55 Symposium Bucharest 07 056 Vacareanu

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International Symposium on Strong Vrancea Earthquakes and Risk MitigationOct. 4-6, 2007, Bucharest, Romania

CASE STUDY ON THE EXPECTED SEISMIC LOSSES

OF SOFT AND WEAK GROUNDFLOOR BUILDINGS

R. Vacareanu1, A.B. Chesca2, B. Georgescu3, M. Seki4

ABSTRACT

Bucharest, one of the earthquake prone largest cities in Europe, has a large building stockwith soft and weak groundfloor buildings erected before the March 4, 1977 Vranceasubcrustal earthquake. This paper presents a case study on the expected seismic losses ofa soft and weak groundfloor building. The case study is conducted for both existing situationof the building as well as for the seismically rehabilitated building. The seismic rehabilitationsolution is prepared within JICA Technical Cooperation Project on Reduction of Seismic Riskfor Buildings and Structures in Romania by a team from JICA/NCSRR in partnership withProiect Bucharest design company. The seismic rehabilitation solution consists of

introducing fluid viscous dampers in the groundfloor and steel jacketing of the groundfloorcolumns and of the upper stories structural walls. The seismic evaluation of the building isperformed using capacity spectrum method [ATC, 1996] and the evaluation of the expectedseismic losses is conducted according to [HAZUS, 1999] methodology. The importantreduction of the expected seismic losses for seismically rehabilitated building is highlighted.Only economic losses are considered; the paper does not discuss the life losses.

INTRODUCTION

Romania is one of the earthquake prone countries in Europe. During the March 4, 1977

Vrancea subcrustal earthquake 31 buildings collapsed in Bucharest. Out of these 31buildings, 28 were built before 1940-1945 and 3 buildings were built in 1960-1970s. Themost affected buildings were the reinforced concrete high-rise buildings built until 1940-1945with no seismic design. The structural system of the buildings consists of RC columns andRC beams not acting as spatial RC frames due to the weak joints. Within this typology 23residential buildings collapsed in Bucharest on March 4 1977. Out of the 3 newer buildingscollapsed on March 4 1977, one belongs to the typology of soft and weak groundfloorbuildings. This building typology consists of a dual structural system in the vertical direction,i.e. RC columns in the ground floor (commercial area) and RC shear walls in the upperfloors (residential area). The major vulnerabilities of this building typology come from theconcentration of most of seismic lateral displacement and seismic dissipated energy in thegroundfloor, insufficient ductility of RC columns in the groundfloor and insufficient shear

capacity of the RC upper shear walls.

The collapsed soft and weak groundfloor building was located in Bucharest at the corner ofStefan cel Mare Boulevard with Lizeanu Street. The 10-stories building was designed anderected in 1961-1962. During March 4, 1977 earthquake, the western part of the body A ofthe building had been displaced over a length of 10 m and needed to be demolishedafterward, Figure 1. The collapse of the building consisted in the failure of the first two floorsalong a portion of part A on the entire height of the building.

1National Center for Seismic Risk Reduction and Technical University of Civil Engineering, Bucharest,

[email protected] Center for Seismic Risk Reduction and University of Architecture, Bucharest, [email protected] Bucuresti SA, Bucharest, [email protected]

4National Center for Seismic Risk Reduction and JICA, [email protected]


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International Symposium on Strong Vrancea Earthquakes and Risk Mitigation 389

As a result of the failure the damaged body become totally independent from the rest of thebuilding, having the upper structure virtually undeformed. The ground floor and the 1

stfloor

of this independent part had sunk in the basement. This dislocation and collapse has beengenerated by the failure of the groundfloor columns, that generated the sunk of the aboveslab and together with it the failure and collapse of the rest of the above slabs and thebreaking of the slabs of the remaining part of the building. Likewise, during the collapse, thebuilding had been displaced 50 cm from the ground floor level to the northeast direction andstopped in an equilibrium position inclined with 10 from the vertical axes. Some of theground floor columns were still standing, after the failure of the superior support, punchingthe above slabs that sunk vertically. The failure of the ground floor columns generated thefailure of other columns that in response determined the dislocation and the severeinclination of the damaged part to the south. All these conclusions reported by Eng. EmilianTitaru were made following the investigations made on site and in the office after theearthquake and from the photos that were taken. It is most likely that the columns failurewas caused by the most disadvantageous stress combination, bending with shear force,which resulted due to the low ductility of the section (caused by the under-reinforcement ofthe column), including the insufficient resistance to shear force (caused by the transversal

