seau 2017 presentation research seismic... · • nist gcr 09-917-2 identified a ... – 24 total...

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1

Assessment of First Generation Performance-Based Seismic Design Methods for New Steel Buildings

Jay Harris

Engineering LaboratoryNational Institute of Standards and TechnologyU.S. Department of Commerce

[email protected]

SEAU5th Annual Education ConferenceFeb. 22, 2017, Provo, UT

Presentation Outline• Introduction

– What is ASCE 41?

– Brief History of ASCE 41

• NIST Project Motivation and Scope

• Archetype Buildings Designed by ASCE 7

• Seismic Assessment using ASCE 41 (2006 and 2013)

• Seismic Assessment Results of Archetype Buildings

• Time Depending: Changes in ASCE 41-17 and AISC 342

• Questions

2

• ASCE 41 is consider to be a 1st generation performance-based seismic design (PBSD) methodology for existingbuildings

• “Design”? Actually, performance-based seismic evaluation of a system and design of a retrofit

– Seismic evaluation is defined as an approved methodology of evaluating deficiencies in components of a building that prevent the building from achieving a selected Performance Objective.

– Seismic retrofit is defined as the design of measures to improve the seismic performance of structural (or nonstructural) components of a building by correcting deficiencies identified in a seismic evaluation relative to a selected Performance Objective.

3

Introduction:What is ASCE 41?

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2

• ASCE 41 is referenced for its intended purpose in the International Existing Building Code (IEBC) as well as mandated guidelines for federal agencies (e.g., RP-10)

• Intended to be a standalone provisions document, that for specific reasons will require some provisions from ASCE 7

• Side note: FEMA is working on next generation of PBSD – ATC-58 Project: Development of Next Generation PBSD Procedures for New and Existing Buildings

4

Introduction:What is ASCE 41?

• ASCE 41 is being used now for evaluation of existingsteel seismic force-resisting systems (SFRS) and theirpotential retrofit options. It is referenced in the IEBC.

• ASCE 41 is a PBSD option for new buildings via Ch. 1of ASCE 7

• GSA PBS-P100: Facility Standards for the PublicBuildings Service requires ASCE 41 to be used for theseismic design of new GSA facilities and that theguidelines from ASCE 41 are intended to be applied tonew buildings.

5

Introduction:Current Usage of ASCE 41?

• The National Institute of Building Sciences (NIBS) isusing PBS-P100 as the basis for developing theirNational Performance Based Design Guide

• ASCE 7-16 has a revised Ch. 16 for NonlinearResponse History Analysis (NLRHA) that referencesASCE 41 for component modeling, and allowablestrengths and deformations for components of adetermined SFRS

6


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• NIST study completed recently regarding assessment of ASCE 41-06 provisions for new steel buildings

– 4 Volumes: SMF, SCBF, EBF, BRBF*

• Assessment results illustrate that some components of the SFRS do not satisfy the acceptance criteria for LS or CP Performance Level

* report nearing completion

7

http://nehrp.gov/library/guidance_pbsd.htm


• 1997 – FEMA published FEMA 273: NEHRP Guidelines for the Seismic Rehabilitation of Buildings (and FEMA 274 - Commentary)

• 1998 – FEMA published FEMA 310: Handbook for Seismic Evaluation of Buildings

• 2000 – FEMA and ASCE published FEMA 356: Prestandard and Commentary for the Seismic Rehabilitation of Buildings—based on FEMA 356

– changes made to FEMA 273 are chronicled in FEMA 357: Global Topics Report on the Prestandard and Commentary for the Seismic Rehabilitation of Buildings

8

Introduction:History of ASCE 41

• 2003 – ASCE published ASCE 31-03: Seismic Evaluation of Existing Buildings—based on FEMA 310

• 2007 – ASCE published ASCE 41-06: Seismic Rehabilitation of Existing Buildings—based on FEMA 356

• 2014 – ASCE published ASCE 41-13: Seismic Evaluation and Retrofit of Existing Buildings

– combines ASCE 31 and ASCE 41

• 2017 – next version of ASCE 41

9

Introduction:History of ASCE 41

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4

• ASCE 41 just completed its final ballot. Publication date is expected in late 2017

• Papers are starting to be publically available about what revisions will be included in ASCE 41-17

• In regards to structural steel, many technical changes were approved this cycle. Several SEAOC (2016) papers discussed these changes. Future papers and reports will provide detailed explanations of the changes

– Alignment between ASCE 41 and AISC 360 and AISC 341

– Steel column provisions went through a major overhaul

– Technical and Editorial Clean Up process – but not done yet!

10

Introduction:Current Status of ASCE 41-17

NIST Project

11

Introduction:Project Motivation

• NIST GCR 09-917-2 identified a critical need to benchmark “first generation” PBSD

– Recent publications have also highlighted needs with ASCE 41

• Calibration/comparison with ASCE 7

• Investigate link between ASCE 7 and ASCE 41

– If a building is designed (ASCE 7) and built today and then assessed (ASCE 41) tomorrow, will it need to be retrofitted?

– Or vice versa (GSA - ASCE 41-13 §9.3.3)

12

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Introduction:Project Motivation

IEBC Table 101.5.4.1

IBCOccupancyCategory

ASCE 41 BSE-1Hazard

ASCE 41 BSE-2 Hazard

ILife Safety

(LS)

CollapsePrevention

(CP)

IILife Safety

(LS)

CollapsePrevention

(CP)

III 80% OC IV 80% OC IV

IVImmediateOccupancy

(IO)

Life Safety (LS)

New Construction Existing BuildingsRehabilitation &

PBSD

Not validated and rejected for inclusion in ASCE 7-10

13

Seismic HazardNotes:1. ASCE 7-10 Hazard2. ASCE 41-06 Hazard3. Per ASCE 7-10 Commentary

Target Building Performance Level1

OperationalImmediate Occupancy

(IO)

Life Safety(LS)

Collapse Prevention

(CP)

Ear

thq

uak

eH

azar

d L

evel 50% / 50 year2 ASCE 41

(nonstructural)ASCE 41 Limited ASCE 41 Limited ASCE 41 Limited

20% / 50 year2 ASCE 41 Enhanced

ASCE 41 ASCE 41 Limited ASCE 41 Limited

“Frequent” 1 ASCE 7 OC III & IV

ASCE 7 OC I & II(anticipated)3 N.A. N.A.

BSE-1 (10% / 50 year) 2 ASCE 41 Enhanced

ASCE 41 Enhanced

ASCE 41 BSO ASCE 41 Limited

(2/3) MCER1 N.A.

ASCE 7 OC III & IV

ASCE 7 OC I & II(design)

N.A.

BSE-2 (2% / 50 year) 2 ASCE 41 Enhanced

ASCE 41 Enhanced

ASCE 41 Enhanced

ASCE 41 BSO

MCER1 N.A. N.A.

ASCE 7 OC III & IV

ASCE 7 OC I & II(objective) 3

ASCE 7-10 considers CP and has implied performance at IO and LS; ASCE 41 has explicit consideration of the seismic hazards at all performance levels.

14

Introduction:Project Scope

15

Design a suite of structures using ASCE 7

• Develop archetype buildings • Occupancy category II (Ordinary Use)• 4, 8 and 16-story buildings• Steel lateral systems:

• SMF, SCBF, EBF, and BRBF• Design using both RSA and ELF methods• Design using the upper bound of Seismic Design

Category D

Assessment of designs using ASCE 41

• Use prescribed analysis methods and acceptance criteria

• Linear Static Procedure (LSP)

• Linear Dynamic Procedure (LDP)

• Nonlinear Static Procedure (NSP)

• Nonlinear Dynamic Procedure (NDP)

Outcomes

• Correlate performance objectives between ASCE 7 & ASCE 41

• Quantify implied target performance levels

• Correlate the results of the four ASCE 41 analysis method results

• Provide input to future ASCE 7 & ASCE 41 editions

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• Archetype Buildings designed per IBC 2012• ASCE 7-10 and referenced design standards

– AISC 360-10, AISC 341-10, AISC 358-10

• 4 Steel Seismic Force-Resisting Systems Investigated

• Special Moment Frames – report complete

• Special Concentrically Braced Frames – report complete

• Eccentrically Braced Frames – report complete

• Buckling-Restrained Braced Frames -- report in review


16

• Reports for SMF, SCBF, and EBF

– Available at www.nehrp.gov


17

Peer Review Team

• Overall project:– Bill Holmes (Chair) (RC)

– Peter Somers (MKA)

– Nico Luco (USGS)

– Bob Hanson (UM)

– Bob Pekelnicky (DE)

• System Specific Members– SMF: Tom Sabol (ES) Mike Engelhardt (UTA)

– SCBF: Rafael Sabelli (WPM) Steve Mahin (UCB)

– EBF: Jim Malley (DE) Charles Roeder (UW)

18

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• Structural Geometry

– 150 feet by 100 feet

• East-West: 5 - 30 ft. bays

• North-South: 5 - 20 ft. bays

– 4-, 8-, and 16-story

• Heights = 60, 116 and 228 feet

– SFRS designed twice for seismic effects

• Using Equivalent Lateral Force (ELF) Procedure

• Using Modal Response Spectrum Analysis (RSA)

– 24 Total Buildings

Archetype Buildings

19

Archetype Buildings

5 @ 30'-0" = 150'-0"

Building Floor Framing Plan - Typical

W14×22

SMF

W14×22W14×22

W16×26

Sym. AboutA B C D E F

1

2

3

4

5

6

W14×22 W14×22W14×22

W14×22 W14×22W14×22

W14×22 W14×22W14×22

W14×22 W14×22W14×22

SCBF

20

• SMF– RBS Beam-to-Column Connections

– Columns sized initially to satisfy Strong Column – Weak Beam

– Column sizes increased to avoid use of doubler plates

Archetype Buildings

ELF SMF

W27×114 RBS 2nd Floor(ELEV = 18 ft.)

