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Selecting a suitable Seismic Fragility Analysis procedure for seismic assessment of old
Reinforced Concrete buildings in Yangon, Myanmar
Kham Yeik Moe
([email protected])
Department of Civil, Environmental, and Infrastructure Engineering
Volgenau School of Engineering
Introduction
People across the world suffer the impacts of unpredictable natural disasters. Among
these disasters, earthquake is a common problem to our society. As earthquake can happen in
anytime and anywhere, even buildings in low-seismic zone should be considered and assessed.
As Reinforced Concrete buildings have been developed for long time ago, there might be some
weakness of construction technique and materials in the old RC buildings (Cardone & Perrone,
2015; Ellingwood, Celik and Kinali, 2007; Jeon, DesRoches, Brilakis and Lowes, 2012).
Moreover, low and mid-rise RC buildings represent a common type of construction in the world
(Ramamoorthy, Gardoni & Bracci, 2008).
For these reasons, engineers try to predict the performance of old existing RC buildings
during earthquake and post-earthquake by using different evaluations. In researches, the authors
revealed that old RC buildings were built without consideration of seismic load and mentioned
that evaluation old RC buildings is required (Celik and Ellingwood, 2009). The main weakness is
that most of the Gravity Load design RC buildings have poor lateral load resistance and
deficiencies in column and beam-column joint (Jeon et al., 2012; Ellingwood et al., 2007).
Previous researches, the performance of the building during and after earthquake was calculated
based on Seismic Fragility Analysis which is the most common method for predict the damage of
old RC buildings (Lowes and Li, 2009). Even though all are based on Seismic Fragility Analysis,
the procedures in each study are different due to the variation of considered parameters. In my
city, Yangon, Myanmar, the assessment of the Seismic performance of the existing RC building is
not developed. Moreover, most of the building in Yangon are low-rise and mid-rise RC building
with only consideration of Gravity Load. Jeon et al., (2012) revealed that these type of building
cannot withstand even for moderate intensity earthquake.
Thus, in this paper, the different procedures required for Seismic Fragility Analysis will be
presented by reviewing the previous researches which only focus on the expected damage of
Reinforced concrete buildings using Fragility curves. And the critical parameters are going to be
investigated. Then we are going to select what procedure or what parameters should be adopted
for applying to existing RC building in Yangon, Myanmar for the sake of accomplishing the
purpose of this paper. The process of how to apply in Yangon, Myanmar should be carried on in
near future. My research question is “Which methodology of assessing the Seismic Performance
of the Reinforced Concrete building based on Seismic Fragility Analysis could be applied to
Reinforced Concrete Buildings in my city, Yangon, Myanmar?”.
The weakness of the old RC Building
The main common weakness of the old RC buildings is lacking of consideration in seismic
load when they were built. As a result, there is not enough lateral-load resistance to withstand
earthquake. Especially, it is found in the reinforcement Steel and Bar. The reasons of vulnerability
of Gravity-load Designed Reinforced Concrete Frames to seismic load are (1) there is little or no
transverse shear reinforcement in the beam–column joints, (2) there is termination of beam bottom
reinforcement within the beam–column joints with a short embedment length, (3) bending moment
capacities of column are close to or less than bending moment in the joining beams, which can
cause column sideway or soft-story mechanisms, (4) the longitudinal reinforcement ratio is seldom
more than 2% in columns (Ellingwood et al., 2007). Celik and Ellingwood (2009) extended the
previous study of Ellingwood et al.,(2007) by adding three more deficiencies of the old RC
building. They are (1) minimum transverse reinforcement in columns (2) inadequate lapped splices
of column reinforcement which are located in potential plastic hinge zones just above the floor
levels (3) placing construction joints immediately below and above the beam–column joints.
Seismic Fragility Analysis
Seismic Fragility Analysis is used to predict the damage of the buildings, to estimate the
cost of retrofitting or repairing, and to assist in decision making for renovation (Lowes and Li,
2009, Pejovic and Jankovic, 2015) . In Seismic Fragility Analysis, forming a fragility curve is a
critical. The procedure to from fragility curve is slightly different from each study. It depends on
what the authors want to emphasize on and the condition of the buildings. For example, if the
authors want to focus on the projected damage due to corrosion rate, the procedure will be included
some addition equations related to corrosion. Or if the authors do not want to consider about
corrosion but more focus on the structural and non-structural damage, they will use another
procedure.