under-reinforcement of the column as well because of the cross size dimensions). The flawsin the earthquake resistant design of the building were due the limitations of the regulationsat that time. Following the earthquake, the part of the building that was mostly affected wascompletely demolished because of the severe damage.

Figure 1. Stefan cel Mare no. 33 building 30 A collapsed in March 4 1977 Vrancea earthquake

(from: http://nisee.berkeley.edu/)


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R. Vacareanu et al.390

For the rest of the building, that did not collapsed during the earthquake, there has beensevere damage of the ground floor columns, consisting either in crushing and spalling ofconcrete together with the buckling of the reinforcements, either in cracks and fissures at65 from the vertical axis that were located at the base of the column or at the superior endof the column under the slab above the ground floor.

Given the lessons learnt in March 4 1977 earthquake on the very poor seismic response ofthe soft and weak groundfloor buildings and the large existing building stock in this typologyin Bucharest, it is a stringent need for searching a seismic rehabilitation strategy. Within theJICA Technical Cooperation Project in Romania it was decided to take actions towards theaim of seismic rehabilitation of soft and weak groundfloor buildings. In order to proceed withthe seismic rehabilitation project it was selected a representative building with soft and weakgroundfloor built in 1960s in Bucharest and located at 90-96 Mihai Bravu Boulevard inBucharest. For the preparation of the feasibility study, technical project and detailed designof the seismic rehabilitation project, National Centre for Seismic Risk Reduction, NCSRRand Japan International Cooperation Agency, JICA made a partnership with ProiectBucuresti SA design institute. In this paper it is presented the seismic rehabilitation strategy

and the solution for the soft and weak groundfloor selected building based on moderntechniques. The seismic rehabilitation solution consists in introducing fluid viscous dampersin the groundfloor and in steel jacketing of the columns in the groundfloor and of thestructural walls in the upper stories.

SEISMIC EVALUATION AND SEISMIC REHABILITATION OF THE BUILDING

The building to be seismically rehabilitated is located on Mihai Bravu Boulevard, at number90-96, in the city of Bucharest, Figure 2. The building was erected in 1960s, it has 11storeys (B+GF+10S) and its main destination is residential in the upper floors andcommercial in the groundfloor, Figure 3. The structural system consists of reinforced

concrete frames in the groundfloor, Figure 4 and RC structural walls in the upper floors,Figure 5. The groundfloor is a soft and weak story, with no structural walls. The buildingconsists of 3 parts (A, B and C). In what concerns the seismic evaluation and retrofitting partA is under discussion hereinafter. The A building has a rectangular base of 11.42x32.85 m.A staircase connects the buildings A and B. Amongst all 3 buildings there are seismicjoints of 3 cm.The ground floor height is 4.80m while the height of the rest of the floors is 2.73m.The soil underneath the building is made of layers of sand with gravel fractions in themedium compacted state, with a 3 daN/cm

2conventional pressure. The buildings footprint

area is 380.07 m2.

The concrete used is B250 (equivalent to C16/20) and the reinforcing steel used is OB37(equivalent to S235).The RC beams sections vary from 15x55 cm up to 37,5x60 cm. TheRC columns sections vary from 40x55 cm to 80x50 cm; there are also two elongatedcolumns of 170x50cm transversally placed in the axes 9 and 10. The structural wallthickness varies from 15 to 20 cm. The slabs are made of reinforced concrete of 8 to 11 cmin thickness. The infrastructure system consists of a rigid box in the basement withcontinuous foundations under all the structural elements.

The total weight of the building is 5528 t. The building first eigenvalue is 0.68s, the secondeigenvalue is 0.56s and the third eigenvalue is 0.45s. The first eigenvector is a translation inthe longitudinal direction; the second eigenvector is a translation in transversal directiontogether with a rigid body rotation around the basement while the third is a rotation around

the vertical axis, Figure 6.


