Design of Welded Connections

Steel ConnectionsSteel Connections

A lecture prepared p pBy

A P D E B MAssis. Prof. Dr Ehab Boghdadi Matar

AcknowledgementAcknowledgement

k l d h f d i hi l h• I acknowledge photos found in this lecture to the scientific teaching aids found in different sources,

i llespecially • AISC digital library• ESDEP lecture notes• AISC‐ connection teaching toolkitAISC connection teaching toolkit• Personal photos taken in Germany, Holland, Austria and EgyptAustria and Egypt.

Ehab matarAssis. Prof. of steel structural

ObjectivesObjectives

Through the following 3 lectures, we shall study together the steel connections. Our main objectives will be:

1. Identify the different types of steel connections1. Identify the different types of steel connections2. Understanding the force transfer through steel

ticonnections3. Practicing the design of bolted and welded

connections through neat self explained calculations and full dwgs details.g

Welded ConnectionsWelded Connections• The most common welding• The most common welding

processes, particularly for welding structural steel, use electrical energy as the heat source; the most often

d i th l t i Thused is the electric arc. The arc consists of a relatively large current discharge between electrode and base metal conducted through a h ll i i d lthermally ionized gaseous column, called plasma. In arc welding, fusion occurs by the flow of material across the arc, without pressure being applied.

• We have two welding procedure types:

Shielded Metal Arc Welding (SMAW)Shielded Metal Arc Welding (SMAW)Submerged Arc Welding (SAW)

Structural Welding (AISC)

• Another common method for connecting structural steel is welding

• Welding can be performed in the shop or in the field• Welding can be performed in the shop or in the field

• Many fabrication shops prefer to weld rather than bolt

• Welding in the field is avoided if possible due to welding condition requirements

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Welding in the field is avoided if possible due to welding condition requirements

• There are several welding processes, types, and positions to be considered in buildingconstruction


• The American Welding Society (AWS) is a nonprofit organization with a goal to advancethe science, technology and application of welding and related joining disciplines

• AWS develops codes, recommended practices, and guides under strict AmericanNational Standards Institute (ANSI) procedures

D1 1 St t l W ldi C d St l f th t lt d d i th ld i

6

• D1.1 Structural Welding Code – Steel, one of the most consulted codes in the world, isproduced by AWS (AWS 2004a)


• Welding is the process of fusing multiple pieces of metal together by heating the filler

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Welding is the process of fusing multiple pieces of metal together by heating the fillermetal to a liquid state

• A properly welded joint is stronger than the base metal

SMAW Welding (AISC)

• Shielded Metal Arc Welding (SMAW) is also known as manual, stick, or hand welding

• An electric arc is produced between the end of a coated metal electrode and the steelpcomponents to be welded

• The electrode is a filler metal covered with a coating

h l d ’ i h• The electrode’s coating has two purposes:

• It forms a gas shield to prevent impurities in the atmosphere from getting into theweld

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• It contains a flux that purifies the molten metal (AISC & NISD 2000)

GMAW Welding (AISC)

G M t l A W ldi (GMAW) i l k MIG ldi• Gas Metal Arc Welding (GMAW) is also known as MIG welding

• It is fast and economical

• A continuous wire is fed into the welding gunA continuous wire is fed into the welding gun

• The wire melts and combines with the base metal to form the weld

• The molten metal is protected from the atmosphere by a gas shield which is fed

9

through a conduit to the tip of the welding gun

• This process may be automated (AISC & NISD 2000)

FCAW Welding (AISC)

• Flux Cored Arc Welding (FCAW) is similar to the GMAW process

• The difference is that the filler wire has a center core which contains flux

• With this process it is possible to weld with or without a shielding gas

This makes it useful for exposed conditions where a shielding gas may be affected

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by the wind

(AISC & NISD 2000)

SAW Welding (AISC)

S b d A W ldi (SAW) i l f d b t ti i t ti• Submerged Arc Welding (SAW) is only performed by automatic or semiautomaticmethods

• Uses a continuously fed filler metal electrode

• The weld pool is protected from the surrounding atmosphere by a blanket of granularflux fed at the welding gun

