Id 165-rapid seismic vulnerability evaluation of residential buildings in agartala city

ICOVP, 13th
International Conference on Vibration Problems
29th
November – 2nd
December, 2017, Indian Institute of Technology Guwahati, INDIA
RAPID SEISMIC VULNERABILITY EVALUATION OF RESIDENTIAL
BUILDINGS IN AGARTALA CITY
N. MAJUMDERPR
Ph. D Scholar, Department of Civil Engineering, NIT Agartala, India
nairita2112@gmail.com
L. HALDER CR
Assistant Professor, Department of Civil Engineering, NIT Agartala, India
erhalder@yahoo.co.in
S. KUMAR
Graduate Student, Department of Civil Engineering, NIT Agartala, India
R.P. SHARMA
Professor, Department of Civil Engineering, NIT Agartala, India
rps.civil@nita.ac.in
Abstract
Poor performance of buildings during past earthquakes in India has demonstrated the need for seismic risk
assessment for disaster management applications. Recently, 5.7 magnitude earthquake of Ambassa, Tripura
have highlighted an urgent need for assessment of existing buildings of the region in terms of seismic
resistance. For dealing with a large building stock, Rapid Visual Screening (RVS) is a better option to
prioritize the buildings for preliminary and detailed evaluations and also to have an idea about expected
damage grade that the building may experience during future earthquake. The present paper utilizes the
current edition of FEMA-154 to assess 350 residential buildings of Agartala city, out of which 59% are RCC
buildings, 33% masonry buildings and 8% composite buildings. Both RCC and masonry building types
belong to G3 to G5 damage grades of EMS-98 which symbolize moderate structural damage to collapse.
Keywords: Seismic vulnerability,rapid visual screening, Agartala
1. Introduction
In the last 7 years, north-east India has experienced 3 devastating earthquakes: 2011
Sikkim earthquake, 2016 Manipur earthquake and 2017 Ambassa earthquake which caused
massive damage to buildings and loss of lives. The main reason for such losses is low
earthquake awareness and poor construction practices.It is therefore, necessary to predict
seismic vulnerability of existing buildings for both risk prioritization and obtaining
building inventory. Most of the seismic evaluation methods follow three level assessment
procedures namely, Rapid visual screening (Tier 1 Evaluation) procedure, Preliminary
assessment (Tier 2 Evaluation) and Detailed evaluation (Tier 3 Evaluation)[1]. Out of
these, rapid visual screening (RVS) procedure is a simple and inexpensive method and can
be applied on a large building stock to evaluate the vulnerability profile of buildings.

Majumder, Halder, Kumar, Sharma2
Using this method, the most critical buildings can be identified for the more complex
evaluation procedure.
The procedure of Rapid Visual Screening of Buildings for Potential Seismic Hazards was
initially proposed in the US in 1988 with the publication of FEMA-154 report, which was
later updated subsequently in 2002 and 2015 to incorporate latest technological
advancements and lessons from earthquake disasters [2,3]. Although the procedure was
originally developed for typical constructions of US, it has been widely used in other
countries with suitable modifications.A simple seismic risk assessment procedure has been
developed for Turkey based on damage data of the 1999 Duzce earthquake [4]. In India,
there have been certain efforts towards developing rapid visual screening methods. Sinha
and Goel have proposed a methodology in 2004 to suit Indian cities conditions, whose
scoring system is similar to that of FEMA 154 [2,5]. This methodology has been utilized
by Nanda and Majhi with slight modifications and applied to NIT Durgapur campus of
India [6]. Arya has developed RVS survey form for all seismic zones II to V based on
probable earthquake intensities, building types and damageability grades [7]. For the first
time in India, Jain et al. have proposed a RVS method for RC framed buildings based on
damaged data of Ahmadabad city impacted during Bhuj 2001 earthquake [8]. However, the
method needs to be updated as well as tested with more data and for other regions of the
country.
Recently, a moderate earthquake of magnitude 5.7 has caused certain damage to buildings
of Ambassa, Tripura whichhave highlighted an urgent need for assessment of existing
buildings of the region in terms of seismic resistance. The present study utilizes the third
edition of FEMA-154 revised on 2015 to assess 350 residential buildings of Agartala city.
Agartala, the capital city of Tripura is located in the north-eastern part of India. It is
identified in seismic zone V, according to the earthquake zonation map of India. The city
has a population of 5,22,613. Although there are 49 wards under Agartala Municipality
Cooperation (AMC) but within a stipulated time period, all buildings of municipality area
cannot be surveyed. Therefore, an area has been chosen based on the high density of
population and a large number of residential buildings. The buildings in the selected area
are representative buildings of the city. A team from NIT Agartala comprising faculties
and students of Civil Engineering Department have surveyed buildings of Dhaleswar, east
zone ward no 25,AMC in a phased manner between 25th
August 2016 to 4th
April 2017.
2. Rapid Visual Screening Method
Rapid visual screening (RVS) has been developed to identify, inventory and screen
buildings that are potentially hazardous without performing structural analysis calculations.
The method is usually based on a sidewalk survey requiring 15-30 minutes on site for each
building. The RVS procedure employs a scoring system that requires the screener to
identify a) the building type material and the elements and b) identify building attributes
that modify the seismic performance. The final score value typically ranges from 0 to 7,
with higher scores corresponding to better expected seismic performance and a lower
potential for collapse.
2.1. Parameters considered in rapid visual screening
The building parameters that affect the seismic behavior of building are explained below in
brief. Among the parameters considered, each building type has its own basic score for
each seismicity region, providing a measure of the expected performance of that building

