Presentation on theme: "Changes to the 2010 AISC Seismic Provisions"— Presentation transcript:
1 Changes to the 2010 AISC Seismic Provisions James O. MalleySenior Principal, Degenkolb Engineersand Chair, AISC TC9
2 TC 9 – “The Hardest Working Committee in Show Biz” Roy Becker (‘05)Michel Bruneau (‘10)Greg DeierleinRick DrakeMike EngelhardtRoger Ferch (‘05)Tim Fraser*Subhash GoelJerry Hajjar (‘10)*Ron Hamburger (‘10)Jim HarrisPat Hassett (’10)John Hooper (‘10)Brian Knight (‘10)Keith Landwehr (‘10)Roberto LeonBob Lyons (‘05)Sanj MalushteBonnie Manley (‘10)*Hank Martin (‘05)*Clarkson PinkhamJohn Rolfes (‘10)Rafael Sabelli*Mark Saunders*Tom SabolBahram ShahroozBob Shaw*Lee ShoemakerKurt SwenssonRobert Tremblay (‘10)Jamie Winans (’10)Cindi Duncan **Plus Corresponding Members* SC Chair** Secretary
3 AISC 341 (2005 and 2010)AISC was now included by reference in 2006 and 2009 IBC. Same for AISC 360.AISC and are included by reference in 2012 IBC.Both the 2005 and 2010 Provisions will be summarized together to highlight update of “newest attractions”Presentation based on order of 2005 EditionFocus of discussion on 2010 changes
4 Overall Philosophy of AISC 341 Identify Target Yield Mechanism for Each SLRSDesignate Deformation-Controlled Elements (Structural Fuse):Design for Reduced Seismic ForcesDuctility Design Is Relatively Straightforward (Prescriptive)Design Remaining Elements as Force-Controlled: Design for Forces to Remain “Essentially Elastic at Capacity of FusesUse Either “Local” or “Global” ApproachCapacity Design Requires Good Judgment and ExperienceCredit: C. M. Uang
5 It’s This Simple…Target Mechanism Plus Ductility Requirements Plus Capacity Design Requirements Equals…Target Yield MechanismsFlexural Yielding Tensile Yielding/Buckling Shear Yielding
6 Major Elements of 2005 Seismic Provisions Part I covers all Major Seismic SystemsFocus on SDC D, E and FCoordinated with ASCE 7-05Incorporate Post-Northridge FindingsFEMA/SAC Project Results (FEMA 350 Series) as Well as Other EffortsComposite Provisions from NEHRP Included (Part II)Note that Both Parts are in the “Unified” Format similar to the Main AISC SpecificationBoth LRFD and ASD included in one set of provisions
7 Summary of Major Changes in AISC 341-10 Re-organized to be More Consistent with AISCFormat for Various Systems Have Been StandardizedIncorporates AWS D1.8Puts Composite Construction on the Same Footing as Steel (No more Parts I and II)Adds Two New Cantilever Column SystemsDeveloping design/analysis provisions explicitly follow capacity design approach for ALL systemsUpdates to member and system requirementsCoordinated with ASCE To be included in 2012 IBC
8 Document Re-organization A. General RequirementsA1. Scope (I-1, II-1)A2. References (I-2, II-2)A3. Materials (I-6, I-7, II-5)A4. Structural Design Drawings and Specifications (I-5, II-18)B. General Design RequirementsB1. General Seismic Design Requirements (I-3)B2. Loads and Load Combinations (I-4, II-4)B3. Design Basis (I-3)B4. System Type
9 Document Re-Organization (Con’t.) C. AnalysisC1. General RequirementsC2. Additional RequirementsC3. Nonlinear AnalysisD. General Member and Connection Design RequirementsD1. Member Requirements (I6-I9, II8)D2. Connections (I7, I8, II-7)D3 Deformation Compatibility of Non-SFRS Members and ConnectionsD4. H-Piles (I-8)
10 Document Re-Organization (Con’t.) E. Moment-Frame SystemsE1. Ordinary Moment Frames (I-11)E2. Intermediate Moment Frames (I-10)E3. Special Moment Frames (I-9)E4. Special Truss Moment Frames (I-12)E5. Ordinary Cantilever Column SystemsE6. Special Cantilever Column Systems
