welding issues - winter 20081

8/13/2019 Welding Issues - Winter 20081

1/4

Technical Bulletin Winter 2008

1

Welding Issues for Seismic Design RequirementsMetal Building Systems

byW. Lee Shoemaker, P.E., Ph.D.

Director of Research & Engineering

BackgroundWelding requirements for buildings designed to resist seismically-induced energy have undergone a variety of changes in thepast dozen years. With the publication of several specifications in 2005, some stability has now emerged. This bulletin isintended to outline and clarify the welding issues for seismic design that are specific to metal building systems.

Applicable Codesand Standards

General WeldingRequirements

Welding requirements arestipulated in a number ofdocuments, including:

(1) AISC Specification for SteelBuildings (AISC 360-05)

(2) AISC Seismic Provisions forStructural Steel Buildings(AISC 341-05)

(3) AISC Prequalified Connectionsfor Special and IntermediateMoment Frames for SeismicApplications (AISC 358-05)

(4) AWS Structural Welding Code Steel (AWS D1.1-04) (asreferenced by AISC 341-05)

(5) AWS Structural Welding Code Seismic Supplement (AWSD1.8/D1.8M:2005)

Also, FEMA 353 Recommended

Welding requirements for theseismic load resisting system (SLRS)depend on whether the weld iscategorized as a demand critical weld,or is just part of the SLRS. The seismicload resisting system is defined as theassembly of structural elements in abuilding that resists seismic loads,including struts, collectors, chords,diaphragms and trusses. Demandcritical welds are those that have beendetermined both to be subject to yield-level stresses and to have the potentialto cause catastrophic results if theyfailed. Demand critical welds caninclude complete-joint-penetrations(CJP) groove welds for column splicesin ductile frames1, CJP groove weldsfor beam flange to column flange

Specifications and Quality AssuranceGuidelines for Steel Moment FrameConstruction for Seismic Applications,

June 2000, was often referenced asa resource before the above codesand standards incorporated the appro-priate information. This is still some-times referenced separately, but shouldnot supersede these newer documents.

AISC 341 and AISC 358 aresupplemental to the requirementsof AISC 360, while AWS D1.8 issupplemental to AWS D1.1. Therequirements of the supplemental doc-uments add to and are not in lieu of,the requirements of the documents they

supplement. AWS D1.8 contains provi-sions that correspond to similar provi-sions in FEMA 353 and AISC 341Appendix W. AWS D1.8 may offeradvantages over FEMA 353 and AISC341 but it may be used only if referredto in a project specification or withapproval of an engineer. Continued on Page 2

1 For ductile moment frames (IMF and SMF) the strong column is necessary to force flexural yielding in the weak beam, which is ensured by the AISC341 beam and column proportioning requirements. For the OMF, which is intended for minimal inelastic deformations only, the weak column strongbeam concept is permitted. Hence, the demand critical weld does not guarantee better performance as long as the OMF column strength can be gov-erned by limit states other than flexural yielding.


2/4

2

moment connections, and beam webto column flange CJP groove welds inmoment connections (See AISC 341Section 7.3b).

Whether a weld is demand criticalor not depends in part on the type ofseismic system involved, such as anordinary moment frame (OMF),

intermediate moment frame (IMF) orspecial moment frame (SMF).

In addition to the other applicableseismic design criteria listed in Section5.1 of AISC 341, the classification of aweld is to be specified by the Engineerin the Contract Documents. This doesnot give the Engineer the authority todisregard the code requirements, butit is intended to makes it clear to thefabricator which welds are demandcritical. Therefore, from this specifiedcriteria, welds can be categorized as

one of the following:(1) Welds that are not part of the

SLRS (AWS D1.1 applies)

(2) Welds that are part of theSLRS, that are not demandcritical (AISC 341, Section 7.3aapplies in addition to AWSD1.1)

(3) Welds that are part of the SLRSthat are demand critical (AISC341, Section 7.3b applies inaddition to the requirements ofAISC 341 Section 7.3a andAWS D1.1)

The typical metal building systemshould have only a few select weldsthat are demand critical. Guidanceis provided below regarding theclassification of common welds.

