Assessing Seismic Vulnerability of Homes in Agartala Using Rapid Screening

SEISMIC VULNERABILITY ASSESSMENT OF RESIDENTIAL BUILDINGS IN AGARTALA
CITY USING RAPID VISUAL SCREENING METHOD
NIT AGARTALA B.TECH PROJECT 2016-17 Page 1
CHAPTER 1 INTRODUCTION
Agartala being a developing city is a commercial and educational hub of Tripura. There has been
a phenomenal increase in population and development program in North East India. This has
resulted to increase vulnerability of human population and physical structures to earthquakes.
Moreover the constructions of buildings here not as per building codes. The contractors here
doesn’t give importance to the building codes so as to earn profit by investing less. They use poor
quality and less durable materials in buildings. So all these factors are responsible for faulty
constructions in the city and as a result making the buildings vulnerable to earthquakes. Agartala
city falls in the highest seismic risk zone (Zone V) in India. Some severe earthquakes have
occurred in this region in the past (notably in 1869, 1918 and latest 2017). Until about 1950 or so,
the typical construction in the entire northeast region comprised simple single storey structures
which possess good earthquake resistant features. With growing urbanization, RC framed
construction has become the standard construction practice in Agartala during the course of the
last five decades. Most of the high-rise constructions in Agartala have come up only in the past 8
years, and they have not yet been tested for their resistance to a high intensity earthquake. Based
on historical occurrence of earthquakes, regions in India are classified into low, moderate, severe
and very severe earthquake prone zones. More than half of the country’s population live in
moderate to very severe zones (refer to the seismic map below Fig 1.1).
Tripura (extends between 22°56'N and 24°32'N latitude and 90°09'E and 92°10'E longitude) is in
the zone of most severe seismic hazard (i.e., zone V; as per Indian standard code of practice for
earthquake-resistant design of structures, IS-1893 2002) in the country. Agartala city falls under
the seismic zone of Zone V, which is a very severe zone i.e most probable to earthquake. So being
in such a high risk zone earthquake resistant design must be adopted to the building construction
in this zone.
Table 1.1 Different seismic zones IS 1893(Part 1):2002
Zone II Low seismic hazard (maximum damage during earthquake may be up to
MSK intensity VI)
Zone III Moderate seismic hazard (maximum damage during earthquake may be up
to MSK intensity VII)
Zone IV High seismic hazard (maximum damage during earthquake may be up to
MSK intensity VIII)
Zone V Very high seismic hazard (maximum damage during earthquake may be of
MSK intensity IX or greater)

Fig 1.1 Seismic Zoning map of India from IS 1893(part 1):2002 ( Google Image)

