13
Bulletin of the New Zealand Society for Earthquake Engineering, Vol. 53, No. 1, March 2020

SEISMIC CAPACITY OF RC FRAME BUILDINGS WITH
MASONRY INFILL DAMAGED BY PAST EARTHQUAKES
Hamood Alwashali1, Md. Shafiul Islam2, Debasish Sen3,
Jonathan Monical4 and Masaki Maeda5(Submitted August 2019; Reviewed September 2019; Accepted November 2019)
ABSTRACT
Many of the buildings which experienced damage in recent earthquakes such as the 2015 Nepal Earthquake
were reinforced concrete (RC) frame buildings with unreinforced masonry infill walls. This study proposesa simplified procedure to estimate the in-plane seismic capacity of masonry infilled RC frame buildings basedon concepts of the Japanese seismic evaluation standard (JBDPA, [1]). The correlation of seismic capacityand observed damage obtained using a database of 370 existing RC frame buildings with masonry infill thatexperienced earthquakes in Taiwan, Ecuador and Nepal is investigated. The Is index, which represents theseismic capacity of buildings in the Japanese standard, showed good correlation with the observed damage
and proved to be effective as a simple method to estimate seismic capacity. The method was then applied to
103 existing buildings in Bangladesh that have not experienced a major earthquake recently. The results
emphasize the necessity for urgent seismic evaluation and retrofitting of buildings in Bangladesh.

INTRODUCTION
Rapid development in the seismic design of RC buildings
enabled newly designed buildings to avoid severe damage orcollapse. However, there is still a large stock of old buildings
designed according to old designed codes. Not all existing old
buildings are vulnerable, but their seismic capacity need to beassessed and if necessarily retrofitted. In this regard, Japan had
developed a practical standard for seismic evaluation forexisting RC buildings (Japan Building Disaster Prevention
Association, JBDPA, 2001, [1]) based on it long experienceswith devastating earthquakes. The standard has proved its
effectiveness in the Great East Japan Earthquake of 2011 wheremost of the evaluated buildings, that were retrofitted, if
necessary, based on the standard evaluation, showed good
performance and retrofits prevented severe structural damage
as shown in study by [2].
The simplicity and effectiveness of the Japanese standard [1]make it an attractive method to evaluate the seismic capacity ofexisting buildings in other countries and this was the main
motivation of this study. However, the buildings in othercountries may have different characteristics from the Japanesebuildings and thus the standard cannot be applied directly. In
this regard, a procedure that incorporates the effect of masonry
infill walls as lateral force resisting members is not mentioned
in the standard because masonry walls are not commonly
constructed in Japan. Many of the damaged buildings inearthquakes such as the 2008 China Wenchuan Earthquake, the2015 Nepal Earthquake and the 2017 Mexico Earthquake were
reinforced concrete buildings with partition walls and cladding
walls made of masonry walls as shown in Figure 1. Masonry
infill walls were commonly considered to be non-structuralelements and the structures were designed as RC moment
resisting frames ignoring the influence of walls. But masonry
infill walls can completely change the behaviour of structures
as noted by many researchers in several studies such as (Paulayand Preistley [3]). There is a need to estimate the capacity ofdifferent orientations of masonry infill walls in other countries
to identify buildings that are vulnerable to damage during

earthquakes. In addition to the masonry infill walls, theseismicity level is unique to each country. Thus, an appropriate
seismic capacity based on the seismic demands of a region
would need to be estimated based on past damage data

Figure 1: Damage of RC building with masonry infill walls
in China 2008 Wenchuan Earthquake.
The purpose of this study is twofold: First, propose a simplified
procedure to estimate in-plane strength and ductility of masonry
infill based on a review of experimental results. Second,evaluate the proposed procedure to estimate the seismic
capacity of 473 existing RC buildings in several countries(Taiwan, Ecuador, Nepal and Bangladesh) based on theevaluation methods of the Japanese standard. The seismic
capacity of the buildings in the database and its correlation toobserved damage are investigated and recommendations forseismic criteria are discussed.
OVERVIEW OF THE JAPANESE STANDARD
The Japanese standard for seismic evaluation of existing RC
building has been widely used since its first publication in
1977, [4]. Another two editions with partial revisions in 1990
and 2001 followed. Application of the standard to existing

