Design Life vs. Seismic Return Period

İSTANBUL SEISMIC DESIGN CODE FOR TALL BUILDINGS

Boğaziçi University Kandilli Observatory and Earthquake Research Institute (KOERI)

Department of Earthquake Engineering Çengelköy, İstanbul

Version – III

May 2008

English translation by Mehmet Nuray Aydınoğlu, PhD

Professor of Earthquake Engineering (KOERI)

İSTANBUL METROPOLITAN MUNICIPALITY

Version III May 2008

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ĐSTA�BUL SEISMIC DESIG� CODE FOR TALL BUILDI�GS

VERSIO� – III May 2008

LIST OF CO�TE�TS 1. GE�ERAL CLAUSES

1.1. NOTATION

1.2. OBJECTIVE AND SCOPE OF CODE, GENERAL APPROACH

1.2.1. Objective and Scope of Code 1.2.2. General Approach of Code: Performance Based Design 1.2.3. Independent Design Review

2. DEFI�ITIO� OF EARTHQUAKE ACTIO�

2.1. EARTHQUAKE LEVELS

2.1.1. (E1) Level Earthquake 2.1.2. (E2) Level Earthquake 2.1.3. (E3) Level Earthquake

2.2. EARTHQUAKE DESIGN SPECTRA

2.3. EARTHQUAKE ACTION IN TIME DOMAIN

3. PERFORMA�CE LEVELS A�D RA�GES, PERFORMA�CE OBJECTIVES FOR TALL BUILDI�GS

3.1. MINIMUM DAMAGE / UNINTERRUPTED OCCUPANCY PERFORMANCE LEVEL (MD – UO)

3.2. CONTROLLED DAMAGE / LIFE SAFETY PERFORMANCE LEVEL (CD – LS)

3.3. EXTENSIVE DAMAGE / NO–COLLAPSE SAFETY PERFORMANCE LEVEL (ED – NC)

3.4. PERFORMANCE RANGES

3.5. MINIMUM PERFORMANCE OBJECTIVES FOR TALL BUILDINGS

4. A�ALYSIS A�D DESIG� PROCEDURES FOR TALL BUILDI�GS

4.1. ANALYSIS PROCEDURES FOR TALL BUILDINGS

4.2. REQUIREMENTS FOR ANALYSIS MODELING

4.3. PERFORMANCE-BASED SEISMIC DESIGN STAGES OF TALL BUILDINGS

4.3.1. Design Stage (I – A): Preliminary Design (dimensioning) with Linear Analysis for Controlled Damage/Life Safety Performance Objective under (E2) Level Earthquake 4.3.2. Design Stage (I – B): Design with Nonlinear Analysis for Controlled Damage/Life Safety Performance Objective under (E2) Level Earthquake 4.3.3. Design Stage (II): Design Verification with Linear Analysis for Minimum Damage/Uninterrupted Occupancy Performance Objective under (E1) Level Earthquake


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4.3.4. Design Stage (III): Design Verification with Nonlinear Analysis for Extensive Damage/No-Collapse Safety Performance Objective under (E3) Level Earthquake

