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Changes to the 2010 AISC Seismic Provisions

Changes to the 2010 AISC Seismic Provisions. James O. Malley Senior Principal, Degenkolb Engineers and Chair, AISC TC9. TC 9 – “The Hardest Working Committee in Show Biz”. Tom Sabol Bahram Shahrooz Bob Shaw* Lee Shoemaker Kurt Swensson Robert Tremblay (‘10)

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Changes to the 2010 AISC Seismic Provisions

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  1. Changes to the 2010 AISCSeismic Provisions James O. Malley Senior Principal, Degenkolb Engineers and Chair, AISC TC9

  2. TC 9 – “The Hardest Working Committee in Show Biz” • Tom Sabol • BahramShahrooz • Bob Shaw* • Lee Shoemaker • Kurt Swensson • Robert Tremblay (‘10) • Jamie Winans (’10) • Cindi Duncan ** • Plus Corresponding Members • * SC Chair • ** Secretary • RoyBecker (‘05) • Michel Bruneau (‘10) • Greg Deierlein • Rick Drake • Mike Engelhardt • Roger Ferch (‘05) • Tim Fraser* • Subhash Goel • Jerry Hajjar (‘10)* • Ron Hamburger (‘10) • Jim Harris • Pat Hassett (’10) • John Hooper (‘10) • Brian Knight (‘10) • Keith Landwehr (‘10) • Roberto Leon • Bob Lyons (‘05) • SanjMalushte • Bonnie Manley (‘10)* • Hank Martin (‘05)* • Clarkson Pinkham • John Rolfes (‘10) • Rafael Sabelli* • Mark Saunders*

  3. AISC 341 (2005 and 2010) • AISC 341-05 was now included by reference in 2006 and 2009 IBC. Same for AISC 360. • AISC 360-10 and 341-10 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 Edition • Focus of discussion on 2010 changes

  4. Overall Philosophy of AISC 341 • Identify Target Yield Mechanism for Each SLRS • Designate Deformation-Controlled Elements (Structural Fuse): Design for Reduced Seismic Forces Ductility Design Is Relatively Straightforward (Prescriptive) • Design Remaining Elements as Force-Controlled: Design for Forces to Remain “Essentially Elastic at Capacity of Fuses Use Either “Local” or “Global” Approach Capacity Design Requires Good Judgment and Experience Credit: C. M. Uang

  5. It’s This Simple… Target Yield Mechanisms Flexural Yielding Tensile Yielding/Buckling Shear Yielding Target Mechanism Plus Ductility Requirements Plus Capacity Design Requirements Equals…

  6. Major Elements of 2005 Seismic Provisions • Part I covers all Major Seismic Systems • Focus on SDC D, E and F • Coordinated with ASCE 7-05 • Incorporate Post-Northridge Findings • FEMA/SAC Project Results (FEMA 350 Series) as Well as Other Efforts • Composite Provisions from NEHRP Included (Part II) • Note that Both Parts are in the “Unified” Format similar to the Main AISC Specification • Both 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 AISC 360-10 • Format for Various Systems Have Been Standardized • Incorporates AWS D1.8 • Puts Composite Construction on the Same Footing as Steel (No more Parts I and II) • Adds Two New Cantilever Column Systems • Developing design/analysis provisions explicitly follow capacity design approach for ALL systems • Updates to member and system requirements • Coordinated with ASCE 7-10. To be included in 2012 IBC

  8. Document Re-organization • A. General Requirements • A1. 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 Requirements • B1. 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. Analysis • C1. General Requirements • C2. Additional Requirements • C3. Nonlinear Analysis • D. General Member and Connection Design Requirements • D1. Member Requirements (I6-I9, II8) • D2. Connections (I7, I8, II-7) • D3 Deformation Compatibility of Non-SFRS Members and Connections • D4. H-Piles (I-8)

  10. Document Re-Organization (Con’t.) • E. Moment-Frame Systems • E1. 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 Systems • E6. Special Cantilever Column Systems

  11. Document Re-Organization (Con’t.) • F. Braced-Frame and Shear-Wall Systems • F1. 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 Systems • G1. 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 Systems • H1. 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 Erection • I1. 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 Assurance • J1. 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 Structures • J10. Inspection of H-Piles

  14. Document Re-Organization (Con’t.) • K. Prequalification and Cyclic Qualification Testing Provisions • K1. 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’lReq’ts. • Intended Primarily for Building Structures • Also incorporated for “building like” non-building structures • Glossary clarifies that SLRS includes diaphragm chords and collectors, and all elements that resist seismic loads • For SDC A, B and C, designer has choice • Use the Seismic Provisions with appropriate R factor • Use AISC LRFD/ASD Provisions with R=3 • Required When Specified by ASCE 7-10 • SDC D, E, and F, typically • Clarifies use of ACI 318 for R/C elements in composite systems