Rapid Seismic Vulnerability Evaluation 3
in that seismicity region. The other parameters are score modifiers which are added or
subtracted to the basic score as shown in equation (1), based on their positive or negative
effect on seismic resistance capacity to arrive at a final score.
Final Score = Basic Score + Score Modifier (1)
2.1.1 Building type
Two key characteristics of seismic performance are construction material (e.g. wood,
concrete, mud, masonry, steel etc.) and type of seismic force-resisting system (moment
frame, braced frame or shear wall). The building vulnerability is generally highest with the
use of local materials without engineering inputs and lowest with the use of engineered
materials [5]. Seventeen different building typeshave been considered byFEMA procedure
based on the building material and construction types [3].
2.1.2 Numerical seismic hazard
Each level of seismic zone forms the basis of Rapid Visual Screening data collection form
and hence, the number of such forms will be equal to the number of seismic zones. Higher
the seismicity, higher will bethe damage inbuilding and hence higher will be its
vulnerability. In FEMA P-154, five Data Collection Forms are provided for each of five
seismicity regions: low, moderate, moderately high, high and very high [3].
2.1.3 Number of storeys
The level of damage a building may sustain is sometimes related to the height of a
structure.The damage data of 1999 Duzce earthquake in Turkey revealed that building
damage increases with the number of stories. Henceforth, a lower value is assigned for
taller buildings by Sucuoglu et al. indicating higher vulnerability [4]. However, this is not
in agreement with FEMA-154 [2]. Recently, the third edition of FEMA-154 revised on
2015is in line with Turkish method, but at variance with FEMA-154(2002). It has provided
higher score modifier for low-rise buildings of soft soil type, indicating low vulnerability.
For instance, -0.2 is added to the score if the building has one to three stories and -0.3 if the
building has greater than 3 stories.
2.1.4 Vertical irregularity of the building
In reality, structures are often irregular as perfect regularity is an idealization that usually
doesnot occur. Irregular configuration either in a plan or in elevation is often considered as
one of the main causes of failure during past earthquakes and therefore, negative score
modifier is assigned for this type of irregularity. Seven common types of vertical
irregularities considered are building on sloping site, weak or soft storey, out-of-plane
setback irregularity, in-plane setback, short column/pier, split level condition where floor
or roof level in one part of the building do not align with floor or roof levels in other part
of the building. Vertical irregularitieshave been divided into two categories: severe (those
that have a significant adverse effect on building performance) and moderate (those that
have less significant adverse effect on building performance). RVS score values depend on
the type and severity of the building’s irregularities.
2.1.5 Plan irregularity of the building
Plan irregularity lowers the performance of a building under ground motions and therefore,
negative score modifier is assigned. Five common types of plan irregularity considered are

