Citation:Durán, S., T. Saito (2021), Basic study on the development of design code for seismically isolatedbuildings in El Salvador, Synopsis of IISEE-GRIPS Master’s Thesis.

BASIC STUDY ON THE DEVELOPMENT OF DESIGNCODE FOR SEISMICALLY ISOLATED BUILDINGS IN
EL SALVADOR.
Susan Durán1,2

Supervisor: Taiki SAITO3

ABSTRACTThe current Urban Regulation in the Metropolitan Area of San Salvador (Master Plan, 2017) encourages thedensification in the territory and promotes the growth in height due to the lack of land. The project developers
are more interested in using new seismic response control systems. This study intends to propose a design
procedure for seismically isolated buildings in El Salvador. A design of a base isolation system for the target
building is conducted, applying the Capacity Spectrum Method and Time History Analysis (THA), following
the Japanese Standard. The effect of the aspect ratio is analyzed by the history of axial forces of models with
two aspect ratios, lower than and higher than 4, by THA and pushover. The capacity curves are associatedwith the tensile failure obtained by pushover, considering the "Ai" and uniform load distribution. The analysisof the history of axial forces of the two models proved the accuracy of the Japanese recommendation in termsof the aspect ratio in the isolated building. The significant effect of the type of horizontal load distribution
was also analyzed on evaluating the tensile failure in the isolation devices using the capacity spectrum method.
It is found that uniform load distribution is more appropriate in the capacity spectrum method.
Keywords: Design procedure, seismically isolated buildings, aspect ratio.
1. INTRODUCTIONEl Salvador is located on the Pacific coast of Central America, in a region with high seismic activities within
the Pacific Ring of Fire and is organized into 262 municipalities, 14 of them are part of the Metropolitan Areaof San Salvador (AMSS), which is the most densely populated area in the country. According to theSalvadoran Chamber of Construction (CASALCO), between 2018 and 2021, the multi-story buildings built
in the country will add 212 projects, representing 35% of the construction projects of the private sector. In2018, the number of projects increased approximately three times the amount of the previous year. This trend
highlights the urgency of updates to the regulations. The seismic isolation technique is new in El Salvador.
The first project that includes this technique began construction in 2019. However, there are no regulations
or technical methodology to analyze buildings with base isolation.
2. DESIGN ISOLATION LAYER OF THE TARGET BUILDING
2.1. Seismic isolation devices.
In the base isolation systems, the devices provide high lateral flexibility and damping properties to absorb
the earthquake energy. The superstructure is separated from the ground movement, reducing the relative

1The Mayors Council and Planning Office of the Metropolitan Area of San Salvador, El Salvador.
IISEE-GRIPS Master’s course student.
3
Professor, Department of Architecture and Civil Engineering, Toyohashi University of Technology.
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lateral displacements of story, structural and non-structural damage, and protecting the content inside thebuildings. This study is focused on the lead rubber bearing (LRB).
2.2. Description of the target building.
The main information of the target building is shown in Figure 1 and Table 1.
Y Direction

X Direction

Figure 1. Typical floor plan and model of the target building. STERA 3D
Table 1. General information of the target building.
X DIRECTIONY DIRECTION
HEIGHT
USE OF BUILDING

55.2
m
18.8
m
42.75
m
12-stories residential building

2.3. Setting of the isolation devices.
The configuration of the isolation devices is shown in Figure 2. The isolated building achieved a naturalperiod equal to 4.73 seconds. As shown in Table 2, the limit design deformation of LRB device is mδd =47.7cm.
Table 2. Characteristics of the isolation devices.

Figure 2. Arrangement of the devices.
2.4. Design procedure of the isolation layer by the Capacity Spectrum Method.
The response spectrum defined in the Salvadoran Technical Standard for Seismic Design (NTDS) with theconditions of the target building (Seismic zone 1, soil type S1, and the occupation category II), was used tocarry out the design by capacity spectrum method, as shown in Figure 3. The deformations of the isolation2

layer are calculated by the capacity spectrum method for standard and lower limit conditions of device
properties as shown in Figure 4. The requirement δresponse < mδd =47.7 cm is satisfied.

Figure 3. Design Acceleration Response Spectrum of El Salvador.

Figure 4. Results of Design by Capacity Spectrum Method.
2.5. Design procedure of the isolation layer by the THA.
Six input ground motions
Table 3. Results of THA (maximum displacement in isolation layer)
are used in the THA:TIME HISTORY ANALYSIS. LOWER LIMIT.
two real data from El
MAXIMUM DISPLACEMENT IN ISOLATION LAYER (CM). LOWER LIMIT.
Salvador (the 1986 San
Original data of Earthquakes Aritificial ground motions with response spectrum compatibleSalvador and the 2001 DIRECTIONin El Salvador
with the design response spectrum of El Salvador
El Salvador) and four
San Salvador El Salvador El Salvador
Random Phase,El Centro, 1940 Kobe, 1995
artificialground
1986
2001
2001
120 sec.
X
10.17
19.99
40.14
31.11
42.33
21.16
motions
compatible
Y
21.36
14.66
45.95
43.89
39.69
27.84
withthedesign
response spectrum of El Salvador (based on the 2001 El Salvador, the El Centro 1940, the Kobe 1995, andrandom phase). The summary of the results of the maximum displacement in the isolation layer is shown inTable 3. The requirement δresponse < mδd =47.7cm is satisfied.