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Figure 2. Satellite view of the building site 90-96 MihaiBravu Blvd., Bucharest (from www.earth.google.com)

Figure 3. Main faade of thebuilding A located at 90-96 Mihai

Bravu Blvd

Figure 4. Groundfloor plan view

Figure 5. Plan view of current floor


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T1=0.68s T2=0.56s T3=0.45s

Figure 6. Modal shapes and eigenvalues of the building

Details on the seismic evaluation and seismic rehabilitation can be found elsewhere(Chesca et.al., 2007). Only information relevant for the present paper are presentedhereinafter.

The seismic evaluation of the existing building and as well as of the seismically rehabilitatedbuilding was performed using capacity spectrum method, CSM [ATC40, 1996] with thealternative approach using strength reduction factors proposed by (Chopra&Goel, 1999).Pushover analyses were performed for each direction of the building using ETABS

TM

computer software. The application of the capacity spectrum method for the existing building

is presented hereinafter. The seismic action considered is according to the Romanian Codefor Earthquake Resistant Design of Buildings, P100-1/2006, considering two levels ofseismic hazard with 80% exceedance probability in 50 years and 40% exceedanceprobability in 50 years. Nevertheless, for the completeness of the analysis, a third level ofseismic hazard with 10% exceedance probability in 50 years was considered. The designpeak ground accelerations in Bucharest for the previously mentioned levels of seismichazard are 0.1g, 0.24g and 0.35g. The corresponding building performance levels are:damage limitation, life safety and collapse prevention, respectively. The results obtainedfrom capacity spectrum method are presented in Table 1 and Figure 7.

Table 1. Expected seismic response of existing building

X direction Y direction

PGA ['g] = PGA['g] =

Expectedseismic

response 0.10 0.24 0.35 0.10 0.24 0.35

SD, cm 4.6 15.5 24.5 3.0 11.3 19.0

SA, 'g 0.22 0.24 0.24 0.26 0.33 0.33

Droof, cm 6.3 21.2 33.5 3.8 14.3 24.1

V, tf 988 1078 1078 994 1224 1224

1.5 5.1 8.0 1.1 3.9 6.5


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Note:X Direction Longitudinal; Y Direction - TransversalSD- spectral displacement; SA- spectral accelerationV- base shear force; W- weight of the buildingDroof- lateral displacement at top of building; PGA- peak ground acceleration

- displacement ductility

0.0

0.1

0.2

0.3

0 5 10 15 20 25 30

SD, cm

SA,

=1 Capacity = 1.5

Performance

point

0.0

0.1

0.2

0.3

0.4

0 5 10 15 20 25SD , cm

SA,g

=1 = 1.1 Capacity

Performance

point

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 10 20 30 40 50 60

SD, cm

SA,

=1 = 5.1 Capacity

Performance

point

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 10 20 30 40 50 60

SD, cm

SA,

=1 = 3.9 Capacity

Performance

point

0.0

0.2

0.4

0.6

0.8

1.0

0 10 20 30 40 50 60 70 80

SD, cm

SA,

=1 = 8.0 Capacity

Performance

point

0.0

0.2

0.4

0.6

0.8

1.0

0 10 20 30 40 50 60 70 80

SD, cm

SA,

=1 = 6.5 Capacity

Performance

point

Figure 7a. Expected seismic response of

existing building for PGA=0.1g(top), 0.24g(middle), 0.35g(bottom) X direction

Figure 7b. Expected seismic response ofexisting building for PGA=0.1g(top), 0.24g

(middle), 0.35g(bottom) Y direction

The seismic rehabilitation/retrofitting objective is to improve the seismic performance of thebuilding without much disturbance for the residents of the building. In this respect it was

considered that any kind of intervention shall be made in the basement and ground floorwhile limiting the amount of works in the upper stories.


