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Soil Dynamics and Earthquake Engineering 28 (2008) 836–850

www.elsevier.com/locate/soildyn

Development of a seismic damage and loss scenario for contemporaryand historical buildings in Thessaloniki, Greece

Andreas J. Kappos�, Georgios Panagopoulos, Gregorios G. Penelis

Civil Engineering Department, Aristotle University of Thessaloniki, Greece

Accepted 19 October 2007

Abstract

The methodologies used in Greece for estimating direct losses in both reinforced concrete (R/C) and masonry buildings (also including

monuments) are summarised, the critical issue of data collection is addressed, and practical solutions that have been tried are discussed.

The development of a seismic risk scenario for contemporary and historical buildings in Thessaloniki is then presented and some key

results are given, including the expected geographical distribution of building damage (due to the scenario earthquake) in the

municipality of Thessaloniki; damage is described both in structural and in economic terms.

r 2007 Elsevier Ltd. All rights reserved.

Keywords: Risk scenarios; Seismic vulnerability; Reinforced concrete buildings; Masonry buildings; Historical buildings

1. Introduction

Over the last decade a decent number of earthquakedamage (and loss) scenario studies appeared wherein someof the most advanced techniques have been applied to anumber of European cities [1–6,10]. By ‘scenario’ it isunderstood here that the study refers to a given earthquake(having a probability of exceedance higher, equal, or lowerthan that of the design earthquake specified in the seismiccode in force) and provides a comprehensive description ofwhat happens when such an earthquake occurs; this isdifferent from ‘risk analysis’ that refers to all the possiblearriving earthquakes, estimating the probability of lossesover a specified period of time. A key feature of the mostrecent among these studies is the use of advanced GIS toolsthat permit clear representation of the expected distribu-tion of damage in the studied area and visualisation of theeffects of any risk mitigation strategy that can be adoptedon the basis of the scenario.

As noted by Dolce et al. [4], preparing a scenariorequires contributions from a wide range of topics anddisciplines, spanning from Seismology and Geology to

e front matter r 2007 Elsevier Ltd. All rights reserved.

ildyn.2007.10.017

ing author. Tel.: +3023 10995743; fax: +30 23 10995614.

ess: ajkap@civil.auth.gr (A.J. Kappos).

Structural and Geotechnical Engineering, from UrbanPlanning and Transport Engineering to Social andEconomic Sciences. However, it often happens that eachspecialist interacts very little (if at all) with the otherspecialists. Furthermore, some key parameters that areparticularly relevant for a scenario, such as the geologicalfeatures that affect seismic hazard, the characteristics of thebuilding stock, and socio-economic conditions, are differ-ent in each country. This makes at best questionable thecommon practice of adopting the same models fordeveloping scenarios in different countries. A goodexample of the problems involved in adopting modelsfrom another country is outlined in the paper by Barbatet al. [1] who adopted the vulnerability models developed forItalian masonry buildings to study the ones in Barcelona.The present study, which is based mainly on work

carried out within the framework of the Europeanprogramme RISK-UE refers to the city of Thessaloniki,the largest city of Macedonia (Northern Greece). This is acity with a population of about 1 million (according to the2001 census) and a building stock (Fig. 1) that, althoughdominated by reinforced concrete (R/C) construction, alsoincludes a decent number of historical buildings (such asRoman monuments, Byzantine churches, and contempor-ary listed buildings from the 19th and early 20th century).

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Fig. 1. Aerial photo of Thessaloniki’s historical centre.

1All buildings in a hospital complex were included, even minor ones;

parts of the same building separated by construction joints (or separation

gaps) were treated as independent buildings.

A.J. Kappos et al. / Soil Dynamics and Earthquake Engineering 28 (2008) 836–850 837

The latest major earthquake occurred in Thessaloniki inJune 1978 with an epicentre located at a distance of about30 km NE of the city, a magnitude of M ¼ 6.5, and a focaldepth estimated to be between 6 and 11 km [18]. Therecorded PGA in one station located in the basement of an8-storey building at the shoreline of the city was rather low(�0.15 g) most probably due to the presence of non-linearsite effects [16]. The earthquake caused a total of 47 deaths[18], 37 of them due to the collapse of a 9-storey R/Cbuilding, a limited number of partial collapses, and slightto moderate damage to a large number of buildings with arepair cost equal to 1.6% the cost of replacing the existingbuilding stock [15]; the total economic damage (includingindirect losses) was certainly much higher.

The paper summarises the methodologies used forestimating direct losses in both R/C and masonry buildingsand also addresses the critical issue of data collection; itthen presents some key results, including the expectedgeographical distribution of building damage (due to thescenario earthquake) in the municipality of Thessaloniki.

