Citation:
Bidhan C. Dey, M. Seki (2021), Seismic evaluation considering infill wall and retrofit of a fivestoried RC building in Bangladesh, Synopsis of IISEE-GRIPS Master’s Thesis.

SEISMIC EVALUATION CONSIDERING INFILLWALL AND RETROFIT OF A FIVE STORIED RC
BUILDING IN BANGLADESH
Bidhan Chandra Dey1,2Supervisor: Matsutaro SEKI3
ABSTRACTThe recent revision of the Bangladesh national building code (BNBC) necessitates the buildings
designed in the old code be assessed for their adequacy to satisfy seismic provisions of the revised BNBC.
The existing evaluation manual in Bangladesh is based on the Japanese second-level evaluation methodthat considers the strong-beam weak-column failure. However, the buildings designed according to theprevious code consider the strong-column weak-beam failure. Therefore, the proposed detailed seismicevaluation (DSE) method capable of capturing this effect and providing a simple index resembling theexisting manual was tested in a low-rise building. Moreover, in design, ignoring the brick infill can alter
the strength and deformation behavior of the columns and the story's capacities accordingly. This
research aims to assess the variation of story-wise performance considering the infill wall for a low-risebuilding designed according to the previous code. Additionally, the low-cost strength-based ferrocement(FC) retrofit was tested as a performance improvement technique. The draft copy of the SATREPS
manual was used as a basis for calculating wall capacity for both untreated and FC treated. This researchfound that the DSE method provides more realistic seismic performance capturing reasonable failure
mechanisms initiated by plastic hinges in beams than the JBDPA second level evaluation. Moreover, thecontribution of suitably configured solid masonry walls can improve both strength and deformation
behavior and thus increase safety, leading to more economic evaluation. Additionally, the Out-of-planecapacity for walls was found to be larger than the in-plane capacity. FC retrofit method proved to be aconvenient way to improve performance without intervening in the columns or RC walls. Therefore, it
is expected to conduct further analysis under other considerations not estimated in the present researchin the future.
Keywords: Detail seismic evaluation method, infill wall effect, ferrocement retrofit.
1. INTRODUCTION
Bangladesh is an earthquake-prone country and experienced several earthquakes of moderate magnitude.
From continuous plate tectonics and previous records on the active fault zone, it is predicted that there
is a high possibility for an earthquake of considerable magnitude in the near future. In the pastearthquakes, the poorly designed and constructed infrastructures suffered the most. Moreover, theBangladesh national building code (BNBC) has upgraded many sections in the 2020 revision, including
seismic design provisions. This necessitates the evaluation of the existing buildings designed based on
previous codes to assess whether the buildings' performance is acceptable. In Bangladesh, the reinforced
concrete (RC) frames are infilled with brick masonry, which also contributes to the lateral strength of1

Public Works Department (PWD), Bangladesh.
IISEE-GRIPS Master’s course student.
3International Institute of Seismology and Earthquake Engineering, Building Research Institute.
21the stories. Therefore, it is necessary to consider the infill wall effect in the evaluation process, giving amore rational result.
2. METHODOLOGY
Currently, the existing manual for RC building’s seismic evaluation is published under CNCRP(Capacity Development on Natural Disaster-Resistant Techniques of Construction and Retrofitting forPublic Buildings) project. It is based on the second level evaluation from Japanese standards for seismicevaluation (JBDPA evaluation guideline, 2001), where strong-beam and weak-column are considered.
However, the philosophy of the designed RC buildings following the BNBC is the strong-column andweak-beam concept. The recently proposed detailed seismic evaluation (DSE) method introducesevaluating the buildings based on nonlinear static pushover analysis that captures the failure sequencein a better way. In this method, the plastic hinges are assigned according to the ASCE 41-13, which isbased on the experimental results. Additionally, considering the wall effect in the evaluation process
makes the evaluation more rational, and performance improvement can lead to a more realisticassessment. Currently, no other studies in Bangladesh consider the combined effect of the frame and theinfill masonry wall in the evaluation, using the DSE method. The current research focuses on studying
the infill wall effect in the capacity enhancement of the seismically inadequate stories of RC buildings
based on the SATREPS manual. Additionally, a low-cost retrofitting technique, i.e., ferrocement
lamination, was tested to improve the seismically inadequate stories. By assessing the infill masonrywalls’ contribution, the more realistic behavior of different stories can be determined, and a retrofitting
plan can be addressed and utilized more economically.
2.1. Seismic evaluation without the masonry infill
The selected building is modeled and assessed using second-level evaluations of Japanese standards asmentioned in JBDPA (2001) and the DSE method proposed by Y. Nakajima, M. Seki, H. Suga, and R.
Islam (2020). The basic difference between these two methods is considering the relative stiffness ofthe beam and column. In the Japanese 2nd level evaluation, the beams are considered more rigid
compared to the column. This consideration ensures the hinge mechanism initiation in the column while
no beam is affected at all. Additionally, for the story-wise evaluation of capacity, the lateral strength ofthe column is considered to be fully utilized. However, in pushover analysis based on the assignment of
the plastic hinge, it may be initiated in either column or beam. It essentially captures both the strongcolumn weak-beam and vice versa based on the plastic hinge property. When assigning the plastic hinge
section, three acceptance criteria are assumed, namely Immediate occupancy (IO), life safety (LS), andcollapse prevention (CP) point. As per the DSE method, the two critical limits were considered to selecta story's ultimate capacity are based on two points. One is LP points, and the other is the CP points. TheLP points, i.e., the limiting points, are determined as per the limitation of drift by revised code provisions.
CP limits are considered to be achieved when one or some member’s plastic hinge crosses the predefined
CP points. The pushover curve obtained thus is converted in the more representative ADRS format. The
capacity of the building is then calculated using Eqs. (1) - (3)Where, C P C andLPCCPI S  CP C  CP F  CP C  CP (1)LPI S  LP C  LP F  LP C  LP 

