welded joint,welded connections.pptx
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Welded connection
Chapter-2
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What is welded connectionsWelding consist of joining two pieces of metal by
establishing a metallurgical bond between them. The
elements to be connected are brought closer and the metal
is melted by means of electric arc or oxy-acetylene flame
along with weld rod which add metal to the joint. After
cooling the bond is established between the two elements
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Advantage of Welded connections1. No use of gusset plates, connecting angles etc., Welded structures
are lighter.2. Welding process is easier as compare to making holes for
fasteners.
3. Welding is more adaptable than bolting or riveting. For example,
even circular tubes can be easily connected by welding
4. 100 % efficiency can be achieved whereas in bolted connection it
can reach a maximum of 70-80 % only
5. Noise produced in welding process is relatively less.
6. Have good aesthetic appearance
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Advantages8) Welded connection is airtight and watertight because of that less
danger of steel structures and welded connection is preferredfor water tanks
9) Welded joint are rigid
10) There is no problems in mismatching of holes in welded
connections whereas in bolted connections mismatching of bolt
holes creates considerable problem.
11) Alterations in connection can be easily made in the design of
welded connections.
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Disadvantages of welded connections1. Due to uneven heating and cooling members are likely to
distort in the process of welding.
2. Possibility of brittle fracture in welding.
3. Welded joint fails earlier than a bolted joint, if the structure is
under fatigue stresses.
4. The inspection of welded joint is difficult and expensive. it
needs non destructive testing
5. Highly skilled person is required for welding
6. Proper welding in field conditions is difficult
7. Welded joint are over rigid
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Types of Welded joints
Butt Weld
Fillet weld
Slot weld and plugweld
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Types of butt weldSquare butt weld on one side
Square butt weld, both sides
Single V butt joint
Double V butt joint
Single U butt joint
Single J-butt joint
Single bevel butt joint
Similarly there can be double U, double J and double bevel butt joints
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Fillet Weld
It is a weld of approximately triangular cross section joining two
surfaces approximately right angles to each other in lap joint, tee
joint or corner joint
When the cross section of fillet weld is isoscele triangle with faceat 45, it is known as standard fillet weld. In special circumstances
60 and 30 angles are also used.
A fillet weld is known as concave fillet weld, convex fillet weld or
as mitre fillet weld depending upon the shape of weld face.
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fillet weld
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Slot weld or plug Weld
A weld in which a plate with circular hole is kept with another
plate to be joined and then fillet welding is made along the
periphery of the hole.
A plug weld in which small holes are made in one plate and is
kept over another plate to be connected and then the entire hole isfilled with filler material
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Important Specifications For welding
Welding shall conform to IS 816 and IS 9595.some important
specifications regarding butt weld, fillet weld and plug and
slot weld as per IS 800-2007
Butt Weld
It shall be specified by the effective throat thickness.
Complete Penetration- thickness of the thinner part joint
taken as a size of butt weld ( Double U, Double V, Double Jand Double bevel butt welds may be generally regarding as
complete penetration butt weld
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Effective throat thickness in case of incomplete penetration
The minimum thickness of the weld metal common to the
part joined, excluding reinforcment. in the absence of actual
data it may be taken as 5/8 of thickness of thinner material.
The effective length of butt weld shall be taken as the length
of full size weld.
The minimum length of butt weld shall be four times the
size of the weld
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If intermittent but welding is
used, it shall have an effective
length of not less than four
times the weld size and space
between the two welds shall not be more than 16 times the
thickness of the thinner part
joined.
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Fillet weldSize of fillet weld
The size of normal fillet weld shall be taken as the
minimum weld leg size.
For Deep penetration welds with penetration not less than2.4mm, size of weld is minimum leg size+2.4mm
For fillet welds made by semi automatic or automatic
processes with deep penetration more than 2.4mm, if
purchaser and contractor agree
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S = minimum leg size + actual penetration
2. Minimum size of fillet weld specified is 3m. To avoid therisk of cracking in the absence of preheating the
minimum size specified are
For less than 10 mm plate 3mm
For 10 to 20 mm plate 5mm
For 20 to 32 mm plate 6mmFor 32 to 50 mm plate 8mm
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3. Effective throat thickness
it shall not be less than 3mm and shall not genrally
exceed 0.7t.t is thickness of the thinner plate of the
element being welded. If the faces of plates being welded
are inclined to each other, the effective throat thickness
shall be taken as K times the fillet size where K depend
upon the angle between fusion faces
4) Effective length should not be less than four times the sizeof the weld.
