AISC Seismic Provisions - S.K. Ghosh Associates

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S. K. Ghosh Associates Inc.

www.skghoshassociates.com

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CHANGES in AISC’s SEISMIC PROVISIONS:

AISC 341-05 to AISC 341-10

Formerly with


Palatine, IL and Aliso Viejo, CA


Jason Ericksen, S.E.

FORSE Consulting, LLC

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AISC Seismic Provisions

AISC Seismic Provisions provide System Ductility

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System Ductility

“System Ductility” is the ability of system to maintain stability after yielding/overload of some elements

Ductility

V

• Ability of yielding/overloaded elements to deform

• Ability of non-yielding elements to withstand forces redistributed by yielding

• Ability of non-yielding elements to withstand deformations caused by yielding

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Seismic Provisions Measures

For each Seismic Force Resisting System

Identify target yield mechanism of the system

Designate deformation-controlled elements

Design remaining elements as force-controlled

Protect critical locations

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Identify target yield mechanism of the system

Flexural Yield

Tension yield and compression buckling

Shear Yield

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Stable yield


Designate deformation-controlled elements

• Design for element ductility

M

θ

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• Design to keep members essentially elastic at capacity of ductile elements

Resist redistributed forces


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Accommodatedeformations



• Design for deformations caused by yielding

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Protected Zones


Amplify forces

Demand Critical Welds

Protect critical locations

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Key Points

Reorganized chapters for consistency with AISC 360

Increased protection of critical locations

Added new systems and connections

Provided consistent capacity analysis requirements

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ROADMAP

Chapter Reorganization

General

Members

Connections

Moment Frames

Braced Frames

ReorderRenameReformat

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Seismic Provisions 341-05 Part I:

1: Scope

2: Referenced Specifications, Codes, and Standards

3: General Seismic Design

4: Loads, Load Combinations, Nominal Strengths

5: Structural Drawings and Specifications, Shop Drawings, and Erection Drawings

6: Materials

7: Connections, Joints, and Fasteners

8: Members

9-17: Structural Systems

18: Quality Assurance Plan (Appendix Q)

Appendices P, R, S, T, W, X

Part II: Composite Systems

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AISC 341-10 Organization

A. General Requirements

B. General Design Requirements

C. Analysis

D. General Member and Connection Design Requirements

E. Moment-Frame Systems

F. Braced-Frame and Shear-Wall Systems

G. Composite Moment-Frame Systems

H. Composite Braced-Frame and Shear-Wall Systems

I. Fabrication and Erection

J. Quality Control and Quality Assurance

K. Prequalification and Cyclic Qualification Testing Provisions

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Preface to AISC 341-10

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AISC 341-05 - Part I

1. Scope

2. Referenced Specifications, Codes, and Standards

AISC 341-10


B. General Design Requirements3. General Seismic Design

4. Loads, Load Combinations, Nominal Strengths



5. Structural Drawings and Specifications, Shop Drawings, and Erection Drawings

6. Materials


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7. Connections, Joints, and Fasteners

AISC 341-10



8. Members D. General Member and Connection Design Requirements

7.3b. Demand Critical Welds A. General Requirements

A3.4b. AWS D1.8


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AISC 341-05 - Part I AISC 341-10

9. Special Moment Frames

10. Intermediate Moment Frames

11. Ordinary Moment Frames

12. Special Truss Moment Frames


E3. Special Moment Frames

E2. Intermediate Moment Frames

E1. Ordinary Moment Frames

E4. Special Truss Moment Frames

E5. Ordinary Cantilever Column Systems

E6. Special Cantilever Column Systems


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13. Special Concentrically Braced Frames

14. Ordinary Concentrically Braced Frames

15. Eccentrically Braced Frames

16. Buckling-Restrained Braced Frames

17. Special Plate Shear Walls

AISC 341-10


F2. Special Concentrically Braced Frames

F1. Ordinary Concentrically Braced Frames

F3. Eccentrically Braced Frames

F4. Buckling-Restrained Braced Frames

F5. Special Plate Shear Walls


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Structural System Chapters: E - H

Consistent organization of system requirements

1. Scope

2. Basis of Design

Intended response/inelasticity

3. Analysis

4. System Requirements

Stability Bracing

Moment Ratio for SMF

Special Configurations (V- or Inverted V-Bracing)

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Structural System Chapters: E - H

Consistent organization of system requirements

5. Member Requirements

Width-to-thickness limitations

Protected Zone

6. Connections

Demand Critical welds

Column Splices

Required Connection Strengths

7. Additional requirements

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18: Quality Assurance Plan (Appendix Q)

AISC 341-10


Appendix P: Connection Prequalification

Appendix S: Qualifying Cyclic Tests of Beam-to-Column and Link-to-Column Connections

Appendix T: Qualifying Cyclic Tests of BRBF Braces



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No significant change within AISC 341

2012 IBC: Special Inspection

• 1705.2.1 Structural steel.