3rd Floor(ELEV = 32 ft.)

4th Floor(ELEV = 46 ft.)





1

1 2 3

2 3 4

5

4 5 6

6 7 8

9

7 8 9

10 11 12

13

10 11 12

14 15 16

17

13 14 15

18 19 20

21

16 17 18

22 23 24

25

19 20 21

26 27 28

29

22 23 24

30 31 32

RBS Dimensions:W24×55 a = 3.75", b = 16", c = 1.75"W27×94 a = 5.00", b = 18", c = 2.50"W27×114 a = 5.25", b = 18", c = 2.50"

= Panel Zone

= Column Splice

Roof(ELEV = 116 ft.)

W27×94 RBS

W27×94 RBS

W27×114 RBS

W27×114 RBS

W27×114 RBS

W24×55 RBS

W24×55 RBS

B C D ESym. About

same

same

same

same

same

same

same

same

Fundamental PeriodsT1 = 2.79 sec (First-Order)T1 = 2.91 sec (1.0D + 0.25Lo)T1 = 2.94 sec (1.2D + 0.25Lo)

2 @ 30'-0" = 60'-0"

W24×84 RBS 2nd Floor(ELEV = 18 ft.)







1

1 2 3

2 3 4

5

4 5 6

6 7 8

9

7 8 9

10 11 12

13

10 11 12

14 15 16

17

13 14 15

18 19 20

21

16 17 18

22 23 24

25

19 20 21

26 27 28

29

22 23 24

30 31 32

RBS Dimensions:W21×44 a = 3.25", b = 14", c = 1.50"W24×55 a = 3.75", b = 16", c = 1.75"W24×76 a = 4.50", b = 16", c = 2.25"W24×84 a = 4.75", b = 16", c = 2.25"

= Panel Zone

= Column Splice


W24×55 RBS

W24×55 RBS

W24×84 RBS

W24×76 RBS

W24×76 RBS

W21×44 RBS

W21×44 RBS

B C D E

RSA SMF

Sym. About

same

same

same

same

same

same

same

same

Fundamental PeriodsT1 = 3.55 sec (First-Order)T1 = 3.81 sec (1.0D + 0.25Lo)T1 = 3.86 sec (1.2D + 0.25Lo)

2 @ 30'-0" = 60'-0"

21

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• SCBF– 4-story uses chevron bracing configuration

– 8- and 16-story use two-story X configuration

– Column sizes controlled by capacity design requirements

Archetype BuildingsW

14×

176

W14

×31

1W

14×

132

W14

×68

W14

×15

9W

14×

283

W14

×13

2W

14×

68

22

• EBF– Links are classified as “short”, e = 30” to 39”

– Capacity design requirements generally controlled column sizes

– Link rotation (i.e., drift) requirements controlled for taller frames

Archetype Buildings

W14

×15

9W

14×

211

W14

×13

2W

14×

82

W14

×13

2W

14×

145

W14

×68

W14

×48

23

• BRBF– 4-story use chevron bracing configuration

– 8- and 16-story use two-story X configuration

– Column sizes controlled by capacity design requirements

Archetype Buildings

W14

×68

W14

×13

2W

14×

53W

14×

48

1 2

3 4

5 6

7 8

9 10

11 12

13 14

15 16

W14

×13

2W

14×

145

W14

×68

W14

×38

9 10

11 12

13 14

15 16

1 2

3 4

5 6

7 8

24

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Overview of ASCE 41-13

25

Overview of ASCE 41• ASCE 41-13

– Ch. 1 – General Requirements

– Ch. 2 – Performance Objectives and Seismic Hazard

– Ch. 3 – Evaluation and Retrofit Requirements

– Ch. 4 – Tier 1: Screening

– Ch. 5 – Tier 2: Deficiency-Based Evaluation and Retrofit

– Ch. 6 – Tier 3: Systematic Evaluation and Retrofit

– Ch. 7 – Analysis Procedures and Acceptance Criteria

– Ch. 8 – Foundations and Geological Site Hazards

– Ch. 9 – Steel

– Ch. 10 – Concrete

– Ch. 11 – Masonry

– Ch. 12 – Wood and Cold-Formed Steel Light Frame

– Ch. 13 – Architectural, Mechanical, and Electrical Components

– Ch. 14 – Seismic Isolation and Energy Dissipation

– Ch. 15 – System-Specific Performance Procedures

26

Overview of ASCE 41• Ch. 1 General Requirements

– §1.4 Seismic Evaluation Process• Does building comply?

– Selection of Performance Objective (§2.2)

– Seismic Hazard and Level of Seismicity (§2.4, §2.5)

– Evaluation Procedure (§3.3)

» Tier 1, 2 or 3

– §1.5 Seismic Retrofit Process• Seismic Evaluation Process (§1.4)

• Seismic Retrofit Procedure (§3.3)

– Selection of Performance Objective (§2.2)

– Seismic Hazard and Level of Seismicity (§2.4, §2.5)

– Evaluation Procedure (§3.3)

» Tier 2 or 3

• Retrofit Strategies and Compliance of the NEW system

27

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Overview of ASCE 41• Ch. 2 Performance Objective and Seismic Hazards

– Target Building Performance Level (BPL) - §2.3 • Structural Performance Level (SPL) - §2.3.1

– 6 SPLs

» Immediate Occupancy (IO) (S=1)

» Damage Control (S=2)

» Life Safety (LS) (S=3)

» Limited Safety (S=4)

» Collapse Prevention (CP) (S=5)

» Not Considered (S=6)

• Nonstructural Performance Level (NPL) - §2.3.2

– 4 NPLs

» Operational (N=A)

» Position Retention (N=B)

» Life Safety (N=C)

» Not Considered (N=D) – E in ASCE 41-0628

(5-D)

N-D

Overview of ASCE 41• Ch. 2 Performance Objective and Seismic Hazards

– Performance Objectives (PO) - §2.2

• ASCE 41 defines four (4) performance objectives

– Basic (BPOE)

– Enhanced (> BPOE)

– Limited (<BPOE)

– Basic PO Equivalent to New Building Standards (BPON)

» Only for Tier 3 Evaluation or Retrofit Procedure

• Recommendations regarding the selection of a Performance Objective for any building are outside the scope of this standard

29

traditional

Overview of ASCE 41• BPOE Performance Objective

– Series of Building Performance Levels coupled with a Seismic Hazard Level

30

BSE = “Basic SafetyEarthquake”

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Overview of ASCE 41• BPOE Performance Objective

– Series of Building Performance Levels coupled with a Seismic Hazard Level

31

Overview of ASCE 41• BPON Performance Objective

– BSE-2N = MCER from ASCE 7-10

– BSE-1N = 2 / 3 × BSE-2N

Does ASCE 41 CP performance objective = ASCE 7 CP performance objective?

32

Overview of ASCE 41• Seismic Hazard Level (SHL) - §2.4

– Dependent on selected Performance Objective

– Response spectrum for horizontal and vertical motion

• Similar to ASCE 7

– Ground Motion Acceleration Histories

33

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12

Overview of ASCE 41• Ch. 3 Seismic Evaluation or Retrofit Procedure

– Selection of appropriate Tier• 1 – Ch. 4

– The purpose of the Tier 1 screening phase of the evaluation process is to quickly identify buildings that comply with the provisions of this standard.

– A Tier 1 screening is required for all buildings so that potential deficiencies may be quickly identified. Further evaluation using a Tier 2 or Tier 3 evaluation then focuses, at a minimum, on the potential deficiencies identified in Tier 1.

• 2 – Ch. 5– Tier 2 deficiency-based evaluation limits the scope of the evaluation to examining

all potential deficiencies associated with Tier 1 noncompliant statements.

• 3 – Ch. 6– The Tier 3 systematic procedure involves an analysis of the entire building, either

in its current condition or with proposed retrofit measures, using the provisions in Chapters 7 through 12 for the structural systems and Chapter 13 for nonstructural components.

