A publication of the James F. Lincoln Arc Welding Foundation

The James F. Lincoln Arc Welding Foundation cele-brates its 65th birthday this year. Far from preparing toretire, the Foundation is actually reinvigorated with anew sense of purpose and energy. We remain the onlyorganization in the United States solely devoted toeducating the public about the art and science of arcwelding. Now, with the aid of electronic technologyand the Internet, we are poised to take a major stepinto the international arena by sponsoring a newJames F. Lincoln Arc Welding Foundation web site.Development work is already underway. Until the new,independent site is up and running, information aboutcurrent Foundation activities is available on the LincolnElectric web site: www.lincolnelectric.comWhen I had my first contact with the Foundation in the1950s, I would hardly have imagined the organizationand its programs going online! Neither the word northe concept existed. Many technological advanceshave been made since that time, but as we contem-plate the challenges of the future, perhaps we shouldalso review our history.Born in the depths of the Great Depression, theFoundation was the idea of its namesake, James F.Lincoln, whose innovative approach to industrial man-agement eventually led The Lincoln Electric Companyto world prominence in the arc welding field. The origi-nal Deed of Trust stated: The object and purpose ofsuch fund and foundation is to encourage and stimulate scientific interest in the development of thearc welding industry and to that end to provide forawards to those persons who by reason of the excel-lence of their papers upon said subject may be selected as the most worthy to receive such awards.The first award, granted in 1936, was for $5,000, anamount about equivalent to the Nobel Prize of that day.Over the last six-and-a-half decades, the individualcash awards granted by the Foundation have rangedfrom a $50 Merit Award in the School/Shop Program toa $25,000 Best of Program Award in the ProfessionalProgram. Literally thousands of students and engi-neers have benefited from participating in the awardprogram.The value of the program to the welding industry hasbeen, if anything, even greater than the sum of itsimportance to individuals, however. Early on, theTrustees of the Foundation realized the importance of

A Foundation for Progress

collecting and publishing the discoveries of those whohad entered their arc welding projects in the competi-tion. The first book, Arc Welding in Design,Manufacture and Construction, ran to 1,402 pages andwhen it was published in 1939, sold for $1.50, postageincluded! The value of the knowledge that has beenshared from the dissemination of this information overthe years is incalculable. We continue to publish awardwinning papers in this magazine today (including thecover story of this issue).In 1948, the Engineering Student Design Competitionwas initiated. Since I have spent most of my career inacademia, I will admit that this program is very close tomy heart. In fact, it was in 1956 when I was a youngassistant professor at Colorado State University that Ifirst learned of the Foundation, and the college awardsserved as my introduction. I have more fully describedthe programs background, objectives and significance inan article on page 13 of this issue, entitled A UniqueMechanism for Enhancing Engineering Education.As we take The James F. Lincoln Arc WeldingFoundation into cyberspace to support a new, interna-tional level of programming, President Roy Morrow,Executive Director Duane Miller and I are focused onthe standards of excellence that have always definedthis organization. We look forward to receiving andresponding to your feedback on our award programs,book publication activities and, of course, WeldingInnovation.

Donald N. ZwiepChairman, The James F. Lincoln Arc Welding Foundation

Australia and New ZealandRaymond K. RyanPhone: 61-2-4862-3839Fax: 61-2-4862-3840

CroatiaProf. Dr. Slobodan KraljPhone: 385-1-61-68-222Fax: 385-1-61-56-940

RussiaDr. Vladimir P. YatsenkoPhone: 077-095-737-62-83Fax: 077-093-737-62-87

INTERNATIONAL SECRETARIES

1Welding Innovation Vol. XVIII, No. 2, 2001

Cover: Welded trusses like this one support the retractable roof of Seattlesnew Safeco Field stadium.

The serviceability of a prod-uct or structure utilizing thetype of information present-ed herein is, and must be,the sole responsibility of thebuilder/user. Many vari-ables beyond the control ofThe James F. Lincoln ArcWelding Foundation or TheLincoln Electric Companyaffect the results obtainedin applying this type of infor-mation. These variablesinclude, but are not limitedto, welding procedure, platechemistry and temperature,weldment design, fabrica-tion methods, and servicerequirements.