• Special inspection provisions for structural steel are now by reference to AISC 360-10 (see Chapter N)

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Appendix X: Weld Metal/Welding Procedure Specification Notch Toughness Verification Test


Appendix W: Welding Provisions

AISC 341-10


A4.4a. AWS D1.8


Appendix R. Seismic Design Coefficients and Approximate Period Parameters


A4.4a. AWS D1.8

REMOVED


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Seismic Provisions 341-05 Part II:

1: Scope

2: Referenced Specifications, Codes, and Standards

3: General Seismic Design

4: Loads, Load Combinations, Nominal Strengths

5: Materials

6: Composite Members

7: Composite Connections

8-17: Structural Systems

18:Structural Design Drawings and Specifications, Shop Drawings, and Erection Drawings

19: Quality Assurance Plan

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AISC 341-05 - Part II

1. Scope

2. Referenced Specifications, Codes, and Standards

AISC 341-10


B. General Design Requirements3. General Seismic Design

4. Loads, Load Combinations, Nominal Strengths


5. Materials

6. Composite Members

7. Composite Connections



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G4. Composite Partially Restrained Moment Frames

G3. Composite Special Moment Frames

G2. Composite Intermediate Moment Frames

G1. Composite Ordinary Moment Frames


8. Composite Partially Restrained Moment Frames

9. Composite Special Moment Frames

10. Composite Intermediate Moment Frames

11. Composite Ordinary Moment Frames

AISC 341-10


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H. Composite Braced-Frame and Shear Wall Systems

H2. Composite Special Concentrically Braced Frames

H1. Composite Ordinary Braced Frames

H3. Composite Eccentrically Braced Frames


12. Composite Special Concentrically Braced Frames

13. Composite Ordinary Braced Frames

14. Composite Eccentrically Braced Frames

AISC 341-10


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H. Composite Braced-Frame and Shear Wall Systems

H4. Composite Partially Restrained Moment Frames

H5. Composite Special Moment Frames

H6. Composite Intermediate Moment Frames


15. Ordinary Reinforced Concrete Shear Walls Composite with Structural Steel Elements

16. Special Reinforced Concrete Shear Walls Composite with Structural Steel Elements

17. Composite Steel Plate Shear Walls

AISC 341-10


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18. Structural Design Drawings and Specifications, Shop Drawings, and Erection Drawings

AISC 341-10



19. Quality Assurance Plan J. Quality Control and Quality Assurance


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ROADMAP


General

• Chapters A, B, and C

Members

Connections

Moment Frames

Braced Frames

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A1. Scope

• “These Provisions shall apply… unless specifically exempted by the applicable building code.”

AISC 341-05;

• R >3, “Provisions shall apply… regardless of seismic design category”

• R ≤ 3, “not required to satisfy these Provisions, unless specifically required by the applicable building code.”

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Including Supplement No. 1

A.1 ScopeApplicable Building Code

AISC 341-05


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AISC 341-05

Including Supplements No. 1 and No. 2

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Loads and load combinations

Systems and limitations

Design requirements

Requirements for steel design codes

AISC 360-10 AISC 341-10

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ASCE 7-10 Table 12.2-1

AISC 341 NOT required

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A3.4b Demand Critical Welds

A. General RequirementsA3.4. Consumables for Welding

• Special CVN requirements for enhanced ductility

• Adjacent to locations of high strain

System chapters

AISC 358

EOR discretion

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A. General RequirementsA3.4b Demand Critical Welds

Demand Critical Weld Requirements

System

Column Beam Flange

to Column

Flange

Beam Web/Shear

Plate to Column

FlangeBases Splices

OMF (E1.6a.) ---- ---- CJP CJP

IMF (E2.6a.) All Types Groove CJP CJP

SMF (E3.6a.) All Types Groove CJP CJP

STMF (E4.6a.) All Types Groove ---- ----

OCCS (E5.6a.) ---- ---- ---- ----

SCCS (E6.6a.) All Types Groove ---- ----

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A. General RequirementsA3.4b Demand Critical Welds

Demand Critical Weld Requirements

SystemColumn Link Flange or

Web to Column

Built-up Link:

Web to FlangeBases Splices

OCBF (F1) ---- ---- ---- ----

SCBF (F2.6a.) All Types Groove ---- ----

EBF (F3.6a.) All Types Groove All Types All Types

BRBF (F4.6a.) All Types Groove ---- ----

SPSW (F5.6a.) All Types Groove ---- ----

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A3.4b Demand Critical Welds at Column Base

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B2. Loads and Load Combinations

• Where “Amplified Seismic Loads” are required for specific members or connections

The seismic load effect including the system overstrength factor shall be applied as prescribed by the applicable building code.