2. Compilation of the building inventory

It is well known that inventory collection is the mostdemanding of tasks for risk scenario development, unlessextensive information on this is already available (which ishardly ever the case, at least in Europe). Things were evenmore complicated by the fact that GIS representationwas a key objective of the scenario. As described in thefollowing, a different approach was adopted for ‘current’(or ‘common’) buildings and for monuments.

2.1. Current buildings

Unfortunately the only complete set of data (i.e. cover-ing the entire city), that is the one collected by the StatisticsAgency of Greece (ESYE) based on the 2000-1 BuildingsCensus, was not available at the time this study was carriedout (spring 2004). Hence, it was decided to carry out the

vulnerability analysis (for the purposes of the risk scenario)on the basis of the 1991 Census data for the Municipalityof Thessaloniki, in combination with re-evaluation ofavailable data and introduction into the GIS platform ofthe city, supplemented by additional in-situ work on anappropriate sample of building blocks. The 1991 data isless reliable than the 2001 one, not only because it is older(changes in the building stock in the centre of the city arenot significant, while the opposite occurs in the suburbs),but because the characterisation of the building system ismade in terms of the material used as exterior cladding andnot that of the structural (load-bearing) system, and dataon area and/or volume of buildings are not included. Inaddition to the aforementioned drawbacks, it is not evenpossible to establish a one-to-one correspondence between,say, number of storeys and structural system.Based on data collection work carried out within another

(nationally funded) programme, all hospital buildings(a total of 330)1 in the metropolitan area, as well as apercentage of school buildings in the centre of Thessaloniki(a total of 170), were added to the ArcView database set upwithin the frame of this study.In view of the situation regarding the inventory, it was

finally decided to proceed as follows:

�

Carry out a global analysis of the building stock in themunicipality of Thessaloniki, based on a combinationof the 1991 ESYE data and those from a previousproject [15] wherein detailed data were collected for atotal of 5740 buildings (75% of which were situated inthe municipality of Thessaloniki) struck by the 1978earthquake. � Carry out a ‘‘block-by-block’’ analysis of a selected part

of the city (where most of the damage from the 1978earthquake occurred) based on an update of the detaileddata concerning the buildings struck by the 1978earthquake using a new in-situ collection of data for anumber of blocks (50); this in-situ work was carried outby the members of the Aristotle University of Thessa-loniki (AUTh) Structural Group, and covered anappropriately selected (410%) sample of the 470 blockscovered by the 1984–86 survey that belong to themunicipality of Thessaloniki.

This pragmatic approach is deemed to lead to areasonable global loss scenario for the entire municipality,as well as to a detailed scenario for a large part of the citycentre (covering about 40% of the municipality, presentedin a GIS format in Fig. 2), where most of the damageexpected by the scenario earthquake will occur. Fig. 3 givesthe geographical distribution of the main typologies ofbuildings, i.e. R/C buildings designed to ‘old’ (pre-1984)and ‘new’ (post-1985) seismic codes, and unreinforced

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Fig. 2. Study area including ‘‘block-by-block’’ analysis of 1984–86 and

2003.Fig. 3. General composition of building blocks.

A.J. Kappos et al. / Soil Dynamics and Earthquake Engineering 28 (2008) 836–850838

masonry (URM) buildings. It is clear that the prevailingtypology in the area (as well as in the entire municipality) isR/C buildings designed to old codes (these include also pre-1959, or ‘pre-code’ buildings whose performance wasfound to be very similar to that of ‘low-code’ buildings,as reported in [14,15]. It is noted that the intermediate area(lying between the two surveyed ones) not covered by thesurveys (Figs. 2,3) mainly includes the University Campus,whose buildings are of generally similar typology as therest, i.e. prevalence of ‘low-code’ R/C buildings. It wasassumed that the composition of the building stock ofthe surveyed area is representative of that of theentire municipality, which, to the writers’ best knowledgeis actually the case. The total number of buildings inthe surveyed area is 5047 (one out of two buildingswas surveyed in 1984), the total in the municipality isabout 19,000.

2.2. Monuments and listed buildings

The historical background of monuments in Greece,including issues such as the definition of a monument, thelegal framework governing protection and maintenance ofmonuments, and existing guidelines for retrofitting ofmonuments are summarised in a RISK-UE report byKappos and Stylianidis [8], and will not be repeated herein

due to lack of space. The most impressive monumentssituated in Thessaloniki are the Byzantine ones, especiallythe churches, but other monuments, including somenotable roman and several contemporary (post-1830) ones,also exist. Five case studies concerning churches and otherimportant monuments of Thessaloniki have been presentedin some detail in another RISK-UE report by Stylianidiset al. [17]; two of these cases, namely the Rotunda (Roman-Christian domed structure), and the St. Panteleimon(13th–14th century crossed compound four-pillar Church),are shown in Fig. 4. The report includes historical data foreach monument, the morphology (configuration) of thestructural system, and the pathology of the load bearingsystem (including damage from previous earthquakes),with emphasis on the causes of damage due to gravity andseismic loads and to soil conditions.All major roman and byzantine monuments in Thessaloniki,