1 Assistant Professor, Tohoku University, Sendai Japan, Hamood@rcl.archi.tohoku.ac.jp.
2 Ph.D. candidate, Tohoku University, Sendai Japan, Shafiul@rcl.archi.tohoku.ac.jp
3 Ph.D. candidate, Tohoku University, Sendai Japan, Dsendip@rcl.archi.tohoku.ac.jp
4 Ph.D. candidate, Purdue University, West Lafayette, United States, Jmonica@purdue.edu
5 Professor, Tohoku University, Sendai Japan, Maeda@rcl.archi.tohoku.ac.jp

14buildings greatly increased after the 1995 Kobe Earthquake
which included enforcement of the law for promotion ofseismic retrofit of buildings and seismic evaluation all overJapan.
The JBDPA standard has three screening levels. The 1st level isthe simplest and most conservative, and the 3rd level is the mostcomplex with detailed calculations. In the 1st level screening,
only the strength of concrete and the sectional areas of columns
and walls are considered to estimate the seismic capacity. This
study will focus on the 1st level evaluation since the investigateddatabase of existing buildings has simple drawings showing
only basic information.

In this equation, Qu is the ultimate lateral load-carrying capacityof masonry infill. ∑W is the weight of the building supportedby the story. τinf is the shear strength of masonry. Ainf is the
cross-sectional area of the masonry infill panel taken as the
product of linf (infill panel length) and tinf (thickness of infill).
The calculation of the cross-sectional area, Ainf, and the weightof the building are straightforward. However, the estimation of
the shear strength of the infill, τinf, varies greatly based on thetype and quality of masonry.

Only an overview of the concept of the standard is presented
here. More details about the Japanese standard are discussed inprevious studies such as [4,5]. The seismic capacity of abuilding is expressed by the Is index and is calculated by Eq. 1
for each story.
(1)

SD and T are reduction factors that modify the basic seismicindex of a structure (Eo) because of structural irregularity anddeterioration after construction, respectively. Eo is the productof the strength index (C), ductility index (F) and story index(n+1/n+i) as shown in Eq. 2, for 1st level evaluation.
n 1
Eo 
 (C1  α2C2  α3C3 )  F1
ni

(2)

C is the strength index that denotes the story-shear coefficientof each structural member, where C1, C2, and C3 represent threedifferent types of structural members with different
deformation capacities. F is the ductility index of each member
ranging from 0.8 (extremely brittle) to 3.2 (most ductile), basedon the inelastic capacity expected of each structural member. F
index in for RC columns depends on the sectional properties
such as bar arrangement, shear-to-flexural-strength ratio etc. In
Eq.2, C1 and F1 represent the stiffest member with limited
deformation capacity which is expected to fail first. (n+1)/(n+i)
is the story index which accounts for the mode shape of the
response along the building height. α is the effective strength
factor which reduces the effective strength of ductile members
at ultimate deformation of stiff members, where α2, α3,represent the effective strength factors for C2 and C3 which areconsidered to have larger deformation capacity than C1.
The calculation procedures of F index (ductility index) and C
index (strength index) for structural members for each
evaluation level is different, where simple and conservative
estimation is used in the 1st level evaluation and more detailed
calculations in the 3rd level. The next section investigates andpropose evaluation procedure of C-index and F-index formasonry infill for the 1st level screening.

Figure 2: Main concept of calculating C-index of masonry
infill.
This paper briefly discusses the results of past experimental
studies in order to understand the parameters influencing theshear strength of masonry infill. Figure 3 shows the relation
between the shear strength of the masonry infill and themasonry prism compressive strength, fm, based on a database ofexperimental results from nine different researchers [6-14] anddetails of the experimental results are summarized in [15]. The
database consists of single-story, single-span RC frames withmasonry infill tested under static cyclic loading with several
types of masonry bricks. As shown in Figure 3, the shear
strength of the masonry infill, τinf, generally ranges between 0.2
and 1 N/mm2. The shear strength, τinf commonly ranges between
0.04fm and 0.1fm.