Where Emh is defined, intended to replace Emh in ASCE 7 Section 12.4.3.

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B2. Load and Load Combinations

12.4.3 Seismic Load Combinations Including Overstrength FactorEm = Emh + Ev

= 0QE ± 0.2SDSD

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B2. Load and Load Combinations (with Amplified Seismic Loads)

AISC 341-10 Provisions

Emh in ASCE 7 Section 12.4.3

Requires “Amplified Seismic Load”

0QE

Defines EDefines Emh

Capacity Analysis

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AISC 341-05:

• Defines E (neglects vertical effect)

• E = Em = Emh + 0

AISC 341-10:

• Defines Emh

• Em = Emh + Ev = Emh + 0.2SDSD

B2. Load and Load Combinations (with Amplified Seismic Loads)

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C. Analysis

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C. Analysis

• C1. General Requirements:

Analysis shall conform to the applicable building code

Elastic analysis of composite systems shall consider cracked sections

• C2. Additional Requirements:

Additional analysis as required for each structural system shall be performed

• C3. Nonlinear Analysis:

When used, nonlinear analysis shall conform to Chapter 16 of ASCE 7

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BREAK!

If you are encountering technical difficulties, please call (847) 991-2700

If you have any questions, please type them in

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Question and Answer Session



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ROADMAP

History and Ductility


General

Members

• D1. General Member Requirements

Connections

Moment Frames

Braced FramesCourtesy of S. MahinU.C. Berkeley, 2004

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D1. General Member Requirements

D1.1 Classifications of Sections for Ductility

• D1.1b Width-to-Thickness Limitations

Highly Ductile

Moderately Ductile

• D1.2 Stability Bracing of Beams

Highly Ductile

Moderately Ductile

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D1.1b Width-to-Thickness Limitations

• Highly Ductile

replaces Seismically Compact (AISC 341-05)

• Moderately Ductile

replaces Compact (AISC 360-05)

Courtesy of S. MahinU.C. Berkeley, 2004

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AISC 341-05: Seismically Compact

Footnotes indicated to which members and structural systems each row applies

Type of member

force

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AISC 341-05: Compact

Type of member

force

AISC 360-05Compact Limits

Compact does not apply for Uniform Compression

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• Limits are based on:

Element type (flange, web, etc.)

Section type (I-shaped, HSS, etc)

Type of member force (flexure, uniform compression)

Member type (beam, column, brace)

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D1.1b Width-to-Thickness Limitations: Table D1.1

Type of member

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Member ductility classificationSystem Beam Column Brace Link

OMF (E1) --- --- --- ---

IMF (E2.5a) Moderately Moderately --- ---

SMF (E3.5a) Highly Highly --- ---

OCBF (F1.5a) --- ---SeismicallyCompact

Moderately---

SCBF (F2.5a) Moderately Highly Highly ---

EBF (F3.5a) Moderately Highly Moderately Highly

BRBF (F4.5a) Highly Highly --- ---

SPSW (F5.5a) Highly Highly --- ---

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Beams and columns: b/t limit comparison

*Includes flanges of built-up I-shapes, channels and tees; legs of single angles or double angles with separators; outstanding legs in pairs of angles in continuous contact

**Includes webs of channels and built-up I-shapes

D1.1b Width-to-Thickness Limitations: Highly Ductile

Table indicates factor on √(E/Fy)

ElementAISC 341-05

Seismically CompactAISC 341-10

Highly Ductile

Flanges of I-Shapes* 0.30 0.30

Web of I-Shapes**

Ca ≤ 0.1253.14(1-1.54Ca)

Ca ≤ 0.1252.45(1-0.93Ca)

Ca > 0.1251.12(2.33-Ca) ≥ 1.49

Ca > 0.1250.77(2.93-Ca) ≥ 1.49

SMFFlanges of Boxed I-Shaped and Built-Up Box Columns

NA 0.60

0.30√(E/Fy)

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W18X40 = 2.11

W18X65 = 1.48

Fy = 50 ksi

Ca = Pu/(cPy) (LRFD)Ca = (cPa)/Py (ASD)

Webs of I-Shaped Beams and Columns: Highly Ductile

hd/√

(E/F

y)

3.14

2.5

2.452.16

1.49

2010: Highly Ductile

2005: Seismically Compact

2005: Seismically Compact for Flexure of SMF Beams

0.125 1.0

(b/t)

√(E/Fy) =

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SCBF braces: b/t ratio limit comparison



