Steel Seismic Force Resisting Systems · Steel Seismic Force Resisting Systems ... Moderately...

Canadian Institute of Steel Construction / Institut canadien de la construction en acier

SteelSeismic Force Resisting Systems

Ontario Building Officials Association2007 Annual Meeting and Training Sessions

Fairmont Chateau Laurier, Ottawa, ONSeptember 24, 2007

David H. MacKinnon, M.A.Sc., P.Eng. Director of Codes and Standards


NBC 2005 Article 4.1.8.9.↑↓

CAN/CSA-S16-01 (S16S1-05)Clause 27

Terminology, Scope and Application


NBCC 2005 Article 4.1.8.9. System Limits

Cases Where

IEFvSa(1.0)

< 0.2 ≥ 0.2 to< 0.35

≥ 0.35 to≤ 0.75

> 0.75 > 0.3

Ductile moment-resisting frames 5.0 1.5 NL NL NL NL NL

Moderately ductile moment-resisting frames 3.5 1.5 NL NL NL NL NL

Limited ductility moment-resisting frames 2.0 1.3 NL NL 60 30 30

Moderately ductile concentrically braced frames

Non-chevron braces 3.0 1.3 NL NL 40 40 40

Chevron braces 3.0 1.3 NL NL 40 40 40

Tension only braces 3.0 1.3 NL NL 20 20 20

Steel Structures Designed and Detailed According to CAN/CSA-S16

Type of SFRS Rd Ro

Restrictions(2)

Cases Where IEFaSa(0.2)


NBCC 2005 Terminology

Rd = ductility-related force modification factor reflecting the capability of a structure to dissipate energy through inelastic behaviour.

Ro = overstrength-related force modification factor accounting for the dependable portion of reserve strength.


CAN/CSA-S16 Terminology

IEFaSa(0.2) = "specified short-period spectral acceleration ratio“

IEFvSa(1.0) = "specified one-second spectral acceleration ratio"



27.1 General27.2 - 4 Moment Resisting Frames27.5 - 6 Concentrically Braced Frames27.7 Eccentrically Braced Frames27.8 Plate Walls27.9 Cantilever Column Structures27.10 Conventional Construction27.11 Special Seismic Construction


General Requirements

Capacity design approach appliesSteel in ductile elements :

Fy < 350 MPa ; Fy < 0.85 Fu

Min. toughness for sections with thick flangesMinimum toughness for weld metalRequirements for bolted connectionsRyFy = 1.1Fy but > 385 MPa for probable capacity of ductile elements


Moment-Resisting Frames

Cases Where

IEFvSa(1.0)

< 0.2 ≥ 0.2 to< 0.35

≥ 0.35 to≤ 0.75

> 0.75 > 0.3

Ductile moment-resisting frames 5.0 1.5 NL NL NL NL NL

Moderately ductile moment-resisting frames 3.5 1.5 NL NL NL NL NL

Limited ductility moment-resisting frames 2.0 1.3 NL NL 60 30 30






Type of SFRS Rd Ro

Restrictions(2)



Moment-Resisting Frames


Collapse Mechanisms


Type D Moment Resisting FramesRd = 5.0, Ro = 1.5

BeamsClass 1braced for seismic design

ColumnsClass 1 or Class 2 except when column hinging is allowed,

Class 1braced for seismic designaxial force < 0.3AFy in high seismicity regions

Some examples of seismic design requirements


Type MD Moment Resisting FramesRd = 3.5, Ro = 1.5

BeamsClass 1 or Class 2braced as plastically analyzed, statically loaded beams

ColumnsClass 1 or Class 2except, when column hinging is allowed,

Class 1 braced for seismic designaxial force < 0.5AFy in high seismicity regions



Type LD Moment Resisting FramesRd = 2, Ro = 1.3

Height limits< 30 m where IEFaSa(0.2) > 0.75

< 60 m where IEFaSa(0.2) > 0.35

BeamsClass 1 or Class 2

ColumnsClass 1



www.cisc-icca.ca


Moment Connections for Seismic Applicationsby CISC

Reduced beam section

Bolted end plate Bolted stiffened end plate


Concentrically Braced Frames





Limited ductility concentrically braced frames




Cases Where

IEFvSa(1.0)

< 0.2 ≥ 0.2 to< 0.35

≥ 0.35 to≤ 0.75

> 0.75 > 0.3


Type of SFRS Rd Ro

Restrictions(2)



Chevron (MDCBF or LDCBF)

Chevron Vee

Balanced, Chevron


Non-Chevron (MDCBF or LDCBF)

Single Brace Panel (General)

Split-Chevron Split-V British Flag

Balanced, Direct-Acting, Single Brace Panels



Split-XDirect-ActingX (Cross)

Balanced


Tension-Only (MDCBF or LDCBF)



Knee-BracingK-Bracing

Not Permitted

Use Conventional Construction, Rd=1.5, Ro=1.3


Type MD - Braces (T/C & T-O)

b/t Ratios:

KL/r < 100RHS: 330/√FyOthers: Class 1

KL/r = 200HSS: Class 1Others: Class 2

100 < KL/r < 200Linear interpolation


Brace Slenderness:

KL/r < 200


Type MD - Brace Connections

Rotation:

Allow rotation to develop upon buckling, or

Design for 1.1 Ry Mpb

R. Tremblay

2tp



Type MD – Column Continuity & Flexure

Columns in braced bays:

Class 1 o 2 in braced bays

Beam-columns with M = 0.20 Mpc

Other Columns:

Class 3 or better


Columns continuous over:

2 storeys (T/C)

Full building height (T-O)

Column splices:

Shear = 0.4 Mpc/hs


Type LD - Requirements

Brace KL/r < 300 for single- and two-storey T-O bracing

Brace b/t limitsNo b/t limit for slender tension-only bracesWhere IEFaSa(0.2) < 0.45, Class 2


Brace connectionsWhere IEFaSa(0.2) < 0.55, no requirements for end rotation when brace KL/r > 100

Column splicesWhere IEFvSa(1.0) < 0.30, requirements for gravity columns waived


Eccentrically Braced Frames

Limited ductility concentrically braced frames




Ductile eccentrically braced frames 4.0 1.5 NL NL NL NL NL

Ductile frame plate shear walls 5.0 1.6 NL NL NL NL NL

Moderately ductile plate shear walls 2.0 1.5 NL NL 60 60 60

Cases Where

IEFvSa(1.0)

< 0.2 ≥ 0.2 to< 0.35

≥ 0.35 to≤ 0.75

> 0.75 > 0.3


Type of SFRS Rd Ro

Restrictions(2)



Eccentrically Braced Frames


EBF – Capacity Design


EBF - Requirements

Links:Fy ≤ 350 MPaClass 1 webs / Class 1 or 2 flanges for “short” links;Class 1 web and flanges for “long” linksMinimum and maximum length of link, eShear resistance = lesser of ø Vp′ and 2 ø Mp′ / eMaximum link beam rotation



EBF - Requirements

Portions of beams outside of links: To resist 1.30 Ry times load corresponding to Vp′ or Mp′Bracing requirements

Braces:Class 1 or 2Braces and end connections to resist 1.30 Rytimes load corresponding to Vp′ or Mp′



EBF - Requirements

Columns:Class 1 or 2To resist 1.15 Ry times load corresponding to Vp′ or Mp′

(or 1.30 Ry times for top two storeys).

Beam-column interaction value ≤ 0.85 (except 0.65 for top tier)



Plate Shear Walls







Conventional construction of moment frames, braced frames or shear walls

1.5 1.3 NL NL 15 15 15

Cases Where

IEFvSa(1.0)

< 0.2 ≥ 0.2 to< 0.35

≥ 0.35 to≤ 0.75

> 0.75 > 0.3


Type of SFRS Rd Ro

Restrictions(2)





+ Clause 20


In the Lab

In the field

Plate Shear Walls


Plate Shear WallCapacity Design

yielding

OverturningMoment

B x MfL

L2 storeys>

Vre

R. Tremblay


Type D – Plate WallRd = 5.0, Ro = 1.6

NBCC term “Ductile frame plate shear walls”Beams

Class 1Column Splice

full flexural resistance of smaller sectionsplice @ ¼ the storey height

Column Joint Panel ZonesBeam-to-Columns Joints and Connections



Type LD – Plate WallRd = 2.0, Ro = 1.5

NBCC “Moderately ductile plate shear walls”proportioned in accordance with Clause 20

no special requirements



Conventional Construction





1.5 1.3 NL NL 15 15 15

Other steel SFRS(s) not defined above 1.0 1 15 15 NP NP NP

Cases Where

IEFvSa(1.0)

< 0.2 ≥ 0.2 to< 0.35

≥ 0.35 to≤ 0.75

> 0.75 > 0.3


Type of SFRS Rd Ro

Restrictions(2)



Height Restriction for Conventional Construction

Commentary J to NBCC 2005 states:

This restriction was intended to retain the traditional 3-storey height limit stipulated in previous editions of the NBCC. However, this height limit does not apply to single-storey steel industrial structures.

However, structures such as stadia, large exhibition halls, arenas, convention centres and other similar structures must satisfy the height restrictions.


Conventional ConstructionRd = 1.5, Ro = 1.3)

Where IEFaSa(0.2) > 0.45 :

design connections for an expected ductile failure mode* or

design for 1.5 E + gravity

* See CISC Commentary on Cl. 27.10 for examples of ductile failure mode in general



Other SFRS





1.5 1.3 NL NL 15 15 15

Other steel SFRS(s) not defined above 1.0 1 15 15 NP NP NP

Cases Where

IEFvSa(1.0)

< 0.2 ≥ 0.2 to< 0.35

≥ 0.35 to≤ 0.75

> 0.75 > 0.3


Type of SFRS Rd Ro

Restrictions(2)



Cantilever Column Systems

Rd = 1.0, Ro = 1.0

(Rd = 1.5, Ro = 1.3, if Class 1 columns)

design base connectionfor 1.1 Ry Mpc

UCV h

f ff s

2 1 125= +⎛

⎝⎜

⎞

⎠⎟ <

Σ ΔΣ

. R. Tremblay



Special Seismic Construction

Systemsspecial bracing and ductile truss segmentsseismic isolation and other energy-dissipating devices

Designpublished research results and design guidesobserved performancespecial investigation

Comparable level of safety and performance


CISC Short Courses Fall 2007

Seismic Design of Steel Framed BuildingsMoncton, NB, (October 11) Vancouver-Richmond, BC, (October 30) Calgary, AB, (November 1) Toronto-Richmond Hill, ON, (November 6) Montréal, QC, (22 novembre)

www.cisc-icca.ca/courses

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