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The structural walls in the upper floors lack shear capacity while the columns in the groundfloor mainly lack ductility.The seismic rehabilitation solution adopted for Mihai Bravu 90-96 building A consists ofintroducing fluid viscous dampers in the groundfloor, steel jacketing of the columns in thegroundfloor and steel jacketing of the structural walls in the upper stories. The fluid viscousdampers layout was chosen taking into account the position of the upper stories structuralwalls. One or two dampers are placed under each structural wall. The reason for this layoutis the proper transfer of the shear force between the dampers and the structural walls atopthem. The dampers are placed in the openings beneath the upper structural walls. In orderto avoid any supplemental forces added to the groundfloor columns, the final dampersconfiguration was a chevron one, with dampers placed in horizontal position, at the upperpart of the groundfloor. In Figure 8 it is presented the layout of the dampers in the groundfloor. The damping constant was chosen to be C=20 kN*s/mm producing an overalldamping ratio of 30% for the rehabilitated building.

Figure 8. Damper layout in the groundfloor (solid thick lines)

Figure 9. represents the time-history of the groundfloor top displacement for the buildingequipped with linear fluid viscous dampers and for the existing building. One may notice a50% reduction in the maximum displacement demand as well as the reduction of thenumber of cycles at high amplitudes.

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

0 2 4 6 8 10 12 14 16 18 20

Time, s

Ground

Floortop

displacem

ent,m

UX C=20kN*mm/s

UX no added damping

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

0 2 4 6 8 10 12 14 16 18 20

Time, s

Ground

Floortop

displacem

ent,m

Uy C=20kN*mm/s

Uy no added damping

Figure 9. Groundfloor top displacement time-history for the building equipped with fluid viscousdampers and for the existing building


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Figure 10. presents the dampers connection details beneath a structural wall. Severalhorizontal damper connections in the same frame were analysed. The optimal solution wasto connect the dampers to the middle RC column in order to avoid the connection of thedampers to tensioned shear weakened corner columns.

The other retrofitting measures consisted of steel jacketing of the ground floor RC columnsand steel jacketing of the first 3 stories RC structural walls.

Figure 10. Damper connection detail

The results obtained with capacity spectrum method for the seismically rehabilitated buildingare presented in Table 2 and Figure 11. The code elastic response spectrum for Bucharestwas reduced according to the provisions of Annex A of P100-1/2006 Code to take intoaccount the damping ratio of 30% for the seismically rehabilitated building.

Table 2. Expected seismic response of seismically rehabilitated building



Expectedseismic

response 0.10 0.24 0.35 0.10 0.24 0.35

SD, cm 1.8 6.9 11.6 1.4 4.6 7.8

SA, 'g 0.15 0.23 0.24 0.15 0.30 0.33

Droof, cm 2.5 9.4 15.9 1.7 5.9 9.9

V, tf 688 1053 1078 568 1129 1234

1.0 2.3 3.8 1.0 1.6 2.7

Note:X Direction Longitudinal; Y Direction - TransversalSD- spectral displacement; SA- spectral accelerationV- base shear force; W- weight of the building

Droof- lateral displacement at top of building; PGA- peak ground acceleration- displacement ductility


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0.0

0.1

0.2

0.3

0 5 10 15 20 25 30

SD, cm

SA,

=1 Capacity

Performance

point

0.0

0.1

0.2

0.3

0.4

0 5 10 15 20 25

SD, cm

SA,

=1 Capacity

Performance point

0.0

0.1

0.2

0.3

0.4

0 10 20 30

SD, cm

SA,

=1 = 2.3 Capacity

Performance

point

0.0

0.1

0.2

0.3

0.4

0 10 20 30

SD, cm

SA,

=1 = 1.6 Capacity

Performance

point

0.0

0.2

0.4

0.6

0 10 20 30 40 50

SD, cm

SA,

=1 = 3.8 Capacity

Performance

point

0.0

0.2

0.4

0.6

0 10 20 30 40 50

SD, cm

SA,

=1 = 2.7 Capacity

Performance

point

Figure 11a. Expected seismic response ofrehabilitated building for PGA=0.1g(top),

0.24g(middle), 0.35g(bottom) X direction

Figure 11b. Expected seismic response ofrehabilitated building for PGA=0.1g(top),

0.24g(middle), 0.35g(bottom) Y direction

One can notice the important reduction of the ductility demands for the rehabilitated building(more than two times reduction), thus alleviating one of the major deficiencies of thestructural system.