***Includes walls built-up box sections and side plates of boxed I-shaped sections


ElementAISC 341-05


Highly Ductile


Webs of I-Shapes**

Ca ≤ 0.1253.14(1-1.54Ca) 1.49

Ca > 0.1251.12(2.33-Ca) ≥ 1.49

Rect. HSS Walls*** 0.64 0.55

Rnd. HSS Walls 0.044 0.038

Stems of tees 0.30 0.30

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D1.1b Width-to-Thickness Limitations: SCBF Braces

Fy = 50 ksi


Webs of I-Shaped Braces: Highly Ductile

hd/√

(E/F

y)

3.14

2.50

1.49

2010: Highly Ductile


0.125 1.0

W10X17 = 1.53

W12X45 = 1.21

(b/t)

√(E/Fy) =

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Beams and columns: b/t ratio limit comparison



D1.1b Width-to-Thickness Limitations: Moderately Ductile


ElementAISC 360-05“Compact”

AISC 341-10Moderately Ductile

Flanges of I-Shapes*0.38 (Flexure)

0.56 (Compression)0.38

Web of I-Shapes**1.49 (Compression)

3.76 (Flexure)

Ca ≤ 0.1253.76(1-2.75Ca)

Ca > 0.1251.12(2.33-Ca) ≥ 1.49

IMFFlanges of Boxed I-Shaped and Built-Up Box Columns

NA 0.55

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Fy = 50 ksi


Webs of I-Shaped Beams and Columns: Moderately Ductile

hd/√

(E/F

y)

3.76

2.50

1.49

2010: Moderately Ductile

2005: NonCompact for Compression

0.125 1.0

2005: Compact for Flexure

W18X40 = 2.11

W18X65 = 1.48

(b/t)

√(E/Fy) =

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EBF braces: b/t ratio limit comparison



***Includes walls built-up box sections and side plates of boxed I-shaped sections


ElementAISC 360-05“Compact”

AISC 341-10Moderately Ductile

Flanges of I-Shapes*0.38 (Flexure)


Webs of I-Shapes**1.49 (Compression)

3.76 (Flexure)1.49

Rect. HSS Walls*** 1.12 0.64

Rnd. HSS Walls0.07 (Flexure)


Stems of tees 0.75 0.38

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D1.1b Width-to-Thickness Limitations: OCBF Braces

OCBF braces: b/t ratio limit comparison:




ElementAISC 341-05


Moderately Ductile


Webs of I-Shapes*

Ca ≤ 0.1253.14(1-1.54Ca) 1.49

Ca > 0.1251.12(2.33-Ca) ≥1.49

Rect. HSS Walls 0.64 0.64Rnd. HSS Walls 0.044 0.044Stems of tees 0.30 0.38

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D1.1b Width-to-Thickness Limitations: OCBF Braces

Fy = 50 ksi


Webs of I-Shaped Braces: OCBF – Moderately Ductile h

d/√

(E/F

y)

3.14

2.50

1.49

2010: Moderately Ductile


0.125 1.0

W12X26 = 1.96

W12X35 = 1.48

(b/t)

√(E/Fy) =

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D1.2 Stability Bracing of Beams

• Maximum unbraced length for Highly Ductile and Moderately Ductile beams

• Strength and stiffness of braces per Appendix 6 of AISC 360

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Maximum unbraced length of beams

*Beams in V or Inverted-V systems only

Member AISC 341-05, Lb AISC 341-10, Lb

SMF Beams (E2.4a) 0.086ry(E/Fy)Highly Ductile

0.086ry(E/Fy)

IMF Beams (E3.4b)

SPSW HBE (F5.4c)0.17ry(E/Fy)

Moderately Ductile

0.17ry(E/Fy)

SCBF Beams* (F2.4b)

BRBF Beams* (F4.4a)[0.12+0.076(M1/M2)](E/Fy)ry

Moderately Ductile

0.17ry(E/Fy)

OCBF Beams* (F1) [0.12+0.076(M1/M2)](E/Fy)ry NONE

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Beams in V- or Inverted V-Braced Frames

M1/M2

L b/[(

E/F

y)r y

]

AISC 341-05 (Appendix 1 of AISC 360-05)Lb = [0.12+0.076(M1/M2)](E/Fy)ry

AISC 341-10: Moderately DuctileLb = 0.17(E/Fy)ry

0.196

0.120

0.044

-1.0 1.000

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D1.4 Columns

All SFRS columns now are required to use amplified seismic load combinations to determine Pr in the absence of moments

AISC 341-05LRFD

Pu/cPn > 0.4

ASDcPa/Pn > 0.4

Amplified Seismic Load Combinations

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ROADMAP



General

Members

Connections

• D2. General Connection Requirements

Moment Frames

Braced Frames

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D2.1 Connections

AISC 341-05: Connections

7.1 Scope

The design of connections for a member that is part of the SLRS shall be configured such that a ductile limit state in either the connection or the member controls the design.