11 Document Re-Organization (Con’t.) F. Braced-Frame and Shear-Wall SystemsF1. Ordinary Concentrically Braced Frames (I-14)F2. Special Concentrically Braced Frames (I-13)F3. Eccentrically Braced Frames (I-15)F4. Buckling-Restrained Braced Frames (I-16)F5. Special Plate Shear Walls (I-17)G. Composite Moment Frame SystemsG1. Composite Ordinary Moment Frames (II-11)G2. Composite Intermediate Moment Frames (II-10)G3. Composite Special Moment Frames (II-9)G4. Composite Partially Restrained Moment Frames (II-8)
12 Document Re-Organization (Con’t.) H. Composite Braced Frame and Shear-Wall SystemsH1. Composite Ordinary Braced Frames (I-13)H2. Composite Special Concentrically Braced Frames (II-12)H3. Composite Eccentrically Braced Frames (II-14)H4. Composite Ordinary Shear Walls (II-15)H5. Composite Special Shear Walls (II-16)H6. Composite Special Plate Shear Walls (I-17)I. Fabrication and ErectionI1. Shop and Erection Drawings (I5, App. W, II-18)I2. Fabrication and Erection (I7)
13 Document Re-Organization (Con’t.) J. Quality Control and Quality AssuranceJ1. Scope (I-18, App Q, II-19)J2. Fabricator and Erector Documents (App. Q)J3. Quality Assurance Agency Documents (App. Q)J4. Inspection and Nondestructive Testing Personnel (App. Q)J5. Inspection Tasks (App. Q)J6. Welding Inspection and Nondestructive Testing (App. Q)J7. Inspection of High-Strength Bolting (App. Q)J8. Other Steel Structure Inspections (App. Q.)J9. Inspection of Composite StructuresJ10. Inspection of H-Piles
14 Document Re-Organization (Con’t.) K. Prequalification and Cyclic Qualification Testing ProvisionsK1. Prequalification of Beam-to-Column and Link-to-Column Connections (App. P)K2. Cyclic Tests for Qualification of Beam-to-Column and Link-to-Column Connections (App. S)K3. Cyclic Tests for Qualification of Buckling-Restrained Braces (App. T)
15 Scope Statement / Gen’l Req’ts. Intended Primarily for Building StructuresAlso incorporated for “building like” non-building structuresGlossary clarifies that SLRS includes diaphragm chords and collectors, and all elements that resist seismic loadsFor SDC A, B and C, designer has choiceUse the Seismic Provisions with appropriate R factorUse AISC LRFD/ASD Provisions with R=3Required When Specified by ASCE 7-10SDC D, E, and F, typicallyClarifies use of ACI 318 for R/C elements in composite systems
16 General Design Requirements SDC, Height Limitations, Design Story Drift per ASCE 7-10Defines how to apply Ω0 and Emh in ASCE 7-10,Required Strength either generated by analysis or the system requirements (capacity based design concepts)Available Strength per LRFD or ASD
17 Project Documentation Requirements New Section to Define Expectations of:Design drawings and specificationsShop DrawingsErection DrawingsRequirements for Shop and Erection Drawings moved to Chapter JIncludes lists of information to be provided such as SLRS designation, connection detailing, welding requirements, protected zones, etc.Consistent with FEMA 353 and AWS D1.8 references incorporated in 2010
18 Material Specifications ASTM Specifications for Materials EmployedAll major structural products incorporatedMaterial Properties for Determination of Required Strength for Connections or Related Members Based on Expected Yield Strength and Expected Tensile Strength (Ry and Rt)Available Strength to consider both expected yield and tensile strengthsIntent is to ensure expected inelastic response and ductile failure modes
19 Material Specifications (Cont.) Requirements for Charpy V-notch testing of heavy shapes and platesExpand use of yield strength above 50 ksiReference to AWS D1.8 for filler metals