as well as all contemporary monuments (even relatively minorones) have been introduced in a GIS map of the city. The GISdatabase of Thessaloniki monuments which is set up in bothEnglish and Greek, currently includes a total of over 340monuments; an example is shown in Fig. 5, while Fig. 6 showsthe main part of the GIS map of Thessaloniki showing thepositions of monuments included in the database. Informationincluded in the database was used to develop the scenario formonuments using the methodology described in Section 3.3.

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Fig. 4. Two Thessaloniki monuments: (a) the Rotunda (cutaway isometric view from the southwest) and (b) the St. Panteleimon Byzantine Church

(elevation from the east).

Fig. 5. Example of entry in the monuments GIS database (data concerns a contemporary monument).

Fig. 6. Part of the GIS map of Thessaloniki showing the locations of monuments included in the database.

A.J. Kappos et al. / Soil Dynamics and Earthquake Engineering 28 (2008) 836–850 839

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Fig. 7. Fragility curves (in terms of PGA) for medium-rise infilled R/C frames, low code (left) and high code design.

Fig. 8. Fragility curves (in terms of Sd) for 2-storey stone masonry

buildings.

A.J. Kappos et al. / Soil Dynamics and Earthquake Engineering 28 (2008) 836–850840

3. Methodology for loss assessment in buildings

3.1. Damage and loss assessment in R/C buildings

In line with other scenarios developed within the RISK-UE programme (and several other studies included in thereference list), vulnerability (fragility) curves were used forestimating damage due to the scenario earthquake, and theassociated direct losses, typically expressed as a percentageof the replacement cost of the building. The methodologyfor deriving these curves is based on the hybrid approach,developed by the first author and his co-workers over thelast decade, which combines statistical data with appro-priately processed (utilising repair cost models) resultsfrom nonlinear dynamic or static analyses, that permitextrapolation of statistical data to PGAs and/or spectraldisplacements for which no data sets are available. Thestatistical data used for deriving the curves reported byKappos et al. [9] were from earthquake-damaged Greekbuildings. An extensive numerical study was also carriedout, wherein a large number of building types (representingmost of the common typologies in S. Europe) weremodelled and analysed. Pushover and capacity curves, aswell as fragility curves for several damage states were thenderived [9] for R/C structures for all typologies present inGreece (frames with or without masonry infills, dualstructures combining frames and R/C walls), using theaforementioned hybrid approach. Two example curves aregiven in Fig. 7; they refer to medium-rise infilled framebuildings (a very common typology in S. Europe), designedto ‘‘Low’’ (old) and ‘‘High’’ (modern) seismic codes; it isworth pointing out that the effect of seismic design wasmuch less pronounced in the case of dual buildings(designated as ‘RC4’ typologies), as found by Kapposet al. [9] and as verified from observation of pastearthquake damage [14,15]. It should be emphasised hereinthat curves used for the Thessaloniki buildings are indeedspecific to Greece and Thessaloniki in particular, since they

have been developed using a combination of analysis andstatistical data, i.e. the aforementioned hybrid approach[4,9,10], both of which are drawn from Greek practice; infact a large portion of the statistical data used is from the1978 Thessaloniki earthquake.The aforementioned fragility curves in terms of PGA

were also used to derive fragility curves in terms of Sd,necessary for the ‘Level II approach’ [12], wherein therequired Sd is calculated by plotting the scenario earth-quake response spectrum against the capacity curve of eachbuilding type, both drawn in terms of Sa vs. Sd (cf. HAZUS[7]). The procedure adopted here was to transform themedian PGA values to corresponding median Sd values,using the average spectrum of the microzonation study [16]and the fundamental period of the typical building for all

ARTICLE IN PRESSA.J. Kappos et al. / Soil Dynamics and Earthquake Engineering 28 (2008) 836–850 841

typologies, assuming the equal displacement approxima-tion applies (inelastic displacement equal to the elasticdisplacement).

Table 1

Damage grading and loss indices for R/C and URM structures

Damage

state

Damage state

label

Range

of loss

index—

R/C

Central

index

(%)

Range

of loss

index—

URM

Central

index

(%)

DS0 None 0 0 0 0

DS1 Slight 0–1 0.5 0–4 2

DS2 Moderate 1–10 5 4–20 12

DS3 Substantial to

heavy

10–30 20 20–40 30

DS4 Very heavy 30–60 45 40–70 55

DS5 Collapse 60–100 80 70–100 85

Fig. 9. Part of the GIS map of Thessaloniki showing the locations of monum

earthquake.