» Ch. 7 Analysis Procedures and Acceptance Criteria

» Ch. 8 Foundations and Geological Site Hazards

» Chs. 9-12 Material-dependent Chapters34

Overview of ASCE 41– Ch. 7 Analysis Procedures and Acceptance Criteria

• ASCE 41 provides four (4) analysis procedures (§7.4)

– Linear Analysis

» Linear Static Procedure (LSP)

» Linear Dynamic Procedure (LDP)

• Response Spectrum or Response History

– Nonlinear Analysis

» Nonlinear Static Procedure (NSP)

» Nonlinear Dynamic Procedure (NDP)

35

Overview of ASCE 41– Acceptance Criteria (§7.5)

• Every component of the structure shall be classified as a primary or secondary component, and each action in the component classified as deformation-controlled or force-controlled.

• Linear Procedures (§7.5.2)– Deformation-controlled actions

» QUD < m (QCE)

– Force-controlled actions

» QUF < QCL

• Nonlinear Procedure (§7.5.3)– Primary and secondary component demands shall be within the

acceptance criteria for nonlinear components at the selected Structural Performance Level. Allowable deformations are specified in Chapters 9 through 12.

m is a component capacity modificationfactor to account for expected ductilityassociated with an action at the selectedStructural Performance Level. m–factorsare specified in Chapters 9 through 12.

36

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Overview of ASCE 41– Alternative Modeling Parameters and Acceptance

Criteria (§7.6)

• Defines a method to derive the backbone curve (force-deformation) for a component and the associated target values for checking the acceptance criteria for nonlinear and linear assessment

37

Overview of Ch. 9• Ch. 9 Steel

– 9.1 Scope

– 9.2 Material Properties and Condition Assessment

– 9.3 General Assumptions and Requirements

– 9.4 Steel Moment Frames

– 9.5 Steel Braced Frames

– 9.6 Steel Plate Shear Walls

– 9.7 Steel Frame With Infills

– 9.8 Diaphragms

– 9.9 Steel Pile Foundations

– 9.10 Cast and Wrought Iron

38

Overview of Ch. 9• 9.2 Material Properties and Condition Assessment

– Mechanical properties for steel materials and components shall be based on available construction documents and as-built conditions for the particular structure, as specified in Section 3.2. Where such documentation fails to provide adequate information to quantify material properties or document the condition of the structure, such documentation shall be supplemented by material tests and assessments of existing conditions, as required in Section 6.2.

39

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Overview of Ch. 9

40

Overview of Ch. 9

• 9.3 General Assumptions and Requirements– 9.3.1 Stiffness

• Component stiffnesses shall be calculated in accordance with Sections 9.4 through 9.10.

– 9.3.2 Strength and Acceptance Criteria • Classification of steel component actions as deformation- or force-

controlled and calculation of strengths shall be as specified in Sections 9.4 through 9.10.

• Strengths for deformation-controlled actions, QCE, shall be taken as expected strengths obtained experimentally or calculated using accepted principles of mechanics. Unless other procedures are specified in this standard, procedures contained in AISC 360 to calculate design strength shall be permitted, except that the strength reduction factor, , shall be taken as 1.0.

• Deformation capacities for acceptance of deformation-controlled actions shall be as specified in Sections 9.4 through 9.10.

41

Overview of Ch. 9– Strengths for force-controlled actions, QCL, shall be taken as

lower-bound strengths obtained experimentally or calculated using established principles of mechanics. Lower-bound strength shall be defined as mean strength minus one standard deviation. Unless other procedures are specified in this standard, procedures contained in AISC 360 to calculate design strength shall be permitted, except that the strength reduction factor, , shall be taken as 1.0.

42

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Overview of Ch. 9• 9.4 – 9.10 System-specific provisions

– 9.4 Moment Frames – Fully and Partially Restrained

• 9.4.2.2 Stiffness of FR Moment Frames

– Linear and nonlinear procedures

– e.g. panel zone modeling – when should it be included?

6 6ye b pe b

yb b

ZF L M L

EI EI

CE CE yeQ M ZF For a beam in double curvature,

NDP: The complete hysteretic behavior of each component shall be determined experimentally or by other procedures approved by the authority having jurisdiction

43

Overview of Ch. 9• 9.4 – 9.10 System-specific provisions

• 9.4.2.3 Strength of FR Moment Frames


– QCE and QCL of MF components (deformation- or force-controlled)

• 9.4.2.4 Acceptance Criteria for FR Moment Frames


– m-factors and allowable deformations of MF components for a given SPL

44

S = secondaryP = Primary

Overview of Ch. 9• m-factors for components in a moment frame

45

UD CEQ m Q

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16

Overview of Ch. 9

• m-factors for components in a moment frame

46

Overview of Ch. 9• Deformations for components in a moment frame

47

, 6ye b

y beamb

ZF L

EI ,CL n AISCP P

, 16

ye by col

b ye

ZF L P

EI P


48

0.0 0.2 0.4 0.6 0.8 1.00.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0.06

0.12

interpolatebetween limits

Wide-Flange Sections35% > Group A 1% > Group B12% > AISC HD 3% > AISC MD

ye

E

F

0.125 2.45 1 0.93

0.125 0.77 2.93 1.49

0.125 3.76 1 2.75

0.125 1.12 2.33 1.49

c y w y c y

c y w y c y y

c y w y c y

c y w y c y y

P h E P

P t F PAISC HD

P h E P E

P t F P F

P h E P

P t F PAISC MD

P h E P E

P t F P F

418

w ye

h

t F

640

w ye

h

t F

Life Safety

Wid

th-t

o-T

hick

ness

Rat

io, h

/tw

Axial Load Ratio, P/Pye

ASCE 41 Group A Compactness Limit ASCE 41 Group B Compactness Limit AISC 341-10 HD Compactness Limit AISC 341-10 MD Compactness Limit

, ( 1.0) 0.6

50

CL n AISC c ye

ye y

P P P

F F ksi

300

w ye

h

t F

260

w ye

h

t F

460

w ye

h

t F

400

w ye

h

t F

2/8/2017

17


49

Assessment Results for the SFRS in the 8-Story Archetype Building

4- and 16-story can be found in NIST reports

50

Seismic Assessment

• Performance objective– Basic Safety Objective

• Collapse Prevention Performance Level at the BSE-2N (MCER in ASCE 7)

• Life Safety Performance Level at the BSE-1N (2/3 of BSE-2)– BSE = Basic Safety Earthquake

• Analysis Procedures– Linear Analysis

• Linear Static Procedure (LSP)

• Linear Dynamic Procedure (LDP)

– Nonlinear Analysis• Nonlinear Static Procedure (NSP)

• Nonlinear Dynamic Procedure (NDP)– 14 Ground Motions

51

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Assessment: Modeling

• Linear Analysis– Modeled in ETABS

• Nonlinear Analysis– Modeled in PERFORM-3D

– Nonlinear components calibrated with tests to verify backbone curve parameters

-8 -6 -4 -2 0 2 4 6 8

-40000

-30000

-20000

-10000

0

10000

20000

30000

40000Specimen DB4 (Engelhardt et al. 1998)

Mom

ent a

t Col

umn

Fac

e (k

ip-i

n)

Tip Displacement (inches)

Test Data Analysis Backbone

W36×194

52

RBS Connection

Mathematical Model

Inel

astic

Col

umn

Inel

astic

Col

umn

d c/2

d c/2

d b/2

d b/2

Ela

stic

B

eam

, E

I b,R

BS

Def

ault

E

nd Z

one

Ela

stic

Bea

m, E

I b

Ela

stic

B

eam

, E

I b,R

BS

Ela

stic

Col

umn,

EI c

Ela

stic

C

olum

n,

EI c

Ela

stic

Col

umn,

EI c

Ela

stic

C

olum

n,

EI c

Assessment: Modeling

53HSS Brace

Shear Link

Elastic Beam, EIb

Gusset Element, 2EIb

Gusset Plate (not modeled)Increased joint stiffness provided by gusset elements

Default End Zone

Gusset Element,

2EIc

Default End Zone

Elastic Column,

EIc

Elastic Column,

EIc

18"

nodenode

Brace stiffness computed from 0.9Lwp

W.P.

Moment release

Panel Zone

Moment-Curvature PMM Hinge, typ.

