Citation: Warah, M., T. Azuhata (2021), Seismic performance evaluation of a RC building with masonry
infill designed by previous seismic code in Bangladesh, Synopsis of IISEE-GRIPS Master’s Thesis.

SEISMIC PERFORMANCE EVALUATION OF A RC
BUILDING WITH MASONRY INFILL DESIGNED BY
PREVIOUS SEISMIC CODE IN BANGLADESH
Supervisor:Tatsuya AZUHATA3*Md. Ibnul Warah1,2
ABSTRACT

Bangladesh is in a moderately seismic-active region. Due to the unplanned construction, many buildings
have been built without proper seismic consideration. Also, the seismic zone factors in the seismic code
were revised in 2020. This revision raised the seismic design force to 1.5 times the previous in someareas. In this situation, it is necessary to check the seismic safety of the existing buildings. This study
aims to evaluate the seismic performance of RC frame buildings considering the effect of infill brickmasonry designed by the previous code. In Bangladesh, the load-bearing capacity of masonry walls is
not considered during structural design. However, for dealing with more severe seismic conditions
assumed in the current code, we attempt to include the effects of infills in the seismic performance
evaluation. To investigate these effects, we execute earthquake response analyses to three models. Onehas high-quality masonry infills, and the other has low-quality infills. The third model is the bare frame
model. To get seismic responses, we apply the capacity spectrum method and response history analyses.
By comparing the earthquake responses for three models, we concluded that high-quality masonry infills
could improve the seismic performance of the RC buildings sufficiently so that the existing building
may resist even against the seismic forces assumed in the current code.
Keywords: Seismic performance, Masonry infill, Seismic code, Artificial ground motion.
1. INTRODUCTION
Bangladesh is a moderately seismic-active region around the world. For the structural design of mid tohigh-rise buildings in the city, earthquakes are of vital concern. Masonry infill RC frame structures arewidespread throughout Bangladesh, like the other developing countries. In general, infill can be grouped
into two different categories: isolated infill and regular infill. Isolated infill is not anchored with theframe of the building. In our country, the masonry infill is isolated from structures. Using infill masonrywalls has been prohibited by modern codes of developed countries unless a special technique has beentaken to ensure that they can withstand lateral loading. To mitigate expected earthquake damage,developing an effective strategy for changing the current system is also necessary. In our country, thefirst building code was published in 1993 (act issued in 2006). The building code has been updated
recently. The revised code was published in 2020 (and came into effect in February 2021). In the newcode, Bangladesh has been divided into four seismic zones. The value seismic zone coefficient has been
1.5 times larger than the previous one. A school building has been analyzed in this study to evaluate theseismic performance of this building considering masonry infill. The model building was designed andconstructed before the publication of the updated code. In this study, a comparative analysis of the1Research Engineer, Housing and Building Research Institute (HBRI), Bangladesh.
IISEE-GRIPS Master’s course student.
3International Institute of Seismology and Earthquake Engineering, Building Research Institute.
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building will be performed to understand its behavior, considering the previous and new ones. Moreover,the effect of masonry walls having different strengths will be discussed. This study is therefore of vital
importance for the seismic assessment procedure of buildings in Bangladesh.
2. STRUCTURAL TEST DATA AND TARGET BUILDING
Infill brick masonry is used as a partition wall in RC frames almost all over the world and is considered
a non-structural Element. But it is observed that this infill masonry has a significant effect, especially inthe case of lateral loading. So, it is significantly necessary to know the level of performance of infill
masonry during an earthquake. To understand the behavior and failure mechanism of infill brickmasonry, laboratory tests on infill frames have been performed in Bangladesh under several projects.
Figure 1 shows one example of them. This laboratory test on the Model Infill RC frames against cyclicload was conducted with a test setup which was constructed in Housing and Building Research Institute(HBRI) workshop.
The cyclic load was applied bymeans of a reverse loading
hydraulic jack mounted on thereaction frame. At the time of
applying cyclic load, thebehavior of the test model
specimens was measured bymeans of the Data Acquisition
System.
Displacementtransducers were fitted atselected locations of the frame tomeasure the deflections. Strain
Figure 1. Photograph of specimen to be tested during loading.
gauges were used for measuring
deformations. We use the test data for force-deformation relationship obtained by this test to verify thenumerical model for RC frames with masonry infill.
Figure 2 shows the plan and the elevation of the school building. Table 2 shows the general
information of it. The building is located in the adjacent city of the capital, Dhaka. The zone co-efficientof this location has been changed due to the revision of the seismic code. Live load and superimposed
load at each floor are considered as 12.4 KN/m2. At the roof, the load is 11.0 KN/m2. The building isconstructed with infill brick masonry in the transverse direction. We suppose that these masonry walls
significantly affect the performance of the building.
For the numerical analysis, the target building was modeled in STERA 3D (Saito). Byusing STERA 3D software (Saito), a model is prepared considering hysteretic behavior corresponding
to materials of structure, design parameters, and loading patterns.
Table 1. General information of the target building.
Time of construction
2018
Number of floors
06
Column, C1, C2
300x450 mm & 300x500 mm
Beam, B1, B2300x375 mm & 300x450 mm
Compressive strength of concrete
20 MPaArea of each floor
Height of the building

