Citation: AIT ALI SLIMANE, N., T. Saito (2022), Comparison of retrofitting methods on an existing
residential RC building in Algeria, heavily damaged by the 2003 Boumerdes earthquake, Synopsis of
IISEE-GRIPS Master’s Thesis.

COMPARISON OF RETROFITTING METHODS ON
AN EXISTING RESIDENTIAL RC BUILDING IN
ALGERIA, HEAVILY DAMAGED BY THE 2003
BOUMERDES EARTHQUAKE
Nassim Ait Ali Slimane1
MEE21707

Supervisor: Taiki SAITO2ABSTRACTThe 2003 Boumerdes earthquake caused a large amount of damage, particularly in the city of Boumerdes.
After the disaster, a revision of Algerian code and the retrofitting of the 1,200 dwellings of Ibn Khaldouncity were made. The study of the city was made by a group of engineers from the National Body forTechnical Control of Construction of the East (CTC-EST), and tests were carried out just after thedisaster by a group of researchers from the National Center for Applied Research in ParaseismicEngineering (CGS) and the Internal Geophysics and Tectonophysics Laboratory (IRD), then other tests
were carried out after the rehabilitation as part of a magister thesis in 2010. The retrofitting method atthat time was based on an experimental approach without following a specific code. Japan, being
especially advanced in seismic evaluation and rehabilitation of different structures, the Japan Building
Disaster Prevention Association (JBDPA) method was used during this study to evaluate and retrofit abuilding of Boumerdes and compare 4 models of retrofitting under 3 different earthquakes. The
comparison was based on the seismic index “Is”, the story drift and shear at each floor, to find the mostsafely and economically effective result. During the study, the Japanese code and factor had to beadapted to Algerian seismic activity and ground proprieties. The use of STERA-3D and the time history
analysis method was also necessary for the calculations. The final result showed the model of the after
earthquake retrofit having higher safety, but the JBDPA method proposed retrofitting model with lower
capacity, which satisfy the minimum safety conditions and were more economical than the retrofit
proposed at that time. Therefore, it would be beneficial for Algeria to be inspired by the JBDPA method
for the future changes in the Algerian seismic code and add to it an evaluation and rehabilitation
procedure adaptable to the different seismic zones of Algeria.
Keywords: Reinforced concrete (RC) building, seismic evaluation, retrofitting, time history analysis.
1. INTRODUCTIONOn May 21, 2003, Boumerdes in the northern part of Algeria were struck by a disaster that damaged alarge part of the residential RC buildings in the city. This disaster led to the revision of the Algerianseismic code in its current version RPA99/V2003 and the retrofitting of housing in the city of Ibn
Khaldoun. After the disaster, a study of 15 heavily damaged 5-floor residential RC buildings in
Boumerdes city was made by a group of engineers from the CTC-EST to evaluate the seismic
performance of the buildings and propose the appropriate rehabilitation measures. A first series of tests
1

University of Science and Technology Houari Boumediene (USTHB), Faculty of Civil Engineering, Bab
Ezzouar, Algeria.
2
Professor, Department of Architecture and Civil Engineering, Toyohashi University of Technology.

