Aluminum Welding - JELF

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Volume XVI, Number 2, 1999


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We, at Lincoln Electric, certainly have a fine tradition

of rewarding our employees accomplishments.However, it is especially gratifying when one of ourown is singled out for recognition by a very respectedrepresentative of the industry. Such was the caserecently, when Engineering News Record namedLincolns Senior Design Consultant Omer W. Blodgettone of the Top People of the Past 125 Years, in cele-bration of the magazines own 125th anniversary. Inthe issue dated August 30, 1999, Omer was namedas a Technology & Materials Innovator with the fol-lowing citation:

Before becoming the nations preeminent authorof weld-design handbooks, Blodgett beseechedhighway officials to allow welded connections andplate girders in place of riveted ones. WithDesign of Welded Structures (1966), he providednecessary analytical tools. A mechanical engi-neer by training, and a Lincoln Electric Co. designconsultant since 1945, he devised the firstmethod for analyzing three-dimensional weldgroups. In the 1980s, he rationalized the need toenlarge weld access holes to reduce cracking ofwelded steel jumbo sections.

Participants in our Lincoln Design Seminar Serieshave known for decades that as a teacher of designtheory, Omer Blodgett has no peer. His observationsare relevant, factual, and down-to-earth. Now, thanksto Engineering News Record , his achievements havebeen recognized as belonging in a league with thoseof John Roebling (1843-1903), designer of theBrooklyn Bridge; Buckminster Fuller (1895-1983),inventor of the geodesic dome; Thomas A. Edison(1847-1931); and the world-renowned architect FrankLloyd Wright (1869-1959). In a nice bit of symmetry,

In Good Company

ENR also included among its Top 125 People R.G.LeTourneau (1888-1964), inventor of large ear thmov-ing equipment and founder of LeTourneau University,where the Omer W. Blodgett Endowed Chair ofWelding and Materials Joining Engineering wasestablished in 1990. All in all, pretty good companyfor a boy from Duluth, Minnesota, who learned to weldat the age of ten using a 200 amp Lincoln welder.

For 54 years, Lincoln Electric and thousands of ourcustomers have had the benefit of Omers insight,wisdom and practical know-how. While quietly goingabout his work of solving the most challenging designproblems, he has managed to make us all look good.And now, he has made us all very proud, as well!

Tony Massaro Chairman & CEO The Lincoln Electric Company

Tony Massaro and Omer Blodgett

Australia andNew ZealandRaymond K. Ryan Phone: 61-29-772-7222 Fax: 61-29-792-1387

CroatiaProf. Dr. Slobodan Kralj Phone: 385-1-6168306 Fax: 385-1-6157124

HungaryDr. Gza Gremsperger Phone: 361-156-3306

IndiaDr. V.R. Krishnan Phone: 91-11-247-5139 Fax: 91-124-321985

JapanDr. Motoomi Ogata Phone: 81-565-48-8121Fax: 81-565-48-0030

Peoples Republicof ChinaDai Shu Hua Phone: 022-831-4170 Fax: 022-831-4179

RussiaDr.Vladimir P. Yatsenko Phone: 07-095-238-5543 Fax: 07-095-238-6934

United KingdomDr. Ralph B.G.Yeo Phone & Fax: 44-1709-379905

INTERNATIONAL ASSISTANT SECRETARIES


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1Welding Innovation Vol. XVI, No. 2, 1999

Cover: Melbournes Colonial Stadium features state-of-the-art technology and a retractable roof that will open and close in just 20 minutes. See story on page 22.

2 Common Mistakes Made in the Designof Aluminum WeldmentsWhen designing with aluminum, the engineer must not rely

on prior experiences with steel or any other material.

7 Framed in Steel: Dwellings for the New MillenniumA small Ohio company is capitalizing on the advantages of usinglight gauge steel in residential construction.

22 Challenging Stadium Project Headedfor On-Time CompletionWeld fabrication of the Colonial Stadium being built in Melbourne, Australia,required special treatment to ensure that the high strength of the steelwould be fully utilized.

The serviceability of a prod- uct or structure utilizing the type of information presented herein is, and must be,the sole responsibility of the builder/user. Many variables beyond the control of The James F. Lincoln Arc Welding Foundation or The Lincoln Electric Company affect the results obtained in applying this type of information. These variables include, but are not limited to, welding procedure, plate chemistry and temperature,weldment design, fabrication methods, and service requirements.

Volume XVINumber 2, 1999

EditorDuane K. Miller,

Sc.D., P.E.

Assistant EditorR. Scott Funderburk

The James F. LincolnArc Welding Foundation

Omer W. Blodgett, Sc.D., P.E.Design Consultant

Features

Award Programs

Departments

10 Key Concepts:Selecting Filler Metals: Matching Strength Criteria

17 Design File:Use Caution When Specifying Seal Welds

21 Opportunities: Year 2000 Professional Programs

Visit Welding Innovation online at http://www.lincolnelectric.com/services/educate/innovate.asp

13 1999 Awards for Engineering and Technology Students

THE JAMES F. LINCOLN ARC WELDING FOUNDATION TRUSTEES & OFFICERS

Dr.Donald N. Zwiep,Chairman Worcester, Massachusetts

John T. Frieg,Trustee Cleveland, Ohio

Leslie L. Knowlton,Trustee Cleveland, Ohio

Roy L. MorrowExecutive Director

Duane K. Miller, Sc.D., P.E.Secretary
http://www.lincolnelectric.com/services/educate/innovate.asphttp://www.lincolnelectric.com/services/educate/innovate.asphttp://www.lincolnelectric.com/services/educate/innovate.asphttp://www.lincolnelectric.com/services/educate/innovate.asp


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2 Welding Innovation Vol. XVI, No. 2, 1999

Common Mistakes Madein the Design of

By Frank G. Armao

Senior Application EngineerThe Lincoln Electric CompanyCleveland, Ohio

Background

As a rule, designers of metallic struc-tures have learned to design usingsteel. When designing with alu-minum, however, the engineer mustnot base the design on prior experi-ences with steel or any other material.The alloy selection, proper joint designand the choice of an optimal weldingprocess may all be a function of thebase material. While aluminum obvi-ously obeys the same laws ofmechanics as all other materials, itmust be approached differently thansteel when welded. Aluminum struc-tures are not necessarily more difficultto design or weld than steel structures,they are just different.

Dont Just Choosethe Strongest Alloy

Aluminum is often chosen as a struc-tural material for applications in whichweight savings are important. Veryoften, the designer will choose thevery strongest alloy available. This isa poor design practice for several rea-sons. First, the critical design limita-tion for many structures often isdeflection, not strength. In such

cases, the modulus of elasticity, notthe tensile properties, will govern thedesign. The modulus of most alu-minum alloys, weak and strong alike,is approximately the same (one-thirdthe modulus of elasticity of steel), sono benefit accrues from using thestrongest alloy. Second, and mostimportantly, many of the strongest alu-minum alloys are not weldable usingconventional techniques.

When we speak about aluminumalloys being weldable or non-weld-able, we are usually referring to thealloys ability to be welded without hotcracking. Alloys that are extremelysusceptible to hot cracking are notconsidered appropriate for structural(load-carrying) applications, and aregenerally put in the non-weldable cate-gory. Hot cracking in aluminum alloysis primarily due to the chemistry of the

alloy and the weld bead. For virtuallyevery alloying addition, the crackingsensitivity varies as alloy contentincreases as shown in Figure 1.Weldable alloys have a compositionthat falls either well above or wellbelow the maximum cracking sensitivi-ty. In some cases, such as that of6061, which is very crack-sensitive ifwelded without filler material, the weldcracking sensitivity can be reduced to

Figure 1. Relative crack sensitivity versus weld composition for various binary aluminum systems.

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Welding Innovation Vol. XVI, No. 2, 1999 3

acceptable levels with the addition ofa high silicon or high magnesium fillermetal. The additional silicon or mag-nesium pushes the solidifying weldmetal below the cracking sensitivitylevel. In other alloys, such as 7075, itis not possible to design a weld filleralloy that results in a crack-resistantchemistry. These are considered to benon-weldable.

A number of common aluminum alloysare shown in Figure 2, along with typi-cal ultimate tensile strength values.These alloys have been broken intotwo groups: heat-treatable alloys and

non-heat-treatable alloys. A relativeassessment of weldability is also givenfor each of these.

