Welded Connections Final

8/3/2019 Welded Connections Final

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W e l d e d Connecti ons

Dr. S. RAVIRAJAssistant Professor of Civil Engineering

Sri Jayachamarajendra College of Engineering, Mysore 06

1.0 INTRODUCTION

Welding is the process to unite variouspieces of metal by creating a strong

metallurgicalbond.Bond is achieved by heat or pressure or both. Welding is

the most efficient and direct way ofconnecting the metalpieces. Over many

decades, differentwelding techniques have been developedtojoin metals.

2.0 TYPES OF WELDING

Welding is generally performed by eitherelectric or gas. Most of the welding is

done using electricsupply. Though gas welding is relatively cheaper, itis a slow

process. Hence this method is generally used for repair and maintenance

purposes.

2.1 Gas Welding

Fig. 1 Gas Welding2.2 Arc Welding

It is also called as oxy-acetylene welding.

Here the mixture of gases namely

acetyleneand oxygen is burned at the tip

of a torch, which produces a very hot

flame. This heats the metalpieces for

cutting and welding process. The features

ofa typical gas welding is shown in Fig. 1.


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Arc welding is used in most of the structuralwelding operations. Here, electric

energy which is usedas the heat source is produced by electric arc. The base

metal and welding rod (orelectrode)are heated to fusiontemperature by the

electric arc. The typical arc welding equipments and accessories are shown inFig. 2. Thewelding rod is connected to one terminal of the current source and

the object to be weldedis connected to the other terminal.Thetemperature in

the region ofwelding ranges from 3300o C to 5500o C.

Fig. 2 Arc welding equipment and accessories

2.2.1 Shielded Metal Arc Welding(SMAW)

This is the most popularmethod of arc welding.Heating is done by means of

electric arc between a coated electrode and the materialbeingjoined. If

uncoated or bare wireelectrodes are used,themoltenmetal gets exposed to

atmosphere and combines chemically with oxygen and nitrogen and forms

defective welds. The coating on the electrode forms a gaseous shield thathelpsto exclude oxygen and protects the moltenmetal from oxidation.The

flux of the electrodecoating,being lighterthan moltenmetal, hardens at the

surface of the weld.This can be removed by gentletapping or bybrushing.The

typical features ofshieldedmetal arc welding are shown in Fig. 3.


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Fig. 3 Shieldedmetal arc welding

The type ofwelding electrode used decides the weldproperties like strength,

ductility and corrosion resistance. The choice ofelectrode depends upon the

type of metalbeing welded, the amount of material to be added, and the

position of work.

There are two types ofelectrodes:

Lightly coated electrodes

Heavily coated electrodes

Heavily coated electrodes are used in structural welding. These electrodes

result in welds thatare stronger, more corrosion resistant, and more ductile

(compared to lightly coated electrodes). Usually the SMAW process is either

automatic or semi-automatic. The main advantage of SMAW is that high

quality welds can be made rapidly at a low cost. The grade and propertiesof

electrodes are listedin Table 1 ofIS 800 : 2007 which is as perIS 814 : 2004.

3.0 ADVANTAGES OF WELDING

There are many advantages of welding. Some of the important ones are as

follows.

1. Weldedjoints are aesthetical to look when compared toboltedjoints.


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2. Welded joints are more rigid than bolted joints. Hence the material at

varioussectionsareutilized more efficiently to resist stresses than that of

lessrigid connections.

3. Welding does not requiredriving ofholes.This reduces the cost incurred fordrilling. Hence, whilecomputing the tensile strength of members, the net

area remains the same as the gross area.

4. Weldedjoints are wellsuited forliquid and gas containingstructures.

5. Welding offers the possibilities of fabricating new sections like castellated

beams orcreatingcomplexjointsin tubulartruss.

4.0 DISADVANTAGES OF WELDING

Some of the disadvantages ofwelding are;

1. Welding requires greater skill than bolting and hence requireshighly skilled

human resources.

2. Improper welding will distort the members and its alignment, and hence

requiresmoreconcentration.

3. Theinspection of weldjointsis more difficult and cumbersome than bolted

joints.

4. The process ofwelding may leave a higherresidual stress in the material.

5. Welding equipment is more expensive and requires larger initial

investment.