torsion, non-parallel systems, re-entrant corner, diaphragm openings and the condition
when beams do not align with columns. Buildings with re-entrant corners, like U, V, +, L,
T shaped in a plan is depicted in figure.1.
Figure.1. Re-entrant corner, Plan Irregularity [9]
2.1.6 Maintenance of the building
The quality of construction has a significant impact on the seismic performance of a
building. By observing the current state of the building and its maintenance i.e. seepage,
spalling of concrete, corrosion of steel, an inference can be made about the apparent
quality of building as roughly good, moderate or poor.A close relationship has been
observed between apparent quality and the damage experienced during the past
earthquakes. Severely damaged buildings were found of lesser quality than buildings in
other damage grades. Detailed investigation of buildings is triggered by FEMA P-154 for
poorly maintained buildings and if signs of deterioration due to weathering of their major
structural elements are observed [3].
2.1.7 Soil type
Soil type has a major influence on amplitude and duration of shaking, and thus on
structural damage. Six soil types considered in RVS procedure by FEMA-154 are hard
rock (type A), average rock (type B), dense soil (type C), stiff soil (type D), soft soil (type
E) and poor soil (type F) [3]. As per Indian Seismic Code IS: 1893 Part1 [9], three soil
types are Type I: Rock or Hard soil types that partly cover A, B and C of FEMA, Type II:
Medium soil types partly cover D and E of FEMA and Type III: Soft soil type roughly
between types E and F of FEMA [6].
2.1.8 Existence of basement
Jain et al. have included this parameter for predicting expected performance score (EPS) of
a building [8]. From damage data of Bhuj earthquake, it was clear that buildings without
basement suffered a higher level of damage as compared to the buildings with basement.
This may be because of raft foundation and reinforced concrete walls all around the
basement boundary for buildings with basement,as compared to buildings without
basementwhich are generally supported on isolated footings. Another reason for the better
performance of buildings with basement is that they tend to receive better engineering
inputs both in design and construction as compared to those without a basement. In FEMA
P-154, although space has been provided to document the information in data collection
form, itdoes not usually bear directly on the probability of sustaining major damage [3].

2.1.9 Building usage
During Bhuj earthquake, nonresidential buildings have performed better as compared to
residential buildings, which may be because of their tendency to be symmetrical with more
regular structural grids. Moreover, the tendency to provide smaller column widths to
ensure equal thickness of walls and columns is also not so pronounced for non-residential
buildings. Therefore, positive performance points have been awarded by Jain et al. for non-
residential buildings [8].In FEMA P-154, the occupancy of a building does not usually
bear directly on the structural hazard, it is of interest and used when determining priorities
for mitigation [3].
2.1.10 Presence of heavy overhangs
A common feature of urban buildings is the difference between footprint area and floor
area above ground level. Heavy overhanging floors of these buildings lead to irregularity in
mass and stiffness distributions. A typical building with heavy overhang is shown in
figure.2. During earthquakes in Turkey, buildings with heavy overhangs sustained heavier
damage as compared to buildings of regular elevation. This building feature can easily be
observed during a walk-down surveyand Sucuogluet al. have included this in the parameter
set [4].But, FEMA P-154 has not included overhang in score calculation, it has only been
considered as an exterior falling hazards [3].
(a) (b) (c)
Figure.2. Building with a)heavy overhang; b)vertical irregularity; and c)regular
configuration
2.2. Rapid visual screening score sheet and expected damage level
The score sheet in the form of data collection form for high seismicity is shown in
Table1.An optional level 2 Data Collection Form (Table2) has been added in the FEMA P-
154 to obtain valuable additional information and more accurate assessment without a
substantial increase in effort or time [3].Based on the data collected during the survey, a
score is calculated that provides an indication of the expected seismic performance of the
building [3].