CHAPTER 2 REVIEW OF LITERATURE
2.1 GENERAL BACKGROUND
The subject revealed that many developed and developing countries around the world like Japan,
Turkey, USA, Switzerland, China, India, Bangladesh etc. has adopted various methodologies for
seismic vulnerability assessment in order to analyze defects in existing structures against
earthquake. Seismic vulnerability refers to the susceptibility of those parts of a building that are
required for physical support when subjected to an intense earthquake or other hazard. This
includes foundations, columns, supporting walls, beams and floor slabs. Many researches are
based on the capacity spectrum method (ATC 40) and are intended to provide a methodology for
determining the performance score of the building. Experimental investigation like rebound
hammer test was also used to assess the compressive strength of concrete structural members
wherever access was provided in reinforced concrete structure.
2.2 PREVIOUS RESEARCH
FEMA 154 (1988) revised in 2002 and 2015 reported that the Rapid Visual Screening (RVS)
procedure was used by private-sector organizations and government agencies to evaluate more
than 70,000 buildings nationwide. FEMA 154 provides a procedure that can be rapidly
implemented to identify buildings that are potentially seismically hazardous. In this method
damage grades has been assigned to each of the buildings. FEMA P-154 defines collapse
probability as the probability that the building will suffer partial or complete collapse. In that part
of the building, the gravity load carrying system (such as beams, columns, floors and shear walls)
loses the ability to carry its own weight and weight of whatever else it supports. That failure leads
to severe structural deformation of a potentially life threatening nature, especially falling of all or
portions of a structure. A potentially seismically hazardous building is one where, with in the
accuracy of the RVS procedure, the collapse probability is estimated to be more than 1% in rate
earthquake shaking (using the default cutoff 2.0).
Sinha and Goyal (2003) developed the methodology Rapid Visual Screening of buildings for
potential seismic vulnerability. As wide variety of construction types and building materials are
used in urban areas of India, they include local materials such as mud and straw, semi -engineered
materials such as burnt brick and stone masonry and engineered materials such as concrete and
steel. The RVS procedure has considered 10 different building types. All buildings have been
divided into six vulnerability class, denoted as Class A to Class F based on the European Macro
seismic Scale (EMS-98) recommendations. The buildings in Class A have the highest seismic
vulnerability while the buildings in Class F have lowest seismic vulnerability.
Alam et al. (2010) made a comparison between seismic vulnerability assessment techniques for
buildings to evaluate their suitability for use in seismic risk assessment. The methods considered
are ‘‘Hybrid’’ vulnerability assessment method, FEMA 154 (Rapid Visual Screening), Euro Code
8, New Zealand Guidelines, Modified Turkish method and NRC Guidelines.

CHAPTER 3 OBJECTIVES OF THE STUDY
Seismic risk in Agartala is increasing with population growth and the encroachment of vulnerable
bultin environment into areas susceptible to seismic hazard. The city lies in zone “V” and is belong
to seven north-eastern states of India. The earthquake resistance of buildings greatly influences
seismic losses. The overwhelming majority of deaths and injuries in earthquakes occur because of
the disintegration and collapse of buildings, and much of the economic loss and social disruption
caused by earthquakes is also attributable to the failure of buildings and other human-made
structures. A Rapid Visual Screening (RVS) survey of residential buildings of Agartala is carried
out to make the general people aware of the faulty constructions in the city and rectify the defects
in the existing buildings thus making it safe against earthquake. In this respect the main objective
of the present study is summarized as follows:
1. To assess the seismic vulnerability of residential buildings in Agartala city using different Rapid
Visual Screening Method proposed by FEMA 154 (2015).
2. To predict the expected damage grade that may be observed in the surveyed buildings in future
severe earthquake.
Fig.3.1 Survey area of Dhaleswar, Agartala

CHAPTER 4 METHODOLOGY
There is an urgent need to assess the seismic vulnerability of buildings in urban areas of India as
an essential component of a comprehensive earthquake disaster risk management policy. Detailed
seismic vulnerability evaluation is a technically complex and expensive procedure and can only
be performed on a limited number of buildings. It is therefore very important to use simpler
procedures that can help to rapidly evaluate the vulnerability profile of different types of buildings,
so that the more complex evaluation procedures can be limited to the most critical buildings.
India’s national vulnerability assessment methodology, as a component of earthquake disaster risk
management framework should include the following procedures:
1. Rapid visual screening (RVS) procedure requiring only visual evaluation and limited
additional information (Level 1 procedure). This procedure is recommended for all
buildings.
2. Simplified vulnerability assessment (SVA) procedure requiring limited engineering analysis
based on information from visual observations and structural drawings or on-site
measurements (Level 2 procedure). This procedure is recommended for all buildings with
high concentration of people.
3. Detailed vulnerability assessment (DVA) procedure requiring detailed computer analysis,
similar to or more complex than that required for design of a new building (Level 3
procedure). This procedure is recommended for all important and lifeline buildings.
4.1 RAPID VISUAL SCREENING PROCEDURE (RVS)
4.1.1 Introduction
Rapid visual screening was first proposed in US in 1988 in the FEMA 154 report, which was latest
modified in 2015 to incorporate latest technological advancements and lessons from earthquake
disasters in the 1990s. This RVS procedure was originally developed for typical constructions in
US, have also been widely used in many other countries after suitable modifications. The most
important feature of this procedure is that it permits vulnerability assessment based on walk-around
of the building by a trained evaluator.
4.1.2 Importance
The Rapid Visual screening is carried out for all considered buildings. It permits quick visual
vulnerability assessment. The purpose of the Rapid Visual Assessment (RVA) is to determine the
adequacy of the structural facility as to whether the facility will be able to withstand the expected
earthquake. For scenario earthquakes, performance levels for existing building stock need to be
assessed.
4.1.3 Procedure
Rapid vulnerability assessment is the first necessary step but may not be sufficient to establish
building stock performance levels. Necessary information for evaluation of structure is obtained
either by conducting a field survey or from building typology, if available or from both. If plan is
available, then the field party must check and verify the present status of the building. In this
method, buildings are evaluated qualitatively in terms of structural characteristics, structural
configuration, and the degree of deterioration of the building. This method is rapid and inexpensive

