Citation: Biswas, R., M. Seki (2020), Detail seismic performance evaluation of a twelve (12) storied
official building in Dhaka and suitable retrofitting technique, Synopsis of IISEE-GRIPS master report.

DETAIL SEISMIC PERFORMANCE EVALUATION OF
A TWELVE (12) STORIED OFFICIAL BUILDING IN
DHAKA AND SUITABLE RETROFITTINGTECHNIQUE
Rajib Kanti BISWAS1,2

Supervisor:

Matsutaro SEKI3

ABSTRACTThe main purpose of this study is the evaluation of the seismic performance of the existing RC building
situated in Dhaka and constructed before the establishment of the National building code, 1993.
Significance changes in seismic provisions have been brought in upcoming Bangladesh National
Building Code (BNBC, 2017, draft). Therefore, it is necessary to evaluate seismic performance and thestrengthening of old buildings to keep compatibility with the requirement of updated building code. This
study compares the seismic evaluation results of building by the 2nd level screening method of Japan
Building Disaster Prevention Association (JBDPA), 2001, and detail seismic evaluation method andsuggests a suitable retrofit technique. To evaluate the seismic performance of the building by detailseismic evaluation method, non-linear static pushover analysis was performed according to ATC 40,
1996 / FEMA 273, 1997 /356, 2000 /440, 2005 and ASCE 41, 2013. The damage distribution andsequence of the collapse of the building were observed. It was found that detail seismic evaluation
method provided most rational and practical results rather than 2nd level screening method of JBDPA,
2001 from the viewpoint of seismic evaluation of the building due to the target building was found tobe weak-beam and high-rise building. Furthermore, the required strength for retrofit was easily
estimated by this method. The new shear wall for retrofit proved to be effective in increasing thenecessary seismic capacity of the building.
Keywords: Seismic evaluation, Detail seismic evaluation method, Non-linear analysis, Retrofit.
1. INTRODUCTION
Bangladesh, a country having more than 160 million people, has suffered from the number of naturalcalamities like earthquakes, fire hazards, floods, and cyclones in the recent past. Bangladesh is locatedin one of the most seismically active regions. There are three tectonic plates around this country named
the Indian plate, the Eurasian plate, and the Burmese plate. Moreover, five major faults around thisregion are also the sources of the incident of earthquakes. The present generation of people of
Bangladesh didn’t witness any severe ground shaking. Due to the activity of the plate boundaries, active
fault zones, and statistical data of previous earthquakes around Bangladesh, there is a possibility to occur
a high magnitude of an earthquake. The first guideline for seismic design named BNBC was publishedin 1993. But due to lack of monitoring system and proper legal enforcement system, a large number ofbuildings have been constructed without considering the requirement of seismic provisions.
__________________________
1

Public Works Department, Bangladesh.
IISEE-GRIPS master course student.
3
Visiting Research Fellow, International Institute of Seismology and Earthquake Engineering, BRI.
2

Moreover, the buildings built before publishing BNBC 1993, did not follow the building
code. Therefore, the majority of the buildings in Bangladesh are under the risk of devastating fate if a1strong earthquake hits this area. At present, Bangladesh National Building Code is updated by the panelof experts and is in its final phase of getting approval. Significant changes in seismic code have been
made in BNBC 2017 (Draft). It is, therefore, necessary to evaluate seismic performance andstrengthening of old infrastructure to keep the compatibility with the requirement of updated buildingcode.
2. THEORY AND METHODOLOGY
The selected building was evaluated by using both the Japanese Building Disaster Prevention
Association (JBDPA), 2001 Standard for second level screening and detail seismic evaluation method
which was proposed by Y. Nakajima, M. Seki, H. Suga, and R. Islam, 2020. In the procedure of 2ndlevel screening of JBDPA, 2001, the beams of the structure are considered as stiff elements. “Theductility capacity of columns and walls is estimatedcrudely for their failure modes (shear or flexure) andbased on shear-to-flexural strength ratios. The
combination of different ductility levels and shear
resistances of vertical members were considered inestimating the earthquake resistance of a structure (Otani,2000)”. On the other hand, the proposed detail seismic
evaluation method is based on both the Japanese and theAmerican methods. The Japanese 2nd seismic evaluation
method targets mainly weak-column buildings designedby the old Japanese building code so that it is insufficientto accurately estimate the weak-beam buildings.
Therefore, the new detail seismic evaluation method is
proposed to estimate the weak-beam buildings. It has anadvantage of the harmonization with the American
seismic evaluation method and of being able to indicate
the seismic capacity of a building as a simple seismicindex as the same as 2nd seismic evaluation method. Thismethod includes nonlinear static pushover analysis. In theAmerican seismic evaluation method, the performancelevel of each structural member on the process of
pushover analysis is decided based on ATC40. The Figure 1. Nonlinear static analysis(Courtesy: Y. Nakajima, M. Seki, H.
example of hinge mechanism and acceptance criteria isshown in the figures. Three acceptance criteria (ATC40, Suga, and R. Islam, 2020).
ASCE41): Immediate Occupancy (IO), Life Safety (LS),Collapse prevention (CP). For the proposed method, CPpoint is adopted as the performance limit displacement
for the capacity of the structure.
The procedure of determination of seismicindex of structure (Is) is given below. The spectral
acceleration vs. spectral displacement curve is shown in
Figure 5. The seismic index CPIS at CP point and LPIS at
LP point shall be calculated as following Eqs. (1) and (2).
𝐶𝑃𝐼𝑠 = 𝐶𝑃𝐶 × 𝐶𝑃𝐹 = 𝐶𝑃𝐶 × 𝐶𝑃𝜇(1)