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2.6. Design procedure proposal based on the Japanese Methodology
The procedure for the design base isolation system proposed in this study based on the Japanese Standard isshown in Figure 5.

Figure 5. Design procedure proposal based on the Japanese Methodology.
3. ANALYSIS OF THE EFFECT OF THE ASPECT RATIO IN THE ISOLATED BUILDINGS.
A frame in the Y direction is chosen to develop the 2D model with an aspect ratio equal to 2.27. The accuracyof the model is checked by comparing the capacity curves of the 3D model with the 2D model, pushing inthe Y and - Y directions. The curves of the 2D model are similar to the curves of the 3D model, as shown inFigure 6 for lower and upper limit conditions.
Y Direction

443 2 1

Figure 6. Device numbering and accuracy of the 2D model (aspect ratio equal to 2.27).
3.1. History of axial forces by the THA
Five input ground motions are used to analyze the history of axial forces by the THA: the 1986 San Salvador,the 2001 El Salvador, artificial ground motion based on the 2001 El Salvador, the El Centro 1940, and theKobe 1995. The graphs of axial forces are obtained to check if the tensile stress is exceeded; this process isexemplified in Figure 7. After performing this analysis with the models with the aspect ratio equal to 2.27
and 4.5, the results showed that in the model with an aspect ratio of 2.27, the allowable tensile stress is notexceeded, but it is exceeded in the model with an aspect ratio 4.5.

Figure 7. Process of the analysis of history of axial forces by THA of the model with the aspect ratio
equal to 4.5. Input ground motion: Artificial Earthquake based on the El Centro 1940.
3.2. History of axial forces by pushover
The history of axial forces is conducted considering the “Ai” and uniform load distributions. The graphs ofaxial forces are obtained, and the displacement where the tensile force reaches the allowable tensile stress isidentified; this process is exemplified in Figure 8, and the results are presented in Table 4. The tensile failure
occurs at smaller displacements when the load distribution “Ai” is considered.
Table 4. Results of ultimate point for tensile failure of themodel with the aspect ratio equal to 2.27. considering “Ai”
and uniform load distribution by pushover.
ULTIMATE POINT FOR

Figure 8. History of axial forces by THA ofthe model with the aspect ratio equal to 2.27.

TENSILE FAILURE (CM)No.
MODEL CONDITION DIRECTION
DEVICE "Ai" load Uniform load
distribution distribution
Y
Lower limit
-Y
39.20
62.50
ASPECT
Y
Standard
4
RATIO
-Y
25.71
44.75
2.27
Y
Upper limit
-Y
12.85
29.00
Y
Lower limit
-Y
31.80
51.50
ASPECT
Y
Standard
4
RATIO
-Y
18.80
35.50
4.50
Y
Upper limit
-Y
7.70
21.25

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3.3. Tensile failure of the device associated with the capacity curve.
The accuracy to consider the uniform load distribution in the capacity spectrum method to evaluate the tensile
failure of devices is verified considering the acceleration displacement response spectrum of the input groundmotions to get the performance points to compare them with the results obtained by the analysis of axial
forces by the THA of the model with aspect ratio equal to 4.50. The results of the capacity spectrum method
considering the uniform load distribution are compatible with the results of the THA, as shown in Figure 9.

Figure 9. Results obtained by the THA and the capacity spectrum method of the model with aspect ratio 4.50
4. CONCLUSIONS
The isolation layer of the target building designed in this study based on the Japanese Standard using Capacity
Spectrum Method includes three important design criteria: the ultimate shear strain of the device, the gap
limitation, and the horizontal deformation at the tensile failure of the device.
The Japanese Standard considers “Ai” load distribution for the pushover analysis. However, in
this study, it was found out that the deformation at the tensile failure of the isolation device largely depends
on the load distribution, and the “Ai” distribution underestimates the deformation. This studied was focusedon the load distribution of the capacity spectrum method. The accuracy of estimating the horizontal
deformation at the tensile failure was discussed by models with two different aspect ratios (lower than andhigher than 4) by comparing the THA. Through this study, it was found that uniform load distribution is more
appropriate in the capacity spectrum method.
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. To God first, the owner ofmy life. I want to express my sincere thanks to my supervisor Dr. Taiki Saito, advisor Dr. H. Suwada, theCourse Leader Dr. T. Azuhata and all IISEE / BRI and JICA staff.
REFERENCES
American Society of Civil Engineers, 2016, Minimum Design Loads and Associated Criteria for Buildings
and other Structures, United States of America.
Higashino, M., Okamoto, Sh., 2006, Response control and seismic isolation of buildings, InternationalCouncil for Research and Innovation in Building and Construction, Japan.
Saito, T., Takano, S., 2017, Design Procedures of Response Spectrum Method and Time History Analysis of
Seismic Isolation Buildings in Japan, Toyohashi University of Technology, Japan.
https://www.eleconomista.net/economia/El-Salvador-proyectos-verticales-suman-305-millones-201910310024.html

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