By: Prof Dr. Akhtar Naeem Khan

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Lecture 05 Welded connections

• By Prof Dr. Akhtar Naeem Khan
• chairciv_at_nwfpuet.edu.pk

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Topics to be Addressed

• Welding
• Types of welds
• Welded Joints
• Welding processes
• Nomenclature of welds
• Welding symbols

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Topics to be Addressed

• Stresses in Welds
• Specifications for Welds
• Code Requirements
• Design Examples

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Welding

• It is a process of joining parts by means of heat
  pressure, causes fusion of parts.
• OR
• Heating metal to fusion temperature with or
  without addition of weld metals.
• Code specification American Welding Society
  (AWS)

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Types of Welds

• Welds are classified according to their shape and
  method of deposition into
• Groove Weld
• Fillet Weld
• Plug Weld
• Slot Weld

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Types of Welds

1. Groove Weld is made in opening between two parts
   being joined.

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Types of Welds

• Fillet Weld triangular in shape, joins surfaces
  which are at an angle with one another.

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Types of Welds
Groove Weld and Fillet Weld

• Groove welds are more efficient than fillet
  welds.
• Have greater resistance to repeated stress and
  Impact loaded. Hence preferable for dynamically
  loaded members.
• Groove welds require less weld metal than fillet
  weld of equal strength.
• But fillet welds are often used in structural
  work. WHY ?

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Types of Welds
Groove Weld and Fillet Weld

• But fillet welds are often used in structural
  work WHY ?
• Partly because many connections are more easily
  made with fillet welds and
• Partly because groove welds require the member of
  structure to be cut to rather close tolerances.

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Types of Welds

1. Plug Weld is made by depositing weld metal in a
   circular hole in one of two lapped places.

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Types of Welds

• Slot Weld similar to plug but the hole is
  elongated.

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Types of Welds
Groove weld
Fillet weld
Plug weld
Slot weld
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Types of Welds

• Welds are classified according to the position of
  weld during welding as
• Flat
• Horizontal
• Vertical
• Overhead

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Types of Welds

• Flat Executed from above, the weld face
  approximately horizontal.

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Types of Welds

• Horizontal Similar to Flat weld but weld is
  harder to make.

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Types of Welds

• Vertical Longitudinal axis of weld is vertical.

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Types of Welds

• Overhead Welding is done from underside of the
  joint.

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Types of Welds
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Welded Joints

• They are classified as
• Butt Joint is groove-welded

1. Lap Joint is fillet-welded

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Welded Joints

1. Tee Joint can be fillet-welded or groove-welded

1. Corner Joint

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Welding processes

• There are three methods of Welding
• Forge welding
• Resistance welding
• Fusion welding

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Welding processes

• Forge welding
• It consists of simply heating the pieces above
  certain temperature and hammering them together

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Welding processes

• Resistance welding
• Metal parts are joined by means of heat and
  pressure which causes fusion of parts.
• Heat is generated by electrical resistance to a
  current of high amperage low voltage passing
  through small area of contact between parts to be
  connected.

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Welding processes

• Fusion welding
• Metal is heated to fusion temperature with or
  without addition of weld metal
• Method of connecting pieces by molten metal
• Oxyacetylene welding
• Electric arc welding

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Welding processes
Metal Arc Welding

• Arc is a sustained spark between a metallic
  electrode and work to be welded.
• At the instant arc is formed the temperature of
  work and tip of electrode are brought to melting
  point.
• As the tip of electrode melts, tiny globules of
  molten metal form.

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Welding processes
Metal Arc Welding

• The molten metal, when exposed to air combines
  chemically with oxygen nitrogen forming oxides
  nitrides, which tend to embrittle it less
  corrosive resistant.
• Tough, ductile weld are produced if molten pool
  is shielded by an inert gas, which envelops
  molten metal tip of electrode.

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Welding processes
Metal Arc Welding
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Shielded Metal Arc Welding (SMAW)
Welding processes

• When an arc is struck between the metal rod
  (electrode) and the work piece, both the rod and
  work piece surface melt to form a weld pool.
• Simultaneous melting of the flux coating on the
  rod will form gas and slag which protects the
  weld pool from the surrounding atmosphere.

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Shielded Metal Arc Welding (SMAW)
Welding processes
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Submerged Arc Welding (SAW)
Welding processes

• A bare wire is fed through welding head at a rate
  to maintain constant arc length.
• Welding is shielded by blanket of granular
  fusible material fed onto the work area by
  gravity, in an amount sufficient to submerge the
  arc completely.
• In addition to protecting weld from atmosphere,
  the covering aids in controlling rate of cooling
  of weld.

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Submerged Arc Welding (SAW)
Welding processes
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Flux Cored Arc Welding (FCAW)
Welding processes

• It utilizes the heat of an arc between a
  continuously fed consumable flux cored electrode
  and the work.
• The heat of the arc melts the surface of the base
  metal and the end of the electrode.
• The metal melted off the electrode is transferred
  across the arc to the work piece, where it
  becomes the deposited weld metal.
• Shielding is obtained from the disintegration of
  ingredients contained within the flux cored
  electrode.

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Flux Cored Arc Welding (FCAW)
Welding processes
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Metal-Arc Inert Gas (MIG) Welding
Welding processes

• MIG Welding refers to the wire that is used to
  start the arc.
• It is shielded by inert gas and the feeding wire
  also acts as the filler rod.