Common Parameters for seismic assessment base on Seismic Fragility Analysis
(a) Building Stock Characteristic
Most of the research rarely mentioned how to collect the building information as
the authors usually took the data information as references from the previous study.
However, Ricci, Gaudio, Verderame, Manfredi, Pollino, and Borfecchia, 2014 emphasized
on how to collect accurate data and what characteristics are essential in assessing the
buildings. According to the condition of the building and the location, the main parameters
which should be considered, can be varied. Building Stock characteristic of the studied
buildings is the most primary necessary to start assessing process. The basic data of
building such as the structural typology, the date of the building built in order to estimate
what kinds of building codes was used at that time, the number of story, the total height of
the building, the soil type on which the studied building was constructed and the quality of
using construction materials should be collected first (Ricci, Gaudio, Verderame,
Manfredi, Pollino, and Borfecchia, 2014). The more the collected data is accurate, the more
accurate result can be out.
(b) The effect of corrosion
There are only few researches which include consideration of corrosion in
assessing. The others neglected about it. But Yalciner, Sensory and Eren (2015) proved
that the corroded buildings can also be hazard to public safety when the earthquake is
happened. He clarified what are the effect of corrosion and the impacts of it. The effect of
corrosion is caused by reduction in diameter of longitudinal bar, cross-sectional area of
tensile steel bar and reinforcement bars. It can produce deformation in rebar ultimate,
cracking in concrete, decreasing in bond-slip relationship. Moreover, the main effect of
corrosion is weakening in performance level of building during earthquake (Yalciner;
Sensoy; and Eren, 2015).
(c) Ground Excitations
Whenever assessing the buildings, the acceleration of ground motions is essential
to predict the damage and to know the current vulnerability of the building. After collecting
the building data, ground excitations must be selected to run the program in order to get
Damage level, Performance level and so on. Ground excitations play one of the main roles
in assessing the performance of the buildings. In the selection of appropriate ground
excitations, Ji, Elnashai, and Kuchma, (2009) and Celik and Ellingwood, (2009) mentioned
that the magnitude of earthquake, the distance to the earthquake focus and the historic high
magnitude earthquake records of the region are essential. But, Ji et al.,(2009) provided
more detail consideration about ground motion, for instance, the impact, when earthquake
occurs far away from the source but the magnitude is high, should also be considered. In
addition, Celik and Ellingwood (2009) stated that artificial seismic loads which are usually
higher than the reality should be considered, if the region is low-seismic zone and there is
no enough record. Ji et al., 2009 concluded that the main role of ground excitation is to
form Fragility Function .
(d) Structural modeling
The structure of building can be modeled by different methods. According to the
researches, Ji et al., (2009) used Uncertainty modeling which contains two parts: Material
uncertainty and Ground Motion uncertainty, Pejovic and Jankovic(2015) used Non-linear
modeling, PERFORM-3D program which is also common method for Structural Analysis,
both Ibrahim and EI-Shami (2011) and Celik and Ellingwood (2009) used Uniaxial
constant confinement concrete model and uniaxial bilinear stress-strain model in order to
form detail structural component modeling , and Jeon et al., (2012) used OpenSees for the
analytical modeling of the interior and exterior SBC sub-assemblages, while Celik and
Ellingwood used Opensess for Finite-Element Structural Models and Bilinear Steel Model.
(e) Damage State
The damage state is got after running structural modeling program with selected
ground accelerations. It is also one of the main parameters to form the Fragility curve which
is the final stage in Fragility Analysis. Sometimes it can be skipped to from Fragility curve.