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EVALUATION OF THE EXPECTED SEISMIC DAMAGE AND LOSSES

In order to investigate the expected seismic damage and losses for the existing and for therehabilitated building, the methodology presented in [HAZUS, 1999] is applied. The buildingtypology was assigned to C1H (high-rise reinforced concrete frames) designed according to

a low code (P13-63 Romanian Earthquake Resistant Design Code), even the structuralsystem is dual on the height of the building. Nevertheless, given the lack of the soft andweak groundfloor typology in HAZUS and the overall behavior of the building given by theRC frames in the groundfloor, the above-mentioned decision was made.The building fragility curves are computed for Slight, Moderate, Extensive and Completestructural and nonstructural damage states. Each fragility curve is characterized by median

and lognormal standard deviation () values. Median values of spectral displacement definethe thresholds of Slight, Moderate, Extensive and Complete damage states. The probabilityof being in or exceeding a given damage state is modeled as a cumulative lognormaldistribution. For structural and nonstructural damage, given the spectral displacement, SD,the probability of being in or exceeding a damage state, ds, is modeled as, (HAZUS, 1999):

[ ]

=dsdds

SDSDds

,Sln

1P

(1)

where: dsd,S is the median value of spectral displacement at which the building

reaches the threshold of the damage state, ds,ds is the standard deviation of the natural logarithm of spectral

displacement of damage state, ds, and

is the standard normal cumulative distribution function.

The parameters of the building fragility curves for structural damage states for C1H building

typology designed according to a low code are [HAZUS, 1999], Table 3:

Table 3. Values of building fragility curve parameters for structural damage states

Slight Moderate Extensive Complete

dsd,S , cm ds dsd,S , cm ds dsd,S , cm ds dsd,S , cm ds

5.1 0.70 8.2 0.81 20.4 0.89 51.1 0.98

The parameters of the building fragility curves for nonstructural damage states for C1Hbuilding typology designed according to a low code are [HAZUS, 1999], Table 4:

Table 4. Values of building fragility curve parameters for nonstructural damage states

Slight Moderate Extensive Complete

dsd,S , cm ds dsd,S , cm ds dsd,S , cm ds dsd,S , cm ds

8.2 0.87 16.4 0.96 51.1 1.02 102.3 1.06

The building fragility curves for both structural and nonstructural damage states arepresented in Figure 12.

Given the expected spectral displacements presented in Table 1 and Table 2 and thebuilding fragility curves presented in Figure 12, the probabilities of being in a givenstructural/nonstructural damage state are reported in Tables 5 and 6 for the existing building

and in Tables 7 and 8 for the seismically rehabilitated building.


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0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 20 40 60 80 100 120

SD, cm

P(>DS|S

Slight

Moderate

Extensive

Complete

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 20 40 60 80 100 120

SD, cm

P(>ds|SD

Slight

Moderate

Extensive

Complete

Figure 12a. Building fragility curves for structural

damage statesFigure 12b. Building fragility curves for

nonstructural damage states

Table 5. Probabilities of being in a given structural damage state existing building


PGA ['g] = PGA['g] =Damage

state, ds0.10 0.24 0.35 0.10 0.24 0.35

None 5.64E-01 5.66E-02 1.28E-02 8.36E-01 1.58E-01 4.04E-02

Slight 2.00E-01 1.59E-01 7.60E-02 8.71E-02 2.29E-01 1.36E-01

Moderate 1.90E-01 4.07E-01 3.33E-01 6.71E-02 3.92E-01 3.97E-01

Extensive 3.93E-02 2.66E-01 3.53E-01 8.85E-03 1.70E-01 2.92E-01

Complete 6.87E-03 1.12E-01 2.25E-01 1.15E-03 5.12E-02 1.35E-01

Table 6. Probabilities of being in a given nonstructural damage state existing building