and helps in identifying structures, which are clearly hazardous and the structures for which
detailed hazard evaluation is sought.
4.1.4 Uses
The results from rapid visual screening can be used for a variety of applications that are an integral
part of the earthquake disaster risk management programme of a city or a region. The main uses
of this procedure are:
1. To identify if a particular building requires further evaluation for assessment of its seismic
vulnerability.
2. To rank a city’s or community’s (or organisation’s) seismic rehabilitation needs.
3. To design seismic risk management program for a city or a community.
4. To plan post-earthquake building safety evaluation efforts.
5. To develop building-specific seismic vulnerability information for purposes such as regional
rating, prioritisation for redevelopment etc.
6. To identify simplified retrofitting requirements for a particular building (to collapse
prevention level) where further evaluations are not feasible.
7. To increase awareness among city residents regarding seismic vulnerability of buildings.
4.1.5 Survey parameters
The most pertinent information required to establish rating for building is based on the parameters
of building. These are:
 General Information: Type of building, Number of stories, Year of construction, Number
of occupants, Maintenance record.
 Structural Irregularities: Vertical irregularities, Plan irregularities.
 Apparent building quality: Quality of materials & construction.
 Soil conditions.
 Frame action
 Diaphragm action.
 Heavy overhangs, Soft story, Short column.
 Pounding effect: Two Adjacent buildings.
 Openings: Large openings in wall, irregular openings in walls.
 Bands: Horizontal Bands at plinth level, lintel level, sill & roof level.
 Falling Hazards.
 Wall thickness at ground floor.
 Water tank at roof: Capacity and location.
4.1.6 Factors affecting building vulnerability
Seismic vulnerability of a building is the amount of probable damage induced to it by a
particular level of earthquake intensity. It occurs large near the building situated above the focus.
It depends upon mainly:-

4.1.6.1 Building Structure
Buildings are designed to resist vertical and horizontal forces acting on them. This quantity is
achieved mainly in three ways:
4.1.6.(a) Frame structure: In this type of structure, the entire load acting on the building are
carried out by the frame of reinforced concrete or steel beams, columns and slabs transmitted
through the foundation to the soil beneath.
4.1.6.(b) Load bearing structure: In this structural system the arrangement of masonry units such
as bricks, stones or concrete blocks bonded by mortar transmit all the load acting in the structure.
4.1.6.(c) Composite structure: This is the combination of frame and load bearing structure.
4.1.6.2 Building Height
Building height and natural period of buildings affects the buildings behavior during occurrence
of an earthquake. Apart from the ground vibrating in multiple directions; buildings also vibrate
in different directions and hence have multiple modes. Each of these modes has a period and the
longest period known as the natural frequency. If the ground motion frequency is close or equal
to natural frequency of building, resonance occurs which amplify the building response.
The approximate frequencies of buildings are 10 for a one storied building, 2 for a 3-4
storied building, 0.5 to 1.0 for a tall building and 0.17 for a high-rise building.
4.1.6.3 Structural Irregularities
4.1.6.3(a) Vertical irregularity
Vertical irregularities can be judged from the structural system like Setbacks in elevation. The
vertical irregularities make a building far more vulnerable as compared to the plan irregularities.
Fig.4.1 Vertical irregularity (Image Courtesy Patel, C.N., and Patel, P.V, 2010)
4.1.6.3(b) Plan Irregularity
Irregularity in the plan caused due to various shapes (L, T, U, +) causes torsion during earthquake
and is responsible for major damage.