The requirement was removed because it was deemed too onerous because the required strengths are capacity controlled.

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D2.5. Column Splices: SFRS

Seismic Force Resisting Column Splices:

• Increased required strength

• More restrictions on partial joint penetration groove welds (PJP)

• “Push” towards complete joint penetration groove welds (CJP)

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D2.5b. Required Strength: largest of

• Required strength of the column (Mr_col, Vr_col, Pr_col)

• Effect of amplified seismic loads (Mr_Em, Vr_Em, Pr_Em)

• Structural system requirements

• Special requirements for columns in net tension determined using load combinations including overstrength

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D2.5c. Required Shear Strength: greater of

• Required strength from D2.5.b

• Mpc/H (LRFD) or Mpc/(1.5H) (ASD)

Where;

Mpc = Lesser nominal plastic flexural strength

H = story height

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SFRS Column Splices: Table Definitions

Mr_col, Vr_col, Pr_col = required strengths of the column

Mr_Em, Vr_Em, Pr_Em = required strengths of the column from of seismic load combinations including overstrength

Mr, Vr, Pr = required strengths of the splice

Mn = lesser nominal flexural strength (includes effects of unbraced length)

Mpc = lesser nominal plastic flexural strength

Mpc = sum of nominal plastic flexural strengths

H = story height (top of beam flange to top of beam flange)

Hc = clear story height (top of beam flange to bottom of beam flange)

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D2.5 Column SplicesRequired Strength for SFRS: LRFD

System Welds

Mr Vr Pr

Largest of Mr_col,

0E, and

Largest of Vr_col,

0E, Mpc/H, and

Largest of

Pr_col, 0E, and

OMF (E1) ---- ---- ---- ----

IMF (E2.6g) No PJP Bolted: RyFyZx ΣMpc/H ----

SMF (E3.6g) No PJP Bolted: RyFyZx ΣMpc/H ----

STMF (E4.6c) No PJP Bolted: RyFyZx ΣMpc/H ----

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D2.5 Column SplicesRequired Strength for SFRS: LRFD

System Welds

Mr Vr Pr

Largest of Mr_col,

0E, and

Largest of Vr_col,

0E, Mpc/H, and

Largest of

Pr_col, 0E, and

OCBF (F1) ---- ---- ---- ----

SCBF (F2.6d) No PJP Mn/2 ΣMpc/Hc ----

EBF (F3.6d) No PJP Mn/2 ΣMpc/Hc ----

BRBF (F4.6d) No PJP Mn/2 ΣMpc/Hc ----

SPSW (F5.6d) No PJP Mn/2 ΣMpc/Hc ----

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D2.5 Column SplicesRequired Strength for SFRS: ASD

System Welds

Mr Vr Pr

Largest of Mr_col,

0E, and

Largest of Vr_col,

0E, Mpc/(1.5H),

and

Largest of

Pr_col, 0E, and

OMF (E1) ---- ---- ---- ----

IMF (E2.6g) No PJP Bolted: RyFyZx/1.5 ΣMpc/(1.5H) ----

SMF (E3.6g) No PJP Bolted: RyFyZx/1.5 ΣMpc/(1.5H) ----

STMF (E4.6c) No PJP Bolted: RyFyZx/1.5 ΣMpc/(1.5H) ----

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D2.5 Column SplicesRequired Strength for SFRS: ASD

System Welds

Mr Vr Pr

Largest of Mr_col,

0E, and

Largest of Vr_col,

0E, Mpc/(1.5H),

and

Largest of

Pr_col, 0E, and

OCBF (F1) ---- ---- ---- ----

SCBF (F2.6d) No PJP Mn/2 ΣMpc/(1.5Hc) ----

EBF (F3.6d) No PJP Mn/2 ΣMpc/(1.5Hc) ----

BRBF (F4.6d) No PJP Mn/2 ΣMpc/(1.5Hc) ----

SPSW (F5.6d) No PJP Mn/2 ΣMpc/(1.5Hc) ----

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D2.6 Column Bases

Like column splices, column bases are also considered critical locations and have similarly increased requirements.