6. Welding at siteis more difficult and alsorequires constant powersupply.

5.0TYPESOF WELDS

There are four types of welds.They are:


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1. Fillet welds

2. Groove welds

3. Slot welds,and

4. Plug welds

Of these welds, fil let is used to a large extent. Groove welds are used to a

lesserextent. However,slot andplug welds are rarelyused.

5.1FilletWelds

Fig. 4 Fillet weld and its cross section

Fillet welds(Fig. 4A) are widely used due to theireconomy, ease offabrication,

and adoptability at site.They are approximatelytriangularin cross section(Fig.

4). These welds require lessprecision in fittingup two sections, due to the

overlapping ofpieces.They are adopted in field as well as in shop welding. It

does not require any edge preparationand hence cheaper than groove welds.

Fillet welds are assumed to fail in shear. They can be present on one side

(single) or on both sides(double) of a member as shown in Table1 and Fig. 5.

Table 1 Single and double fillet welds

SINGLE DOUBLE


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FILLET

Fig. 5 Idealised and actual fillet weld

5.2 GROOVE WELDS

In this type of weld, grooves are generally made in the base metal before

welding and hence are called as groove weld. They are generally used to

connect structural members aligned in thesameplane, such as in butt joints.

Thedetails of a typical groove weld are shown in Fig. 6.

Fig. 6 Details of typical groove weld


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Some of the commonly used groove weldsinbutt joints are shown in Fig. 7.

Fig. 7 Types of groove welds in butt joint

The square groove weld is used to connect plates up to 8 mm thickness.They

are also used inT-connections. The grooves have a slope of 30O and 60O with

the vertical, which depend on the thickness of the plate and the welding

operation. Partialpenetration groove welds should not be used especially in

fatiguesituations.Root opening or gap (see Fig. 6) isprovided for the electrode

to access the base of the joint.Thebevelangle (see Fig. 6) for typical root

openingsis shown in Table2.

Table 2 Root openings and bevel angle for groove weld

Root openings Bevel angle

3 mm 60O

6 mm 45O

9 mm 30O


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Weld metalis more expensive than the base metal. Hence, the choice between

single or doublepenetration depends on the availability of access on both

sides, the thickness ofplate to be welded, the type of welding equipment

available and theposition of weld.

When the plate thickness is more than 12 mm, the groove can be either

double-bevelordouble-V type. When the platethicknessis more than 40 mm,

the groove can be eitherdouble - U ordouble - J type. Forplates between 12

to 40 mm, the groove can be withersingle-J and single-U type.

Groove welds are chosen in situations where the members need to transmit

the full load ofthe members they join. Hence, the strength of welds shouldbe

more than orequal to the strength of the members they join. To ensure this,

fullpenetration groove welds are used more frequently.

5.3 SLOT AND PLUGWELDS

Slot and Plug welds (Fig. 8) are limitedly used to connect the steel members.

They are generallyused to complement the fillet weldsin situations where itis

notpossible toprovidesufficientlengthoffillet welds due to some constraints.

These welds fail in shear. The extent ofpenetration of these welds into the

parent metal is difficult to determine since it is difficult to inspect it. They are

to be avoided when the members are subjected to tensile forces. The

calculation ofdesignstrength ofslot orplug welds are similarto that of fillet

welds.


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Fig. 8 Typical slot and plug welds

6.0WELDINGPOSITON

The weldingpositions can be of four types, which are:

Flat - On the floor

Overhead - Under the roof

Vertical - On the wall

Horizontal - On the wall

Figure 9 shows the different weld positions which exist during weldingoperation.

a) Flat - On the floor b) Overhead - Under the roof


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c) Vertical - On the wall d) Horizontal - On the wall

Fig. 9 Different weldpositions

7.0 TYPES OF JOINTS

There are fivebasic types of common joints.They are

Buttjoint

Lapjoint

Tjoint

Cornerjoint,and

Edgejoint

Each joint is suitable for a specific situation. The choice of the joint for a

particularjob depends on the size and shape of the members to be welded at

the joint, the type of loading, area available for welding at the joint, and

relative cost ofvarious types of welds.