Elastic Column,

EIc

Elastic Column,

EIc

Elastic Beam

Inelastic Brace Strut

Mathematical Model

-0.18 -0.15 -0.12 -0.09 -0.06 -0.03 0.00 0.03 0.06 0.09 0.12 0.15 0.18-150

-100

-50

0

50

100

150UTA Specimen 4A-RLP (Richards et al. 2007)

She

ar F

orce

, V

Plastic Shear Strain, p

Test Data Analysis Backbone

W10×33e = 23"

BRB

-3 -2 -1 0 1 2 3-400

-300

-200

-100

0

100

200

300

400

Forc

e (k

ips)

Deformation (inches)

CoreBrace StarSeismic Analysis

Seismic Assessment

• ASCE 41 Acceptance Criteria for a Target Performance Level

– Linear Assessment Procedures

• Deformation-Controlled Actions

• Force-Controlled Actions

1.0UDN

CE

QDCR

m Q

1.0UFN

CL

QDCR

Q

54

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19

Seismic Assessment• ASCE 41 Acceptance Criteria for a Target Performance

Level

– Nonlinear Assessment Procedures

• Deformation-Controlled Actions

• Force-Controlled Actions

1.0

0

elastic

UFyN

CLplastic

TotalQDCR or

QPlastic

,

,

1.0

plastic elastic

y pe p ACUDN

CE plastic

p AC

TotalQ

DCRQ

Plastic

55

Seismic Assessment• ASCE 41 Acceptance Criteria for a Target Performance

Level

– Nonlinear Dynamic Procedure

• 14 Ground Motions

– See NIST reports for selection and scaling of records for each building height

• Take “average”

– Mean (Arithmetic)

– Median

– Mean plus one standard deviation,

– 84th Percentile

56

Seismic Assessment• 8-story ELF-designed SMF Beam-to-Column Connection

Performance, CP at the BSE-2N

0 2 4 6 8 10 12 14

2

3

4

5

6

7

8

Base

Roof

Bay B-C

Nonlinear: DCRN = Total Deformation / Total CP Permissible Deformation

Linear: DCRN = Force / CP Permissible Strength

Flo

or I

D

0 2 4 6 8 10 12 14

Bay C-D

0 2 4 6 8 10 12 14

1 = Left Beam Hinge2 = Right Beam Hinge

Bay D-E

_ y_ _ _ _ _ _ _Nonlinear:

NDP 1-Median NDP 1-Mean NDP 2-Median NDP 2-Mean

NDP 1-84th Percenitle NDP 1-Mean+ NDP 2-84th Percenitle NDP 2-Mean+ NSP 1 (Push to Left) NSP 2 (Push to Left)

Linear: LSP (max 1 or 2) LDP (max 1 or 2)

57

2/8/2017

20

Seismic Assessment• 8-story RSA-designed SMF Beam-to-Column Connection

Performance, CP at the BSE-2N

0 2 4 6 8 10 12 14

2

3

4

5

6

7

8

Base

Roof

Bay B-C



Flo

or I

D

0 2 4 6 8 10 12 14

Bay C-D

0 2 4 6 8 10 12 14


Bay D-E

Nonlinear: NDP 1-Median NDP 1-Mean NDP 2-Median NDP 2-Mean



58

• ELF

• RSA

0 2 4 6 8 10 12 14

2

3

4

5

6

7

8

Base

Roof

Bay B-C



Flo

or I

D

0 2 4 6 8 10 12 14

Bay C-D

0 2 4 6 8 10 12 14


Bay D-E

_ y_ _ _ _ _ _ _Nonlinear:

NDP 1-Median NDP 1-Mean NDP 2-Median NDP 2-Mean



0 2 4 6 8 10 12 14

2

3

4

5

6

7

8

Base

Roof

Bay B-C



Flo

or I

D

0 2 4 6 8 10 12 14

Bay C-D

0 2 4 6 8 10 12 14


Bay D-E

Nonlinear: NDP 1-Median NDP 1-Mean NDP 2-Median NDP 2-Mean



59

Seismic Assessment• 8-story ELF-designed SMF Panel Zone Performance,

CP at the BSE-2N

0.0 0.2 0.4 0.6 0.8 1.0

2

3

4

5

6

7

8

Base

RoofCol. Line B



Flo

or I

D

0.0 0.2 0.4 0.6 0.8 1.0

Col. Line C

0.0 0.2 0.4 0.6 0.8 1.0

Col. Line D

0.0 0.2 0.4 0.6 0.8 1.0

Col. Line E

Nonlinear: NDP Median NDP Mean NDP 84th NDP Mean+ NSP (Push to Left)

Linear: LSP LDP

60

2/8/2017

21

Seismic Assessment• 8-story RSA-designed SMF Panel Zone Performance,

CP at the BSE-2N

0.0 0.2 0.4 0.6 0.8 1.0

2

3

4

5

6

7

8

Base

RoofCol. Line B



Flo

or I

D

0 1 2 3

Col. Line C

0 1 2 3

Col. Line D

0.0 0.2 0.4 0.6 0.8 1.0

Col. Line E

Nonlinear: NDP Median NDP Mean NDP 84th NDP Mean+ NSP (Push to Left)

Linear: LSP LDP

61

Seismic Assessment

1.1

0.95 5940.98

6050.6 1.1

pr x y

bpr

y y c wc

C Z F

dV

V F d t

W24×76 beam frames to a W18×106 column

This indicates that the panel zone may notyield until the connection approaches its peak(probable) strength, generally associated withCP

AISC 358

ASCE 41

-32 -28 -24 -20 -16 -12 -8 -4 0 4 8 12 16 20 24 28 32-1200

-900

-600

-300

0

300

600

900

1200

rang

e of

app

licab

ility

Dif

fere

nce

in B

eam

Mom

ents

, M

(ki

p-in

)

Shear Strain / Yield Shear Strain, /y

Test Data Analysis

Specimen A-2 (Krawinkler 1971)

Strength predicted by AISC 360-10 Eq. J10-11using 0.55F

ye

62

• Force-controlled flexural hinges in SMF columns, P > 0.5PCL

2nd Floor(ELEV = 18 ft.)








B C D E

ELF NDP LS & CPELF NSP LS & CP

RSA NDP LS & CPRSA NSP LS & CP

All columns are deformation-controlled (DC) for flexure unless indicated as force-controlled (FC) in figure

Column is force-controlled for flexure if P > 0.5×PCL, where P is computed at the target displacement for the NSP and as the maximum value for the NDP

Sym. About

11.00

4.48

11.00

2.86 4.48

8.00 8.00

3.58 4.484.48

11.00 11.00

4.72 8.00

4.78

11.00

3.82 4.78

11.00

7.33 8.00

3.82 4.784.78

11.00 11.00

5.07 8.00

11.003.85 4.814.81

11.004.20 8.00

3.85 4.824.81

11.00 11.00

2.00 8.00

11.00

4.81 4.824.81

11.001.00 8.00

4.81

11.00 11.004.81 4.82

1.00 7.47

2.47

11.00

3.86 3.86

11.00

7.82 8.00

3.86 3.8611.00

3.08

11.002.64 8.00

4.48 4.48

11.00

3.58

11.001.00 8.00

4.48 4.48

11.00 11.003.58

1.00 8.00

11.00 11.004.51 4.523.61

2.02 8.00

3.61 4.51 4.52

11.00 11.00

1.00 8.00

3.63 4.54 4.54

11.00 11.00

2.80 7.66

3.63 3.633.63

11.00 11.00

1.00 6.10

m-factorsLSP: ELF

m-factorsLSP: RSA

Nonlinear Procedures:ELF and RSA 63

Seismic Assessment

2/8/2017

22

Seismic Assessment

• 8-story ELF-designed SMF Column Hinge Performance, CP at the BSE-2N

0 1 2 3 4 5 6

2

3

4

5

6

7

8

Base

RoofCol. Line B



Flo

or I

D

0 1 2 3 4 5 6

Col. Line C

0 1 2 3 4 5 6

Col. Line D

0 1 2 3 4 5 6

DCRN for the LSP and

LDP are based oninteraction equations.

Col. Line E

Nonlinear: NDP Median NDP Mean NDP 84th NDP Mean+ NSP (Push to Right)

Linear: LSP (max) LDP (max)

F.C.F.C.

F.C. = Force-Controlled Column 64

Seismic Assessment

• 8-story RSA-designed SMF Column Hinge Performance, CP at the BSE-2N

65

0 2 4 6 8 10

2

3

4

5

6

7

8

Base

RoofCol. Line B



Flo

or I

D

0 2 4 6 8 10



Col. Line C

0 2 4 6 8 10

Col. Line D

0 2 4 6 8 10

Col. Line E



F.C.F.C.

Seismic Assessment

• Column Hinge Performance

– Deformation-Controlled

– Force-Controlled

66

0.2 1.02

80.2 0.5 1.0

9

yUFUF x

CL CL x CEx y CEy

yUFUF x

CL CL x CEx y CEy

MPP MP P m M m M

MPP MP P m M m M

0.5 1.0UFyUF UF UFx

CL CL CLx CLy

MP P MP P M M

member section

Where did PCL come from?