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• Results in a deeper weld penetration than the other process

• Only flat or horizontal positions may be used (AISC & NISD 2000)

Welding Equipment (AISC)

• Equipment used for welding will vary depending on the welding process and whetherthe welding is being done in the shop or in the field

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• A Flux Cored Arc Welding machine for shop welding is pictured above left

• A Shielded Metal Arc Welding machine for field welding is pictured above right

Welding Terminology (AISC)

• Tack Weld (above left)

A temporary weld used to hold parts in place while more extensive, final weldsare made

• Continuous WeldContinuous Weld

A weld which extends continuously from one end of a joint to the other

• Stitch Weld (above right)

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Stitch Weld (above right)

A series of welds of a specified length that are spaced a specified distance fromeach other

WeldabilityWeldability

ld bili d fi d i h [3] i• Weldability as defined in Johnson [3], is a measure of the ease of producing a crack‐free d d t t l j i t S f th diland sound structural joint. Some of the readily

available structural steels are more suited to welding than otherswelding than others.

• Welding procedures should be based on a steel’s h i i d f h bli h d ichemistry instead of the published maximum alloy limits set by its specification. The following t bl h th id l h i l l i f thtable shows the ideal chemical analysis of the carbon steels.

Most mild steels fall well within this range, while higher strength

steels may exceed the ideal analysis shown in the table.

Electrodes (Salmon and Johnson)

Welding PositionsWelding Positions• Th Fl t P iti i hi h th• The Flat Position: in which the

weld metal can be deposited faster because gravity is acting with the welder so largewith the welder, so large electrode sizes and high currents may be used.

• The Over Head Position: It is• The Over Head Position: It is the most difficult position in welding process and usually executed in field Electrodesexecuted in field. Electrodes diameters below 5mm are to be utilized otherwise weld metal runs down.

• The Vertical and Horizontal Positions.

Advantages of welded connectionsAdvantages of welded connections

Si th d t i l d i i h l• Since the process dose not involve driving holes, the gross sectional area of the welded member is used which result in less member weightused which result in less member weight.

• Welded connections are more rigid.• Repairs and further new constructions of• Repairs and further new constructions of connections can be done easily.

• Welded structure has better finish and• Welded structure has better finish and appearance.

• There will be in many cases no need forThere will be in many cases no need for connecting angles or splicing plates.

Disadvantages of welded connectionsDisadvantages of welded connections

It i kill d l b• It requires skilled labor.• Testing of welding connections is difficult and very expensivevery expensive.

• Due to an even heating and cooling, the welded member is likely to get warped at the weldedmember is likely to get warped at the welded surface causing distortion.

• Internal stresses in the welded zone are likely to• Internal stresses in the welded zone are likely to be setup.

• Welded metals have less fatigue strength thanWelded metals have less fatigue strength than metal connected by bolts because of its brittleness.


ButtLap Corner

TeeEdge

• Shown above are types of structural joints which are established by positions of theconnected material relative to one another

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connected material relative to one another

• Lap, tee, and butt joints are most common (AISC)

Types of welded connectionsTypes of welded connections

• In principle there are four main types:1. Fillet weld1. Fillet weld2. Butt weld3. Slot weld4 Plug weld4. Plug weld


Fillet Full penetration single bevel groove weld

Partial penetration single bevel groove

weldgroove weld weld

Full penetration Partial penetrationPlug

Full penetration double vee groove weld

Partial penetration single J groove weld

W ld t d fi th fi ti f th ld d it d l i d i h• Weld types define the configuration of the weld and its underlying design approach

• Fillet welds and groove welds are most common

• Groove welds fall into two categories• Groove welds fall into two categories

Full penetration – the entire member cross‐section is welded

Partial penetration – just part of the member cross‐section is welded

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Partial penetration just part of the member cross‐section is welded

(AISC)

Fillet weldFillet weld

Fill ld d• Fillet welds are made between plate surfaces, which are met at rightwhich are met at right angles or overlapping. The angle between the plates usually varies between 60o and 120o. The minimum angle forThe minimum angle for flat welding position is 60o, for vertical welding , g70o, and for overhead position 80o.