Fig.4.2 Irregular Plan Configuration and separation joints (Image Courtesy Patel, C.N.,
and Patel, P.V, 2010)
4.1.6.4 Apparent Quality
Visible Quality of the material used in the construction works is known as apparent quality. It
also depends upon workmanship and materials used during construction.
4.1.6.5 Soil Condition
Soil is classified as hard, medium and soft. The hard soil is considered to be better than any other
type of soil.
4.1.6.6 Frame action
Frame Action is to be present in the RCC buildings to transfer the load uniformly to the ground.
Fig.4.3Complete and Incomplete Frame action (Image Courtesy Patel, C.N., and Patel, P.V,
2010)
4.1.6.7 Diaphragm Action
The main function of a horizontal element is to distribute and transfer horizontal seismic load to
the vertical load-bearing element that is the wall below it.
4.1.6.8 Heavy Overhangs
Heavy overhangs refer to extra projections of a building; can be dangerous because they are
subjected to greater seismic forces during an earthquake.

Fig 4.4 heavy overhanging (Image Courtesy Patel, C.N., and Patel, P.V, 2010)
4.1.6.9 Soft Stories
Absence of partition walls in ground or any intermediate stories for shops or other commercial
use.
Fig.4.5 Soft Storey (Image Courtesy Patel, C.N., and Patel, P.V, 2010)
4.1.6.10 Short Column Effect
Partial height walls adjoining to columns, give rise to short column effect in RC building. These
short columns are not free to deflect over the entire length.
Fig.4.6 Short Column Effect (Image Courtesy Patel, C.N., and Patel, P.V, 2010)

4.1.6.11 Pounding Effect
Pounding is the result of irregular response of adjacent building of different heights and different
dynamic characteristics. When two buildings are too close to each other, they may pound on each
other during strong shaking.
Fig.4.7 Pounding Effect (Image Courtesy Patel, C.N., and Patel, P.V, 2010)
4.1.6.12 Large and Asymmetrical Openings
Large openings weaken the masonry walls against vertical as well as soft storey effect for
horizontal seismic load.
4.1.6.13 Structural Bands
4.1.6.13(a) Plinth band: This band is provided at base level for even distribution of the super
structure load to the foundation structure. This is important where soil is soft or uneven.
4.1.6.13(b) Lintel band: This is the most important band and should be provided in all storeys in
buildings.
4.1.6.13(c) Roof band: This band will be required at eave level of trussed roofs and also below or
in level with such floors, which consists of joists and covering elements so as to properly integrate
them at ends and fix into the walls.
4.1.6.14 Water Tank at roof:
It has lot of dead load and if they are placed near the center of plan they may cause large amount
of torsion. They can be classified into three categories:
(a) Doesn’t exist (b) Capacity < 5000 liter (c) Capacity > 5000 liter
4.1.6.15 Falling Hazards
Falling Hazards have contributed more to the causalities than any feature of a building. Towers
and large hoardings that is likely to fall during earthquake.
4.1.6.16 Basement
The buildings without basement suffered higher level of damage as compared to the buildings with
basement. This may be because buildings without basement tend to have significantly larger storey
height in the lowest storey.