2/8/2017

23

Seismic Assessment• Column Hinge Performance

67

AISC 360 says ---

Seismic Assessment• Column Hinge Performance

68

Seismic Assessment

• 8-story ELF-designed SCBF Brace Performance, CP at the BSE-2N

69

0.0 0.5 1.0 1.5 2.0 2.5 3.0

2

3

4

5

6

7

8

Base

Roof

T

C

C

T

T

C

DCRN,C controls acceptance

criteria except NSP as indicated

(DCRN,T > DCRN,C at 2nd and 4th

Story)

Left Brace



Flo

or I

D

C

T

C

T

C

T

C

T

T

C

0.0 0.5 1.0 1.5 2.0 2.5 3.0

T = TensionC = Compression

Right Brace

Nonlinear: NDP Median NDP NDP Mean NDP

NDP 84th Percentile NDP Mean+ NSP (Push to Left)

Linear: LSP LDP

2/8/2017

24

Seismic Assessment

• 8-story RSA-designed SCBF Brace Performance, CP at the BSE-2N

70

0.0 0.5 1.0 1.5 2.0 2.5 3.0

2

3

4

5

6

7

8

Base

Roof


TC

T

T

C

C

CT

T

C

DCRN,C

controls acceptance

criteria except NSP as indicated

(DCRN,T

> DCRN,C

at 3rd and 6th

Story)

Left Brace



Flo

or I

D

0.0 0.5 1.0 1.5 2.0 2.5 3.0

C

C

C

T

T

T

Right Brace



Linear: LSP LDP

Seismic Assessment

• 8-story EBF Link Performance, CP at the BSE-2N

71

0 1 2 3 4 5 6 7 8 9 10

2

3

4

5

6

7

8

Base

Roof

Nonlinear: DCRN = Plastic Deformation / CP Permissible Deformation


Flo

or I

D

Nonlinear: NDP Median NDP Mean


Linear: LSP LDP

0 1 2 3 4 5 6 7 8 9 10

2

3

4

5

6

7

8

Base

Roof

Nonlinear: DCRN = Plastic Deformation / CP Permissible Deformation


Flo

or I

D

Nonlinear: NDP Median NDP Mean


Linear: LSP LDP

ELF-Designed Frame RSA-Designed Frame

Seismic Assessment

• 8-story ELF-designed BRBF Brace Performance, CP at the BSE-2N

72

0.0 0.5 1.0 1.5 2.0 2.5 3.0

2

3

4

5

6

7

8

Base

Roof

T

C

Flo

or I

D

T

C

T

C

T

C

T

C

T

C

T

C

T

C

T

C

T

C

T

C

T

0.0 0.5 1.0 1.5 2.0 2.5 3.0





NDP 84th Percentile

NDP Mean+ NSP (Push to Left)

Linear: LSP LDP

Left Brace Right Brace

2/8/2017

25

Seismic Assessment

• 8-story RSA-designed BRBF Brace Performance, CP at the BSE-2N

73

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0

2

3

4

5

6

7

8

Base

Roof

Floo

r ID

C

T

C

T

C

T

C

T C

T

C

T

C

T

C

T

Left Brace


Right Brace

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0





Linear: LSP LDP

Statistical Analysis for NDP• ASCE 41 §7.4.4.3:

– Where component response is independent of the direction of action, the average shall be calculated as the mathematical mean of the maximum absolute response from each response history analysis

– Where component response is dependent on the direction of action, the average response parameter shall be calculated independently for each direction and axis as the mathematical means of the maximum positive and minimum negative response from each response history analysis.

• Assumption of distribution type– Normal

– lognormal

74

Statistical Analysis for NDP• 8-story ELF-designed SMF Beam-to-Column Connection

Performance, CP at the BSE-2N – Hinge 1 (left) – 3 col– Positive and negative action lead to same damage state

0 1 2 3

2

3

4

5

6

7

8

Base

Roof

Hinge 1Bay D-E

Floo

r ID

DCRN = Total Deformation / Total CP Acceptance Criteria

A.M. - 14 Records A.M. - 28 Records LgN.M. - 14 Records LgN.M. - 28 Records

A.M. = (Arithmetic) Meanof Normal DistrubtionLgN.M. = Mean of LognormalDistribution

EQ +DCR -DCR Max1 0.502 0.210 0.5022 0.629 0.115 0.6293 0.418 0.475 0.4754 0.348 0.603 0.6035 0.351 0.303 0.3516 0.453 0.196 0.4537 0.578 0.176 0.5788 0.053 11.714 11.7149 0.457 0.311 0.457

10 0.164 11.293 11.29311 0.690 0.236 0.69012 0.054 0.52 0.52013 0.238 6.303 6.30314 1.407 0.297 1.407

2.57NDMean 2.24LogNDMean

0.45NDMean 2.34NDMean

ND = Normal Distribution

28 1.40NDMean

75

2/8/2017

26

Statistical Analysis for NDP• 8-story ELF-designed SCBF Brace Performance, CP at

the BSE-2N – 1st Story (all completed)– Positive and negative action do not lead to same damage state

1.20LogNDMean

Left Brace Right BraceEQ T C T C1 0.094 1.134 0.127 1.0262 0.162 1.723 0.087 0.9373 0.139 3.136 0.610 1.0334 0.096 0.752 0.085 0.9835 0.533 0.285 0.528 3.4966 0.271 2.007 0.092 1.8507 0.094 0.818 0.081 0.8818 0.111 1.062 0.095 0.7219 0.091 1.532 0.146 1.10710 0.073 0.558 0.096 0.45911 0.104 0.748 0.089 1.20612 0.09 1.516 0.092 0.73313 0.125 1.333 0.115 1.18314 0.075 0.897 0.088 1.319


1.21NDCMean

0.17NDTMean

1.56NDLRCMean

28 1.23NDLRCMean

0.19NDLRTMean

28 0.16NDLRTMean

1.25NDCMean

0.15NDTMean

1.21NDMean

76

Statistical Analysis for NDP• 8-story ELF-designed BRBF Brace Performance, CP at

the BSE-2N – 1st Story (all completed)– Positive and negative action lead to possibly same damage state


Left Brace Right BraceEQ T C T C1 0.695 0.32 0.248 0.7772 0.510 0.475 0.391 0.5793 1.043 0.163 0.099 1.1534 0.055 1.298 1.192 0.0925 0.076 1.242 1.133 0.1286 1.291 0.606 0.52 1.3737 2.211 1.02 0.994 2.3048 0.777 0.318 0.248 0.8689 0.455 0.218 0.154 0.54410 0.789 0.11 0.054 0.88911 0.198 0.779 0.692 0.25612 0.683 0.607 0.552 0.7713 2.617 0.416 0.338 2.79514 0.497 1.48 1.393 0.566


0.65NDCMean

0.85NDTMean

1.20NDLRCMean

28 0.79NDLRCMean

1.11NDLRTMean

28 0.71NDLRTMean

0.94NDCMean

0.57NDTMean

77

Assessment Conclusions

• Many conclusions and observations are detailed in NIST reports. Too many to discuss here.

• Primary Observations

– Analytical results based on component-level performances indicate that new SFRSs designed in accordance with ASCE 7, and its referenced standards, can have difficulty achieving the ASCE 41 BSO for an existing building intended to be equivalent to a new building. This observation is driven by the performance of the specific system components

– Assuming the archetype buildings meet the collapse performance objective of ASCE 7, the results of the assessment procedures indicate that ASCE 41 is generally conservative for steel SFRSs. ASCE 41 analysis would require retrofit or replacement of specific components of a code-compliant SFRS to satisfy the CP BPL, given an MCE event

78

2/8/2017

27

Assessment Conclusions– A significant number of columns, primarily at the base of the

frames, did not satisfy the ASCE 41 acceptance criteria (force-controlled). The results for columns can be enhanced by more mechanistically consistent assessment provisions and analytical modeling parameters for columns

– Results from this study indicate that for ASCE 41 to be used as a seismic design procedure for new steel buildings, as a performance-based alternative to ASCE 7 (see ASCE 7 §1.3.1.3), acceptance criteria for the various analysis methods must be calibrated to each other to consistently result in a uniform collapse risk (e.g., 10% P(collapse) given MCE shaking).

– NIST reports provide comprehensive list of recommend future research

79

Assessment Conclusions• Link between ASCE 7 and ASCE 41

– acceptance criteria for a component in ASCE 41 are not directly calibrated to the seismic performance objective of ASCE 7 (10% probability of partial or total collapse given an MCE event—or 1% probability of partial or total collapse in 50 years).

– equating the two objectives of the standards would imply that only one structural performance level with an associated earthquake hazard level can be coupled: CP at the MCER. However, this would be difficult based on a member-level binary performance solution in ASCE 41. What percentage of components needs to fail the associated CP SPL to achieve a 10% probability of total or partial collapse given an MCER event?