EST
Table.1. Rapid Visual Screening of Buildings for Potential Seismic Hazards (High
Seismicity) Level 1
PHOTOGRAPH
Address: ____________________________________________________________
_______________________________________ Zip: ________________________
Other Identifiers: ____________________________________________________
Building Name: ______________________________________________________
Use: _______________________________________________________________
Latitude: _______________ Longitude: ________________________________
Screener:___________________ Date/Time: ______________________________
No. Stories: Above Grade: _____ Below Grade: _____Year Built: ______________
Total Floor Area (sq. ft.): ______________________ Code Year: _____________
Addition: None Yes, Year(s) Built: _________________________________
Occupancy:Assembly Commercial Emer. Service Historic Shelter
IndustrialOffice School Government
Utility Warehouse Residential
Soil Type: A B C D E FDNK
Hard Avg. Dense Stiff Soft Poorassume Type D
Soil SoilSoilSoilSoilSoil
Geological Hazards:
Liquefaction: Yes/No/DNK Landslide: Yes/No/DNK Surf.Rupt.: Yes/No/DNK
Adjacency: Pounding Falling hazards from taller adjacent building
Irregularities:Vertical (type/severity) _____________________________
Plan (type) _______________________________________
Exterior Falling Unbraced Chimneys Heavy Cladding or Heavy Veneer
Hazards: Parapets Appendages
Other: __________________________________________
COMMENTS:
SKETCH
BASIC SCORE, MODIFIERS, AND FINAL LEVEL 1 SCORE, SL1
FEMA BUILDING TYPE
C3
(URM INF)
URM
Basic Score
Severe Vertical Irregularity, VL1
Moderate Vertical Irregularity,VL1
Plan Irregularity, PL1
Soil type A or B
Soil type E (1-3 stories)
Soil type E (>3 stories)
1.2
-0.7
-0.4
-0.5
0.3
-0.2
-0.3
1
-0.7
-0.4
-0.4
0.3
-0.2
-0.2
Minimum Score, Smin 0.3 0.2
FINAL LEVEL 1 SCORE, SL1> SMIN
EXTENT OF REVIEW
Exterior: PartialAllSidesAerial
Interior:NoneVisibleEntered
Drawings Reviewed:YesNo
Soil Type Source: ___________________
Geological Hazard Source: ___________
Contact person: ____________________
OTHER HAZARDS
Are there Hazards that trigger a Detailed
Structural Evaluation?
Pounding potential (unless SL2 >
cut-off, if known)
Falling hazards from taller adjacent building
Geological hazards or Soil type F
Significant damage/deterioration tothe structural
system
ACTION REQUIRED
Detailed Structural Evaluation Required?
Yes, unknown FEMA building type or other
building
Yes, score less than cut-off
Yes, other hazards present
No
Detailed Nonstructural Evaluation
Recommended?
Yes, nonstructural hazards identified that
should be evaluated
No, nonstructural hazards exist that may
require mitigation, but a detailed evaluation
is not necessary
No, no nonstructural hazards identified
DNK
Level 2 Screening Performed?
Yes, Final Level 2 Score, SL2 _ No
Nonstructural hazards? Yes No