Masonry infill shear strengthτinf (MPa)Is  Eo  SD  T

2Experimental results

1.5

1
0.5
0
0

5
10
15
Compressive strength fm (MPa)20

Figure 3: Relation of prism compressive strength to shear
strength of masonry infill.

SEISMIC CAPACITY OF MASONRY INFILL
Lateral Strength and C-Index of Masonry Infill
The proposed evaluation considers masonry infill and boundary
columns as two separate elements. This is assumed because
masonry infill eventually delaminates from the surface of thesurrounding columns and may fail before the boundary
columns. Thus, the C-index of masonry infill and C-index ofcolumns are calculated separately. If ductile enough, thecolumns would continue to carry the lateral load and would failat a larger drift as shown in Figure 2.

Another important parameter influencing the shear strength ofmasonry infill is the ratio of lateral strength of boundary frame
to shear strength of masonry infill. In general, a strong boundary
RC frame around the masonry infill will increase theconfinement of masonry infill and thus increase its shear
strength. To classify the frames into weak and strong ones, theβ index is used, which is defined in this study, as shown in
Eq. 4. β-index is the ratio of expected bare frame lateral strength
to the expected masonry infill strength as shown in Eq.4.

Cmasonry for the 1st level evaluation for every element is shownin Eq. 3.

  Vf /V inf

Cmasonry Qu inf  A inf

W W

(3)

(4)

Where Vf is the lateral strength of boundary frame which is
calculated to be the ultimate flexural capacity, assuming plastic

15

V inf =0.05 fm  t inf  l inf(5)

Figure 4 shows the relation between β-index (ratio of frame
strength to masonry strength) and increase in masonry shear
strength, τinf (Normalized shear strength by dividing by prism
compressive strength, fm).
Evaluating the β-index requires some investigative effort suchas knowing the reinforcement details of the RC frame. In thispaper, the scope was limited to the simplified 1st levelevaluation, thus the influence of the β-index was ignored andthe lower bound of shear strength is used. A more detailed
evaluation method considering the β-index is proposed
elsewhere [15].
Additionally, acquiring the data of the prism compressive
strength of masonry infill in the site, might be difficult during
1st level evaluation process. Therefore, for simplicity in theabsence of material test results from the field, the shear strengthof masonry infill in the first level evaluation is proposed to betaken as the lower boundary of expected masonry compressive
strength as shown in Table 1 and Figure 3.

parameter is the β-index (indicating the relative strength offrame to masonry infill strength as shown in Eq. 4). Figure 5
shows the relation between the β-index and Ru. A higher β-index(relatively stronger frame) would correspond to a greater
ductility and β<0.5 (relatively weak frame) would indicate
lower ductility. Such a relation between deformation limits andβ-index was also noted in other seismic evaluation standards
such as ASCE/SEI [16] and NZSEE assessment guideline [17].
Also, experimental results showed that specimens with valuesof β <0.5 (relatively strong infill and weak frame) showedbrittle response and a sudden drop of strength after reaching its
maximum strength as shown in Figure 6 which shows test
specimen F-0.4 in [14].
4
3.5
3
2.5
2
1.5
1
0.5
0

Ru (%)(drift at 80% of max strength)

hinges at the ends of the column as in bare frame (or plastic
hinges at the end of the beams in the case of weak beam andstrong column). Vinf is the expected lateral capacity of infill,computed by Eq. 5. This is a simple prediction assuming the τinf
as 0.05fm. This value gives an average value of experimental toanalytical results of 0.83 as shown in the study [15].

