Need for Pre-Earthquake Risk Assessment of Buildings in
Moderate-to-Severe Earthquake Prone Areas in India
by
Pradeep Kumar Ramancharla
in
nternational Conference on Forensic Civil Engineering, Nagpur, India 21,22,23 January 2016
(FCE-2016)
: 15
ACCE, Bengaluru
Report No: IIIT/TR/2016/-1
Centre for Earthquake Engineering
International Institute of Information Technology
Hyderabad - 500 032, INDIA
January 2016
Proceedings of the International Conference on Forensic Civil Engineering, Nagpur, India
21,22,23 January 2016
Need for Pre-Earthquake Risk Assessment of Buildings in
Moderate-to-Severe Earthquake Prone Areas in India
R. Pradeep Kumar
Professor of Civil Engineering & Head
Earthquake Engineering Research Centre
IIIT Hyderabad
ramancharla@iiit.ac.in
ABSTRACT
Due to rapid urbanization of Indian cities in last few decades, there is a tremendous
pressure on housing industry to cater to the needs. This fast pace of construction
activity with no planning has led to the growth of medium to highrise buildings,
causing serious threat to life and property. The same is clearly evident from the losses
during earthquakes in the recent past including twin major earthquakes in Nepal.
Hence there is a need to understand the earthquake risk and take corrective
measures.
Seismic risk assessment has three components viz., Hazard, Exposure and
Vulnerability. Vulnerability assessment of buildings consists of following three stages
viz., 1) Rapid Visual Survey (RVS), 2) Preliminary Assessment and 3) Detailed
Assessment. Following the above three stages, on a sample of around 10,000
buildings, graphs have been developed to assess the damage of buildings in cities
prone to earthquake hazard. These graphs can be used to perform pre-earthquake
exercise. Graph will indicate the type of damage a building will have when subjected
to a particular level of shaking which depends on the magnitude of an earthquake. The
information on level of shaking will come from seismological inputs. These graphs are
being tested in different areas to validate the study in future earthquakes.
INTRODUCTION
Earthquake Risk is the projected aggregated effect of the expected number of lives
lost, persons injured, property damaged and economic activity disrupted due to an
expected strong earthquake in an area. Usually, it is represented as the product of
the prevalent earthquake hazard (H) of the area, the number of persons exposed to
the earthquake hazard (E), and the known vulnerability (V) of the houses in that
area, as:
Risk H  E  V
(1)
Each of these components of risk has its own characteristics, which can be spatial
(e.g., hazard) temporal (e.g., exposure) and thematic (e.g., vulnerability of houses).
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Proceedings of the International Conference on Forensic Civil Engineering, Nagpur, India
21,22,23 January 2016
Figure 1: Seismic Hazard Map
Seismic Hazard (H)
Earthquake Hazard is defined as the potential threat of occurrence of a damaging
earthquake, within the design life of the house in a given area. The hazard due to
an earthquake can be reflected by expected intensity of ground shaking (quantified
by PGA, PGV and PGD), soil liquefaction, surface fault rupture and slope instability.
India has experienced several major earthquakes in the past few decades and
according to IS 1893 (Part I):2007 around 60% (12% in Zone V, 18% in Zone IV,
26% in Zone III and 44% in Zone II) of its landmass is prone to moderate to severe
earthquake shaking intensity [1, 2 & 3].
Especially, in the last 23 years, the country has witnessed several moderate
earthquakes (Table 1) (Bihar-Nepal border (M6.4) in 1988, Uttarkashi (M6.6) in
1991, Killari (M6.3) in 1993, Jabalpur (M6.0) in 1997, Chamoli (M6.8) in 1999, Bhuj
(M6.9) in 2001, Sumatra (M8.9) and Kashmir (M7.6) in 2005) caused around 40,000
fatalities due to collapse of buildings. Seismic Hazard Assessment quantifies the
physical expression of the hazard, in the form of intensity of earthquake shaking.
Rational understanding of the seismic hazard of the different areas is critical to a
meaningful risk assessment exercise.