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Metal-Arc Inert Gas (MIG) Welding
Welding processes
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Tungsten-Arc Inert Gas (TIG) Welding
Welding processes

• The arc is started with a tungsten electrode
  shielded by inert gas and filler rod is fed into
  the weld puddle separately.
• The gas shielding that is required to protect the
  molten metal from contamination is supplied
  through the torch.

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Tungsten-Arc Inert Gas (TIG) Welding
Welding processes
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Important considerations
Welding processes

• Large fillet welds made manually require two or
  more passes.
• Each pass must cool, and slag must be removed
  before next pass.
• Most efficient fillet welds are those which can
  be made in one pass.

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Important considerations
Welding processes

• Largest size can be made in one pass depends upon
  welding position should not exceed the
  following.
• 5/16 Horizontal or overhead
• 3/8 Flat position
• 1/2 Vertical position
• Thickness of weld Thickness of material 1/16

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Important considerations
Welding processes

• A fillet weld that is too small compared with the
  thickness of the material being welded is
  affected adversely during cooling.
• The amount of heat required to deposit a small
  weld is not sufficient to produce appreciable
  expansion of the thick material, and as hotter
  weld contracts during cooling it is restrained by
  being attached to the cooler material and tensile
  stresses produce, may cause crack of the weld.

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Nomenclature of Welds

• The part of weld assumed to be effective in
  transferring stress is Throat.
• The faces of weld in contact with the parts
  joined is called its Legs..
• For equal-legged fillet weld throat is 0.707s,
  where s is leg size.

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Standard Welding symbols
Fillet Weld
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Standard Welding symbols
Fillet Weld
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Standard Welding symbols
Fillet Weld
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Standard Welding symbols
Fillet Weld
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Standard Welding smbols
Fillet Weld
Unequal legs
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Standard Welding symbols
Groove Weld
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Standard Welding symbols
Groove Weld
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Standard Welding symbols
Groove Weld
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Standard Welding symbols
Plug Slot Weld
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Stresses In Welds

• Groove weld may be stressed in tension,
  compression, shear, or a combination of tension,
  compression and shear, depending upon the
  direction and position of load relative to weld.

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Stresses In Welds

• f P / (LTe)

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Stresses In Welds

• The load P in Fig is resisted by shearing force
  P/2, on the throat of each fillet weld. f (P
  /2) / (LTe)

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Stresses In Welds

• It is customary to take the force on a fillet
  weld as a shear on the throat irrespective of the
  direction of load relative to throat.

P ?2 / 4
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Stresses In Welds

• Tests have shown that a fillet weld transverse to
  the load is much stronger than a fillet weld of
  same size parallel to the load.

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Stresses In Welds

• Load sharing of P, between two longitudinal
  fillet one transverse fillet weld depends
  either on

• Proportional to their length if welds are of same
  size.
• Proportional to the area for different size weld.

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Stresses In Welds

• Any abrupt discontinuity or change in section of
  member such as notch or a sharp reentrant corner,
  interrupts the transmission of stress along
  smooth lines.

• Joint is elongated in direction of load to
  produce a more uniform transfer of stress
• These concentrations are of no consequence for
  static loads, but they are significant where
  fatigue is involved.

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Specifications for Welded Connections

• Welding electrodes are classified on the basis of
  mechanical properties of weld metal, Welding
  position, type of coating, and type of Current
  required.
• Each electrode is identified by code number
  EXXXXX.
• E stands for Electrode and each X represents
  number.

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Specifications for Welded Connections

• First two or three numbers denote the tensile
  strength in Ksi.
• Next No. position in which electrode can be used.
  
• e.g. 1 all positions, 2 flat horizontal
  fillet welds, 3 flat welding only
• Last No. denotes type of covering, type of
  current polarity.

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Specifications for Welded Connections

• Example E7018 means
• Tensile strength 70 Ksi
• 1 means can be used in all positions
• 8 means it is iron-powder, low-hydrogen electrode
  used with A.C or D.C but only in reverse polarity.

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Code Requirements

• AISC/ASD
• Allowable stress in welded connection is given in
  Table 2-21
• AISC/LRFD
• Design strengths of welds are given in Table
  2-22 with resistance factor ?.

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Code Requirements

• AASHTO
• Allowable stress are more conservative than AISC.
  e.g. 0.27Fu for fillet weld, Fu is tensile
  strength of electrode but not less than tensile
  strength of connected part.
• AREA
• Allowable shear stress on fillet welds are given
  as function of base material and strength of weld
  metal. e.g.
• A36. Electrode or electrode-flux combinations
  with
• 60,000 psi tensile strength 16,500 psi
• 70,000 psi tensile strength 19,500 psi

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Code Requirements
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Code Requirements
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Code Requirements
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Code Requirements
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Code Requirements
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Design Problem
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Example Problem 1 - ASD
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Example Problem 1 - ASD
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Example Problem 1 - ASD
Final Design
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Example Problem 1 - ASD
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Example Problem 2 LRFD
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Example Problem 2 LRFD
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Example Problem 2 LRFD
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Example Problem 2 LRFD
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Example Problem 3 LRFD
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Example Problem 3 LRFD
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Example Problem 3 LRFD
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Example Problem 3 LRFD
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Example Problem 3 LRFD
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Example Problem 3 LRFD
Final Design
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Thanks