X direction Y directionPGA ['g] = PGA['g] =Damage

state, ds0.10 0.24 0.35 0.10 0.24 0.35

None 5.64E-01 5.66E-02 1.28E-02 8.36E-01 1.58E-01 4.04E-02

Slight 2.00E-01 1.59E-01 7.60E-02 8.71E-02 2.29E-01 1.36E-01

Moderate 1.90E-01 4.07E-01 3.33E-01 6.71E-02 3.92E-01 3.97E-01


Complete 6.87E-03 1.12E-01 2.25E-01 1.15E-03 5.12E-02 1.35E-01

Table 7. Probabilities of being in a given structural damage state seismically rehabilitatedbuilding


PGA ['g] = PGA['g] =Damagestate, ds

0.10 0.24 0.35 0.10 0.24 0.35

None 9.34E-01 3.37E-01 1.25E-01 9.82E-01 6.08E-01 3.24E-01

Slight 3.59E-02 2.49E-01 2.15E-01 9.47E-03 1.85E-01 2.50E-01

Moderate 2.67E-02 3.04E-01 4.04E-01 7.58E-03 1.69E-01 3.11E-01


Complete 3.05E-04 2.02E-02 6.32E-02 5.86E-05 5.47E-03 2.15E-02


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Table 8. Probabilities of being in a given nonstructural damage state seismicallyrehabilitated building


PGA ['g] = PGA['g] =Damagestate, ds

0.10 0.24 0.35 0.10 0.24 0.35

None 9.60E-01 5.80E-01 3.50E-01 9.87E-01 7.76E-01 5.69E-01

Slight 2.93E-02 2.37E-01 2.95E-01 9.76E-03 1.44E-01 2.42E-01

Moderate 9.89E-03 1.58E-01 2.83E-01 2.92E-03 7.19E-02 1.64E-01


Complete 6.60E-05 5.40E-03 1.94E-02 1.25E-05 1.32E-03 5.79E-03

The cost of damage is expressed as a percentage of the complete damage state. Theassumed relationship between damage states and repair/replacement costs, for bothstructural and non-structural components, is as follows [HAZUS, 1999]:

Slight damage: 2% of completeModerate damage: 10% of completeExtensive damage: 50% of complete

These values are consistent with and in the range of the damage definitions andcorresponding damage ratios presented in ATC-13 Earthquake Damage Evaluation Data forCalifornia.

Given the repair/replacement costs previously mentioned and the distribution of probabilitiesin Tables 5-8, the expected cost of damage given the incidence of an earthquake can beobtained. The expected costs of damage presented in the following are for structural and

nonstructural elements and are expressed as percentage of the replacement cost obtainedas weighted averages. The expected costs of damage for the existing building are reportedin Table 9 and the expected costs of damage for the seismically rehabilitated building arepresented in Table 10.

Table 9. Expected cost of damage for the existing building (% of replacement cost)



0.10 0.24 0.35 0.10 0.24 0.35

Structural damage 4.95 28.84 43.64 1.40 17.99 32.34

Nonstructural damage 1.68 12.07 20.84 0.48 6.83 13.96

Table 10. Expected cost of damage for the seismically rehabilitated building (% ofreplacement cost)



0.10 0.24 0.35 0.10 0.24 0.35

Structural damage 0.51 10.03 20.45 0.13 4.24 10.45

Nonstructural damage 0.19 3.55 7.94 0.05 1.44 3.71


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The design earthquake with 40% exceedance probability in 50 years (PGA=0.24g) isconsidered in the following for comparison purposes. Considering the occurrence of theseismic action in X and Y direction equally probable events forming a complete set, then theexpected cost of damage for the building (structural and nonstructural) is simply obtained asthe arithmetic mean of the expected costs in X and Y direction, Table 11. The reduction ofthe expected cost of damage by the seismic rehabilitation is also reported in Table 11.