5. DESIG� REQUIREME�TS FOR �O�STRUCTURAL ARCHITECTURAL A�D MECHA�ICAL/ELECTRICAL ELEME�TS/COMPO�E�TS

5.1. GENERAL REQUIREMENTS

5.2. EQUIVALENT SEISMIC LOADS

5.3. LIMITATION OF DISPLACEMENTS

5.4. NONSTRUCTURAL FACADE ELEMENTS AND CONNECTIONS

6. STRUCTURAL HEALTH MO�ITORI�G SYSTEMS

7. I�DEPE�DE�T DESIG� REVIEW

7.1. INDEPENDENT REVIEW BOARD

7.2. QUALIFICATIONS OF INDEPENDENT REVIEWERS

7.3. TALL BUILDINGS ENGINEERING HIGH COMMISSION OF ISTANBUL

8. E�FORCEME�T

A��EX A: SEISMIC HAZARD MAPS FOR CITY OF ISTA�BUL

A��EX B: DEFI�ITIO� OF SOIL CLASSES


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CHAPTER 1 GE�ERAL CLAUSES

1.1. �OTATIO�

Ae = Maximum acceleration acting on architectural element or mechanical/electrical component Aen = Maximum acceleration acting in n’th vibration mode on architectural element or mechanical/electrical component Be = Amplification factor applied to architectural element or mechanical/electrical component (EI)e = Effective bending rigidity fce = Expected strength of concrete fye = Expected strength of steel fck = Characteristic strength of concrete fyk = Characteristic strength of steel Fa = Soil factor for short period spectral acceleration Fe = Equivalent seismic load acting on architectural element or mechanical/electrical component Fv = Soil factor for 1.0 second period spectral acceleration hx,hy = Height of connection points of architectural element or mechanical/electrical component measured from the related story bottom ke = Effective stiffness coefficient of the connection of architectural element or mechanical /electrical component to the building structural system me = Mass of architectural element or mechanical/electrical component mj = j’th story mass Mxin = Effective participating mass corresponding to i’th story-shear in n’th mode for an x direction earthquake MN = Nominal plastic moment MY = First-yield moment � = Number of stories of building above ground n = Live Load Participation Factor R = Structural Behaviour Factor Ra = Seismic Load Reduction Factor Re = Behaviour factor applied to architectural element or mechanical/electrical component Sae = Elastic spectral acceleration Saen = n’th mode elastic spectral acceleration SS = Short-period spectral acceleration for reference soil class S1 = 1.0 second period spectral acceleration for reference soil class SMS = Short-period spectral acceleration for actual soil class SM1 = 1.0 second period spectral acceleration for actual soil class T = Natural vibration period Te = Natural vibration period of connection of architectural element or mechanical/ electrical component to the building structural system To = Spectrum corner period TL = Transition period to long-period range TS = Spectrum corner period Vxin = x direction i’th story-shear in n’th mode under same direction earthquake Vt,min = Minimum base shear W = Total building weight considered for calculating minimum base shear


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βv = Dynamic shear amplification factor of reinforced concrete structural wall δe = Drift related to architectural element or mechanical/electrical component (δi)max / hi = Maximum story drift ratio permitted for the i’th story of building structural system εcg = Upper limit of concrete compressive strain in the extreme fiber inside the confinemet reinforcement εs = Upper limit of strain in steel reinforcement Γxn = n’th mode participation factor for an x direction earthquake ϕen = n’th mode shape amplitude at the location of architectural element or mechanical/ electrical component in a given direction ϕxjn = n’th mode mode shape amplitude of mass centre at j’th story in x direction ϕyjn = n’th mode mode shape amplitude of mass centre at j’th story in y direction ϕθjn = n’th mode mode shape amplitude in terms of rotation with respect vertical axis passing through mass centre at j’th story ϕy = Yield curvature corresponding to nominal plastic moment ϕy’ = Curvature corresponding to first-yield

ξ = Damping ratio


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1.2. OBJECTIVE A�D SCOPE OF CODE, GE�ERAL APPROACH 1.2.1. Objective and Scope of Code This Code shall be applied to earthquake-resistant design of tall buildings to be constructed within the borders of Đstanbul Metropolitan Municipality. Tall buildings are minimum 60 meter high buildings measured from the lowest ground level, excluding basement stories completely underground and surrounded with high-stiffness peripheral walls all around. 1.2.2. General Approach of Code: Performance Based Design In principle, this Code is based on performance-based design under earthquake action. In this approach, the damage to occur in the elements of structural system under given levels of earthquake ground motion is quantitatively estimated and checked in each element whether it exceeds the acceptable damage limits. The acceptable damage limits are specified under various earthquake levels in conformity with the performance objectives identified for the structure. Since the earthquake damage to be estimated at element level is generally represented by the nonlinear deformations to occur beyond the elastic strain limits, performance-based design approach is directly related to nonlinear analysis methods and the deformation-based design concept. Nevertheless, linear analysis methods are permitted in the Code as well in the framework of strength-based design approach for performance objectives where limited damage is expected. 1.2.3. Independent Design Review The earthquake-resistant designs of tall buildings to be realised to the requirements of this Code shall be checked and approved by an Independent Review Board as described in Chapter 7.


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CHAPTER 2 DEFI�ITIO� OF EARTHQUAKE ACTIO�

