ORI GIN AL PA PER

Seismic risk assessment of buildings in Izmir, Turkey

Kasım A. Korkmaz Æ Ayhan Irfanoglu Æ Ali H. Kayhan

Received: 1 September 2008 / Accepted: 24 August 2009 / Published online: 23 September 2009� Springer Science+Business Media B.V. 2009

Abstract Izmir, the third largest city and a major economic center in Turkey, has more

than three million residents and half million buildings. In this study, the seismic risk in

reinforced concrete buildings that dominate the building inventory in Izmir is investigated

through multiple approaches. Five typical reinforced concrete buildings were designed,

modeled and assessed for seismic vulnerability. The sample structures represent typical

existing reinforced concrete hospital, school, public, and residential buildings in Izmir. The

seismic assessments of the considered structures indicate that they are vulnerable to

damage during expected future earthquakes.

Keywords Izmir � Reinforced concrete � Buildings � Seismic risk assessment �Nonlinear analyses � Probabilistic assessment

1 Introduction

Heavy destruction caused by the 1999 Marmara (Mw = 7.4) and the 1999 Duzce

(Mw = 7.2) earthquakes in northwestern Turkey and the 2003 Bingol (Mw = 6.4) in

eastern Turkey has increased interest in seismic risk assessment of building stock in urban

areas in Turkey. A comparison of the building, structural system and damage types

reported by various researchers indicate that the basic features and the vulnerabilities of the

reinforced concrete structures that sustained heavy damage or collapsed were similar. It is

reported that majority of the damaged and partially or totally collapsed buildings were

K. A. Korkmaz (&)Civil Engineering Department, Suleyman Demirel University, Isparta, Turkeye-mail: armagan@mmf.sdu.edu.tr

A. IrfanogluSchool of Civil Engineering, Purdue University, West Lafayette, IN, USAe-mail: ayhan@purdue.edu

A. H. KayhanCivil Engineering Department, Pamukkale University, Denizli, Turkeye-mail: hkayhan@pau.edu.tr

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Nat Hazards (2010) 54:97–119DOI 10.1007/s11069-009-9455-3

older reinforced concrete buildings with moment-resisting frame lateral load resisting

structural systems (Sezen et al. 2000; Sucuoglu 2000; Ozcebe et al. 2004). Typical building

damages following the 1999 Marmara earthquake, Turkey are shown in Fig. 1. The

building stock in Izmir is similar to the building stock in other major cities of Turkey and

dominated by multistory reinforced concrete structures.

Izmir was a subject of the 1997 RADIUS (Risk Assessment Tools for Diagnosis of

Urban Areas against Seismic Disaster) project (RADIUS 1997). Following the RADIUS

investigation, an earthquake master plan for the city was published by the Metropolitan

Municipality of Izmir (MMI 2000). The current study contributes to the previous studies on

Izmir by providing extensive information about the representative public and private

buildings and presenting performance assessments for them using different engineering

approaches.

In the current study, the seismic risk in reinforced concrete buildings that dominate

the building inventory in Izmir is investigated in detail through multiple approaches. Five

typical reinforced concrete buildings were designed and modeled. These structures

represent typical existing reinforced concrete hospital, school, public, and residential

buildings in Izmir. The seismic risks in these buildings are estimated using the following

methods. First, a simple vulnerability ranking method, known as the Hassan index

(Hassan and Sozen 1997), that considers ratios of the areas of the lateral load resisting

elements and the total floor area is used. Results for the considered structures are

compared with those from reinforced concrete structures affected by the 1999 earth-

quakes in Turkey (Donmez and Pujol 2005). Second, nonlinear static analyses are made

to develop capacity curves, i.e., so-called ‘‘pushover’’ curves. Then, a displacement

coefficient method is used to estimate whether the capacities of the considered structures

are sufficient to meet the displacement demands during expected future earthquakes.

Fig. 1 Typical building damages from the 1999 Marmara earthquake, Turkey

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Third, nonlinear dynamic analyses using a series of artificial ground motion data com-

patible with the design response spectra of the current (2007) Turkish seismic code

(‘‘design-basis earthquakes’’) and considering two site soil classes are made to get

another set of performance estimates. Finally, probabilistic evaluations are made to

provide performance likelihoods during design-basis earthquakes expected in the future.

2 Seismic setting

Izmir is located in a very active seismic region in western Anatolia, Turkey (see

Fig. 2). The seismicity of the region is governed by the Aegean Graben System and the

Aegean Trench (Akinci et al. 2000). Western Anatolia is at the west end of the

Anatolian micro tectonic plate that is in interaction with the Arabian tectonic plate

(Ocakoglu 2005).