Experimental data

0

0.5

1

1.5

2

2.5

3

β index

300

Experimental results
lower boundary

0

0.5

1

1.5

2

2.5

3

β index(bare frame strength/ expected masonry strength )lateral load (kN)

τinf /fm
Normalized shear strength

Figure 5: Relation of between β-index and Ru drift.
0.16
0.14
0.12
0.1
0.08
0.06
0.04
0.02
0

200
100
0
0

Figure 4: Relation of β index to shear strength of infill.
Table 1: Proposed shear strength of masonry infill for Firstlevel evaluation.
Compressive strength ofmasonry fm (N/mm2)

Proposed shear strength ofmasonry infill (N/mm2)

3 <fm<90.2

9<fm<15

0.4

fm>15

0.6

0.5

1
1.5
story drift (%)

2

Figure 6: Specimen with β <0.5 (weak frame).
The 1st level screening in the Japanese standard conservatively
limits the ductility index to a maximum value of F=1 for ductile
vertical-resisting elements (RC columns and RC walls). This
corresponds to a story drift of about 0.4%. In other words, thecolumns and RC walls are assumed to fail as brittle elements at
a story drift of about 0.4%. As this study focuses on the 1st levelevaluation, the F-index for masonry infill is taken as 1 and theinfluence of the β-index is conservatively ignored.
A more detailed evaluation of the F-index for masonry infill forthe 2nd level screening is discussed in another study by theauthor [15].

Ductility of Masonry Infill and Proposed F Index
This paper briefly discuss the results related to deformation
limits for masonry infill based on database of experimental
studies [6-14], that are summarized in [15]. Rmax and Ru,
represent the story drift at maximum strength and story drift
when the lateral strength degraded to 80% of maximum lateralstrength, respectively. Rmax has an average of 0.72% andstandard deviation of 0.36%. Ru has an average of 1.71% andstandard deviation of 0.77%.
There are several parameters influencing the deformation limitsof masonry infill such as brick type, mortar strength and therelative strength of the surrounding frame. An important

APPLICATION OF THE EVALUATION METHOD
Three different recent earthquakes in Taiwan, Ecuador and
Nepal are investigated. These countries were selected based on
the availability of documented damage data. The data arecollected from an open data website named Datacenterhub [1820]. The data is from field surveys of RC buildings damaged by
the earthquakes collected as a reconnaissance effort led by theAmerican Concrete Institute (ACI) and several otherorganizations. The data of the buildings contains locations withGPS coordinates, simple sketches of plans for each building

16

showing cross-sectional areas of columns and masonry infill,
and photos of damage.
The classification of damage level of the buildings in the
database is as follows:
I. Light: Hairline (crack width < 0.13 mm) inclined andflexural cracks were observed in structural elements.
II. Moderate: Wider cracks or spalling of concrete.
III. Severe: At least one element had a structural failure.

Several ground motion stations in Tainan city recorded valuesof PGA between 0.2g and 0.4g. The maximum recorded peakground acceleration (PGA) was 0.45g and was measured bystation CHY 62. The response acceleration plots use 5%
damping and are shown in Figure 8. Most of the response
spectra have values of acceleration less than 0.8g for shortperiods (less than 0.5 seconds), except for station CHY 62.

Station CHY062

As the database does not contain detailed drawings or material
specifications, the following assumptions are used in thecalculations:

Using the above consideration and assumptions into Eq. 1 andEq. 2, and considering the 1st story of a building, then theseismic capacity, Is index, is taken as Eq.6:
Is  (C masonry  αC column )  Fmasonry(6)

Surveyed buildings [6]Ground motion stations

Figure 7: Locations of the investigated buildings.