CHAPTER 5 DETAILS OF CASE STUDIES
Agartala, the capital of Tripura has an area of about 58.84 sq. km. And the total Ward Numbers of
Agartala Municipality Council are 17. As in this stipulated time period the buildings of
municipality area cannot be surveyed. So, to assess the vulnerability of buildings of Agartala city
by Rapid visual Screening Method three different areas have been chosen to carryout door to door
survey for collecting the information regarding various parameters. The details of the selected
areas are given below.
5.1 CASE STUDY OF RESIDENTIAL BUILDINGS IN DHALESWAR AREA
In this phase, visual screening was carried out for Dhaleswar area. Dhaleswar, east zone ward no.-
4, Agartala Municipal Council, is located at latitude 23 ̊49’53.57”N & longitude 91 ̊17’44.54”E.
The side walk survey was conducted in a phased manner between 25 August,2016 to 4th April
,2017.The road no’s are respectively – 7,8,9,10,13,14,15,16 and 17, which was surveyed during
this period. From the side walk survey information of the building was collected in data sheet as
given in Table no.5.1 and Table no. 5.2.The time required per building to complete the data sheet
was 20- 30 minutes. A digital photograph was taken after permission of building owner. Total 350
no’s of residential buildings are surveyed. Among them 205 comprise RCC structures, 116
comprise masonry constructions, 29 are Composite structures and the remaining is mixed type.
Our case study of seismic vulnerability of Dhlaeswar area reveals a gloomy picture as few
buildings are not suitable to sustain seismic shocks as those were built approximately 30 to 40
years back and as a result consciousness of people should be increased about the same. This is
very surprising that the the building construct 29 to 35 years ago have a very good appearance and
well design than the building constructed after 2000. Its Also interested that the most of building
are one storey which indicate very less damage during earthquake. During the observation we
observe most of people are hesitating to share the information. Part from that as mass gathering
happens there, structural material condition should also be checked in parallel. So there is an urgent
need to understand the seismic vulnerability of existing buildings and take appropriate measures
to reduce the risk.
The reason for choosing this area is due to
(i) large population and
(ii) large number of residential buildings both RCC and masonry constructions. RVS formats
usually record the important components of seismic vulnerability and propose a scoring system
that forms the basis for classifying buildings in different risk categories.
The RVS format of Masonry building and RCC buildings are shown in the following table:

Table 5.1 Rapid Visual Survey for Masonry building

Table 5.2 Rapid Visual Survey for RCC buildings

5.2 FEMA 154 (2015)
FEMA 154(2015) was published originally in 1988 in US and latest revised in 2015 to categorize
the potentially Seismically hazardous buildings of USA by Rapid visual screening method. It is
relatively a quick procedure in developing a list of potentially risky buildings. The method
considers 17 different building types based on the building materials and construction types
commonly found in urban areas of USA. Five regions of seismicity: low (L), moderate (M),
moderately high (MH) high (H) and Very high (VH) is considered in this guidelines. This Method
also assigns a basic structural score based on the lateral force resisting system of the building. The
number of stories, plan and vertical irregularities, pre-code or post-benchmark code detailing, and
soil type effects the Performance modifiers. The basic scores and the modifiers assigned by FEMA
154 (2015) for moment resisting frame buildings based on 10 scales. It shows a pre-code penalty
and post-benchmark positive attribute for buildings constructed after the significant improvements
in the code. The pre-code and post-benchmark modifiers have been given significant importance
when compared to the basic structural scores.
5.3 Damage Grades
The damage classifications based on the European Macro-seismic Scale (EMS-98) define building
damage to be in Grade 1 to Grade 5 which is shown in Table 5.3. These are used in RVS to predict
potential damage of a building during severe earthquake.
Table 5.3 Predicted damage grades.
RVS Score Damage Potential
S < 0.4 High probability of Grade 5 damage; Very high probability of Grade 4
damage
0.4 ≤ S ≤ 0.9 High probability of Grade 4 damage; Very high probability of Grade 3
damage
damage
damage
2.0 < S Probability of Grade 1 damage

Table 5.4 Classification of damage grade to buildings (EMS-98)
Classification of damage to masonry
buildings
Classification of damage to reinforced concrete
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
nonstructural damage)
Cracks in many walls.
Fall of fairly large pieces of plaster.
Partial collapse of chimneys and mumptys.
Grade 2: Moderate damage
(Slight structural damage, moderate
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
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
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.