Table.2. Rapid Visual Screening of Buildings for Potential Seismic Hazards (High
Seismicity) Level2
Level 2 (Optional)
HIGH Seismicity
Building name: Final Level 1 Score: SL1=
Screener: Level1 Irregularity Modifiers: VL1 = PL1=
Date /Time: ADJUSTED BASELINE SCORE: S'= (SL1-VL1-PL1) =
STRUCTURAL MODIFIERS TO ADD TO ADJUSTED BASELINE SCORE
Topic Statement (If statement is true, circle “Yes” modifier; otherwise cross out the modifier) Yes Subtotals
Vertical
Irregularity,
VL2
Sloping site Non-W1 building: There is at least a full story grade change from one side of the building
to the other.
-0.3
VL2=_______
(Cap at -1.2)
Weak and/or
SoftStorey
Non-W1 building: Length of lateral system at any storey is less than 50% of that at storey
above or height of any storey is more than 2.0 times the height of the story above.
-0.9
Non-W1 building: Length of lateral system at any storey is between 50% and 75% of that
at storey above or height of any storey is between 1.3 and 2.0 times the height of the story
above.
-0.5
Setback Vertical elements of the lateral system at an upper storey are outboard of those at the
storey below causing the diaphragm to cantilever at the offset.
-1.0
Vertical elements of the lateral system at an upper storey are inboard of those at lower
stories.
-0.5
There is an in-plane offset of the lateral elements that is greater than the length of the
elements.
-0.3
Short
Column/
Pier
C3: At least 20% of columns (or piers) along a column line in the lateral system have
height/ depth ratios less than 50% of the nominal height/depth ratio at that level.
-0.5
C3: The column depth (or pier width) is less than one half of the depth of the spandrel, or
there are infill walls or adjacent floors that shorten the column.
-0.5
Split level There is a split level at one of the floor levels or at the roof. -0.5
Other
Irregularity
There is another observable severe vertical irregularity that obviously affects the
building's seismic performance.
-1.0
There is another observable moderate vertical irregularity that may affect the building's
seismic performance.
-0.5
Plan
Irregularity,
PL2
Torsional irregularity: Lateral system does not appear relatively well distributed in plan in either or both
directions.
-0.7
PL2 =______
(Cap at -1.1)
Non-parallel systems: There are one or more major vertical elements of the lateral system that are not
orthogonal to each other.
-0.4
Re-entrant corner: Both projections from an interior corner exceed 25% of the overall plan dimension in
that direction.
-0.4
Diaphragm opening: There is an opening in the diaphragm with a width over 50% of the total diaphragm
width at that level.
-0.2
Other irregularity: There is another observable plan irregularity that obviously affects the building's seismic
performance.
-0.7
Redundancy The building has at least two bays of lateral elements on each side of the building in each direction. +0.3
Pounding Building is separated from an
adjacent structure by less than 1% of
the height of the shorter of the
building and adjacent structure and:
The floors do not align vertically within 2
feet. (Cap total
pounding
modifiers at -1.2)
-1.0
M=________
One building is 2 or more stories taller than
the other.
-1.0
The building is at the end of the block. -0.5
S2 Building 'K' bracing geometry is visible. -1.0
C1 Building Flat plate serves as the beam in the moment frame. -0.4
PC1/RM1
Bldg
There are roof-to-wall ties that are visible or known from drawings that do not rely on cross-grain bending.
+0.3
PC1/RM1
Bldg
The building has closely spaced, full height interior walls (rather than an interior space with few walls such
as in a warehouse).
+0.3
URM Gable walls are present. -0.4
MH There is a supplemental seismic bracing system provided between the carriage and the ground. +1.2
Retrofit Comprehensive seismic retrofit is visible or known from drawings. +1.4
FINAL LEVEL 2 SCORE, SL2 = (S' +VL2 + PL2 + M) > SMIN:
OBSERVABLE NONSTRUCTURAL HAZARDS
Location Statement Yes No Comment
Exterior There is an unbraced unreinforced masonry parapet or unbraced unreinforced
masonry chimney.
There is heavy cladding or heavy veneer.
There is a heavy canopy over exit doors or pedestrian walkways that appears
inadequately supported.
There is an unreinforced masonry appendages over exit doors or pedestrian
walkways.
There is a sign posted on the building that indicates hazardous materials are
present.
There is a taller adjacent building with an unanchored URM wall or unbraced
URM parapet or chimney.
Other observed exterior nonstructural falling hazard.
Interior There are hollow clay tile or brick partitions at any stair or exit corridor.
Other observed interior nonstructural falling hazard.

