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WELDED CONNECTIONS I

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Efficient and direct way of connecting is by weldingMetallurgical 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

INTRODUCTION

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BASIC WELDING PROCESSES

Gas welding - Oxyacetelene welding , simple , slow,

repair and maintenance work

Arc welding - All structural welding

Electric arc by use of electric energy

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WELDING PROCEDURE

Environment

Welding position

Current : controls heat input

Shrinkage

Preheating

Weldability of steels

Economic welds, good , crack free

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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

(d) Corner joint(a) Butt joint (b) Lap joint (c) Tee joint

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A

Ends shall be semi

circular

A

Section A-A

(c) Slot weld

(a) Groove welds

(b) Fillet welds

AA

Section A-A

(d) Plug weld

COMMON TYPES OF WELDS

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Groove welds

Selection of a particular type of groove weld depends

Size of the plate to be joined

welding by hand or automatic

Type of welding equipment

Accessibility of both sides

Position of weld

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Size of butt weld

Thickness of connected plate for full penetration

Depth of penetration for partial penetration

Advantages

High strength,high resistance to impact and cyclic

stress

Disadvantages

High residual stress , edge preparation and proper

aligning

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Root face

Depth of

penetration

Electrod

eArc

(a) Depth of penetration Root gap

Included angle

(b) Root gap

Root run

Capping run Filling run

(c)Root run

GROOVE WELD DETAILS

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QUALITY OF WELDED CONNECTIONS

Proper electrodes , welding apparatus and

procedures

Welding sequence

Doubling up method

Planned wandering method

Step back method

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13 12 7 5 1 6 8 1817

11 10 9 3 2 4 14 1615

SEQUENCE OF WELDING OF FILLET WELDS

Doubling - up method for vertical member

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RESIDUAL STRESSES

Residual stresses - due to rapid heating and

cooling

Yield strength of material is upper limit for residual

stresses

LONGITUDINAL RESIDUAL STRESS DUE TO WELD

- -

Tension

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a)Transverse shrinkage(b) Angular change

(d) Longitudinal shrinkage

(e) Longitudinal bending

distortion

(c) Rotational

distortion

(f) Bucklingdistortion

WELD DISTORTION

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WELD SYMBOLS

Symbolic representation of welds

(Ref. IS:813 - 1986 Scheme of symbols for welding )

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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

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WELD INSPECTION

Visual inspection

Liquid penetrantsMagnetic particles

Ultrasonic testing

Radiography

CONNECTION DESIGN

Static strength of welded joint

Type and size of the weld

Manner of welding

Type of electrode used

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BUTT WELDS

Critical form of loading - Tension intransverse direction

Yield stress of weld metal and parent metal

in HAZ (Heat affected Zone) is much higher

Failure always occurs away from the weld

Toughness and ductility properties are

affected

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(a) Square(b) Single V (c) Double V (d)Single Bevel

(e)Double

Bevel

(f) Single U (g) Single U(h) Single J

(i)Double J

DIFFERENT TYPES OF BUTT JOINTS

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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 weldslower design strengths

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FILLET WELDS

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.

1

11

11

1

11

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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

Fillets of equal leg length

Size

Size

Fillets of unequal leg length

Size (Min. Leg size)

Leg length

Size = leg length * 2.4 mm

Penetration

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SLOT AND PLUG WELDS

Provided along with fillet welds in lap joints

Strength of a plug or slot weld - allowable stress

and nominal area in the shearing planeEnds shall be semi circular or

have corners rounded to a radius

not less than thickness of partcontaining slot

Section A-

A

AA

(a) Slot weld

Section A-

A

AA

(b) Plug

weld

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ECCENTRIC JOINTS

Shear and torsion

Torsion , F = (T s ) / Jfh = (T v) / Jfv = (T h ) / J

= R / L

Shear and bending

Weld is designed to withstand maximum bendingstress and maximum shear stress separately.

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(a) WELDS SUBJECTED TO SHEAR AND TORSION,

(b) WELDS SUBJECTED TO SHEAR AND BENDING

xx

y

y

e

c.g of welds

P

M

(a)

e

(b)

Pe P

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SUMMARY

Fundamentals of welding , details of various

welding processes, types of welds, common weld

defects and weld inspection have been

presented.

Advantages of welding are mentioned.

Behaviour and design of butt - and fillet - welded

connections in steel structures are explained .

Truss connections and beam connections are

discussed.