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Changes to the 2010 AISC Seismic Provisions

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

2 TC 9 – “The Hardest Working Committee in Show Biz”
Roy Becker (‘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) Sanj Malushte Bonnie Manley (‘10)* Hank Martin (‘05)* Clarkson Pinkham John Rolfes (‘10) Rafael Sabelli* Mark Saunders* Tom Sabol Bahram Shahrooz Bob Shaw* Lee Shoemaker Kurt Swensson Robert 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 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 Mechanism Plus Ductility Requirements Plus Capacity Design Requirements Equals… Target Yield Mechanisms Flexural Yielding Tensile Yielding/Buckling Shear Yielding

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 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 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’l Req’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 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 -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.) 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 Fracture Shear Stud weld

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 Width-Thickness Ratio Ductility
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 , 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.) Panel Zone Design Intended to share yielding with beam
Mp2 Mp1 Mp1 at column face 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.) 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 Mc2 Mc1 Mpc2 Mpc1 C L

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 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/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.) 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. Pbr Pu

45 Approach similar to EBF
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 ) 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

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 beams Confine inelastic deformation to the girders and column bases with limited yielding in panel zones. Protected zones in inelastic region of girders Demand critical welds at connections, splices and base plates Other 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 performance SCWB 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 Connection Composite CFT Moment-Resisting Connection

54 Composite Ordinary Shear Walls C-OSW: Section H4
Limited inelastic deformation Ensure yielding of the coupling beams in shear or flexure Account for cracked section properties for concrete per ACI 318 Chapter 10 or ASCE 41 Structural steel or composite coupling beams May redistribute coupling beam forces up to 20% provided Vertical Redistribution of Coupling Beam Shear

55 Composite Special Shear Walls C-SSW: Section H5
Significant inelastic deformation Ensure shear yielding of the coupling beams System 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 piers Apply a wall overstrength factor ωo to the wall design forces The axial design strength of the wall at the balanced condition (Pb) shall equal or exceed the sum of 1.1RyVn of the coupling beams Use 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 base Demand critical welds for splices, base plates, and HBE-to-VBE connections Provisions for required strength in steel anchor connectors Detailing provisions refer to SPSW

58 QC and QA Detailed 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 D1.8 QA plan required in conjunction with IBC Chapter 17. Covers both QA and QC. Documentation requirements listed Visual Inspection Points and Frequency Defined For before, during and after welding or bolting by both QA and QC. Shown in tabular format “Observe, Perform and/or Document” vs. Periodic/Continuous NDT 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. 1 Included in 2012 IBC Work is underway on 2016 Edition To be referenced in ASCE 7-16 and 2018 IBC First ballot to COS underway Changes not as dramatic as , but… Public ballots next Spring, complete late next year Your 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 Manual Available for purchase. Work on 2018 underway.

61 Concluding Comments Unified Process for Steel Seismic Provision Development "Single Point of Responsibility" eliminates duplicative effort and minor differences that result in major confusion Allows rapid incorporation of new information 2010 Provisions Another Step Forward (We HOPE!) Format improved, technical updates and incorporates AWS D1.8 WE WANT YOUR INPUT AND RECOMMENDATIONS FOR IMPROVEMENTS!

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