However, if the cost of repair and retrofitting program is considered, this state is essential
as there is relationship between the cost of loss and damage state. The level of damage can
be determined depends on the harshness of concrete cracking, crushing and buckling of
reinforcing steel. Moreover, it is mainly derived from the value of median drifts. But,
Lowes and Li (2009) mentioned that sometimes it can be related with the coefficient of
variation (R2). The damage state of the building due to earthquake can be categorized into
four states: slight damage, moderate damage, extensive damage and complete damage. All
these damage states count for both structural and non-structural damage (HAZUS, National
Institute of Building Sciences,1999). Pejovic and Jankovic (2015) calculated the maximum
inter-story drift by dividing story displacement to height of the story while the other authors
used different method, for example, drawing the graph to read the value of Drift ratio.
Although the inter-story drift(displacement) can be calculated from different methods, the
maximum inter-story drift is represented to the level of damage.
Table1. Drift ratio (%) limits associated with various damage level for reinforced
concrete structure (Ghoborah, 2004)
State of
Ductile MRF
damage
Non-ductile
MRF with
MRF
Infills
No damage
<0.2
<0.1
<0.1
Light
0.4
0.2
0.2
Damage
Moderate
<1.0
<0.5
<0.4
1.8
0.8
0.7
>3
>1
>0.8
damage
Severe
Damage,
Collapse
(f) Performance level
The calculation of performance state is the most important state as fragility curves are
usually formed based on the level of performance. The performance level can be calculated
after selection of appropriate intensity of the earthquakes. It is mainly selected depending
on the limit state (Celik and Ellingwood, 2009). Ji et al., (2009) explained detail about what
is limit state which Celik and Ellingwood (2009) mentioned, that is, performance level of
the building can be derived from two approaches: Qualitative approach which is same as
FEMA 273/356 (2000) and Quantitative approach. There are three limit states in
Quantitative approach such as Serviceability, Damage Control and Collapse Prevention. Ji
et al (2009) also argued that the performance level of the building is also related with
structural damage and the levels of inelastic behavior. Because when the damage of the
building is high, the structural behavior may go beyond elastic limit, in order words, the
building cannot return to original condition itself and it is required to retrofitted. According
to the FEMA 273/356 (2000), the limit states to get performance level of the building is
categorized into four level: Operational (O), Immediate Occupancy (IO), Life Safety (LS)
and Collapse Prevention (CP). Ibrahim and EI-Shami (2011) defined detail because these
limits are widely used. They are,

Operational: The building is immediately suitable for normal use with minimal or
no structural and non-structural damage.

Immediate occupancy: The building suffers minimal or no structural damage and
only minor non-structural damage. Immediate occupancy may be possible.
However, some repair and restoration process may be required before next
earthquake.

Life safety: There are extensive structural and non-structural damage and before
re-occur earthquake the buildings need repair which cause economic loss.

Collapse prevention: The building may create a significant risk to life safety and
be considered as a complete economic loss.
Table 2. Maximum inter-story drift ratio for different performance level (Xue et al, 2008)
Performance
OP
IO
DC
LS
CP
0.005
0.01
0.015
0.02
0.025
level
Maximum
inter-story
drift ratio
Fig (1) – Relationship of Damage state and Performance level
(g) Fragility curve
This is the final state of the assessment. Based on the performance level and the
selected ground accelerations, the probability of the damage is calculated. The function
fragility curve is to display the damage state of the building. And it is more likely to
predict a particular damage state depend on the displacement of the story due to
earthquake. It can be calculated from lognormal distribution parameter which is different
in each case (Lowes and Li, 2009). Likewise, Ibrahim and EI-Shami (2011) defined the
fragility curves as the lognormal function which shows the probability of reaching or
exceeding a specific damage state. And it can be derived from different lognormal
equations which depend on what kinds of ground acceleration is considered, for example,
Spectral acceleration, Spectral displacement, peak ground velocity and PGA. There are
four kinds of fragility curves: Empirical Fragility curve, Expert Fragility Curve,
Analytical Fragility Curve and Hybrid Fragility Curve. Moreover, fragility curve is a kind
of tool using in assessing whether the building needs repair or replacement. It is also
useful for making decision for retrofitting (Pejovic and Jankovic, 2015).