7.1 ButtJoint

Fig. 10 Typicalbutt joint


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Buttjoints are used to join the ends of flatplates ofnearlyequalthickness.A

typicalbutt jointis shown in Fig. 10. Thisjointavoidseccentric transfer of force

at the connection.Itispreferable to havefullpenetration of welds at the butt

joints so that the jointis fully efficient.Thesize ofconnectionisquitesmall andhence is very economical.Itis aesthetical to look at. Face reinforcement(weld

beyond the surface) is normallyprovided in Butt joints. This increases the

efficiency of the jointand ensures that depth of weld is at leastequal to the

thickness of theplate.

7.2 LapJoint

Fig. 11 Typical lap joint

Lapjoints are easy to fit and join any two members. A typical lapjointis shown

in Fig. 11. Itis themost commonly used joint. It does not require any specialpreparation. Lap joints utilize fil let welds. They are well suited for shop and

field welding. Lap joints can accommodate minor errors in fabrication and

minoradjustment in length. The main advantage oflap joints is that it canjoin

plates with different thicknesses without any difficulty (Fig. 12). The main

disadvantage ofthisjointisthat itintroduceseccentric transfer ofloads at the

connection.

Fig. 12 Lap joint with plates of different thickness


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7.3 TJoints

Fig. 13 Typical T -joint

A T-joint is usually used to fabricatebuilt-up sections from simple members. Atypical T-shaped joint is shown in Fig. 13. Some of the commonly used built-up

shapes where T-joints are seen are I-sections,Plate girders, Hangers, Brackets,

and Stiffeners. The members in the built-up sections are joined by means of

fillet welds or groove welds.

7.4 CornerJoint

Cornerjoints are normally seen inbuilt - up rectangularbox sections.A typical

cornerjoint is shown in Fig. 14. They are generally seen at places which are

subjected to high torsionalmoments.

Fig. 14 Typical cornerjoint


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Corner joints are seen in the built - up rectangular box sections. A typical

cornerjoint is shown inFig. 14. They are commonly seen at placeswhich are

subjected to high torsionalmoments.

7.5 EdgeJoint

Fig. 15 Typical cornerjoint

Edge joints are generally not used in structuralapplications.They are used to

keep two or moreplates in position in a given plane. A typical edge joint is

shown in Fig. 15.

8.0 WELDSYMBOLAND WELDINGSYMBOL

A weldsymbol is a symbol which indicates the type of weld to be adopted to

joint the metalpieces. However, a welding symbol is a concise way of

describingallparticularinformationrelated to the weld on drawings.

8.1 Weld Symbol

Weld symbol is unique for each specific type of weld. Hence the weldsymbol

used is differentforfillet, groove,plug, and slot welds.

8.1.1 Basic Weld Symbols

Thebasic weldsymbols for the commonly used welds are shown in Table3.


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Table 3 Basic weld symbols

Weld symbol is only a part of the informationregarding the welding operation

to be performed at ajoint. As indicated in Table 3, whenever a weld symbol

consists of both vertical and inclined legs, theverticalis always drawn towards

the leftside of the inclinedline.

8.2 Welding Symbol

The welding symbol containsall the information necessary in connection with

a welding operation. Italso includes the type of weld, where welds are to be

located, the type ofjoint to be used, and thesize and amount of weldmetal tobe depositedin the joint.

The symbols used are standardized by the various codes ofpractice so that the

entireinformationcan be concisely represented in a drawing.

Thebasicwelding symbol comprises of three parts, namely

a reference line

an arrow, and

a tail


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Apart from this there are alsosupplementarywelding symbols to represent

Dimensions and otherdata

Supplementarysymbols

Finish symbols Specification,process or other reference

8.2.1 Basic Welding Symbols

Fig. 16 Basic welding symbols

Reference Line

The reference line is always drawn horizontally. It is mandatory and forms the

foundation of a welding symbol. All information with respect to the welding

process is to be indicated around thisline.

Arrow

The arrow line is present at one end of the reference line. Itsimply connects

one end ofthe reference line to the joint or area to be welded.Thedirection of

the arrow has nobearing on thesignificance of the reference line.Some of the

possible types of arrows used in the welding symbol are shown in Fig. 17.


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Fig. 17 Different types of arrows used in welding symbol

Tail

The tailis shown on the other end (away from arrow end) of the reference line.

It is not mandatory.The tail is used to specify a certainwelding process. It is

used only when necessary. Itis used tomention some specialcharacteristic ofthe weld like type of electrode, some type of reference or specification,

welding orcutting process, procedures or other supplementary information.If

additional information is not needed, then the tail will be omitted. The

representation oftai withadditionalinformationis shown in Fig. 18.

