Find
the diameter of rivets.

Unit 5.1 Riveted joints

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Unit 5.1 Riveted joints