3.2. Damage and loss assessment in ‘common’ masonry

buildings

Pushover and capacity curves, as well as fragility curves(in terms of both PGA and spectral displacement Sd) formasonry structures are given for all typologies common inGreece (low-rise stone masonry and brick masonrybuildings) in Kappos et al. [9]; these fragility curves arebased on the 5 damage states (DS0, i.e. no damage, to DS4,i.e. heavy damage or failure) used in the well-known lossassessment methodology Hazus [7]. A typical set ofvulnerability curves referring to a very common buildingtypology (2-storey stone masonry buildings) is given inFig. 8, plotted against some actual data from the empiricaldatabases. It is noted that these curves are drawn as afunction of Sd (rather than PGA, cf. Fig. 7), but both typesof curves were derived. Details of the procedure forderiving such curves, which involves using representative

ents included in the database and the expected PGAs from the scenario

ARTIC

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PRES

S

Table 2

Assessment of the vulnerability index for monumental buildings

Name Typology Year Kind of

use

Frequency Crowd Maintenance Damage

level

Arch

tran

Rec.

inter

Masonry

quality

Site Plan

regul.

Position iv

The Customs Palaces–Villas 1910 Offices in the main

building and

warehouses in the

rest of the

buildings

Daily Yes Good Severe No Yes Yes Flat ground Yes Isolated 0.576

Ioniki and Laiki Bank Palaces–Villas 1929 Bank Daily Yes Medium Nihil No No Yes Flat ground Yes Corner

in the

block

0.656

Vlatadon Monastery Monasteries 1351 – Occasional Yes Good Medium No Yes Yes Ridge Yes Isolated 0.676

The Rotunda Churches 300 – Occasional Yes Good Severe Yes Yes Good Flat ground Central Isolated 0.97

The Church of Achiropiitos Churches 500 Church Daily Yes Good Severe No Yes Good Sloping Three Isolated 0.99

The Church of St. Panteleimon Churches 1300 Church Daily Yes Good Severe No Yes Good Flat ground One Isolated 0.95

The Church of Ayia Sophia Churches 800 Church Daily Yes Good Light No Yes Good Flat ground Three Isolated 0.99

The Church of Ayios Nikolaos Orphanos Churches 1400 Church Daily Yes Medium Good Flat ground Three Isolated 0.95

The Church of Hosios David Churches 600 Church Daily Yes Good Severe No Yes Good Flat ground One Isolated 0.89

The Rotunda Minaret Minaret 1590 – Occasional Yes Good Severe No Yes Good Flat ground Circular Isolated 0.736

The White Tower Tower 1430 Museum Daily Yes Good Light No Yes Good Slopping Circular Isolated 0.796

Galerios Arch (Kamara) Arch 305 – Daily Yes Good Light Yes Yes Good Flat ground Not

meaningful

Isolated 0.456

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al.

/S

oil

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mics

an

dE

arth

qu

ak

eE

ng

ineerin

g2

8(

20

08

)8

36

–8

50

842

ARTICLE IN PRESSA.J. Kappos et al. / Soil Dynamics and Earthquake Engineering 28 (2008) 836–850 843

response spectra of the earthquakes from which thestatistical data is taken, are given in Kappos et al. [9] andPitilakis et al. [16].

To obtain a more complete scenario, it was decided touse 6 damage states (DS0–DS5) in the present study,mainly along the lines of the ‘Level I’ approach [9,12], i.e.the one based on the macroseismic intensity scale (EMS 98)and/or the PGA; since the Sd fragility curves were derivedfrom the corresponding PGA curves, and given that aseparation between DS4 (heavy damage) and DS5 (col-lapse) would be necessary, e.g. for the estimation of thecasualties, an extra DS5 fragility curve was derived in termsof Sd as well. The damage states used are given in Table 1for R/C and URM structures, both in descriptive termsand as loss indices (ratio of repair cost to replacementcost); consistent with the approach adopted by otherRISK-UE groups [12], loss indices are somewhat higher forURM than for R/C, for the same damage state.