Fig. 18 Representation of tail with additional information

8.2.2 Interpretation of Symbols

Fillet weld on arrow side

Symbol Meaning


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Fig. 19 Fillet weld, Arrow side

Fillet weld on otherside

Symbol Meaning

Fig. 20 Fillet weld, Other side

Fillet weld onboth sides

Symbol Meaning

Fig. 21 Fillet weld, Bothsides

Bevel edge

Symbol Meaning


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The symbol indicates that one edge of a joint is to be beveled. The arrowshould points towards the member to be beveled. Hence, the arrow shouldshow a definite break so that the member to be beveled can be clearlyidentified.

Fig. 22 Bevel edge

8.2.3 StandardLocation ofElements of a Welding Symbol

The standard location ofvariouselements of a welding symbol to be indicated

in drawingissummarizedbelow.

Fig. 23 Standard location of welding symbols

8.3 Supplementary Symbols


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There are some supplementary weld symbols used in addition to the basic

weld symbols which are indicated in section 8.1. These include Finish and

contour symbols, All round weld, and Field or site weld which are shown in

Table4.

Table 4 Supplementary weld symbols

8.3.1 Finish and contoursymbols

Finish symbol shows the method of finish to be carried out to a weld.

Generally, the finish ofwelding is eitherby chipping (C) or by machining (M) or

by grinding (G). Contoursymbols are used with weldsymbols to show how the

face of the weldis to be formed. The face of the weldwillbe eitherflat, convex

or concave as shown in Table4.

8.3.2 All round weld

Fig. 24 Typical representation of all round weld


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The all round symbol (Table 4) indicates that the welds are continued all

around the joint.Atypical all round weld and itsrepresentationis shown in Fig.

24.

8.3.3 Field orsiteweld

Fig. 25 Representation of field or site weld

The symbol used for field or site weld is a flag (Table 4). Itpoints toward the

tail of welding symbol. If no symbol is present, it indicates the weld as shop

weld.A typical representation offieldorsite weldis shown in Fig. 25.

9.0 WELD D EFECTS

As mentionedearlier,welding requires greater skill so that the defects can be

avoided.Some ofthecommonly observed defects in weldsare;

1. Incompletefusion

2. Incompletepenetration

3. Porosity

4. Undercutting

5. Inclusion ofslag

6. Cracks

7. Lamellartearing

1. Incompletefusion


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This occurs when the surfaces have not been cleanedproperly, and are coated

with oxides, mill scales, and other foreign materials. Insufficient current

supplied by the welding equipment or high rate (speed) of welding can also

lead to incompletefusion.

2. Incompletepenetration

Incomplete penetration can be due to impropergrooves orunsuitable groove

design made forthewelding process. This can also be a result of the usage of

largesize electrodes,insufficient welding current, and excessivewelding rates.

3. Porosity

Improper welding techniques will result in air voids being entrapped in the

molten metal during the cooling process resulting in porosity. Some of the

common reasons are excessively high current, longerarc length, poorwelding

procedures, and careless use ofback-strips.

4. Undercutting

In case of groove welds, grooves are made at the edges of the base metal to

accommodate the welding process. If the grooves are not completely filled

with weld,itresultsin undercutting ofthe base metal(i.e., the thickness of the

base metal will be less in that region). This may lead toplaces of stress

concentrations during the process of force transfer and can be dangerous.

Hence to eliminateundercutting, it is mandatory to have face reinforcement

(welding over the surface ofbase metal)in all groovejoints.

5. Inclusion ofslag


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Slag is formed from the coating of the electrodes which are used to shield the

molten material fromoxides during the cooling process. The slag is generally

removed after the weld cools by either wirebrushing or by gentletapping. If

the process ofcooling is done rapidly, the slag gets trapped inside the weld.This weakens the weld strength and is not desirable. When the required weld

thicknessislarge,itis made by several passes. In such cases, the slag should be

removed after the completionofeach pass. If thisis not done properly,italso

resultsin the inclusion ofslag.

5. Cracks

Cracks are the most serious weld defects since it reduces the weld strength

directly. This resultsmostly due the relative differences in internal stresses in

the weld. The direction of the weld can be either along the longitudinal or

transverse direction of weld.They can be seen on the surface orpresent inside

the weld. They can be avoided by using good quality electrodes, adopting

uniform rate ofwelding and ensuringslowercoolingperiods.

