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Seismic Desi n of Hi h-r

Buildings

Andrew Whittaker, University at Buf

Michael Willford, Arup

Ron Klemencic, MKA

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CTBUH Seismic Working Group

Formed in early 2007

Tasked with drafting international bpractice recommendations for seism

-

Lead authors Willford, Whittaker, Klemencic

Draft published in early 2008

Review comments received in April

Final recommendations in August 2

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CTBUH Working Group goals

Review international best practice f-

Japan, China, USA

Identify shortcomings in existing staand codes vis--vis high-rise buildin

1997 Uniform Building Code -

2006 International Building Code

Draft internationally appropriate proor ana ys s an es gn across a re

seismic hazard

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International practice

Practices vary widely around the wo erna e or no per ormance o ec v

Use of unsuitable codes, standards, gu

Reliabilit safet of resultant desi ns

Traditional practice 1997 UBC and derivatives

Emerging practice

Performance-based design

n erp ns ecommen a ons

Best practice in Japan and China

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Traditional practice

1997 Uniform Building Code and de any perm ss e s ruc ura ram ng sy

None amenable to high-rise buildings

Minimum lateral seismic forces

No technical basis

Prescriptive rules

- -

Single level design (life safety + 0.67*M

No performance check

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Uniform Building Code u ng co e ase on ue

SEAOC Blue Book

USA West Coast ractice

Low- and medium-rise buildings

First published in late 1950s

Three performance objectives

Single level check (life safety in rare ea

-

Response modification factors

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d

CR

,a

VR

=

=x vx

k

x x

n

w hC =

Framing system

Steel

Special moment f

1

k

i ii

w h

=

=

Eccentrically braced frameSpecial concentrically braced fMoment frame (25%) an

Reinforced Concrete

i d e

Special bearing shea

Moment frame (25%) and special she

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2003 NEHRP Recommended Prov accep a e ram ng sys ems

Seismic design category E height limit

RC bearin walls, 49 m

Steel braced frames, 49 m

RC and steel moment frames (MFs), N

,

RC and steel MFs tube construct

-

Questionable performance at best

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Efficient framing systems in tall buil cores

RC, steel and composite perimeter tub

RC cores outri ers erimeter colum

Steel braced cores and perimeter fram

None of the above are permitted pestandards and guidelines

No technical basis to set aside these s

because performance is not proven

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High-rise buildings Multiple modes of

seismic response Shears moments

High gravity stresses Cores and columns Limited rotation capacity

Single value of R? How com uted?

Which mode?

Wind loadings

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Emerging practice (USA)

Performance-based seismic design en an en proce ures

Multiple user-selected performance ob

Desi n freedom

User-selected framing system and mat

Design burden

e a e azar groun mo on comp

Nonlinear analysis

Component checking for deformations

First principles mechanics for deformat

Expert peer review

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Gen 1 performance-based eq engin ,

ASCE41 (06)

ImmediateOccupancy

C

POperationalLife

Safety

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100 years

1000

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hear

Bas

e

s

Structural displacement (earthquake i

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Gen 1 procedures ac one curves or componen mo e

Nonlinear static analysis

First mode lateral load rofiles

Appropriate for low- and mid-rise build

Inappropriate for high-rise buildings

Gen 2 procedures (ATC-58 project)

Nonlinear response-history analysis

Appropriate selection and scaling of paground motions

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Best practice in Japan and Chi

Performance based design

Mandatory for buildings exceeding heights

Depend on hazard and structural form User-specified framing systems and

Multiple performance objectives Nonlinear res onse-histor anal sis Element ductility check

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Best practice in Japan

Two performance objectives Typically five ground motion sets per le

Level 1: PGV = 25 cm/s (approx 0

Elastic response required Storey drift < 1:200

eve : = cm s approx . Expected material strength Storey drift < 1:100 Storey ductility factor < 2

Expert panel peer review

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Best practice in China

Three performance objectives -

Elastic response

475-year return period spectrum (1 Repairable damage

Critical members to remain elastic 2475- ear return eriod s ectrum

No collapse Story drift limits

Expert panel peer review

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CTBUH Recommendations

Introduction abackground

es gn o ecphilosophy

Seismic hazaassessment

Foundation e

Structural anmodeling pro

nergy ss p References Appendices

Assessmen

low seismic

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Design objectives and procedu