2.1. EARTHQUAKE LEVELS The earthquake levels to be considered in the performance-based design of tall buildings within the scope of this Code are defined in the following sections. 2.1.1. (E1) Earthquake Level This earthquake level represents relatively frequent but low-intensity earthquake ground motions with a high probability to occur during the service life of tall buildings within the scope of this Code. The probability of exceedance of (E1) level earthquake in 50 years is 50%, which corresponds to a return period of 72 years. 2.1.2. (E2) Earthquake Level This earthquake level represents the infrequent and high-intensity earthquake ground motions with a low probability to occur during the service life of tall buildings within the scope of this Code. The probability of exceedance of (E2) level earthquake in 50 years is 10%, which corresponds to a return period of 475 years. 2.1.3. (E3) Earthquake Level This earthquake level represents the highest intensity, very infrequent earthquake ground motions that tall buildings within the scope of this Code may be subjected to. The probability of exceedance of (E3) level earthquake in 50 years is 2%, which corresponds to a return period of 2475 years. 2.2. EARTHQUAKE DESIG� SPECTRA 2.2.1 – Spectral accelerations corresponding to short period (0.2 second) and 1.0 second natural vibration periods (respectively SS ve S1), are given for (E1), (E2) and (E3) earthquake levels in Annex A for a reference soil defined at the boundary between B and C soil classes (shear wave velocity in the upper 30 m = 760 m/s). For other soil classes, the spectral accelerations SMS ve SM1 corresponding to the same natural vibration periods shall be calculated with the following relationships:

MS a S

M1 v 1

S F S

S F S

= ×

= × (2.1)

The soil parameters Fa and Fv are given in Table 2.1 and Table 2.2, respectively. Soil classes referred to in those tables are defined in Annex B.


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2.2.2 – Design spectrum for a horizontal earthquake is defined as follows (Fig.2.1):

MSae MS o

o

ae MS o S

M1ae S L

M1 Lae 2

( ) 0.4 0.6 ( )

( ) ( )

( ) ( )

( )

SS T S T T T

T

S T S T T T

SS T T T T

T

S TS T

T

= + ≤

= ≤ ≤

= ≤ ≤

= L( )T T≤

(2.2)

Spectrum corner periods To and TS are defined as:

M1S o S

MS

; 0.2S

T T TS

= = (2.3)

Transition period to long-period range shall be taken for Istanbul as TL=12s.

Tablo 2.1. Short period soil factor Fa

Short period spectral acceleration (g)a Soil class*

SS ≤≤≤≤ 0.25 SS = 0.50 SS = 0.75 SS =1.0 SS ≥≥≥≥ 1.25 A 0.8 0.8 0.8 0.8 0.8 B 1.0 1.0 1.0 1.0 1.0 C 1.2 1.2 1.1 1.0 1.0 D 1.6 1.4 1.2 1.1 1.0 E 2.5 1.7 1.2 0.9 0.9 F –b –b –b –b –b

* See Annex B a Linear interpolation to be applied for intermediate values of SS b Site-specific geotechnical investigation and dynamic site response analysis are required.

Tablo 2.2. 1.0 s period soil factor Fv

1.0 sec period spectral acceleration (g)a Soil class *

S1 ≤≤≤≤ 0.1 S1 = 0.20 S1 = 0.3 S1 = 0.4 S1 ≥≥≥≥ 0.5 A 0.8 0.8 0.8 0.8 0.8 B 1.0 1.0 1.0 1.0 1.0 C 1.7 1.6 1.5 1.4 1.3 D 2.4 2.0 1.8 1.6 1.5 E 3.5 3.2 2.8 2.4 2.4 F –b –b –b –b –b

* See Annex B a Linear interpolation to be applied for intermediate values of S1 b Site-specific geotechnical investigation and dynamic site response analysis are required.


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Figure 2.1 2.3. EARTHQUAKE ACTIO� I� TIME DOMAI� 2.3.1 – A minimum seven sets of earthquake ground motions (acceleration records in two perpendicular horizontal directions) with the following properties shall be selected for the analysis to be performed in the time domain. Real earthquake accelereration records compatible with the scenario earthquake parameters shall be used for each set of ground motion. A strike-slip eartquake source mechanism with a 7.0 < Mw < 7.5 moment magnitude and a soil class B or C shall be considered in the selection of records for the city of Đstanbul. The earthquake distance shall be taken as the shortest distance between the building and the main Marmara Fault line (See Fig.2.2). Acceleration records may be obtained from the following data banks:

Cosmos Virtual Data Center http://db.cosmos-eq.org/

Peer Strong Motion Database http://peer.berkeley.edu/smcat/

European Strong- Motion Database http://www.isesd.cv.ic.ac.uk/ESD/frameset.htm

Japan K-NET NIED http://www.k-net.bosai.go.jp/ 2.3.2 – In the cases where sufficient number of acceleration records cannot be found, artificial earthquake ground motions generated as compatible with the earthquake simulations or the design spectrum may be used. The same acceleration record (accelerogram) shall not be used for both directions. 2.3.3 – The ground motion simulations shall be based on a physical model considering the fault mechanism, rupture characteristics and the geological structure of the medium between the earthquake source and recording station. In the cases where the distance between the building and the main Marmara Fault line is shorter than 15 km (See Fig.2.2), a minimum three sets of earthquake ground motions shall be generated by simulation in order to account for directivity effects.

