the aisc seismic provisions for structural steel buildings aisc

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AISC Seismic Provisions

James O. MalleySenior Principal, Degenkolb Engineers

and Chair, AISC TC9

The AISC Seismic Provisions For The AISC Seismic Provisions For Structural Steel BuildingsStructural Steel Buildings


Process of Developing the ProvisionsProcess of Developing the Provisions

•• 1992 AISC Seismic (E.1992 AISC Seismic (E. PopovPopov, Chair), Chair)•• 1997 NEHRP Adoption of 1997 AISC Seismic 1997 NEHRP Adoption of 1997 AISC Seismic

ProvisionsProvisionsCooperation of AISC and BSSC establishedCooperation of AISC and BSSC establishedSimilar for 2000 and 2003 NEHRP ProvisionsSimilar for 2000 and 2003 NEHRP ProvisionsRoles defined to minimize duplication of Roles defined to minimize duplication of efforteffort

AISC/NEHRPAISC/NEHRP

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AISC Review/Approval ProcessAISC Review/Approval Process•• ANSI Consensus Process Procedures Being ANSI Consensus Process Procedures Being

FollowedFollowedAISC now ANSI Accredited OrganizationAISC now ANSI Accredited Organization

•• AISC Seismic Provisions UpdatesAISC Seismic Provisions Updates1997 AISC Seismic Provisions1997 AISC Seismic Provisions•• Supplement No. 1, February 15, 1999Supplement No. 1, February 15, 1999•• Supplement No. 2, November 10, 2000Supplement No. 2, November 10, 2000

2002 Provisions, May 21, 20022002 Provisions, May 21, 2002


Building Code Adoption ProcessBuilding Code Adoption Process

•• 1997 Seismic Provisions, through 1997 Seismic Provisions, through Supplement No. 1 included with Main LRFD Supplement No. 1 included with Main LRFD Specifications into 2000 IBCSpecifications into 2000 IBC

2002 Seismic Provisions in 2003 IBC2002 Seismic Provisions in 2003 IBC•• 2002 NFPA also includes 2002 AISC Seismic2002 NFPA also includes 2002 AISC Seismic•• 2006 IBC adopted 2005 AISC Seismic 2006 IBC adopted 2005 AISC Seismic

(ANSI/AISC 341(ANSI/AISC 341--05) and AISC Main Spec 05) and AISC Main Spec (ANSI/AISC 360(ANSI/AISC 360--05)05)

•• Single Set of Unified National Seismic Single Set of Unified National Seismic Provisions for Steel BuildingsProvisions for Steel Buildings

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Major Elements of 2005 Seismic Major Elements of 2005 Seismic ProvisionsProvisions

•• Part I covers all Major Seismic SystemsPart I covers all Major Seismic SystemsFocus on SDC D, E and FFocus on SDC D, E and F

•• Coordinated with ASCE 7Coordinated with ASCE 7--0505•• Incorporate PostIncorporate Post--Northridge FindingsNorthridge Findings

FEMA/SAC Project Results (FEMA 350 Series) FEMA/SAC Project Results (FEMA 350 Series) as Well as Other Effortsas Well as Other Efforts

•• Composite Provisions from NEHRP Included (Part Composite Provisions from NEHRP Included (Part II)II)

•• Note that Both Parts are in the Note that Both Parts are in the ““UnifiedUnified”” Format Format similar to the Main AISC Specificationsimilar to the Main AISC Specification

Both LRFD and ASD included in one set of Both LRFD and ASD included in one set of provisionsprovisions


Scope StatementScope Statement

•• Intended Primarily for Building Structures Intended Primarily for Building Structures Also incorporated for Also incorporated for ““building likebuilding like”” nonnon--building structures building structures Glossary clarifies that SLRS includes Glossary clarifies that SLRS includes diaphragm chords and collectors, and all diaphragm chords and collectors, and all elements that resist seismic loadselements that resist seismic loads

•• Required for SDC D, E and FRequired for SDC D, E and FFor SDC A, B and C, designer has choiceFor SDC A, B and C, designer has choice

•• Use the Seismic Provisions with appropriate Use the Seismic Provisions with appropriate R factorR factor

•• Use AISC LRFD/ASD Provisions with R=3Use AISC LRFD/ASD Provisions with R=3•• Design Directly Linked to ASCE 7Design Directly Linked to ASCE 7--0505

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Project Documentation RequirementsProject Documentation Requirements

•• New Section to Define Expectations of:New Section to Define Expectations of:Design drawings and specificationsDesign drawings and specificationsShop DrawingsShop DrawingsErection DrawingsErection Drawings

•• Includes lists of information to be Includes lists of information to be provided such as SLRS designation, provided such as SLRS designation, connection detailing, welding connection detailing, welding requirements, protected zones, etc.requirements, protected zones, etc.