The damage classifications used in this study is shown in table.3 based on the European
Macro seismic scale (EMS-98) where building damage is defined to be in Grade 1 to
Grade 5. They are used in RVS to predict likely damages the buildings may experience
during code-level earthquake. The reason for this classification is to separate buildings
with high risk from the ones with low risk. Consequently, high-risk buildings can be
strengthened or demolished, so that practically there is no loss of life.
Table.3. Classification of damage to buildings
Classification of damage to masonry buildings Classification of damage to RCC buildings
Grade 1: Negligible to slight damage
(No structural damage, slight non-structural
damage)
Hair-line cracks in very few walls.
Fall of small pieces of plaster only.
Fall of loose stones from upper parts of buildings in
very few cases.
Grade 1: Negligible to slight damage
(No structural damage, slight non-structural
damage)
Fine cracks in plaster over frame members or in
walls at the base.
Fine cracks in partitions and infills.
Grade 2: Moderate damage
(Slight structural damage, moderate non-
structural damage)
Cracks in many walls.
Fallof fairly large pieces of plaster.
Partial collapse of chimneys and mumptys.
Grade 2: Moderate damage
(Slight structural damage, moderate non-
structural damage)
Cracks in columns and beams of frames and in
structural walls.
Cracks in partition and infill walls; fall of brittle
cladding and plaster. Falling mortar from the
joints of wall panels.
Grade 3: Substantial to heavy damage (moderate
structural damage, heavy non-structural damage)
Large and extensive cracks in most walls.
Roof tiles detach. Chimneys fracture at the roof line;
failure of individual non-structural elements
(partitions, gable walls etc.).
Grade 3: Substantial to heavy damage
(moderate structural damage, heavy non-
structural damage)
Cracks in columns and beam-column joints of
frames at the base and at joints of coupled walls.
Spalling of concrete cover, buckling of reinforced
bars.
Large cracks in partition and infill walls, failure
of individual infill panels.
Grade 4: Very heavy damage (heavy structural
damage, very heavy non-structural damage)
Serious failure of walls (gaps in walls); partial
structural failure of roofs and floors.
Grade 4: Very heavy damage (heavy
structural damage, very heavy non-structural
damage)
Large cracks in structural elements with
compression failure of concrete and fracture of
rebars; bond failure of beam reinforcing bars;
tilting of columns.
Collapse of a few columns or of a single upper
floor.
Grade 5: Destruction (very heavy structural
damage)
Total or near total collapse of the building.
Grade 5: Destruction (very heavy structural
damage)
Collapse of ground floor parts (e.g. wings) of the
building.

RVS score can be used to estimate the probable grade of damage, the building may
experience during future earthquakes. Table 4 provides the guidelines for expected damage
level as a function of RVS score as suggested by Sinha and Goel [5]. However, it should
be kept in mind that the actual damage may also depend on so many other factors that are
not considered in RVS procedure. Therefore, this table should only be used to get the
preliminary idea about the vulnerability of any building and to get complete information
further evaluation is required.
Table.4. Expected damage level as function of RVS score [5]
RVS Score Damage Potential
S < 0.3 High probability of Grade 5 damage; Very high probability of Grade 4 damage
0.3 < S < 0.7 High probability of Grade 4 damage; Very high probability of Grade 3 damage
0.7 < S < 2.0 High probability of Grade 3 damage; Very high probability of Grade 2 damage
2.0 < S< 3.0 High probability of Grade 2 damage; Very high probability of Grade 1 damage
S > 3.0 Probability of Grade 1 damage
3. Case Study of Agartala City
The rapid screening based on FEMA P-154 procedure has been implemented inward no 25
of Agartala Municipal Cooperation (AMC) as marked in figure.3. A total of 350 buildings
have been evaluated in terms of age of buildings, number of stories, presence of soft
storey, short column, heavy overhang, pounding effects etc. Out of 350 buildings, 122 are
unreinforced masonry bearing wall buildings (URM) and 228 are concrete frame buildings
with unreinforced masonry infill walls (C3).
Figure.3.Map showing the study area
INDIA
TRIPURA STATE
AGARTALA MUNICIAL
CORPORATION
Ward No. 25
(a)
(b)
(c)