T0 TS 1.0 TL T

0.4SMS

SM1

Sae

SMS

Sae = ____ SM1

T

Sae = ____ TL

T 2

SM1


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2.3.4 – The phase spectrum of artificially generated spectrum-compatible ground motions should be similar to the phase spectrum of real acceleration records consistent with the scenario earthquake parameters.

2.3.5 – The average of 5% damped spectral amplitudes calculated at zero period from each set of earthquake ground motion shall not be less than zero-period spectral amplitude of the design spectrum (0.4 SMS).

2.3.6 – The duration between the two points where acceleration amplitude first and last exceed ±0.05g shall not be shorter than 5 times the dominant natural vibration period of the building nor 15 seconds for each earthquake ground motion record. 2.3.7 – The resultant spectrum of an earthquake ground motion set shall be obtained through square-root-of-sum-of-squares of 5% damped spectra of the two directions. The amplitudes of earthquake groud motions shall be scaled according to a rule such that the amplitudes of the resultant spectrum between the periods 0.2T and 1.2T (T = Dominant natural vibration period of the building) shall not be less than 1.3 times the amplitudes of the design spectrum along the same period range. The scaling of both components shall be made with the same factors. 2.3.8 – In the cases where needed, the parameters related to vertical component of the earthquake ground motion may be specified, subject to approval of the Independent Review Board.

Figure 2.2


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CHAPTER 3 PERFORMA�CE LEVELS A�D RA�GES,

PERFORMA�CE OBJECTIVES FOR TALL BUILDI�GS Performance levels of tall buildings are defined below with respect estimated damages to occur in earthquakes. The acceptable damage limits for those performance levels shall be quantitatively defined seperately for each structural type or element.

3.1. MI�IMUM DAMAGE / U�I�TERRUPTED OCCUPA�CY PERFORMA�CE LEVEL (MD – UO) Minimum Damage (Uninterrupted Occupancy) Performance Level describes a performance condition such that no structural or nonstructural damage would occur in tall buildings and in their elements under the effect of an earthquake or, if any, the damage would be very limited. In this condition, the tall building can be occupied uniterruptedly and the problems, if any, can be fixed in a few days. 3.2. CO�TROLLED DAMAGE / LIFE SAFETY PERFORMA�CE LEVEL (CD – LS) Controlled Damage (Life Safety) Performance Level describes a performance condition where limited and repairable structural and nonstructural damage is permitted in tall buildings and in their elements under the effect of an earthquake. In this condition, short term (a few weeks or months) problems related to occupancy of the building may be expected. 3.3. EXTE�SIVE DAMAGE / �O–COLLAPSE SAFETY PERFORMA�CE LEVEL (ED – �C) Extensive Damage (�o-collapse Safety) Performance Level describes a performance condition where extensive damage may occur in tall buildings and in their elements under the effect of an earthquake prior to the collapse of the building. In this condition, long term problems related to occupancy of the building may occur or the occupancy of the buildings may be terminated. 3.4. PERFORMA�CE RA�GES The regions in between the above-defined performance levels are identified as performance ranges (Fig. 3.1). The region below (MD – UO) Performance Level is defined as Minimum

Damage / Uninterrupted Occupancy Performance Range, the region in between (MD – UO) Performance Level and (CD – LS) Performance Level is defined as Controlled Damage / Life Safety Performance Range, the region in between (CD – LS) Performance Level and (ED – NC) Performance Level is defined as Extensive Damage / �o-collapse Safety Performance Range and the region above the (ED – NC) Performance Level is defined as Collapse Range. 3.5. MI�IMUM PERFORMA�CE OBJECTIVES FOR TALL BUILDI�GS Minimum performance objectives identified for tall buildings are given below (Table 3.1) depending upon the earthquake levels defined above:


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Figure 3.1

3.5.1 – The performance of tall buildings in �ormal Occupancy Class (residence, hotel, office building, etc.) is identified to be in Minimum Damage / Uninterrupted Occupancy

Performance Range under (E1) level earthquake, in Controlled Damage / Life Safety Performance Range under (E2) level earthquake, and in Extensive Damage / �o-collapse Safety Performance Range under (E3) level earthquake. 3.5.2 – The performance of tall buildings in Special Occupancy Class (health, education, public administration buildings, etc.) is identified to be in Minimum Damage / Uninterrupted

Occupancy Performance Range under (E2) level earthquake, and in Controlled Damage / Life Safety Performance Range under (E3) level earthquake 3.5.3 – Upon the preference of the owner, higher performance objectives may be identified for tall buildings in �ormal Occupancy Class (residence, hotel, office building, etc.) with respect to those defined in 3.5.1.