Both historic and modern era records indicate that strong earthquakes occurred

frequently in Izmir region. Figures 3 and 4 (Emre et al. 2005) show the locations of the

major earthquakes in the last two millennia. Figure 5 shows count of earthquakes with

magnitude Ms C 4.9 that occurred between 1900 and 2005 near Izmir. One of the

destructive earthquake with an estimated magnitude of Ms = 7 occurred in the year 17

A.D. In fact, most of the ancient Aegean cities including Smyrna (the historic Izmir)

were destroyed by the earthquakes in the history (Baykara 1974). In 1688, an earth-

quake in the region killed nearly 20,000 people. In 1944, an earthquake of magnitude

Ms = 6.8 occurred near Gulf of Edremit, 125 km north of Izmir. One of the most

severe earthquakes occurred in 1953 and had a magnitude of Ms = 7.2 and epicentral

distance of 170 km (N). In 1974, during an earthquake of magnitude Ms = 5.2 and

Fig. 2 Location of Izmir and fault setting in the region (adapted from Ocakoglu et al. 2005; satellite imagesfrom Google Earth 2008)

Nat Hazards (2010) 54:97–119 99

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with an epicentral distance of approximately 10 km (NNE), 47 apartment buildings

were damaged and 2 people died in Izmir. In 1992, an earthquake with magnitude of

Ms = 6.0 and epicentral distance of approximately 50 km (SSW) caused damage in

100 buildings (Ilhan et al. 2004; RADIUS 1997). In 2003, a Mw = 5.8 earthquake

occurred 50 km southwest of Izmir but caused no damage in the city. Most recently, in

2005, a sequence of three earthquakes with Ms = 5.5, 5.9 and 5.9 occurred in the same

region as the 2003 event, but caused no damage in Izmir.

Fig. 3 Significant earthquakes in Izmir region, before 1900. (source: Emre et al. 2005)

Fig. 4 Significant earthquakes in Izmir region, during 1900–2005. (modified from Emre et al. 2005)

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3 Building characteristics

3.1 Profile of structures in Izmir

Izmir has experienced rapid population increase over the last three decades (Fig. 6).

During this population boom, most of the older buildings in the city were replaced with,

typically, low- to mid-rise reinforced concrete buildings. Majority of these buildings were

designed according to 1975 Turkish seismic design code (MRR 1975). Two examples of

typical RC construction in Izmir are shown in Fig. 7. Buildings of this type are ubiquitous

in Turkey. Many such buildings were subjected to strong ground motions during recent

earthquakes in Turkey (Ozcebe et al. 2004; Donmez and Pujol 2005). The large number of

casualties due to heavy damage or collapse of this kind of buildings demonstrates the

vulnerability of such reinforced concrete buildings during strong earthquakes.

The characteristics of typical reinforced concrete buildings in Izmir is illustrated in the

following section, in which details of representative hospital, school, public, and resi-

dential reinforced concrete buildings are given.

0

2

4

6

8

10

12

14

16

18

20

1900

1905

1910

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1930

1935

1940

1945

1950

1955

1960

Years

Co

un

t

1965

1970

1975

1980

1985

1990

1995

2000

2005

Fig. 5 Number of earthquakes with M [ 4.9 occurred in Izmir region during 1900–2005

0

500,000

1,000,000

1,500,000

2,000,000

2,500,000

3,000,000

1927

1935

1940

1945

1950

1955

1960

1965

1970

1985

1990

2000

2007

Census Year

Po

pu

lati

on

Fig. 6 Population of the metropolitan city of Izmir

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3.2 Review of representative buildings

The following five buildings are chosen to represent the typical building types that dom-

inate the building inventory in Izmir: a 5-story public building, a 6-story hospital building,

a 4-story school building, a 6-story residential building and a 10-story residential building.

These buildings were designed per the 1975 Turkish seismic design code to illustrate the

expected structural performance of majority of the existing buildings in Izmir.

The 1975 Turkish seismic design code included detailed requirements for ductile design

and construction of reinforced concrete structures and provided explicit definitions for

modern ductile design concepts such as confinement zones and minimum longitudinal

transverse reinforcement requirements (Sezen et al. 2000). The 1975 Turkish seismic

design code was followed by the 1997 code. The current 2007 code is similar to the 1997

code it replaced and calls for more detailed analysis. It should be noted that while the

recent codes did not change the fundamental design and construction concepts introduced

in the 1975 code, they call for higher design loads and stiffer structures. For example, in

the case of reinforced concrete school buildings, the 1997 and 2007 codes increased the

design load by 15–45% and, effectively, required the structures to be built 45–80% stiffer

compared to the 1975 code (Irfanoglu 2009).

As a representative public building, a 5-story reinforced concrete moment-frame

building, which is a typical model applied all over Turkey, was selected. Plan and elevation

views of the example public building are given in Fig. 8. All but four columns of the

structure are oriented to have their strong bending axes in the transverse (i.e., shorter)

direction of the plan. For the ground story, the story height is 3.4 m; the rest of the stories

are 3.1 m high each. 26 columns are grouped in seven classes regarding dimension and

reinforcement. Column dimensions are either 80 9 30 cm or 100 9 35 cm. Perimeter

beams are 60 9 35 cm in cross-section; interior beams are 60 9 30 cm. Layout, size and

reinforcing details for the beams and columns are repeated at each story. The longitudinal

reinforcement ratio in the columns varies between 1 and 1.4%.

Fig. 7 Typical reinforced concrete building construction in Izmir, Turkey

102 Nat Hazards (2010) 54:97–119

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For a typical hospital building, a 6-story reinforced concrete moment-frame building

was selected. Figure 9 shows the plan and elevation views of the hospital building model.

Interior columns are 70 9 25 cm and perimeter columns are 40 9 30 cm in cross-section.

Longitudinal reinforcement ratio is 1.3% in the interior columns and 1% in the external

columns. The story height is 3.2 m throughout the building.