Demand Critical Weldsin Metal Buildings

In typical metal building gableframes, the only welds that would

be considered demand critical in anOMF are CJP groove welds of theend-plates at the haunch connection.For IMFs, a prequalified connectionwould have to be used for this con-nection, but the bolted end-plateconnections in AISC 358 do not haveany additional demand critical weldrequirements other than what AISC341 requires for OMFs. Other weldrequirements of the web to flange inan IMF given in AISC 358 are dis-

cussed separately in this paper. Notethat fillet welds used to weld the end-plate to the beam end would not beconsidered demand critical welds.Also, end-plate connections elsewherein the frame, e.g. the ridge, are notdefined as demand critical.

Weld Filler MetalRequirements

Weld filler metal requirements canbe categorized as follows:

(1) Welds that are part of theseismic load resisting systemthat are not demand critical(AISC 341, Section 7.3a) shallhave a minimum CVN tough-ness of 20 ft-lb at 0F as deter-mined by AWS A5 classificationor manufacturer certification.

Most MBMA members use gasmetal arc welding (GMAW) forsemi-automatic welding, andautomatic submerged arc weld-ing (SAW) for web-to-flangebuilt-up sections. Other weldingprocesses are possible andacceptable, but these are themost common combinations.For GMAW, a typical fillermetal is ER70S-3. For SAW,Lincoln 781/L50 or 781/L61 iscommonly used. These fillermetal combinations satisfy thisrequirement.

Self shielded flux cored arcwelding (FCAW-S) is not com-monly used for metal buildingfabrication today. However, inwelded joints where FCAW-Sis mixed with other processesincluding FCAW-G, the fillermetal combination must betested in accordance with D1.8section 6.3.4.

(2) Welds that are part of theseismic load resisting systemthat are demand critical (AISC341, Section 7.3b) shall havea minimum CVN toughness of20 ft-lb at -20F as determinedby AWS A5 classification ormanufacturer certification, and40 ft-lb at 70F as determinedby AISC 341 Appendix X, AWSD1.1 Annex A, or otherapproved method.

As previously discussed, theonly applicable welds that aredemand critical in an OMF orIMF are the CJP groove welds ofthe end-plates at the haunchconnection. In the metal build-ing industry, this weld wouldtypically be made with GMAW,

and the typical filler metal usedis classified as ER70S-3. TheAWS A5.18 classification forER70S-3 requires CVN tough-ness of 20 ft-lb at 0F, not the-20F required by AISC 341.However, AISC 341 also permitsmanufacturer certification asan acceptable alternative todemonstrate that the fillermetal is capable of achieving20 ft-lb at -20F in a filler metaclassification test. A manufac-

turers typical certificate of con-formance that lists 20 ft-lb at-20F is suitable documentationfor this purpose. Alternately,ER70S-6 may be used, which isclassified at -20F.

For the prequalified boltedend-plate moment connec-tions included in AISC 358,the reinforcing fillet weld onthe inside face of the flangeshall also be demand critical(AISC 358, Section 6.9.7(3)).

Regarding testing in conform-ance with Appendix X or otherapproved method, solidGMAW electrodes are exempt-ed from this requirement whenthe aforementioned 20 ft-lb at-20F is achieved. Thus, in thetypical situation where GMAWis utilized, testing in accordancewith Appendix X will not berequired.

(3) For all welds, self shielded fluxcored arc welding (FCAW-S) is

not commonly used for metalbuilding fabrication today.However, in welded jointswhere FCAW-S is mixed withother processes includingFCAW-G, the filler metalcombination must be tested inaccordance with D1.8 Section6.3.4.

Continued on Page 3


3/4

3

Protected Zones inMetal Buildings

The concept of Protected Zoneis used in AISC 341, AISC 358 andAWS D1.8. A weld that is within theprotected zone is not required to meetthe demand critical requirements. The

intent is to eliminate unintendedstresses and fracture initiators inselected regions subject to significantinelastic deformations.

There are no protected zonesspecified for OMFs. However forIMFs, the extent of the protectedzone is given in AISC 358 for pre-qualified connections and in AISC 341Section 10.2d.