Tablo 3.1. Minimum performance objectives identified for tall buildings under various earthquake levels

Building Occupancy Class

(E1) Earthquake

Level

(E2) Earthquake

Level

(E3) Earthquake

Level �ormal occupancy class: Residence, hotel, office

building, etc. MD / UO CD / LS ED / �C

Special occupancy class: Health, education, public admin. buildings, etc.

–– MD / UO CD / LS

Strength

Minimum Damage / Uninterrupted Occupancy Performance Range

CD/LS ED/�C

Controlled Damage / Life Safety

Performance Range

Ext. Damage / No-collapse Safety

Performance Range

Collapse Range

MD/UO

Displacement or Deformation


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CHAPTER 4 A�ALYSIS A�D DESIG� PROCEDURES FOR TALL BUILDI�GS

4.1. A�ALYSIS PROCEDURES FOR TALL BUILDI�GS 4.1.1 – In the linear elastic analysis of tall buildings required for design stages described in 4.3.1 and 4.3.2, Response Spectrum Analysis procedure shall be employed. Complete Quadratic Combination Rule shall be used for modal combination to be applied to each response quantity of interest. 4.1.2 – Sufficient number of modes to be included in Response Spectrum Analysis shall be determined according to modal story shears to be calculated for each story in each direction as follows:

N

xin xin aen xin xn j xjnj=i

= ; = V M S M mΓ Φ∑ (4.1)

where Saen respresents n’th mode spectral acceleration and Mxin is the effective participating modal mass associated with the story shear at (i)’th story in n’th mode for an earthquake in x direction. jm refers to the mass of the j’th story, xjnΦ is the n’th mode shape amplitude at the mass centre of (j)’th story in x direction, N represents the total number of stories and xnΓ is the modal participation factor of the n’th mode for an earthquake in x direction:

N

j xjnj=1

xn N2 2 2

j xjn j yjn θj θjnj=1

=

+ +

m

m m m

Φ

Γ

Φ Φ Φ

∑

∑ (4.2)

The above-given relationships are based on an assumption of infinitely rigid floor diaphgrams in their own planes. 4.1.3 – In the nonlinear analysis of tall buildings required for design stages described in 4.3.2 and 4.3.4, Direct Integration procedure shall be employed in the time domain. 4.1.4 – In nonlinear analysis, a minimum seven eartquake ground motion sets shall be used in accordance with 2.3 and the acceleration records in the two perpendicular directions shall be applied simultaneously along the principal axes of the structural system. Subsequently directions of acceleration records shall be rotated by 90o and the analysis shall be repeated. Design basis seismic demands shall be calculated as the average of results obtained from the minimum 2*7 = 14 analysis. 4.1.5 – In the linear or nonlinear analysis of tall buildings, damping ratio shall be taken ξ = 0.05 as a maximum. It is mandatory to take into account second order (P – ∆) effects. 4.1.6 – In the linear or nonlinear analysis of tall buildings, Live Load Participation Factor, n, given in Eq.(2.6) of (SBCSZ – Specification for Buildings to be Constructed in Seismic Zones – 2007) shall be defined as follows for the case indicated in the third row of Table 2.7 of SBCSZ (2007), but its value shall not exceed 0.30.


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= 0.01(50 ) 40

= 0.10 40

n � �

n �

− ≤

> (4.3)

4.1.7 – In the cases where needed, vertical component of the earthquake ground motion may be considered as well, subject to approval of the Independent Review Board. 4.2. REQUIREME�TS FOR A�ALYSIS MODELI�G 4.2.1 – Modeling of frame elements shall be made with frame finite elements in linear analysis. Modeling in nonlinear analysis can be made with plastic sections (plastic hinges) in the framework of lumped plasticity approach or through fiber elements in the framework of distributed plasticity approach. Regarding the plastic hinge length, an appropriate empirical relationship may be selected from the literature, subject to approval of the Independent Review Board. In nonlinear analysis, alternative modeling approaches may be followed upon the approval of Independent Review Board. In linear and nonlinear models of steel frames, shear deformation in the beam-column panel zone shall be considered. 4.2.2 – In linear analysis, modeling of reinforced concrete walls and their parts shall be made with shell finite elements. In order to be consistent with the effective bending rigidities of the frame elements with cracked sections, elastic modulus (E) of shell elements can be reduced by using the empirical relationships given in 7.4.13 of SBCSZ (2007). 4.2.3 – In modeling reinforced concrete walls and their parts for nonlinear analysis, fiber elements or alternative modeling options may be used in the framework of distributed plasticity approach, subject to approval of the Independent Review Board. The cross-section requirements given in 3.6.1 of SBCSZ (2007) may not be applied to reinforced concrete walls of tall buildings with heights exceeding 70 m. Shear stiffnesses of reinforced concrete walls shall be considered. 4.2.4 – Effective bending rigidities shall be used for reinforced concrete frame elements with cracked sections. In the preliminary design stage described in 4.3.1, empirical relationships given in 7.4.13 of SBCSZ (2007) may be utilized. In other design and verification stages described in 4.3, effective bending rigidity shall be obtained from the section’s moment-curvature relationship as follows (Fig.4.1):

