Post on 04-Jun-2018
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WELDED CONNECTIONS I
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Efficient and direct way of connecting is by weldingMetallurgical 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
INTRODUCTION
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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
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
Joints:Lap,Tee,Butt and Corner
Welds: Groove, fillet, plug and slot
Welded joint description - Type of joint and weld
Position of welding
(d) Corner joint(a) Butt joint (b) Lap joint (c) Tee joint
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A
Ends shall be semi
circular
A
Section A-A
(c) Slot weld
(a) Groove welds
(b) Fillet welds
AA
Section A-A
(d) Plug weld
COMMON TYPES OF WELDS
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Groove welds
Selection of a particular type of groove weld depends
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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Root face
Depth of
penetration
Electrod
eArc
(a) Depth of penetration Root gap
Included angle
(b) Root gap
Root run
Capping run Filling run
(c)Root run
GROOVE WELD DETAILS
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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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13 12 7 5 1 6 8 1817
11 10 9 3 2 4 14 1615
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
LONGITUDINAL RESIDUAL STRESS DUE TO WELD
- -
Tension
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a)Transverse shrinkage(b) Angular change
(d) Longitudinal shrinkage
(e) Longitudinal bending
distortion
(c) Rotational
distortion
(f) Bucklingdistortion
WELD DISTORTION
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WELD SYMBOLS
Symbolic representation of welds
(Ref. IS:813 - 1986 Scheme of symbols for welding )
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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 penetrantsMagnetic 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 intransverse 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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(a) Square(b) Single V (c) Double V (d)Single Bevel
(e)Double
Bevel
(f) Single U (g) Single U(h) Single J
(i)Double J
DIFFERENT TYPES OF BUTT JOINTS
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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 weldslower design strengths
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FILLET WELDS
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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1
11
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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
Fillets of equal leg length
Size
Size
Fillets of unequal leg length
Size (Min. Leg size)
Leg length
Size = leg length * 2.4 mm
Penetration
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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 planeEnds shall be semi circular or
have corners rounded to a radius
not less than thickness of partcontaining slot
Section A-
A
AA
(a) Slot weld
Section A-
A
AA
(b) Plug
weld
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ECCENTRIC JOINTS
Shear and torsion
Torsion , F = (T s ) / Jfh = (T v) / Jfv = (T h ) / J
= R / L
Shear and bending
Weld is designed to withstand maximum bendingstress and maximum shear stress separately.
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(a) WELDS SUBJECTED TO SHEAR AND TORSION,
(b) WELDS SUBJECTED TO SHEAR AND BENDING
xx
y
y
e
c.g of welds
P
M
(a)
e
(b)
Pe P
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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.