SEISMIC PERFORMANCE ASSESSMENT OF
REINFORCED CONCRETE BUILDINGS WITH
MASONRY INFILL WALLS IN EL SALVADOR
Jorge Alberto Stanley Flores Gonzalez
MEE17711

Supervisor: Shunsuke SUGANOABSTRACTIn this study, two buildings of 3-story with reinforced masonry walls are evaluated, which belong toschool typologies, following the methodology proposed by the JBDPA standard and proposing amethodology to estimate the strength of the masonry infills. The increase of the constructions ofbuildings with concrete frames with reinforced masonry walls has become very popular, and it isimportant to understand the behavior of the infill walls. It should be noted that the JBDPA does notinclude provisions to assess buildings of concrete frames with reinforced masonry infill walls. Therefore,
this study proposes a methodology to consider the reinforced masonry infill walls. A comparative
analysis is done to consider only the bare frame and frame with reinforced infill walls. An approach of
how to estimate the strength of reinforced masonry infill walls is proposed.
Keywords: Reinforced Masonry Infill, Seismic Protection Index, Seismic Evaluation.
1. INTRODUCTION
The need for a method of seismic evaluation of the buildings of El Salvador is becoming increasingly
necessary, due to the damage caused by previous earthquakes, which left important economic losses,
and at the same time, human losses. Although there have been field surveys of visual inspections ofbuildings damaged by past earthquakes, these remain only in the stage of rapid inspection. There is no
methodology to follow in the national code to rehabilitate these structures; damages were reported forthe 1986 and 2001 earthquakes due to many factors such as the lack of the control of illegal
constructions, that do not follow any national code or standard and the lack of engineering criteria, whichleads to non-earthquake-resistant buildings. In the same way, old buildings which are still in use,
suffered damage due to past earthquakes and not much attention was given to them, although theirdesigns followed the oldest version of the national codes which were not reinforced so that they cancomply with the current code.
2. DESCRIPTION OF THE ANALYZED BUILDINGS
Two buildings of three levels were chosen. The walls are of reinforced masonry infill walls with athickness of 150 mm in all floor levels, with a Compressive Strength of Masonry of 7.83 Mpa with wallsthat has openings. The compressive strength of Concrete is 20.6 Mpa, and the yield strength of thereinforcing bars of the columns and walls is 412.00 MPA. This building was examined with the Japaneseseismic capacity evaluation to evaluate numerically and through Stera 3D to check the validity of thecalculation.

Mayors Council and Planification Office of the Metropolitan Area of San Salvador, El Salvador.
**Professor Emeritus, Hiroshima University, and Visiting Research Fellow, IISEE, BRI, Japan.

1Figure 1. Target Building 1.

Figure 2. Target Building 2.

Figure 3. Details of Infill Masonry Walls for Building 1 and 2.
3. THEORY AND METHODOLOGY
3.1. Proposed methodology for seismic evaluation of low-rise RC buildings with reinforced
masonry walls
Two levels of seismic evaluation are proposed for a two school buildings; based on the philosophy of
the Japanese standard and considering the effect of the reinforced masonry infill walls. A first levelscreening is made considering only the geometrical properties of the vertical members and the second
level of seismic evaluation is performed considering the reinforcement of the vertical members. The

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seismic judgment is done by comparing the seismic index of the structure, Is, and the seismic demandindex which is proposed based on the seismicity of El Salvador.
3.1.1. Basic principles of seismic evaluation methods
The evaluation of the seismic performance of the Japanese standard involves the strength anddeformability of the structure, as it is well known that buildings resistant to earthquakes are not only afunction of the lateral force but also that of deformation.
In a structural evaluation, it is necessary to know the structural details of the building of interest
with which the strength and capacity of deformation can be calculated. What remains to be found is theintensity of the external disturbance.
I s  E0 S DT

(1)

where SD is the irregularity index based on the engineering judgment of the plan irregularity andunbalance distribution of stiffness, and the value of T is the time index where the effects of aging,cracking and deflection are considered in this term.
In the Japanese Standard, the value of Is must be higher than the seismic demand index, Iso,of the JBDA Standard which is expressed according to Eq. (2).
I so  E s C G C I(2)where Es is the basic demand protection index, 0.8 for the first level procedure and 0.6 for the second
level procedure, CG is the correction factor for geology and CI is the importance factor.
Since SD and T are considered as one, thus the basic seismic index E0 becomes identical to theseismic index Is, and for the evaluation of the safety this value can be compared with a protection index,
expressed as a product of ground peak acceleration and the response magnification factor in the form of
linear response spectrum (Hiroyuki 1981).
3.1.2. First Level Screening
In the analysis of the building in the first level screening evaluation, the first level screening of theStandard for Seismic Evaluation of Existing Reinforced Concrete Buildings (JBDPA) is taken as a guidefor the strength and ductility index of concrete columns, and for the strength of masonry infill theTechnical Standard for Reinforced Masonry of El Salvador is used. The ductility index in this study isconservatively taken as 1.0. The strength capacity of the building for the masonry infill walls is givenby the following equation:cw 