(2)

I S  min( CP I S , LP I S )(3)are the strength indexes at the CP and LP points, respectively. C P F andF

are the ductility indexes at the CP and LP points, respectively. The resulting capacity obtained
thus is also compared with that found using the 2nd level evaluation of the JBDPA guideline (2001).
However, both X and Y directions were found not to conform to the seismic demand while using theLP

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DSE method in the selected building. Therefore, story-wise pushover analyses were performed, and thecapacity of each story was assessed.
2.2. Seismic evaluation considering the infill masonry
To consider infill walls, two critical parameters, i.e., strength index and ductility index, since notprovided in either the JBDPA standard or the proposed DSE method, the calculation procedure isadopted from the SATREPS manual. According to the manual, the equations were provided forevaluating strength and ductility index based on the experimental results. Four types of failure werecategorized. Based on the test result, conservative ductility indexes were suggested for the different
failure modes of walls in the SATREPS manual. To get the overall capacity of the stories, the result
obtained thus are combined with those found earlier for the bare frame using the DSE method following
the basic principle described in the JBDPA evaluation guideline.
3. DATAThe RC framed five-storied office building is selected for this research purpose. It contains brickmasonry infilled RC frames that includes walls with opening also. The building does not have any RCwalls. All vertical lateral-load-resisting elements are columns. The various essential properties,
including geometrical and material-related properties, are shown in Table 1. The ground floor plan of
the building is shown in Figure 1.
Table 1. Basic properties of the building
geometry and its material
Geometrical, load and material related
properties
Building
name:5(five)storiedadministrative government building.
Number of story: 5 (five)Framing: RC frame only (no RC shear wall)
Occupancy category: II
Importance factor: 1.00
Seismic zone: 3 (Z=0.28 in BNBC 2020)
Soil type: SC (BNBC 2020)
Concrete strength: 25 MPa
Steel yield strength: 414 MPa
Brick prism strength: 6 MPa
Total seismic weight: 27486 kN
Total area: 2295.20 m2.

Figure 1. 1st floor plan showing the location and typeof infill wall

4. RESULTS AND DISCUSSION
The seismic demand index was calculated from the revised BNBC and found 0.43, as shown in Figure2(i). Pushover analysis was performed to obtain the governing limit between CP and LP points. For thisbuilding in each direction, CP points were found to be governing. Two sample elevation for both X
direction and Y direction is shown in Figure 2(ii) and (iii). However, after the ADRS conversion andgetting the IS values using Eq. (3), it was found that the seismic index of the building was not satisfactory.
Therefore, to identify the seismically deficient stories and the story-wise capacity, restrained pushover
analysis was performed. in this analysis, stories lower than the concerned stories were kept
translationally restrained in the corresponding direction while performing the pushover analysis.

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(i)
(ii)
(iii)
Figure 2. (i) Seismic demand index as per revised BNBC (2020). Plastic hinge
crosses the CP limit for different members in (ii) elevation 01 (X dir.) and(iii) in Elevation A (Y dir.)From
thestory shear vs. story drift
graph, the seismic capacity(IS) of each story wasdetermined. It was foundthat the lower two stories inX direction and the lowest
stories in the Y direction
have unsatisfactory seismicperformance.
To compare,the bare-framed building
was also evaluated using
the second-level evaluation
method of the JBDPA
evaluation guideline.

Figure 3. Comparison of the Story-wise capacity in X (left) and Y(right) direction using the DSE method and JBDPA second levelevaluation.

(i)(ii)(iii)
Figure 4. (i) C-F relation for 3F before and after considering the brick masonrywall, (ii)C-F relation of all stories (Y direction) considering the brick masonrywall and (iii) story-wise variation of IS index (X direction).
However, the result for the bottom stories varies (Figure 3) from that found from theanalysis using the DSE method. In the JBDPA method, the bottom-most two stories in Y direction
and lowest story in X direction were found to have inadequate seismic performance.