Testing done at UC Davis by Dr. Amit Kanvide

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D2.6 Column Bases: SFRS

D2.6a Required Axial Strength: Sum of vertical components:

• Braces: required member connection strength

• Columns: greater of

Required member strength

Axial load from 0E combinations

Required axial strength of column splices

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Axial: SCBF - LRFD

D2.6 Column Bases: SFRSRequired Axial Strength

Pr_col

≥ 0E

Pr = Σ vertical components

T = RyFyAg

or C = 1.1*Min RyFyAg

1.14FcreAg

Fcre = Fcr with RyFyL ≤ distance from brace end to brace end

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D2.6 Column Bases: SFRSRequired Axial Strength

T = RyFyAg

Pr_col

≥ 0E

Axial: SCBF w/ Compression Buckling - LRFD

Pr = Σ vertical components

C = 0.3*Min RyFyAg

1.14FcreAg

Compression force from SCBF analysis requirements, Section F2.3

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D2.6 Column Bases: SFRSRequired Axial Strength - LRFD

Example member vs. connection required strength

• SCBF: A500 Gr B; Fy = 46 ksi; Ry = 1.4; KL = 19 ft

• 0 = 2 for SCBF

Brace KL/r cPn RyFyAg (RyFyAg)/cPn

HSS8x8x5/8 76.3 459 kips 1056 kips 2.30

HSS6x6x1/2 102 200 kips 627 kips 3.14

HSS4x4x5/16 163 39.6 kips 264 kips 6.66

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D2.6 Column Bases: SFRSRequired Shear Strength

D2.6b Required shear strength: Sum of horizontal components:

• Braces: required connection strength

• Columns: greater of

Shear load from 0E combinations

2RyFyZx/H (LRFD) (2/1.5)RyFyZx/H (ASD)

Required shear strength of column splices

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Column Component - LRFD

System

AISC 341-05 (8.5b) AISC 341-10

Lesser of2RyFyZx/H and 0E

Largest of Vr_col,0E,

Mpc/H, and

OMF (E1), OCBF (F1) ---- ----

IMF (E2.6g), SMF (E3.6g),

STMF (E4.6c)---- ΣMpc/H

SCBF (F2.6d), EBF (F3.6d),

BRBF (F4.6d), SPSW (F5.6d)---- ΣMpc/Hc

ΣMpc/Hc = 2Mpc/Hc = 2FyZx/Hc ≤ 2RyFyZx/H

2Mpc/Hc ≥ 0E

44



- 87 -


T = RyFyAg

Largest ofVr_col, 0EMpc/Hc

Shear: SCBF - LRFD

Vr = Σ horizontal components

C = 1.1*Min RyFyAg

1.14FcreAg

Required connection strength in compression, Section F2.6c(1)

- 88 -


Column Component - ASD

System

AISC 341-05 (8.5b) AISC 341-10

Lesser of(2/1.5)RyFyZx/H, 0E

Largest of Vr_col,0E,

Mpc/(1.5H)

OMF (E1), OCBF (F1) ---- ----

IMF (E2.6g), SMF (E3.6g),

STMF (E4.6c)---- ΣMpc/(1.5H)

SCBF (F2.6d), EBF (F3.6d),

BRBF (F4.6d), SPSW (F5.6d)---- ΣMpc/(1.5Hc)

45



- 89 -

D2.6 Column Bases: SFRSRequired Flexural Strength

D2.6c Required Flexural Strength: Sum of flexural components:

• Braces: required connection strength

Based on critical buckling axis

Rotation capacity may be provided in place of flexural strength

• Columns: lesser of

1.1RyFyZ (LRFD) or (1.1/1.5) RyFyZ (ASD)

Moment from 0E combinations

• User Note: Ignore moments for pinned bases

- 90 -

D2.6 Column Bases:Columns Not Part of SFRS

D2.6b Required Shear Strength: Non-SFRS Columns:

• Required shear strength of column splices

Mpc/H (LRFD) or Mpc/(1.5H) (ASD)

Vr

Mpc

Vr

46



- 91 -

D2.6 Column Bases: Anchorage

AISC 360 and 341

ACI 318 Appendix D

- 92 -

D2.6 Column Bases: Anchorage

AISC 341-10 Section D2.6

• Exception: “The special requirements in ACI 318, Appendix D for regions of moderate or high seismic risk, or for structures assigned to intermediate or high seismic performance or design categories need not apply”.

47



- 93 -

*ACI 318-11 no longer applies a 0.75 factor on shear strength

AISC 341 and ACI 318 Appendix D.

Design for AISC 341 Required Strengths

Codes and

Standards

0.75 Strength Factor

(0.75Nn)

Ductility Requirements

Appendix D.

AISC 341-05

2006 IBC: ACI 318-05

2009 IBC: ACI 318-08

D.3.3.3Exempted

D.3.3.4Exempted

AISC 341-10

2012 IBC: ACI 318-11

D.3.3.4.4 – Tension*:

Applied to concrete

failure modes

D.3.3.4.3 - Tension:

Option (c) or (d) satisfied

D.3.3.5.3 – Shear:

Option (b) or (c) satisfied

- 94 -

BREAK!