Volume XVIIINumber 2, 2001

EditorDuane K. Miller,

Sc.D., P.E.

Assistant EditorR. Scott Funderburk, P.E.

The James F. Lincoln Arc Welding Foundation

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

Features

Departments

8 Lessons Learned in the Field: Persistence Pays OffContributor D.R. Lawrence of Butler Manufacturing Co. shares the lessons he learned while developing a WPS for fabricating the roof beams of a metal factory building.

10 Opportunities: Lincoln Electric Professional Programs

11 Key Concepts: Selecting Electrodes for Stress Relieved Applications

16 Design File: Mixing Welds and Bolts, Part 1

2 Out-of-Plane Fatigue Cracking in Welded Steel BridgesResearchers review the causes of cracking, outline the evolution of AASHTO specs for connection plate design details, and discuss methods of repair.

13 A Unique Mechanism for Enhancing Engineering EducationParticipating in award programs gives engineering students an edge in preparing for their careers; faculty involvement is the key to success.

19 Tri-Chord Roof Trusses Enhance Safeco FieldModern arc welding enabled the design and construction of the spectacular tri-chord roof trusses featured in Seattles new stadium.

THE JAMES F. LINCOLN ARC WELDING FOUNDATION

Dr. Donald N. Zwiep, ChairmanOrange City, Iowa

John Twyble, TrusteeMosman, NSW, Australia

Roy L. MorrowPresident

Duane K. Miller, Sc.D., P.E.Executive Director & Trustee

R. Scott Funderburk, P.E.Secretary

2 Welding Innovation Vol. XVIII, No. 2, 2001

Out-of-Plane Fatigue Cracking in Welded Steel BridgesWhy It Happened and How It Can Be Repaired

By W. M. Kim RoddisProfessor, Ph.D., and P.E.

Yuan ZhaoGraduate Research AssistantDepartment of Civil and Environmental EngineeringUniversity of KansasLawrence, KS

BackgroundThe Interstate construction boom fromthe late 1950s through the 1970s builtmany of the steel highway bridges cur-rently in service in the United States.However, due to the lack of in-depthresearch on the fatigue performance

of both the structural components andthe connection details, a large portionof the bridges constructed during thatera have developed fatigue cracks inservice. Often, welded bridge detailsare more susceptible to fatigue crack-ing than bolted or riveted ones.Discontinuities in the welds form crackinitiation sites at imperfections such as

entrapped porosity, lack of fusion orpenetration, or incomplete removal ofslag. Fractures can also initiate fromgeometrical stress risers, such as filletweld toes. Subsequent crack propa-gation would occur if the surroundingmaterial is exposed to a cyclic tensilestress field. Unfavorable residualstresses can exacerbate the alreadysevere condition of stress concentra-tion and accelerate the process offatigue crack propagation in theselocalized regions. Since attachedplates are fused together by welding, a continuous path is provided for crackgrowth from one plate to another. Ofthe various crack types observed inwelded steel bridges, those caused by out-of-plane distortion have beenrecognized as the largest category offatigue cracking nationwide [Fisherand Menzemer, 1990].

Out-of-Plane DistortionOut-of-plane fatigue cracking occursmostly at locations where transversestructural components such as floor-beams, diaphragms, or cross-framesare framed into longitudinal girdersthrough connection plates. Before andduring the early 1980s, the connectionplate detail was designed by followingthe early European practice of notwelding to the girder tension flange toavoid having a category C fatiguedetail. Sometimes the connectionplate was not attached to the com-pression flange, either. However, asshown in Figure 1, an unstiffened portion of the web gap was then leftduring service and was susceptible tobeing pulled out-of-plane when theend of the transverse structural member rotated under traffic loading.Distortion-induced cracks developedunexpectedly at both the web-to-flangeand web-to-connection-plate fillet

Out-of-Plane Rotation Due to Differential Girder Deflection

Small Web Gap

Deck Slab

Connection Plate Not Attached to the Top Flange

Girder Top Flange

Horizontal Crack

Girder WebConnection Plate

Horseshoe Crack

Figure 1. Formation of out-of-plane distortion-induced fatigue cracking.