The non-heat-treatable alloys arecomposed of the 1XXX, 3XXX, 4XXX,and 5XXX series. It is not possible tostrengthen these alloys by heat treat-ment. They can only be strengthenedby cold working (also called strainhardening). The 1XXX alloys, such as1100, 1188, or 1350, are essentially

pure aluminum (99+% purity). Theyare relatively soft and weak, with goodcorrosion resistance, and are usuallyused where high electrical conductivityis required, such as for bus bars or aselectrical conductors. They are alsoused in certain applications that

require a high degree of resistance tocorrosion. All of these alloys are read-ily weldable.

The 3XXX series of alloys have vari-ous levels of manganese (Mn) addedto strengthen them and improve theirresponse to cold work. They are ofmoderate strength, have good corro-sion resistance, and are readily weld-able. They are used for air conditioningand refrigeration systems, non-structur-al building trim, and other applications.

The 4XXX series of alloys have silicon(Si) added as an alloying element toreduce the melting point and increasetheir fluidity in the molten state. Thesealloys are used for welding and braz-ing filler materials and for sand anddie castings. They are the least crack-sensitive of all the aluminum alloys.

The 5XXX series of alloys have mag-nesium (Mg) added in order toincrease their strength and ability towork-harden. They are generally verycorrosion resistant and have the high-est strengths of any of the non-heat-treatable alloys. Increasingmagnesium content in these alloysresults in increasing strength levels.These alloys are commonly availablein the form of sheet, plate and strip,and are the most common structuralaluminum alloys. They are generallynot available as extruded sections,because they are expensive to

extrude. They are readily weldable, inmost cases, with or without filler metal.However, there is an Al-Mg crackingpeak at approximately 2.5% Mg, socare must be used in welding alloyssuch as 5052. It should not be weldedautogenously (i.e., without adding fillermetal). Weld filler metal with a highMg content, such as 5356, should beused to reduce the crack sensitivity.

The heat-treatable alloys are con-tained in the 2XXX, 6XXX, and 7XXXalloy families. The 2XXX family ofalloys are high strength Al-Cu alloysused mainly for aerospace applica-tions. In some environments, they canexhibit poor corrosion resistance. In

general, most alloys in this series areconsidered non-weldable. A primeexample of a non-weldable alloy in thisseries, which is attractive to designersbecause of its high strength, is alloy2024. This alloy is commonly used inairframes, where it is almost alwaysriveted. It is extremely crack-sensitiveand almost impossible to weld suc-cessfully using standard techniques.

Only two common structural alloys inthe 2XXX series are weldable: 2219and 2519. Alloy 2219 is very easilyweldable and has been extensivelywelded in fabricating the externaltanks for the U.S. space shuttle. Thisalloy gets its good weldability becauseof its higher copper content, approxi-mately 6%. A closely related alloy,

which is also very weldable, is 2519.It was developed for fabrication ofarmored vehicles. Although there aredetailed exceptions to this rule, thedesigner should probably consider allother alloys in the 2XXX series to benon-weldable.

The 6XXX series of alloys are thealloys probably most often encoun-tered in structural work. They are rela-tively strong (although not as strong asthe 2XXX or 7XXX series) and havegood corrosion resistance. They aremost often supplied as extrusions. Infact, if the designer specifies an extru-sion, it will almost certainly be sup-plied as a 6XXX alloy. 6XXX alloysmay also be supplied as sheet, plate

The criticaldesign limitation

for many structuresoften is deflection,not strength

Figure 2. Various aluminum alloys and their relative strengths.

AlloyTypical UltimateTensile Stress

1XXX Alloys1100-01350-0

1350-H182XXX Alloys

2219-T622024-T62

3XXX Alloys3003-0

3003-H184XXX Alloys

4143-05XXX Alloys

5083-05052-0

6XXX Alloys6061-0

6061-T46061-T6

7XXX Alloys7075-T67178-T6

ksi131118

5464

1627

17

4025

203040

7884

MPa9075

125

370440

110185

115

275170

140210275

540580

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and bar, and are the most commonheat treatable structural alloys.Although all alloys in this series tendto be crack-sensitive, they are all con-sidered weldable and are, in fact,welded every day. However, the cor-rect weld filler metal must be used to

eliminate cracking. Additionally, thesealloys will usually crack if they arewelded either without, or with insuffi-cient, filler metal additions.

The 7XXX alloys are the ones thatusually trip designers up. They are thevery high strength Al-Zn or Al-Zn-Mg-Cu alloys that are often used in aero-space fabrication, and are supplied inthe form of sheet, plate, forgings, andbar, as well as extrusions. With thefew exceptions noted below, the

designer should assume that the7XXX alloys are non-weldable. Themost common of these alloys is 7075,which should never be welded forstructural applications. In addition,these alloys often suffer from poor corro-sion performance in many environments.

A few of the 7XXX series defy thegeneral rule and are weldable. Theseare alloys 7003 and 7005, which areoften seen as extrusions, and 7039,which is most often seen as sheet orplate. Some common uses of thesealloys today are bicycle frames andbaseball bats, both of which are weld-ed. These alloys are easily weldedand can sometimes offer strength

advantages in the as-welded conditionover the 6XXX and 5XXX alloys.

There is one other exception to thegeneral rule that 2XXX and 7XXXalloys are unweldable. There are anumber of thick cast and/or wroughtplate alloys designed as mold platematerial for the injection moldingindustry. These alloys, which include

Alca Plus, Alca Max, and QC-7, are allvery close in chemistry to 7075 or2618. The designer should absolutelyavoid structural welds on these alloys.However, welding is often performedon these alloys to correct machiningmistakes, die erosion, etc. This is

acceptable because there are only lowstresses on such welds and, in fact,the weld is often in compression.

This discussion has tried to makea few points: First, when designing a structure of

any kind, dont scroll through thenearest list of aluminum alloys andpick the strongest.

Realize that some alloys, often thestronger ones, are non-weldable.Make sure the selected alloy isreadily weldable.

Recognize that some alloys or alloyfamilies are more suitable for someapplications than others.

One more caveat: when welding alu-minum, the designer must not assumethat the properties of the starting mate-rial and the properties of the weld areequivalent.

Why Isnt the Weld asStrong as the OriginalBase Metal?A designer of steel structures general-ly assumes that a weld is as strong asthe parent material, and the weldingengineer who is responsible for fabri-cating the structure expects to make aweld which is as strong as the steelbeing used. It would be tempting toassume that the situation is the samewhen designing and fabricating alu-

minum structures, but it isnt. In mostcases, a weld in an aluminum alloy isweaker, often to a significant degree,than the alloy being welded.

In order to understand why this is so,we must discuss the heat-treatableand non-heat-treatable alloys sepa-rately and define the temper designa-tions used for aluminum alloys.

Non-Heat-TreatableAlloysAlloys in this category (i.e., 1XXX,3XXX, 4XXX, and 5XXX families) areproduced by a cold working process:rolling, drawing, etc. After the cold

working process, the alloy is given thedesignation of an F temper (as-fabri-cated). Alloys are then often given asubsequent annealing heat treatment,after which they are classified as an Otemper (annealed). Many alloys aresold in this condition. Thus the correctdesignation for a plate of 5083 whichwas annealed after rolling is 5083 O.One of the attractive properties ofthese alloys is that they can be signifi-cantly increased in strength if they arecold worked after annealing. Figure 3shows what happens to several alloyswith varying amounts of cold work.

For example, alloy 5086 rises in yieldstrength from approximately 18 ksi

(125 MPa) to 40 ksi (275 MPa) and isnow said to be strain-hardened. Acomplete designation for this alloywould be 5056-H36. The H temperdesignation can be somewhat compli-cated, since it is used to designate anumber of processing variables.However, the last digit, which rangesfrom 1 to 8, designates the level ofcold working in the alloy, with 8 denot-ing the highest.

some alloys, oftenthe stronger ones,are non-weldable

Figure 3. Effect of cold work on yield strength of several work-hardening alloys.

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A common mistake in designing weld-ed structures using non-heat-treatablealloys is to look down a list of proper-ties, disregard the O temper material,and choose an alloy of the highesttemper because it is significantlystronger. This would seem to makesense, but it often doesnt, becausethe heat of welding acts as a localannealing operation, significantlyweakening the heat affected zone(HAZ) of the weld. If one plots theyield or tensile stress versus distancefrom the weld, a curve such as thatseen in Figure 4 is obtained. If thedesign is based on the strain hard-ened properties, the allowable designstress will usually be above the actualyield point of the HAZ. Although itmay seem counter-intuitive, the fact isthis: No matter what temper one startswith, the properties in the HAZ will bethose of the O temper annealed mate-rial due to the welding operation.Therefore, the design must be basedon the annealed properties, not on thestrain-hardened properties. Because

of this, it usually doesnt make senseto buy the more expensive strain hard-ened tempers for welded fabrications.One should design with and specifythe alloy in the O temper and up-gauge as necessary.