6. Lamellartearing

This is the formation of cracksbeneath the weld. The high temperature during

welding causes largerelativestrainsin the base metal due to localised stresses

and results in tearing of the base metal. This can be prevented by choosing

properwelding techniques and adoptinguniform rate of welding.

10.0 WELDDISTORTIONS

During welding operation, proper care must be ensured to avoid weld

distortions. Improperwelding techniquesresults in welddistortions.Someof


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the commonly observed distortions during welding are Transverse shrinkage,

Longitudinal shrinkage, Angular change, Rotational distortion, Longitudinal

bendingdistortion and Bucking distortion.Thesedistortions are shown in Fig.

26.

a) Transverse shrinkage b) Longitudinalshrinkage

c) Angular change d) Rotationaldistortion

e) Longitudinal bending distortion f) Buckling distortion

Fig. 26 Typical weld distortions

11.0 IMPORTANT CODAL PROVISIO NS OF IS 800 : 2007 WITH RESPECT TO

WELDING

The welds and welding shall conform to the following codes:


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IS 816 : 1969 Code ofpractice for the use ofmetal arc welding forgeneral

constructionin mildsteel

IS 9595 : 1996 Metal arc welding of carbon and carbon manganese steels

Cl. 10.5.1.1 EndReturn s

>2a

a = weld

size

>2a

Fig. 27 Details of end returns ofweld

Fillet welds terminating at the ends or sides of parts should be returned

continuously aroundthe corners fordistance of not less than twice the size of

the weld, unless it is impractical. This isparticularly important on the tension

end of parts carryingbendingloads.

Cl. 10.5.1.2 Lap Joint

Fig. 28 Typical lapjoint

Inlapjoints the minimum lapshould be not less than fourtimes the thickness

of the thinnerpartjoined.Single end filletshould be used only when lapped

parts are restrained from openings.When end of an elementis connected only


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byparallel longitudinal fil let welds, the length of the weldalong eitheredge

should be not lessthan the transverse spacing between longitudinal welds.

Cl. 10.5.2 Size of weld

10.5.2.1 The size ofnormal fillets shallbe taken as the minimum weld leg size.

For deep penetration welds, where the depth ofpenetration beyond the root

run is 2.4 mm (minimum), the size of the fil letshould be taken as the minimum

leg sizeplus 2.4 mm.

Fig. 29 Size ofweld

10.5.2.2 For fillet welds made by semi-automatic or automatic processes,

where the depth ofpenetration is considerably in excess of 2.4 mm, the size

shall be taken considering actual depth ofpenetration subject to agreement

between the purchaser and the contractor.

10.5.2.3 Thesize offillet weldsshall not be less than 3 mm. Theminimumsize

of the first run or ofasingle run fillet weldshall be as given in Table 5, to avoid

the risk ofcracking in the absence ofpreheating.

Table 5 Minimum weld size

Thickness ofThickerPart Minimum Size

Over, mm Upto and including, mm mm

-- 10 3

10 20 5


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20 32 6

32 50 8 for first run

10 for min. size ofweld

10.5.2.4 The size of butt weld shall be specified by the effective throatthickness.

Fig. 30 Typicalbutt joint

Cl. 10.5.3 Effective Thro at Thickness, te

10.5.3.1

Fig. 31 Effective throat thickness of fillet weld

The effective throat thickness te (Fig. 31) of a fillet weldshall not be less than 3

mm and shallgenerally not exceed 0.7t, and 1.0t under specialcircumstances,

where t is the thickness of the thinnerplate ofelementsbeing welded.

10.5.3.2 For the purpose of stress calculation in fillet weldsjoining facesinclined to each other, the effective throat thicknessshall be taken as K times

the filletsize, where K is a constant, depending upon the angle between fusion

faces, as given in Table6.


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Anglebetweenfusionfaces, Constant K

600900 0.70

9101000 0.65

10101060 0.60

10701130 0.55

11401200 0.50

Table 6 Values of k for different angles between fusion faces

10.5.3.3 Theeffective throat thickness te (Fig. 32) of a completepenetration

butt weldshallbe taken as the thickness of the thinnerpart joined, and that of

an incompletepenetration butt weldte(Fig. 32) shall be taken as the minimum

thickness of the weld metal common to the parts joined, excluding

reinforcement.