195 sqm
19.2 meter

Seismic zone co-efficient

0.15 (According to previous code, BNBC-2006)
0.28 (According to current code, BNBC-2020)2

Figure 3. Elevation of building

Figure 2. Plan of typical floor

3. ANALYSIS PROCEDURE AND RESULTS
3.1. Strut model for masonry infill
In this study, we used strut model to evaluate non-linear of masonry infill and defined force-deformation
relationship as the poly-linear slip model. The characteristic values, Qc, Qy, and Qu are obtained basedon the formulation described in the reference (Paulay and Priestley, 1992). The shear resistance, Qy, iscalculated to be the minimum value between the shear strength by sliding shear failure, Vf, and the shear
strength of diagonal compression failure, Vc, that is;
Qy = min (Vf, Vc).
The shear displacement at the maximum resistance, γy, is obtained as (Madan et al.,1997),
γy =

ɛ(1)

where ɛ’m is compression strain at the maximum compression stress (ɛ’m =0.0018, Hossein andKabeyasawa, 2004).
Initial elastic stiffness is assumed as (Madan et al., 1997)
k0 =2Qy /γy.

(2)

The shear resistance and displacement at crack are obtained by,Qc=(3)γc= Qc / k0(4)where α is the stiffness ratio of the second stiffness and assumed to be 0.2.
Shear resistance and displacement at the ultimate stage are assumed as (Hossein & Kabeyasawa, 2004),
Qu = 0.3Qy(5)

γ u =3.5(0.01hm- γy)(6)where hm is the height of masonry wall.
Shear force vs. drift relation of lab tested specimen and numerical analysis in STERA 3D are as follows.

3Base shear (KN)30
20100-4-3-2-1-1001

2

3

STERA 3D-20
Lab tested
specimen-30
Drift %Figure 4. Force-drift relation for laboratory-tested specimen and numerical analysis
3.2. Nonlinear analysis for target building
For the proper understanding of the behavior of the target building with infill, capacity spectrum method
and response history analyses are performed in this study. In the capacity spectrum method, the capacity
curve and demand spectrum are used for the assessment of building behavior due to the ground motion.
An intersection point of the capacity curve and demand spectrum represents the performance point of
the structure. The response spectral acceleration and displacement are reduced by the followingcoefficient,
Fh =.

(7)

where heq is the equivalent damping ratio, heq= (1- ).
√To perform response history analysis in this study, artificial ground motions are applied
for previous and new seismic code. Seismic responses are obtained according to two different zone coefficient of BNBC- 2006 and BNBC-2020.
3.3. Effect of material property
To investigate effects of masonry infills, three kinds of frame structure are considered.
i.
High quality infill (fcb=14Mpa and fm=10 Mpa)
ii.
Low quality infill (fcb= 4 Mpa and fm= 2 Mpa)
iii.
Bare frame
As the target building has solid infill along transverse direction, static nonlinear pushover and response
history analysis are performed along the transverse direction.
6

Non-linear pushover analysis is performed todetermine the displacement changing behavior
in this study. In the right-sided figure
demonstrates the maximum story drift of eachfloor by the capacity method following thecurrent seismic code.

5

Story Number

3.4. Result of capacity spectrum method

4High quality

3

Low quality

2

Bare frame

1

In figure 6, the capacity curvesof three frames intersect the demand
spectra of the damped hysteresis system.
This graph is constructed according to theupdated seismic code.