20 Connections - Bolted Joints Fully Tensioned HSB, Class A Slip-Critical, design for bearing strength.No sharing of load with welds in a joint or the same force component in a connection.Standard holes, or short slots perpendicular to line of force.Oversized holes in one ply of brace diagonals allowedOther conditions allowed if verified by testingDuctile limit - state controls design.Yielding rather than fractureRemoved in 2010
21 Connections - Welded Joints New Appendix W with welded joint requirements beyond standard AWS D1.1Consistent with FEMA 353Being incorporated into new AWS D1.8Published in late Future editions of AISC Seismic will reference as appropriate. Referenced in 2010.WPS required / Approved by EORContinuity plate welding and detailing specified
22 Connections - Welded Joints Filler metal CVN 20 -0° F for all welds in the seismic load resisting system (SLRS)Reduction from -20° F in 2002Two level toughness required for designated Demand Critical Welds in SMF, IMF, OMF and EBFbased on FEMA recommendationsConsistent with previous testingAppendix provides requirements for qualificationReferred to AWS D1.8. Locations defined in AISC 341
23 Welded Joints (cont.)Defines term “Protected Zone” where special care is requiredEliminates welding and other attachments in plastic hinge zones (shear studs, e.g.). Spot welds acceptableOK outside hinge zones, but need to verify net section strengthDiscontinuities caused by welding or other construction operations must be repaired.Locations of Protected Zones defined for each systemFractureShear Stud weld
24 MembersWidth-thickness ratios often stricter than main specification requirements2010 Defines new terms, “Moderately” and “Highly” Ductile (MD and HD)Used for width-thickness and bracing reqt’sWidth-thickness table parallels B4.1 in AISC 360MD like compact, HD, like seismically compactHSS values reduced due to test resultsBoxed WF sections includedComposite elements included
25 Width-Thickness Ratio Ductility Plastic BucklingMpInelastic BucklingMoment CapacityMrElastic BucklingpsprWidth-Thickness RatioDuctility
26 Members – Cont. New paragraph on diaphragm design Load transfer details requiredNominal shear strength defined as concrete above deck, w/o ACI Ch. 22, or test resultsBracing requirements made uniform for various systemsSpecial requirements at plastic hingesColumns with high axial load to be checked for amplified seismic loadingSimilar to , but ALL columns checked for Ω0 level axial forcesNew requirements for composite columns
27 Column Splices/BasesStrength requirement for partial penetration and fillet welded splices of 200% of required strength.Beveled transitions not required where partial penetration welds are permitted.Requirements for shear strength check of non-frame columns in all systems.Only location in the provisions that refers to elements not part of the SLRSClarifies use beveled transitions in CJP splices and removal of weld tabs (but not backing) per D1.8Column base weld backing reqt’s also defined
28 Members (cont.) Column base design (Con’t) General intent to design column base for same forces that the elements connecting to the base are designed for.Axial, shear and flexural strength requirements presentedInteraction with concrete elements referred to ACI 318 Appendix D.Clarifying language addedH-pile requirements included
29 Deformation Compatibility New Section highlights need to check non-SLRS members and connections for gravity load effects and deformations at the Design Story Drift as defined in ASCE 7-10User Note added to justify shear tab connections and allow self-limiting inelastic deformations in other connections
30 Chapter C – Analysis (2010) Entirely new chapter Defines section properties for elastic analysesElastic sections for steelCracked sections for concrete and composite elementsRefers to system chapters for additional (capacity based requirements)Refers to ASCE 7-10 Chapter 16 when nonlinear analyses used