2   c . Ac   . inf . AifW(3)

where τinf is the average shear strength of masonry infill walls, τinf = 0.4√f’m, α is the opening reduction
factor of infill wall, ΣAif is the total area of the infill walls, and W is the total weight of the building.
3.1.3. Second Level Screening
In order to include the infill walls in the seismic evaluation for the second level screening, Matsumura
equation is suggested for the maximum strength of the infill panel and reaching a drift of 1/250 with a
F = 1.0, that at this drift is assumed that reach the Life Safety limit state, at larger values of inter-story
drift, the infill wall loses the ability to withstand more forces. The calculations of the strength of thecolumns and concrete wall is based on the JBDPA Standard. The model proposed by Hossein andKabeyasawa (2004) is the one used in this research, which is the one adopted by Stera 3D, which
proposes a simple model based on the diagonal strut, which is represented as a horizontal spring, which
considers the effect of the openings. At the same time Al-Chaar, considers the model of the infill walls3

as a strut model, but taking into consideration that the openings change the properties of the wall. Thisis reflected in the fact that the reduction factor modifies the width of the diagonal strut, which wasconsidered in this investigation.





0.76


'
'

Vn  k u k p  0.012  Fm  0.18 p h f yh f m  0.2 0  0.875td h  0.7

 d




(4)
𝑎

where Ku= 0.64, Kp: 1.16 𝜌𝑣0.3 is the coefficient of the effect of flexural reinforcement ratio 𝜌𝑣 𝑣 %,𝑡∗𝑑is the vertical reinforcement ratio, av is the area of the vertical reinforcement, t is the thickness of thewall, d is the total length of the wall - t/2, h is the height of the wall, F’m is the compressive strength ofmasonry, 𝛾 = 0.6, 𝛿 = 1, 𝜌ℎ , is the lateral reinforcement ratio, 𝑓𝑦ℎ , Yield strength of the horizontal
reinforcement and 𝜎𝑛 is the axial force.
3.2. Seismic protection index
PSHA studies that have been carried out to date in the country have been investigated. A well-known
study in this field is the work carried out by researchers Benito et al. (2009), which was based on an
initiative carried out throughout the Central American countries and determine the seismic hazard onrock conditions. A uniform hazard spectrum and several seismic hazard curves have been proposed bythese researchers for the city of San Salvador in rock conditions, highlighting three hazard levels of 500,
1000 and 2475 years of return period. To be consistent with the methodology of PSHA Benito et al.
(2009) for El Salvador, an approximation of the relationship between the PGA with the return periods
will be made. This approximation is based on plotting in log-log scale the values coming from theseismic hazard curves of PGA, thus obtaining a power law linear function, which allows predicting
return periods for lower peak ground motions values.
The above, with the aim of covering most of the possible, the spectrum of the existing
variability in the seismic records, and subjecting the targets buildings to more recurrent acceleration
values and observing their performance in respect to the exceedance of their performance levels. Next,
the graph obtained from the PEM seismic hazard curve of the PSHA study by Benito et al. (2009),
assuming a constant site amplification value of 20% for this intensity measure (PGA).
Table 1. Basic Seismic Protection Index. Upper
values for flexural failure type building, lower
values for Shear failure type building.

Figure 4. Approximation of the seismic hazard
levels from the result of PSHA of Benito et al.
(2009).
4. RESULTS AND DISCUSSION
4.1. First level screening
As a first part of the evaluation, reinforced concrete walls were analyzed as a proposal for the retrofit.
In the following tables show a summary of the strength values provided by each of the vertical elements,
including concrete walls.

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Figure 5. Comparison of bare frame and framewith Reinforced masonry wall in the First Level
Screening, building 1.

Figure 6. Comparison of bare frame and framewith Reinforced masonry wall in the First Level
Screening, building 2.