An obvious question is whether any-thing can be done to restore materialproperties after welding a strain-hard-ened material. Unfortunately, theanswer is almost always no. The onlyway to harden these materials isthrough mechanical deformation, and

this is almost never practical for weld-ed structures.

Heat-Treatable AlloysThe situation is somewhat differentwhen welding the heat-treatable alloys.Alloys are heat-treated by initially heat-ing the material to approximately1000F (540C), holding the tempera-ture for a short time, and then quench-ing it in water. This operation isintended to dissolve all the alloyingadditions in solution and hold themthere at room temperature. Alloys inthis condition are said to be in the T4temper and have significantly higherstrengths than the same alloy in the Otemper. Depending on the alloy, natu-ral aging at room temperature can

lead to further strength increases overtime. This takes place over a matter ofdays or, at most, a few weeks. Afterthat, the properties will remain stableover decades. If one buys T4 material,it is stable and the properties will notchange over the course of a lifetime.

However, most alloys are given anadditional heat treatment to obtain thehighest mechanical properties. Thisheat treatment consists of holding thematerial at approximately 400F

(205C) for a few hours. During thistime, the alloying additions that weredissolved in the prior heat treatmentprecipitate in a controlled manner,which strengthens the alloy. Materialin this condition is designated as T6(artificially aged) temper, the most

common heat-treated alloy temper.

Again, the complete temper designa-tion system is actually much morecomplex than this, but understandingthe T4 and T6 tempers will help toovercome some of the most commonmistakes made when designing alu-minum weldments. It is important tonote that heat treatable alloys can alsobe strain-hardened after heat treat-ment, and this can further complicatethe temper designation.

Remember that the aging treatment isperformed at approximately 400F(205C). Any arc welding process getsthe HAZ much hotter than this.Therefore, welding constitutes an addi-tional heat treatment for the HAZ.Some alloys experience an additionalsolution heat treatment, while otheralloys become overaged in the HAZ.This results in degradation of materialproperties, especially if the as-weldedproperties are compared to T6 proper-ties. For example, the minimum speci-fied tensile strength in ASTM B209 for6061 T6 is 40 ksi (275 MPa). Mostfabrication codes require a minimum as-welded tensile strength of 24 ksi (165MPa), which is a significant degradation.

As when designing for the non-heat-treatable alloys, the designer must notuse the parent material properties indesign. Realistic as-welded propertiesmust be used. It is difficult to general-

ize what these properties are. Theychange from alloy to alloy and dependstrongly on the starting temper of thealloy. Most design codes contain as-welded properties for aluminum alloysand these should be used.

Understanding the T4 and T6 tempers will

help to overcome someof the most commonmistakes

Figure 4. Tensile stress vs. distance from weld fusion line.

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With heat-treatable alloys, however,there are some ways to recover someof the material properties of the par-ent. Figure 5 shows a plot of tensilestress versus distance from the weldfor 6061, revealing curves for both T4and T6 material in both the as-welded(AW) and post-weld-aged (PWA) con-ditions. The PWA condition representsa weld that is subsequently aged forone hour at approximately 400F(205C). Post weld aging improvesthe mechanical properties for both T4and T6 starting materials. In fact,often times it is better to weld in the T4

condition and post weld age after thewelding process.

There is one final alternative to dis-cuss. If after welding, the structure isgiven a complete heat treatment (i.e.,solution treat at 1000F [540C],quench, age at 400F [205C]), all ofthe material properties (even in theweld) will be recovered and T6 proper-

ties will be obtained. This practice isfrequently followed on small structuressuch as bicycle frames, but it isimpractical for larger structures.Furthermore, the quenching usuallycauses enough distortion of the struc-ture that a straightening operation isnecessary before aging.

ConclusionsIn the design of welded aluminumstructures, too often the differencesbetween steel and aluminum are nottaken into account. To recap, commonmistakes include:

Not all aluminum alloys are weld-able. In general, the least weldablealloys are also the strongest alloys.

The weld will rarely be as strong asthe parent material.

The HAZ will have O temperannealed properties for non-heat-treatable alloys regardless of the ini-tial material temper.

For the heat treatable alloys, the as-welded properties will be significant-ly lower than the properties of theT6 alloy temper.

Post-weld heat treatment can help torestore the mechanical properties ofwelds in heat treatable alloys.

Figure 5. Tensile stress profiles of the heat affected zone for 6061-T4 and T6 starting material in the As-Welded (AW) and Post-Weld Aged (PWA) conditions.

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At Enertech Systems, Inc., inCleveland, Ohio, Michael Whitticar andhis two partners are preaching agospel new to the midwestern UnitedStates: the advantages of using lightgauge steel in residential construction.Despite the fact that most American-produced steel comes from thisregion, area builders have so far beenslow to embrace this alternative towood. In the U.S., the popularity ofsteel-framed housing continues to begreatest in Hawaii and California,where steels ability to withstand highwinds and earthquakes has been asignificant selling point, according toGeoffrey C. Stone, director of corpo-rate programs for the North AmericanSteel Framing Alliance (NASFA).

Whitticar notes that Enertech Systemswas formed in 1994, when lumberprices had hit a peak, sparking a sud-den interest in steel. Investors WilliamTuttle and Nicholas Russo had alreadyidentified residential construction as ahuge potential market for light gaugesteel. When they discovered Whitticar,

a third generation carpenter who hadlearned how to frame houses withsteel while living in Canada, they knewthey had found the technical expertiseneeded to round out their team. Forthe first year of its existence, the fledg-ling company simply offered its servic-es on a consulting basis. In 1995,Enertech began to get involved in thefabrication of steel trusses.

Workshop Case StudyIn the mid-1990s, LTV Steelapproached Greater Cleveland Habitatfor Humanity with an offer to donatelight gauge steel, detailed drawings,some tools, and design assistance if

Habitat would consent to use steelframes to construct some of its afford-able homes. Agreeing with alacrity,Habitat soon secured a building ininner city Cleveland where it couldpanelize its own trusses. When theproject reaches completion, more than30 steel-framed Habitat houses willhave been constructed in theCleveland area.

In August, 1999, Enertech joinedforces with NASFA (an affiliate of theAmerican Iron and Steel Institute), theLincoln Electric Company, and LTVSteel to co-sponsor a four-dayWorkshop on Applications andPractices for Cold-Formed SteelFraming. The practical case for theworkshop was a 1,300 sq ft steel-

framed Habitat for Humanity houseunder construction at 2205 East 100thSt. in Cleveland (Figure 1). LTV andRysar Homes donated the time andmaterials to build the house, withEnertech donating some time, andalso being reimbursed by LTV Steel forsome of its participation.

Framed in Steel:Dwellings for the New Millennium

Figure 2. Prefabricated light gauge steel frame trusses were towed to the site.

Light gauge steel isused in 3-4 percentof homes currently

being built

By Carla Rautenberg

Welding Innovation Contributing WriterJames F. Lincoln Arc Welding FoundationCleveland, Ohio

Figure 1. This rendering of a modest traditional Habitat for Humanity house betrays no hint of the actual structures steel frame.

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An introductory seminar featured threepresentations: Geoff Stone presented the mission

and goals of NASFA. Hank Mailand, general manager of

cost reduction for NASFA, describedthe organizations cost reduction

program. Mike Whitticar lectured on Cold-

Formed Steel Framing Applications and Practices.

Following the formal program, work-shop attendees traveled to the con-struction site, where, after watchingdemonstrations by Enertech personnel,they assisted in the construction offloor joists and sheathing, exterior andinterior wall framing, and the erectionof roof/truss framing (Figures 2 and 3).In addition, Lincoln Electric personneldemonstrated the use of a LincolnSP175 Plus welder and a Pro-Cut 25plasma cutter (Figure 4).

Fastening productivity is a critical issuefor steel at this stage of its marketdevelopment, says Don Moody, NASFApresident. NASFA has dedicated agreat amount of effort and resources tohelp develop a fastening system thatwill connect steel members as quicklyand cost-effectively as wood membersare connected. Spot welding is onemethod we are reviewing.