31 System Formats Unified in 2010! Scope – defines system titleBasis of Design – defines expected system response (yielding and protected members etc.)Analysis – defines special analyses for capacity definitions (SCBF, e.g.)System Reqt’s – stability bracing and other system-wide reqt’sMembers – sets b/t limits, lists protected zones and defines individual member reqt’sConnections – defines demand critical welds, and connection reqt’s, including splices
32 Special Moment Frames (SMF) Designs based on cyclic test results to 0.04 radiansAppendix S provides test requirementsFor either project specific or “public” testsAppendix P provides basis for “pre-qualification” of connectionsConnections designed in accordance with AISC 358 standardShear connection capacity sufficient to develop force generated by fully plastic beam
33 (N) AISC Moment Connection Prequalification Standard Official title: “Prequalified Connections for Special and Intermediate Steel Moment Frames for Seismic Applications”Developed by separate ANSI standards development committee (Ron Hamburger, Chair)Allows engineers to submit moment frame designs without producing connection test resultsFirst edition focuses on RBS and End Plate connectionsMore connections included (WUF-W, e.g.)Adopted by 2005 & 2010 AISC Seismic
34 SMF (Cont.) Panel Zone Design Intended to share yielding with beam Mp2Mp1Mp1 at column faceMp2 at column facePanel Zone DesignIntended to share yielding with beamEquation differs from FEMA 350Doubler plate configurations may be adjusted to avoid “k” areaContinuity plates to match tested configurations
35 SMF (Cont.) SCWB Check required for SMF frames Attempting to avoid weak storiesExceptions provided2010 clarifies use of Ω0 for axial force reductionColumn splices pushed towards CJPMc2Mc1Mpc2Mpc1CL
36 SMF (Cont.) Lateral Bracing of Beams Nominal bracing required along length for both strength and stiffness based on main spec. equationsBracing at hinges (6%) required as wellBut, not IN hinge zones!
37 IMF/OMF Requirements Intermediate (IMF) provisions similar to SMF Tested capacity to 0.02 radians, beam shear, etc.Other requirements (SCWB, panel zone, etc.) not as restrictive as SMF. MD designation for members.DC welds at splicesOrdinary (OMF) provisionsAllows calculation only, but for strength above 1.1 Ry MpSpecific welding and detailing requirements (access holes, e.g.)
38 STMF Concept Similar to EBF’s Ductile Special Segment (SS) Other Parts of the Truss Remain ElasticBoth Cross-braced and Vierendeel configurationsSpan limited to 65 feetDepth limited to 6 feetMinor change to SS capacityDC welds added for column splices
39 Cantilever Columns (2010)Two (N) sections to be consistent with ASCE 7-10(N) SDC and height limits in ASCE 7-10Ordinary System (OCCS)Column axial loads low (15% of available at Ω0)AISC 360 b/t ratios, no DC welds or protected zonesSpecial System (SCCS)HD b/t ratios, stability bracing for MD, protected zone at base, DC welds at base
40 Special CBF Provisions KL / r < 4 / E/Fy with exception to higherStricter b/t Ratios and Built-up Member RequirementsConnection RequirementsStrength to Develop Tensile StrengthDuctility to Allow Buckling in Member or Gusset PlateRestrictions on Chevron and K-BracingStronger Column Splices RequiredCapacity Design Requires two load distributions be checkedConnection Reqts. Increased (EBF and BRBF also), to accommodate driftDC welds at column splices and bases. No PJP groove welded splices
41 2010 Analysis Req’t. - SCBF oF3 oF2 oF1 Uplift in Center Column!