Figure 7. Retrofit with infill wall in Building 1.

Figure 8. Retrofit with infill wall in Building 2.

It can be seen that when considering the reinforced masonry infill walls, which are part of theelements that are capable of resisting lateral forces, the performance of the structure grows significantly
in strength, as many authors have described it in other investigations with different types of masonry. Itshould be noted that for strength analysis in this study the strength of reinforced masonry was takenfrom the National Masonry code of El Salvador, which is a value that depends on the Compressive
Strength of Masonry.
From Figure 7 and Figure 8, it can be highlighted that by increasing structural elements withgreater capacity to resist lateral forces such as concrete walls, it reaches a higher level of safety, and thestructure is safe considering the seismic demand index proposed.
4.2. Second level screening
The level of calculation of the vertical elements is more detailed in this stage, considering that the beams
are strong enough not to fail. Therefore, the calculation of the strength of the columns and the type of
failure is made, then the strength of the masonry walls was calculated using the proposed equation of
Matsumura.

Figure 9. Retrofit with infill wall in Building 1.

Figure 10. Retrofit with infill wall in Building 2.

Figure 11. Comparison of 1st and 2nd levelscreening in Building 1.

Figure 12. Comparison of 1st and 2nd levelscreening in Building 2.

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When performing the seismic evaluation by the second level screening it can be seen in Figures
11 and Figure 12 that more strength can be perceived because this method is more detailed and considers
the contribution to the strength provided by the reinforcement of the infill wall.
5. CONCLUSIONS
When observing the results obtained from the analysis of the seismic capacity of the target buildings, it
is noted that when considering the infill walls in the evaluation process, the capacity of the building is
improved as we increase the capacity to withstand lateral forces. The method to choose for the evaluationof the building should be the most appropriate, either the first level screening or second level screening
depending on the type of project that is targeted.
The Seismic Protection index (Iso) is cross-related with the characteristic period of the soil
and the Peak ground acceleration which a specific site could have or experience, respectively. For
specific sites with long period characteristics (such as Tg = 0.6 sec) the value of the Iso is increased.
Thus the structure located on the site will need a higher capacity requirement. The above is also
influenced by the hazard level to be considered in the design. As for less recurrent scenarios, PGA values
are higher.
In order to take care of the integrity of the infill masonry walls, this study focuses on thevulnerability of these type of elements, so for the calculation of the seismic index of the structure focuseson the evaluation given by the equation that defines strength dominant, since these elements represent a
potential danger for people inside the building.
The reinforced masonry infill walls contribute to the improvement of the structures to be able
to resist large lateral forces since these provide lateral stiffness. The behavior of the interaction between
the frame and the wall is complicated, but many authors model it as a diagonal strut. It should be notedthat the modeling of the infill walls should continue to be investigated, given that there are different
types of infill walls, which could present different types of behavior.
ACKNOWLEDGMENTS
I would like to express my greatest gratitude to my supervisor Dr. Shunsuke Sugano for all the valuable
help he has given me during my research process, for respecting my suggestions and ideas and for the
direction and rigor that he has facilitated. At the same time to Dr. Tatsuya Azuhata, Mr. Inukai Mizuo
and Dr. Haruhiko Suwada for all their advice and encouragement that they gave me at every moment
during this process.
REFERENCES
AlWashali, H., Suzuki, Y., and Maeda, M., 2017, 16th World Conference of Earthquake Engineering,
Paper No. 788, Santiago Chile.
Benito, M.B., Lindholm, C., Camacho, E., Climent, A., Marroquín, G., Molina, E., Rojas, W., Escobar,
J. J., Talavera, E., Alvarado, G., and Torres, Y., 2012. Bulletin of the Seismological Society ofAmerica., 102, 504–523.
Japan Building Disaster Prevention Association (JBDPA), 2001, Standard for Seismic Evaluation of
Existing Reinforced Concrete Buildings (English Version).
Matsumura, A. (1987). Proceedings of the Fourth North American Masonry Conference. USA.
Ministry of Public Works (MOP) of El Salvador, 1994.
Hossein Mostafaei, Toshimi Kabeyasawa, 2004, Bulletin Earthquake Research Institute, The
university of Tokyo.
Regina Medina, 2001, OPAMSS.
Saito, T., 2004, Structural Response Analysis 3D (STERA 3D v.9.6 in 2018), Technical Manual, Japan.
Seki M., 2017, 16th World Conference Earthquake Engineering, Santiago, Chile, Paper No. 566.

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