– Future research should assess the archetype buildings in FEMA P695 analysis to ascertain the collapse probability in relation to the ASCE 7 performance objective. Results from that study can be used to probabilistically relate the R-factor in ASCE 7 to the m-factors and inelastic deformations using story drift. 80

Assessment Conclusions• Link between ASCE 7 and ASCE 41

– A consequence of a deterministic-type component evaluation (i.e., pass or fail) is that analytical results, depending on the accuracy of the model and analysis algorithms, can be independent of the behavior of the system. Individual member performance and the potential need to retrofit or replace it are therefore based on an analysis output rather than the influence of the component performance on the system performance.

– ASCE 41 is available now and being used for PBSD of building systems and components. In many cases, the acceptance criteria in ASCE 41 are being used to justify computed seismic performance to buildings officials as being satisfactory. The question is what seismic performance is being justified: the objective defined in ASCE 41 or that intended in ASCE 7?

81

2/8/2017

28

Changes to the Provisions for Seismic Evaluation of Structural Steel Components in ASCE 41-17 and AISC 342

82

Introduction• Since the inception of the provisions in FEMA 273 in

1997, there has not been a significant update to what isnow found in Chapter 9 Steel in ASCE 41-13.

– with the exception of modifications to some provisions in FEMA356 in 2000 which primarily focused on implementing the resultsfrom the SAC project.

– some new material was introduced in ASCE 41-06 and ASCE41-13 regarding buckling-restrained braced frames and steelplate shear walls.

• Significant effort was made this code cycle to update theprovisions for evaluation of structural steel components

83

Introduction• Parallel with the ASCE 41-17 efforts, work is ongoing at

American Institute of Steel Construction (AISC) todevelop a standard focusing on the seismic evaluationand retrofit of existing structural steel buildings. Thisstandard is currently referred to as AISC 342: SeismicEvaluation and Retrofit of Structural Steel Buildings.

– the work has highlighted differences between provisions forevaluation of a structural steel component and provisions fordesign of the same component in accordance with AISC 360 andAISC 341.

– effort to align the standards where needed is important becauseASCE 41 is beginning to see use for the design of new steelbuildings in order to demonstrate seismic performance.

84

2/8/2017

29

Revised Provisions in Ch. 9The revisions presented are preliminary until after balloting has beencompleted and ASCE 41-17 has gone through the public reviewprocess. Some material shown here may change.

• Revision 1: Material Properties for HSS Added to ASCE 41 Table 9-1

• Revision 2: Shear Deformation Included in Yield Chord Rotation ofBeams and Columns

• Revision 3: Axial Load Effects Added to Link Beams

• Revision 4: Axial Load Effects Added to Panel Zones

• Revision 5: Revised Yield Surface for Column Hinges

• Revision 6: Revised Column Assessment Provisions

• Revision 7: Acceptance Criteria Added for Weak Panel Zones

85

Revision 1• Revision 1: Material Properties for HSS Added to ASCE 41

Table 9-1• Values are taken as mean minus one standard deviation reduced by 10%

to account for uncertainties in material values during coupon testing at themills and the variation of material properties between cross-sectionelements—aligns with current approach in existing values in Table 9-1.

Material Shape Samples Strength Mean Mean- 0.9×(Mean-)

Ratio to Mean

FLBTranslation

Factor

A53 Gr. B Round 1362Yield 56 4.9 51 46 1.22 45 1.2

Tensile 64 4.3 60 60 1.07 60 1.1

A500 Gr. B

Round 3603Yield 61 6.4 54 49 1.24 48 1.2

Tensile 69 6.3 63 58 1.19 60 1.2

Rectangular 72144Yield 60 5.4 55 49 1.22 50 1.2

Tensile 73 5.4 68 61 1.20 62 1.2

A500 Gr. C

Round 1149Yield 61 6.4 55 49 1.24 50 1.2

Tensile 73 5.5 67 62 1.17 62 1.2

Rectangular 14140Yield 62 5.8 56 51 1.23 50 1.2

Tensile 74 5.1 59 62 1.19 62 1.2

A1085 Gr. A(50 ksi)

Rectangular 2240

Yield 62 5.5 57 51 1.22 50 1.25

Tensile 75 4.7 70 65 1.16 65 1.25

86

Revision 2• Revision 2: Shear Deformation Included in Yield Chord

Rotation of Beams and Columns

• The term (1+) is added to account for the increase in the elasticcurve for shear deformation. Aligns links with beams and columns.

• Nomenclature to align with AISC standards

1

6pce

yb

M L

E I

for 0.2 12

9for 0.2 1

8

peye ye

CE pce

peye ye

P PM

P PM M

P PM

P P

2

12

s

EI

L GA

87

2/8/2017

30

Revision 3• Revision 3: Axial Load Effects Added to Links Beams

• P-V interaction added to strength and acceptance criteria of linkswhen P / Pye > 0.2.

• Reduction because tests have shown that link beams subjected toshear and axial force show premature flange and web buckling ascompared to a case with no axial load.

• Align with AISC standards

2

for 0.2 0.6

for 0.2 0.6 1

ye sye

CE ye

ye sye ye

PF A

PV V

P PF A

P P

88

Revision 4• Revision 4: Axial Load Effects Added to Panel Zones

• P-V interaction added to strength and acceptance criteria of panelzones when P / Pye > 0.4.


2

13

yey y

ye

F P

PG

for 0.4 0.55

for 0.4 0.55 1.4

ye c pye

CE ye

ye c pye ye

PF d t

PV V

P PF d t

P P

89

Revision 5• Revision 5: Revised Yield Surface for Column Hinges

• Revised P-M interaction for the plastic capacity of a column hinge.


for 0.2 12

9for 0.2 1

8

peye ye

CE pce

peye ye

P PM

P PM M

P PM

P P

90

2/8/2017

31

Revision 6• Revision 6: Revised Column Assessment Provisions

• Axial force basis revised from P / PCL to P / Pye (back to FEMA 273)

• Column not force-controlled for flexure at P / PCL > 0.5. No flexuralyielding when some axial load > 0.6Pye.

• Web compactness criteria revised to align with AISC standards

0.2 2.45 1 0.71

0.2 0.77 2.93 1.49

ye w ye ye

ye w ye ye ye

P h E P

P t F P

P h E P E

P t F P F

0.2 3.76 1 1.83

0.2 1.12 2.33 1.49

ye w ye ye

ye w ye ye ye

P h E P

P t F P

P h E P E

P t F P F

Compact sections

Noncompact sections

91


• Nonlinear acceptance criteria revised for columns in compression

• Regression analysis performed on the first cycle envelope of thehysteresis of 220 column specimens that were subjected to fully-reversed cyclic loading protocols using revised axial load basisand web compactness and constant axial load, PG.

Modelling Parameters Acceptance Criteria

Plastic rotation angle a and b (radians)Residual strength ratio c

Plastic rotation angle (radians)Performance Level

IO LS CPColumns in Compression—Flexure

0.5a 0.75b b

2.2 1

0.8 1 0.1 0.8 0.0035 0G

ye y w

P L ha

P r t

2.3 1

7.4 1 0.5 2.9 0.006 0G

ye y w

P L hb

P r t

0.9 0.9 G

ye

Pc

P

Compactsections

92


• Nonlinear acceptance criteria revised for columns in compression

• Regression analysis performed on the first cycle envelope of thehysteresis of 220 column specimens that were subjected to fully-reversed cyclic loading protocols using revised axial load basisand web compactness and constant axial load, PG.

Modelling Parameters Acceptance Criteria

Plastic rotation angle a and b (radians)Residual strength ratio c

Plastic rotation angle (radians)Performance Level

IO LS CPColumns in Compression—Flexure

0.5a 0.75b b

Noncompactsections

1.2 1

1.2 1 1.4 0.1 0.9 0.0023 02

fG

ye y w f

bP L ha

P r t t

1.8 1

2.5 1 0.1 0.2 2.7 0.0097 02

fG

ye y w f

bP L hb

P r t t

0.5 0.5 G

ye

Pc

P

93

2/8/2017

32


• Linear acceptance criteria for columns revised slightly

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

m‐factor for flexure

Axial Load Ratio, P / Pye

ASCE 41 IO

ASCE 41 LS

ASCE 41 CP

Proposed IO

Proposed LS

Proposed CP

P-M interaction equationsresult in m = 1 when noyielding is permitted

94


• Acceptance criteria revised to a two-step process

– Step 1: Verify capacity of plastic hinge using the yield surface

0.22

80.2

9

UDyUFUF UDx

ye ye x pex y pey

UDyUFUF UDx

ye ye x pex y pey

MPP MP P m M m M

MPP M

P P m M m M

Linear assessment is shown here, nonlinear assessment is similar—plastic rotation verified directly from the yield surface model.

95



– Step 2: Verify stability of member

0.22

80.2

9

0.75

UyUFUF Ux

ye CL x CxLTB y Cy

UyUFUF Ux

ye CL x CxLTB y Cy

UF

ye

MPP MP P m M m M

MPP MP P m M m M

P

P

Linear assessment is shown here, nonlinear assessment is similar.

