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The butt joints may be
1. Square butt joint, 2. Single V-butt joint 3. Single U-butt joint,
4. Double V-butt joint, and 5. Double U-butt joint.
These joints are shown in Fig. 10.3.
The other type of welded joints are corner joint, edge joint and T-joint as shown in Fig. 10.4.
( ) Corner joint.a ( ) Edge joint.b ( ) -joint.cT
Fig. 10.4. Other types of welded joints.
The main considerations involved in the selection of weld type are:
1. The shape of the welded component required,
2. The thickness of the plates to be welded, and
3. The direction of the forces applied.
10.12 Basic 10.12 Basic
10.12 Basic 10.12 Basic
10.12 Basic
WW
WW
W
eld Symbolseld Symbols
eld Symbolseld Symbols
eld Symbols
The basic weld symbols according to IS : 813 – 1961 (Reaffirmed 1991) are shown in the
following table.
TT
TT
T
aa
aa
a
ble 10.1.ble 10.1.
ble 10.1.ble 10.1.
ble 10.1.
Basic w Basic w
Basic w Basic w
Basic w
eld symbolseld symbols
eld symbolseld symbols
eld symbols
.
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10.13 Supplementar10.13 Supplementar
10.13 Supplementar10.13 Supplementar
10.13 Supplementar
y y
y y
y
WW
WW
W
eld Symbolseld Symbols
eld Symbolseld Symbols
eld Symbols
In addition to the above symbols, some supplementary symbols, according to IS:813 – 1961
(Reaffirmed 1991), are also used as shown in the following table.
TT
TT
T
aa
aa
a
ble 10.2.ble 10.2.
ble 10.2.ble 10.2.
ble 10.2.
Supplementar Supplementar
Supplementar Supplementar
Supplementar
y wy w
y wy w
y w
eld symbolseld symbols
eld symbolseld symbols
eld symbols
.
10.14 Elements of a 10.14 Elements of a
10.14 Elements of a 10.14 Elements of a
10.14 Elements of a
WW
WW
W
elding Symbolelding Symbol
elding Symbolelding Symbol
elding Symbol
A welding symbol consists of the following eight elements:
1. Reference line, 2. Arrow,
3. Basic weld symbols, 4. Dimensions and other data,
5. Supplementary symbols, 6. Finish symbols,
7. Tail, and 8. Specification, process or other references.
10.15 Standar10.15 Standar
10.15 Standar10.15 Standar
10.15 Standar
d Locad Loca
d Locad Loca
d Loca
tion of Elements of a tion of Elements of a
tion of Elements of a tion of Elements of a
tion of Elements of a
WW
WW
W
elding Symbolelding Symbol
elding Symbolelding Symbol
elding Symbol
According to Indian Standards, IS: 813 – 1961 (Reaffirmed 1991), the elements of a welding
symbol shall have standard locations with respect to each other.
The arrow points to the location of weld, the basic symbols with dimensions are located on one
or both sides of reference line. The specification if any is placed in the tail of arrow. Fig. 10.5 shows
the standard locations of welding symbols represented on drawing.
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Both
.
Arrow
side
Sides
.
Other
side
Field weld symbol
Weld all around symbol
Unwelded length
Length of weld
Finish symbol
Contour symbol
Reference line
Specification
process or
other reference
Tail (omit when
reference is not
used)
Basic weld symbol
or detail reference
Arrow connecting reference
line to arrow side of joint,
to edge prepared member
or both
LP-
S
F
T
Size
Fig. 10.5. Standard location of welding symbols.
Some of the examples of welding symbols represented on drawing are shown in the following table.
TT
TT
T
aa
aa
a
ble 10.3.ble 10.3.
ble 10.3.ble 10.3.
ble 10.3.
Repr Repr
Repr Repr
Repr
esentaesenta
esentaesenta
esenta
tion of wtion of w
tion of wtion of w
tion of w
elding symbolselding symbols
elding symbolselding symbols
elding symbols
.
S. No. Desired weld Representation on drawing
1.
2. Single V-butt weld -machining
finish
3. Double V- butt weld
4.
5.
Fillet-weld each side of
Tee- convex contour
Staggered intermittent fillet welds
Plug weld - 30° Groove-
angle-flush contour
40
40
60
40
40
40
80
100
100
100
5
m
m
(80) 40
(100)
40
(100)
5
5
5
m
m
5
m
m
5
M
10
m
m
10
30º
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10.16 Str10.16 Str
10.16 Str10.16 Str
10.16 Str
ength of ength of
ength of ength of
ength of
TT
TT
T
ransvransv
ransvransv
ransv
erer
erer
er
se Fillet se Fillet
se Fillet se Fillet
se Fillet
WW
WW
W
elded Jointselded Joints
elded Jointselded Joints
elded Joints
We have already discussed that the fillet or lap joint is obtained by overlapping the plates and
then welding the edges of the plates. The transverse fillet welds are designed for tensile strength. Let
us consider a single and double transverse fillet welds as shown in Fig. 10.6 (a) and (b) respectively.