3.3. Damage and loss assessment in historical buildings

The damage scenario for monuments has different aimsthan the general scenario since its objective is theestimation of the ‘cultural damage’ that Thessaloniki willsustain when subjected to the design earthquake. As notedin Section 2.2, the ‘‘monuments’’ database includes allbuildings that have been listed by the Ministry of Culture,

0 1.500750

Meters

IMM=7

0.00–0.01

0.01–0.10

0.10–0.30

0.30–0.60

0.60–1.00

Fig. 10. Expected damage distribution for various inten

many of which are residential masonry buildings ofthe early 20th century, hence from the structural point ofview they are broadly similar to the ‘current’ URMbuildings, and from the importance point of view theyare not as important as the exquisite monuments of theRoman and Byzantine period of Thessaloniki. Therefore,the former have been included in the damage scenarioalong with the ‘current’ URM buildings, whereas47 important monuments–landmarks of Thessaloniki(Roman, Byzantine, and the most important contemporarymonuments) were treated separately, as described in thefollowing.The damage scenario for monuments is based on the

combination of two parameters:

�

siti

The peak ground accelerations (PGAs) estimated foreach building block of Thessaloniki with 10% prob-ability of exceedance in 50 years (475 return period) [16],which are shown graphically in Fig. 9.

� The estimated vulnerability index of each monumental

building, which has been assessed using the methodol-ogy adopted in the RISK-UE project, the main featuresof which are described in Lagomarsino et al. [11]. Themethodology is based on a survey form including severalweighted parameters such as type of structure, quality ofconstruction, existence of specific vulnerable elements,etc., which are combined to derive a final index.

0 1.500750

Meters

IMM=9

0.00–0.01

0.01–0.10

0.10–0.30

0.30–0.60

0.60–1.00

es (assumed to be uniform in the studied area).

ARTICLE IN PRESSA.J. Kappos et al. / Soil Dynamics and Earthquake Engineering 28 (2008) 836–850844

The features that are considered for deriving thevulnerability index can be seen in Table 2, which givesexamples of estimation of this index for a number ofmonumental buildings in Thessaloniki. The combination ofthe above factors is performed using the expression:

mD ¼ 2:5 1þ tanhI þ 3:44iv � 8:91

3

� �� �, (1)

where mD is the mean damage grade varying from 0 to 5(cf. DS1–DS5 in Table 1), I the macroseismic intensitywhich is linked to PGA (from the earthquake scenario)using the expression (pertinent to Greece [13])

logðPGAÞ ¼ 0:29I þ 0:21 (2)

and iv the vulnerability index of each monumental building.Eq. (1) is based on empirical data from earthquake damage

in Italian monuments, mainly in churches [11]; it was adoptedherein since no such expression is available to date for Greece.

4. Key results

4.1. Scenarios for ordinary buildings

Two types of scenarios can be developed using theanalytical tools presented in the previous section. In its

0 1.500750

Meters

LEVEL I

Damage Distribution

DS0

DS1

DS2

DS3

DS4

DS5

Fig. 11. Number of buildings suffering damage states DS

most rudimentary form the earthquake scenario would besimply an assumption of a uniform intensity for the areastudied (the municipality of Thessaloniki); note that anestimation of ‘local’ intensities for the last (1978) strongmotion that occurred in Thessaloniki using the question-naire method (reported in [18]), has shown that intensitiesin the aforementioned area varied from 6.0 to 7.5. The(idealised) distribution of damage in the area considered,when subjected to different uniform macroseismic inten-sities (I ¼ 7 and 9) is shown in Fig. 10. The damage levelswere estimated using the aforementioned ‘Level I’ fragilitycurves for each building type (intensity and PGA werecorrelated using appropriate empirical relationships de-rived for Greece, see Pitilakis et al. [16]), and the indexplotted is a weighted one, SðMDFiV iÞ=V tot, where volumeVi of each building type is used to weigh the mean damagefactor MDFi (central index in Table 1) for this type. Suchmaps give a good picture of the most vulnerable parts ofthe city, regardless of the specifics of the scenario earth-quake (and local amplifications due to particular soilconditions), and they are a useful tool in emergencyplanning, keeping in mind that even an ‘accurate’ scenarioearthquake is just one possible description of the seismicrisk in the considered area (i.e. vulnerable buildings notheavily struck by a specific scenario earthquake, might be

0 1.500750

Meters

LEVEL II

Damage Distribution

DS0

DS1

DS2

DS3

DS4

0–DS5 in each building block (scenario earthquake).

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23

357

635

885

0

0

198

483

61

15

72

179

3979

3059

1615

5288

0

15

4

0

0

137

555

171

144

0

0

15

57

30

0

0

53

019

72

357

0

160

110

42

40

0

4

15

8

46

110

0

0

27

0

4

464

1003

0

0

46

0

0

4

0

11

958

479

530

0

175

110

281

110

438

304

513

76

87

00011

80

23

42

23

114

46

42

0

0%

RC4.

1LL

RC4.

1HL

RC4.

1ML

RC4.

2LL

RC4.

2ML

RC4.

2HL

RC3.

1LL

RC3.

1ML

RC3.

1HL

RC3.

2LL

RC4.

1LH

RC4.

1MH

RC4.

1HH

RC4.

2LH

RC4.