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A significant difference is found for the second story, where the evaluation result obtainedis contradictory for these two methods for both directions. It essentially shows the conceptual difference
between these two methods, i.e., the variation in assumption regarding the relative lateral stiffness ofthe frame element. In the JBDPA 2nd level evaluation method, all the columns are considered to bereached their full potential strength by forming hinge only in the column. Therefore, when using theresult from this evaluation, judgment for buildings or stories could give drastic value changes andpossibly be erroneous. On the contrary, since the DSE method considers the actual design philosophy,
this evaluation method could be more economical for the low-rise buildings in Bangladesh.

(i)
(ii)
Figure 5. (i) Out-of-plane demand and capacity for the walls in Y direction.
(ii) Improvement in C-F relation after retrofit. Illustration shown for 2F-X dir.
From the range of the values of the seismicindex, it is observed that it varies in a wide range forevaluation results using the DSE method compared tothe JBDPA 2nd level evaluation method. It indicates theDSE method is relatively more sensitive than the 2ndlevel evaluation method as per JBDPA.
It is observed that the consideration ofwalls can show a more realistic behavior by improving
the deformation behavior providing sufficient strength
at lesser ductility (Figure 4). Therefore, consideration ofthis property should give a more economical result.
Thus it also shows the higher margin of safety for thenon-structural elements by reducing the lateral drift of astory.
The building contains various sizes ofFigure 6. Comparison of Story-wisewalls with different thicknesses. All are checked using
seismic index value before and after
three different equations for out-of-plane capacity andretrofit.
compared to the limit design value recommended in
BNBC 2020. Thus, the adequacy of out-of-plane failure is tested, and it is observed that all the walls
considered as structural walls are safe against out-of-plane failure. From Figure 5(i), it is observed
that, the demand is significantly low compared to the capacity calculated using different equations inmost cases. Therefore, for this type of buildings and wall configuration, out-of-plane failure may notgovern.
However, the installing connection between the surrounding frame element and the FC
layer during retrofitting would provide an additional safety margin. It is observed that the inclusion ofwalls in the evaluation process could increase the seismic capacity of the story. Therefore, an additional
number of masonry walls will increase the strength of the building. However, the ductility range of the5wall is very small compared to the frames of the stories. Therefore, considerable strength is required
from the masonry wall to achieve the additional strength needed in the lower ductility (Figure 5 (ii)).
The retrofitting calculation shows that FC retrofitting can be very effective andstraightforward in improving seismic index (Figure 6) since this method primarily involves nonstructural elements, e.g., masonry wall and reduces interference with the structural element, e.g., beam,column, etc.
5. CONCLUSIONS
From the results of this research, it can be concluded that the DSE method for seismic evaluation ofbuilding can assess the seismic performance and capture the failure initiation process effectively for thestrong-beam weak-column cases comparing to JBDPA second level evaluation. Since the story’s
capacity is based on the two sets of limiting criteria, i.e., CP points and LP points found from thepushover analysis, this is more advantageous because it additionally provides identification of
structurally vulnerable members. Moreover, since it is more sensitive with a wide variation range of IS
value than the JBDPA second level evaluation method, this can lead to a more accurate evaluation andthus economic retrofit accordingly for the low-rise RC buildings of Bangladesh.
Again, from the results of the story’s capacity, when the infill wall effect is considered, it
is found that the lateral load capacity can be increased, and the deformation behavior can be improved.
Therefore, a proper layout plan of these masonry walls can increase the story’s capacity and make thenon-structural members safer.
The out-of-plane failure is found not to be governing for this selected typical low-risebuildings composed of brick masonry walls.
Finally, the ferrocement retrofit method was tested on the building for retrofitting purposes
and found to effectively improve the lateral load capacity of the seismically deficient stories without
intervening with the primary structural member e.g. vertical lateral load resisting frame elements.
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 would like to express
my sincere gratitude to my supervisor Dr. Matsutaro Seki, Advisor Dr. T. Kashima for his valuable
support and guidance that helped me to accomplish my research successfully.
REFERENCES
American Society of Civil Engineers, ASCE, 2013, Seismic Rehabilitation of Existing Buildings, inASCE /SEI Standard 41-13, New York.
BNBC 2020, 2020, Bangladesh National Building Code 2020, Housing and Building Research Institute,
Ministry of Housing and Public Works, Bangladesh.
H. A. Washali, D. Sen, March 2021 draft version, Seismic retrofit guidelines by ferrocement laminationfor existing RC frame with infilled brick masonry wall, SATREPS-TSUIB project, Bangladesh.
Japan Building Disaster Prevention Association (JBDPA), 2001, Standard for Seismic Evaluation ofExisting Reinforced Concrete Buildings.
Y. Nakajima, M. Seki, H. Suga, R. Islam., 2020, Proposal of a new detail seismic evaluation method
based on Japanese and American evaluation standards for the existing RC buildings.

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