00.0030.006
Story drift

0.009

0.012

Figure 5. Maximum story drift by CSM

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600
500

Demand spectrum
Capacity curve_high quality

Sa (gal)400

Capacity curve_low quality
Capacity curve_bare frame

300

Sa-Sd Curve_High quality

200

Sa-Sd Curve_low quality
Sa-Sd Curve_bare frame

100
0012

34

567Sd (cm)

89101112

Figure 6. Capacity curve vs. demand spectra for current code
3.5. Result of response history analysis
After conducting response history analysis in this study, the following graph can be obtained for highquality, low-quality, and bare frame structure.
6Story Number

5432
1
0.000

0.005

0.010
0.015
Maximum story drift

High Quality_Hachinohe
Bare frame_Hachinohe
Low quality_Kobe

0.020

0.025

Low Quality_HachinoheHigh quality_Kobe
Bare frame_Kobe

Figure 7. Maximum story drift for response history analysis for current code
4. DISCUSSION
From the result of the capacity spectrum method and response history analysis, it is obtained that seismic
responses of the high-quality infill model are the smallest. This result shows that high-quality infill canreduce the seismic response of the structure.
The following figures are for the comparative damage aspect of RC building with highquality infill model and the bare frame model due to response history analysis for Kobe phase. In thefigures, U (ductility factor) > 5 indicates severe damage, and U < 5 indicates moderate damage. After
applying the Kobe phase, the columns do not yield for high-quality masonry infill, although Masonrywalls at levels 2 and 3 are severely damaged. It is found that the structure with high-quality masonry
infill may not collapse even considering the revised seismic code. But masonry infill may damage
severely. In the case of bare frame, some of the columns damage severely, which will result in thecollapse of the building.

5Figure 8. Comparison of damage aspect for high-quality infill and bare frame
5. CONCLUSIONS






To investigate seismic performance of existing buildings designed by the previous seismic code,
one typical school building was analyzed, considering the effects of masonry infills in it.
A numerical model for shear-story drift relation of RC frames infilled masonry was verified byusing an existing laboratory test result. According to this model, deformation capacity can be
estimated larger than about 2 % of the story drift angle. However, shear strength gradually
decreases after about 1 % of story drift angle.
Seismic response analysis results showed that seismic deformation responses of the target
school building with high-quality masonry infills did not exceed the corresponding limits evenagainst earthquake ground motions assumed in the current design code.
Columns surrounding masonry infill were not damaged seriously for the target structure withhigh-quality infills. The damage possibility of these columns should be checked for otherbuildings if the relatively high deformation capacity of masonry infills is counted like this case.

ACKNOWLEDGEMENTS
This research was conducted as the individual study of the training course “Seismology, Earthquake
Engineering and Tsunami Disaster Mitigation” by IISEE/BRI, JICA, and GRIPS. I want to express myheartfelt gratitude to Dr. Tatsuya Azuhata for supervising me and giving me continuous guidance,support, encouragement, and suggestions during the entire period of my individual study. I am thankfulto Dr. Taiki Saito, who has helped me a lot at different stages of my study. I am genuinely grateful to
all the professors. Also, thanks are given to all the staff members at IISEE/BRI for their support andeffort during this training program. My sincere gratitude also goes to Mr. Md. Ashraful Alam, Mr.
Mohammad Shamim Akhter and HBRI officials to give me a chance to participate in this course. Finally,I would like to express my deepest gratitude to JICA for giving me a chance to conduct this course
through financial and logistical support. I also like to express my deep gratitude to National Graduate
Institute for Policy (GRIPS) to provide me the opportunity to participate in this course.
REFERENCES
Al-Chaar Ghassan. (2002), “Evaluation Strength and Stiffness of unreinforced Masonry infilled
Structures”, Engineering Research and development Center, US Army Corps of Engineers.
BNBC 2006, “Bangladesh National Building Code”, Housing and Building Research Institute, Ministryof Housing and Public Works, Bangladesh.
BNBC 2020, “Bangladesh National Building Code”, Housing and Building Research Institute, Ministryof Housing and Public Works, Bangladesh.
Saito T. , STERA 3D “Technical Manual”, Toyohashi University of Technology (TUT), Japan.
Zaman and monira (2017), “A Study of Earthquakes in Bangladesh and the Data Analysis of theEarthquakes that were generated In Bangladesh and Its’ Very Close Regions for the Last Forty Years(1976-2016)”.

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