Acceleration (gal)1600

CHY 89 NS
CHY 89 EW
CHY 131 NS
CHY 131 EW
CHY 62 NS
CHY 62 EW

1200
800
400

0
0

0.5

1
T (sec)1.5

2Figure 8: Acceleration response spectra in Taiwan EQ.
1.6
None

1.4

Is (NS direction)a) The average weight per unit area of RC buildings is taken
as 11kN/m2 in the absence of data.
b) The effective strength factor used for columns, α, is 0.7,
(Figure 2 and Eq. 2), which is recommended in anexperimental study by [21].
c) The shear strength of columns commonly ranges
0.7N/mm2~1.5N/mm2, which is indicated in the Japanesestandard [1]. In this study, an average of 1N/mm2 is used if
no material property data exists. However, in this study, the
1 N/mm2 is then multiplied by α index (see Figure 2) taken
as 0.7 in Eq. (2), which indicates that the actual shear
strength of columns is taken as 0.7N/mm2.
d) The strength contribution of masonry infill walls with large
openings (greater than 40%) is ignored. The cross-sectional
area of infill, Ainf, is calculated by deducting cross-sectional
area of the openings. In addition, the location of opening is
also important, partial infill walls and masonry wall that are
not surrounded by RC frame from all sides are ignored.
e) SD and T (reduction factors for structural irregularity anddeterioration after construction respectively) are taken as 1
for simplicity.
f) Masonry infill is commonly confined by the boundary
columns and thus in-plane failure is considered to occur
prior to out-of-plane failure. This assumption is consideredbased on two main reasons: first, several experimental
studies and observations of performance of infill panels
under out-of-plane loads conducted by several studies thatshowed a significant out-of-plane resistance due to theformation of an arching mechanism [22-24]. The otherreason is the observation of the photos showing damage ofthe investigated buildings shown in [18-20] which showedthat failure of masonry infill was generally in-plane failure.

Light

1.2
1

Moderate

0.8

Severe0.6
Is = 0.6

0.4
0.2
00 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

Is (EW direction)

As discussed previously, Fmasonry is taken as 1 and α is taken as
0.7, for 1st level evaluation.
Taiwan Earthquake 2016
Overview of the Data and the Earthquake
An earthquake of magnitude 6.7 occurred in Meinong, Taiwan
on February 6, 2016. The earthquake caused large-scale damage
in Tainan city which was 40 km from the epicenter. The data ofdamaged existing RC buildings are provided by (Datacenter
hub [18]). A total of 65 RC buildings with masonry infill areinvestigated in this study and their locations are shown in
Figure 7.

Figure 9: Relation of Is-index and damage in Taiwan EQ.
The number of stories ranged between one and five stories, withthe majority of buildings having two or three stories. Details of
the investigated buildings are stated in [15]. Masonry infill
walls in Taiwan are commonly made of red clay bricks and are
200 to 300mm thick. The types and strengths of masonry infill
were not stated in the database, but have been stated in several
studies such as [25], an expected shear strength of 0.4 N/mm2
is used for seismic evaluation.

17

Seismic Capacity Results for Taiwan EQ
Figure 9 shows the Is-indices for North-South (NS) and EastWest (EW) directions in the 1st story of the investigatedbuildings with observed damage levels. Figure 10 shows thevariation of the Is-index with number of buildings. There is aclear trend between damage level and low values of the Is-index.
In Japan, the Iso-index (demand criteria) is 0.8 and 0.6 for 1st
and 2nd level screening, respectively.

10
8
6
4
2
0

The masonry infill type is not stated in the database, but as
noticed from photos of the survey, both concrete blocks andburnt clay bricks are commonly used. In a study by [26], it was
found that solid clay bricks had unit compressive strengths
between 7.3 and 7.9 MPa and most concrete block units had
strengths between 1.0 and 1.5 MPa. Thus, the masonry infill
shear strength was taken as 0.2 N/mm2 using the lower boundvalue as listed in Table 1.

Surveyed buildings

All surveyed buildings
Severely damaged buildings
AMNT station

Figure 12: Locations of the investigated buildings.
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0.55
0.6
0.65
0.7
0.75
0.8
0.85
0.9
0.95
1

No. of buildings

Table 2 shows the average and standard deviation of the Isindex for the investigated buildings. Figure 11 shows the lognormal distribution. For severely damaged buildings in
Figure 11 shows the ratio of severely damaged buildings to allbuildings, the curve of which is adjusted by multiplying thevalues by ratio 17/65 (severely damaged/ all surveyedbuildings). An Is-index of 0.5 or 0.6 would be sufficient to avoid
severe damage. However, the problem is that most of theinvestigated buildings, as shown in Figure 11, have seismic
capacities lower than 0.6 and retrofitting such large stock ofbuildings would be expensive.