1was carried out just after the earthquake in 2003 by a group of researchers from the CGS and IRD thena second after the rehabilitation as part of a magister thesis in 2010. The evaluation of the seismic
performance was possible using the Algerian code, RPA99, but concerning the retrofitting method itself,
it was based on an experimental approach using RC column jacketing and RC shear walls added to thebuilding without following a specific code, due to the absence of a rehabilitation code implemented at
the time. The objectives of this research is to compare different methods of retrofitting for RC buildings
applicable in Algeria (column jacketing and shear walls) with the retrofitting done after the 2003
earthquake, using the JBDPA method for the evaluation, rehabilitation and retrofitting, and test theapplication of the JBDPA method and the different factors in the Algerian zone.
2. TARGET BUILDING
The 1200 housing units of the Ibn-Khaldoune city were made of RC residential buildings with 5-floors
and a basement, with a floor height of 3 m, forming 1 to 4 blocks separated by expansion joints of 2 cm,
the plan dimensions of the building were 10.9*21.7 m² or 10.9*18 m², for this study the dimensions of
10.9*21.7 m² were taken. The plan of the building is shown in Figure 1. The building is composed of 6
spans in the longitudinal
direction and 2 in thetransverse direction, the roof
total area (ARoof) is 236.53 m²
with a weight (Qroof) of 10 kN/m², the standard floor area
without balcony (AFloor) is
179.03 m² with a weight(Qfloor) of 13 kN /m², and thebalcony area (ABalcony) is 57.51
m² with a weight (QBalcony) of
Figure 1. Standard plan of the building.
6.5 kN/m². The load for theroof (Proof) was calculated 2365.30 kN and the load for a standard floor (Pfloor) was calculated 2701.11
kN.
The RC columns were oriented transversely, for the edge columns (C1) and for the central
columns (C2). The transverse RC beams are (B1), the longitudinal RC beams are for the edge beams(B1), the central RC beams (B2), and (B3), (B4), for the RC balcony’s beams. The main bars were 8D16
and the hoops were 2ф8 with 150mm spacing. The concrete minimum design compressive strength (Fc)
was taken at 25 N/mm², and the yield strength of reinforcing bars (σy) and the yield strength of shear
reinforcement bars (σyw) were both taken at 413 N/mm².
The neglected basement was formed by a peripheral RC wall. The stairs were oriented in
the transverse direction, supported by transversal RC walls with a thickness of 150 mm. The exterior
fillings were masonry walls, made up of hollow bricks of 10*20*30 cm3 in the plane of the porticoes.
3. SEISMIC EVALUATION AND RETROFITTING
3.1. Seismic performance by JBDPA 2nd level screening procedure
By the JBDPA method, the calculation of the seismic index and the seismic demand index of the target
building was done using Eq. (1) and Eq. (2), and the evaluation of its safety by Eq. (3) and Eq. (4).
𝐼𝑠 = 𝐸0 ∗ 𝑆𝐷 ∗ 𝑇,

(1)

𝐼𝑠𝑜 = 𝐸𝑠 ∗ 𝑍 ∗ 𝐺 ∗ 𝑈,
𝐼𝑠 ≥ 𝐼𝑠𝑜 ,

(2)
(3)

2

𝐶𝑇𝑈 ∗ 𝑆𝐷 ≥ 𝐷𝑆 ∗ 𝑍 ∗ 𝐺 ∗ 𝑈,

(4)

Where, Is is seismic index of the structure, E0 is basic seismic index of structure, SD is irregularity index,
T is time index, ISO is seismic demand index of structure, ES is basic seismic demand index of structure,
Z is seismic hazard zoning factor, G is ground index, U is usage index, CTU is cumulative strength index
at the ultimate deformation of structure, and DS is structural characteristic factor.
With Algeria having a different seismic intensity, the seismic hazard zoning factor wasrecalculated using the target response spectrum and the natural period of the building to get Z=0.12 and
Z=0.82. The structural characteristic factor “Ds” were also modified to Ds=0.2. The result for Z=0.12
and Ds=0.2 gave safe judgment, the rest of the calculations were conduct for Z=0.82 and Ds=0.2.
Table 1 shows the first and second conditions to evaluate the building safety, using
Japanese factor adapted with the Japanese target response spectrum at safety limits. It is found that all
stories of the target building need retrofitting.

