FILLET WELD
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
WELDING PROCEDURE
• Environment
• Welding position
• Current : controls heat input
• Shrinkage
• Preheating
Weldability of steels
Economic welds, good , crack free
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
(a) Butt joint
(b) Lap joint
(c) Tee joint
(d) Corner joint
COMMON TYPES OF WELDS
(b) Fillet welds
(a) Groove welds
Ends shall be semi
circular
A
A
A
A
Section A-A
(d) Plug weld
Section A-A
(c) Slot weld
• Fillet welds
• Ease of fabrication and adaptability
• Less precision
• No special edge preparation
• Throat of a weld
• Concave and convex surfaces
Weld and leg size
s
t
Root of weld Te
Face of weld
Theoretical throat (t=0.707s)
QUALITY OF WELDED CONNECTIONS
• Proper electrodes , welding apparatus and
procedures
• Welding sequence
Doubling up method
Planned wandering method
Step back method
SEQUENCE OF WELDING OF FILLET WELDS
Doubling - up method for vertical member
13
12 7
5
1
6
8
17
18
11
10
9
3
2
4
14
15
16
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
-
-
WELD DISTORTION
a)Transverse shrinkage
(b) Angular change
(c) Rotational distortion
(e) Longitudinal bending distortion
(d) Longitudinal shrinkage
(f) Buckling distortion
DEFECTS IN WELDS
•
•
•
•
•
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
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
•
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
•
•
•
•
•
•
•
•
•
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
FILLET WELDS
11
1
1
1 1
11
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.
(A) CONNECTIONS WITH SIMPLE WELD DESIGN,
(B) CONNECTIONS WITH DIRECTION- DEPENDENT WELD DESIGN
Tension
Shear
P
P
(a)
P
(b)
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
(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)
18
SUMMARY
• Fundamentals of welding , details of fillet welding
process, types fillet weld design, common weld
defects and weld inspection have been presented.
• Advantages of fillet welding are mentioned.
• Behaviour and design of fillet-welded connections
in steel structures are explained .
• Truss connections and beam connections are
discussed.
19