SEISMIC EVALUATION AND RETROFIT OF RC
BUILDING, IN NEPAL
Bir Bahadur KHADKAMEE12614

Supervisor:

Masanori TANIABSTRACTThe evaluation based on both site inspection and structural calculation to represent the seismic
performance of building in terms of the seismic index of structure IS and seismic index of
nonstructural elements IN is called seismic evaluation. The seismic performance is evaluated bychecking its ultimate strength capacity and deformation capacity. There are three different levels of
screening methods to find the seismic capacity of RC buildings in Japanese standard and guidelines. In
this study, the first and the second level of screening methods are used to evaluate an existing RC
building in Nepal. After the evaluation, it was found that the first and second floors are judged as
unsafe in both directions. For retrofit, optimum techniques shall be adopted. In this case shear wallswith two boundary columns are installed. After retrofitting, again, analysis is done by using
STERA-3D software. The result is compared as the second screening versus push over static (before
and after retrofit) and dynamic analysis (before and after retrofit). The criteria of seismic capacity
based on Nepalese standard are proposed by comparing Japanese and Nepalese standards.
Keywords: Seismic Evaluation, Nonlinear Frame Analysis, Seismic Retrofit.

1. INTRODUCTION
Nepal is a mountainous country and it lies in Earthquake prone zone. The seismic record shows thatmajor earthquakes strike the region in every 75-100 years period. The oldest record available of amajor earthquake dates back to 1255 AD. Three major earthquakes occurred in Kathmandu valley inthe 19th century in 1810, 1833 and 1866 AD. These earthquakes have devastated Kathmandu time andagain by claiming lives and livelihoods of thousands of people. The earthquake that occurred in 1255
not only killed one third of the population of the city but also killed the then incumbent king – Abhaya
Malla. Similarly, the earthquake occurred in 1934 was the largest earthquake in Nepal having
magnitude 8.3 on the Richter scale. More than 8000 people were killed in that earthquake.
Many buildings, especially in urban areas are constructed without proper structural designs andsupervision. It is necessary to check the seismic performance of such buildings. From the safety pointof view, the safety of human life is a primary concern. The purpose of this study is to be able to checkthe seismic performance of such buildings and retrofit if necessary which is the main part of thedisaster mitigation.

2. METHODOLOGYEnglish Version of the “Japanese Standard, Guidelines and Technical Manual for Seismic Evaluationand Seismic Retrofit of Existing Reinforced Concrete Buildings,2001” is used in this study. Afterevaluating and retrofitting by using this standard and guidelines, STERA 3D-V5.9 software is used forDisaster Management Section, Urban Development Department, Kathmandu Metropolitan City Office, Nepal.
International Institute of Seismology and Earthquake Engineering, Building Research Institute, Ibaraki, Japan.

1nonlinear analysis. There are three levels of screening procedure, the first, the second, and the thirdlevel screening. In the first level screening method, material strength and contribution of crosssectional areas of vertical members are considered. In the second level of screening method, theductility or deformation capacity of vertical members as well as their strength are considered. The
second method is more accurate than the first method. For the third level of screening method, thecontribution of strength and ductility of beams and diaphragm wall areas are also considered. It is
more detailed and accurate method than the second level. In all above mentioned methods, we have tofind the seismic index (IS) of the structure. The seismic index represents the seismic performance ofthe structure. This IS index is compared with the seismic demand index IS0. The seismic index of target
structure shall be calculated by Eq. (1) at each story and in each principal horizontal direction of abuilding. The irregularity index SD and the time index T may be used commonly for all stories anddirections.
Basic seismic index of the structures (E0) is a product of strength index C, ductility index F and story
modification factor φ. Structural irregularity index (SD) is to modify the basic seismic index ofstructure E0 and time index (T) is also used to reduce the seismic index of the target structure.

IS

(1)

= E0 . S D T

The seismic demand index of structure IS0 should be calculated by Eq. (2)IS0.= ES.Z.G.U(2)

The basic seismic demand ES is 0.8 for first screening and 0.6 for second and third screening level where
Z is zone index, G is ground index and U is usage index.
2.1. First level Screening Method:
The basic seismic index of structure E0 shall be calculated by using the following Eqs. (3) and (4) basedon approximate evaluation of the strength index C, the ductility index F, and the effective strength factor
α. The larger value is taken as E0 of the structure. If the story consists of extremely short columns E0
value shall be taken only by equation (4).

n 1(CW+α1.CC) FW
ni

(3)

n 1
(CSC+α2.CW+α3.CC).FSC
ni

(4)