Story
5
4
3
2
1
Story
5
4
3
2
1

Table 1. Seismic performance evaluation of the target building.
ϕF
Ctu*SD
Ds*Z*G*U
Evaluation
0,6
2,59
0,19
0,2*0,82*1*1
Safe
0,67
2,59
0,12
0,16
Not safe
0,75
2,59
0,10
0,16
Not safe
0,86
2,59
0,10
0,16
Not safe
1,00
2,59
0,10
0,16
Not safe
E01
E02
IS
ISO
Evaluation
0,49
0,49
0,488
0,489
Need Retrofitting
0,31
0,31
0,311
0,489
Need Retrofitting
0,26
0,26
0,264
0,489
Need Retrofitting
0,25
0,25
0,248
0,489
Need Retrofitting
0,25
0,25
0,247
0,489
Need Retrofitting

3.2. Retrofitting of the target building

By the JBDPA method, the required additional strength at each story was calculated using the following
Eq. (5) and the evaluation using Eq. (3) and Eq. (4).
∆𝑄𝑢𝑖 = ∆𝐼𝑠𝑖 ∗ ∑ 𝑤𝑖 = (𝐼𝑠𝑜 − 𝐼𝑠 ) ∗ ∑ 𝑤𝑖

(5)

The retrofitting was made in 3 different cases, by jacketing of all the columns, RC Infill
walls, and using both methods. The 3 retrofits are shown in Figure 2-4.

Figure 2. Retrofit plan for both column jacketing and infill walls.

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Table 2. Column dimensions for RC
jacketing retrofitting.

Figure 3. Column RC jacketing
retrofitting.

Figure 4. Retrofit plan for RC infill walls.

The result of evaluation for the building without retrofitting, with column jacketing andwith infill walls are shown in Figure 5. It is confirmed that the building with retrofitting is safe for all
stories. The building with both column jacketing and infill walls was not included in the comparison
because of a lack of information regarding the method to calculate the Is index for this case.

5.00
4.00
3.00
2.00
1.00
0.00

Jacketing

Infill Walls

Without

Floor

Floor

Without

0.50
1.00
Seismic index “Is”

1.50

5.00
4.00
3.00
2.00
1.00
0.00

Jacketing

0.50

Infill Walls

1.00

1.50

Ctu*SD

Figure 5. Comparison of the seismic index “Is” and the second safety condition “Ctu*SD” .

4. TIME HISTOTRY ANALYSIS
4.1. Analysis method and results
Before comparing the 4 models, a first test on STERA-3D was made comparing the results of thebuilding with and without considering the masonry walls using the 2003 Boumerdes Eq. The result(Figure 6) showed considerable change by considering the secondary masonry walls, so the rest of thecalculation were made considering the secondary masonry wall.
Using the 3 earthquakes (2003 Boumerdes Eq, 1995 Kobe Eq, 1940 El centro Eq), time
history analysis was applied on the 4 models to get the story drift sdx and shear sfx on each floor. The
results are shown in Figures 6-8.

4

Infill Walls

No MasonryJacketing

5
4
3
2
1

Floor

Floor

Both

0

5

10

With Masonry

5
4
3
2
1

15

0

2000

sdx(cm)

4000

6000

sfx(kN)

Figure 6. Story drift “sdx” and shear “sfx” for the record of 2003 Boumerdes Eq.
Infill Walls

5
4
3
2
1

Floor

Floor

Both

0

5

10

JacketingWith Masonry06000
sfx(kN)

5
4
3
2
1

15

3000

sdx(cm)

9000

12000

Figure 7. Story drift “sdx” and shear “sfx” for the record of 1995 Kobe Eq.
Infill Walls

5
4
3
2
1

Floor

Floor

Both

0

2

4
sdx(cm)6

JacketingWith Masonry04000
sfx(kN)

5
4
3
2
1

8

2000

6000

8000

Figure 8. Story drift “sdx” and shear “sfx” for the record of 1940 El Centro Eq.
The comparison of story drift and shear on each floor using time history analysis on Figures
6-8 showed better results with the model of both methods, followed by infill walls and column jacketing.