Fig. 10.6. Transverse fillet welds.
In order to determine the strength of the fillet joint, it is assumed that the section of fillet is a
right angled triangle ABC with hypotenuse AC making equal angles with other two sides AB and BC.
The enlarged view of the fillet is shown in Fig. 10.7. The length of each side is known as leg or size
of the weld and the perpendicular distance of the hypotenuse from the intersection of legs (i.e. BD) is
known as throat thickness. The minimum area of the weld is obtained at the throat BD, which is given
by the product of the throat thickness and length of weld.
Let t = Throat thickness (BD),
s = Leg or size of weld,
= Thickness of plate, and
l = Length of weld,
From Fig. 10.7, we find that the throat thickness,
t = s × sin 45° = 0.707 s
! *Minimum area of the weld or throat area,
A = Throat thickness ×
Length of weld
= t × l = 0.707 s × l
If ∀
t
is the allowable tensile stress for the weld
metal, then the tensile strength of the joint for single fillet weld,
P = Throat area × Allowable tensile stress = 0.707 s × l × ∀
t
and tensile strength of the joint for double fillet weld,
P = 2 × 0.707 s × l × ∀
t
= 1.414 s × l × ∀
t
Note: Since the weld is weaker than the plate due to slag and blow holes, therefore the weld is given a reinforcement
which may be taken as 10% of the plate thickness.
10.17 Str10.17 Str
10.17 Str10.17 Str
10.17 Str
ength of Pength of P
ength of Pength of P
ength of P
arallel Fillet arallel Fillet
arallel Fillet arallel Fillet
arallel Fillet
WW
WW
W
elded Jointselded Joints
elded Jointselded Joints
elded Joints
The parallel fillet welded joints are designed for shear strength. Consider a double parallel fillet
welded joint as shown in Fig. 10.8 (a). We have already discussed in the previous article, that the
minimum area of weld or the throat area,
A = 0.707 s × l
s
s
t
45º
D
B
A
Reinforcement
C
Fig. 10.7. Enlarged view of a fillet weld.
* The minimum area of the weld is taken because the stress is maximum at the minimum area.
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If # is the allowable shear stress for the weld metal, then the shear strength of the joint for single
parallel fillet weld,
P = Throat area × Allowable shear stress = 0.707 s × l × #
and shear strength of the joint for double parallel fillet weld,
P = 2 × 0.707 × s × l × # = 1.414 s × l × #
P
P
P
P
( ) Double parallel fillet weld.a
( ) Combination of transverse
and parallel fillet weld.
b
l
1
l
2
Fig. 10.8
Notes: 1. If there is a combination of single transverse and double parallel fillet welds as shown in Fig. 10.8 (b),
then the strength of the joint is given by the sum of strengths of single transverse and double parallel fillet welds.
Mathematically,
P = 0.707s × l
1
× ∀
t
+ 1.414 s × l
2
× #
where l
1
is normally the width of the plate.
2. In order to allow for starting and stopping of the
bead, 12.5 mm should be added to the length of each weld
obtained by the above expression.
3. For reinforced fillet welds, the throat dimension
may be taken as 0.85 t.
Example 10.1. A plate 100 mm wide and
10 mm thick is to be welded to another plate by means
of double parallel fillets. The plates are subjected to
a static load of 80 kN. Find the length of weld if the
permissible shear stress in the weld does not exceed
55 MPa.
Solution. Given: *Width = 100 mm ;
Thickness = 10 mm ; P = 80 kN = 80 × 10
3
N;
#∃= 55 MPa = 55 N/mm
2
Let l =Length of weld, and
s = Size of weld = Plate thickness = 10 mm
(Given)
We know that maximum load which the plates can carry for double parallel fillet weld (P),
80 × 10
3
= 1.414 × s × l × # = 1.414 × 10 × l × 55 = 778 l
! l = 80 × 10
3
/ 778 = 103 mm
Adding 12.5 mm for starting and stopping of weld run, we have
l = 103 + 12.5 = 115.5 mm
Ans.
Electric arc welding
* Superfluous data.
Welded Joints
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351
10.1810.18
10.1810.18
10.18
Special Cases of Fillet Special Cases of Fillet
Special Cases of Fillet Special Cases of Fillet
Special Cases of Fillet
WW
WW
W
elded Jointselded Joints
elded Jointselded Joints
elded Joints
The following cases of fillet welded joints are important from the subject point of view.