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4. Lap jointMinimum lap should be four times the thickness of thinner
part joined or 40 mm whichever is more. The length of weldalong either edge should not be less than the transversespacing of welds
5. Intermittent welds
Length shall not be more than 4 times the weld size or 40mm whichever is more.Minimum clear spacing------ 12t for compression joint
16t for tensile jointt is the thickness of the thinner plate joined.it will not be used in positions subject to dynamic, repetitiveand alternating stress.
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Plug weld
The effective area of a plug weld shall be considered the
nominal area of the hole
Design Stress in weld
Butt weld
It shall be treated as parent metal with a thickness equal to the
throat thickness and the stresses shall not exceed those
permitted in the parent metal.
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Fillet Weld, Slot or Plug weldDesign strength shall be based on its throat area and shall be
given by f wd = f wn / mw
f wn = fu/3 Fu smaller of the ultimate stress of the weld or of t parent metalmw = 1.25 for shop weld and 1.5 for filled weld
The following provisions are made in the code for the fillet wapplied to the edge of a plate or section
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1. If a fillet weld is to the square edge of a part, the specified size of
the weld should generally be at least 1.5 mm less than the edge
thickness
2. If fillet weld is to the rounded toe of a rolled section, the specified
size of the weld should generally not exceed 3/4 th of the thickness
of the toe.3. In members subject to dynamic loading, the fillet weld shall be of
full size with its leg length equal to the thickness of the plate
4. End fillet weld , normal to the direction shall be of unequal size
with throat thickness not less than 0.5t.the difference in the
thickness of weld shall be negotiated at a uniform slope.
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Reduction in design stresses for long joints
If the length of the welded joint lj is greater than 150t ,where t is
throat thickness, the design capacity of weld fwd shall be redu
by the factor
l ld d
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Example on welded jointA 18 mm thick plate is joined to a 16 mm plate by
200 mm long (effective) butt weld. Determine thestrength of joint ifi. A double V butt weld is usedii. A single V butt weld is used
Assume that Fe 410 grade plates and shop welds areused
Case (i) double V butt weldThroat thickness= thickness of thinner plate t= 16mmEffective lengthLw = 200mm, fu = 410 N/mm, shop weld =
1.25Effective area of weld = effective length x Throat thickness
Design strength of weld =( Lw x t x fu/3)/
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(200 x 16 x 410/3)/1.25 = 605987N (605.987kN)
Case (ii) Single V butt weld jointSince penetration is not complete, effective throat
thickness t = (5/8) x 16=10 mm
Design strength = =( Lw x t x fu/3)/ mv(200 x 10 x 410/3)/1.25 = 378.742kN
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A tie member in a truss girder is 250 mm x 14 mmin size. It is welded to a 10 mm thick gusset plateby a fillet weld. The overlap of the member is 300mm and the weld size is 6mm. Determine thedesign strength of the joint, if welding is done asshown in fig below. What is the increase instrength of the joint, if welding is done all around.Assume shop welding.
300 mm
250
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For Fe 410 grade steel fu = 410 Mpa and fy = 250 MpaFor shop weld: partial safety factor for material= 1.25
Effective length of the weld Lw = 2x 300+250 =850 mmEffective throat thickness t = KS= 0.7x 6= 4.2mmDesign strength of the weld, fwd = (L w x t x(fu /3 x )) ( 850 x 4.2 x(410/ 3x1.25))
676050 N , 676.05 kNWhen the weld ing i s d one a ll aroun d
300 mm
250
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Effective length of the weld Lw = 2x (300+250) = 1100mm
(L w x t x(fu /3 x )) ( 1100 x 4.2 x(410/ 3x1.25))
874890 N , 874.890 k N
Inc rease in s treng th o f th e joint = 874.89- 676.05
198.85k N
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A tie member 75mm x 8mm is to transmit a factoredload of 145kN. Design fillet weld and necessaryoverlaps for the case shown in figure below The steelused is of grade Fe 410. Assume gusset plate to be 12mm thick.