Example of verification of acceptance criteria is provided in paper96

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Linear assessment is shown here, nonlinear assessment is similar.

97

0

500

1000

1500

2000

2500

3000

0 50000 100000 150000 200000 250000

Axi

al F

orce

, P(k

ips)

Moment, Mx (kip-in)

Yield Surface

Hinge Strength

Member Strength

Demand


ASCE 41-13

98

0.0

0.2

0.4

0.6

0.8

1.0

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0

1

2

3

4

5

6

7

Primary Component

Notes:1. Knowledge Factor, , taken as unity.2. Beam-Column with P / Pye < 0.1 can be treated as a beam.

m-factorAxial Load Ratio, P/PCL

ye

E

F

Life Safety

0.6

50

CL ye

ye y

P P

F F ksi

ASCE 41 Group A Compactness Limit ASCE 41 Group B Compactness Limit AISC 341-10 HD Compactness Limit AISC 341-10 MD Compactness Limit

Wid

th-t

o-T

hick

ness

Rat

io, h

/tw

0.0

0.2

0.4

0.6

0.8

1.0

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0

1

2

3

4

5

6

7

Primary Component

Notes:1. Knowledge Factor, , taken as unity.2. Beam-Column with P / Pye < 0.1 can be treated as a beam.

m-factorAxial Load Ratio, P/PCL

ye

E

F

Life Safety

0.6

50

CL ye

ye y

P P

F F ksi

ASCE 41 Group A Compactness Limit

Wid

th-t

o-T

hick

ness

Rat

io, h

/tw

ASCE 41-17

Revision 6

ASCE 41-13

99

ASCE 41-17

0 2 4 6 8 10

2

3

4

5

6

7

8

Base

RoofCol. Line B


Flo

or I

D

0 2 4 6 8 10

Col. Line C

0 2 4 6 8 10

Col. Line D

0 2 4 6 8 10

Col. Line E

Nonlinear: NDP Median NDP Mean NDP 84th NDP Mean+

0 2 4 6 8 10

2

3

4

5

6

7

8

Base

RoofCol. Line B



Flo

or I

D

0 2 4 6 8 10



Col. Line C

0 2 4 6 8 10

Col. Line D

0 2 4 6 8 10

Col. Line E



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Revision 7• Revision 7: Acceptance Criteria Added for Weak Panel

Zones

• Weak panel zones can be a primary source of inelastic actions

• Large panel zone deformations can trigger CJP weld fracture.

• Independent of criteria for beam-to-column connections

• Equations are applicable for welds that meet AISC 341 CVNrequirements and estimated for pre-Northridge era welds.

,

2

,

0.183 3.451

2 p pz

y

ye cf

F P

G P

b

cf

d

t

plastic shear strain computedfrom ASCE 41 Table 9-6

100

ASCE 41-17 Revision Notes

• Significant effort was made this code cycle to update the provisions for evaluation of structural steel components

• More updates will be forthcoming as AISC 342 progresses

101

Thank you

Q & A

102

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35

Lower-bound and ExpectedMaterial Properties for Structural Steel

ASCE 41 Table 9-1 and 9-3

Jay Harris• Chair, ASCE 41 Steel Subcommittee

• Vice-Chair, AISC Task Committee 7, Evaluation and Retrofit

History of Table 9-1• FEMA 273 Table 5-2

• The term “expected” represents “lower-bound”. There was no translation factor. One material property used for both QCE and QCL. However, FEMA 274 recommended a second analysis be done using an upper-bound material property for braces and beams that is 30 to 50% greater than the values given in Table 5-2 while using lower-bound values for columns and connections.

• Note 1: Values for pre-1960 steels were taken from Iron and Steel Beam 1873 to 1952 . These values are based on minimum specified material properties.

• Tensile strength taken as lower of the range specified in reference document.

• Note 2 is not applicable to these steels.

104

• FEMA 273 Table 5-2• The term “expected” represents

“lower-bound”. There was no translation factor. One material property used for both QCE and QCL. However, FEMA 274 recommended a second analysis be done using an upper-bound material property for braces and beams that is 30 to 50% greater than the values given in Table 5-2 while using lower-bound values for columns and connections.

• Note 1 is not applicable to these steels. Values for post-1960 steels came from SAC project—FEMA 351 Table 2-7 (and also FEMA 355F Table 4-3 and 8-1)—based on Statistical Analysis of Tensile Data for Wide-Flange Structural Shapes (K. Frank and D. Read 1994)

• FEMA 351 values are applicable for wide-flange shapes and extracted from the web—recommend a 5% reduction for flanges.

• “Lower-bound” values in FEMA 273 were reduced by 10% from those given in FEMA 351 Table 2-7—see next slide.

105

History of Table 9-1

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36

History of Table 9-1• 1994 Report to SSPC - K. Frank and D. Read

• Statistical Analysis of Tensile Data for Wide-Flange Structural Shapes (K. Frank and D. Read 1994)

• Data is for web steel

106

History of Table 9-1• FEMA 351 Table 2-7 (FEMA 355F Table 4-3 and 8-1)

• Both “lower-bound” and “expected” are provided.

• Expected properties are mean values of the data sets from Statistical Analysis of Tensile Data for Wide-Flange Structural Shapes.

• Lower-bound properties are mean minus two standard deviations values of the data sets. Generally slightly higher than minimum specified (or “nominal”).

• Values are applicable for wide-flange shapes and extracted from the web. Reduce values by 5% for flange properties.

• FEMA 273 reduced “lower-bound” values by 10% to account for rate of loading effects. Mill certificates are typically higher due to testing speed—see FEMA 355F Ch. 8. Other factors included in 10% – like variations between web and flange?

107

History of Table 9-1• FEMA 273 – FEMA 351 (Yield Stress)

Steel

FEMA 351 FEMA 273

Mean"Expected"

Std. Dev.Mean – 2

"Lower-Bound"“LB”×0.9 "Expected"

ASTM A36 Group 1 51 5.00 41 36.9 37Group 2 47 4.00 39 35.1 35Group 3 46 5.00 36 32.4 32Group 4 44 5.00 34 30.6 30Group 5 47 4.00 39 35.1 35

ASTM A572 Group 1 58 5.50 47 42.3 41Group 2 58 5.00 48 43.2 42Group 3 57 3.50 50 45.0 44Group 4 57 4.00 49 44.1 43Group 5 55 2.50 50 45.0 44

ASTM A36 Dual Grade 50

Group 1 55 3.50 48 43.2 43Group 2 58 5.00 48 43.2 43Group 3 57 2.50 52 46.8 46Group 4 54 2.00 50 45.0 44

108

=

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37

History of Table 9-1• FEMA 356 Table 5-2

• The term “expected” changed to “lower-bound” for consistency.

• Developed the translation factor from lower-bound to expected for QCE and QCL.

• Note 1: Values for pre-1960 steels were taken from Iron and Steel Beam 1873 to 1952 . These values are based on minimum specified material properties.

• Values for pre-1960 steels match FEMA 273, with a few simplifying changes. ASCE 41-13 changed some rivet steel properties.

• Note 2 is not applicable to all steels listed.

109

History of Table 9-1• FEMA 356 Table 5-2 (cont.)

• The term “expected” changed to “lower-bound” for consistency.

• Developed the translation factor (Table 5-3) between lower-bound and expected for QCE and QCL.

• Note 1: Values for post-1960 steels are changed from FEMA 273 to mean minus one standard deviation. Generally slightly higher than minimum specified (or “nominal”).

• FEMA 356 does not mention the 10% reduction, but it is maintained in the revised values—see next slide.

• Note 2: Values representative of material extracted from flanges of wide-flange shapes. This is a change from FEMA 351 which states extracted from web. (Uncertain?: 10% reduction exceeds the recommended 5% reduction in FEMA 355F – but for different reasons.)

110

History of Table 9-1 and 9-3• FEMA 356 – FEMA 273 (Yield Stress)

Steel

FEMA 351 FEMA 273 FEMA 356

Mean"Expected"

Std. Dev.

Mean – 2"Lower-Bound"

“LB”×0.90.9×(Mean – 2)

"Expected"Eq. (1)

Mean – "Lower-Bound"

MeanMean –

ASTM A36 Group 1 51 5.00 41 36.9 37 44.0 44 1.10Group 2 47 4.00 39 35.1 35 41.0 41 1.09Group 3 46 5.00 36 32.4 32 39.0 39 1.12Group 4 44 5.00 34 30.6 30 37.0 37 1.13Group 5 47 4.00 39 35.1 35 41.0 41 1.09

ASTM A572 Group 1 58 5.50 47 42.3 41 49.5 50 1.10Group 2 58 5.00 48 43.2 42 50.0 50 1.10Group 3 57 3.50 50 45.0 44 50.5 51 1.06Group 4 57 4.00 49 44.1 43 50.0 50 1.08Group 5 55 2.50 50 45.0 44 49.5 50 1.05

ASTM A36 Dual Grade 50

Group 1 55 3.50 48 43.2 43 49.0 49 1.07Group 2 58 5.00 48 43.2 43 50.5 50 1.10Group 3 57 2.50 52 46.8 46 51.5 52 1.04Group 4 54 2.00 50 45.0 44 49.0 49 1.05

FEMA 356 = Mean – one std. dev.