42 OCBF Provisions Limited use in high SDC’s For V or inverted V, KL/r < 4.23/E/FyConnection strength to develop brace tension capacity or amplified forceReorganized language to clarify expected compression strengthChevron bracing restrictionsTension Only Bracing Systems Allowed for Low and PenthousesNo K-Bracing & define minor eccentricities (similar for SCBF’s)
43 EBF Provisions Inelastic behavior limited to link beams Remainder of system (braces and columns) to remain elasticBest results for shear link elements, but local demands are higher than SMF’sExtensive stiffening requirementsBuilt-up Boxes added for linksBased on recent Bruneau researchClarification on calc for inelastic rotation angleOther changes similar to SCBF
44 EBF Provisions (Cont.) Link-to-column connections Require testing like SMFException allowedBeam outside link, braces and columns designed for link capacity, including strain hardening (1.25 & 1.1)Lateral bracing requirements similar to SMF6% at ends of linksElsewhere, strength and stiffness as required in main spec.PbrPu
45 Approach similar to EBF BRBF ProvisionsBRBF FramesSCBF development improves braced frame performance, but still limited by brace bucklingConcept developed in Japan, with many applicationsHysteretic behavior similar to elastic - perfectly plasticDevelopment of provisions in U.S.Joint AISC/SEAOC effortApproach similar to EBFAnalytical work indicates good performanceU.S. practice will lead to larger driftsIncluded in 2003 NEHRP
46 BRBF Provisions (cont.) Steel core restrained from bucklingBraces tested for twice Design Story DriftAppendix T specifies testing requirementsBrace strength addresses strain hardening and compression strength increase due to confining systemConnections designed for adjusted strengthChevron requirements less demanding than SCBFColumn splices similar to SCBFIncreased Connection Reqt’s, DC welds at column splices and base, and no PJP groove welded splices similar to SCBF
47 SPSW ProvisionsSPSW like plate girder design approach (tension field theory)Can generate tremendous strength and stiffness as compared to CBFSPSW concept developed in CanadaNBCC Code provisions in placeUC Berkeley work as wellProvisions incorporated into 2003 NEHRPPanel Capacity Based on Simple FormulaIncludes panel aspect ratioL/h between 0.8 and 2.5
48 SPSW Provisions (cont.) Panels with Openings to have boundary elements (BE)Connection between web and BE’s for plate capacityBE’s to develop panels. OMF style connectionsLateral bracing spacing like SMF.Vertical BE’s also have bending stiffness requirementsPerforated Webs and corner cut-outs addedAdded HBE stiffnessProtected zones addedIncreased Connection Reqt’s, DC welds at column splices and base, and no PJP groove welded splices similar to SCBF
49 Composite Systems Part II - Composite Construction Provisions First Developed for 1994 NEHRPIdentifies Numerous System Options (10 total in 2010)Provides Detailed Requirements for Member and Connection DesignModified and Made Consistent with Part INo longer Part II. Made Fully Consistent with Chapters E and FMANY changes required
50 Chapter D: General Member and Connection Requirements SRC Beam-Columns:Moderately and highly ductile detailing procedures (comparable to AISC )CFT Beam-Columns:Shear strengths is based on steel section aloneConnections:Non-seismic provisions include clearer text on load transfer for general composite conditions:Bond interactionDirect bearingSteel anchorsNon-seismic provisions include new provisions for steel anchors in shear, tension, and interaction for conditions beyond composite beamsSplice connection provisions for SRC refer to ACI Ch. 21 provisions for mechanical splicingSeismic connection detailing provisions are mainly for steel girders framing into RC or SRC beam-columnsWritten in early 1990’s
51 Chapter D: General Member and Connection Requirements Steel Anchors: Where steel headed stud anchors or welded reinforcing bar anchors are part of the intermediate or special SFRS of Sections G2, G3, G4, H2, H3, H5 and H6, their shear and tensile strength shall be reduced by 25% from the specified strengths given in Specification Chapter I.User Note: The 25% reduction is not necessary for gravity and collector components in structures with intermediate or special seismic force resisting systems designed for the amplified seismic load.