(a) Shop welding
75mm
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(b) Shop Welding
75mm
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(c) Site Welding
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Eccentric connection-Plane of momentand the Plane of welds is the same
The eccentric load P is equivalent to A direct load P at the centre of gravity of the group ofweld A twisting momentP x e
d
e
X X
Y
Y
rmax
G
b
P
q 1q 2
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Let a w eld o f u n i fo rm s ize be p rov ided th rou gh ou t
and t b e the e ffec t ive throa t th ick ness . if d i s d epth
of th e w eld and b i s the w id th . The d i rec t sh ear
s t ress in th e w eld i s
q 1 = (p /(2b +d )x t)
Due to tw is t ing m om ent the s t r es s in the we ld i s
m axim um in the w eld a t the ex t rem e d i s t ance f rom
C. G of the gro up of w eld and ac ts in the d i rec t ion
perpendic ular to th e rad iu s vec to r. The m axim um
st ress d ue to the mom ent
=
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C bi d i l d h t
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Combined axial and shear stressCombined axial and shear stress
If weld is subjected to axial stresses, compression ortension due to axial force or bending momentsimultaneously with shear, IS 800:2007 made the followingprovisions
Fillet Weld : equivalent stress e = fa + 3q u/3mw
fa- axial stress, direct due to bending.
q- shear stress due to shear force or tension
Check for the combination of stresses need not to bedone for :
(a) side fillet weld joining cover plates and flange plates,
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Eccentric connection- Moment at right angles tothe plane of weld
P is a factored load at an eccentricity eh is the effective depth of the fillet weldFillet welding is on both sides of the bracket plate effectivearea of the weld 2ht e
X X
Y
Y
G
P
hh
Throatthickness
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Direct shear stress q= p/2htBending stress at the extreme edge of the weld f =m/z P.e/((2ht)x1 = 6pe/2th
Equivalent stress- e = fa + 3q u/3mwFor the purpose of finding the effective depth hrequired, firs depth required for bending only may befound. To take care of shear a;so. Increase this valueby about 10 %.
h = 6M/(2tfw d)Hence try h = 1.1h
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Load = 100 kN
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Load = 100 kN
Factored load, p = 100 x 1.5= 150 kN
Thickness of the flane pf ISHB 300 @ 618 N/m is 10.6mm
Minimum size of the weld= 5mm
Use 8mm fillet weld on each side of bracket plate.
Throat thickness t = 0.7x8
Resistance of weld fwd = (fu/3)/(1/1.25)
(410/3) /(1/1.25) = 189.37 N/mm Depth of weld required to resist bending alone = h =(6x150x1000x150)/(2x0.7x8x189.37) = 252.3mm
About 10% extra depth is to be provided.
Let h= 280mm
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Check for the stressesDirect shear stress q = p/(2th)
150x1000/(2x0.7x8x280)Bending stress f = M/Z = (6M/2th) (6x150x1000x150)/2x0.7x8x280)
=153.744 n/mm
f +3q = 153.744 +3x47.83 = 174.6 N/mm < 189.37 N/mm Hence design is safe.
E l
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ExampleDesign a fillet weld for the bracket shown in fig below,
eccentricity e= 250mm. Thickness of the bracket plateis 12mm and the column used is ISHB 300 @ 618 N/m
Throatthickness
X XG
w
400mm
250mm
400mm
250mm
165mm
A i l fill ld
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Assuming normal fillet welds
Throat thickness of the weld=0.7x10=7mm
Throat thickness of the web weld=0.7x5=3.5mmTotal throat thickness of web welds= 165x7x2+250x3.5x2=4060mm
Ixx= (3.5x250)/12 +((165x7)x200) x2 = 101514583mm4. Bending moment to be transferred= p x 2250kN-mm, if P isthe factored load in kN
Consider flange weld which is subjected to maximum stress=qv =Px1000/4060 = 0.2463N/mm
Due to bending = qh= ((250x1000P)/(101514583)x200) =
h
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q= qv+qh P x0.2463+0.49254 =0.5507P
0.5507P=(410/3)x(1/1.5) equating it to design stress p = 286.57kN
Working load that can be permitted= P/1.5 = 191.04kN
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