2MH

RC4.

2HH

M1L

M1M M

3L

M3M

20%

40%

60%

80%

100%

DS5DS4DS3DS2DS1DS0

0%

RC4.

1LL

RC4.

1HL

RC4.

1ML

RC4.

2LL

RC4.

2ML

RC4.

2HL

RC3.

1LL

RC3.

1ML

RC3.

1HL

RC3.

2LL

RC4.

1LH

RC4.

1MH

RC4.

1HH

RC4.

2LH

RC4.

2MH

RC4.

2HH

M1L

M1M M

3L

M3M

10%

20%

30%

50%

40%

60%

70%

80%

90%

100%

DS4DS3DS2DS1DS0

0

46

11

15

0

657

806

80

464

315

4280

817

4564

2546

1167

274

4

15

0

76

467

680

676

0

65

418

384

95

46

0

23

57

23

0

84

285

1115

106

8

156

72

30

49

0

57

11

38

72

000

4

0

4

0

1167

334

0

49

137

0

194

42815

992

0

46

0

129

008

34

167

0

19

0

68

Fig. 12. Damage distribution (% of buildings) for all building types (Municipality of Thessaloniki)—Level I approach (top) and Level II approach

(bottom).

A.J. Kappos et al. / Soil Dynamics and Earthquake Engineering 28 (2008) 836–850 845

heavily damaged by a different scenario earthquake notconsidered due to lack of time and/or lack of data at thetime of the study).

The remainder of the maps and related materialpresented herein refer to the particular earthquake scenarioshown in Fig. 9, developed as described in [16]. The mapsof Fig. 11 show the number of buildings suffering damagestates DS0–DS5 in each building block of the studied area,based either on the PGA in each building block (Fig. 9) andthe corresponding Level I fragility curves for each buildingtype, or the spectrum derived for the pertinent zone fromthe microzonation study [16] and the capacity curve of thetypical building in each typology, entering the correspond-ing Level II fragility curve with the Sd value found from theintersection of the spectrum and the capacity curve. Aftercalculating the discrete probabilities of each damage state

(from the fragility curve) for each building type present in ablock, the number of buildings suffering each damage stateis calculated accordingly; for example, if in a block thereare 4 buildings of a particular typology, and the discreteprobabilities (derived by subtracting the values determinedfrom the intersection points of the fragility curves and thevertical line corresponding to the given PGA) forDS0–DS5 are, say, 6, 17, 53, 21, 2, and 1 (%), respectively,two buildings will suffer DS2, one will suffer DS3 and oneDS1 (no buildings in the DS0, DS4 and DS5 categories). Itis pointed out that this is only one of the possible ways ofestimating the number of buildings suffering each damagestate; it is the most reasonable one (to the writers’ opinion),but its potential drawback is that in (hypothetical) cases ofvery uniform distribution of PGA (or any other measure ofearthquake intensity) in the studied area, damage states

ARTICLE IN PRESSA.J. Kappos et al. / Soil Dynamics and Earthquake Engineering 28 (2008) 836–850846

associated with very low probability (e.g. DS4 and DS5 inthe previous example) might never appear on the map ofDS distribution. As seen in Fig. 11, a non-zero number ofbuildings exists for all damage states, including even DS5(collapse), for the considered scenario.

A clearer picture of the total number of buildings in eachBTM category that suffer each damage state can beobtained from Fig. 12, which refers to the entiremunicipality (subject to the already discussed assumptionregarding the composition of building blocks); noteparticularly that the number of buildings in each categoryis very different (hence it is given with numbers inside of

Table 3

Total number of buildings in each damage label

Damage label Green Yellow Red

Level I

Number of buildings 7467 9432 2280

Percentage (%) 38.93 49.18 11.89

Level II

Number of buildings 11,343 5928 1908

Percentage (%) 59.14 30.91 9.95

0 1.500750

Meters

LEVEL I

0.00–0.01

0.01–0.10

0.10–0.30

0.30–0.60

0.60–1.00

Fig. 13. Expected distribution of the damag

each portion of histogram). It is seen that the most heavilydamaged typologies are low-rise, ‘low-code’ R/C buildingswith infilled frame systems (typologies RC3.1LL andRC3.2LL) and low-rise masonry buildings; the latter wasanticipated, whereas the particularly high vulnerability oflow-rise old R/C buildings is not a surprise either, but partof the problem might be their location with respect to thespecific considered scenario (high PGA values in thewestern part of the studied area, see Fig. 9), i.e. not onlytheir own (absolute) vulnerability (cf. Fig. 10). It is alsoseen that the Level I approach results in a relativelydifferent damage distribution than the Level II for eachbuilding typology, e.g. M1M and M3M buildings areheavily damaged (DS4) for the Level II approach, while forthe Level I most of them are slightly damaged (DS1) or notdamaged at all (DS0).A picture of the expected distribution of post-earthquake

tagging of buildings using the familiar Green, Yellow, andRed tag scheme is desirable for earthquake planningpurposes. The correspondence between tag colour andDS was assumed as follows:

�

e in

Green: DS0 and DS1,

� Yellow: DS2 and DS3, � Red: DS4 and DS5.