1. Circular fillet weld subjected to torsion. Consider a circular rod connected to a rigid plate
by a fillet weld as shown in Fig. 10.9.
Let d = Diameter of rod,
r = Radius of rod,
T = Torque acting on the rod,
s = Size (or leg) of weld,
t = Throat thickness,
*J = Polar moment of inertia of the
weld section =
3
4
td
%
We know that shear stress for the material,
# =
./2
Tr T d
JJ
&
∋
=
32
/2 2
/4
Td T
td td
&
∋
%%
#
()
∋
∗+
,−
∵
T
Jr
This shear stress occurs in a horizontal plane along a leg of the fillet weld. The maximum shear
occurs on the throat of weld which is inclined at 45° to the horizontal plane.
! Length of throat, t = s sin 45° = 0.707 s
and maximum shear stress,
#
max
=
22
22.83
0.707
TT
sd sd
∋
%& & %
2. Circular fillet weld subjected to bending moment. Consider a circular rod connected to a
rigid plate by a fillet weld as shown in Fig. 10.10.
Let d = Diameter of rod,
M = Bending moment acting on the rod,
s = Size (or leg) of weld,
t = Throat thickness,
**Z = Section modulus of the weld section
=
2
4
td
%
We know that the bending stress,
∀
b
=
22
4
/4
MM M
Z
td td
∋∋
%%
This bending stress occurs in a horizontal plane along a leg of the
fillet weld. The maximum bending stress occurs on the throat of the
weld which is inclined at 45° to the horizontal plane.
! Length of throat, t = s sin 45° = 0.707 s
and maximum bending stress,
∀
b(max)
=
22
45.66
0.707
MM
sd sd
∋
%& & %
Fig. 10.9. Circular fillet weld
subjected to torsion.
* See Art, 10.24.
* * See Art, 10.24.
Fig. 10.10. Circular fillet weld
subjected to bending moment.
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3. Long fillet weld subjected to torsion. Consider a
vertical plate attached to a horizontal plate by two identical
fillet welds as shown in Fig. 10.11.
Let T = Torque acting on the vertical plate,
l = Length of weld,
s = Size (or leg) of weld,
t = Throat thickness, and
J = Polar moment of inertia of the weld section
= 2 ×
33
12 6
tl tl
&&
∋
(∵ of both sides weld)
It may be noted that the effect of the applied torque is
to rotate the vertical plate about the Z-axis through its mid
point. This rotation is resisted by shearing stresses developed between two fillet welds and the horizontal
plate. It is assumed that these horizontal shearing stresses vary from zero at the Z-axis and maximum
at the ends of the plate. This variation of shearing stress is analogous to the variation of normal stress
over the depth (l) of a beam subjected to pure bending.
! Shear stress, # =
32
/2 3
/6
Tl T
tl tl
&
∋
&&
The maximum shear stress occurs at the throat and is given by
#
max
=
22
3 4.242
0.707
TT
sl sl
∋
&&
Example 10.2. A 50 mm diameter solid shaft is welded to a flat
plate by 10 mm fillet weld as shown in Fig. 10.12. Find the maximum
torque that the welded joint can sustain if the maximum shear stress
intensity in the weld material is not to exceed 80 MPa.
Solution. Given : d = 50 mm ; s = 10 mm ;∃#
max
= 80 MPa = 80 N/mm
2
Let T = Maximum torque that the welded joint can sustain.
We know that the maximum shear stress (#
max
),
80 =
22
2.83 2.83 2.83
78550
10 (50)
TTT
sd
∋∋
%& %&
! T = 80 × 78 550/2.83
= 2.22 × 10
6
N-mm = 2.22 kN-m
Ans.
Example 10.3.
A plate 1 m long, 60 mm thick is welded to
another plate at right angles to each other by 15 mm fillet weld, as
shown in Fig. 10.13. Find the maximum torque that the welded
joint can sustain if the permissible shear stress intensity in the
weld material is not to exceed 80 MPa.
Solution. Given: l = 1m = 1000 mm ; Thickness = 60 mm ;
s = 15 mm ; #
max
= 80 MPa = 80 N/mm
2
Let T = Maximum torque that the
welded joint can sustain.
Fig. 10.11. Long fillet weld subjected
to torsion.
s
Fig. 10.12
Fig. 10.13
Welded Joints
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353
We know that the maximum shear stress (#
max
),
80 =
226
4.242 4.242 0.283
15 (1000) 10
TTT
sl
∋∋
&
! T =80 × 10
6
/ 0.283 = 283 × 10
6
N-mm = 283 kN-m
Ans.
