Transcript No Slide Title

WELDED CONNECTIONS
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INTRODUCTION
Efficient and direct way of connecting is by welding
Metallurgical bond by heat or pressure or both
Advantages of welding
• Direct transfer of stress - minimum weight ,
efficiency
• Less fabrication
• Economy - 15% saving in weight in bridges,less
labor
• Neat appearance
• More rigid
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BASIC WELDING PROCESSES
Gas welding - Oxyacetelene welding , simple , slow,
repair and maintenance work
Arc welding - All structural welding
Electric arc by use of electric energy
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WELDING PROCEDURE
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Environment
Welding position
Current : controls heat input
Shrinkage
Preheating
Weldability of steels
Economic welds, good , crack free
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TYPES OF JOINTS OR WELDS
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Joints:Lap,Tee,Butt and Corner
Welds: Groove, fillet, plug and slot
Welded joint description - Type of joint and weld
Position of welding
(a) Butt joint
(b) Lap joint
(c) Tee joint
(d) Corner joint
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COMMON TYPES OF WELDS
(b) Fillet welds
(a) Groove welds
Ends shall be semi
circular
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A
A
Section A-A
(d) Plug weld
Section AA
(c) Slot weld
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Groove welds
Selection of a particular type of groove weld depends
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Size of the plate to be joined
welding by hand or automatic
Type of welding equipment
Accessibility of both sides
Position of weld
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Size of butt weld
Thickness of connected plate for full penetration
Depth of penetration for partial penetration
Advantages
High strength,high resistance to impact and cyclic
stress
• Disadvantages
High residual stress , edge preparation and proper
aligning
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GROOVE WELD DETAILS
Arc
Included angle
Electrod
e Depth of
penetration
Root face
Root gap
(b) Root gap
(a) Depth of penetration
Filling run
Capping run
Root run
(c) Root run
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• Fillet welds
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Ease of fabrication and adaptability
Less precision
No special edge preparation
Throat of a weld
Concave and convex surfaces
Weld and leg size
Face of weld
Theoretical throat
s
(t=0.707s)
t
Root of weld Te
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QUALITY OF WELDED CONNECTIONS
• Proper electrodes , welding apparatus and
procedures
• Welding sequence
Doubling up method
Planned wandering method
Step back method
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SEQUENCE OF WELDING OF FILLET WELDS
Doubling - up method for vertical member
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RESIDUAL STRESSES
• Residual stresses - due to rapid heating and
cooling
• Yield strength of material is upper limit for residual
stresses
Tension
LONGITUDINAL RESIDUAL STRESS DUE TO WELD
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WELD DISTORTION
a)Transverse shrinkage(b) Angular change (c) Rotational
distortion
(e) Longitudinal bending
distortion
(d) Longitudinal shrinkage
(f) Buckling
distortion
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WELD SYMBOLS
Symbolic representation of welds
(Ref. IS:813 - 1986 ‘ Scheme of symbols for welding’ )
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DEFECTS IN WELDS
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Incomplete fusion
Porosity
Inadequate preparation
Undercutting - Excessive current or long arc
Slag inclusion - Failure to remove slag between
runs
• Cracks - Breaks in the weld metal
• Lamellar tearing - Occurs in the base metal
beneath the weld
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WELD DEFECT TOLERANCE
For joints welded from both sides
• Incomplete penetration - 5% of parent metal
thickness < 2mm
• Length of flaw < 200 mm / meter length
Welded on one side
• Incomplete penetration - 15% of thickness < 3mm
• Slag inclusion < 200 mm / meter weld length
• Total gas pores < 5 per square centimeter of weld
• Thickness upto 10mm , undercut < 0.5mm
• For thickness > 10mm undercut < 1mm
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WELD INSPECTION
Visual inspection
Liquid penetrants
Magnetic particles
Ultrasonic testing
Radiography
CONNECTION DESIGN
Static strength of welded joint
• Type and size of the weld
• Manner of welding
• Type of electrode used
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BUTT WELDS
• Critical form of loading - Tension in
transverse direction
• Yield stress of weld metal and parent metal
in HAZ (Heat affected Zone) is much higher
• Failure always occurs away from the weld
• Toughness and ductility properties are
affected
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DIFFERENT TYPES OF BUTT JOINTS
(a) Square
(e)Double
Bevel
(b) Single V
(f) Single U
(c) Double V
(g) Single U
(d)Single Bevel
(h) Single J
(i)Double J
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DESIGN
Direct tension or compression
Design strength same as parent metal strength
Effective area equals effective length times
throat size
For full penetration,thickness of weld ,equals
thickness of thinner part of connection
Partial penetration welds are avoided
Throat thickness - 5/8 thickness of thinner part
Average stress concept
Permissible stresses - Parent metal values
Site welds – lower design strengths
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FILLET WELDS
11
1
1
1 1
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Behaviour
• Lap joints splices
• Shear is the main design consideration
• Side fillets and end fillets
• End fillet loaded in tension - high strength and low ductility
• Side fillet loaded - Limited to weld shear strength (50%
tensile strength) Improved ductility
• Average stress in weld throat
• Fillet weld shape is important for end fillets.
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(A) CONNECTIONS WITH SIMPLE WELD DESIGN,
(B) CONNECTIONS WITH DIRECTION- DEPENDENT WELD DESIGN
Tension
Shear
P
P
(a)
P
(b)
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DESIGN
Simple approach - Uniform strength
Size of fillet weld  3mm or thickness of thinner part
Effective throat thickness  3 mm
< 0.7t and 1.0t
= k  fillet size
Size
Size (Min. Leg size)
Fillets of unequal leg length
Penetration
Size
Fillets of equal leg length
Leg length
Size = leg length * 2.4 mm
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SLOT AND PLUG WELDS
• Provided along with fillet welds in lap joints
• Strength of a plug or slot weld - allowable stress
and nominal area in the shearing plane
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Ends shall be semi circular or
have corners rounded to a radius
not less than thickness of part
containing slot
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Section AA
Section AA
(a) Slot weld
(b) Plug
weld
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ECCENTRIC JOINTS
• Shear and torsion
Torsion , F = (T  s ) / J
fh = (T  v) / J
fv = (T  h ) / J
 =R/L
• Shear and bending
Weld is designed to withstand maximum bending
stress and maximum shear stress separately.
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(a) WELDS SUBJECTED TO SHEAR AND TORSION,
(b) WELDS SUBJECTED TO SHEAR AND BENDING
y
M
e P
x
x
c.g of welds
(a)
y
e P
P
e
(b)
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SUMMARY
• Fundamentals of welding , details of various
welding processes, types of welds, common weld
defects and weld inspection have been
presented.
• Advantages of welding are mentioned.
• Behaviour and design of butt - and fillet - welded
connections in steel structures are explained .
• Truss connections and beam connections are
discussed.
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