The acceleration response spectra using 5% damping are shownin Figure 13. The acceleration record comes from the groundmotion station AMNT and it is the nearest station to thesurveyed buildings in Manta city. The acceleration response forbuildings with short periods (less than 0.5 seconds) in NS and
EW directions exceeded 1g.

1600

Is index (min of both directions)

Acceleration (gal)Station Name: AMNT

Freqeuncy

Figure 10: Distribution of Is index in Taiwan EQ.
All surveyed buildings
Severely damaged

1
0.8
0.6
0.4
0.2
0

1200

NS

EW
800
400
0

0
0

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

1

Is index ( min of both directions)Figure 11: Normal distribution of Is index in Taiwan EQ.
Table 2: Average Is-index of buildings in Taiwan EQ 2016.
All buildings

Severely damaged

Number of bldgs.

65

17

Average Is index(min direction)

0.458

0.306

standard deviation

0.221

0.11

Ecuador Earthquake 2016

0.5

1
T (sec)1.5

2Figure 13: Acceleration spectra in Ecuador EQ.
Seismic Capacity Results in Ecuador EQ
Figure 14 shows the Is-indices for NS and EW directions in the
1st story of the investigated buildings with observed damagelevels. Figure 15 shows the variation of Is-index with thenumber of buildings. Table 3 shows the average and standard
deviation of the Is-index of the investigated buildings. The
average Is-index of the investigated buildings in Ecuador is0.32, which is lower than in Taiwan. Figure 16 shows thelogarithmic normal distribution of the Is-index. Like Taiwan,
buildings with Is index greater than 0.5 avoided severe damage.
However, most of the buildings lie below this range as shownin Figure 14.
Table 3: Average Is-index of buildings in Ecuador EQ 2016.

Overview of the Data and the Earthquake
An earthquake with a moment magnitude Mw = 7.8 occurred in
Ecuador on April 16, 2016. The reconnaissance data consists of
171 low-rise RC buildings in the cities of Manta, Portoviejo,
Chone, and Bahía de Caráquez which are located in theprovince of Manabí [19], as shown in Figure 12.

All buildings

Severely damaged

Number of bldgs.

171

77

Average Is index(min direction)

0.316

0.255

standard deviation

0.159

0.087

18

800

1.4

Is (NS direction)

1.2

1

Acceleration (gal)Light
Moderate

0.8

Severe0.6
0.4

Is =0.6

600

Nepal
KATNP station

400

EW
NS

200
0

0.2

0

0

0

0.2

0.4

0.6

0.8

1

1.2

1.4

20
10

0
0.05 0.15 0.25 0.35 0.45 0.55 0.65 0.75 0.85 0.95
Is index ( min of both directions)

Seismic Capacity Results in Nepal EQ

Freqeuncy

Figure 15: Distribution of Is-index in Ecuador EQ.
All surveyed buildings
Severely damaged

02

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
Is (min of both directions)

The damage observed of masonry infilled RC buildings in
Nepal Earthquake and construction details are investigated inprevious study by [27]. The thicknesses of the masonry infill
walls were 110 to 230 mm. The types and strengths of masonry
infill were not stated in the database, but it was noticed from thephotos of the survey that solid burnt clay bricks were the mostcommon as well as mentioned in the study [27]. The prism
compressive strengths of masonry within the same region wasinvestigated in other studies by [28], where the compressive
strength was approximately 4.1 MPa. Therefore, the masonry`s
shear strength is taken as 0.2N/mm2 as listed in Table 1.