For a school building, a 4-story reinforced concrete building, a common type widely

applied in Turkey, was selected. Figure 10 shows the plan and elevation views of the

structure. The dual-system structure has six shear walls placed along the transverse

(shorter) direction of the floor plan. Thickness of the shear walls is 30 cm. The shear walls

are 210, 600 and 720 cm in length. There is no irregularity in plan. The ground story is

4.2 m high and the rest of the stories are 3.4 m high. Interior columns are 60 9 50 cm and

the perimeter columns are 50 9 40 cm in cross-section. Beams are 40 9 80 cm in cross-

section in the first story; for the rest of the structure, beam cross-sections are 30 9 80 cm.

165

450

240

450

360360360360360

A

B

C

D

EE

D

C

B

A

1 2 3 4 5 6

654321

340

310

310

310

a

b

Fig. 8 Public building a plan and b elevation views. Dimensions are given in centimeters

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Beams supporting the stairs are 100 9 40 cm. Longitudinal reinforcement ratio is 1.5–2%

for the first story and 1% in the upper stories.

To represent residential buildings, a 6-story and a 10-story building are chosen. In Fig. 11,

plan and section views are given for the 6-story building, named Residential-1. Plan and

elevation views for the 10-story building, named Residential-2, are given in Fig. 12. In both

buildings, the story height is 2.7 m. Columns have a cross-section of 25 9 55, 60, 65, 70, 80,

85, 90 or 100 cm. The longitudinal reinforcement ratio varies between 1 and 1.2%.

For reinforcement, S220 (fy = 220 MPa) steel was used. Concrete design strength fc’was taken as 12 MPa (approximately 2/3 of the code required level) based on field data

obtained from existing buildings. According to 1975 and 1997 Turkish seismic design

codes, the volumetric ratio of transverse reinforcement in column confinement regions

should be taken to be 1% and in column middle regions, the volumetric ratio of transverse

A

A

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C

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33

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550

186 186 186 186 186 186 186 186 186 186 186 186 186 186 186 186

320

320

320

320

320

320

a

b

Fig. 9 Hospital building a plan and b elevation views. Dimensions are given in centimeters

104 Nat Hazards (2010) 54:97–119

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reinforcement be half of that for the column confinement regions. However, in the

applications especially before 1997, field observations indicate that, typically, the column

confinement region details were ignored during construction and the column middle region

transverse reinforcement details were used through the height of the columns. To obtain

realistic capacity estimates, in all of the representative buildings considered in this study,

the transverse reinforcement steel in the columns was taken to be 8 mm-dia hoops with

20 cm spacing, i.e., typical column middle region reinforcing detail per the code,

throughout the height of the columns.

4 Earthquake performance estimation

Expected performances of existing typical reinforced concrete buildings in Izmir during

possible strong earthquakes in the future are estimated using several approaches. First, a

BB

AA

CC

DD

EE

9

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350 350 350 350 350 350 350 350

720

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575

125

340

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420

a

b

Fig. 10 School building a plan and b elevation views. Dimensions are given in centimeters

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simple vulnerability ranking method, called the Hassan index approach (Hassan and Sozen

1997), is used to compare the considered buildings with those reinforced concrete struc-

tures affected by the 1999 earthquakes in Turkey (Donmez and Pujol 2005). Based on this

simple comparison, general performance estimates could be given for majority of buildings

in Izmir. Second, nonlinear static analyses were made to obtain base shear–roof dis-

placement capacity curves for each building. P-delta effects were included in these

A A

1

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145 230 197 415

325

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345

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270

270

270

a

b

Fig. 11 6-story residentialbuilding (Res1) a plan and belevation views. Dimensions aregiven in centimeters

106 Nat Hazards (2010) 54:97–119

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A A

1

1

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4

4

5

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6

6

D D

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C C

B B

145 230 197 415

325

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345

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270

270

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270

270

270

a

b

Fig. 12 10-story residentialbuilding (Res2) a plan and belevation views. Dimensions aregiven in centimeters

Nat Hazards (2010) 54:97–119 107

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so-called ‘‘pushover’’ analyses. Then, a displacement coefficient method-based determin-

istic analysis was used to estimate whether the capacity of the considered buildings would

meet the displacement demands. Two different site soil classes, known as Soil Z2 that is

similar to class B soil of FEMA, 356 (FEMA 2000) and Soil Z3 that is similar to class C

soil of FEMA, 356, are considered in the analyses. The chosen two soil types refer to

typical soil sites in southern and eastern parts of Izmir (MMI 2000) on which majority of

the buildings were constructed during the boom during 1970s and early 2000s. There are

pockets of areas with soft soil conditions (Z4) along the southern and eastern parts of the

shoreline and over a large region in the recently developed northwestern region of Izmir.

To obtain another set of performance estimates, a series of nonlinear dynamic analyses are

made for each structure and considering the two site soil types. For these dynamic anal-

yses, artificial ground motion data (‘‘design-basis earthquakes’’) compatible with the

design response spectra of the current (2007) Turkish seismic design code (MPWS 2007)

are generated and used. Finally, probabilistic evaluations for drift levels are made to

provide performance likelihoods during design-basis earthquakes expected in the future.