NYe '

yy

( )MM

EI = =φφ

(4.4)

where YM , represents the state of first-yield in the section. The corresponding curvature 'yφ

represents a state where either concrete strain attains a value of 0.002 or steel strain reaches the yield value, whichever occurs first. The nominal plastic moment NM corresponding to effective yield curvature yφ is calculated with concrete compressive strain reaching 0.004 or steel strain attaining 0.015, whichever occurs first. In calculating the moment strengths of columns, axial forces due to gravity loads only may be considered. 4.2.5 – Material models given in Informative Annex 7B of SBCSZ (2007) can be used for confined concrete and steel reinforcement. Use of high strength concrete exceeding C50 is subject to approval of the Independent Review Board.


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Figure 4.1 4.2.6 – In preliminary design stage described in 4.3.1, design strengths, (fd), of concrete, reinforcing steel and structural steel are defined as the relevant characteristic strengths, (fk), divided by material safety factors. In other design and verification stages in 4.3, expected strentghs, ( fe ), shall be used as design strengths without any material safety factors. The following relationships may be considered between the expected and characteristic strengths:

ce ck

ye yk

ye yk

ye yk

Concrete 1.3

Reinforcing steel 1.17

Structural steel (S 235) 1.5

Structural steel (S 275) 1.3

Structural steel

f f

f f

f f

f f

=

=

=

=

ye yk(S 355) 1.1f f=

(4.5)

4.2.7 – Bi-linear backbone curves may be considered in hysteretic relationships of plastic sections (plastic hinges) of frame elements. Stiffness and strength degradation effects may be disregarded in hysteretic relationships of newly constructed buildings. 4.2.8 – In floor planes at which abrupt changes (in particular downward changes) are present in lateral stiffnesses of vertical structural elements, a special care shall be paid for the arrangement of transfer floors with sufficient in-plane stiffness and strength. 4.2.9 – The stiffness of the foundation and the soil medium shall be considered by appropriate models to be approved by the Independent Review Board. When needed, nonlinear behaviour of soil-foundation system may be taken into account in design stages described in 4.3.2 and 4.3.4.

MN

MU

MY

M

ϕy’ ϕy ϕ ϕu

(EI)e


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4.3. PERFORMA�CE-BASED SEISMIC DESIG� STAGES OF TALL BUILDI�GS 4.3.1. Design Stage (I – A): Preliminary Design (dimensioning) with Linear Analysis for Controlled Damage/Life Safety Performance Objective under (E2) Level Earthquake 4.3.1.1 – In this design stage aiming at preliminary dimensioning for Controled Damage/Life Safety performance objective, a linear analysis shall be performed in the framework of Strength-Based Design approach with reduced seismic loads similar to Chapter 2 of SBCSZ (2007) under (E2) level earthquake for �ormal Occupancy Buildings according to Table 3.1, and under (E3) level earthquake for Special Occupancy Buildings (Table 4.1). Preliminary design shall follow Chapter 3 and/or Chapter 4 of SBCSZ (2007). 4.3.1.2 – Seismic Load Reduction Factor to be used for reducing elastic seismic loads depending on Structural System Behaviour Factor given in 4.3.1.3 below and on natural vibration period is defined as follows:

a SS

a S

( ) = 1.5 + ( 1.5) (0 )

( ) = ( )

TR T R T T

TR T R T T

− ≤ ≤

<

(4.6)

where TS represents the spectrum corner period defined by Eq.(2.3). 4.3.1.3 – In the preliminary design of the following tall building structural systems, Structural System Behaviour Factor may be taken at most R = 7, subject to the approval of Independent Review Board:

(a) Building structural systems where seismic loads are resisted by coupled reinforced concrete structural walls;

(b) Building structural systems where seismic loads are resisted by eccentric or buckling restrained concentric brace frames;

(c) Building structural systems where seismic loads are resisted by moment resisting reinforced concrete or steel frames arranged as tube or tube-in-tube systems;

(d) Building structural systems where seismic loads are resisted by solid or coupled reinforced concrete structural walls combined with steel braced frames described in (b) and/or moment resisting reinforced concrete or steel frames;

(e) Other building structural systems whose seismic behaviour is endorsed by the Independent Review Board to be equivalent to those given above (R factors to be applied to such systems shall be proposed by the design engineer and approved by the Independent Review Board).