Fig. 32 Effective throat thickness of butt weld

Cl. 10.5.4 Effective Length

10.5.4.1 Theeffective length of fillet weldshall be taken as only that length

which is of the specified size and required throat thickness. Inpractice the

actuallength of weldis made oftheeffectivelength shown in drawingplustwo


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times the weld size, but itshould not be less than four times the size of the

weld.

10.5.4.2 Theeffective length of butt weldshall be taken as the length of the

continuousfull size weld, but itshould not be less than fourtimes the size of

the weld.

Cl. 10.5.5 Intermittent Welds

10.5.5.1 Theintermittentfilletwelding shall have an effectivelength of not less

than fourtimesthe weldsize, with a minimum of 40 mm, except as otherwise

specified.

10.5.5.2 Theclearspacing between the effective lengths of intermittent fillet

weldshall not exceed 12 and 16 times the thickness ofthinnerplatejoined, for

compression and tensionjointrespectively, and in no case be more than 200mm.

10.5.5.3 The intermittent butt weldshall have an effective length of not less

than fourtimesthe weldsize and the longitudinal space between the effective

length of weldsshall not more than 16times the thickness of the thinnerpart

joined, except as otherwisespecified.Theintermittent weldsshall not be usedinpositions subject to dynamic,repetitive and alternatestresses.

Cl. 10.5.7 Design Stresses in Welds


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10.5.7.1 Shop welds

10.5.7.1.1 Fillet welds Thedesign strength of a fillet weld, fwd, shall be based

on its throat area.

fwd = fwn / mw in which fwn = fu / 3

where

fu = smallerof the ultimate stress of the weld and the parent metal

mw = 1.25 =partial safety factor

10.5.7.1.2 Butt welds Butt welds shall be treated as parent metal with athicknessequal to the throat thickness, and the stresses shall not exceed those

permittedin the parent metal.

10.5.7.2 SiteWelds Thedesign strength in shear and tension forsite welds

made during erection ofstructural members shall be calculated as per 10.5.7.1

but using apartial safety factor mw of1.5.

Cl. 10.5.8.1 Fillet Weld Applied to Edge of a Plate

Square edge


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10.5.8.1 Where a fillet weld is applied to the square edge of a part, the

specified size of the weld shouldgenerally be at least 1.5 mm less than the

edge thicknessin order to avoid washing down of the exposed arris(Fig. 33).

1.5 mm

a

Fig. 33 Fillet weld on square edge ofplate

10.5.8.2 Where the fillet weldis applied to the rounded toe of a rolledsection,the specifiedsize ofthe weldshouldgenerally not exceed 3/4 of the thickness

of the section at the toe (Fig. 34).

1/4 t

t

Fig. 34 Fillet weld on round toe of rolled section

10.5.8.3 Where the size specified for a fillet weldis such that the parent metal

will not project beyond the weld, no melting of the outer cover or covers shall

be allowed to occur to such an extent as to reduce the throat thickness(Fig.

35)


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most unfavorable conditions of loading, the equivalent stress fe is obtained

from the following formulae:

where

fe

=2

fb +2

fbr + fb fbr+ 3q2

fe = equivalentstress

fb = calculated stress due tobendinginN/mm2

fbr=calculated stress due tobearinginN/mm2, and

q = shearstress inN/mm2

Cl. 10.8 Intersections

Members or components meeting at a jointshall be arranged to transfer the

designactionsbetween the parts, whereverpracticable, withtheircentroidal

axes meeting at apoint. Where there iseccentricity at joints, the members and

components shall be designed for the designbending moments, which result

due to eccentricity.

The disposition of fillet welds to balance the design actions about the

centroidalaxis or axes for end connections of single angle,doubleangle and

similar type members is not required for statically loaded members but is

required for members, connection components subject to fatigueloading.

Eccentricity between the centroidal axes ofangle members and the gauge lines

for their bolted end connections may be neglected in statically loaded

members, but shall be considered in members and connection components

subject to fatigueloading.