4.1 Hassan index-based vulnerability ranking

Hassan and Sozen (1997) have proposed a measure called the priority index to rank

reinforced concrete buildings with moment-frame and/or shear wall structural systems in

seismic vulnerability. Since the 1992 Erzincan earthquake in Turkey, performances of

several hundred buildings affected by strong earthquakes have been reviewed using the

priority index (Ozcebe et al. 2004; Donmez and Pujol 2005; Gur et al. 2009). The priority

index for a building is computed as the ratio of ‘‘effective’’ column and wall cross-

sectional areas to the total floor area of the building:

Priority Index ¼ Column IndexþWall Index ð1Þ

Column Index ¼ 1

2

AcolumnPAfloor

ð2Þ

Wall Index ¼ARC walls þ 1

10Amasonrywalls

PAfloor

ð3Þ

where Acolumn is the cross-sectional area of all columns at base level, ARC walls is the cross-

sectional area of reinforced concrete walls at base level, Amasonry walls is the cross-sectional

area of masonry walls filling entire frame bays and RAfloor is the summation of floor areas

above the base of the structure (Hassan and Sozen 1997). The wall index is calculated

considering the axes of the reinforced concrete walls and the infill walls for each principal

plan direction. The lower of the two priority indices for a building is chosen to represent

the building.

In Fig. 13, priority index values for the buildings reviewed for this study are compared

with those for the buildings in Duzce inspected after the 1999 earthquakes (Donmez and

Pujol 2005). As the graph in Fig. 13 indicates, the priority index values for buildings in

Izmir are not higher than for those in Duzce. The comparison indicates that if buildings in

Izmir were to experience ground motions similar to those in 1999 in Duzce (Donmez and

Pujol 2005), heavy damage and collapse could be expected. According to the seismic

hazard zonation map of Turkey (MPWS 1996), referred to in the 2007 Turkish seismic

design code (MPWS 2007), both Izmir and Duzce are considered among the highest

seismic hazard areas and given Zone 1 classification. It should be noted that there is no

108 Nat Hazards (2010) 54:97–119

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scaling for earthquake ground motion parameters in the priority index and the damage

states in Fig. 13 could be carried over to Izmir if similar ground motions would occur. In

Izmir earthquake master plan (MMI 2000), in terms of peak ground acceleration on rock

site and with 10% probability of exceedance in 50 years (10%-50 years), the seismic

hazard for Izmir is estimated to be in the 0.30–0.40 g range. In another study (Korkmaz

et al. 2009), the 10%-50 years PGA on rock site is estimated to be 0.34 g at Izmir city

center. Kalkan et al. (2009) provide a seismic hazard map for the Marmara region of

Turkey from which the 10%-50 years PGA on rock site in Duzce is estimated to be 0.40 g.

Accordingly, the priority index comparison of the buildings analyzed in this study with the

buildings inspected in Duzce after the 1999 earthquakes gives additional insight about the

relative seismic vulnerability of the structures considered herein.

4.2 Nonlinear static analyses

Nonlinear static analyses, also known as pushover analyses, were carried out to examine

the deformation and associated damage levels in the buildings under large displacements.

Even though during large displacements buildings behave inelastically and change their

dynamic characteristics, through pushover analysis one could estimate member forces as

well as global and local deformation capacity of each structure (Turker and Irtem 2007;

Hasan et al. 2002). In pushover analysis, lateral loads are applied in patterns that represent

approximately the relative inertial forces generated at each story level when the structure

responds dynamically in a given natural mode, typically the fundamental mode. The load

level is increased proportionally and the displacement levels and the deformation patterns

are monitored. Typically, the base shear force versus the roof displacement are considered

together to obtain capacity curve for each structure (Fajfar and Feri 2000).

In the present study, for pushover analyses, buildings were loaded with live and dead

loads for gravity loading, and then laterally loaded. For each building, the total weight

of the building (W), total height (H), fundamental translational mode period (T), roof

displacement (D) and lateral load capacity (Vy) were recorded. Vertical and lateral loads

were combined based on the rules of the 2007 Turkish design code (MPWS 2007), and

0.0%

0.2%

0.4%

0.6%

0.8%

1.0%

1.2%

1.4%

0 2 4 6 8 10 12

Number of Stories

Pri

ori

ty In

dex

Duzce 1999: Severe Damage and Collapse

Duzce 1999: No Damage to Moderate Damage

Izmir: Reviewed Buildings

Fig. 13 Comparison of the priority index (Hassan and Sozen 1997) values for the reviewed buildings inIzmir with those for the buildings investigated in Duzce after the 1999 earthquakes (modified from Donmezand Pujol 2005)

Nat Hazards (2010) 54:97–119 109

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capacity curves including the load combinations were obtained for each building. The

equivalent static lateral load pattern defined as an inverted triangular load, corre-

sponding to generic fundamental mode response, per the 2007 Turkish design code was

used. The load was increased monotonically and the structure was analyzed at each load

level. P-delta effects were included in the analyses. The SAP2000NL structural analysis

program (Wilson and Habibullah 1998) was used in the pushover analyses. Nonlinear

bending and axial deformations were assumed to occur at certain locations, i.e., plastic

regions, whereas the other portions of the building were assumed to remain elastic.