0 1.500750

Meters

LEVEL II

0.00–0.01

0.01–0.10

0.10–0.30

0.30–0.60

0.60–1.00

dex due to the scenario earthquake.

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0 1.500 750

Meters

LEVEL I

COST (EURO×1000)

0–400

400–800

800–1200

1200–2000

2000–3500

3500–7000

0 1.500 750

Meters

LEVEL II

COST (EURO×1000)

0–400

400–800

800–1200

1200–2000

2000–3500

3500–7000

Fig. 14. Repair cost (in 103h) distribution in the building blocks of the studied area.

A.J. Kappos et al. / Soil Dynamics and Earthquake Engineering 28 (2008) 836–850 847

Based on experience from past earthquakes it might wellbe argued that at least part of DS3 could go to the red tagcategory. The total number and percentage of buildings ineach tag category are summarised in Table 3. The figuresshown confirm that the city is rather vulnerable to theconsidered earthquake, as about 12% for the Level I or10% for the Level II approach of the buildings will suffervery heavy damage or collapse; this is clearly a far moresevere situation than in the 1978 earthquake when therewas only one collapse of multistorey R/C building (and atthat time all R/C buildings were ‘low-code’ or ‘pre-code’ones) and heavy damage was observed mainly in masonrybuildings.

Given the limitations of the procedure for assigning eachindividual building within a block to a discrete damagestate, it is important to map also the damage index for eachblock, this time as a weighted one SðMDFiV iÞ=V tot, asdiscussed previously; this map is given in Fig. 13 and it putsthe damage distribution ‘into scale’ in the sense that thedegree of damage is now associated with the volume of thebuildings (e.g. a collapsed single-storey masonry buildinghas a smaller influence on the index than a 9-storey R/Cbuilding suffering ‘‘substantial to heavy’’ damage, i.e.DS3). Last but not least, the economic loss predicted for

the scenario earthquake is of particular importance, inseveral ways (earthquake protection and emergency plan-ning, earthquake insurance). The fragility models devel-oped by the AUTh group [9] originate from repaircost considerations, hence it was relatively straightforwardto use them for economic loss assessment purposes. Themap of Fig. 14 shows the estimated total cost of repairrequired in each building block, derived using the lossindices of Table 1 and assuming an average replacementcost of h700/m2, i.e. calculating S[(ViMDFi]?700 in eachblock. The distribution of cost is, of course, consistent with(and conditional on) the distribution of the degree ofdamage (Fig. 13). A very heavy cost of over 460 million h

for the Level I, or 330million h for the Level II approach ispredicted for the area studied (the figure should bemultiplied by about 4 for the entire municipality), againan indication of the severity of the estimated scenarioearthquake.

4.2. Scenarios for historical buildings

As mentioned in Section 3.3, the procedure used for thebuildings characterised as monuments was different fromthat used for ‘current’ (or ordinary) buildings. In Fig. 15

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Fig. 15. Part of the GIS map of Thessaloniki showing the locations of

monuments and the estimated damage grade (0–5).

Table 4

Results of the earthquake scenario for selected monumental buildings

Monument PGA (g) iv Damage grade

Rotunda 0.45 0.97 4.25

Rotunda minaret 0.45 0.74 3.84

Acheropiitos church 0.44 0.99 4.27

Agios Panteleimon church 0.42 0.95 4.19

A.J. Kappos et al. / Soil Dynamics and Earthquake Engineering 28 (2008) 836–850848

the damage grade estimated using the Level I procedure(Section 3.3) for each monument is plotted on the GIS mapusing an appropriate colour and size scale. It is interestingto check the final prediction of the scenario in the case ofsome specific monuments described in more detail in theRISK-UE Report by Stylianidis et al. [17]; the estimatedvulnerability indices for these monuments and the damagegrades corresponding to the PGA values from the scenarioearthquake (Fig. 9) are summarised in Table 4.

It is clear from Fig. 15 and Table 4 that the majority ofmonuments will suffer a damage grade of 3–4 while asignificant number will sustain damage of 4–5 (nearcollapse). This prediction is, of course, related to theseverity of the scenario earthquake, and one should pointout that the level of damage predicted here for the majormonuments of Thessaloniki does not appear to beconsistent with their (long) ‘seismic history’ (i.e. exposure

to past earthquakes). This apparent over-prediction ofdamage should be either due to overestimation of hazard,or of the vulnerability (this is perhaps more true in the caseof monuments where the rating method applied has notbeen calibrated against local data), or, indeed, a combina-tion thereof.