𝐿𝑃𝐼𝑠 = 𝐿𝑃𝐶 × 𝐿𝑃𝐹 = 𝐿𝑃𝐶 × 𝐿𝑃𝜇(2)

Figure 2. Evaluation of C index and F
index by CP point and LP point(Courtesy: Y. Nakajima, M. Seki, H.
Suga, and R. Islam, 2020).

where CP point: A point where the collapse prevention at some members in the structure occurred.
𝐶𝑃𝐶 : Strength index at CP point
𝐶𝑃𝐹 : Ductility index at CP point2

LP point: A point where the limited
displacement defined in the seismic code
occurred. Generally, the 0.02 story drift ratio isdefined as criteria.
𝐿𝑃𝐶 : Strength index at LP point
𝐿𝑃𝐹 : Ductility index at LP point
𝐼𝑠 = 𝑀𝑖𝑛( 𝐶𝑃𝐼𝑆 , 𝐿𝑃𝐼𝑆 )Table 1. Legend of eachpoint in Figure
2.
Collapse
Limited
Point
Yield Prevention displacementof memberof building
Notation
YPCPLP
Strength
𝑌𝑃𝐶
𝐿𝑃𝐶
𝐶𝑃𝐶
Deformation
𝑌𝑃𝛿
𝐿𝑃𝛿
𝐶𝑃𝛿

(3)

The judgement of seismic safety: The following equation will judge the seismic safety ofthe structure.
𝐼𝑠 = 𝑀𝑖𝑛( 𝐶𝑃𝐼𝑆 , 𝐶𝑃𝐼𝑆 ) ≥ 𝐼𝑠0(4)

The procedure of determination of each story’s Is is given below. After the judgement of
the seismic safety of the building as a whole, the seismic index Is of each story of the building can beeasily estimated under consideration of CP point and yield point for each story. The following equation
can represent the Is value for each story.
𝑄𝑖
× 𝐹𝑖 × 𝜑
𝑛
∑𝑖 𝑊𝑖

(5)

Shear Force, Q𝐼𝑠 =where 𝑄𝑖 = Story Shear at level i∑𝑛𝑖 𝑊𝑖 = Part of the total seismic weight of thestructure assigned to level i𝛿
𝐹𝑖 = 𝑖 = 𝜇𝑖 = ductility index at level i

At CP occurrence step
𝛿𝑦1
𝛿𝑦2
𝛿𝑦3
𝛿𝑦n

𝛿1
𝛿2

𝛿n

𝛿3

1F
2F
3F
(nF)

Story Drift𝛿𝑦𝑖Figure 3. The calculation procedure of theseismic index Is for each story of the building.