Minimum design objectives -

Negligible damage for spectral demandreturn period of about 50 years

non-structural components

Collapse-level assessment

period of 2475 years

Limit deformations for ductile actions aforces for non-ductile actions in structucomponents

Limit damage in those non-structural cwhose failure might trigger building col

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Seismic hazard analysis Selection and scaling of pairs of ground mo

3D nonlinear building model What to include? How to model? ASCE-41 backbone curves

Perform nonlinear response-history anal

Pairs of ground motions Assess results

u ng e orma ons r s Component deformations (ductile actions) Component forces (non-ductile action s)

Major shortcoming of Gen 1 procedures

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Seismic design basis oa map or ana ys s an es gn

Building description, description of sewind resisting systems, performance se sm c azar resu ts, w n stu y re

methods of analysis, modeling and accriteria, drift criteria, criteria for nonstr

Mandatory peer review

Instrumentation

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Seismic hazard assessment

Probabilistic seismic hazard assessme

Maximum versus geomean demands

2009 USGS seismic design maps

Near source effects and long period dema

Site response analysis

No consensus on best procedures

#1: Matching to maximum spectrum (3x1)

#2: Matching to maximum and minimum s

#3: Matching to maximum and minimum C

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Foundation effects

Geotechnical parameters

Consider credible variations in soil propert

Bounding analysis

- -

Soil flexibility will influence the dynamic prothe structure

Foundation size (kinematic interaction)

Modeling n rect mo e s us ng equ va ent near spr

Explicit nonlinear soil models

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Foundation effects

Foundation embedment e sm c npu a un ers e o asemen

Difference between basement and freemotions

Greatest when surface soils are weak

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Structural analysis and modeli

Analysis procedures -

Collapse-level: nonlinear response his

Capacity-design approaches

Building models Components that contribute strength a

Component force-deformation relation Lumped plasticity models

appropr a e

Fiber models

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Structural analysis and modeli

Damping Viscous (pre-yield) versus hysteretic (post-y

Response-spectrum analysis CQC method to combine the modes Apply (Max, Min) or (100, 30 Max) ax mum componen response or assessm

Nonlinear response-history analysis Pairs of ground motions for analysis

Coexisting forces and deformations

Deformation capacities in lumped plasticity m ASCE41 or first principles

Deformation capacities in fiber models

Force capacities

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Examples of PBD of high-rise b

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One Rincon Hill, San Francisco

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One Rincon Hill, San Francisco

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St. Francis Towers, Manila (Aru

60 storey RC building m rom ac ve au

M 7.5

T1 = 6 seconds

design V 0.05W

Dual system required

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1997 UBC design Dual system

Feasible?

Sensible?

High gravity stressin core and columns Maximize floor space

Relative shortening

Onl solution is abearing wall

But not permitted

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1997 Uniform Building Code set as

Performance-based solution

Probabilistic seismic hazard analysis

Core walls only (no dual system) Damped outriggers to achieve = 0.07

Lateral strength to resist wind loads

Nonlinear response-history analysis

ASCE41 and first principles mechanics

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Core analysis Low axial load

= 0.009

M /M = 1.25 700800

p = 0.05

High axial load300

400

500

600

Moment

= 0.003

Mu/My = 1.08

= 0.005

0

100

200

0 0.002 0.004

C

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Nonlinear building-

Nonlinear responsehistor anal sis 2475-year spectrum

Pairs of motions

Yielding in cores andcolumns at base

excess of UBC

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Core wall checkingShear W

Rotation capacityvaries as a function 1

1

1

)

of (P,M)

First principlesanalysis

lForce(MN

Shear strengthcomputed usingcapacity principles

-200 -150 -100 -50

Axi

Reserve strength

Mome

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1997 UBC Performa

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Performanes gn

30% redu

40% redu(core, col

$10+M US

Higher sh un

Known pe

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The Future Holds

Application of Gen 2 PBD procedur

Risk based procedures such as

10% robabilit of colla se/2475 ear s

MAF of collapse = 0.0001

Development of innovative structurarc ec ura an mec an ca sys emare damage tolerant

as knowledge is gained

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aw a u a o.e u

[email protected]

r emenc c m a.com

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0802 slides

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