E0 =

E0 =

Then, irregularity index (SD) and time index (T) are calculated with the standard guidelines. After that,the seismic index of the target structure (IS) is compared with seismic demand index of the target
building (IS0). If IS value is larger, the seismic performance of the building is judged as safe and wehave to evaluate it by the second screening method if the value is less than the demanded IS0 value.
2.2. Second level Screening Method:2

In this method, the axial force in the columns, reinforcement of the columns and shear walls are
considered to calculate the strengths and ductility of the vertical members. The vertical elements areclassified into five different categories. The shear force at ultimate flexural capacity (Qmu) andultimate shear capacity of columns and walls (Qsu) are calculated, and then their results werecompared.
Ductility dominant basic seismic index of structure is calculated as:
Vertical members shall be classified by their ductility indices F into three groups or less defined as thefirst, the second, and the third group. The basic seismic index, E0 is calculated as the following:

E0 =

n 1
2
2
2
E1  E2  E3
ni

(5)

Strength-dominant basic index of structure is calculated as:
The effective strength factor α in the second and higher groups should be calculated considering theeffects of yield deformations and clear heights of vertical members on the relationships between thestory shear forces and the drift angles. The minimum effective strength factor of the vertical members
should be used in each group. The basic seismic coefficient is calculated as:
E0 =





n 1
C1   j  j C j F1
ni

(6)

The strength index C is calculated by dividing the ultimate load-carrying capacity of the verticalmembers in the story concerned by the weight of the building including live load for seismic calculation
supported by the story concerned. Qu is the minimum of Qmu and Qsu.

C=

Qu
W

(7)

In this method we have to check the CTU*SD index which should be greater or equal to 0.3*Z*G*U. If
we supposed the value of Z, G and U is unity than CTU*SD ≥ 0.3.
2.3. Nonlinear frame analysis by STERA 3D:
Nonlinear static push over analysis and dynamic analysis were carried out by using STERA 3D
software. After the analysis of the target building with STERA 3D, the results are compared as second
screening versus push over static analysis before and after retrofit and dynamic analysis (nonlinear
earthquake response analysis) before and after retrofit. In dynamic analysis El Centro earthquake wasused as input ground motion.

3. CASE STUDY OF EXIXTING BUILDING IN NEPAL
3.1. Introduction of the Target Building
The target building in this study is the Alapot Health Post Building. This health post building is situatedat Alapot V.D.C., which is very near to Kathmandu Metropolitan City. It is a RC frame structure with
infill brick wall and was built in 2007. It represents the majority of the existing building quality of Nepal.
The size of the column is 230 mm * by 230 mm and beam size is 230 mm.* by 340 mm. The thickness ofthe slab is 110mm. The characteristic strength of concrete, fck =20 N/mm2 and yield strength of steel,3σy=415 N/mm2. The following Figs. 1 and 2 show picture of the building and first floor plan
respectively.

Figure 1. Alapot Health Post Building

Figure 2. First floor plan(dimensions are in cm).

3.2. Seismic Evaluation Results
The building is evaluated by considering brick wall as spandrel wall and without considering brickwall. In first screening level the building was judged as unsafe in all floors in both cases in both
directions. After that the building was evaluated by the second screening method. Tables 1 and 2 show
the results of seismic evaluation for original building by the second screening. In this method thebuilding was judged as safe in third story only in all conditions. Therefore, retrofit is needed in both
direction and four shear walls (two in each direction) in first floor and three shear walls (two in X
direction and one in Y direction) in second floor were installed. The seismic evaluation results of thetarget building before and after retrofit (the second screening method) are shown in Tables 1 and 2. As
shown in Tables 1 and 2, the retrofitted building was judged as safe in all floors in both directions.
Table 1. X- Direction
Conditionwith wallwithout wall

Story
3
2
1
3
2
1

Is
1.32
0.72
0.67
1.32
0.68
0.50

Before retrofit
Calculated CTU*SD Judgement
0.41
Safe
0.28
Unsafe0.26
Unsafe
0.41
Safe
0.21
Unsafe0.16
Unsafe

4

Is
1.32
1.44
0.88
1.32
1.43
0.83

After retrofit
Calculated CTU*SD Judgement
0.41
Safe
1.44
Safe
0.88
Safe
0.41
Safe
1.43
Safe
0.83
Safe

Table 2. Y- Direction
Conditionwith wallwithout wall

Story
3
2
1
3
2
1

Is
1.32
0.48
0.46
1.32
0.57
0.41

Before retrofit
Calculated CTU*SD Judgement
0.41
Safe
0.33
Unsafe0.17
Unsafe
0.41
Safe
0.17
Unsafe0.13
Unsafe

