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CVL342
Ch.4: Welded Connections
PROF. SVETHA VENKATACHARI
DEPT. OF CIVIL ENGINEERING
IIT DELHI
Introduction
There are four main welding processes that are used in structural applications –
◦ Shielded Metal Arc Welding (SMAW)
◦ Gas-Shielded Metal Arc Welding (GMAW)
◦ Flux Core Arc Welding (FCAW)
◦ Submerged Arc Welding (SAW)
Each method has its advantages and disadvantages.
◦ Let’s look at each of these welding processes.
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Shielded Metal Arc Welding (SMAW)
Also known as ‘stick’ welding.
◦ An electrode is a filler material covered with
a coating.
◦ The electrode is coated with a flux that
purifies the molten metal.
◦ The coating forms a gas shield to protect the
electrode tip, the metal, and the molten pool
from atmospheric contamination due to
oxidation.
◦ Electrons flowing through the gap between
the electrode and the metal produce an arc
that melts the electrode metal and the base
metal.
◦ As the electrode moves away from the
molten pool, the mixture solidifies, and the
weld is completed.
https://www.thefabricator.com/thefabricator/article/a
https://leadrp.net/blog/what-is-shielded-metal-arc-welding-smaw/
rcwelding/shielded-metal-arc-welding-smaw-primer-1
Gas Metal Arc Welding (GMAW)
Also known as ‘MIG’ welding.
◦ Metal Inert Gas.
◦ A continuous wire is fed into a welding gun.
◦ The molten metal is protected from the atmosphere by a
gas shield which is fed through a conduit to the tip of the
welding gun.
https://www.millerwelds.com/resources/article-library/understanding-the-basics-
of-mig-welding-for-mild-steel
https://bancrofteng.com/how-to-choose-shielding-gas-types-for-gmaw/
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Flux Core Arc Welding (FCAW)
Similar to the GMAW process.
◦ A continuous wire is fed into a welding
gun.
◦ The difference is that the filler wire has a
center core which contains the flus.
◦ With this process it is possible to weld
with or without shielding gas.
◦ This makes it useful for exposed conditions
where a shielding gas may be affected by
wind.
https://www.mechanicalengineering.blog/2024/12/flux-cored-arc-welding.html
Submerged Arc Welding (SAW)
Only performed by automated methods.
◦ The weld pool is protected from the surrounding atmosphere by a
blanket of granular flux fed at the welding gun.
◦ Results in a deeper weld penetration than the other processes.
◦ Only flat or horizontal positions may be used.
https://ate-engg.com/submerged-arc-welding-saw/
https://www.adorfon.com/key-differences-between-smaw-
and-saw-welding/
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Welding Electrodes
Welding electrodes are classified using the following numbering system for SMAW.
Exxxbc
◦ E stands for electrodes
◦ xxx stands for two- or three-digit numbers establishing the ultimate tensile strength of the welding
metal.
◦ As per IS 814, the following values are available: 40, 41, 42, 43, 44, 50, 51, 52, 53, 54, 55, and 56 kg/cm2
◦ b indicates the suitability of welding positions; b = 1 indicates suitability for all positions, b = 2 indicates
suitability for flat position, and b = 4 indicates suitability for flat, horizontal, overhead, and vertical
down.
◦ c indicates coating and operating characteristics.
◦ IS814 Table 6 provides the various grades of electrodes and tensile properties.
Types of Welds
There are various types of welds that are
utilized io structural engineering applications
◦ Groove welds: a weld is made in a groove
between workpieces
◦ Mostly used to splice two plates together
◦ Filler welds: the most common type of weld
◦ A bead of weld is placed along two adjacent members
◦ Slot welds/Plug welds: not as common
◦ Can be used to transmit shear in lap joints or to join
components in built-up members
◦ Can be used to prevent buckling of lapped parts
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Welded Joints and Welding Positions
The five basic types of welded joints are:
◦ Butt joint
◦ Lap joint
◦ T-joint
◦ Corner joint
◦ Edge joint
Another important factor to consider is the
weld position.