In typical IMFs that might be usedin metal buildings when an OMF is

not permitted, the protected zone isdefined in AISC 358 Section 6.4(8) asfollows:

(1) For an unstiffened extendedend-plate, the protected zoneextends from the face of thecolumn to the lesser of (a) thedepth of the beam, or (b) 3times the width of the flangefrom the face of the column.

(2) For a stiffened extendedend-plate, the protected zoneextends from the face of the

column to a location from theend of the stiffener plus thelesser of (a) the depth of thebeam, or (b) 3 times the widthof the flange from the face ofthe column.

The protected zone requirementsare stated in AISC 341 Section 7.4 asfollows:

(1) Discontinuities created byfabrication or erectionoperations shall be repaired.Examples include tack welds,

erection aids and cuts.

(2) Shear studs and pins or screwsare not permitted (arc spotwelds for attaching deck arepermitted)

(3) Welded, bolted, screwed orshot-in attachments forperimeter edge angles, exteriorfacades, partitions, duct work,piping or other construction arenot permitted in the protected

additional qualification testing iscarried out, as noted in Section W5.2,AISC 341.

Welder Qualification - AWS D1.8requires that welders pass a supple-mental qualification test if they will bemaking welds that meet all of thefollowing requirements: a) demand

critical, b) join the bottom beamflange to the column flange and c)are made through a weld access hole.Such conditions are rarely if everencountered on metal building sys-tems, and accordingly, the supple-mental welder qualification tests willtypically not be required for metalbuilding applications, even if therequirements of AWS D1.8 arespecifically invoked in the contractdocuments.

Other IMFRequirements

AISC 358, Section 6.4, has arequirement that at the haunch ofwelded built-up sections, within atleast the depth of the beam or 3 timesthe width of the flange, whichever isless, the web to flange weld shall beeither a CJP groove weld or a pair offillet welds each having a size 34 timesthe beam web thickness but not less

than1

4 inch. This would typicallyrequire a change from the typicalpractice of single sided fillet welds.

Quality Assurance Plan

Quality assurance inspectionperformed by an independentinspection agency, is not a require-ment of AWS D1.1. Inspection isrequired by AWS D1.1, but isaddressed generically in a form that

includes both the fabricators orerectors inspection and the outsideinspection that is provided by, but atthe prerogative of, the owner. AWSD1.1 does include visual qualitycriteria, nondestructive testing (NDT)methodology and NDT qualitycriteria, but does not specify thelocation or types of welds that requireNDT. This task is left to the engineer.

Continued on Page 4

zone except that bolt holes inthe beam web are permitted asnoted in Section 2.6 of AISC358.

Note that a butt splice of a webplate that falls within the protectedzone must be free of discontinuitiescreated by fabrication or erection

operations, such as tack welds,erection aids, air-arc gouging andthermal cutting. However they arenot specifically addressed in thecodes, so they would only be classifiedas demand critical if specified by theEngineer in the Contract Documents.Discontinuities shall be repaired asrequired by the Engineer of Record.As part of the SLRS, these welds arerequired to be made with filler metalswith a minimum CVN toughness of20 ft-lb at 0F as determined by AWS

A5 classification or manufacturercertification.

In the protected zone, tack weldsattaching backing and weld tabsshall be placed where they will beincorporated into a final weld, asnoted in Section 3.5 of AISC 358.

Welding Procedure Specifications(WPSs) WPSs have to show the

filler metal manufacturer and tradename for all welds. For demandcritical welds only, the WPS mustshow a combination of variablesthat results in a heat input within theenvelope to which the filler metal wastested and certified.

Filler Metal Atmospheric Exposure -While not a commonly used weldingprocess, if FCAW is used, the fillermetals must not be exposed to theatmosphere longer than 72 hours orthe exposure limits for which they aretested.

The maximum diffusible hydrogenis limited in welding electrodes. Theyshall meet the requirements forH16 (16 mL maximum diffusiblehydrogen per 100 grams of depositedweld metal) as noted in Section W5.2,AISC 341. Note that this does notapply to GMAW solid electrodes.