  16. General Design Requirements • SDC, Height Limitations, Design Story Drift per ASCE 7-10 • Defines 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 specifications • Shop Drawings • Erection Drawings • Requirements for Shop and Erection Drawings moved to Chapter J • Includes 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 Employed • All major structural products incorporated • Material 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 strengths • Intent is to ensure expected inelastic response and ductile failure modes

  19. Material Specifications (Cont.) • Requirements for Charpy V-notch testing of heavy shapes and plates • Expand use of yield strength above 50 ksi • Reference 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 allowed • Other conditions allowed if verified by testing • Ductile limit - state controls design. • Yielding rather than fracture • Removed in 2010

  21. Connections - Welded Joints • New Appendix W with welded joint requirements beyond standard AWS D1.1 • Consistent with FEMA 353 • Being incorporated into new AWS D1.8 • Published in late 2005. Future editions of AISC Seismic will reference as appropriate. Referenced in 2010. • WPS required / Approved by EOR • Continuity plate welding and detailing specified

  22. Connections - Welded Joints • Filler metal CVN 20 ft.-lbs. @ -0° F for all welds in the seismic load resisting system (SLRS) • Reduction from -20° F in 2002 • Two level toughness required for designated Demand Critical Welds in SMF, IMF, OMF and EBF • based on FEMA recommendations • Consistent with previous testing • Appendix provides requirements for qualification • Referred to AWS D1.8. Locations defined in AISC 341

  23. Welded Joints (cont.) Fracture Shear Stud weld • Defines term “Protected Zone” where special care is required • Eliminates welding and other attachments in plastic hinge zones (shear studs, e.g.). Spot welds acceptable • OK outside hinge zones, but need to verify net section strength • Discontinuities caused by welding or other construction operations must be repaired. • Locations of Protected Zones defined for each system

  24. Members • Width-thickness ratios often stricter than main specification requirements • 2010 Defines new terms, “Moderately” and “Highly” Ductile (MD and HD) • Used for width-thickness and bracing reqt’s • Width-thickness table parallels B4.1 in AISC 360 • MD like compact, HD, like seismically compact • HSS values reduced due to test results • Boxed WF sections included • Composite elements included

  25. Plastic Buckling Mp Inelastic Buckling Moment Capacity Mr Elastic Buckling ps p r Width-Thickness Ratio Ductility

  26. Members – Cont. • New paragraph on diaphragm design • Load transfer details required • Nominal shear strength defined as concrete above deck, w/o ACI Ch. 22, or test results • Bracing requirements made uniform for various systems • Special requirements at plastic hinges • Columns with high axial load to be checked for amplified seismic loading • Similar to 341-05, but ALL columns checked for Ω0 level axial forces • New requirements for composite columns

  27. Column Splices/Bases • Strength 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 SLRS • Clarifies use beveled transitions in CJP splices and removal of weld tabs (but not backing) per D1.8 • Column 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 presented • Interaction with concrete elements referred to ACI 318 Appendix D. • Clarifying language added • H-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 7-10 • User 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 analyses • Elastic sections for steel • Cracked sections for concrete and composite elements • Refers 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 title • Basis 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’s • Members – sets b/t limits, lists protected zones and defines individual member reqt’s • Connections – defines demand critical welds, and connection reqt’s, including splices

  32. Special Moment Frames (SMF) • Designs based on cyclic test results to 0.04 radians • Appendix S provides test requirements • For either project specific or “public” tests • Appendix P provides basis for “pre-qualification” of connections • Connections designed in accordance with AISC 358 standard • Shear 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 results • First edition focuses on RBS and End Plate connections • More connections included (WUF-W, e.g.) • Adopted by 2005 & 2010 AISC Seismic

  34. SMF (Cont.) Mp1 at column face Mp1 Mp2 Mp2 at column face • Panel Zone Design • Intended to share yielding with beam • Equation differs from FEMA 350 • Doubler plate configurations may be adjusted to avoid “k” area • Continuity plates to match tested configurations

  35. SMF (Cont.) L L C C Mpc2 Mc1 Mc2 Mpc1 • SCWB Check required for SMF frames • Attempting to avoid weak stories • Exceptions provided • 2010 clarifies use of Ω0 for axial force reduction • Column splices pushed towards CJP