◦ The skill of the welder becomes critical for
vertical and overhead welds.
Weld Symbols
Consider the following example of T-joint:
The welding notation is as follows:
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Groove Weld
Groove welds are provided when members to
be joined are lined up. Can be used for T-joints
as well.
◦ Groove welds require edge preparation, hence
costly.
◦ Single grooves like V, U, J, etc. are cheaper than
double grooves.
◦ Square groove welds are used for plates up to
8mm thick
◦ Groove welds are better in highly stresses
structures when a smooth flow of stress is
necessary.
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Groove Weld Specifications
◦ The effective throat thickness of a complete penetration
groove weld is taken as the thickness of the thinner part
joined.
◦ The effective throat thickness of T- or L-joints are taken as the
thickness of the abutting part.
◦ The effective throat thickness of a partial penetration weld is
taken as the minimum thickness of the weld metal common
to the parts joined.
◦ For calculation, the effective throat thickness in partial
penetration weld is taken as 5/8th the thickness of the thinner
member (IS816 : 1969).
◦ The unwelded portion in incomplete penetration welds should
not be greater than 0.25 times the thickness of the thinner
part joined.
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Design Strength of Groove Weld
As per IS800 : 2007, the groove welds in butt joints will be treated as parent metal with a thickness equal to the
effective throat thickness.
◦ For tension or compression parallel to the axis of the weld,
𝑓𝑦 𝐿𝑤 𝑡𝑒
𝑇𝑑𝑤 =
𝛾𝑚𝑤
where 𝑇𝑑𝑤 is the design strength of the weld in tension
𝑓𝑦 is the smaller of the yield stress if the weld and the parent metal (MPa)
𝐿𝑤 is the effective length of the weld (mm)
𝑡𝑒 is the effective throat thickness of the weld (mm)
𝛾𝑚𝑤 is the partial safety factor for weld material; 𝛾𝑚𝑤 = 1.25 for shop welding and 𝛾𝑚𝑤 = 1.5 for site welding
◦ The design strength of the butt weld in shear is given by
𝑓𝑦 𝐿𝑤 𝑡𝑒
𝑉𝑑𝑤 =
3𝛾𝑚𝑤
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Design Strength of Groove Weld
◦ The effective length of a groove weld in butt joints is taken as the length of the continuous
full-size weld.
◦ The effective length of the weld should not be less than four times the size of the weld.
Design Checks:
◦ In the case of a complete penetration groove weld, design calculations are not required as
the weld strength at the joint is equal to the strength of the member connected.
◦ In the case of incomplete penetration of the butt weld, the effective throat thickness is
computed, and the required effective length is determined to check if the strength of the
weld is equal to or greater than the strength of the members connected.
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Fillet Weld
Fillet welds are widely used as they are
cheaper, can be easily fabricated and can be
adopted at site.
◦ They are triangular in cross-section
◦ Less precision is required in fitting up two
members due to overlapping pieces
◦ No edge preparation is required
◦ Different intersection angles can be used
(60o to 120o)
◦ Fillet welds are assumed to fail in shear.
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Fillet Weld
The effective throat dimension of the fillet weld is
the shortest distance from the root to the face of
the weld.
◦ The effective throat thickness should not be less
than 3mm and should not exceed 0.7a, where a
is the size of the weld.
◦ When θ=0o, the weld axis is normal to the load
vector (transverse weld)
◦ Has high strength but low ductility
◦ When θ=90o, the weld axis is parallel to the load
vector (longitudinal weld)
◦ Has low strength but high ductility
◦ The IS 800 does not differentiate the two welds.
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Fillet Weld
The effective throat thickness in fillet welds joining faces inclined to each other is calculated as follows
(Clause 10.5.3.2):
𝐸𝑓𝑓𝑒𝑐𝑡𝑖𝑣𝑒 𝑡ℎ𝑟𝑜𝑎𝑡 𝑡ℎ𝑖𝑐𝑘𝑛𝑒𝑠𝑠 = 𝐾 × 𝑠𝑖𝑧𝑒 𝑜𝑓 𝑤𝑒𝑙𝑑
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Fillet Weld Specifications
Minimum size of weld: To ensure proper fusion,
minimize distortion and risk of cracking
◦ The size of fillet welds is taken as the minimum
weld leg size.