•• Consistent with FEMA 353 and AWS D1.8Consistent with FEMA 353 and AWS D1.8


Material SpecificationsMaterial Specifications•• ASTM Specifications for Materials EmployedASTM Specifications for Materials Employed

All major structural products incorporatedAll major structural products incorporated•• Limited to 50 Limited to 50 ksiksi, except for , except for ““elasticelastic”” columnscolumns

Relaxed to 55 Relaxed to 55 ksi ksi limit for OMF and OCBFlimit for OMF and OCBF•• Material Properties for Determination of Required Material Properties for Determination of Required

Strength for Connections or Related Members Based Strength for Connections or Related Members Based on Expected Yield Strengthon Expected Yield Strength

RRyy = = RRy y FFy y

RRyy = 1.5 for A36= 1.5 for A36 1.5 x 36 = 541.5 x 36 = 54 ksiksiRRyy = 1.1 for A992= 1.1 for A992 1.1 x 50 = 55 1.1 x 50 = 55 ksiksiRRyy = 1.1 to 1.6 for other steels grades= 1.1 to 1.6 for other steels grades

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Material SpecificationsMaterial Specifications•• Available Strength to consider both expected Available Strength to consider both expected

yield and tensile strengthsyield and tensile strengths•• RRtt term added for tensile strength, with range term added for tensile strength, with range

of 1.1 to 1.3of 1.1 to 1.3Intent is to ensure expected inelastic Intent is to ensure expected inelastic response and ductile failure modesresponse and ductile failure modes


Notch Tough SteelNotch Tough Steel

•• For Seismic Force Resisting System,For Seismic Force Resisting System, CharpyCharpyVV--Notch Toughness of Notch Toughness of 20 ft.20 ft.--lbs. @ 70lbs. @ 70°° FF is is required for:required for:

ASTM A6 GROUPS 4 and 5, and forASTM A6 GROUPS 4 and 5, and forASTM A6 GROUP 3 with flanges > 1 1/2 ASTM A6 GROUP 3 with flanges > 1 1/2 inches thickinches thickPlate material thicker than 2 inchesPlate material thicker than 2 inches

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Connections Connections -- Bolted Joints Bolted Joints

•• Fully Tensioned HSB, Class A SlipFully Tensioned HSB, Class A Slip--Critical, Critical, design for bearing strength.design for bearing strength.

•• No sharing of load with welds in a joint or the No sharing of load with welds in a joint or the same force component in a connection.same force component in a connection.

•• Standard holes, or short slots perpendicular to Standard holes, or short slots perpendicular to line of force.line of force.

Oversized holes in one ply of brace diagonals Oversized holes in one ply of brace diagonals allowedallowedOther conditions allowed if verified by testingOther conditions allowed if verified by testing

•• Ductile limit Ductile limit -- state controls design.state controls design.Yielding rather than fractureYielding rather than fracture


Connections Connections -- Welded Joints Welded Joints

•• New Appendix W with welded joint requirements New Appendix W with welded joint requirements beyond standard AWS D1.1beyond standard AWS D1.1

Consistent with FEMA 353Consistent with FEMA 353Being incorporated into new AWS D1.8Being incorporated into new AWS D1.8

•• To be published later this year. Future To be published later this year. Future editions of AISC Seismic will reference as editions of AISC Seismic will reference as appropriateappropriate

•• WPS required / Approved by EORWPS required / Approved by EOR•• Continuity plate welding and detailing specifiedContinuity plate welding and detailing specified

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Test Temperature (°F)-100 -50 0 50 100 150 200 250

CV

N Im

pact

Ene

rgy

(ft-lbf)

0

20

40

60

80

100

120

Test Temperature (°C)

-50 0 50 100

CVN

Impa

ct E

nerg

y (J

)