Plastic hinges were assumed to occur under pure bending moment in beams and

combined bending moment and axial force in columns. Shear force and torsional

moment capacities of beams and columns were also checked separately in the analyses.

Moment–plastic rotation relationships of column and beam sections were assumed as

rigid-plastic. Cracked section stiffness values for columns and beams were taken as

proposed in FEMA 356 (FEMA 2000). The force–displacement results and bilinear

curve fits for the weak direction of the buildings are given in Fig. 14. Values for the

parameters defining the bilinear curve fits are given in Table 1.

4.3 Performance estimation using displacement coefficient method

The performance of the sample structures was estimated by using displacement coefficient

method. This method estimates the target displacement, providing a direct numerical

process for calculating the displacement demands. The nonlinear force–displacement

relationship between base shear and roof displacement is replaced by an idealized

Fig. 14 Force–displacement curves obtained through pushover analyses for the reviewed buildings

110 Nat Hazards (2010) 54:97–119

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relationship to calculate the effective lateral stiffness (Ke), and effective yield strength (Vy).

The effective lateral stiffness (Ke) is the secant stiffness calculated at the base shear force

equal to 60% of the effective yield strength. The effective fundamental period is based on

the idealized force–displacement relationship. Calculation of the target displacement on

the capacity curve is illustrated in Fig. 15 (FEMA 2005). In this methodology, target

displacement can be found using:

dmax ¼ C0C1C2SaT2

e

4p2g ð4Þ

where C0 is the modification factor related to spectral displacement of an equivalent single-

degree-of-freedom system to the roof displacement of multi-degree-of-freedom system, C1

is the modification factor to relate expected maximum inelastic displacements to dis-

placements calculated for linear elastic response and C2 is the modification factor to

represent the effect of pinched hysteretic shape, stiffness degradation and strength dete-

rioration on maximum displacement response (FEMA 2005).

Design spectra given in the 2007 Turkish seismic design code were taken as the demand

spectra. These spectra were considered to have a probability of exceedence of 10% in

50 years. Two different site soil classes, known as Soil Z2 and Z3 in the 2007 Turkish

seismic code, were considered. These soil classes are similar to class B and class C soil,

respectively, in FEMA, 356 (FEMA 2000). In Figs. 16 and 17, design spectra for soil Z2

and Z3 are shown, respectively. The calculated maximum displacements for sample

structures are given in Table 2 and compared with ultimate capacity of the associated

building in Table 3.

Table 1 Results from pushover analyses

Building W (kN) H (m) T (s) Vy (kN) Vy/W Dy (cm) Du (cm) Dy/H (%) Du/H (%)

Public 15,610 17.0 0.87 1,700 0.109 3.5 27.1 0.21 1.6

Hospital 34,020 19.2 1.39 1,920 0.056 4.3 37.6 0.22 2.0

School 19,770 14.4 0.76 3,450 0.175 3.0 14.5 0.21 1.0

Residential-1 9,460 16.2 0.66 1,310 0.138 2.6 21.1 0.16 1.3

Residential-2 15,760 27.0 1.09 1,550 0.098 5.4 22.0 0.20 0.8

e

iie K

KTT =

0.60Vy

Ks

Target Displacement

Ke

δy δT

Vy

VT

δmax

Ki

Bilinear representation

Fig. 15 Determination of target displacement in displacement coefficient method

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4.4 Nonlinear dynamic analysis

Nonlinear dynamic analyses of the described representative buildings were made to

incorporate the effects of variations in the dynamic characteristics of the structures in

response estimation directly. The same structural models described for the pushover

analyses were used in the dynamic analyses.

Unfortunately, very limited number of actual ground motion records exists from

earthquakes in Izmir region. In this study, dynamic analyses of the buildings were carried

out using artificially generated earthquake ground motions. The records were generated

taking the design spectrum as the basis. For each building on each site soil condition, 30

different artificially generated ground motion data were used. To generate the input ground

motions, RSCTH software (ESL 2004) was used. The generated ground motions have

different strong motion durations, frequency contents and peak ground accelerations.

Table 4 lists the peak ground accelerations (PGA) and peak ground velocity (PGV) of the

artificial records.

Design Spectra-Soil Z2

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40

Period (sec)

Spe

ctra

l Acc

eler

atio

n (g

)

Public & School

Hospital

Residential

Fig. 16 Design spectra for soil Z2

Design Spectra-Soil Z3

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40

Period (sec)

Spe

ctra

l Acc

eler

atio

n (g

) Public & School

Hospital

Residential

Fig. 17 Design spectra for soil Z3

112 Nat Hazards (2010) 54:97–119

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The maximum displacement result for each building under each ground motion and site

soil class are presented in Table 5. Relevant statistics for each building are given in Table 6.

4.5 Probabilistic seismic response assessment

Probabilistic seismic response assessment was used on the representative buildings to take

probabilistic aspects of the earthquake ground motion and building response into consid-

eration. Drift demand versus exceedence probability curves are developed based on

analysis results and simplified probabilistic modeling. For each building, nonlinear

dynamic analyses were made using the generated design-basis ground motions and max-

imum drift demands were recorded. For each building, the mean and standard deviation

values of these maximum drifts were assumed as parameters of normal distribution

functions (see Table 6). Using these distribution functions, probability of exceeding dif-

ferent drift levels are computed for each building in each soil condition. These distribution

functions give the probabilistic drift demand curves (see Figs. 18, 19). Using these drift

demand curves, probability of exceeding different displacement capacity thresholds (dis-

placement limits), chosen from displacement capacity curves for each structure, could be

estimated. Different displacement limits were considered: yield displacement capacity Dy,

50% of ultimate displacement capacity Du, 75% of Du and 100% of Du. In Table 7, these

drift limits and corresponding exceedence probabilities are given.