CHAPTER 6 RESULTS AND DISCUSSIONS
This study presents seismic vulnerability assessment of residential buildings in Agartala city using
RVS methodology. Survey of buildings was conducted and data on various parameters like type
of buildings, age of buildings, number of stories, apparent quality, heavy overhangs, diaphragm
action, horizontal bands, vertical irregularities and plan irregularities have collected. Based on
these data the performance score of each building has calculated from which the predicted damage
grade has assigned for each building. Below mentioned sections shows the results of the present
study in the pie and bar charts for both residential and school buildings.
RESIDENTIAL BUILDINGS OF DHALESWAR
6.1 Type of Structures
Based on survey data, Fig.6.1 shows that a variety of building types exist, however 59% of
buildings are constructed with RCC, 33% of the buildings are masonry types and 8% are composite
structures. The reinforced concrete structural type consists of clay brick bearing walls, confined
with caste in place concrete columns and beams, which imports some ductility. But, URM
structures, which have clay brick bearing walls and no concrete columns, are not contributing any
ductility.
Fig.6.1 Building distribution
6.2 Age of buildings The age of the building is one of the most important factors that should be
taken in account in order to study the seismic vulnerability assessment. Fig 6.2 shows that
maximum number of buildings constructed near about 15 years ago (73 buildings) and 20 years
ago (63 buildings). The minimum number 5 buildings are above 50 years ago constructed.
Buildings are constructed after 2005 are sustainable for Earthquake.
33%
59%
8%
MASONRY RCC COMPOSITE

Fig.6.2 Age of buildings
6.3 Analysis of stories
The buildings of this area are mostly single or two storied. All the surveyed buildings are
residential type. In the case of masonry buildings, all the buildings in the area are up to 2 storied.
In the case of RCC buildings, all the buildings are below 4 storied or mostly up to 3 storied. General
observation is that most the RCC buildings have been constructed after 2001 and will have
naturally some shear capacity to tolerate low level of seismic shaking. But in the case of masonry
buildings, due to lack of reinforcement, the capacity of resisting the seismic load is quite doubtful.
Fig.6.3 shows the number of stories of buildings.
Fig.6.3 Number of Stories
13
38
53
70
63
39 37
17
9 6 5
0
20
40
60
80
NUMBEROFBUILDINGS
AGE OF BUILDINGS
211
124
12
0
50
100
150
200
250
1ST STOREY 2ND STOREY 3RD STOREY
NUMBEROFBUILDINGS
NUMBER OF STORIES

6.4 Analysis of apparent quality
Material, workmanship and maintenance create a building’s quality. Fig. 6.4 shows the apparent
quality of buildings. It is observed that 128 buildings are of good quality out of 206 buildings.
Among these good quality buildings some are constructed in recent past and the buildings which
are constructed recently are followed by the guideline of seismic codes and for that reason crack
and dampness are negligible. 78 buildings are of moderate quality, as these are constructed earlier
and are not followed by the guidelines of seismic codes. And the remaining 48 buildings are of
poor quality which is constructed 40 or 60 years ago as a result excessive cracks and dampness are
found
Fig.6.4 Apparent quality
6.5 Analysis of Heavy Overhangs, Plan Irregularity and Vertical Irregularities
The plan irregularities in buildings (L-shaped, T shaped or U-shaped) cause torsion during
earthquake and are responsible for major damage. Among the surveyed buildings most of them
are L shape, and very few are U shape. Vertical irregularities can be judged from the structural
system like Setbacks in elevation. The vertical irregularities make a building far more vulnerable
as compared to the plan irregularities. Fig. 6.5 shows that 80 buildings have heavy overhangs or
horizontal projection, 115 buildings having plan irregularities and 78 buildings are found with
presence of setbacks.
Fig.6.5 Heavy Overhangs, Plan Irregularity and Vertical Irregularities
67
155
128
0
50
100
150
200
BAD MEDIUM GOOD
NUMBEROFBUILDINGS
115
78 80
0
20
40
60
80
100
120
140
HI VI HEAVY OVERHANG
NUMBEROFBUILDINGS