Currently, Enertech uses screws tofasten light gauge steel memberstogether. Whitticar readily admits,Were new to the welding industry, butwe certainly see the technologyspotential to create a superior connec-tion as far as providing shear valuegoes. He and his employees haveexperimented with Lincolns new

equipment for one-sided spot welding,and found it to be quick and efficientwhile offering a better shear valuethan a screwed connection.Ultimately, however, Whitticar expectswelding will be fastest and thereforemost cost effective for shop paneliza-tion of walls and roof trusses.

The American Society for Testingand Materials (ASTM) has

announced that its SubcommitteeA05.11 on Sheet Specifications iscurrently developing two draft stan-dards to govern the use of steelsheet to make cold-formed framingmembers for studs, joists, purlins,girts and track in residential con-struction. According to Don Moody,president of the North AmericanSteel Framing Alliance, The fact thatASTM is currently developing thesetwo important standards for cold-formed steel in residential construc-tion is a testament to thefast-growing interest in steel for thismarket. NASFA strongly supportstheir efforts.

The draft standards now underdevelopment are:

Standard Specification for SteelSheet, Carbon, Metallic and Non-Metallic Coated For Cold-FormedFraming Memberscovers coatedsteel sheet used in the manufac-ture of cold-formed framing mem-bers. Sections includeterminology, classification, materi-als and manufacture, mechanicaland coating properties, certifica-tion, chemical composition tables,and more.

Standard Practice for EstablishingConformance to the Minimum

Cold Formed Steel Framing StandardsUnder Development

Expected Corrosion Characteristicsof Metallic, Painted-Metallic, and

Non-Metallic Coated Steel SheetIntended for Use as Cold FormedFraming Memberscovers proce-dures used to establish the accept-ability of metallic coated steelsheet, and painted metallic or non-metallic-coated steel sheet for useas cold-formed framing members.This practice assesses whethermaterials used for cold-formedframing members satisfy therequired minimum expected corro-sion characteristics. In-depth sec-tions on teminology, summary ofpractice, use, procedure, and relat-ed topics are included.

Donald Mongeon, chairman ofSubcommittee A05.11, reports:There were people involved in thetask group who use, specify, andmanufacture the cold-formed framingmembersspecifiers, architects,engineers, steel producers. Weretrying to reach compromise amongthose disparate interests who havetheir own set of priorities and wereusing the ASTM balloting method toget there.

Editors Note: Committee A-5 is one of 129 ASTM technical standards-writing committees.Organized in 1898, ASTM has more than 34,000 members from around the globe and is one of the largest voluntary standards development organizations in the world.Participation in ASTM is open to any interest- ed party. Web Site: www.astm.org.

Potentialand BarriersWhitticar sees the most potential forsteel to penetrate the residential mar-ket with applications that are essential-ly a hybrid of steel and woodconstruction. For example, he sug-gests that home builders consider theuse of steel floor joists for elevatedfloor framing because:

Steel floor joists are dimensionallystable, which eliminates the need tocull and crown each member.

Steel joists are lighter and will out-span traditional dimensional wood

joists of equal size. Steel is cost-competitive with engi-

neered wood.

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According to NASFA, barriers togreater use of steel in residential con-struction include:

The higher cost of construction. Thermal performancesteel alone

conducts heat through the wallsmore than wood, but with appropri-ate insulation, steel can exhibitequivalent or better performance.

Lack of infrastructurethe fact thatcarpenters and lumberyards areaccustomed to working with wood,not steel.

Lack of standardsalthough this isnow being addressed by ASTM (seesidebar).

Geoff Stone notes, At NASFA, we aresystematically addressing these barri-ers, and our goal is to fully enable thehome-building market for the wide-spread and economic use of steel

framing, in any application that makessense. NASFA estimates that lightgauge steel is used in one or all fram-ing applications (floors, walls, ceilingsand roofs) in approximately 3-4 per-cent of homes currently being built.

Commercial Useof Cold-Formed SteelAnother area that interests the princi-pals of Enertech is the use of cold-formed steel for low-rise commercialconstruction, which typically includesapplications such as schools, assisted

care living facilities, hotels and motels,multiple occupancy residences,

churches and certain types of retailstructures. As an example of this mar-ket, Mike Whitticar cited his companyswork on the recently completed ElizaBryant Center in Cleveland, which isthe first HUD-financed assisted livingfacility to be framed in steel (Figure 5).HUD officials jumped on the lightgauge steel frame bandwagon whenthey became convinced of the materi-als benefits:

Non-combustible framing at a lowerprice than comparable fire-treatedwood framing components.

Commercial sub-trades are familiarwith using steel framing.

With the highest strength-to-weightratio of any building material, steel isconducive to long spans.

Attic sprinklers could be eliminated.

On September 13, 1999, the ElizaBryant Center was officially opened.Whitticar notes that the three-story,52,000 sq ft structure was built bycombining panelization and traditionalstick framing. The framing portion ofthe job, which consumed 212 tons ofcold-formed steel, was completed inapproximately 3-1/2 months, and nosite crane was required.

Fastening productivityis a critical issue

for steel

Figure 3. Volunteers installed the site- fabricated steel frame.

Figure 4. The Habitat for Humanity house was used to demonstrate plasma cutting of light gauge steel.

Figure 5. Clevelands Eliza Bryant Center was framed in cold-formed steel.

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12/28


Key Concepts in Welding Engineering by R. Scott Funderburk

IntroductionThis column is the first of a series thatwill address topics related to filler metalselection. The focus will be on the con-cerns of design engineers, beginningwith filler metal strength. The strengthof weld metal vs. base metals may bedefined as matching, overmatching orundermatching. This column willaddress matching filler metal.

What isMatching Strength?

What is matching strength fillermetal? The AWS A3.0 Standard Welding Terms and Definitions doesnot contain such a term, although ithas been used for years. Matchingstrength, on the surface, would seemto imply that the filler metal will depositweld metal of the exact strength as (ormatching) the base metal. Codeshave tables with lists of matching fillermetals, such as the AWS D1.1Structural Welding Code Steel , Table3.1, as do various filler metal suppli-ers. A careful review of AWS D1.1,

Table 3.1, shows that the matchingelectrodes do not deposit welds withexactly the same strength as the basemetal, and in reality, this is not what ismeant by matching.

In Table 3.1, A36 and A570 Gr. 50 areboth listed in the Group I category.Matching filler metal is shown asboth E60 and E70 electrode andflux/electrode classifications. A36 andA570 Gr. 50 have different minimumspecified yield and tensile strengths,as do E60 and E70 filler metals.Obviously, matching cannot be as sim-ple as matching the base metalstrength (see Table 1).

While AWS D1.1 calls the precedingcombinations matching, clearly theminimum specified weld metal proper-ties are not the same as the minimumspecified base metal properties. Thematching combinations for AWS D1.1,Table 3.1, Group III materials providesome additional insight, where the min-

imum specified filler metal propertiesare more closely matched to the basemetal, and the tensile strength valuesare very similar (see Table 2).

All of the preceding examples areconsidered matching, although thedegree of match is different. The

common element is that the minimumspecified tensile strength of the fillermetal is always the same as or greaterthan the minimum specified tensile

Selecting Filler Metals:Matching Strength Criteria

Table 1. Filler/Base Metal Strength Comparison in AWS D1.1, Table 3.1, Group I.

Base MetalAWS D1.1,Table 3.1,

Group I

Matching Filler Metal

E60, Fy = 48 ksi (330 MPa)Fu = 60 ksi (415 MPa)

Yield,ksi (MPa)

Tensile,ksi (MPa)

A36 36 min.(250)58-80

(400-550)

50 min.(345)

65 min.(450)

Weld is 12 ksi(80 MPa)greater

Weld is 2 ksi(15 MPa) less

Weld is 5 ksi(35 MPa) less



Weld is between2 ksi (15 MPa)

greater to 20 ksi(135 MPa) less

Weld is 22 ksi(150 MPa)

greater

Weld is between12 ksi (80 MPa)greater to 10 ksi(70 MPa) less

A572Gr. 50

Yield Tensile Yield Tensile


Matching tensilestrengths often do not

result in matching yield strengths

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13/28

11Welding Innovation Vol. XVI, No. 2, 1999

strength of the base metal. The com-parison is of the minimum specifiedproperties, not the actual properties ofthe delivered steel, or of the depositedweld metal. Since these are minimumproperties, actual deposited welds onthe actual steel will routinely exceedthose values.