The maximum interpass temper-ature shall not exceed 550 F unless

Other PertinentWelding Requirements


4/4

4

AWS D1.1 does not contain specificquality criteria applicable for seismicloading, low cycle fatigue or plastichinging regions, addressing onlystatic (elastic) and high-cycle fatigueapplications. Any special qualityrequirements for seismic applicationsare left to the engineer.

AISC 341 contains provisionsfor and requirements of a qualityassurance plan in Section 18 andAppendix Q. The plan must meet anybuilding code requirement such asthose in the 2006 IBC, in addition toany requirements of the engineer.

The emphasis is placed upon visualinspection. Nondestructive Testing(NDT), however, is required for CJPand PJP groove welds along with otheritems as detailed in Appendix Q. Theform of NDT is specified within

Appendix Q, based on the testeditem.

The 2006 IBC requires specialinspection for steel construction, witha few exceptions as noted in Section1705.3. Special inspection is per-formed by independent, qualifiedindividuals or agencies approved toperform such inspections by thebuilding official. Special inspectionincludes an inspection of the fabri-cators operations and quality controlprocedures, unless the fabricator is

otherwise approved by the buildingofficial. Structural steel weldingoperations must receive continuousspecial inspection, except for single-pass fillet welds 516 or less, forwhich periodic special inspection ispermitted (IBC Section 1707.2).

Section 1705 of IBC 2006 requiresa quality assurance plan for seismic-force-resisting systems in SeismicDesign Categories C, D, E or F. Thequality assurance plan must beprepared by a registered design

professional and specify the specialinspection requirements and testingrequirements, including the type oftesting and frequency of testing.Structural observation by the engineeror his or her designated representativeis also a requirement. The exact extentof additional special inspection,testing and structural observation forseismic applications is not definedwithin the IBC, but is rather left tothe determination of the registered

design professional. AISC 341,Appendix Q gives appropriateguidance in this area.

The fabricator and erector mustcomplete a statement of respons-ibility acknowledging their awarenessof the quality assurance plan, theirplans and procedures for providing

quality control to achieve thecontract requirements, and identi-fication of those individualsresponsible for performing suchfunctions. The 2006 IBC Section1704.2.2 allows in-shop qualityassurance activities to be waivedif welding is performed on thepremises of an approved fabricator.

Summary

For metal buildings, the followingare the changes in practice that maybe required in order to comply withAISC 341:

(1) The complete-joint-penetrationwelds of the end-plate at thehaunch connection must meetthe requirements for demandcritical welds. Filler metalsused for these welds mustmeet AWS classificationrequirements of 20 ft-lbs at

-20F, or be tested by themanufacturer as meeting thesame requirement. Additionally,the filler metals are required tomeet 40 ft-lbs at 70F whentesting in accordance withAppendix X, unless the par-ticular electrode is exemptfrom this requirement(GMAW with solid electrodesare exempt from AISC 341Appendix X testing).

(2) Welds that are part of the

SLRS must be made with filler

metals meeting 20 ft-lbs at 0F.For most metal building man-ufacturers, commonly usedwelding products will meetthese requirements.

(3) For IMF applications, fabrica-tion restrictions apply to theportion of the member identi-

fied as the protected zone.(4) For IMF applications, the welds

at the end of built up sectionsbetween the web and flange wilneed to be CJP groove welds, ordouble sided fillet welds meet-ing certain size requirements.Additionally, the weld betweenthe end of the beam and end-plate needs to be a CJP grooveweld with a reinforcing fillet.

Disclaimer

The welding requirements thatare discussed in this bulletin apply totypical metal building structures. Thereader should confirm that theirapplication is within the scope ofthese assumptions.

Acknowledgements

The information and code inter-pretations in this bulletin are thoseof the author on behalf of the MetalBuilding Manufacturers Association.However, several individuals provid-ed review comments that providedinvaluable guidance. We thereforegratefully acknowledge the assist-ance of Duane Miller of LincolnElectric, Tom Schlafly of AISC,Robert Shaw of Steel Structures

Technology, and Ronald Hamburgerof Simpson Gumpertz and Heger.

For Further Information:

Metal Building Manufacturers Association, Inc.1300 Sumner Avenue Cleveland, Ohio 44115-2851

216-241-7333 216-241-0105 (fax)

Email: [email protected] Website: www.mbma.com