◦ Size of the fillet weld should not be less than 3
mm and should not be more than the thickness
of the thinner part.
◦ Large welds require more than one run of
welding. This requires chipping and cleaning of
weld to remove slag.
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Fillet Weld Specifications
Maximum fillet size used along the edge of the pieces
being joined: To prevent melting of base metal at the
location where the fillet would meet the corner of the
plate
◦ For plates less than 6mm-thick, the max. size of the
weld is equal to the thickness of the plate
◦ For plates thicker than 6mm, where the fillet is applied
to the square edge of a part, the specified size of the
weld should be at least 1.5mm less than the edge
thickness.
◦ For plates thicker than 6mm, where the fillet is applied
to the rounded toe of a rolled section, the size of the
weld should not exceed ¾ of the thickness of the
section at the toe.
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Fillet Weld Specifications
◦ End fillet weld normal to the direction of force
shall be of unequal size with a throat thickness
not less than 0.5t, where t is the thickness of the
part. The difference in thickness of the parts shall
be negotiated at a uniform slope.
Overlap:
◦ The overlap of plates to be fillet welded in a lap
joint should not be less than four times the
thickness of the thinner part.
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Fillet Weld Specifications
Minimum Effective Length of Fillet Weld:
◦ When placing a fillet weld, there is always a slight tapering at the beginning
and the end.
◦ Minimum length of weld is four times the size of the weld.
◦ In practice, the actual length of the weld is made of the effective length
(shown in the drawing) plus two times the size of the weld, but not less than
four times the size of the weld.
◦ End returns: Fillet welds terminating at the ends or sides of parts should be
returned continuously around the corners for a distance not less than twice
the size of the weld.
◦ The length of the longitudinal weld should not be less than the width of the
plate.
◦ The perpendicular distance between longitudinal fillet welds is restricted to
16 times the thickness of the thinner plate.
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Design Strength of Fillet Weld
The design strength of fillet weld is given by (Clause 10.5.7.1.1):
𝑓𝑤𝑑 = 𝑓𝑤𝑛 /𝛾𝑚𝑤
𝑓𝑤𝑛 = 𝑓𝑢 / 3
𝑓𝑢 is the smaller of the ultimate stress of the weld or the parent metal
𝛾𝑚𝑤 is the partial safety factor for weld material
The design strength of Lw length of the weld is given by:
𝐿𝑤 𝑡𝑡 𝑓𝑢
𝑃𝑑𝑤 =
3𝛾𝑚𝑤
𝑡𝑡 is the effective throat thickness of the weld (mm)
Long joint (Clause 10.5.7.3):
When the length of the welded joint (lj) exceeds 150tt, the design capacity fwd of the weld is reduced by
0.2𝑙𝑗
𝛽𝑙𝑤 = 1.2 − ≤ 1.0
150𝑡𝑡
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Design Strength of Fillet Weld
Combination of stresses (Clause 10.5.10.1.1):
When fillet welds are subjected to a combination of normal and shear stress, the equivalent stress fe shall satisfy:
𝑓𝑢
𝑓𝑒 = 𝑓𝑎2 + 3𝑞2 ≤
3𝛾𝑚𝑤
𝑓𝑎 is the normal stress due to compression or tension, due to axial force or bending moment
𝑞 is the shear stress due to shear force or tension
Stresses due to Individual Forces (Clause 10.5.9):
When subjected to either compressive or tensile or shear force alone, the stress in the weld is given by:
𝑃
𝑓𝑎 𝑜𝑟 𝑞 =
𝐿𝑤 𝑡𝑡
where 𝑃 is the force transmitted (axial force N or the shear force Q)
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Design Strength of Fillet Weld
Design Procedure:
◦ Assume the size of the weld based on the thickness of the connected member.