Matching tensile strengths often do notresult in matching yield strengthsbecause the yield-to-tensile ratio formost hot rolled steels is lower than thatof most as-deposited welds. Therefore,a match of both yield and tensilestrength is improbable. However, forhigher strength steels, the yield-to-ten-sile ratio typically approaches the val-ues for welds and provides for a closermatch of both the yield and tensilestrengths. Table 3 shows the averageyield-to-tensile ratio for all the basemetals contained in Groups I and IIIand the corresponding matching fillermetals of the AWS D1.1-98 Code,Table 3.1. The difference between thefiller metal and base metal yield-to-ten-sile ratio is much less of the higherstrength combination (Group III) thanthat of the mild steel combination(Group I) as shown by the percent dif-

ference (% Diff.).

Ultimately, matching compares weldand base metal properties. However,welds are not specified per se; fillermetals are. Thus, tables of matchingproducts typically are called matchingfiller metals, not matching weld metals.

Joints RequiringMatching Filler Metal

The need for matching filler metals isdependent upon joint type and loadingcondition. AWS D1.1, Table 2.3Allowable Stresses in NontubularConnection Welds shows that match-ing filler metal is required for only onecombination of loading and joint type tension loading of CJP groove welds,but is permitted for all other welds andloading conditions. Thus, a simpleconclusion could be to always usematching filler metal. However, thismay preclude better options such asundermatching combinations where

cracking tendencies may be mini-mized. A common misuse of tablesof matching filler metals occurs whenother options are never considered.Particularly for high strength materials(>70 ksi [480 MPa] yield), under-matching filler metals may significantly

reduce cracking tendencies.

Actual vs. MinimumSpecified Properties

The traditional definition of matchingcompares minimum specified proper-ties, not actual properties. For mostapplications, this has proven to beadequate, even though, based onactual properties of either the basemetal or the weld, the weld may be the

lower strength element. For example,A572 Gr. 50 with matching strengthE70 filler metal may have matching,undermatching or overmatching rela-tionships, based on actual properties.

In theory, specified service loadswould be limited to some percentageof the minimum specified yield or ten-

Table 2. Filler/Base Metal Strength Comparison in AWS D1.1, Table 3.1, Group III.

Table 3. Varying yield-to-tensile ratios prevent matching both the yield and tensile strengths (data from AWS D1.1-98, Table 3.1).

*Based on minimum specified values

Base MetalAWS D1.1,Table 3.1,

Group III

Base Metals

Avg.Fy/Fu*

Group I(mild steel)

Group III(higher strength)

.62

.80

E60

E70

E80 .85 6%

.83 25%

.80 22%

Weld Fy/Fu* % Diff

Matching Filler Metals

Matching Filler Metal


Yield,ksi (MPa)

A572 Gr. 65

A913 Gr. 60

65 min. (450) 80 min. (550)

60 min. (415) 75 min. (520)

Tensile,ksi (MPa) Yield Strength

Weld is 3 ksi(20 MPa) greater Weld is equivalent

Weld is 8 ksi(55 MPa) greater

Weld is 5 ksi(30 MPa) greater

Tensile Strength

A common misuse oftables of matching

filler metals occurswhen other options are

never considered

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14/28


sile strength. If this were the case, theweaker component in the systemwould not limit the design even at themaximum design load.

This is not necessarily the case forwelded components that are expectedto be loaded into the inelastic range.Examples would include componentsin buildings subject to inelastic (plastic)deformations in large earthquakes, androll-over protection devices on con-struction equipment. Under thesesevere loading conditions where yield-ing is expected, it is preferred that suchdeformations be distributed throughoutthe base metal, and therefore, theundermatching combination shown in

Table 4 may be unacceptable. Furtherdefinition of matching properties as afunction of the actual materials may benecessary.

It is sometimes desirable to evaluateactual, or typical, properties of basemetals and filler metals. For example,an electrode classified as an E70(such as E71T-1) may also meet E80

requirements. For an applicationwhere E80 is required, the E70 prod-uct could be used, providing there isadequate assurance that the deposit-ed weld metal will still deliver E80

properties given variability in the pro-duction of the filler metal, as well asdifferences in procedures.

The yield and tensile strength proper-ties for the base and weld metal are alldetermined by standard tensile testcoupons, uniaxially loaded, slowlystrained, smooth specimens. Underdifferent conditions of loading, andwith different geometries, thesemechanical properties will vary, gener-ally resulting in higher yield and tensilestrengths and reduced ductility.

ConclusionMatching strength is not formallydefined by AWS. However, theaccepted interpretation is that the fillermetal tensile strength will be equal toor greater than that of the base metal.The need for matching filler metal isdependent upon the joint type andloading condition, and it is generallyrequired for CJP groove welds in ten-sion applications. Matching can beused for most applications, but insome cases, it may not be the mosteconomical or conservative choice.

For high strengthmaterialsunder-

matching filler metalsmay reduce cracking

tendencies

Table 4. Matching (M), Undermatching (U) and Overmatching (O) tensile strength combinations for A572 Gr. 50 with E70 filler metal.

Base Metal - A572 Gr. 50

E70 Filler Metal - Strength Levels

Min. - 65 ksi (450 MPa)

Med. - 80 ksi (550 MPa)

High - 90 ksi (620 MPa)

M

U

U

O

M

U

O

O

M

S t r e n g t h

Minimum70 ksi (480 MPa)

Medium80 ksi (550 MPa)

High90 ksi (620 MPa)

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15/28


In addition to the following awards to undergraduate and graduate students,The James F. Lincoln Arc Welding Foundation also provided grants of $250 to the following universities in recognition of each Best of Program, Gold,Silver, or Bronze Award received by students of that university:

Prof. Thomas Conry University of Illinois atUrbana-Champaign

Prof. James D. McBrayerUniversity of Central Florida

Prof. James RiclesLehigh University

Donald N. ZwiepChairman of the Jury Chairman, The James F. Lincoln Arc Welding Foundation

Charles J. Bersback Erich M. McCoy Ken Schmidt Roark Wolfe

Jacob J. LoverichCollege of Engineering & Technology Northern Arizona University Faculty: David Hartman

JURY OF AWARDS

Golf Swing Tracking System Algis BaliunasDavid LederMichael LeeGeneral Engineering Dept.University of IllinoisFaculty: James Carnahan

Design of a Picosatellite Theresa KuhlmanDina HadiMechanical Engineering Santa Clara University Faculty: Tim Hight

WPI Parking Structure DesignBrendan FitzPatrick Michael PockoskiCivil Engineering Dept. Worcester Polytechnic InstituteFaculty: Leonard Albano & Robert DAndrea

$2,000

UNDERGRADUATE DIVISION

$1,000

$750 Each

Santa Clara University Stanford University University of Connecticut

University of Illinois University of Northern ArizonaWorcester Polytechnic Institute

Off-Road Mobility Vehicle for the Disabled

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AC-R Servicing Manifold DesignGautam BaksiEverett HafenrichterNathan Searcy Mechanical & Industrial Engineering Dept.University of IllinoisFaculty: J.W. Nowak

Economic Insulation Choice for a Warehouse Shane Cisco

Gina Woloszyn Joseph WoolumsGeneral Engineering Dept.University of IllinoisFaculty: Ramavarapu S. Sreenivas

The Burnt Bagel Conundrum Jeffrey Chow Michael Gredlics Andrew McGrathMechanical & Industrial Engineering DUniversity of Wyoming Faculty: David Walrath

PMI System for Characterization of Load

Resisting Structures Emily J. Pryputniewicz Mechanical Engineering Dept. Worcester Polytechnic InstituteFaculty: Ryszard J. Pryputniewicz

1999 Mini Baja Shaun Fought Benjamin C. RubensonMark L. AndersonRyan WellmanMechanical Engineering Dept.Santa Clara University Faculty: Tim Hight

Design of an Underwater Remotely Operated Vehicle Aaron B. Weast Tevor D. Wigle William B. Perkins Jason F. Cook Mechanical Engineering Dept.Santa Clara University Faculty: Jeff Ota

Design of a Mini-Baja Vehcile: ACustomer-Driven Approach Brent D. ZollingerMechanical Engineering Dept.Brigham Young University Faculty: Robert Todd

Thermal Redesign of a Low Voltage Outdoor Halogen FloodlampPaul DynowskiPaul Kawka James NonnenmannMechanical & Industrial Engineering Dept.University of IllinoisFaculty: J.W. Nowak