5. Conclusions and recommendations for future studies

The paper summarised the methodologies used by theAUTh group for estimating direct losses in both R/C andmasonry buildings and also addressed the critical issue ofdata collection; the choices made in the case of the city ofThessaloniki were presented and discussed. Then some keyresults were presented, including the expected geographicaldistribution of building damage due to a scenario earth-quake in the municipality of Thessaloniki. The followingconclusions were drawn from the scenarios presentedherein:

�

The vulnerability assessment of current buildings wasestimated using both Level I and Level II approach. TheLevel I approach (cast in PGA terms) has a number ofadvantages, but also ignores, to an extent that dependson the spectral characteristics of the motions consideredfor deriving the fragility curves and their relationship tothe characteristics of the scenario motions, the possiblylower damageability of motions with high PGA andspectra peaking over a very narrow band and/or withvery short duration (both these characteristics are moreor less typical in strong motions recorded in Greece).The Level II approach takes into account the spectralcharacteristics of the motion but further research isneeded in several points such as the case where theCapacity Spectrum Method does not result in asolution, or the equal displacement rule assumption isnot valid. � All the evidence provided by the present study clearly

points to the fact that the scenario earthquake estimatedin [16] is an event significantly stronger than thehistorical Thessaloniki (1978) earthquake whose con-sequences for the city are known. It is beyond the scopeof this work to discuss whether some assumptions ormethods have led to a certain degree of overestimationof the 475 yr earthquake for the city.

� Both Level I and Level II approaches resulted in similar

results, the Level II approach resulting in a little lowerpredictions of the damage degree. However, it has to be

ARTICLE IN PRESSA.J. Kappos et al. / Soil Dynamics and Earthquake Engineering 28 (2008) 836–850 849

emphasised that the Level I and Level II fragility curvesare not completely independent in this study, sincethe first were used to derive the second, as described inthe paper.

� The level of damage predicted here for the major

monuments of Thessaloniki does not appear to beconsistent with their (long) ‘seismic history’ (i.e.exposure to past earthquakes). This apparent over-prediction of damage should be either due to over-estimation of hazard, or of the vulnerability (this isperhaps more true in the case of monuments wherethe rating method applied has not been calibratedagainst local data), or, indeed, a combination thereof. Itis worth pointing here that in the case of monuments,their long and documented history permits to readilyrecognise cases that the considered earthquake motion isstronger than those that struck the monument in pastcenturies.

� It is within the scope of the work envisaged by the

AUTh research group to improve the methodologies forassessing the vulnerability of both common and monu-mental structures, using damage information from pastearthquakes in combination with nonlinear analysis ofcarefully selected representative structures. This is still achallenging goal, particularly in the case of monuments,wherein the very definition of a ‘representative structure’is a controversial issue.

Acknowledgements

Most of the work reported in this paper was carried outby the writers within the framework of the RISK-UEproject, funded by the European Commission (Contract:EVK4-CT-2000-00014). Part of the dynamic time-historyanalyses of R/C buildings was carried out after the end ofthe RISK-UE project, within the frame of a nationallyfunded (by the General Secretariat of Research andTechnology of Greece) project, ARISTION (2003–2007),concerning the vulnerability of the building stock of R/Cand masonry buildings in Greece, and the development ofseismic retrofit techniques using new materials.

The writers wish to acknowledge the assistance of Prof.K. Stylianidis (AUTh) and his contribution to thevulnerability assessment of the URM buildings, particu-larly in the selection of generic building to be analysed, ofProf. S. Lagomarsino (University of Genoa) for hiscontribution to the proper interpretation of availabledamage statistics for URM buildings and for sharing withthe writers his experience from the vulnerability assessmentof the Italian masonry building stock, and of Prof. K.Pitilakis (AUTh) for making available to the writers datafrom the microzonation study of Thessaloniki carried outby his group, as well as developing the scenario earthquakeused herein for risk and loss assessment. The fruitfuldiscussions with, and the critical comments of, all membersof the RISK-UE team that contributed to the activities

related to loss assessment was a major stimulus for thewriters and guided them in improving their existing modelsand integrating them within the scenario developmentprocedure.Last and not least, the contribution of the following

individuals should be acknowledged:

�

Ch. Panagiotopoulos, Ph.D. student at AUTh, whocontributed to the numerical part of the study, notablyin the analysis of URM buildings and infilled R/Cbuildings. � V. Papanikolaou, Ph.D. student at AUTh, who con-

tributed significantly to the development of the monu-ments and public buildings database.

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