Out-of-plane distortionaccounts for

the largest category of fatigue cracking

nationwide

Welding Innovation Vol. XVIII, No. 2, 2001 3

welds, typically as horizontal or horse-shoe cracks, as indicated in Figure 1.

A research project currently underwayat the University of Kansas is studyingthe fatigue behavior and repairapproaches for the out-of-plane distor-tion-driven cracks experienced bymany Kansas Department ofTransportation (KDOT) welded plategirder bridges. Figures 2 and 3 exhibitdevelopment of typical horizontal andhorseshoe cracks in two KDOTbridges. Web gaps near the girder topflanges are the most common locationfor these cracking problems. The topflange is held rigid by the deck slababove, so a more abrupt stiffnesschange occurs than that at the bottomflange, which is relatively free to movelaterally. Cracks most frequently occurin the positive moment regions of thebridge girders, where the differentialgirder deflections are the largest andthe out-of-plane bending moments arethe highest. The common conditionsobserved in KDOT bridges that haveled to web gap cracking are: 1) nopositive attachments provided betweenthe connection plates and the girderflanges; and 2) no additional stiffenerplates erected on the other side of thegirder web as would have been doneat bearing stiffeners. If either one ofthese two countermeasures had beencarried out, a rigid load path couldhave been formed between the trans-

verse members and the longitudinalgirders, and the chances of formingout-of-plane fatigue cracking wouldhave been slight.

In order to better understand the historyof the distortion-induced fatigue and toobtain more information about crackrepair solutions and experiences, theauthors of this article reviewed the differ-ent editions and interims of the AASHTObridge design specifications published inthe past twenty years, and conducted

two surveys among different DOTs andothers with an interest in steel bridges.The first survey was carried out in 1999within the North Central States andFederal Highway Administration Region 3, and the second one was performed in 2000 through the email list of AASHTO/NSBA Steel BridgeCollaboration (thelist@steelbridge.org).The input from the surveys provided bothvaluable insights into the retrofit mecha-nism of the out-of-plane fatigue crackingand detailed implementations employedin the repair of other DOTs bridges.

Evolution of Connection PlateDesign Detail SpecsGenerally speaking, the detailing ofconnection plates has never beenspecified independently as an individ-ual section in the AASHTO StandardSpecifications for Highway Bridges.From the first time it was mentioned inthe specifications (1982 Interim),design of connection plates has beenalways included in either the sectioncovering transverse intermediate stiff-eners or the section coveringdiaphragms and cross-frames. It wasnot until the issuance of the firstAASHTO LRFD edition in 1994 thatthe rationale of distortion-inducedfatigue was fully explained and theconnection plate design detail wasclearly and correctly specified in aseparate section.

The story of the connection platedetail should date back to the 1981Interim, which states thatIntermediate stiffeners may be inpairs with a tight fit at the compres-sion flanges When stiffeners areused on one side only of the webplate, they shall be fastened to thecompression flange and Transverseintermediate stiffeners need not be inbearing with the tension flange.Strictly speaking, stiffeners and con-nection plates are different concepts in terms of their structural purposes.However, the same plate can fulfillboth functions. Since distortion-induced fatigue was not a widely recognized problem at that time, the specifications were normally

Cracks most frequently occurin the positive moment

regions of the bridge girders

Figure 3. Horseshoe cracks observedin the Hump Yard Bridge.

Figure 2. Cracking and repair condition on each side of a connection plate in the Fancy Creek Bridge.

(a) north side of connection plate (b) south side of connection plate

4 Welding Innovation Vol. XVIII, No. 2, 2001

interpreted as having the stiffenerdetails requirements also applying to connection plate details. In otherwords, the connection plate functionwas seen as subordinate to the inter-mediate stiffener function.