3.1 Assessment of building database
Figure. 4 shows the distribution of buildings according to the age of building, the number
of stories, construction quality, the presence of vertical and horizontal irregularities and
soil type.
Considering the distribution of buildings according to the period of construction as shown
in Figure 4a, two periods have been distinguished. Before 1995, there was a strong
dominance of masonry buildings (about 70%) andthe period after 1995 is characterized by
an expansion of RCC buildings. So, the general observation is that most of the new
constructions are of RCC types which have better seismic resistance as compared to
masonry structures.
Considering the distribution of buildings according to the number of storeys, the buildings
are mostly single or two storied as shown in figure 4b. Of the buildings studied, 81% of the
assessed masonry buildingsare single storied and rest are double storied. It is seen that
nearly 45% of RCC buildings are single storied, 49% are double storied and 6% are three
storied.
The apparent quality of the building is found to be moderate as depicted in Figure 4c. The
rate of buildings with poor construction quality is only 20%, while about 50% are
classified moderate and 30% buildings are defined good in terms of visual construction
quality. Material deterioration and corrosion of reinforcement are some of the defects that
may be encountered in old buildings.
Figure 4d shows that horizontal irregularities (most of them are L-shaped and few are U-
shaped) are most prominent feature among masonry buildings. In general, vertical
irregularity makes a building far more vulnerable as compared to plan irregularity. It is
observed that only 18% of the surveyed RC buildings have vertical irregularities, 24%
have plan irregularities and 27% have overhang.
Figure 4e shows about type of soil of the surveyed area. It is noted that for both masonry
and RCC buildings, the underneath soil is considered as medium type as mentioned in IS-
1893 [9]. However, it is important to mention here that this data is given here based on the
information provided by the respective house owner during the survey.
Distribution of presence of soft storey and short column isshown in figure 5(a) and 5(b)
respectively. A soft storey exists when the stiffness of one storey is dramatically less than
that of most of the others and short columns occur when columns are confined along the
length of the masonry wall to accommodate openings or in the case of a mezzanine floor.
Columns that are narrow compared to the depth of spandrels are also a matter of
concern.Both soft storey and short column are considered as a severe vertical irregularity.
However, of the buildings surveyed, only 10%buildings have soft stories and 5%have a
short column.
An insufficient separation between adjacent buildings can lead to pounding, which may
cause several types of damage during earthquakes. The pounding score modifier varies
according to the severity of the type of pounding condition that exists as mentioned in
FEMA P-154 [3].The conditions are (a) when floors do not align vertically within 2 feet,
(b) one of the buildings is two or more stories taller than the other, (c) the building is at the
end of the block. From the assessment of different buildings, it was found that 19% have
pounding possibilities as shown in figure 5(c).

(a) (b)
(c) (d)
(e)
Figure.4. Distribution of masonry and RCC buildings according to a) age class;b) number
of stories; c) apparent quality; d) presence of irregularities and e) soil type
Another potential concern to beobserved during the survey isnon-structural falling hazards.
The hazards includeunbraced unreinforced masonry chimneys or parapets, heavy canopy
over exit doors, heavy cladding or veneers, taller adjacent building with an unanchored
URM wall or unbraced URM parapet or chimney whichcan pose hazards to life safety if
not properly anchored to the building. The screener can use judgment to estimate the
Masonry
RCC
0
10
20
30
40
50
%ofbuildings
Age class
Masonry
RCC
0
20
40
60
80
100
1 2 3
%ofbuildings
Number of storeys
Masonry
RCC
0
20
40
60
Good Moderate Poor
%ofbuildings
Apparent quality
Masonry
RCC
0
10
20
30
40
Overhang VI HI
%ofbuildings
Masonry
RCC
0
20
40
60
80
100
Soft Medium Hard
%ofbuildings
Soil type

nonstructural seismic performance of the building and recommend if detailed evaluation is
required. Figure 5 (d) depicts 36% buildings with exterior falling hazards.
(a) (b)
(c)(d)
Figure.5. Presence of a) soft storey; b) short column; c) poundingand d) falling hazard
Figure.6. Distribution of percentage of buildings with respect to number of members in a
building
Although the number of members in a building does not usually bear directly on the
structural hazard or probability of sustaining major damage, it is of interest and used when
Does not
exist
90%
Exist
10%
Does not
exist
95%
Exist
5%
Does not
exist
81%
Exist
19%
Does not
exist
64%
Exist
36%
Masonry
RCC
0
10
20
30
40
50
2 3 4 5 6 7 8
%ofbuildings
Number of members

