DESIGN OF WELDED JOINTS - staff.psu.edu.eg
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DESIGN OF WELDED JOINTS
Dr. Hassan Abd Elhafez
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TYPES OF WELDED JOINTS
• 1. Lap joint or fillet joint, and 2. Butt joint.
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• BUTT JOINTS
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The main considerations involved in the selection
of weld type are:
1. The shape of the welded component required,
2. The thickness of the plates to be welded, and
3. The direction of the forces applied.
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STRENGTH OF TRANSVERSE FILLET WELDED JOINTS
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t = s × sin 45° = 0.707 s
Minimum area of the weld or throat area,
A = Throat thickness ×Length of weld
= t × l = 0.707 s × l
If σt is the allowable tensile stress for the weld
The tensile strength of the joint for single fillet weld,
P = Throat area ×Allowable tensile stress = 0.707 s × l × σt
and tensile strength of the joint for double fillet weld,
P = 2 × 0.707 s × l × σt = 1.414 s × l × σt
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STRENGTH OF PARALLEL FILLET WELDED JOINTS
A = 0.707 s × l
P = 2 × 0.707 × s × l × τ = 1.414 s × l × τ
shear strength of the joint for
double parallel fillet weld
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P = 0.707s × l1 × σt + 1.414 s × l2 × τ
Single transverse and double parallel fillet
welds as shown in Fig. (b), the strength of the
joint is given by the sum of strengths of single
transverse and double parallel fillet welds.
Mathematically;
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Example 10.5; p. 370
Example 10.6; 371
In order to allow for starting and stopping of
the bead, 12.5 mm should be added to the
length of each weld obtained by the above
expression.
For reinforced fillet welds, the throat
dimension may be taken as 0.85 t.
REMARKS
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SPECIAL CASES OF FILLET WELDED JOINTS
1. CIRCULAR FILLET WELD SUBJECTED TO TORSION.
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Example 2; 3 P.367
SPECIAL CASES OF FILLET WELDED JOINTS
2. CIRCULAR FILLET WELD SUBJECTED TO BENDING MOMENT.
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SPECIAL CASES OF FILLET WELDED JOINTS
3. LONG FILLET WELD SUBJECTED TO TORSION
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STRENGTH OF BUTT JOINTS
In case of butt joint, the
length of leg or size of weld is
equal to the throat thickness
which is equal to thickness of
plates.
Tensile strength of the butt
joint (single-V or square butt
joint),
P = t × l × σtl = Length of weld. It is generally equal to the width of plate.
P = (t1 + t2) l × σt 13Dr. Hassan Abd Elhafez
The following table shows the stresses for welded joints for joining ferrous
metals with mild steel electrode under steady and fatigue or reversed load.
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AXIALLY LOADED UNSYMMETRICAL WELDED SECTIONS
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Example 10.8; P.375
ECCENTRICALLY LOADED WELDED JOINTS
The joint will be subjected to the following two
types of stresses:
1. Direct shear stress due to the shear force P acting
at the welds, and
2. Bending stress due to the bending moment P × e.
Bending moment, M = P × e
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ECCENTRICALLY LOADED WELDED JOINTS
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ECCENTRICALLY LOADED WELDED JOINTS
Case 2: When a welded joint is loaded
eccentrically as shown in Fig., the
following two types of the stresses are
induced:
1. Direct or primary shear stress, and
2. Shear stress due to turning moment.
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Dr. Hassan Abd Elhafez
Example
10.14; P. 384