6.6 Analysis of diaphragm action, soil condition, soft stories and short column
Diaphragm action 37%, in soil having maximum 71% medium condition and many few percentage
buildings constructed on hard soil, 10% buildings having soft stories and 5% building having short
column.
(a) (b)
(c) (d)
Fig.6.6 Showing attributes of buildings, (a) Diaphragm action, (b) Soil condition, (c) Soft
stories and (d) Short column
6.6 Analysis of number of member
The Fig.6.7 shows the maximum number of family have 4 members and minimum having 9
members. The family member varies door to door, which indicate intensity of earthquake varies
with buildings. Average family member in the survey area is 4. 103 buildings having 4 members,
86 building having 3 members, 44 buildings having 5 members etc.
9%
71%
20%
SOFT MEDIUM HARD
7%
56%
37%
EXIST DON'T EXIST DON’T KNOW
10%
90%
EXISTS DON’T EXISTS
5%
95%
EXIST DON'T EXIST

Fig.6.7 Number of members
6.8 Analysis of falling hazards and ponding
36% buildings having falling hazards and 19% buildings having pounding.
(a) (b)
Fig.6.8 Showing (a) Falling hazards and (b) Ponding
6.9 Analysis of horizontal bands
Fig 6.9 shows that 49% of the total surveyed buildings have three horizontal bands i.e. plinth band,
lintel band and roof band. 32% buildings have two horizontal bands and 12% buildings have only
one horizontal band, whereas surprisingly some very old constructions have no band.
Fig.6.9 Horizontal bands
36%
64%
EXIST DON'T EXIST
6
33
86
103
44
29
10 14
4 6
15
0
50
100
150
1 2 3 4 5 6 7 8 9 10 >10
NUMBEROFBUILDINGS
NUMBER OF MEMBER
19.00%
81.00%
EXIST DON'T EXIST
12%
32%
49%
5%
1 BAND 2 BAND 3 BAND NO BAND

6.10 Analysis of RVS Performance Score by FEMA 154-2015
Fig.6.10 shows that the performance scores of the surveyed buildings of Dhaleswar area for both
masonry & RCC structures are predominantly ranging between 0.2 through 1.5. 149 buildings
have performance score greater than 1.0, 88 buildings have also scored between 0.4 to 1.0 and 69
buildings have scored less than 0.4. From the visual assessment, it is seen that these buildings are
in moderate condition and will not get collapse under low seismic action. But there is a need of
further evaluation i.e. preliminary evaluation. Guide Lastly a large number of structures i.e. As per
this line all the building need further evaluation as the performance score of all these buildings are
less than 2 which is considered as cut-off score.
Fig.6.10 FEMA 154-2015 Final level 2 Score
6.11 Damage Grade of residential buildings
In Agartala 350 residential buildings was surveyed during the period of 25 th August 2016 to 4th
April 2017. As R.C.C structures can only be evaluated by the two methods so a representative
sample of 206 buildings was taken out of the total buildings. These buildings had been assigned
different grades of damage (G1: slight damage to G5: collapse) where G1 is slight nonstructural
damage, G2 is slight structural damage, G3 is moderate structural damage, and G4 is severe
structural damage, G5 is collapse. The performance score of these RCC buildings was calculated
by the three methods namely FEMA 154 (2015) Method. In the survey all buildings belong to G3
to G5 grade for both RCC and masonry. Fig 6.11 showing the damage grades.
0
53
0
9
3
28
6
0
28
7
45
0 0
16
13
3
5
18
10
0
7
2
49
0 0
4
0
2
0
10
20
30
40
50
60
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
NUMBEROFBULIDINGS
RCC MASONRY