1

Figure 16: Normal distribution of Is-index in Ecuador EQ.
Nepal Earthquake 2015
Overview of the Data and the Earthquake
A strong ground shaking with a moment magnitude Mw= 7.8
struck near the center of Nepal on April 25, 2015. Surveys of
134 RC buildings with masonry infill located in the capital city,
Kathmandu [20] are shown in Figure 17. The response spectrausing 5% damping are shown in Figure 18. The response
acceleration spectra for short periods for NS and EW directions
is 0.3g and 0.6g, respectively. The ground motion station isrelatively near the investigated buildings (Figure 17).

Figure 19 shows the Is-indices for NS and EW directions in the
1st story of the investigated buildings with observed damagelevels. Figure 20 shows the variation of the Is-index with thenumber of buildings. Table 4 shows the average and standard
deviation of the Is-index of the investigated buildings. Figure 21
shows the log-normal distribution of the Is-index. The average
seismic capacity of buildings in Nepal is lower than that ofbuildings in Taiwan and Ecuador. Like Ecuador and Taiwan,
the buildings in Nepal with Is-indices greater than 0.5 avoided
severe damage. It should also be noted that the response
acceleration in Nepal is much smaller than that for Taiwan and
Ecuador earthquakes as shown in Fig. 18. Thus, in Nepal, an Isindex of 0.5 is relatively high compared with the earthquake
demand and this point needs further investigation.
Table 4: Average Is-index of buildings in Taiwan EQ 2015.
All buildings

Severely damaged

Number of bldgs.

134

58

Average Is index(min direction)

0.261

0.209

standard deviation

0.157

0.108

1.4

None

Kathmandu city

1.2

Light

Surveyed buildings

KATNP Station≈2 kM

Is (NS direction)

No. of buildings

All surveyed buildings
severly damaged

1
0.8
0.6
0.4
0.2
0

1.5

Figure 18: Acceleration response spectra in Nepal EQ.

Figure 14: Relation of Is-index and damage in Ecuador EQ.

30

1

T (sec)Is (EW direction)

40

0.5

1

Moderate

0.8

Severe0.6

Is =0.6

0.4
0.2

0
0

Figure 17: Locations of the investigated buildings.

0.2 0.4 0.6 0.81

1.2 1.4

Is (EW direction)

Figure 19: Relation of Is-index and damage in Nepal EQ.

30

Seismic Capacity of Buildings and Comparison with Nearby
Countries

All surveyed buildings
Severely damaged

20

There have been no major earthquakes in Bangladesh in the last
100 years. As Bangladesh and Nepal both border India, there isa similar construction practice for RC buildings with masonry
infill walls.

10
00.05 0.15 0.25 0.35 0.45 0.55 0.65 0.75 0.85 0.95
Is index ( min of both directions)Freqeuncy

Figure 20: Distribution of Is-index of buildings in Nepal
EQ.
1
0.8
0.6
0.4
0.2
0

All surveyed buildings
Severely damaged0

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
Is ( min of both directions)1

Figure: 21 Normal distribution of Is-index.
APPLICATION IN COUNTRIES WITH NO RECENT
EARTHQUAKES

The design spectral acceleration curves are calculated based on
the 2015 BNBC Code (draft) for soil type SC for Dhaka city.
The design spectra are compared with the response spectra of
the 2015 Nepal Earthquake in Figure 23.
A comparison of the observed damage in buildings in Nepal
with the seismic capacities of the investigated buildings in
Dhaka is shown in Figure 24. The Bangladeshi buildings havevery low seismic capacity when compared to Nepalesebuildings and may suffer severe damage if an earthquake
similar to the Nepal Earthquake were to occur. These results
emphasize the importance and urgency for earthquake
retrofitting in Bangladesh, otherwise the ratio of damage andpercentage of total number of causalities could be more thanthat of the Nepal 2015 earthquake.
40

No. of buildings

No. of buildings

19

Surveyed buildings in Bangladesh

30
20
10
0

Overview of the Data in Bangladesh

Data from 103 existing RC buildings were collected from twosources:12Comprehensive Disaster Management Program (CDMP)
collected data between 2010 and 2015 in a collaborative
project between the Bangladeshi Ministry of Disaster
Management and United Nations Development Program(UNDP). The building data contains sketches of plans ofbuildings that include dimensions of columns and masonry
infill walls. More details included in the database are
mentioned in [15].
A site investigation for a Japanese project called SATREPSTSUIB 2015 consisted of a team of researchers fromTohoku University including the author and governmental
engineers from the Public Works Department in Bangladesh.
Four existing RC buildings were surveyed in January 2018.
Structural drawings of the buildings are mentioned in [15].