Fig (2) – Fragility curves for Frame C and D
Selecting a suitable procedure of seismic assessment for Yangon, Myanmar
(a) Building Stock Characteristic
This is an essential procedure for every assessment. The detail building data should
be collected as much as possible. Assuming basic average building characteristics in
Yangon: the average number of story is 8, soil type is clayey soil which is not strong enough
for high-rise buildings and the quality of building materials is between low and moderate.
Yangon is not included in a high-humidity area, therefore, the effect of corrosion can be
neglected. The detail data of structural components such as the detail drawing plan of the
buildings is possible, the more accurate result will be out.
(b) Structural Modeling
As there has not so developed in computer software, non-linear modeling and
Finite-Element Structural modeling would be more suitable as they are already being used
for Structural Analysis and Design in Yangon, Myanmar. Furthermore, they are suitable
for every type of building.
(c) Ground Excitation
Yangon, Myanmar is between low and moderate seismic zone and it is also close
to Bago-Fault. As the accurate past seismic records for Yangon is unavailable, artificial
ground excitations should be created (Celik and Ellingwood, 2009). More than three
ground motions should be collected to get more accurate estimate.
Fig (3) – Zoning map of Sagaing Fault
(d) Damage State
Generally, in Yangon, the damage of the building is surveyed by walk-in survey
and collected only observable damage. As a result, it is not safe for public as sometime
deficiencies and damage may occur in the reinforcement but it is not visible and repaired.
Thus, in this paper, a systematic advanced method is recommended to use. That is, after
running a program of modeling with selected ground motions, the values of inter-story drift
(displacement) will be out. These values represent to the state of damage. To determine the
damage state, the maximum inter-story drift is divided by the height of story (Pejovic and
Jankivic, 2015). The reasons of using that equation are the authors revealed that calculation
in 2015 which could be regarded as latest and it is also easy to calculate. The level of
damage will be categorized as Figure (1).
(e) Performance level or state
According to the damage state and story drift, performance level can be calculated.
For Yangon, Myanmar, performance level of FEMA 273/356 (2000) is adopted as most of
the building codes using in Myanmar are adopted from the authorized Civil Engineering
building codes of USA. So Table (2) data will be applied for Myanmar.
(f) Fragility Curve
In Myanmar, ground accelerations are mostly measured in PGA (Peak Ground
Acceleration). So, the lognormal distribution function equation which related to PGA is
going to use for Yangon.
PD/PGA= (ln(PGA)-) /
where  is the standard normal cumulative distribution function;  and  are the mean
value and standard deviation of the natural logarithm of PGA at which the building reach
a specific damage state or performance level, D. After that Analytical Fragility Curve can
be drew using lognormal distribution, performance level and ground excitations.
According to the data from fragility curve, the probability of damage can be assumed.
Conclusion
Assessing before earthquake can reduce not only the rate of fatality and damage but also
the global economics. Even in low-earthquake zone, buildings should be assessed the
vulnerability as the nature phenomenon of the world is getting worse and worse. The above
mentioned procedure is selected only base on the accessible and low cost. This implementation
of selecting suitable procedure may arouse engineers in Yangon, Myanmar to focus more on
seismic preventions process, to form a protocol for seismic assessment, to collect the past
significant earthquake records. Every first implementation in everywhere may face difficulties.
So, how could assessment of old RC buildings in Yangon implement? How would experts
make a decision for what kind of ground excitations are going to use, for example, collecting
the past records or creating a suitable artificial acceleration? If we can solve these basic
problems, we can easily take over future big problems, as an illustration, now we are trying to
figure out how to start our assessment, after that there are many steps left such as retrofitting,
repairing and replacement process. Similarly, collecting the earthquake records might be
beneficial not only for vulnerability assessment but also for designing field which could give
more safety to public. If we can solve these basic problems, we can easily take over future big
problems, as an illustration, now we are trying to figure out how to start our assessment, after
that there are many steps left such as retrofitting, repairing and replacement process. Similarly,
collecting the earthquake records might be beneficial not only for vulnerability assessment but
also for designing field which could give more safety to public.
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