Ball Mountain Dam Access Bridge

Jacob Argiro Jennifer CopponiChristina WatsonGeneral Engineering Dept. Worcester Polytechnic InstituteFaculty: Leonard D. Albano

A Rotational Molding Machine Benjamin S. SheenMechanical Engineering Dept.University of Wyoming Faculty: David Walrath

Point-to-Point Wireless Network Link Antenna Positioner Sothy Chhe Alexander JassoPatrick KimMatthew Lee SchwallMechanical Engineering Dept.Stanford University Faculty: Drew Nelson

Failure Analysis of Cracks in Small Diameter Taps Melody Langeneckert Dave Lash Jason PelchMechanical & Industrial Engineering Dept.University of IllinoisFaculty: J.W. Nowak

Machine Design for the Treatment & Prevention of Shin Splints David A. Brady Thomas A. ToyeKenneth J. Tardif Mechanical & Industrial Engineering Dept.University of Massachusetts - Amherst Faculty: David Kazmer

Overload Clutch Mechanism for

AC-Powered Drills Simon Beland Dante CantieriCezar VelascoLorena SolorzanoDennis OdulioMechanical Engineering Dept.University of Illinois-ChicagoFaculty: Foster

Redesign of Spray Profile Test OperatMae Lee Chung Christy ClausKevin KellerMichael Stock General Engineering Dept.University of IllinoisFaculty: Henrique Reis

Redesign of a Compressed Air LoopDavid Grover Jason Oliva Chris RasMechanical & Industrial Engineering DUniversity of IllinoisFaculty: J.W. Nowak

Design of a Piano Maintenance Time Jeff Ernst John WhittenhallRobert ZellerMechanical & Industrial Engineering DUniversity of IllinoisFaculty: J.W. Nowak

Gearmotor Noise Test & EvaluationKevin BollmanDavid HinkleLeo Wrigley General Engineering Dept.University of IllinoisFaculty: Henrique Reis

$250 Each

$500 Each


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17/28


Innovative Composite Crutch Dorota Shortell Jeff Kucer W. Lawrence Neeley Mechanical Engineering Dept.Stanford University Faculty: Mark Cutkosky

Parallel Parking Assistive SystemCasey P. Hare Jeremy T. Dabrowiak Kendra J. Cermak Mechanical Engineering Dept.Stanford University Faculty: Mark Cutkosky

An Implement Hitching System for the Controlled Traffic Farming System Andrew J. Holtz Bioresource & Agricultural Engineering Dept.

California Polytechnic State University Faculty: Andrew Holtz

Mercury-Free Oven Control SystemTim Jager Yi Tang Jayson ValluzziMechanical & Industrial Engineering Dept.University of IllinoisFaculty: J.W. Nowak

Warehouse Layout OptimizationNathan Kennedy Joseph Lambert James LutgenGeneral Engineering Dept.University of IllinoisFaculty: R.S. Sreenivas

Mensical Repair Device-Delivery SystemTodd W. JenkinsScott D. Kennedy Carlos Marron

Mechanical Engineering Dept.Santa Clara University Faculty: Tim Hight

Failure Analysis of Bus Leaf Springs David HoppColin Horn John Frana Mechanical & Industrial Engineering Dept.University of IllinoisFaculty: J.W. Nowak

$250 Each

$2,000

$1,000

GRADUATE DIVISION


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18/28


Shift Simulator Design Document Christopher R. Carlson Wendy Cheng Juli SatohNeeta Verma Mechanical Engineering Dept.Stanford University Faculty: Mark Cutkosky

Laser Methodologies for Characterizing Behavior of MEMS

Gordon C. BrownMechanical Engineering Dept. Worcester Polytechnic InstituteFaculty: Ryszard J. Pryputniewicz

Relaxation in High-Strength Bolted Connections Using Galvanized Steel Jun Yang Civil Engineering Dept.University of Connecticut Faculty: John T. DeWolf

Inspection Device for Detecting Contaminated Blades David CavazosSekou Crawford Mike EodiceMechanical Engineering Dept.Stanford University Faculty: Mark Cutkosky

Automatic Door Project Kevin R. KopczynskiHuck B. DornDerek S. PaiMechanical Engineering Dept.Stanford University Faculty: Mark Cutkosky

$750 Each

$500 Each

$250 Each

GRADUATE DIVISION

FlexRim Low Impact Wheelchair Pushrim W. Mark RichterMechanical Engineering Dept.Stanford University Faculty: Larry Leifer

Seismic Rehabilitation of Pre-Northridge Steel Moment Connection with Welded Haunch Qi-Song YuStructural Engineering Dept.University of California, San DiegoFaculty: Chia-Ming Uang

Valve Timing by Means of a Rotary Actuator Pete FitsosMechanical Engineering Dept.California State University, SacramentoFaculty: Joe Harralson

Power Extendable Towing Motors Adam C. Gold Eric C. OlsonChristopher Van Wert Michael A. PradosMechanical Engineering Dept.Stanford University Faculty: Mark Cutkosky

Master Stress-Strain Curves for Adhe Jianmin YouMechanical Engineering Dept.University of Maryland Faculty: Pedro Albrecht

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Use Caution When SpecifyingSeal WeldsPractical Ideas for the Design Professional by Duane K. Miller, Sc.D., P.E.

Design File

IntroductionWhat is a seal weld? AWS A3.0, Standard Welding Terms and Definitions , defines a seal weld as: Any welddesigned primarily to provide a specific degree of tight-ness against leakage. The purpose of a seal weld maybe to contain a fluid either gaseous or liquid. In themechanical and structural fields, seal welds are used mostoften not to prevent leakage out of a container, but to pre-vent entry of a fluid into a space where some type ofharmful behavior, often corrosion, is expected to occur. Inthese fields, seal welds are frequently used to precludemoisture and oxygen-laden air and water from enteringthat cavity.

Seal welds may be specified on parts to be galvanized toprohibit pickling acids and/or liquid zinc from entering into aspecific region. For architecturally exposed steel that is tobe painted, seal welds may be specified to prevent unsight-ly rust bleeding. Seal welds may be required for someapplications where the sealed joint is more conducive tocleanup than an exposed joint would be. Food processingfacilities are one such example.

The characteristic common to all of the aforementionedexamples of seal welds is as follows: none of them areplaced for traditional strength-related reasons, and for this

reason, caution should be exhibited when seal welds arespecified. In some cases, the application of a seal weldmay result in a conflict of code requirements. In others,the seal weld may perform structural functions that wereunintended, resulting in undesirable load paths. Sealwelds may affect inspection practices, in particular, theinterpretation of ultrasonic inspection results. Finally, sealwelds may be treated in a casual manner by thoseresponsible for making them, resulting in weld qualityproblems. Each of these examples will be examined, aswill be some issues related to galvanizing that need to beconsidered as well.

Code ConflictsA common inquiry is as follows:

The drawings call for seal weld, but in order for me tocomply with that requirement, I need to violate AWS D1.1-98 , Section 2.4.7.5. What should I do?

The specific code provision cited is the one that calls forthe interruption of welds which occur on opposite sides ofa common plane, and under these conditions, the weldsare required to be interrupted at the corner (Figure 1).This provision has a practical foundation: it is difficult tomake a continuous weld in these conditions, and the prob-ability of undercutting the corners is great when the weldsare made continuous. This is one problem associated withseal welds when applied to these situations.

Figure 1.

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Other code provisions can be violated, including AWS D1.1 , Section 2.4.7.3, which addresses flexible connec-tions that rely on the flexibility of the outstanding leg ofangles (Figure 2). Examples would include framing angles,top angles of seated beam connections, and simple endplate connections. A seal weld around a flexible connec-tion reduces such flexibility and may change the overallbehavior that is expected.

AWS D1.1 , Section 2.4.7.4, calls for welds on stiffeners tobe cut short not less than 4 times, nor more than 6 times,the thickness of the web from the weld toe of the web-to-flange welds (Figure 3). This provision was incorporated toprovide for a degree of flexibility in this region. Previous

experience in shipping had shown this to be an area thatwas prone to cracking when the weld extended too far.Seal welds applied to this area effectively preclude suchflexibility.

The designer who calls for a seal weld should review thesecode provisions if the project is governed by the D1.1

code, and in the situations where the code is not applica-ble, examine these principles and determine their relativesuitability to the components where seal welding has beenutilized. To handle the issue of consistency between jobspecifications and code requirements, the engineer canaddress how these issues are to be resolved in the projectspecifications. The preceding list of code examples is illus-trative only, and may not be comprehensive in its coverageof issues where seal welding requirements may violatecode provisions.