𝜑 = Story shear modification factor

The calculation procedure of required shear strength for retrofit is given below. After thejudgement of seismic safety of the structure, if the seismic capacity is insufficient, the retrofit plan shallbe applied. The procedure of calculation of the required strength is described below. The outline of theprocedure is presented in Figure 4.
Steps:
After Retrofit
Step 1: RIS0: Newly defined based on structural type afterC
retrofit
R
R∆C[Moment resisting type or Dual type]
CC
Step 2: IS = C x F: Current IS index
Step 3: Assume RF: F index after retrofit
Before Retrofit
RF < F
Step 4: R∆C: Required shear coefficientF
F F
R∆C = RIs0/RF - C
RStep 5: R∆Q: Required shear force
Figure 4. The calculation procedure of requiredR∆Q = R∆C x W
strength for retrofit.
3. DATA
Twelve (12) Storied Government building is one of the first high rise buildings constructed by Public
Works Department. The building was built more than fifty years ago and located in the seismic zone -II(as per BNBC 2017 draft). The building does not have an architectural and structural drawing. The detailinvestigations were done under the guidelines of “CNCRP” manuals. Finally, the as-built drawing of3

the structure was prepared. The various essential features of the target building are shown in Table 2.
This building has three blocks, which are separated by an expansion gap. The typical floor beam layout
plan is presented in Figure 1. The building has a 150 mm thick slab. The concrete core test was conducted
to get the concrete compressive strength. In the time of the subsoil investigation, the soil type is foundto be SC as per the BNBC 2017 draft. The first block of the building is selected for this research. Thereis a total of 06 (six) columns and 04 (four) shear walls.
Table 2. Important features of Target building.
Information
Name of the building: Twelve (12) Story
Government Building
Number of stories: Twelve (12)Structure and building type: Reinforced
Concrete Office Building
Occupancy Categories: III
Importance factor: 1.25
Seismic Zone: 2 (Z=0.2, BNBC 2017 draft)
Soil Type: SC (BNBC 2017 draft)
Concrete Strength: 13.5 MPa
Steel: 275 MPa
Total seismic weight (Block 1): 51856 kN
Total area (Block 1): 4704.61 m2

Figure 5. Typical floor plan.

4. RESULTS AND DISCUSSION
The seismic demand of the target building is evaluated considering the different structure types. In Xdirection, structural type is concrete moment resisting frame system and in Y-direction, structural typeis dual frame system. Iso values are found to be 0.21 and 0.36 in X and Y -direction respectively.
Seismic evaluation of the building by using 2nd level screening evaluation: Three blocks ofthe building are separated by an expansion gap (25 mm). Due to the poor expansion gap, the irregularity
index is set as 0.95. The Time Index is set as 0.90 taking into consideration of deterioration ofreinforcement. Figure 6 illustrates the comparison of the seismic evaluation of the target building forboth directions. It is seen that the 1F to 9F requires retrofitting in the X-direction and 1F to 7F requires
retrofitting in the Y-direction.

0.00

0.20
0.40
Seismic Index

0.60

0.00

Safe

(Y-Direction)

ISO = 0.36

12
11
10
9
8
7
6
5
4
3
2
1

UnsafeStory ID

Safe

ISO = 0.21

UnsafeStory ID

(X-Direction)
12
11
10
9
8
7
6
5
4
3
2
1

0.50

1.00
1.50
Seismic Index

2.00

Figure 6. Evaluation by 2nd level screening.
Seismic evaluation of the building by using detail seismic evaluation method:
X-direction: Figure 7 (Left) shows the result of the pushover analysis at the occurrence offirst CP point and the final step, respectively. CP occurred at the end of the floor beam of 4F and 5F of
Frame 2 in Step 7. At these connecting joints of beam and shear are vulnerable due to insufficientembedment length. After the first CP, many plastic hinges occurred to the surrounding beams, which
finally led to the collapse. Figure 7 (Right) shows the result of the seismic evaluation. Since the building
4

collapses before it reached LP, evaluation is not performed on LP. In this direction, the requirement ofseismic demand, IS0, is 0.213, but the calculated seismic index of the structure is found to be 0.127, whichis less than seismic demand. Therefore, it is judged that this building may not have adequate seismic
capacity.

Spectral Acceleration, Sa(X-Direction)
0.2

0.1

IS0 = 0.213 > IS = 0.127
Judgement: Unsafe
I=
0.0385 ✕ 3.308 = 0.127
CP S
CPC = 0.0385

Initial Stiffness

YPCP

CPF = 254.7/76.99 = 3.308

0.0
0

200
400
Spectral displacement, Sd

Figure 7. Evaluation by detail seismic evaluation (X-direction).