Cl. 10.11 Analysis of a Bolt/WeldGroup

10.11.1 Bolt/Weld Group Subject to In-planeLoading


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10.11.1.1 General Method of Analysis The design force in a bolt/weld in a

bolt/weld group ordesign force perunitlengthin abolt/weld group subject to

in-planeloadingshall be determinedin accordance with the following:

a) Theconnectionplatesshall be considered to be rigid and to rotate relative

to each other about apoint known as the instantaneous centre ofrotation

of the group.

b) In the case of a group subject to a pure couple only (Fig. 37a), the

instantaneouscentreof rotationcoincides with the group centroid. In the

case of in-plane shear force applied at the group centroid (Fig. 37b), the

instantaneous centre of the rotation is at infinity and the design force isuniformly distributed throughout the group. In all other cases (Fig. 37c),

eithertheresults of independentanalyses for a pure couplealone and for

an in-plane shear force appliedat the group centroid shall be superposed,

or a recognized method ofanalysis shall be used.

c) Thedesign force in abolt ordesign force per unitlength at anypointin the

group shallbeassumed to act at rightangles to the radius from that pointto the instantaneous centre, and shall be taken as proportional to that

radius.


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a) Pure coupleatcentroid

b) In-plane shear forceatcentroid

c) In-plane shear forceaway from centroid

Fig. 37 Location of Pure couple and In-plane shear with respect to centroid

10.11.2 Bolt/Weld group Subject to Out-of-PlaneLoading

10.11.2.1 General Method ofAnalysis The design force of abolt inbolt group

ordesign force per unit length in the fillet weld group subject to out-of-plane

loading(Fig. 38) shall be determinedin accordance with the following:

a) Thedesign force in the bolts perunitlengthin the fillet weld group resulting

from any shear force oraxial force shall be considered to be equally shared

by allboltsin the group oruniformlydistributed over the length of the fillet

weld group.

b) The design force resulting from a design bending moment shall

be considered to vary linearly with the distance from the relevant

centroidal axes.


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i) Inbearing type ofbolt group plates in the compression side of the

neutralaxis and onlyboltsin the tensionside of the neutralaxis may be

considered forcalculating the neutralaxis and second moment ofarea.

ii) In the friction grip bolt group only the bolts shall be considered in thecalculation ofneutralaxis and second moment ofarea.

iii) Thefillet weld group shall be consideredin isolation from the connected

element; forthecalculation ofcentroid and second moment of the weld

length.

e V

Z Z

B r a c k e t

Fig. 38 Out-of-plane shear force with respect to weldplane

10.11.2.2 Alternative Analysis The design force per unit length in a fillet

weld/bolt group mayalternatively be determined by considering the fillet weld

group as an extension of the connected member and distributing the design

forces among the welds of the fillet weld group so as to satisfy equil ibrium

between the fillet weld group and the elements of the connected member.


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12.0 Numerical Problems

1. Twoplates of size 200 x10 mm and 200 x 8 mm are connectedby a weld groove having (i)Single

V groove weldjoint, and (ii) Double V groove weldjoint. Determinethe maximum

tension which thejoints can resist.Thesteelplates are of grade Fe 410 grade with yield

strength of250

MPa. Assume shop welding.

Solution

Case(i):SingleV groove weld (Fig. 39)

In this case, incompletepenetration results due to singleVgroove.

Fig. 39 Single V groove weld

Single V is an incomplete penetration welding. Hence the throat thickness is 5/8th ofthe

thickness of thinnerplate.

te = 5/8t = (5/8) x 8 = 5 mm

Effective length of weld Lw = width of plate = 200 mm.

Strength of weld, P = L x tt x fy / mw Cl. 6.2

= 200 x 5 x200/1.25 = 200,000N= 200kN

Case(ii) : DoubleV groove weld (Fig. 40)

In this case, complete penetration results due to DoubleVgroove.

Fig. 40 Double V groove weld

Effective throat thickness is 8mm whichis the thickness ofthe thinnerplate.

te = 8 mm

Strength of weld, P = L x tt x fy / mw Cl. 6.2

= 200 x 8 x200/1.25 = 320,000N = 320kN


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2. Find the size and length ofthefillet weld forthe lapjoint to transmit a factored load of

120 kN as shown inFig. 41. Assume site welds, Fe 410 grade steel and E41 electrode.

Assume width ofplate as 75 mm andthickness as 8 mm.