  36. SMF (Cont.) • Lateral Bracing of Beams • Nominal bracing required along length for both strength and stiffness based on main spec. equations • Bracing at hinges (6%) required as well • But, 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 splices • Ordinary (OMF) provisions • Allows calculation only, but for strength above 1.1 Ry Mp • Specific 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 Elastic • Both Cross-braced and Vierendeel configurations • Span limited to 65 feet • Depth limited to 6 feet • Minor change to SS capacity • DC 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 7-10 • Ordinary System (OCCS) • Column axial loads low (15% of available at Ω0) • AISC 360 b/t ratios, no DC welds or protected zones • Special 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 higher • Stricter b/t Ratios and Built-up Member Requirements • Connection Requirements • Strength to Develop Tensile Strength • Ductility to Allow Buckling in Member or Gusset Plate • Restrictions on Chevron and K-Bracing • Stronger Column Splices Required • Capacity Design Requires two load distributions be checked • Connection Reqts. Increased (EBF and BRBF also), to accommodate drift • DC welds at column splices and bases. No PJP groove welded splices

  41. 2010 Analysis Req’t. - SCBF oF3 T 0.3P F F oF2 T 0.3P F F oF1 F F 0.3P T T  0 in Center Column Uplift in Center Column!

  42. OCBF Provisions • Limited use in high SDC’s • For V or inverted V, KL/r < 4.23/E/Fy • Connection strength to develop brace tension capacity or amplified force • Reorganized language to clarify expected compression strength • Chevron bracing restrictions • Tension Only Bracing Systems Allowed for Low and Penthouses • No 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 elastic • Best results for shear link elements, but local demands are higher than SMF’s • Extensive stiffening requirements • Built-up Boxes added for links • Based on recent Bruneau research • Clarification on calc for inelastic rotation angle • Other changes similar to SCBF

  44. EBF Provisions (Cont.) Pbr Pu • Link-to-column connections • Require testing like SMF • Exception allowed • Beam outside link, braces and columns designed for link capacity, including strain hardening (1.25 & 1.1) • Lateral bracing requirements similar to SMF • 6% at ends of links • Elsewhere, strength and stiffness as required in main spec.

  45. BRBF Provisions • BRBF Frames • SCBF development improves braced frame performance, but still limited by brace buckling • Concept developed in Japan, with many applications • Hysteretic behavior similar to elastic - perfectly plastic • Development of provisions in U.S. • Joint AISC/SEAOC effort • Approach similar to EBF • Analytical work indicates good performance • U.S. practice will lead to larger drifts • Included in 2003 NEHRP

  46. BRBF Provisions (cont.) • Steel core restrained from buckling • Braces tested for twice Design Story Drift • Appendix T specifies testing requirements • Brace strength addresses strain hardening and compression strength increase due to confining system • Connections designed for adjusted strength • Chevron requirements less demanding than SCBF • Column splices similar to SCBF • Increased Connection Reqt’s, DC welds at column splices and base, and no PJP groove welded splices similar to SCBF

  47. SPSW Provisions • SPSW like plate girder design approach (tension field theory) • Can generate tremendous strength and stiffness as compared to CBF • SPSW concept developed in Canada • NBCC Code provisions in place • UC Berkeley work as well • Provisions incorporated into 2003 NEHRP • Panel Capacity Based on Simple Formula • Includes panel aspect ratio • L/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 capacity • BE’s to develop panels. OMF style connections • Lateral bracing spacing like SMF. • Vertical BE’s also have bending stiffness requirements • Perforated Webs and corner cut-outs added • Added HBE stiffness • Protected zones added • Increased 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 NEHRP • Identifies Numerous System Options (10 total in 2010) • Provides Detailed Requirements for Member and Connection Design • Modified and Made Consistent with Part I • No longer Part II. Made Fully Consistent with Chapters E and F • MANY changes required

  50. Chapter D: General Member and Connection Requirements • SRC Beam-Columns: • Moderately and highly ductile detailing procedures (comparable to AISC 341-05) • CFT Beam-Columns: • Shear strengths is based on steel section alone • Connections: • Non-seismic provisions include clearer text on load transfer for general composite conditions: • Bond interaction • Direct bearing • Steel anchors • Non-seismic provisions include new provisions for steel anchors in shear, tension, and interaction for conditions beyond composite beams • Splice connection provisions for SRC refer to ACI Ch. 21 provisions for mechanical splicing • Seismic connection detailing provisions are mainly for steel girders framing into RC or SRC beam-columns • Written in early 1990’s

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