Fillet Welds (AISC)

Symbolic ProfilesSymbolic Profiles

Actual Profiles

• The most commonly used weld is the fillet weld

• Fillet welds are theoretically triangular in cross‐section

• Fillet welds join two surfaces at approximately right angles to each other in lap, tee, and corner joints

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and corner joints

(AISC & NISD 2000)

Butt weldButt weld

B ld d• Butt welds are made between the edges of abutting plates that meetabutting plates that meet at the same plane without overlapping. The edge preparation chosen for a particular size of butt weld must ensurebutt weld must ensure that a complete penetration can be pachieved with minimum weld metal.

Full Penetration Groove Welds (AISC)

• The bevel or “J” preparation extends over most of or the entire face of the materialbeing joined

• Complete fusion takes place

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• In some types of full penetration groove welds the material will be beveled from oneside of the plate with a separate plate on the opposite side – called backing or abacking bar (AISC & NISD 2000)

Partial Penetration Groove Welds (AISC)

Partial joint penetration welds are used when it is not necessary for the strength of the

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Partial joint penetration welds are used when it is not necessary for the strength of thejoint to develop the full cross section of the members being joined

(AISC & NISD 2000)

Slot and Plug weldsSlot and Plug welds• A i i l f l l t• A principle use for plug or slot

welds is to transmit shear in a lap joint when the size of the connection limits the lengthconnection limits the length available for fillet or other edge welds.

• Slot and plug welds are also• Slot and plug welds are also useful in preventing overlapping parts from bucklingbuckling.

• The shear capacity is calculated as the product of the area of the hole or slotthe area of the hole or slot and the design shear stress for fillet weld.

Weld Accessibility• Access holes are required for someAccess holes are required for some

welds, such as the welded flangeconnection shown to the right

The top access hole allows for

Extension Bar

The top access hole allows fora continuous backing bar tobe placed under the topflangeflange

The bottom access hole allowsfor complete access to weldth ti idth f th

Weld Access l

Backing Bar

the entire width of thebottom flange

• A detail of a weld access hole for a

Colu

Holes

welded flange connection is shownbelow

umn

Seat Angle

29 (Adapted from AISC 2001)(Adapted from AISC 2002a)

• Weld symbols are used to

Weld Symbols (AISC)Weld symbols are used tocommunicate the specificdetails and requirementsof each weld to thewelder

• Weld symbols areincluded on fabricationincluded on fabricationand erection drawings

Horizontal Weld LineHorizontal Weld Line

TailNote

(Indicating this is aField Weld Symbol

Leader Line

(Indicating this is a typical weld)

Length and Spacing of weld(In Inches)

Size of weld

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Basic Weld Symbol (Fillet weld symbol shown)

Size of weld(In Inches)

Examples (Salmon and Johnson)

Weld Size (AISC)

• The size of a weld must match the size specified on the drawings

• Some welds may meet the required size after a single pass of the welder

• Larger weld sizes may require multiple passes to meet the size requirement

• Common single pass welds include fillet welds up to and including 5/16 inch (8mm)and thin plate butt welds with no preparation

• Common multiple pass welds include single bevel full penetration groove welds single

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• Common multiple pass welds include single bevel full penetration groove welds, singlebevel partial penetration groove welds, and fillet welds over 5/16 inch (8mm)

• The weld in the above picture is a multiple pass fillet weld

Allowable stresses in Butt WeldingAllowable stresses in Butt Welding• The permissible stressesThe permissible stresses

under the application of static loads for butt welded connections depend on the welding execution where two values are given for the allowable stresses; the first for good welding which fulfills the

i t f threquirements of the specifications while the second value for excellent welding where all thewelding where all the welds are examined to guarantee the efficiency of the jointof the joint

Allowable stresses for Fillet weldAllowable stresses for Fillet weld• Fillet welds as indicated in

ECP clause 5 6 3 1 areECP clause 5.6.3.1 are stressed across the throat (t) of the weld while their size is specified by the legsize is specified by the leg length (S); where t=k.S. The value of k shall be related to the angle between the twothe angle between the two surfaces as shown

• Effective area of weld is i L *k*S hgiven as Leffw*k*S where Leffw is the effective welding length

• The allowable stresses is 20% of the ultimate strength of the base metalstrength of the base metal for all kinds of stresses.