0

50

100

150

UTA(2)

UTA E70T-6 RootUTA E70T-6 Mid-thicknessUTA E70T-6 Near SurfaceEWI E70T-6 Mid-thickness

Connections Connections -- Welded JointsWelded Joints

•• Filler metal CVN 20 ft.Filler metal CVN 20 ft.--lbs. @ lbs. @ --00°° F for F for all welds in the seismic load all welds in the seismic load resisting system (SLRS)resisting system (SLRS)

Reduction from Reduction from --2020°° F in 2002F in 2002•• Two level toughness required for Two level toughness required for

designated Demand Critical Welds in designated Demand Critical Welds in SMF, IMF, OMF and EBFSMF, IMF, OMF and EBF

based on FEMA based on FEMA recommendationsrecommendationsConsistent with previous testingConsistent with previous testingAppendix provides requirements Appendix provides requirements for qualificationfor qualification


Welded Joints (cont.)Welded Joints (cont.)•• Defines term Defines term ““Protected ZoneProtected Zone”” where where

special care is required special care is required Eliminates welding and other Eliminates welding and other attachments in plastic hinge zones attachments in plastic hinge zones (shear studs, e.g.). Spot welds (shear studs, e.g.). Spot welds acceptableacceptable

•• OK outside hinge zones, but OK outside hinge zones, but need to verify net section need to verify net section strengthstrength

Discontinuities caused by welding Discontinuities caused by welding or other construction operations or other construction operations must be repaired.must be repaired.Locations of Protected Zones Locations of Protected Zones defined for each systemdefined for each system

Fracture

Shear Stud weld

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MembersMembers•• WidthWidth--thickness ratios often stricter than main thickness ratios often stricter than main

specification requirementsspecification requirements•• Columns with high axial load to be checked for Columns with high axial load to be checked for

amplified seismic loadingamplified seismic loading•• Column SplicesColumn Splices

Strength requirement for partial penetration and fillet Strength requirement for partial penetration and fillet welded splices of 200% of required strength.welded splices of 200% of required strength.Beveled transitions not required where partial Beveled transitions not required where partial penetration welds are permitted.penetration welds are permitted.Requirements for shear strength check of Requirements for shear strength check of nonnon--frameframecolumns in columns in all all systems.systems.

•• Only location in the provisions that refers to Only location in the provisions that refers to elements not part of the SLRSelements not part of the SLRS


Mr

Mom

ent C

apac

ity

λp λr Width-Thickness Ratio

Mp

Plastic Buckling

Inelastic Buckling

Elastic Buckling

λps

Duct

ility

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Members (cont.)Members (cont.)•• Column base designColumn base design

General intent to design column base for same General intent to design column base for same forces that the elements connecting to the base forces that the elements connecting to the base are designed for.are designed for.•• Axial, shear and flexural strength Axial, shear and flexural strength

requirements presentedrequirements presentedInteraction with concrete elements referred to Interaction with concrete elements referred to ACI 318 Appendix D.ACI 318 Appendix D.

•• HH--pile requirements includedpile requirements included


Special Moment Frames (SMF)Special Moment Frames (SMF)

•• Designs based on cyclic test Designs based on cyclic test results to 0.04 radiansresults to 0.04 radians

Appendix S provides test Appendix S provides test requirementsrequirements

•• For either project specific For either project specific or or ““publicpublic”” teststests

Appendix P provides basis for Appendix P provides basis for ““prepre--qualificationqualification”” of of connectionsconnectionsConnections designed in Connections designed in accordance with AISC 358 accordance with AISC 358 standardstandard

•• Shear connection capacity Shear connection capacity sufficient to develop force sufficient to develop force generated by fully plastic beamgenerated by fully plastic beam

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(N) AISC Moment Connection (N) AISC Moment Connection Prequalification StandardPrequalification Standard

•• Official title: Official title: ““Prequalified Prequalified Connections for Special and Connections for Special and Intermediate Steel Moment Frames for Seismic Intermediate Steel Moment Frames for Seismic ApplicationsApplications””

Developed by separate ANSI standards development Developed by separate ANSI standards development committee (Ron Hamburger, Chair)committee (Ron Hamburger, Chair)

•• Allows engineers to submit moment frame designs Allows engineers to submit moment frame designs without producing connection test resultswithout producing connection test results

First edition focuses on RBS and End Plate First edition focuses on RBS and End Plate connectionsconnectionsMore connections to be included in future editionsMore connections to be included in future editions

•• Adopted by 2005 AISC SeismicAdopted by 2005 AISC Seismic


SMF (Cont.)SMF (Cont.)