10.1910.19
10.1910.19
10.19
StrStr
StrStr
Str
ength of Butt Jointsength of Butt Joints
ength of Butt Jointsength of Butt Joints
ength of Butt Joints
The butt joints are designed for tension or compression. Consider a single V-butt joint as shown
in Fig. 10.14 (a).
Fig. 10.14. Butt joints.
In case of butt joint, the length of leg or size of weld is equal to the throat thickness which is
equal to thickness of plates.
! Tensile strength of the butt joint (single-V or square butt joint),
P = t × l × ∀
t
where l = Length of weld. It is generally equal to the width of plate.
and tensile strength for double-V butt joint as shown in Fig. 10.14 (b) is given by
P =(t
1
+ t
2
) l × ∀
t
where t
1
= Throat thickness at the top, and
t
2
= Throat thickness at the bottom.
It may be noted that size of the weld should be greater than the thickness of the plate, but it may
be less. The following table shows recommended minimum size of the welds.
TT
TT
T
aa
aa
a
ble 10.4.ble 10.4.
ble 10.4.ble 10.4.
ble 10.4.
Recommended minim Recommended minim
Recommended minim Recommended minim
Recommended minim
um size of wum size of w
um size of wum size of w
um size of w
eldselds
eldselds
elds
.
Thickness of 3 – 5 6 – 8 10 – 16 18 – 24 26 – 55 Over 58
plate (mm)
Minimum size 356101420
of weld (mm)
10.2010.20
10.2010.20
10.20
StrStr
StrStr
Str
esses fesses f
esses fesses f
esses f
or or
or or
or
WW
WW
W
elded Jointselded Joints
elded Jointselded Joints
elded Joints
The stresses in welded joints are difficult to determine because of the variable and unpredictable
parameters like homogenuity of the weld metal, thermal stresses in the welds, changes of physical
properties due to high rate of cooling etc. The stresses are obtained, on the following assumptions:
1. The load is distributed uniformly along the entire length of the weld, and
2. The stress is spread uniformly over its effective section.
The following table shows the stresses for welded joints for joining ferrous metals with mild
steel electrode under steady and fatigue or reversed load.
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TT
TT
T
aa
aa
a
ble 10.5.ble 10.5.
ble 10.5.ble 10.5.
ble 10.5.
Str Str
Str Str
Str
esses fesses f
esses fesses f
esses f
or wor w
or wor w
or w
elded jointselded joints
elded jointselded joints
elded joints
.
Bare electrode Coated electrode
Type of weld
Steady load Fatigue load Steady load Fatigue load
(MPa)(MPa)(MPa)(MPa)
1. Fillet welds (All types) 80 21 98 35
2. Butt welds
Tension 90 35 110 55
Compression 100 35 125 55
Shear 55 21 70 35
Electric arc melts metal
Mask protects welder’s face
Electricity and
gas supply
In TIG (Tungsten Inert Gas) and MIG (Metal Inert Gas) welding processes, the formation of oxide is
prevented by shielding the metal with a blast of gas containing no oxygen.
10.21 Str10.21 Str
10.21 Str10.21 Str
10.21 Str
ess Concentraess Concentra
ess Concentraess Concentra
ess Concentra
tion Ftion F
tion Ftion F
tion F
actor factor f
actor factor f
actor f
or or
or or
or
WW
WW
W
elded Jointselded Joints
elded Jointselded Joints
elded Joints
The reinforcement provided to the weld produces stress concentration at the junction of the
weld and the parent metal. When the parts are subjected to fatigue loading, the stress concentration
factor as given in the following table should be taken into account.
TT
TT
T
aa
aa
a
ble 10.6.ble 10.6.
ble 10.6.ble 10.6.
ble 10.6.
Str Str
Str Str
Str
ess concentraess concentra
ess concentraess concentra
ess concentra
tion ftion f
tion ftion f
tion f
actor factor f
actor factor f
actor f
or wor w
or wor w
or w
elded jointselded joints
elded jointselded joints
elded joints
.
Type of joint Stress concentration factor
1. Reinforced butt welds 1.2
2. Toe of transverse fillet welds 1.5
3. End of parallel fillet weld 2.7
4. T-butt joint with sharp corner 2.0
Note : For static loading and any type of joint, stress concentration factor is 1.0.
Example 10.4. A plate 100 mm wide and 12.5 mm thick is to be welded to another plate by
means of parallel fillet welds. The plates are subjected to a load of 50 kN. Find the length of the weld
so that the maximum stress does not exceed 56 MPa. Consider the joint first under static loading and
then under fatigue loading.
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