Fig.6.11 Damaged grades
6.12 Seismic mapping of RVS score analysis
Seismic mapping shows 49% belongs to G3 grades, 28% G4 grades and remaining 23% G5 grades.
All buildings potential have moderate structural damage to collapse.
Fig.6.12 Seismic mapping
53
46
96
16
42
49
0
20
40
60
80
100
120
G5 G4 G3
NUMBEROFBUILDINGS
RCC MASONRY

CHAPTER 7 CONCLUSIONS
Through this project our main objective is to check over the faulty construction of buildings going
on in the city which makes the buildings vulnerable to earthquake and to rectify the defects in that
particular building Recently a rising trend is observed in constructing a Residential building that
building codes are not being followed properly which is a practice code for design of the building
components such as to providing ductility or special confining reinforcement and thus is a major
aspect in case of an earthquake. So we undertook an initiative to create awareness among people
regarding these faulty constructions to prevent the risk of vulnerability of the building and its users
to earthquake. Thus, we suggest the people to mandatorily consult a structural engineer in case of
constructing a new building regarding its plan, design and construction. The main results of this
present study are as below
1. In light of above results and discussions it has been seen that out of total surveyed 350 buildings
more than half of the buildings (59%) are RCC structures, 33% are load bearing walls, 8%
composite structures building.
2. It is observed that 21% buildings constructed about 25 years ago are not suitable to sustain the
strong seismic shock. Moreover 11% buildings constructed about 30-35 years back are obviously
masonry buildings should be strengthened immediately.
3. It is seen that 23% buildings have Vertical Irregularities and 33% buildings have Plan
irregularities. Fortunately the percentage of Vertical irregularities is less than Plan irregularities,
as the former is much more vulnerable than the latter. Lastly 23% buildings have heavy overhangs
in buildings.
4. The performance score of the residential buildings is calculated by FEMA 154 (2015). it is seen
all the building need further evaluation as the performance score of all these buildings are less than
“2” which is considered as cut-off score. All buildings belong to G3 to G5 grades.
5. Near about 149 buildings may experience G3 type of damage, 88 numbers of buildings may be
experienced G4 type damage and 69 buildings may be experience G5 type damage in severe future
earthquake estimated by FEMA 154 (2015).

CHAPTER 8 FUTURE SCOPE OF THE STUDY
The seismic vulnerability assessment of existing structures is very much essential in the city of
Agartala as it is situated in the seismic zone V, the worst zone in India. Accordingly to judge the
vulnerability condition of building in this city, in the present study few areas like Dhaleswar area
has been selected which will not show the vulnerability as whole so, in future other municipal area
of Agartala city has to be selected to carry out the same work. All other important building like
hospital, school buildings may be considered for future study. However, the preliminary and detail
study on the few surveyed building can be carry out to judge the findings of RVS methods.

REFERENCES
Bernardini, A.,Giovinazzi, S.,Lagomarsino, S., Parodi, S. (2007). The vulnerability assessment of
current buildings by a macroseismic approach derived from the EMS-98 scale. 3° National
Congress of Earthquake Engineering, Girona, Spain
Federal Emergency Management Agency (FEMA 154), (1988). Rapid Visual Screening of
Building for Potential Seismic Hazards: A Handbook (FEMA 154, 2015),
Google Earth for valuable image and QGIS
Indian Standard 13920:1993 Code of practice for ductile detailing of reinforced concrete structures
subjected to seismic forces Indian Standards, New Delhi.
Indian Standard 456:2000 Code of practice for plain and reinforced concrete Indian Standards,
New Delhi. Indian Standard 1893 (Part 1): 2002 Criteria for earthquake resistant design of
structures (Fifth Revision) Indian Standards, New Delhi.
Sinha, R., and Goyal, A., (2004). “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, Indian Institute of Technology Bombay, India.
Wikipedia.

Assessing Seismic Vulnerability of Homes in Agartala Using Rapid Screening

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