Alternate Load PathsThe second major series of problems associated with sealwelds involves those applications where unintended loadpaths are created. For example, a lapped connection maybe joined by bolts with no welds expected at all. However,a seal weld is specified around the connection. AWS D1.1 ,Section 2.6.3, may be applicable in this situation. In bear-ing connections, the code does not allow bolts and weldsto share the load. Of course, in this particular situation, thedesigner would probably not consider the seal welds asmembers that would share loads with welds, but in fact,they will. The seal welds would be small in size and proba-bly incapable of transmitting the applied loads by them-selves. In actual service, the first thing that would happenwould be for the welds to fracture, violating the purpose ofthe seal weld, before the bolts would load up and carry thetransferred forces.

The welding adage, There are no secondary members inwelded design, is applicable when considering seal welds.An example arose several years ago where a tub-type rockcrusher had been designed with a series of stiffeners. Thedetailing had been carefully thought through so as to avoidstress risers. A stainless steel nameplate was to beapplied to the unit, and a seal weld was called for to attachthis nameplate. The entire unit received a special, multi-

coat paint system to preclude corrosion, and the seal weldensured that the material under the stainless steel name-plate would not be exposed to the elements. The name-plate was put into a high stress region, and whether

Figure 2.

Figure 3.

4tw L 6twwhere,

L = length of unwelded stiffener

tw = weld thickness

18 Welding Innovation Vol. XVI, No. 2, 1999 Return to TOC


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intended or not by the designer, the nameplate becamepart of the load bearing system, and the weld introducedresidual stresses as well.

The seal weld around the nameplate became the design-limiting fatigue detail that resulted in crack initiation in serv-ice. The intention of the designer was circumvented by an

ill-conceived plan for a seal weld around a nameplate. Inthis particular example, any weld (including an intermittentweld) may have created a poor fatigue detail.

Casual Treatment of Seal WeldsThe minimum heat input requirements imposed by AWS D1.1 may be violated when the seal weld is made. Table5.8 of that code prescribes certain minimum sizes of weldsthat must be maintained, regardless of the level of loading,in order to ensure that adequate heat input is achievedwhen the weld is made. The size of the seal weld may notbe specified, resulting in a weld that would otherwise bedisallowed by Table 5.8. It is still important that good weld-ing practices be followed when seal welds are made,including adherence to the minimum fillet weld size.Failure to do so may result in weld cracking or incompletefusion defects.

The welder who is charged with the responsibility of mak-ing a seal weld may approach it in a very casual manner,as might the welders supervisor. The welder should havethe same qualifications as the welder charged with theresponsibility for making a similar weld that would have astructural purpose. The welding procedures, including theselection of the electrode and the required preheat level,

are deserving of the same attention as a weld that trans-fers calculated loads. The claim It is only a seal weld isoften a prescription for problems.

Inspection IssuesThe presence of seal welds around steel backing that isleft in place after welding may have implications for theultrasonic testing (UT) of such connections. ConsiderFigure 4 in which a CJP groove weld with steel backing isinspected with UT. An alternate sound path is createdwhen the seal welds are placed around the left-in-placebacking. Such implications should be understood beforeinspection begins.

If backing is to be seal welded to the base material, thenone may consider making the backing a little wider (Figure 5).With the seal welds further from welded joint, the UT soundwaves will have a better opportunity to see the root withoutsecondary reflections through the seal welds.

Galvanizing IssuesOne of the more common applications for seal welds is inassemblies that are required to be hot dip galvanized(Figure 6). The American Galvanizers Association (AGA)defines three classes for welded assemblies that will begalvanized. Class 1 Joints are held together by a full sealweld. Class 2 Joints are held together by seal welds, butthe overlapped area is large enough to require venting, i.e.,provision of an escape hole for the release of expanding

trapped gases. Class 3 Joint details do not contain sealwelds.Figure 4.

Figure 5.

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AGA documents require a vent to be provided wheneverthe overlapping area exceeds 16 in 2 (100 cm 2). Specificdiameters of the holes and locations are also spelled out.Thus, a Class 1 detail is only applicable for an overlappedarea of 16 in 2 (100 cm 2) or less. Class 1 represents thehighest degree of corrosion protection that is attainable,and while Class 2 is not quite equal to Class 1, it is possi-

ble to plug the vent hole after galvanizing to upgrade aClass 2 to Class 1.

Class 3 details provide a degree of corrosion protectionthat meets or exceeds the protection provided by mostindustrial coatings. It is noted that the unsealed overlapsfrom Class 2 and 3 details may stain the surface of thecoating, or steaming from unsealed overlaps may result inslight bare spots along the line of the exhaust.

Special caution is noted for Class 1 seal applicationsbecause porosity may result in an explosion as trappedliquid-acid vaporizes and expands when the part is dippedinto the hot zinc. Venting minimizes that concern.

This edition of Design File is not intended to be a treatiseon galvanizing and preferred details for corrosion resist-ance. However, it does identify concerns that are associat-ed with seal welding and the galvanizing practice. The useris encouraged to review AGA documents in this regard.The American Galvanizers Association can be contactedthrough their website at www.galvanizeit.org, or by phone at(800) 468-7732.

ConclusionsSeal welds can perform an important function both in con-taining fluids, and in precluding the entry of fluids intoregions where harmful effects can result. However, sealwelds also can unintentionally cause differences in the struc-tural behavior of the attached members, and the designershould be aware of these potential interactions. The weldingpractices employed when seal welds are made should notbe any different than those associated with welds that aredesigned to carry loads. When seal welds are applied togalvanized assemblies, caution should be taken to makesure that venting is appropriate, and for Class 1 Joints wherevents are not required, that the weld is porosity-free so that

no seepage is experienced. Once seal welds have beencarefully thought through, the designer needs to clearly com-municate in the job specifications how the fabricator is todeal with code restrictions which may specify practices thatare inconsistent with seal welding.

Figure 6.

Figure 7.

Figure 8.

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Lincoln Electric Professional Programs


Opportunities

Fracture & Fatigue Control in Structures:Applications of Fracture MechanicsOctober 31 November 2, 2000Fracture mechanics has become the primary approach to analyzing and controlling britfractures and fatigue failures in structures. This course will focus on engineering appliusing actual case studies. Guest seminar leaders: Dr. John Barsom and Dr. Stan RolfeCEUs. Fee: $595.

Space is limited, so register early to avoid disappointment. For full details, visit our wat www.lincolnelectric.com/services/educate/educate.asp, call 216/383-2240, or write toRegistrar, Professional Programs, The Lincoln Electric Company, 22801 Saint Clair AvCleveland, OH 44117-1199.

Production WeldingBasic May 9-11, 2000

Advanced September 19-21, 2000Each section of Production Welding is a 3-day program conducteLincoln Electrics staff of expert welding engineers. The Basic includes: arc welding processes and procedures; arc blow and prgrounding; wire feeding techniques; distortion; destructive testinsafety; and more. The Advanced curriculum includes: pulse GMtandem GMAW; twin and tandem SAW; aluminum welding; stasteel welding; surface tension transfer (STT); robotic welding; wform development; nondestructive testing; and more. 2.0 CEUsFee: $395.

Blodgetts Design of Steel StructuresMarch 7-9, 2000October 24-26, 2000Blodgetts Design of Steel Structures is an intensive 3-day program that addresses metof reducing costs, improving appearance and function, and conserving material througefficient use of welded steel in a broad range of structural applications. Seminar leadeOmer W. Blodgett, Duane K. Miller, and R. Scott Funderburk. 2.0 CEUs. Fee: $595.

Blodgetts Design of Steel Weldments April 11-13, 2000September 12-14, 2000Blodgetts Design of Steel Weldments is an intensive 3-day program for those concern with manufacturing machine tools, construction, transportation, material handling, andcultural equipment, as well as manufactured metal products of all types. Seminar leadOmer W. Blodgett, Duane K. Miller, and R. Scott Funderburk. 2.0 CEUs. Fee: $595.

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It was evident from the projects incep-tion that the Colonial Stadium, current-ly under construction in Melbourne,Australia, would be a challenging fabri-cation project due to the structuresdesign. The stadium will feature aretractable roof that will fully open andclose in just twenty minutes. AlfasiConstruction was awarded the job inJanuary 1998 by BaulderstoneHornibrook for the fabrication of thestadiums steel structure. This incorpo-rated more than 5,000 tonnes of steel-work, including major tubular trusseswith lengths up to 220 m (722 ft).