5 Review of the results from the analyses

The results from the simple, Hassan index-based vulnerability ranking approach when

compared with data from 1999 Duzce earthquake indicates that; the priority index values

Table 3 Roof drift capacityversus demand from displace-ment coefficient method

Building Roof drift capacity(Du/H) (%)

Roof drift demand (Du/H)

Soil Z2 (%) Soil Z3 (%)

Public 1.6 1.9 2.6

Hospital 2.0 3.0 4.1

School 1.0 2.0 2.7

Residential-1 1.3 1.4 2.0

Residential-2 0.8 1.7 2.3

Table 2 Maximum displacement demands estimated using displacement coefficient method

Building Te (s) C0 Sa-Z2 (g) Sa-Z3 (g) Displacement demand (cm) Displacement demand(D/H)

Soil Z2 Soil Z3 Soil Z2 (%) Soil Z3 (%)

Public 0.87 1.26 1.33 1.84 32 44 1.9 2.6

Hospital 1.39 1.29 0.92 1.27 57 79 3.0 4.1

School 0.76 1.32 1.50 2.07 28 39 1.9 2.7

Residential-1 0.66 1.27 1.67 2.32 23 32 1.4 2.0

Residential-2 1.09 1.36 1.11 1.54 45 62 1.7 2.3

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for buildings in Izmir are not higher than for those in Duzce and Izmir has an important

earthquake risk for a possible future earthquake.

The soil class is found to have a significant effect on displacement demands and

therefore on the expected performance of each structure.

According to displacement coefficient method results, for the public building, maximum

global drift demand is 0.019 for Z2 soil class and 0.026 for Z3 soil class. The maximum

global drift capacity of the public building was calculated as 0.010. Accordingly, the public

Table 4 Peak ground motion parameters for the generated earthquake data used in nonlinear dynamicanalyses

Eq.No.

Soil Z2 Soil Z3

Public &school

Hospital Residential Public &school

Hospital Residential

PGA(g)

PGV(cm/s)

PGA(g)

PGV(cm/s)

PGA(g)

PGV(cm/s)

PGA(g)

PGV(cm/s)

PGA(g)

PGV(cm/s)

PGA(g)

PGV(cm/s)

1 70 44 54 44 44 31 58 48 73 54 46 27

2 67 37 65 50 46 33 66 49 70 54 54 39

3 59 45 54 55 44 31 61 51 68 69 44 39

4 60 37 68 44 43 34 61 54 62 48 43 34

5 54 41 60 45 41 30 64 59 64 55 51 49

6 59 44 60 40 41 36 71 65 63 51 47 37

7 67 45 68 43 43 30 62 52 67 51 46 44

8 68 42 76 48 42 32 63 51 63 53 49 37

9 60 38 62 38 48 26 68 74 64 54 44 36

10 64 35 72 42 45 28 59 39 69 58 48 33

11 49 40 69 46 39 27 58 45 66 76 55 47

12 56 38 69 46 40 28 67 49 66 76 44 46

13 60 41 58 36 46 30 63 50 65 56 42 44

14 57 38 64 47 43 28 58 55 61 66 43 34

15 54 42 68 48 40 29 58 55 62 58 47 39

16 59 40 64 46 42 27 54 50 74 55 49 40

17 61 38 68 51 44 29 57 46 82 53 41 35

18 57 50 58 47 41 33 61 52 62 66 55 35

19 67 41 60 38 43 25 71 64 73 60 41 40

20 57 40 58 51 42 31 62 56 69 49 49 36

21 61 44 59 43 44 31 64 48 66 49 42 42

22 61 44 58 47 42 34 68 61 76 46 41 40

23 59 33 70 49 47 28 65 48 63 57 46 43

24 60 39 67 53 44 28 64 44 74 51 48 35

25 65 35 59 53 47 34 61 57 66 66 46 41

26 56 46 63 44 40 32 67 44 65 54 43 39

27 55 41 64 40 46 29 58 67 65 54 41 37

28 65 42 64 40 46 29 56 64 66 62 41 38

29 57 39 66 46 48 25 57 48 63 64 46 38

30 68 46 64 52 44 28 70 64 73 56 45 41

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building fails to meet the displacement demand for either soil class. For the hospital

building, maximum global drift demand for the hospital building is 0.030 for Z2 soil class

and 0.041 for Z3 soil class. The maximum drift capacity of the hospital is calculated as

0.020. For the school building, maximum global drift ratio demand is estimated to be 0.020

for Z2 soil class and 0.027 for Z3 soil class. The maximum global drift ratio capacity of the

school was calculated as 0.010 using the nonlinear static analyses. Even though the base

shear force capacity of the school building is approximately 0.18 W, fatal hinging develop

in the columns throughout the ground story. For the 6-story residential building, base shear

capacity is approximately 0.14 W, and the maximum global drift demand is 0.014 for Z2

Table 5 Results from nonlinear dynamic analyses

Eq.No.