The volume of additional reinforced concrete added foreach retrofitting method was calculated to have an idea
about the difference in price for each model. The results
are shown in Figure 9.
The comparison of additional reinforced concrete for the 3
retrofitting methods on Figure 3 showed lower additional
RC for column jacketing retrofit, than, infill walls retrofit,with the higher value for the model with the both methods.
Higher volume of reinforced concrete implies higher costfor the building retrofit, while those additional cost are notalways needed to satisfy the building safety.

5

Vrc.add (m3)

4.2. Additional reinforced concrete volume after retrofitting
40.00
30.00
20.00
10.00
0.00

25.03

28.35

Jacketing

Infill
Walls

33.57

Both

Figure 9. Volume in m3 of additional
reinforced concrete, added for eachretrofitting method.

5. CONCLUSIONSTo adapt and apply the Japanese method for evaluation and retrofitting on Algerian geological andseismic conditions, some factors, particularly the seismic hazard zoning factor “Z” and the structuralcharacteristic factor “DS” in Japanese code were modified according to Algerian conditions.
The JBDPA pointed that it is important to include masonry walls in the rest of calculations
even for secondary masonry walls.
By comparing 4 models (without retrofitting, with RC column jacketing retrofitting, with
RC infill walls retrofitting, and with both column jacketing and infill walls that was applied on the target
building after the 2003 Boumerdes Eq) based on the story drift and the shear, using STERA-3D and thetime history analysis method showed the efficiency of RC infill walls compared to RC column jacketing.
The model applied after the 2003 Boumerdes earthquake was as much efficient if not more efficientthan the retrofitting with RC infill walls in some case.
The comparison of additional volume of reinforced concrete for the 3 retrofitting methods
showed that even if the retrofitting applied by Algerian engineers in the 4th model gave better result, it
could have cost less while still satisfying the safety conditions by just using a different method ofretrofitting. The same applies to the retrofitting with infill walls that will give better results than column
jacketing retrofit but cost more regarding only the volume of reinforced concrete needed for its execution.
ACKNOWLEDGEMENTSFirst and foremost, I would like to express my sincere gratitude to Dr. T. Saito (Professor, Departmentof Architecture and Civil Engineering, Toyohashi University of Technology, Japan) for supervising me
and giving me his time, advice, suggestions, and welcoming me at Toyohashi University during myindividual study and also my advisor Dr. M. Ito and all the other staff members at IISEE/BRI for theirsupport and encouragement during this training program. Thanks, are also due to Dr. A. BOURZAM(Researcher, Department of Structures and Materials, University of Science and Technology Houari
Boumediene, Algeria) for recommending and permitting me to join this program. Further, I am
extremely thankful to Dr. T. AZUHATA (BRI) for his advice and comments regarding the topic of myindividual studies. I would like to also express my gratitude to JICA for giving me chance to follow thiscourse by financial supporting.
REFERENCES
Kacimi el-hassani, A.A, 2010, Magister thesis on evaluation des rehabilitations menees sur desbatiments affectes par le seisme de boumerdes du 21 mai 2003.
Youcef, M., inoue, A., 2008, WCEE14 paper on seismic evaluation and retrofit plan of existing
reinforced concrete buildings of algiers in algeria.
Khellafi, A.M., 2017-2018, Thesis on Caractérisation sismique de sites à partir d’enregistrements
accélérométriques en surface libre.
Nwetnwet, Y., 2020, Master thesis on seismic evaluation and retrofitting of existing reinforced concretebuilding in myanmar.
Japan code: Standard for Seismic Evaluation of Existing RC Buildings, and Technical Manual for
Seismic Evaluation and Seismic Retrofit of Existing RC Building, 2001.
Algerian code: Algerian earthquake resistant regulations (RPA99/v2003).
Saito, T., STERA-3D Software Ver5.8.
Saito, T., STERA-3D User Manuel Ver5.8, BRI.
Saito, T., STERA-3D Technical Manual, Building Research Institute Ver3.2, BRI.
CRAAG web site, http://www.cgs-dz.org/index.php/fr/service-en-ligne-telechargement/109-demanded-enregistrements-accelerometriques.

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