As the project progressed, severalcommon construction issues wereaddressed. From this experience, thefollowing lessons were learned:

Materials with higher strength andalloy content are weldable, but atten-tion to details such as hydrogen and

preheat control are essential.

Tubular construction requiresextremely close fit-up and tolerancecontrol.

Pre-production planning and trainingpays big dividends.

Main Roof ChordsThe steel (European EN1021O) sup-plied for the construction of the mainroof chords is a newly developed 460MPa (65 ksi) micro-alloyed high-strength steel for structural use. Theweld fabrication required special treat-ment to ensure that the high strengthcharacteristics of the steel would befully utilized.

As Terry Phelan, general manager ofAlfasi Construction explained, I wasconfident of our ability to handle the

fabrication of the projects steelwork.We fabricated the complex compo-nents used in Sydneys Olympic railstation and Melbournes new Museum,so we knew what we were in for.

The higher alloy content and thickersections of the main support beams(up to 58 mm [2.3 in]) required that

close attention be paid to three mainelements: the selection of the correctwelding consumable; the developmentof realistic and reproducible weldingprocedures; and a focus on welderskills to ensure quality throughout. Itwas clear that the project schedulewould not allow time for delays or re-work. In effect, we had to get it rightfrom the very first joint, said Phelan.

Aware that accurate fabrication isdependent on good preparation, Alfasipurchased a Maruhide CNC controlledtube profiler. Since some of the mostcostly and time critical elements oftubular construction are the prepara-

Challenging Stadium ProjectHeaded for On-time CompletionBy Peter LawlorSouthern Regional Manager

Lincoln Electric AustraliaVictoria, Australia

Figure 1. Installation of a section of the retractable roof.

Welding the mainbeams involved careful

control of preheatand heat input

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tion, fit-up and tolerances of the tubu-lar members, this step was essential.This machine is capable of plasmacutting complex profiles in tubularmembers up to 12 m (39 ft) in lengthand with a 60 mm (2 1/2 in) wall thick-ness, and is the only one of its kind in

South Eastern Australia. Throughoutthe project, this unit was used to cutand prepare complex weld profiles onmost of the tubular sections.

Although there was an assortment ofwelded joint configurations, there werethree main types of joints to be consid-ered:

Grade 460 MPa (65 ksi) steelto 460 MPa (65 ksi), for the mainchords;

Grade 460 MPa (65 ksi) steel toGrade 350 MPa (50 ksi) steel, forconnections to the main supportframe; and

Grade 350 MPa (50 ksi) to Grade350 MPa (50 ksi) steel, for generalconnections and supports.

Matching the WeldMetal PropertiesThe governing code for the construc-tion of the beams was AS1554 Part 1.However, the higher alloy content ofthe steel (carbon equivalent of 0.63-

0.68) meant the construction specifica-tion required further clarification toensure optimum strength and qualitywere achieved. For instance, care wastaken to ensure weld metal propertiesclosely matched the parent plate andweldments returned heat affectedzone hardness of less than 300HV.

In order to meet the high strength prop-erties of the tubular steel (minimumspecified yield strength of 460 MPa [65ksi] and minimum ultimate tensilestrength of 560 MPa [80 ksi]), as wellas meet the minimum specified CharpyV-Notch impact properties, while main-taining low hydrogen values, an E81T1-Ni1 (Outershield 81Ni1-H) gas shielded

flux cored electrode was used to jointhe main chords. Straight lengths were

joined by a submerged arc combinationof F7A6-EM14K-H8 (LA71 electrodewith 880M flux).

Initial weld tests indicated that the 460

MPa (65 ksi) steel was prone to highheat-affected zone hardness if preheatand welding heat input requirementswere not followed. To ensure that oper-ators were aware of the importance ofthese factors, additional training wasprovided to the construction crew toexplain the correct handling of thesteel and the importance of followingthe proper welding protocol. The mini-mum preheat temperature for each

joint (varied between 125C [250F]and 225C [440F] depending on thespecific joint details) was maintainedand monitored using electric heatblankets. It was this pre-productionplanning and training that enabled theconstruction to move along at such anefficient pace.

Achieving DesiredMechanical Properties

Welding the main beams involvedcareful control of preheat and heatinput to achieve good mechanicalproperties. The welding of the highstrength 460 MPa (65 ksi) steel to350 MPa (50 ksi) steel created a fewproblems.

As Merril Degee, workshop foreman ofAlfasis Dandenong facility explained,The welding of the 460 to 460 jointswas relatively straight-forward once wedetermined the effect of preheat andheat input on joint strength and hard-

ness values. However, providing forelasticity and a smooth transition ofstrengths between the 460 MPa and350 grade material wasnt so easy.When I first went to do a procedurefor a T type joint made up of a Grade

Figure 2. Shop fabrication of some of the large tubular trusses used in the Colonial Stadium.

The governing coderecommended that HAZ

hardness values bekept below 350 HV

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The end result was a joint with goodflexibility, strength and low hydrogencontents. The welders liked using theelectrode. For joining the Grade 350steel we used a GMAW ER70S-4electrode (L54) and an FCAW-g E71T-1 electrode (Outershield 71M).

Currently, (the project is 85% com-plete) were a little ahead of schedule.Its obvious now that without the earlyfocus on welding processes, proce-dures and electrode selection wewouldnt be in this position, saidDegee.

Over 5,000 tonnes of steel have beenprocessed so far, using more than 6tonnes of electrode with very few welddefects.

Construction LogisticsGiven the considerable size of someof the weldments, distortion was apotential problem. However, with care-ful fixture building and continuousmonitoring of dimensions during fabri-cation, distortion was kept to a mini-mum. The main chords werefabricated in Alfasis Dandenong work-

shop in lengths up to 40 m (130 ft),then transported to the site where theywere joined using field welding proce-dures.

Engine driven welders and portablewire feeders were used to complete

the final field welds on the main truss-es. Small site tents were erected toensure that preheat and gas shieldingwould not be affected by the elements.

For joining the Grade 350 steel toitself, an all-position E71T-8J self-shielding electrode (InnershieldNR203MP) was used.

ConclusionTerry Phelan summed up the currentstatus of the Colonial Stadium as fol-lows: Weve just passed a landmarkproject date on schedule. Most of thesteelwork has been fabricated and itsnow a matter of lifting and fixing sec-tions into place. Its a tight schedule, butwere meeting it thanks to dedicatedstaff and the support of major suppliers.You need that type of partnership whenthe pressure is on.

Editors Note: The A$460 million (US$293 million) stadium is scheduled to be completed by February 2000. It will have 52,000 fixed seats,plus retractable seating on the lower tier that will allow the stadium to be reconfigured to suit a wide variety of needs. It will be primarily a venue for Australian Football League (soccer) games and other sporting events. However, an advanced acoustic design and audio system will make it suitable for music concerts as well.Selected seats will be equipped with individual touchscreen video units. More information on the stadium can be obtained online at www.docklandstadium.com.au.

350 vertical plate with a 460 cap, Iused a standard E71T-1 electrode,which did not meet the bend testacceptance criteria. Therefore, it wasdetermined that a different electrodewas required.

An electrode with a controlled hydro-gen content was selected for these

joints (Outershield 71C-H) to meet thetesting criteria. The electrode, whichmeets the E71T-1 classification, was

designed to meet 5 ml (max) of hydro-gen per 100 grams of weld metal.The new welding procedure withOS71C-H and careful bead placementgave excellent results. The moderateyield and tensile strength of the weldmetal gave a smooth transitionbetween the Grade 350 steel and thehigh strength Grade 460 steel.

Figure 3. After field welding, a tubular truss awaits installation as part of the retractable roof assembly.

The new weldingprocedure with

Outershield 71C-H andcareful bead placementgave excellent results

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http://www.docklandstadium.com.au/http://www.docklandstadium.com.au/


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Welding Innovation Vol. XVI, No. 2, 1999 25 Return to TOC


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P.O. Box 17035Cleveland, Ohio 44117-0035

TheJames F. LincolnArc WeldingFoundation

NON-PROFIT ORG.U.S. POSTAGE

PAIDJAMES F. LINCOLN

ARC WELDING FND.

Volunteers erected the steel frame for this Habitat for Humanity house in less than three days. See story

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