•• Panel Zone DesignPanel Zone DesignIntended to share Intended to share yielding with beamyielding with beamEquation differs from Equation differs from FEMA 350FEMA 350

•• DoublerDoubler plate plate configurations may be configurations may be adjusted to avoid adjusted to avoid ““kk””areaarea

•• Continuity plates to Continuity plates to match tested match tested configurationsconfigurations

Mp2Mp1

Mp1 at column face

Mp2 at column face

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•• SCWB Check required SCWB Check required for SMF framesfor SMF frames

Attempting to avoid Attempting to avoid weak storiesweak storiesExceptions providedExceptions provided

•• Column splices pushed Column splices pushed towards CJP towards CJP

01.*

*

≥pb

pc

MM

Σ

Σ

Mc2Mc1

Mpc2

Mpc1

CL

CL



•• Lateral Bracing of Lateral Bracing of BeamsBeams

Nominal bracing Nominal bracing required along length required along length for both strength and for both strength and stiffness based on stiffness based on main spec. equationsmain spec. equationsBracing at hinges Bracing at hinges (6%) required as well(6%) required as well

•• But, not IN hinge But, not IN hinge zones!zones!

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IMF/OMF RequirementsIMF/OMF Requirements

•• Intermediate (IMF) provisions Intermediate (IMF) provisions similar to SMFsimilar to SMF

Tested capacity to 0.02 Tested capacity to 0.02 radians, beam shear, etc.radians, beam shear, etc.Other requirements (SCWB, Other requirements (SCWB, panel zone, etc.) not as panel zone, etc.) not as restrictive as SMFrestrictive as SMF

•• Ordinary (OMF) provisions Ordinary (OMF) provisions Allows calculation only, but Allows calculation only, but for strength above 1.1for strength above 1.1 RRyy MMpp

Specific welding and Specific welding and detailing requirements detailing requirements (access holes, e.g.)(access holes, e.g.)


STMFSTMF

•• Concept Similar to Concept Similar to EBFEBF’’ss•• Ductile Special Segment (SS)Ductile Special Segment (SS)•• Other Parts of the Truss Other Parts of the Truss

Remain ElasticRemain Elastic•• Both CrossBoth Cross--braced and braced and

Vierendeel Vierendeel configurationsconfigurations•• Span limited to 65 feetSpan limited to 65 feet•• Depth limited to 6 feetDepth limited to 6 feet

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Special CBF ProvisionsSpecial CBF Provisions

•• KL / r < 4 / KL / r < 4 / ëëE/E/FFyy•• Stricter b/t Ratios and BuiltStricter b/t Ratios and Built--up up

Member RequirementsMember Requirements•• Connection RequirementsConnection Requirements

Strength to Develop Strength to Develop Tensile StrengthTensile StrengthDuctility to Allow Buckling Ductility to Allow Buckling in Member or Gusset Platein Member or Gusset Plate

•• Restrictions on Chevron and Restrictions on Chevron and KK--BracingBracing

•• Stronger Column Splices Stronger Column Splices RequiredRequired


OCBF ProvisionsOCBF Provisions

•• Limited use in high Limited use in high SDCSDC’’ss•• For V or inverted V, KL / r < For V or inverted V, KL / r <

4.23 / 4.23 / ëëE/E/FFy y

•• Connection strength to Connection strength to develop brace tension develop brace tension capacity or amplified forcecapacity or amplified force

•• Chevron bracing restrictionsChevron bracing restrictions•• Tension Only Bracing Systems Tension Only Bracing Systems

Allowed for Low Buildings Allowed for Low Buildings (Less than Two Stories) and (Less than Two Stories) and PenthousesPenthouses

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EBF ProvisionsEBF Provisions

•• Inelastic behavior Inelastic behavior limited to link beamslimited to link beams

•• Remainder of the Remainder of the system to remain elastic system to remain elastic

•• Best results for shear Best results for shear link elements, but local link elements, but local demands are higher demands are higher than than SMFSMF’’ss