In general, the surveyed buildings have two thicknesses ofmasonry wall. The exterior walls are 250mm thick and theinterior walls are 125mm thick. The walls are made of burnt
clay brick. The compressive strength of these types of bricks is
expected to be 15 MPa. The mortar strength is expected to be
between 3 and 5 MPa. The expected masonry prism
compressive strength may vary between 6 and 10 MPa.
Therefore, the shear strength of the masonry infill is taken as
0.2 N/mm2 as proposed in Table 1.
The distribution of the seismic capacities of the investigatedbuildings in Dhaka that are calculated based on the proposed
method is shown in Figure 22. The average Is-index is 0.19 witha standard deviation of 0.11.

Is-index (minimum of both directions)Figure 22: Distribution of Is-index of the investigatedbuildings in Dhaka city.

Figure 23: Response spectra for Dhaka (based on 2015
BNBC draft) and Nepal EQ.
1
None (Nepal)

0.8Light (Nepal)

Is (NS direction)

Bangladesh is a densely populated country located in amoderately seismic-prone region. The data in this study arecollected in Dhaka, the capital city of Bangladesh.

0.6

Moderate(Nepal)0.4

Severe((Nepal)0.2

Bangladeshbuildings

0
0

0.2

0.4
0.6
0.8
Is (EW direction)

1

Figure 24: Comparison of existing RC buildings in
Bangladesh and damage observed in Nepal EQ.

20

CONCLUSIONSThis study proposes a simplified procedure to include masonry
infill walls into the Japanese Seismic Evaluation Standard ofexisting RC buildings [1]. The seismic capacities (Is-index) ofmasonry infilled RC frame buildings in several countries areinvestigated and the following conclusions are drawn:
1

2

3

There is a clear relation between the decrease of Is index
and damage level in the investigated buildings in the three
past earthquakes, which are: Nepal Earthquake in 2015,
Ecuador Earthquake in 2016 and Taiwan Earthquake in2016.
Severe damage is concentrated in buildings with Is smaller
than 0.3. On the other hand, buildings with Is index greaterthan 0.6 avoided severe damage. Hence, an Is index of 0.6
for masonry infilled buildings would be sufficient to avoid
severe damage in case of major earthquakes with groundmotion levels comparable to those studied in this paper.
The unfortunate reality is that most of the investigatedbuildings have seismic capacity indices smaller than 0.6.
These results emphasize the importance and urgency ofearthquake retrofitting particularly in developing countries.

It should be noted that several assumptions have been made forthe calculations as noted before, such as in-plane failure
precedes the out of plane failure based on damage reported inliterature [6-8]. However, this is not a general rule, and should
be taken with precautions especially with masonry infill withgaps around the frames, large openings and masonry walls
without bounding frame.
In addition, the investigated buildings in this paper are only RC
frame buildings with masonry infill. However, the proposed
seismic capacity method considering masonry infill could bealso applied to RC buildings with RC walls and RC frames
since it is within the scope of the Japanese Building Assessment
Standard [1]. The calculations of strength (C-index) andductility (F-index) for RC walls can be used as indicated in theJapanese Standard [1].
ACKNOWLEDGMENTS
This is an updated and extended version of a paper presented at
the Eleventh Pacific Conference on Earthquake Engineering(PCEE) at Auckland in April 2019.
The study was supported by the SATREPS project TSUIB(project in Bangladesh) 2015 directed by Professor Nakano
Yoshiaki, University of Tokyo and JSPS KAKENHI Grant
Number JP 19K15070. This support is gratefully
acknowledged.
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