52 Composite Special Moment Frames C-SMF: Section G3 Composite or RC columns + steel, SRC or composite beamsConfine inelastic deformation to the girders and column bases with limited yielding in panel zones.Protected zones in inelastic region of girdersDemand critical welds at connections, splices and base platesOther provisions are intended to limit or prevent excessive panel zone distortion, failure of connectivity plates or diaphragms, column hinging, splice failure, and local buckling that may lead to inadequate frame performance in spite of good connection performanceSCWB similar to steel SMF
53 Composite Special Moment Frames C-SMF: Section G3 Beam-to-composite column connections used in the SFRS shall satisfy the following requirements:(1) Accommodate a story drift angle of at least 0.04 rad.(2)The measured flexural resistance of the connection shall equal at least 0.80Mp of the connected beam at a story drift angle of 0.04 rad.Composite SRC Moment-Resisting ConnectionComposite CFT Moment-Resisting Connection
54 Composite Ordinary Shear Walls C-OSW: Section H4 Limited inelastic deformationEnsure yielding of the coupling beams in shear or flexureAccount for cracked section properties for concrete per ACI 318 Chapter 10 or ASCE 41Structural steel or composite coupling beamsMay redistribute coupling beam forces up to 20% providedVertical Redistribution of Coupling Beam Shear
55 Composite Special Shear Walls C-SSW: Section H5 Significant inelastic deformationEnsure shear yielding of the coupling beamsSystem requirements similar to C-OSW with the following exceptions:Coupling beams yield over the building height followed by yielding at the base of the wall piersApply a wall overstrength factor ωo to the wall design forcesThe axial design strength of the wall at the balanced condition (Pb) shall equal or exceed the sum of 1.1RyVn of the coupling beamsUse 1.1RyVn or 1.1RyVp to compute the embedment length (Le).
56 Typical Coupling Beam Detailing This slide shows what coupling beams are and shows examples of steel/composite coupling beams.
57 Composite Plate Shear Walls C-PSW: Section H6 Inelastic deformation capacity through yielding in the steel plate webs (steel alone is used to assess strength) and yielding of the vertical boundary element (VBE) at the baseDemand critical welds for splices, base plates, and HBE-to-VBE connectionsProvisions for required strength in steel anchor connectorsDetailing provisions refer to SPSW
58 QC and QADetailed Appendix Q replaced general set of provisions in previous editions. (Changed to Chapter J in 2010)Consistent with FEMA 353 and AWS D1.8. References AWS D1.8QA plan required in conjunction with IBC Chapter 17. Covers both QA and QC.Documentation requirements listedVisual Inspection Points and Frequency DefinedFor before, during and after welding or bolting by both QA and QC. Shown in tabular format“Observe, Perform and/or Document” vs. Periodic/ContinuousNDT locations and requirements specified. Both UT and Magnetic Particle incorporated. All results documented.Adds parallel composite construction requirements
59 Status and Upcoming Activities AISC approved by reference in ASCE 7-10, Supplement No. 1Included in 2012 IBCWork is underway on 2016 EditionTo be referenced in ASCE 7-16 and 2018 IBCFirst ballot to COS underwayChanges not as dramatic as , but…Public ballots next Spring, complete late next yearYour comments/suggestions welcome!
60 AISC Documents Related to Seismic Design 2010 AISC Seismic Provisions (ANSI/AISC 341)Available via download.2010 AISC Moment Connection Prequalification Standard (ANSI/AISC 358).2010 AISC Specification for Structural Steel Buildings (ANSI/AISC 360)2012 AISC Seismic Design ManualAvailable for purchase. Work on 2018 underway.
61 Concluding CommentsUnified Process for Steel Seismic Provision Development"Single Point of Responsibility" eliminates duplicative effort and minor differences that result in major confusionAllows rapid incorporation of new information2010 Provisions Another Step Forward (We HOPE!)Format improved, technical updates and incorporates AWS D1.8WE WANT YOUR INPUT AND RECOMMENDATIONS FOR IMPROVEMENTS!