Extensive stiffening Extensive stiffening requirementsrequirements


EBF Provisions (Cont.)EBF Provisions (Cont.)•• LinkLink--toto--column connectionscolumn connections

Require testing like SMFRequire testing like SMF•• Exception allowedException allowed

•• Beam outside link, braces Beam outside link, braces and columns designed for and columns designed for link capacity, including link capacity, including strain hardeningstrain hardening

•• Lateral bracing Lateral bracing requirements similar to SMFrequirements similar to SMF

6% at ends of links6% at ends of linksElsewhere, strength and Elsewhere, strength and stiffness as required in stiffness as required in main spec.main spec.

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BRBF ProvisionsBRBF Provisions•• BRBF FramesBRBF Frames

•• SCBF development improves SCBF development improves braced frame performance, but braced frame performance, but still limited by brace bucklingstill limited by brace buckling

•• Concept developed in Japan, with Concept developed in Japan, with many applicationsmany applications

Hysteretic behavior similar to Hysteretic behavior similar to elastic elastic -- perfectly plasticperfectly plastic

•• Development of provisions in U.S.Development of provisions in U.S.Joint AISC/SEAOC effortJoint AISC/SEAOC effort

•• Approach similar to EBFApproach similar to EBFAnalytical work indicates good Analytical work indicates good performanceperformanceU.S. practice will lead to larger U.S. practice will lead to larger driftsdriftsIncluded in 2003 NEHRPIncluded in 2003 NEHRP


BRBF Provisions (cont.) BRBF Provisions (cont.)

•• Steel core restrained from bucklingSteel core restrained from bucklingBraces tested for twice Design Story DriftBraces tested for twice Design Story Drift

•• Appendix T specifies testing requirementsAppendix T specifies testing requirementsBrace strength addresses strain hardening and Brace strength addresses strain hardening and compression strength increase due to confining compression strength increase due to confining systemsystem

•• Connections designed for adjusted strengthConnections designed for adjusted strength•• Chevron requirements less demanding than SCBFChevron requirements less demanding than SCBF•• Column splices similar to SCBFColumn splices similar to SCBF

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SPSW ProvisionsSPSW Provisions

•• SPSW SystemSPSW System•• SPSW like plate girder SPSW like plate girder

design approach (tension design approach (tension field theory)field theory)

•• Can generate tremendous Can generate tremendous strength and stiffness as strength and stiffness as compared to CBFcompared to CBF

•• SPSW concept developed SPSW concept developed in Canadain Canada

•• NBCC Code provisions NBCC Code provisions in placein place

UC Berkeley work as wellUC Berkeley work as wellProvisions incorporated Provisions incorporated into 2003 NEHRP into 2003 NEHRP


SPSW Provisions (cont.) SPSW Provisions (cont.)

•• Panel Capacity Based on Simple FormulaPanel Capacity Based on Simple FormulaIncludes panel aspect ratioIncludes panel aspect ratio•• L/h between 0.8 and 2.5L/h between 0.8 and 2.5

•• Panels with Openings to have boundary elements (BE)Panels with Openings to have boundary elements (BE)•• Connection between web and Connection between web and BEBE’’s s for capacityfor capacity•• BEBE’’s s to develop panels. OMF style connectionsto develop panels. OMF style connections•• Lateral bracing spacing like SMF.Lateral bracing spacing like SMF.•• Vertical Vertical BEBE’’s s also have bending stiffness requirementsalso have bending stiffness requirements

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Quality Assurance Quality Assurance

•• Detailed Appendix Q replaces general set of provisions Detailed Appendix Q replaces general set of provisions in previous editionsin previous editions

•• Consistent with FEMA 353 and AWS D1.8Consistent with FEMA 353 and AWS D1.8•• QA plan required. Covers both QA and QC.QA plan required. Covers both QA and QC.•• Documentation requirements listedDocumentation requirements listed•• Visual Inspection Points and Frequency DefinedVisual Inspection Points and Frequency Defined

For before, during and after welding or bolting by For before, during and after welding or bolting by both QA and QC. Shown in tabular formatboth QA and QC. Shown in tabular format

•• ““Observe, Perform and/or DocumentObserve, Perform and/or Document””•• NDT locations and requirements specified. Both UT and NDT locations and requirements specified. Both UT and

Magnetic Particle incorporated. All results documentedMagnetic Particle incorporated. All results documented..