Maximum roof drift (D/H)

Soil Z2 Soil Z3

Public(%)

Hospital(%)

School(%)

Res-1(%)

Res-2(%)

Public(%)

Hospital(%)

School(%)

Res-1(%)

Res-2(%)

1 0.7 1.6 0.8 1.2 0.6 0.9 2.4 2.0 0.9 0.7

2 0.9 1.4 2.3 0.5 0.4 0.8 4.0 1.3 0.8 0.7

3 0.8 1.7 1.4 0.8 1.1 0.8 2.2 1.7 1.0 0.6

4 0.4 2.8 2.5 1.2 0.4 1.0 2.3 1.1 0.7 0.6

5 1.0 1.1 1.8 0.7 0.6 1.2 2.2 2.4 0.8 0.7

6 0.5 1.8 0.8 1.0 0.5 1.0 1.8 2.1 0.7 0.6

7 0.8 0.8 0.7 0.4 0.5 0.9 1.3 1.4 1.4 0.9

8 0.3 0.8 2.7 1.0 1.0 1.0 3.1 3.4 0.7 0.8

9 0.8 0.6 0.8 1.3 0.7 1.0 1.3 2.0 1.0 0.7

10 0.5 2.7 1.9 0.4 0.6 0.9 1.3 1.5 0.7 1.0

11 0.5 2.5 1.2 0.3 0.8 0.9 1.6 1.5 0.8 0.7

12 1.1 1.2 1.6 0.4 0.5 1.0 1.5 2.0 0.8 0.8

13 1.2 0.7 1.1 0.4 0.8 1.0 1.2 1.7 0.9 0.6

14 1.1 0.8 0.8 1.2 0.8 0.9 2.0 1.4 0.7 1.0

15 0.5 1.4 1.8 1.0 1.2 1.0 2.5 3.8 0.9 0.9

16 0.5 1.1 1.4 0.5 0.4 0.8 1.8 3.0 0.7 0.7

17 0.6 1.1 1.3 0.5 0.4 0.9 1.1 2.5 0.7 0.8

18 1.4 0.6 0.8 1.4 0.6 1.2 1.1 2.3 0.8 0.5

19 0.8 0.7 1.1 0.4 0.8 1.1 3.1 4.5 1.2 0.6

20 0.6 0.8 1.1 0.4 0.9 1.4 2.2 2.3 0.7 0.7

21 0.8 0.8 1.3 1.0 0.5 0.8 1.4 2.3 1.0 0.7

22 1.2 1.9 0.9 1.2 0.6 1.5 1.4 2.1 1.1 0.8

23 1.4 1.4 0.8 0.6 0.5 0.9 1.4 2.7 0.7 0.7

24 1.3 1.0 0.8 0.7 0.4 0.9 2.7 3.1 0.9 0.7

25 1.2 0.8 1.6 1.3 0.4 0.9 1.9 1.7 0.7 0.9

26 0.9 0.7 1.2 1.0 1.2 0.8 3.4 4.4 1.5 0.7

27 0.6 1.6 2.7 1.2 0.4 1.2 2.9 2.1 1.1 0.7

28 0.5 1.6 0.8 1.1 0.6 0.7 2.3 1.0 0.8 0.5

29 0.7 3.8 1.9 0.5 0.6 1.0 0.8 1.7 0.7 0.8

30 0.7 0.6 1.4 1.6 0.4 0.6 2.0 1.8 1.0 0.5

Nat Hazards (2010) 54:97–119 115

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soil class and 0.020 for Z3 soil class. The maximum global drift capacity of the 6-story

residential building was calculated as 0.013, i.e., not meeting the demand in either soil

class. For the 10-story residential building, maximum global drift demand is estimated as

0.017 for Z2 soil class and 0.023 for Z3 soil class. The maximum global drift capacity of

the 10-story residential building was calculated as 0.008, much smaller than the demand

for either soil class condition.

According to the time history results, displacement demands for soil Z3 is more critical

than soil Z2. For each building, mean values of the displacements for 30 different earth-

quake data increase when the site soil is changed from class Z2 to class Z3. In both soil

Table 6 Statistics for the roof drift demand from nonlinear dynamic analyses

Building Mean Standard deviation

Soil Z2 (%) Soil Z3 (%) Soil Z2 (%) Soil Z3 (%)

Public 0.8 1.0 0.3 0.2

Hospital 1.3 2.0 0.8 0.8

School 1.4 2.2 0.6 0.9

Residential-1 0.8 0.9 0.4 0.2

Residential-2 0.6 0.7 0.2 0.1

Drift vs. Exceedence Probability on Soil Z2

0.00

0.20

0.40

0.60

0.80

1.00

0.0% 0.5% 1.0% 1.5% 2.0% 2.5% 3.0%

Drift

Exc

eede

nce

Pro

babi

lity

Public

Hospital

School

Res1

Res2

Fig. 18 Drift demand versus exceedence probability curves for reviewed buildings on soil Z2