The above-described tall building structural systems are those located above the basement floors sorrounded by stiff peripheral walls. 4.3.1.4 – Being independent of R factor used, the base shear to be considered in the preliminary design shall not be less than the value given by the following expression:

t,min MS(D2)= 0.04 V S W (4.7)

Where MS(D2)S represents the short-period spectral acceleration specified for (E2) level earthquake and W is a weight representing the buildimg mass. All internal force quantities obtained from Response Spectrum Analysis shall be scaled such that the base shear calculated by the same procedure would be equal to that given by Eq.4.7.


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4.3.1.5 – Accidental eccentricity effects shall be considered according to 2.8.2.1 of SBCSZ (2007). 4.3.1.6 – Internal force quantites in principal axes of elements shall be calculated according to 2.7.5 of SBCSZ (2007). 4.3.1.7 – Interstory drifts of vertical structural elements shall be calculated and bounded in each direction according to 2.10.1 of SBCSZ (2007). Minimum base shear requirement given in 4.3.1.4 may not be considered in the calculation of interstory drifts. 4.3.1.8 – Minimum confinement reinforcement given in Chapter 3 of SBCSZ (2007) for high-ductility systems shall be used in all reinforced concrete elements. 4.3.1.9 – Capacity design principles given for shear safety of columns and beams in Chapter 3 and/or Chapter 4 of SBCSZ (2007) shall be applied. 4.3.1.10 – Regarding the shear safety of vertically cantilever or nearly cantilever reinforced concrete walls, the requirements of 3.6.6.3 of SBCSZ (2007) shall be applied where minimum value of dynamic shear amplification factor given in Eq.(3.16) shall be taken βv = 2. 4.3.2. Design Stage (I – B): Design with �onlinear Analysis for Controlled Damage/Life Safety Performance Objective under (E2) Level Earthquake 4.3.2.1 – The structural system of a tall building with a height exceeding 75 m, which is preliminarily designed in Design Stage (I – A) with Strength-Based Design approach under (E2) level earthquake for �ormal Occupancy Buildings according to Table 3.1 or under (E3) level earthquake for Special Occupancy Buildings, shall be designed under the same level of earthquake for Controlled Damage / Life Safety performance objective with nonlinear analysis to be performed according to the requirements of 4.2 (Table 4.1). Accidental eccentricity effects need not to be considered in this analysis. 4.3.2.2 – The seismic demands obtained according to 4.1.4 as the average of the results of minimum 2*7=14 analysis shall be compared with the following capacities:

(a) Interstory drift ratio of each vertical structural element shall not exceed 0.025 at each story in each direction.

(b) Upper limits of concrete compressive strain at the extreme fiber inside the confinement reinforcement and the reinforcing steel strain are given in the following for reinforced concrete sections satisfying the confinement requirements of SBCSZ (2007):

cg s = 0.0135 ; = 0.04ε ε (4.8)

(c) Deformation capacities of structural steel frame elements shall be taken from ASCE/SEI 41-06* for Life Safety performance objective.

(d) Shear capacities of reinforced concrete structural elements shall be calculated from SBCSZ (2007) using expected strengths given in 4.2.6.

(e) In the event where any of the requirements given in (a) through (d) above is not satisfied, all design stages shall be repeated with a modified structural system. *ASCE/SEI 41-06: Seismic Rehabilitation of Existing Buildings, American Society of Civil Engineers, 1st edition, 15/05/2007.


