DESIGN OF WELDED JOINTS - staff.psu.edu.eg

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

7Dr. Hassan Abd Elhafez

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

Dr. Hassan Abd Elhafez 18Example 10.9; P. 380

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