Drift vs. Exceedence Probability on Soil Z3

0.000.100.200.300.400.500.600.700.800.901.00

0.0% 0.5% 1.0% 1.5% 2.0% 2.5% 3.0%

Drift

Exc

eede

nce

Pro

babi

lity Public

Hospital

School

Res1

Res2

Fig. 19 Drift demand versusexceedence probability curves forreviewed buildings on soil Z3

116 Nat Hazards (2010) 54:97–119

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types, the mean displacement demand for the hospital building is higher than those for the

other buildings. For the public building, displacement demands are 0.8% (=14 cm) and

1.0% (=17 cm) for soil Z2 and soil Z3, respectively. For the hospital building, mean values

of displacement demands are 1.3% (=26 cm) and 2.0% (=39 cm) for Soil Z2 and Soil Z3,

respectively. For the school building, displacement demands are 1.4% (=20 cm) and 2.2%

(=32 cm) for Soil Z2 and Soil Z3, respectively. For the 6-story residential building, dis-

placement demands are around 0.8–0.9% (=14 cm) for each soil class. For the 10-story

residential building, displacement demands are 0.6% (=17 cm) and 0.7% (=19 cm) for Soil

Z2 and Soil Z3, respectively.

For probabilistic assessment, the displacement limits determined in nonlinear analysis

part were evaluated in terms of exceedence probability. Taking the half of the ultimate

displacement capacity as a critical displacement level, the following exceedence proba-

bilities are found. It should be noted that typically the exceedence probability increases

when the site soil is changed from class Z2 to class Z3. For the public building, exceedence

probability is 39% (soil class Z2) and 65% (soil class Z3). For the hospital building,

exceedence probability is 63% (soil class Z2) and 88% (soil class Z3). For the school

building, exceedence probability is 90% (soil class Z2) and 97% (soil class Z3). For the

6-story residential building, exceedence probability is 62% (soil class Z2) and 77% (soil

class Z3). For the 10-story residential building, exceedence probability is 71% (soil class

Z2) and 94% (soil class Z3). The results show that, probabilistically, school building is

more critical. It should be noted that the displacement demand value for the hospital

building is higher than those for the other buildings.

Table 7 Capacity curve parameters and exceedence probabilities for select drift levels

Public Hospital School Res1 Res2

Dy 0.21% 0.22% 0.21% 0.16% 0.20%

Dplastic (= Du-Dy) 1.4% 1.7% 0.8% 1.1% 0.6%

Du 1.6% 2.0% 1.0% 1.3% 0.8%

Dcritical = Du 1.6% 2.0% 1.0% 1.3% 0.8%

Dcritical = 0.75Du 1.2% 1.5% 0.8% 1.0% 0.7%

Dcritical = 0.5Dp 0.9% 1.1% 0.6% 0.7% 0.5%

Soil Z2

Mean 0.8% 1.3% 1.4% 0.8% 0.6%

Standard deviation 0.3% 0.8% 0.6% 0.4% 0.2%

Soil Z3

Mean 1.0% 2.0% 2.2% 0.9% 0.7%

Standard deviation 0.2% 0.8% 0.9% 0.2% 0.1%

Probability of exceedence on soil Z2

Dcritical = Du 0.01 0.21 0.74 0.11 0.23

Dcritical = 0.75Du 0.08 0.41 0.83 0.32 0.46

Dcritical = 0.5Dp 0.39 0.63 0.90 0.62 0.71

Probability of exceedence on soil Z3

Dcritical = Du 0.00 0.52 0.92 0.03 0.24

Dcritical = 0.75Du 0.07 0.73 0.95 0.28 0.67

Dcritical = 0.5Dp 0.65 0.88 0.97 0.77 0.94

Nat Hazards (2010) 54:97–119 117

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It should be noted that Akkar et al. (2005) developed displacement-based fragility

functions for two to five stories high ordinary concrete buildings based on probabilistic

review of information from performance of 32 structures affected by the 1999 Duzce

earthquake. They have developed performance level estimates under various levels of

shaking intensity, expressed in terms of PGV, using equivalent single-degree-of-freedom

systems. In our study, we have used detailed nonlinear numerical models for the buildings

and considered only design-basis earthquakes. The performance estimates we have

obtained, in terms of overall drift levels, for the 5-story public building under design-basis

earthquake agrees with the range of equivalent event estimates deduced from the perfor-

mance curves provided in Akkar et al. (2005). However, in the case of the 4-story school

building, we estimate that the school building would perform worse than that estimated by

Akkar et al. for 4-story buildings. The 4-story building they considered had shear walls in

both plan directions, but the school building we have considered had no shear walls active

along the plan longitudinal direction. We believe that is a major source of difference due to

the fact that lateral load resisting systems consisting of moment-frames with unreinforced

hollow clay-tile infill walls have very limited displacement capacity. In fact, the extremely

poor performance of school buildings with moment-frame systems with unreinforced

hollow clay-tile infill walls during the 1999 Duzce and the less intense 2003 Bingol,

Turkey earthquakes have been documented extensively (Gur et al. 2009).

6 Conclusion

In this study, the expected earthquake performance of typical reinforced concrete buildings

in Izmir, Turkey is investigated using different estimation approaches. Results from the

assessments indicate that considered type of existing reinforced concrete buildings in Izmir

face risk of poor performance, including heavy damage or collapse, during possible strong

earthquakes in the future.

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