high seismic detailing and fabricating

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march 2008 MODERN STEEL CONSTRUCTION

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seismic design

ThE 2005 AISC SEISMIC PROvISIONS OR STRUCTURALSTEEL BUILDINgS govern the design, abrication, and erec-tion o structural steel members and connections in the seismic

load resisting systems (SLRS) and splices in columns that are notpart o the SLRS, in buildings and other structureswhere otherstructures are dened as those structures designed, abricated, anderected in a manner similar to buildingswith building-like verti-cal and lateral load-resisting-elements.

The seismic provisions apply when the seismic response modi-cation coecientR, as specied in the applicable building code,is taken greater than 3, regardless o the seismic design category.

WhenR is taken as 3 or less, the structure is not required to satisythe provisions unless specically required by the applicable build-ing code. Members and connections o the SLRS must satisy therequirements o the applicable building code, the AISC specica-tion, and the seismic provisions.

The AISC seismic provisions give specic inormation to thestructural engineer as to what to include on the structural designdrawings and in the structural specications. This inormation,provided by the structural engineer, is essential or the detailer,abricator, and erector to ensure proper understanding and execu-tion o the contract requirements. Although the structural engi-neers responsibilities are beyond the scope o this presentation,the ollowing inormation is necessary as a background to whata detailer and abricator should expect to nd on the structuraldesign drawings and in the structural specication:

Designation o the SLRS.Designation o the member and connections that are part o

the SLRS.Conguration o the connections.Connection material specications and sizes.Locations o demand-critical welds.Lowest anticipated service temperature o the steel structure, ithe structure is not enclosed and maintained at a temperatureo 50 F or higher.Locations and dimensions o protected zones.Locations where gusset plates are to be detailed to accommo-date inelastic rotation.

Welding requirements as specied in Appendix W, SectionW2.1.The detailer, abricator, and erector must have a knowledge and

understanding o the ollowing terms rom the seismic provisions whendetailing and abricating a project designated as high seismic:

Seismic desin cateory is a classication assigned to abuilding by the applicable building code based upon its seismic usegroup and the design spectral response acceleration coecients.

Seismic response modifcation coefcient (R) is a actorthat reduces seismic load eects to a strength level specied by theapplicable building code.

Seismic load resistin system (SLRS) is an assembly ostructural elements in the building that resist seismic loads, includ-ing struts, collectors, chords, dia-phragms, and trusses.

Special Moment rames

(SM) are expected to withstandsignicant inelastic deormations

when subjected to the orces result-ing rom the motions o the designearthquake.

Intermediate Moment rames

(IM) are expected to withstand lim-ited inelastic deormations in theirmembers and connections when sub-

jected to the orces resulting rom themotions o the design earthquake.

Ordinary Moment rames

(OM) are expected to withstandminimal inelastic deormations intheir members and connections

when subjected to the orces result-ing rom the motions o the designearthquake.

Special Truss Moment

rames (STM) are expectedto withstand signicant inelas-tic deormation within a specially

Projects designated as high seismic require special attention.

Heres an introduction to some of the complexities of detailing

and fabricating high seismic projects.

By Tom Ferrell, P.e., and Tony hazel, P.e.

hi Seismic Detailin and abricatin

NASCC: The SteelCONFeReNCe

Tony Hazel is senior designengineer or Ferrell Engi-neerings Columbia, S.C.

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Tis ti s b xpt f pp t b pst t T St cf, api 2-5 i nsvi,T. l but T St cf twww.aisc.or/nascc. T pt pp wi b vibwit t iv vsi f tis ti twww.modernsteel.com/backissues.

Tom Ferrell is president o Ferrell Engineering, Inc.,Birmingham, Ala.


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MODERN STEEL CONSTRUCTION march 2008

designed segment o the truss when sub-jected to the orces rom the motions o thedesign earthquake.

Special Concentrically Braced

rames (SCB) are expected to withstandsignicant inelastic deormations whensubjected to the orces resulting rom themotions o the design earthquake.

Ordinary Concentrically Braced

rames (OCB) are expected to withstandlimited inelastic deormations in theirmembers and connections when subjectedto the orces resulting rom the motions othe design earthquake.

Eccentrically Braced rames (EB)

are expected to withstand signicantinelastic deormations in the links whensubjected to the orces resulting rom themotions o the design earthquake.

Bucklin-Restrained Braced rames

(BRB) are expected to withstand signi-cant inelastic deormations when subjected

to the orces resulting rom the motions othe design earthquake.

Special Plate Sear Walls (SPSW) areexpected to withstand signicant inelasticdeormations in the webs when subjectedto the orces resulting rom the motions othe design earthquake.

Protected zones are areas o membersin which limitations apply to abricationand attachments.

Demand-critical welds are welds thatare part o the SLRS that are deemed tobe critical, since they transer importantearthquake loads.