Fig. 41 Lap joint connection

S o lu tio n Minimum sizeofweld for8 mm thick section = 3 mm (Table5,

Cl. 10.5.2.3) Maximum sizeofweld = 81.5 = 6.5 mm (Cl. 10.5.8.1)

Choose the sizeofweld, a =6mm

Effective throat thickness = te = 0.70 a = 4.2 mm

Strength of6 mm weld / mm length = 4.2 x 410 /(3x 1.5) Cl.10.5.7.1.1

= 662.7

N/mm Assuming only two longitudinal welds along

the sides Required length ofweld =120x 103/

662.7= 181 mm Length tobe provided on each side

=181/2= 90.5 mm

> 75 mm (width ofplate) Hence,

provide 90.5 mm weld on each side with an end return of2x 6 = 12 mm

Overall length oftheweld provided = 2 x(90.5+ 2 x6)= 205 mm

3. Two plates are connected to form a fillet joint using 6mm weld. Welding is provided on

three sides with a lap of 300mm as shown in Fig.42. Find the strength of the joint. If

welding is provided on all foursides (Fig. 44), determine the strength ofthe joint. Also

find the percentage increase inthestrength. Use Fe 410 steelwith yield stress 250 MPa.

Assume shop welding.


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Solution

Fig. 42 Lap joint connection with weld on three sides

Case (i) : Welding on three sides (Fig. 42)

Lw= 300 + 200 + 300 =800mm

Design strength of fillet weld joint, P1 = 0.7a fwd Lw /mw Cl.10.5.7.1.1

= 0.7 x6x(410/3)x 800 /1.25

= 6,36,286

N Hence, allowable load = 6,36,286 / 1.5 = 4,24,191

N

Case (ii) : Welding on four sides (Fig.4 3)

Fig. 43 Lap joint connection with weld on foursides

Lw= 300 + 200 + 300 +200= 1000 mm

Design strength of fillet weld joint, P2 = 0.7a fwd Lw /mw Cl.10.5.7.1.1

= 0.7 x6x(410/3)x1000/1.25

= 7,95,358

N Hence, allowable load = 7,95,358 / 1.5 = 5,30,239

N

Percentage increase in strength = (P2P1)/ P1 x 100 = 25 %


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4. Determinethe size ofthe weld required forthe bracket connection shown in Fig. 44.

Assume shopwelding.

Solution

Eccentricity, e = 100 + 75 = 175 mm

Torsional moment ,M= 60 x 175 = 10,500 kN-

mm Considering unit thickness ofweld at root

Ip = Izz+Iyy = 3.08 x 106 mm4

Shear stress due to direct force, f1 = 60,000 / (400x1) = 150 MPa

Fig. 44 Bracket connection showing load and resultant stress in weld

Further, rmax = 125 mm

Shear stress due to torsional moment, f2 =Mx rmax /Ip

= 426 MPa

Resultant stress in the critical part of the weld / mm width

R= (f12

+ f22

+2f1f2 cos ) 0.5 = 530 MPa

Strength ofthe weld per unit length andthickness, P P = 0.7a fwd Lw /mw

= 0.7 a (410/3) 1 / 1.25 = 132.6 aN

Equating the resultant, Rwith the strength ofweld, P (i.e.,R= P)

a = 3.99 mm

Size of weld to be provided =4mm


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5. Determinethe load, V that can be applied on the bracket shown in Fig. 45. Use 6 mm

field fillet welding.

Solution

Shear stress due to direct force, q =V/(2x 200 x 1)

= 0.0025 V

N/mm2

Moment on weld, M= 200 VN-mm

Considering unit thickness ofweld at root,

Moment of inertia Iz= 2 (1x2003)/ 12 = 1.33 x 10

6mm

4

Fig. 45 Bracket connection showing load out ofplane

Normal stress due to bending in tension, fa = M y/Iz

Here, M= 200 VN-mm,y= 100 mm, Iz= 1.33 x 106 mm4

Hence, fa = 0.015 V

Equivalent stress, fe is computed as (cl. 10.5.10.1.1)

fe =( fa2

+ 3 q2 ) 0.5 =

0.0156 V For6 mm fillet weld (field

weld)

Strength ofweld/mm, fwd =0.7x6(410/3)/ 1.50 = 662.8N/mm

Equating the equivalent stress, fe with the strength of6 mm weld,

fwd fe =fwd

0.0156 V=662.8

Hence, V= 42487 N =42.5 kN Forthe current bracket

a load of42.5kN can be safelyapplied.


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Welded Connections Final

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