General requirements for Welded connections According to ECP

• Fill t ld i d fi d b t t Si S d ff ti• Fillet weld is defined by two parameters : Size S and effective welding length Leff where Leff= Loverall – 2S

• S≥4mm for buildings,• S≥6mm for bridges• For two connected parts with different thickness t1, t2 where t1>>t2,

thenS4mm for t1 10mmS5mm for 10 t1 20mmS6mm for 20 t 30mmS6mm for 20 t1 30mmS8mm for 30 t1 50mmS10mm for 50 t1 100mm

And in all cases S should not exceed the minimum thickness of the connected parts i.e. t2connected parts i.e. t2

• Leff≥ 50mm ≥4S• L ≤ 70S• Leff ≤ 70S• If Leff > 70S a reduction factor should be used for the area

of the weld. This reduction factor is given by

• Effective area of welding A=Leff*t=Leff*K*SF fill ld d i bj d M M M N

0.1)70/(2.02.1 SL

• For a fillet welded connection subjected to Mx, My, Mt, N and Qx and Qy,

yx MMN

tx

yx

x

MQ

xI

yIA

..

x tLeff = lines weldof areas theofsummation theisA

ty

p

txx

MQ

yIA

Qq .

stress.principletheisFIy +Ix = lines welded theof inertia ofmoment polar theis Ip

C.Gr about thei lines welded theof inertia of moments theisIy Ix,

p

tyy

qqq

xIM

AQ

q .

22

p p

pw

yx

FqF

qqq

1.13 22

• Single line of fillet weld should not bend about their longitudinal axis.

• Intermittent welds shall not be used in parts intended to withstand dynamic loading. In other load cases, the distance between ff ti l th feffective lengths of consecutive intermittent fillet welds whether chained (L ) or staggeredchained (L1) or staggered (L2) shall not exceed 12 times the thickness of the thinner part when inthe thinner part when in compression or 16 times the thickness of the thinner part when in t e pa t etension, but shall in no case exceed 20cms as shown in Fig. (5.17).

ExamplesExamples

• Given: The following steel truss members designed for case I loading from Steel 37

• Required: Design this connection using fillet welding and a gusset plate thickness of 10mm

• Solution: Assuming that the thi k f fill t ldthickness of fillet weld >5mm and < 9mm for member 1 and <10mm formember 1 and <10mm for member 2 and 3. Take S = 6mm then the force resisted6mm, then the force resisted by each 1cm of fillet weld is 1cm x 0.2Fu S = 0.2 3.6 u0.6 x0.7= 0.301 t/cm.

• The welding in member 1 The welding in memberhas two solutions: either use all around welding or use two parallel welding lines. Assuming the weld lines lengths are a,b and c which is known to be 9 cm.

• The design force is 14.142t .• From equilibrium of forces, (a + b + c) 0.301 = 14.14• Then a + b = 37 98 cm (1)• Then, a + b = 37.98 cm (1)• Taking the moments of forces about the weld line b, then• 9 a 0.301 + 9 0.301 4.5 = 14.14 ( 9 – 2.54) a =

29.2cm.• From (1) then b 8 76cm• From (1), then b = 8.76cm• Then the overall lengths of weld is a = 29.2 + 20.6 • = 30.4cm 310mm• b = 8.76+ 2x0.6 =9.96cm 100mm• On the other hand if we assume only two weld lines a,b

then,• ( a + b ) 0.301 = 14.14t a + b = 46.98cm (2)• Taking the moments of forces about weld line b, then• 9 a 0.301= 14.14 ( 9 – 2.54) a = 33.72cm.• From (2), then b = 13.26cm• Then the overall lengths of weld is a = 33.72 + 20.6• = 34.92 cm 350mm• b = 13.26 + 2x0.6=14.46cm 150mm