◦ Calculate the effective length of the weld to be provided by equating the design strength of the weld to
the externally applied factored load.
◦ The length of the weld may be provided either as longitudinal fillet weld or as transverse fillet weld or
as both by treating that the welds are stressed equally.
◦ If the length of the weld exceeds 150tt, the design capacity of the weld is reduced as per Clause
10.5.7.3.
◦ If only longitudinal fillet weld is provided, then check whether the length of the longitudinal weld is
greater than the perpendicular distance between them.
◦ End returns as per Clause 10.5.1.1 are to be provided at each end of the longitudinal fillet welds.
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Intermittent Fillet Weld
Intermittent fillet welds are provided when the strength of the weld required is less than that developed by
a continuous fillet weld of minimum practical size.
Design Procedure:
◦ Assume the size of the weld and calculate the total length of the weld required.
◦ The minimum effective length and clear spacing specifications (Clause 10.5.5) of IS800 have to be
followed.
◦ At the ends, the longitudinal intermittent fillet weld should be of length not less than the width of the
member.
◦ If transverse welds are provided along with longitudinal fillet welds, the total length of the weld at the
ends should not be less than twice the width of the member.
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Slot or Plug Welds
Longitudinal fillet welds in slots are considered to have the same strength as ordinary longitudinal fillet
welds (Clause 10.5.7.1.3).
Points to consider in the design calculations (as per IS816:1969):
◦ The width or diameter of the weld should not be less than three times the thickness or 25mm,
whichever is greater.
◦ Corners at the enclosed ends or slots should be rounded with a radius not less than 1.5 times the
thickness or 12mm whichever is greater.
◦ The distance between the edge of the part and the edge of the slot or hole or between adjacent slots or
holes should be not less than twice the thickness and not less than 25mm for the holes.
◦ A combination of slot/plug welds and other types of welds is permissible, and the strength of the joint is
taken as the sum of individual capacities of the weld.
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Example 4.1
Two plates of thickness 14mm and 12mm are to be joined by a groove weld. The joint is subjected to a
factored tensile force of 350 kN. Assuming an effective length of 150 mm, check the safety of the weld for
a) Single V groove weld joint
b) Double V groove weld joint
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Example 4.2
Determine the size and length of the fillet weld for a lap joint to transmit a factored load of 120 kN,
assuming site welds, Fe410 steel, and E41 electrode. Assume the width of the plate is 75 mm and
thickness is 8 mm.
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Design of Fillet Welds for Truss Members
◦ The welds connecting the truss member (in compression or tension) should be as strong as the
members they connect and should not result in significant eccentricity.
◦ Truss members often consist of single or double angles, t-shapes, and channels.
◦ To eliminate the eccentricity caused by unsymmetrical welds, the connection is designed by balancing
the weld.
Consider the following example:
◦ The axial force T in the member will act along the
centroid.
◦ The forces P1 and P3 will act along the weld line
(edges of the angle).
◦ The force P2 will act at the centroid of the weld
length (at d/2).
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Design of Fillet Welds for Truss Members
For eliminating the eccentricity caused by
unsymmetric welding,
𝑃2 𝑑
𝑀𝐴 = 0 ⟹ 𝑇𝑦 − 𝑃1 𝑑 − =0
2
𝑇𝑦 𝑃2
⇒ 𝑃1 = − (1)
𝑑 2
For horizontal eqbm., 𝑇 − 𝑃1 − 𝑃2 − 𝑃3 = 0 (2)
From (1) and (2), we get
𝑦 𝑃2
𝑃3 = 𝑇 1 − −
𝑑 2
The force 𝑃2 is equal to the strength of the weld
per mm times the length of the weld (d).
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Example 4.3
A tie member of a truss consisting of an angle section ISA 65 x 65 x 6 of Fe410 grade, is welded to an 8-
mm gusset plate. Design a weld to transmit a load equal to the full strength of the member. Assume shop
welding.
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