determining priorities for mitigation. Figure 6 shows that most of the buildings have 4
members.
3.2 RVS performance score as per FEMA P- 154
Based on building type, the surveyed buildings can be categorized as C3, concrete frame
buildings with unreinforced masonry infill walls and unreinforced masonry building
(URM). Final scores typically range from 0 to 7, with higher scores corresponding to better
seismic performance and a lower potential for collapse. Using cut-off score of 2, buildings
with a final score of 2 or less are investigated by a design professional experienced in
seismic design. Figure 7 shows performance score of masonry and RCC buildings
predominantly ranging between 0.2 through 1.5 and therefore, these buildings need further
evaluation. Here, damage grades are marked as G5, G4 and G3 which represent Grade 5,
Grade 4 and Grade 3 as mentioned in the Table 3 and 4.
Figure.7. Distribution of masonry and RCC buildings with respect to final level 2 score of
FEMA 154-2015
3.3 Damage grades
The final score is used to calculate the expected damage grade of a building by using the
guideline as mentioned in table 4. Figure 8 illustrates the percentage of buildings with
respect to damaged grades that the building may experience in the event of a design-level
earthquake. It is observed from figure that about 55% of both masonry and RCC buildings
are subjected to heavy damage (G3), 35% of masonry and 20% of RCC are subjected to
very heavy damage (G4), where10% of masonry and 25% of RCC are at risk of
destruction, which may lead to extensive physical and socioeconomic damage.
0
10
20
30
40
50
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5
%ofbuildings
Final level 2 Score as per FEMA P-154
G5 G4 G3
RCC
Masonry

Figure.8. Distribution of masonry and RCC buildings with respect to damaged grades
Finally, vulnerability map of the study area has been developed and depicted in Figure 9 to
visualize the damage grades of buildings in a spatial manner and to prepare emergency
plans for earthquake risk mitigation.
Figure.9. Distribution of seismic vulnerability of buildings.
4. Conclusion
Agartala lies in the most seismically active zone of India and therefore, the possibility of
future earthquakes of moderate to great nature cannot be ruled out. In this regard, a
comprehensive study of seismic risk assessment of Agartala has been found to be
necessary. As a pilot study, RVS procedure has been conducted on 350 residential
buildings of ward no 25, AMC. Data collected from the street survey show that concrete
frame buildings with unreinforced masonry infill walls (C3) are the most representative
system in the surveyed area. The screened buildings are found to be mostly dominated by
the presence of re-entrant corners and overhangs. Low final scores as per FEMA P-154 [3]
Masonry
RCC
0
10
20
30
40
50
60
G3 G4 G5
%ofbuildings
Damaged grades

indicate that in general buildings are of low quality and are highly vulnerable to future
earthquakes.
The current study only focuses a particular ward of Agartala Municipal Cooperation
(AMC). However, to get the complete idea about the most vulnerable area under this
AMC, more number of wards have to be considered for study so that proper mitigation
measure can be taken in time to save both life and property.
References
1. FEMA 310, ‘Handbook for the seismic evaluation of buildings-A pre-standard’, Federal Emergency
Management Agency, Washington DC,1998.
2. FEMA 154, ‘Rapid Visual Screening of Buildings for Potential Seismic Hazard: A Handbook’,
2nd
Edn. (Washington, D.C, USA, 2002).
3. FEMA 154, ‘Rapid Visual Screening of Buildings for Potential Seismic Hazard: A Handbook’, 3rd
Edn. (Washington, D.C, USA, 2015).
4. Sucuoglu H., Yazgan U., Yakut A. “A Screening Procedure for seismic risk assessment in urban
building stocks”, Earthquake Spectra, Vol 23 No 2, p 441-458, 2007.
5. Sinha R., Goyal A., ‘A national policy for Seismic Vulnerability Assessment of Buildings and
Procedure for Rapid Visual Screening of Buildings for Potential Seismic vulnerability’, Department
of civil Engineering, IIT Bombay, India, 2004.
6. Nanda R.P., MajhiD.P., “Rapid Seismic Vulnerability Assessment of Building Stocks for
Developing Countries”, KSCE Journal of Civil Engineering, 2014.
7. Arya, A.S., Agarwal, A., ‘Rapid Visual Screening of RCC Buildings’, Prepared under GOI-UNDP
Disaster Risk Management Programme.
8. Jain S.K., Mitra K., Kumar M., Shah M., “A proposed rapid visual screening procedure for seismic
evaluation of RC frame buildings in India”, Earthquake Spectra, Vol 26, No 3, p 709-729, 2010.
9. IS-1893 Part 1:2002, ‘Criteria for earthquake resistant design of structures’, Part 1 General
Provisions and Buildings (Fifth Revision).

Id 165-rapid seismic vulnerability evaluation of residential buildings in agartala city

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