48



- 95 -




- 96 -

ROADMAP



General

Members

Connections

Moment Frames

• Chapter E

• AISC 358-10

Braced Frames

49



- 97 -

AISC 341-10 Organization



C. Analysis





H. Composite Braced-Frame and Shear-Wall Systems




- 98 -


Summary of changes

• Ordinary Moment Frames

Text revised to allow use of non wide-flange members

Continuity plate requirements removed (E1.6b.)

• Intermediate and Special Moment Frames

Prequalified connections added to AISC 358-10

• Ordinary Cantilever Column Systems (OCCS) added

• Special Cantilever Column Systems (SCCS) added

50



- 99 -

Prequalified ConnectionsAISC 358-10

- 100 -

Prequalified ConnectionsAISC 358-10

51



- 101 -

Extended End-Plate

Prequalified ConnectionsAISC 358-05Reduced Beam Section

- 102 -

Welded Unreinforced Flange – Welded Web (WUF-W)

Prequalified ConnectionsAISC 358-05 with Supplement No. 1Bolted Flange Plate

52



- 103 -

Prequalified ConnectionsAISC 358-05 with Supplement No. 1Kaiser Bolted Bracket ™

By Steel Cast Connections, LLC

- 104 -

Conxtech® CONXL™

Prequalified ConnectionsAISC 358-10 with Supplement No. 1

By ConXtech Inc.

53



- 105 -

E5 and E6. Cantilever Column Systems

- 106 -

E5 and E6. Cantilever Column Systems

New to AISC 341-10

ASCE 7-10:

• Table 12.2-1:

OCCS: R= 1.5, Limited to 35 ft and SDC B and C

SCCS: R = 2.5, Limited to 35 ft in all SDC

• 12.2.5.2:

Required axial strength for seismic load combinations, shall not exceed 15% of available axial strength, Pr ≤ 0.15Pc

Foundations used for overturning resistance shall be designed to resist amplified seismic load combinations

54



- 107 -

E5. Ordinary Cantilever Column Systems

E5.2. Provides minimal inelastic drift capacity through flexural yielding of the columns

Flexural yielding of columns

• E5.4a. Axial Load

Based on amplified seismic load combinations

For seismic load combinations, Prc ≤ 0.15Pc

- 108 -

E6. Special Cantilever Column Systems

E6.2. Provides limited inelastic drift capacity through flexural yielding of the columns

Flexural yielding of columns

• E6.4a. Axial Load

Based on amplified seismic load combinations

For seismic load combinations, Prc ≤ 0.15Pc

• E6.4b. Unbraced length: Moderately Ductile

• E6.5a. b/t limitations: Highly Ductile

• E6.5c. Protected Zone: 2dc from column base

55



- 109 -

ROADMAP



General

Members

Connections

Moment Frames

Braced Frames

- 110 -

F1 and F2: Concentrically Braced-Frame Systems

Summary of Changes

• Ordinary Concentrically Braced Frames

F1.4b. K-Braced frames prohibited

• Special Concentrically Braced Frames

F2.3. Analysis requirements added

F2.6b. Connection deformation compatibility requirement added

F2.5b(1). Brace slenderness ratio limit relaxed from Kl/r ≤ 4√(E/Fy) to Kl/r ≤ 200

F2.5b(3). Effective net area requirements for braces edited

56



- 111 -

F. Deformation Compatibility

F2.6b. Beam-to-Column Connections: Brace connects to beam and column

• Provide “simple” connection per B3.6a. of AISC 360

• Design connection for Mr; lesser of:

1.1RyMp_bm (LRFD) or (1.1/1.5)RyMp_bm (ASD)

1.1RyFyZcol (LRFD) or (1.1/1.5)RyFyZcol (ASD)

Welds are Demand Critical

- 112 -

F. Deformation Compatibility

Provide “simple” connection per B3.6a. of AISC 360

57



- 113 -

F2. Special Concentrically Braced Frames

F2.3. Analysis

• Determine required strengths of beams, columns, and connections using capacity analysis

• Capture large forces caused by post-elastic behavior of braces

- 114 -

F2.3. SCBF Analysis

Two analyses to determine Emh

1. Expected strength

Brace in Tension - consider expected strength

Brace in Compression - consider expected strength

2. Post-Buckling strength

Brace in Tension - consider expected strength

Brace in Compression - consider post-buckling strength

• It is permitted to neglect flexural forces resulting from seismic drift.

58



- 115 -

F2.3. SCBF Analysis

Braces in Tension or Compression?