Example 5 9Example 5.9Gi Th h b k t• Given: The shown bracket column connection. The fillet weld size is 6mm for the web connection and 8mm for the flange connection knowing thatconnection knowing that the bracket and the column are made of St. 5252

• Required: Determine the maximum load carrying y gcapacity W of this connection

• Solution:• The weld lines are assumed all

d th b k t tiaround the bracket cross section. This weld lines will be subjected to a shearing force W and a bending moment 20 x Wbending moment 20 x W

• Properties of area of weld lines:• A = 2 15 0.8 0.7+ 2 20

0.6 0.7= 33.6 cm20.6 0.7 33.6 cm• I = 2 0.6 0.7 (20)3 / 12 + 2

0.80.7 15 (12.5)2 = 2412.2 cm4

• 3‐ The weld lines is subjected to shear stress q and normal stress f

• Where:• q = W / A = W / 33.6 t/cm2

• σ = My/I = 20W x 12.5 / 2412.2 = W / 10.96 t/cm2

• The principal stress is given as

222

22 /1277033 cmWtWWqF

/1277.0

96.106.3333 cmWtqF

• The principal stress should not exceed the maximum allowable stress of 0.2 Fu 1.10.1277W 0.2 5.21.1 W 8.96 ton.

Weld Inspections (AISC)

• In addition to the erector’s quality control program, tests and inspections are specifiedby the Engineer of Record and/or the local building authorityby the Engineer of Record and/or the local building authority

• A local building inspector may request that tests in addition to those specified by theEngineer of Record be performed

• Some problems that can be found in welds include:

Lack of fusion Cracks Wrong size

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Porosity Insufficient penetration

• There are several weld tests and inspections that are commonly used

Poor workmanship

Visual Inspection (AISC)

• Visual inspection is the most frequently used inspection and is the only inspectionp q y p y prequired unless the specification calls for a more stringent inspection method

• Inspection is done by the welder before, during, and after welding

• When outside inspection is required it should also be done before, during, and afterwelding

• Minor problems can be identified and corrected before the weld is complete

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• Minor problems can be identified and corrected before the weld is complete

(AISC & NISD 2000)

Dye Penetrant Test (AISC)

• Dye penetrant testing locates minute surface cracks and porosity

• Dye types that may be used include:

Color contrast dye ‐ which shows up under ordinary light

Fluorescent dye – which shows up under black light

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• The dye is normally applied by spraying it directly on the weld

(AISC & NISD 2000)

Magnetic Particle Inspection (AISC)

• Magnetic particle inspection uses powdered magnetic particles to indicate defects in• Magnetic particle inspection uses powdered magnetic particles to indicate defects inmagnetic materials

• A magnetic field is induced in the part

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• The magnetic powder is attracted to and outlines cracks within the material

(AISC & NISD 2000)

Ultrasonic Inspection (AISC)

• Ultrasonic inspection can be used to detect flaws inside welds

• High frequency sound waves are directed into the metal with a probe held at a specificangleangle

• The flaws reflect some energy back to the probe

• Flaws show up as indications on a screen (above) and are subject to interpretation by

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• Flaws show up as indications on a screen (above) and are subject to interpretation byan inspector

(AISC & NISD 2000)

Radiographic Inspection (AISC)

• Radiographic inspection or X ray can also be used to detect flaws inside welds• Radiographic inspection, or X‐ray, can also be used to detect flaws inside welds

• Invisible rays penetrate the metal and reveal flaws on an x‐ray film or fluorescentscreen (above)

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• This is the most costly of the inspection methods

(AISC & NISD 2000)

Welding Cost Considerations (AISC)

• Fillet weld is less expensive than groove weldFillet weld is less expensive than groove weld

No special preparation

No backing requiredg q

Less volume of weld

• Partial penetration groove weld is less expensive than full penetration

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groove weld

• Labor represents the majority of the cost associated with welding

Th ks Thanks you

Design of Welded Connections

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