Prequalifed connections are connec-tions that comply with the requirements o

Appendix P o the Provisions (ANSI/AISC358)

Continuity plates are column stien-ers at the top and bottom o the panel zone;they are also known as transverse stieners.

Te k-area is the region o the web thatextends rom the tangent point o the weband the fange-web llet (AISCs k dimen-sion), a distance o 1 in. (38 mm) into the

web beyond the k dimension.

Detailin hi Seismic

Sop Drawins: AISC Seismic ProvisionsPart 5.2 and Appendix W, Section W2.2.

Shop drawings shall include itemsrequired by the AISC specication and theollowing, as applicable:

Designation o the members and con-1.nections that are part o the SLRS.Connection material specications.2.Locations o demand-critical shop3.welds.

Locations and dimensions o protected4.zones.Gusset plates drawn to scale when they5.are detailed to accommodate inelasticrotation.

Welding requirements as specied in6.Appendix W, Section W2.2 Shop draw-ings shall include, as a minimum, theollowing inormation:

Access hole dimensions, surace pro-a.le, and nish requirements.Locations where backing bars are tob.be removed.Locations where weld tabs are to bec.removed.NDT to be perormed by the abri-d.cator, i any.

Erection Drawins: AISC Seismic Provi-sions Part 5.3 and Appendix W, SectionW2.3.

Erection drawings shall include items

required by the AISC specication and theollowing, as applicable:Designation o the members and con-1.nections that are part o the SLRS.Field connection material specications2.and sizes.Locations o demand-critical eld3.welds.Locations and dimensions o protected4.zones.Locations o pretensioned bolts.5.Field welding requirements as specied6.in Appendix W, Section W2.3 Erection

drawings shall include, as a minimum,the ollowing inormation:

Locations where backing bars are toa.be removed.Locations where supplemental lletsb.are required when backing is permit-ted to remain.Locations where weld tabs are to bec.removed.

Those joints or groups o jointsd.in which a specic assembly order,

welding sequence, or welding tech-niqueor other special precau-

tionsare required.

abricatin hi Seismic

Personnel Requirements

Welders shall pass the Supplemental1. Welder Qualication or restrictedaccess welding; see AWS D1.8 AnnexC. Tack welders are not required to per-orm the SWQRA.Each welder shall be assigned an identi-2.cation symbol or mark.QC welding inspectors shall be associ-3.

ate welding inspectors (AWI) or higher.

QA welding inspectors shall be weld-4.ing inspectors (WI) or senior weldinginspectors (SWI).Nondestructive testing (NDT) techni-5.cians shall meet special qualicationrequirements.

These requirements are in addition to6.normal AWS D1.1 qualications.

Structural Steel Material Require-

mentsCharpy V-Notch (CVN)1.Hot-rolled shapes with fanges 1 in.2.thickPlates 2 in. and thicker3.20 t-lb at 70 F4.

Weld Requirements Welding Procedure Specications1.(WPS) shall meet AWS D1.1 andrequirements or demand-critical welds.

WPS shall list electrode manuacturer2.and trade names.

WPS shall list one or more combina-3.tions o welding variables that produceheat inputs within acceptable estab-lished AWS ranges.

Must use approved processes or4.demand-critical welds (SMAW, GMAW,FCAW, and SAW). Other processes areallowed, provided certain criteria aremet.Gas-shielded process is allowed when5.air velocity does not exceed 3 mph.Filler Metal Diusible Hydrogen: max-6.imum o 16 ml per 100 grams depos-ited weld metal. Certain variances andexemptions may be applicable.Intermix o FCAW-S ller metal.7.

Weld tabs.8.Bottom fange welding sequence.9.Notch-toughness characteristics.10.Storage and exposure o FCAW elec-11.trodes.

Maximum interpass temperature.12.

abricationDemand-critical welds.1.Forbidden items within the protected2.

zone: Tack welds, erection aids, arc-aira.gouging, thermal cutting, etc. Repairwhen required.Welded shear studs and penetratingb.decking attachments. Decking arcspot welds to secure the deck arepermitted.

Welded, bolted, screwed, or shot-inc.attachments or perimeter edge angles,exterior acades, partitions, duct work,piping, or other construction.

Continuity Plates and Stieners


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MODERN STEEL CONSTRUCTION march 2008

Inside corner clips (curved or straight).1.CJP or heavy llets.2.Hold llets back in. rom edge.3.

Where specied backing bars are to be4.removed, back gouged, and re-welded.

Where specied supplemental llet5.welds may be used where backing barsare permitted to remain.

Joints or groups o joints may speciy6.

a specic assembly order, weldingsequence, welding technique, or otherspecial precautions.

Access hole dimensions, surace prole,7.and nish requirements.

Tack WeldsAll bolted aying suraces shall meet

requirements or Class A suraces orbetter.

Reerences

AISC Seismic Provisions or Structural Steel

Buildings, including Supplement No. 1,2005; Appendices P, Q, and W.AISC Seismic Design Manual, 2006.AWS D1.8

high seismic detailing and fabricating

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