Table 11. Expected cost of damage for PGA= 0.24g(% of replacement cost)

Existing buildingSeismicallyrehabilitated

building

Reduction byseismic

rehabilitation

Structural damage 23.42 7.14 16.28

Nonstructural damage 9.45 2.49 6.96

One can notice from Table 11 the important decrease of the expected losses (2.5 to 3times) due to the seismic rehabilitation of the building. If one considers the replacement cost

of the structural components at 400 Euro/sq.m. and the replacement cost of thenonstructural components at 500 Euro/sq.m, the expected reduction of the cost of damagein the case of incidence of the design earthquake might amount 100 Euro/sq.m(16.28%x400+6.96%x500). Moreover, if the building content is evaluated as the sum of thereplacement costs of structural and nonstructural components [HAZUS, 1999], the expectedreduction of the losses likely amount 200 Euro/sq.m.

CONCLUSIONS

The seismic rehabilitation solution presented in this paper provides good results for anexisting soft and weak groundfloor building in Bucharest. The employment of the fluid

viscous dampers in the groundfloor of the building provides supplemental energydissipation. The damper configuration is chosen in such a way as to use as much aspossible the interstory velocity in the groundfloor. The upper structural walls are retrofittedwith steel plates in order to increase the capacity in shear. The assessment of the seismicrisk for both existing building and seismically rehabilitated building revealed the importantreduction of the expected seismic losses (2.53 times) for the latter case and the neteconomic benefit in the case of incidence of the design earthquake. Only economic lossesare assessed in this case study. The life losses are far beyond any economic losses and thelife safety of the residents is the strongest incentive for seismic rehabilitation of existingvulnerable buildings. Nevertheless, the economic issue is an important one for the residentsfor making the decision of seismic rehabilitation of the building. Moreover, the soft and weakgroundfloor buildings, along with pre 1940 RC high rise buildings, are now included in the

Romanian legal framework for urgent retrofitting.

ACKNOWLEDGEMENTS

NCSRR deeply acknowledge the generous, continuous and long-lasting financial support ofJapan International Cooperation Agency, JICA during the implementation of the TechnicalCooperation Project for Reduction of Seismic Risk for Buildings and Structures in Romania.The authors also acknowledge the strong technical support provided by engineer TateyoshiOkada (Affect Engineering, Japan short term JICA expert at NCSRR) in performingnonlinear analyses for the building and the valuable technical advices given by engineer

Takashi Kaminosono (Center for Better Living, Japan former JICA expert at NCSRR) andengineer Hiroto Kato (Building Research Institute, Tsukuba - JICA expert at NCSRR).


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REFERENCES

ATC 40 - Seismic Evaluation and Retrofit of Concrete Buildings, Report ATC-40, AppliedTechnology Council, Redwood City CA., 1996

Chesca, A.B., Seki, M., Vacareanu, R., Okada, T., Georgescu, B., Kaminosono, T., Kato, H.

Seismic Rehabilitation of an Existing Soft and Weak Groundfloor Building. Case Study -Proceedings of the International Symposium on Seismic Risk Reduction, ISSRR2007,Bucharest, 2007

Chopra A. K., Goel R. K. - Capacity-Demand-Diagram Methods For Estimating SeismicDeformation Of Inelastic Structures: SDF Systems, Report No. PEER-1999/02, PacificEarthquake Engineering Research Center, 72 p., 1999

FEMA 356 - Prestandard and Commentary for the Seismic Rehabilitation of Buildings,Federal Emergency Management Agency, 2000

FEMA - HAZUS Technical Manual. Earthquake Loss Estimation Methodology, 3 Vol. 1999Hwang, J.S. Seismic Design of Structures with Viscous Dampers, International Training

Programs for Seismic Design of Building StructuresKelly T. E. - In-Structure Damping and Energy Dissipation, Holmes Design Group,

www.holmesgroup.com, 2001Miyamoto, H. K. & Scholl R. E. - Seismic Rehabilitation of a Historic Non-Ductile Soft Story

Concrete Structure Using Fluid Viscous Dampers,http://www.quakepro.com/new/prod_pages/dampening/rehab.htm, viewed March 14th,2007

Ramirez, O. M. Constantinou, M. C., Gomez, J. D., Whittaker A. S., & Chrysostomou, C. Z. -Evaluation of Simplified Methods of Analysis of Yielding Structures with DampingSystems, Earthquake Spectra, Vol. 18, No. 3, pages 501530, August 2002

55 Symposium Bucharest 07 056 Vacareanu

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