The 1982 Interim mentioned connec-tion plate details explicitly for the firsttime in AASHTO. The aforementionedstatement for the stiffener-to-compres-sion-flange connection was revised toStiffeners provided on only one sideof the web must be in bearing againstbut need not be attached to the com-pression flange for the stiffener to be

effective; however, consideration shallbe given to the need for this attach-ment if the location of the stiffener orits use as a connector plate for adiaphragm or cross-frame will produceout-of-plane movements in a weldedweb to flange connection. Theauthors understand this statement tomean that the connection plate wasallowed, but was not required, to beattached to the compression flange.The connection plate to tension flangedetail was still not explicitly addressed.By default, the relationship between astiffener and the tension flange wouldbe applied, implying that no welded orbolted connection was needed.

In 1983, the 13th AASHTO editionchanged to the now current format.The former description of the stiffener-to-compression-flange connectionappeared in section 10.34.4.6, andthat of the stiffener-to-tension-flangeconnection appeared in section10.34.4.9. The contents of these twosections were the same as in the 1982Interim and were kept unchanged until1995. Design of diaphragms andcross-frames was specified in section

10.20. No information about connec-tion plate details was mentioned in the1983 Interim.

The 1985 Interim added the importantstatement to section 10.20.1 thatVertical connection plates such astransverse stiffeners which connectdiaphragms or cross-frames to thebeam or girder shall be rigidly con-nected to both top and bottomflanges. This is the first time AASHTOrequired that connection plates beattached to both girder flanges.However, those related provisions pre-viously covered in section 10.34.4 fortransverse intermediate stiffenersremained the same, which made thespecifications very unclear.Unwillingness to change the olddesign habit, in addition to the ambi-guity of the specifications, delayed theprocess of preventing or eliminatingout-of-plane fatigue cracking in newlybuilt bridges. For example, KDOTstarted welding or bolting connectionplates to both girder top and bottomflanges in early 1989. Fatigue crack-ing has not been observed to date inbridges designed since this practicewas adopted. However, almost allthose welded plate girder bridges builtwith the pre-1989 detail were foundwith fatigue cracks in the web gaparea.

Finally, in the 1995 Interim, the con-nection plate detail was made clearand the following revised statementwas repeated both in section 10.34.4.6for the compression flange connectionand in section 10.34.4.9 for the ten-sion flange connection. However,transverse stiffeners which connectdiaphragms or cross-frames to thebeam or girder shall be rigidly con-nected to both the top and bottomflanges.

The AASHTO LRFD Bridge DesignSpecifications, available since 1994,clearly specify that Connection platesshall be welded or bolted to both thecompression and tension flanges ofthe cross-section. Explanation of

distortion-induced fatigue is given insection 6.6.1.3 and its correspondingcommentary, and the requirement ofrigid attachment between connectionplates and girder flanges is addressedin section 6.6.1.3.1 for transverse connection plates, section 6.7.4.1 fordiaphragms and cross-frames, andsection 6.10.8.1.1 for transverse inter-mediate stiffeners.

Retrofitting Out-of-Plane Fatigue CracksDifferent repair methods, either havingalready been used in actual bridgeretrofits by DOTs, or still beingresearched, are described as below. This is a summary based on responses to the two surveys previously mentioned.

Hole drillingThe traditional repair method shown in Figure 4 consists of drilling a hole at the crack tip. The hole diameter issized to be at least 2, where isdetermined by Equation 1 [Barsomand Rolfe, 1999].

(1)

is the stress intensity factor rangeand y is the yield strength of thespecified steel. This repair is especiallyeffective when arresting crack propagation in low stress regions.However, cracking may recur if thehole size is not large enough or thestress range at the crack locationincreases. If this is the case, a

Stop Holes

Top Flange

Connection Plate

Figure 4. Repair by drilling stop holesat the crack tips.

Stiffeners and connection plates

are different conceptsin terms of their

structural purposes

ksi)in (for 4 yyK