• Neglect the effects of gravity loads

• Consider only the first mode of deflection

- 116 -

Expected Strength

Expected strength in compression:

Cexp = Min RyFyAg

1.14FcreAg

Expected strength in tension:Texp = RyFyAg


F2.3. SCBF Expected Strength Analysis

59



- 117 -

Expected StrengthElastic

Compression

Tension


- 118 -


Expected StrengthElastic

Shear

60



- 119 -

Post-Buckling

Post-Buckling strength in compression:

Cpb = 0.3*Min RyFyAg

1.14FcreAg

Expected strength in tension:Texp = RyFyAg


F2.3. SCBF Post-Buckling Analysis

- 120 -


Post-BucklingElastic

Compression

61



- 121 -


Compression

Uplift

- 122 -


Unbalanced shear force

AISC 341-05 considered this force

Post-Buckling

62



- 123 -


- 124 -


63



- 125 -


Summary of Changes

• F3.3. Analysis requirements revised

• F3.5b(1). Built-up box sections allowed (no HSS)

• F3.6b. New connection deformation compatibility

- 126 -


F3.3 Analysis

• Emh = forces in beams, columns, braces, and connections when ALL links reach their adjusted shear strength

• Adjusted shear strength

I-shaped links: 1.25RyVn

Box links: 1.40RyVn

64



- 127 -


I-Shapes: 1.25RyVn

orBoxes: 1.40RyVn

Determine forces in beams, columns,

braces, and connections

- 128 -


F3.3 Analysis

• Permitted to take Emh = 0.88 times forces from analysis for:

Beams outside link

Columns in frames with 3 or more stories

• Permitted to neglect effects of seismic drifts on the moments

65



- 129 -


Required Strength in AISC 341-05

• 15.6a. Diagonal Brace

E = forces in brace when shear in link reaches 1.25RyVn

• 15.6b. Beam Outside Link

E = forces in brace when shear in link reaches 1.1RyVn

• 15.8. Columns

E = forces in brace when shear in link reaches 1.1RyVn in ALL levels above the column

- 130 -


Effective shear in links

ElementAISC 341-05

I-Shaped Links

AISC 341-10

I-Shaped Links

AISC 341-10

Box Links

Braces 1.25RyVn 1.25RyVn 1.40RyVn

Beams 1.10RyVn0.88*(1.25RyVn) =

1.10RyVn

0.88*(1.40RyVn) = 1.23RyVn

Columns < 3

stories1.10RyVn 1.25RyVn 1.40RyVn

Columns ≥ 3

stories1.10RyVn

0.88*(1.25RyVn) = 1.10RyVn

0.88*(1.40RyVn) = 1.23RyVn

66



- 131 -


Required Strength in AISC 341-05

• 15.4 Link-to-Column Connections

Must be tested or prequalified

• 15.6c. Bracing Connections

At least required strength of brace (when shear in link reaches 1.25RyVn)

• 15.7. Beam-to-Column Connections

At least required strength of beam (when shear in link reaches 1.1RyVn)

If moment connection, meet OMF requirements

- 132 -


Required Connection Strengths

• F3.3. Required connection strengths are determined from the same capacity analysis as the members

• F3.6e. Link-to-Column connections

Must be tested or prequalified

• Beam-to-column moment connections must meet OMF requirements

67



- 133 -


Summary of Changes

• Buckling-Restrained Braced Frames

F4.3. Analysis requirements added

F4.6b. Connection deformation compatibility requirement added

- 134 -


F4.6b. Beam-to-Column Connections

• Brace connection to Beam and Column (2 options)

Provide “simple” connection

68



- 135 -

F5. Special Plate Shear Walls

Summary of Changes

• Special Plate Shear Walls

F5.4a. Horizontal Boundary Element stiffness minimum added

F5.4b. Beam-Column moment ratio limit added

F5.5c. Protected Zones added

F5.7. Requirements for perforated webs and corner cut-outs added

- 136 -

Closing Comments

69



- 137 -

Key Points

Reorganized chapters for consistency with AISC 360

Increased protection of critical locations

Added new systems and connections

Provided consistent capacity analysis requirements

- 138 -

Resources

Download AISC 341-10 FREE from www.aisc.org/FreePubs

• Commentary to AISC 341-10

Download AISC 358-10 FREE from www.aisc.org/FreePubs

AISC Steel Solutions Center

• Free technical support email: [email protected]

2010 AISC T.R. Higgins Award Lecture by James O. Malley

• “The AISC Seismic Provisions: Past, Present, and Future”

• http://www.aisc.org/content.aspx?id=572

70



- 139 -

Resources

The AISC Seismic Design Manual, 2nd, Edition

www.aisc.org/Store

- 140 -


71



- 141 -

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- 142 -




72



- 143 -

Jason Ericksen, S.E.

[email protected]

www.FORSEconsulting.com

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- 144 -

Thank You!!

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