Part II Part II -- Composite ProvisionsComposite Provisions

•• Part II Part II -- Composite Construction ProvisionsComposite Construction ProvisionsFirst Developed for 1994 NEHRPFirst Developed for 1994 NEHRPIdentifies Numerous System OptionsIdentifies Numerous System OptionsProvides Detailed Requirements for Provides Detailed Requirements for Member and Connection DesignMember and Connection DesignModified and Made Consistent with Part 1Modified and Made Consistent with Part 1

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Composite CBF Composite CBF ConnectionConnection

Composite Shear Composite Shear Wall DetailWall Detail


Status and Upcoming ActivitiesStatus and Upcoming Activities•• AISC 341 approved by reference in ASCE 7AISC 341 approved by reference in ASCE 7--

05, Supplement No. 105, Supplement No. 1•• Included in 2006 IBCIncluded in 2006 IBC•• AWS D1.8 completed and publishedAWS D1.8 completed and published•• Work is underway on 2010 EditionWork is underway on 2010 Edition

Suggestions and comments welcomed Suggestions and comments welcomed and encouraged!and encouraged!

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Status of Work on 2010 EditionStatus of Work on 2010 Edition•• Some reSome re--formatting being done to make formatting being done to make

document more consistent with AISC 360document more consistent with AISC 360•• Incorporating Composite Provisions Incorporating Composite Provisions

directly into the document (No more Part I directly into the document (No more Part I and Part II)and Part II)

•• Developing design/analysis provisions that Developing design/analysis provisions that will explicitly follow capacity design will explicitly follow capacity design approach for ALL systemsapproach for ALL systems

•• Updates to specific member and system Updates to specific member and system requirementsrequirements

•• First internal ballots this yearFirst internal ballots this year•• To be included in ASCE 7To be included in ASCE 7--10 and 2012 IBC10 and 2012 IBC


AISC Documents Related to AISC Documents Related to Seismic DesignSeismic Design

•• 2005 AISC Seismic Provisions (ANSI/AISC 340)2005 AISC Seismic Provisions (ANSI/AISC 340)Available via downloadAvailable via download

•• 2005 AISC Moment Connection Prequalification 2005 AISC Moment Connection Prequalification Standard (ANSI/AISC 358)Standard (ANSI/AISC 358)

Available via downloadAvailable via download•• 2005 AISC Specification for Structural Steel 2005 AISC Specification for Structural Steel

Buildings (ANSI/AISC 360)Buildings (ANSI/AISC 360)Available via downloadAvailable via download

•• 2005 AISC Seismic Design Manual2005 AISC Seismic Design ManualAvailable for purchaseAvailable for purchase

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AISC Seismic Design ManualAISC Seismic Design Manual•• 11stst Edition to Assist designers in applying AISC 341Edition to Assist designers in applying AISC 341

Practical guide similar to SEAOC SDC SeriesPractical guide similar to SEAOC SDC Series•• Common systems addressed with detailed design Common systems addressed with detailed design

examplesexamplesSMF, IMF, OMFSMF, IMF, OMFCBF, EBFCBF, EBFOther systems (BRBF and SPSW) discussedOther systems (BRBF and SPSW) discussedBoth R=3 and R>3 designs addressedBoth R=3 and R>3 designs addressed

•• Special elements (chords and collectors) and issues Special elements (chords and collectors) and issues (maximum force that can be delivered) addressed(maximum force that can be delivered) addressed

•• ONLY in LRFD format, though ASD is also allowed in ONLY in LRFD format, though ASD is also allowed in AISC 341 AISC 341


Concluding CommentsConcluding Comments

•• Unified Process for Steel Seismic Provision Unified Process for Steel Seismic Provision DevelopmentDevelopment

"Single Point of Responsibility" eliminates "Single Point of Responsibility" eliminates duplicative effort and minor differences that duplicative effort and minor differences that result in major confusionresult in major confusionAllows rapid incorporation of new information Allows rapid incorporation of new information

•• WE WANT YOUR INPUT AND WE WANT YOUR INPUT AND RECOMMENDATIONS FOR IMPROVEMENTS!RECOMMENDATIONS FOR IMPROVEMENTS!