Is
1.32
0.85
0.91
1.32
0.93
0.84

After retrofit
Calculated CTU*SD Judgement
0.41
Safe
0.77
Safe
0.91
Safe
0.41
Safe
0.84
Safe
0.84
Safe

3.3. STERA 3D Results
The nonlinear static pushover analysis was conducted by assuming the lateral loading condition as Ai
distribution. Before retrofit, the yielding at the exterior ends of the beams and both ends of thecolumns was observed in the first story, but there was no yielded member in the second and the third
stories in both directions. After retrofit, the strength of the first and the second stories were larger than
the third story, although the third story had a large IS value. The large value of IS for the third story wasdue to the slender columns having large F values. Therefore, being the third story as the weakest story,
the columns were started to yield from the third story in the STERA 3D analysis and these results werealso in similar pattern with second screening method.
Nonlinear earthquake response analysis was conducted by applying the strong ground motion of the El
Centro Earthquake. The results of the dynamic analysis with the El Centro earthquake ground motion
are shown in the Figures. 3 and 4.

Figure 3. Nonlinear dynamic analysis
with El Centro earthquake groundmotion (before retrofit).

Figure 4 Nonlinear dynamic analysis
with El Centro earthquake groundmotion (after retrofit).

Before retrofit, the yielding at both ends of the first floor columns and yielding at the exterior end of
the beams were observed in the first story. After retrofit, the first and second stories became stronger
and no damage occurred, but the third story suffered by the yielding of all columns because it became
weak as compared to the other two stories. In fact, the pattern of the result was similar as in case of thestatic analysis.

54. COMPARISON OF JAPANESE STANDARD WITH NEPALESE STANDARD
In Japanese standard, CTU*SD shall be larger than 0.3*Z*G*U, where 0.3 corresponds to structuralcharacteristic factor (Ds) and base shear coefficient (C0) corresponding to high ductile structure forsecond phase design. In the same way, in Nepalese standard, the value corresponding to structural
performance factor K (which is 1 for high ductile structure) and basic seismic coefficient C (which is0.08), will be 0.08. Therefore for Nepalese standard CTU*SD ≥ 0.08*Z*I should be appropriate.
Seismic demand index IS0 = 0.6 in Japanese standard which is very close to basic seismic index E0
which is calculated by C*F*φ. In the same way E0 for Nepalese standard is 0.12 to 0.256. Therefore
the suitable value for demand index IS0 will be 0.25. But it needs a lot of theoretical and practicalinvestigations to finalize the demand indices and it is the most challenging job.
5. CONCLUSION AND RECOMMENDATIONSIn the first screening method the building was judged as unsafe in all stories in both directions whereas
in the second screening the third story was judged as safe. After retrofit, it was safe in all the stories inboth directions. In the static push-over analysis and dynamic analysis by STERA 3D with the El
Centro Earthquake ground motion yielding of columns is started in the third floor. It is because, after
retrofit, the first and the second stories become very strong than the third story and failure was started
from the weakest part.
On the basis of this study the following are some recommendations to increase the efficiency andaccuracy of this standard.

It is recommended to consider the contribution of non-structural elements like brick walls,
hollow concrete blocks etc.

The demand value of IS0 and CTU*SD index in Japan may be slightly larger in case of Nepal due
to its low seismicity. Therefore, further study to get accurate value of demand indexes isstrongly recommended.

There is no any provision in case of the foundation which is one of the very important parts ofany structure. Therefore, a further study is strongly recommended towards the foundation.

ACKNOWLEDGEMENTS
Foremost, I would like to express my sincere gratitude to my supervisor Dr. Masanori TANI, researchengineer from IISEE for the continuous support to my master paper. His useful comments, remarks,
motivation and engagement through the learning process helped me in all aspects. Furthermore, I
would like to thank my advisor Dr. Koichi MORITA, chief research engineer from IISEE for
introducing me to the topic as well for his support to my individual study.

REFERENCES
Bilham, R, V.K. Gaur and P. Molnar, 2001, Himalayan Seismic Hazard, 293, 1442-4.
Indian Standard Code of practice for design loads (other than earthquake) for building andstructures, Part (1) and (2) 1987.
JICA, 2002, final report vol-I,II,III and IV.
Minister of Home Affairs of Nepal, 2009 Oct., Nepal Disaster Report 2009
Muangnok S, Master thesis of graduate School of Kasetsart University, page-34.
NBC volumes 101, 102, 103, and 105, 1994.
Saito T., STERA_3D Ver.5.9.
The Japan Building Disaster Prevention Association (JBDPA) (first English version 2001).

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