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4.3.3. Design Stage (II): Design Verification with Linear Analysis for Minimum Damage/ Uninterrupted Occupancy Performance Objective under (E1) Level Earthquake 4.3.3.1 – The tall building structural system, which is preliminarily designed in Design Stage (I – A) with Strength-Based Design approach under (E2) level earthquake for �ormal Occupancy Buildings according to Table 3.1 or under (E3) level earthquake for Special Occupancy Buildings, and subsequently designed in Design Stage (I – B) under the same earthquake level, shall be verified for Minimum Damage / Uninterrupted Occupancy

performance objective under (E1) level earthquake for �ormal Occupancy Buildings and under (E2) level earthquake for Special Occupancy Buildings with linear analysis to be performed according to requirements given in 4.2 (Table 4.1). Accidental eccentricity effects need not to be considered in this analysis. Design of tall buildings with heights not exceeding 75 m shall terminate at this stage. 4.3.3.2 – Internal force quantites in principal axes of elements shall be calculated according to 2.7.5 of SBCSZ (2007). 4.3.3.3 – Verification-basis internal forces shall be obtained as those calculated from linear elastic analysis divided by a factor of Ra = 1.5, irrespective of the type of the structural system. Those forces shall be shown not to exceed the strength capacities of cross sections calculated with expected material strengths given in 4.2.6. 4.3.3.4 – Interstory drift ratio of each vertical structural element obtained according to 2.10.1 of SBCSZ (2007) shall not exceed 0.01 at each story in each direction. 4.3.3.5 – In the event where 4.3.3.3 and/or 4.3.3.4 is not satisfied, all design stages shall be repeated with a modified structural system. 4.3.4. Design Stage (III): Design Verification with �onlinear Analysis for Extensive Damage/�o-Collapse Safety Performance Objective under (E3) Level Earthquake 4.3.4.1 – The tall building structural system with a height exceeding 75 m, which is preliminarily designed in Design Stage (I – A) with Strength-Based Design approach under (E2) level earthquake for �ormal Occupancy Buildings according to Table 3.1 and subsequently designed in Design Stage (I – B) under the same earthquake level, shall be verified for Extensive Damage / �o-collapse Safety performance objective under (E3) level earthquake with nonlinear analysis to be performed according to requirements given in 4.2 (Table 4.1). Accidental eccentricity effects need not to be considered in this analysis. 4.3.4.2 – The seismic demands obtained according to 4.1.4 as the average of the results of minimum 2*7=14 analysis shall be compared with the following capacities:

(a) Interstory drift ratio of each vertical structural element shall not exceed 0.035 at each story in each direction.

(b) Upper limits of concrete compressive strain at the extreme fiber inside the confinement reinforcement and the reinforcing steel strain are given in the following for reinforced concrete sections satisfying the confinement requirements of SBCSZ (2007):

cg s = 0.018 ; = 0.06ε ε (4.9)


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(c) Deformation capacities of structural steel frame elements shall be taken from ASCE/SEI 41-06* for Collapse Prevention performance objective.

(d) Shear capacities of reinforced concrete structural elements shall be calculated from SBCSZ (2007) using expected strengths given in 4.2.6.

(e) In the event where any of the requirements given in (a) through (d) above is not satisfied, all design stages shall be repeated with a modified structural system.

Table 4.1. Performance-based design stages of high-rise buildings

Design Stage Design Stage

I – A Design Stage

I – B Design Stage

II Design Stage

III

Design type Prelim. design (dimensioning)

Design Verification† Verification

�ormal class

buildings

(D2) earthquake

�ormal class

buildings

(D2) earthquake

�ormal class

buildings

(D1) earthquake Earthquake

Level Special class

buildings

(D3) earthquake

Special class

buildings

(D3) earthquake

Special class

buildings

(D2) earthquake

�ormal class

buildings

(D3) earthquake

Performance

objective Life Safety Life Safety

Immediate Occupancy

Collapse Prevention

Analysis type

3-D Linear Response Spectrum Analysis

3-D Nonlinear Time-history Analysis

3-D Linear Response Spectrum Analysis

3-D Nonlinear Time-history Analysis

Structural Syst.

Behavior Coef. R ≤ 7 – R = 1.5 –

Story drift

ratio limit % 2 % 2.5 % 1 % 3.5

Section

stiffness in R/C

frame members

kesit rijitliği

Effective stiffness

(from SBCSZ 2007)

Effective stiffness

(from moment-curvature analysis

Effective stiffness


Effective stiffness


Material

strengths

Characteristic strength

Expected strength

Expected strength

Expected strength

Acceptance

criteria

Strength & Story drift ratio

Strains & Story drift ratio



† Design of tall buildings with heights not exceeding 75 m shall terminate at this stage.

*ASCE/SEI 41-06: Seismic Rehabilitation of Existing Buildings, American Society of Civil Engineers, 1st edition, 15/05/2007. Final note: Translation of Chapters 5,6,7,8 is pending.

Design Life vs. Seismic Return Period

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