Eq. (1) FEMA 356 = Expected (FEMA 351) – ((Expected (FEMA 351) – Expected (FEMA 273)) / 2)

• Translation factor between lower-bound and expected for QCE and QCL.

• FEMA 356 does not mention the 10% reduction, but it is maintained in the revised values—see Eq. (1).

• Values representative of material extracted from flanges of wide-flange shapes. Since 10% reduction was maintained, this reduction could convert web to flange, but then partially removes the concept of revising values from the original mill certificates for rate of loading effects.

111

=

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38

History of Table 9-1 and 9-3• FEMA 356 Table 5-3

• Develop the translation factor between lower-bound and expected for QCE and QCL.

• Values for post-1960 steels range from 1.05 to 1.10 and are based on mean / 0.9×(mean – 1).

• Values for pre-1960 steels selected as 1.10. Value matches potential range of tensile stress but uncertain if applicable to yield stress (no range specified in ref. doc).

• Last line item is for all steels not listed—not conforming to a listed ASTM specification (e.g., A500 Grade B HSS).

112

History of Table 9-1 and 9-3

• A992 Added to ASCE 41-06 – 2003 Report to SSPC• 2000

113

Paradox of ASCE 41-13 Ch. 9• ASCE 41-13 Section 9.2.2

• “For material grades not listed in Table 9-1, lower-bound material properties shall be taken as nominal or specified properties or shall be based on tests where the material grade or specified value is not known.”

• “Nominal material properties specified in AISC 360 or properties specified in construction documents shall be taken as lower-bound material properties.”

• Nominal or specified properties from the ASTM specification (i.e., AISC 360) are minimum specified material property.

• “Corresponding expected material properties shall be calculated by multiplying lower-bound material values by an appropriate factor taken from Table 9-3 to translate from lower-bound to expected values.”

• Table 9-3, the factor is 1.1 for all steels not listed.

Take for example, ASTM A500 Grade B HSS rectangular shape.

• Not listed in Table 9-2; therefore, Fy,LB = Fy,n = 46 ksi

• Fy,e = 1.1×46 = 50.6 ksi

• New Steel Design [Fy,e = RyFy = 1.4×46) = 64.4 ksi (27% higher than above)]

• QCE can be underestimated, QCL can be overly conservative.

114

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39

Paradox of ASCE 41-13 Ch. 9• ASCE 41-13 Section 9.2.2

• “For material grades not listed in Table 9-1, lower-bound material properties shall be taken as nominal or specified properties or shall be based on tests where the material grade or specified value is not known.”

• Need to define “Nominal” or specified properties in the ASTM specification as the minimum specified material property.

• “Corresponding expected material properties shall be calculated by multiplying lower-bound material values by an appropriate factor taken from Table 9-3 to translate from lower-bound to expected values.”

• Add text about using Ry for known steels adopted in AISC 341 to be used with minimum specified properties per ASTM Specification only.

• In a perfect world,• Fy,e = RyFy

• Fy,LB = RLBRyFy where RLB a factor that reduces expected to lower-bound

115

How do we add steels to Table 9-1?• Add A500 Gr. B and C and A53 Gr. B to Table 9-1

• Take “expected” value as the mean value of a large data set.• Include all sizes, not just ones that satisfy AISC 341 requirements

• Take “lower-bound” value as the mean minus one standard deviation value, multiplied by an adjustment factor

• Adjust value by reducing by 10% for loading rate effects.• Is 10% the best choice or does it include multiple effects, like conversion of web to flange

properties? For an HSS, 10% may be too high since there is no flange? Reduction value could even be different between a round and rectangular shape?

• Value should not be less than ASTM Specification (minimum specified property).

• Compute translation factor as the ratio of expected / lower-bound.

116

• A53 Gr. B Pipe• Round Shapes (2 data sets from multiple producers)

A53 Grade B (738 Tests) PipeYield Tensile

Mean 56 63

Std Dev. 4.5 2.9

Mean-1 52 60

Factor 1.21 1.05

10% reduction 46 60

15% Pecentile 51 60

Nominal 35 60

A53 Grade B (228 Certs, 571 Tests) Pipe

Yield Tensile

Mean 56 69

Std Dev. 6.0 3.9

Mean-1 50 66

Factor 1.25 1.16

10% reduction 45 60

15% Pecentile 48 66

Nominal 35 60

Fy,LB = 45 ksi

Ft,LB = 60 ksi

Translation Factor = 1.2 and 1.1

Ft,LB = Ft,n

117

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40

• A500 Gr. B Round and Rectangular

• Round Shapes

• Rectangular Shapes

A500 Grade B (25 Certs, 645 tests) Round

Yield Tensile

Mean 57 72

Std Dev. 4.3 3.3

Mean-1 53 69

Factor 1.19 1.16

10% reduction

48 62

15% Pecentile

53 70

Nominal 42 58

A500 Grade B (2958 Tests) RoundYield Tensile

Mean 61 69

Std Dev. 6.4 6.4

Mean-1 54 63

Factor 1.24 1.19

10% reduction 49 58

15% Pecentile 54 62Nominal 42 58

A500 Grade B (31264 Tests) RectangularYield Tensile

Mean 60 73

Std Dev. 5.4 5.4

Mean-1 55 68

Factor 1.22 1.2010%

reduction49 61

15% Pecentile 58 68

Nominal 46 58

A500 Grade B (309 Certs, 40880 Tests) Rect

Yield Tensile

Mean 60 74

Std Dev. 4.9 3.0

Mean-1 55 71

Factor 1.20 1.16

10% reduction

50 64

15% Pecentile

56 72

Nominal 46 58

Fy,LB = 48 ksi

Ft,LB = 60 ksi

Translation Factor = 1.2

Fy,LB = 50 ksi

Ft,LB = 62 ksi


Ft,LB = Ft,n

118

• A500 Gr. C Round and Rectangular• Round Shapes

• Rectangular ShapesA500 Grade C (14140 Tests) Rectangular

Yield Tensile

Mean 62 74

Std Dev. 5.8 5.1

Mean-1 56 69

Factor 1.23 1.1910%

reduction51 62

15% Pecentile

62 72

Nominal 50 62

A500 Grade C (1149 Tests) RoundYield Tensile

Mean 61 73

Std Dev. 6.4 5.5

Mean-1 55 67

Factor 1.24 1.1710%

reduction49 62

15% Pecentile

55 68

Nominal 46 62

Fy,LB = 50 ksi

Ft,LB = 62 ksi


Fy,LB = 50 ksi

Ft,LB = 62 ksi


Ft,LB = Ft,n

Ft,LB = Ft,n119

same

• A1085 Gr. A 50 ksi Rectangular• Rectangular Shapes

• Pure A1085 data only, does not include A500 Gr. C that satisfies A1085

• A1085 has an Ry value of 1.25 in AISC 341-16. • What is the effect of cold-forming the HSS on Ry for section strength?

A1085 (24 Certs) RectangularYield Tensile

Mean 60 73

Std Dev. 2.2 3.5

Mean-1 57 69

Factor 1.15 1.12

10% reduction 52 65

15% Pecentile 57 69

Nominal 50 65

Fy,LB = Fy,n = 50 ksi

Ft,LB = Ft,n = 65 ksi

Translation Factor = Ry = 1.25

120

A1085 (2216 Certs) RectangularYield Tensile

Mean 62 75

Std Dev. 5.5 4.7

Mean-1 57 70

Factor 1.22 1.16

10% reduction 51 65

15% Pecentile 57 71

Nominal 50 65

2/8/2017

41

• A501 Gr. B Round and Rectangular• Round Shapes

• Rectangular ShapesA501 Grade B (402 Tests) Rectangular

Yield Tensile

Mean 59 76

Std Dev. 5.2 2.8

Mean-1 54 74

Factor 1.18 1.09

10% reduction

50 70

15% Pecentile

54 73

Nominal 50 70

A501 Grade B (196 Tests) RoundYield Tensile

Mean 58 76

Std Dev. 4.5 2.8

Mean-1 54 74

Factor 1.16 1.09

10% reduction

50 70

15% Pecentile

54 74

Nominal 50 70

Fy,LB = 50 ksi

Ft,LB = 70 ksi


Fy,LB = 50 ksi

Ft,LB = 70 ksi


Fy,LB = Fy,n

Ft,LB = Ft,n

Fy,LB = Fy,n

Ft,LB = Ft,n121

same

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