Spectral Acceleration, Sa(Y-Direction)
IS0 = 0.36 < IS = 0.513
Judgement: Safe
I=
0.134 ✕ 3.83 = 0.513
CP S

0.5
0.4
0.3
0.2
0.1
0.0

Initial Stiffness
C
CP = 0.134
CP
CPF = 88.6/23.13 = 3.826
YP

0

50
100
Spectral displacement, Sd

Figure 8. Evaluation by detail seismic evaluation (Y-direction).
Y-direction: Figure 8 (Left) shows the result of the pushover analysis at the occurrence offirst CP point and final step. CP occurred at both ends of floor beams of 5F to Roof of frame-E in Step
15. Figure 8 (Right) shows the result of the seismic evaluation. Since the building collapses before it
reached LP, evaluation is not performed on LP. In this direction, the requirement of seismic demand, IS0,is 0.36, but the calculated seismic index of the structure is found to be 0.513, which is larger than seismic
demand. Besides, each story Is values are determined for both direction of the buildings and also
compared with Iso values. The judgement is that the building needs retrofit technique in X-direction
only.
To increase the strength and stiffness of the building in X-direction, the insertion of a newshear wall retrofit technique is adopted for the target building. With this option, the structural system
type of the building in X-direction will change from the moment-resisting frame to dual system. The
new seismic demand of the building in this direction is 0.36. The required strength of the building in Xdirection are evaluated by considering RF value as 3.0. According to JBDPA, 2001, the ultimate strengthof the inserted shear wall is found to be 4776.73 kN which is greater than the required strength 4710.51
kN.
Structural safety checking of the retrofitted structure by detail seismic evaluation:

5

Spectral Acceleration, Sa(X-Direction, After retrofitting)

0.6

IS0 = 0.36 < IS = 0.609
Judgement: Safe
CPIS = 0.165 ✕ 3.689 = 0.609
Initial StiffnessF
CP = 124.30/33.70 = 3.689
CP
YP

0.5
0.4
0.3
0.2
0.1
0.0

0

100
200
300
Spectral displacement, Sd

Figure 9. Evaluation by detail seismic evaluation (X-direction, after retrofitting).
X-direction: Figure 9 (Left) shows the result of the pushover analysis at the occurrence offirst CP point and the final step. CP occurred at the end of the floor beam of 6F to 8F of frame-2 in Step
10. These connecting joints of beam and shear are vulnerable due to insufficient embedment length.
After the first CP, many hinges occurred at the floor beams of the roof to 1F, and finally, shear wall
failed to resist the load showing the CP on the ground floor, which subsequently led to the collapse of
the building. Figure 9 (Right) shows the result of the seismic evaluation. Since the building collapses
before it reached LP, evaluation is not performed on LP. In this direction, the requirement of seismic
demand, IS0, is 0.36, but the calculated seismic index of the structure is found to be 0.609, which is larger
than seismic demand. Therefore, it is judged that this building now has adequate seismic capacity after
inserting the shear wall.
The key findings from this research are summarized below: The target building wasrecognized as weak-beam type building due to the formation of collapse prevention (CP) hinges atbeams from the nonlinear pushover analysis. This building is also considered as a high-rise building.
Consequently, the 2nd level screening method of the JBDPA, 2001 can provide an inaccurate result for
the target building’s seismic performance. The detail seismic evaluation method can evaluate the actual
behaviors of the weak-beam buildings. Therefore, this method is a very effective and rational approachfor seismic evaluation of the target building. With this new method, the seismic capacities of the target
building for each direction were easily estimated by the ADRS format of the capacity curve of thebuilding. The detail seismic evaluation method makes the calculation procedure of the required strength
for retrofit easier. Retrofitting with new shear can be a practical solution since the goal of retrofitting
was strength and ductility up-gradation. The detail seismic evaluation is a more rational and practical
one to evaluate the seismic performance of the building and also for the retrofit plan.
ACKNOWLEDGEMENTS
This research was conducted during the individual study period of the training course “Seismology,
Earthquake Engineering and Tsunami Disaster Mitigation” by the Building Research Institute, JICA,
and GRIPS. I want to express my heartiest gratitude to my supervisors Dr. Eng. Matsutaro Seki, Eng.
Yosuke Nakajima, advisor Dr. T Kashima and Mr. Md. Rafiqul Islam for their valuable guidance andsuggestions.
REFERENCES
Applied Technology Council (ATC), 1996, Redwood City, California.
ASCE, 41-13, Reston, Virginia.
BNBC, 2017, Draft Version Bangladesh National Building Code 2017.
FEMA-356, 2000, Federal Emergency Management Agency, Washington, USA.
Japan Building Disaster Prevention Association (JBDPA), 2001.
Otani, S., 2000, Journal, Faculty of Engineering, University of Tokyo, Series B, Vol. XLVII, pp. 5-28.
Y. Nakajima, M. Seki, H. Suga, R. Islam., 2020, submitted to 17WCEE.
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