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Proceedings of the International Conference on Forensic Civil Engineering, Nagpur, India
21,22,23 January 2016
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Proceedings of the International Conference on Forensic Civil Engineering, Nagpur, India
21,22,23 January 2016
Figure 2: Housing Density in districts of India [Based on Census of India, 2011]
Table 1: Human fatalities during past earthquake events [4]
Year
1988
1991
1993
1997
1999
2001
2004
2005
2006
Location
Bihar
Uttarkashi
Killari
Jabalpur
Chamoli
Bhuj
Sumatra
Kashmir
Sikkim
Casualties
1,004
768
8,000
38
100
13,805
10,805
~1,500
2
Buildings Collapsed
2,50,000
42,400
30,000
8,546
2,595
2,31,000
Not available
4,50,000
Not available
Table 2: Intensity corresponding to different zones as per IS 1893 (Part I)-2007 and
number of houses in each zone
Zone
Seismic
Zone
Factor (Z)
Shaking
Intensity
0.10
VI (or lower)
0.16
VII
0.24
VIII
0.36
IX (or higher)
II
III
IV
V
Houses
Number
%
4,39,86,51 17.78
7
%
11,58,68,0
46.8
42
6
6,32,83,12
25.6
8
0
2,41,44,35
9.76
0
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Proceedings of the International Conference on Forensic Civil Engineering, Nagpur, India
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Exposure (E)
Presently, India is home for 1.2 about billion people. Over the last six decades,
there has been a great shift of population from rural to urban areas, thus increasing
the densities of population in urban areas. This suggests that about 300 million
houses are necessary to house them. According to National Housing Policy 2007 [5],
the housing shortage is estimated to be about 25 million. And according to 2011
Census [MHA, 2011], Indian urban population constitutes 32.25%. However, it is
increasing at an alarming rate of 4% per year. The number and proportion of cities
with a population of one million or more has grown significantly in recent decades.
From 12 in 1981 with 26.8% share of the total population, the number of millionplus cities has increased to 35 in 2001 with 37% share of the total urban
population. In addition housing shortage is already higher in urban areas,
notwithstanding the ever increasing housing densities. Figure 2 shows the districtwise spatial distribution of population density in India. Population in India is
distributed unevenly with minimum of 50 persons per km2 in some districts and up
to 14000 persons per km2 in some other districts. Rural districts have up to 100
houses per km2, towns 1000-1500 km2, cities 1500-2500 houses per km2 and
urban centers and metro go as high as 7000 houses per km2. As per 2011 census,
district-wise density of housing is higher near urban areas. Many of these high
density areas also lie in moderate to high seismic zones.
Vulnerability (V)
Earthquake vulnerability of a house is the amount of expected damage induced to it
by a certain level of earthquake intensity. The earthquake performances of the
buildings, especially in the last two decades (Table 1), indicate around 40,000
human fatalities caused primarily by collapse of buildings. Except for Killari
earthquake, all other events occurred in known moderate to high seismic zones.
Damage caused to these buildings is unreasonably high compared to any other
country for similar level of ground shaking. Serious departures are observed
especially in performance of RC buildings. During the 2001 Bhuj earthquake, they
collapsed at an intensity of shaking of VII, when MSK scale expects them to collapse
only after intensity IX of ground shaking. Thus, there is urgent need to understand
the housing risk in the country to minimize the future losses of life and property.
Earthquake Threat Map of Housing in India
Since Indian cities are built with varied varieties of building typologies, comprising
of poorly designed and less maintained ones, the seismic safety of these
constructions became the most challenging task. Therefore, a simple measure is
required to set a priority for starting the formal initiatives of quantification of risk
and then taking up the mitigation initiatives. Proposed Housing Threat Factor gives
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Proceedings of the International Conference on Forensic Civil Engineering, Nagpur, India
21,22,23 January 2016
a broad idea of relative status of each district (and not about individual houses) and
where the work can be started urgently.
Figure 1 shows the housing threat factor in different districts in India. It is used to
understand the overall status of housing. This factor is obtained by multiplying
seismic zone factor (Z) of the seismic zone by number of houses per km2 for each
district in India. For example, Level IV risk areas are those with high hazard and
higher population densities. Low housing risk areas are those with low hazard and
moderate to low population densities.
Housing Threat
Figure 3: Housing Threat Factor (HxEx1)
How to Use the HRF Index
Risk assessment results in a quantitative index (it does not have any physical
significance) that gives a qualitative feel of the level of severity of the problem. The
actual process of risk assessment is a detailed exercise and time consuming. Even
to begin such an exercise, a basis is needed to start work of risk assessment from
one quarter and move forward. For instance, it is necessary to know which districts
have relatively larger problem compared to all the districts in seismic zones III, IV
and V. Therefore, a simple measure is required to set a priority for starting the
formal initiatives of quantification of risk and then taking up the mitigation
initiatives. Proposed Housing Risk Factor gives a broad idea of relative status of
each district (and not about individual houses) and where the work can be started
urgently.
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Vulnerability Assessment
Seismic vulnerability is a measure of the seismic strength or capacity of a structure,
hence it is found to be the main component of seismic risk assessment. Detailed
seismic risk 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 develop simpler procedures that can help to rapidly evaluate the vulnerability
and risk of different types of buildings, so that more complex evaluation procedures
can be limited to the most critical buildings.
Vulnerability assessment of buildings consists of following three stages:
Rapid Visual Survey (RVS)
Preliminary Assessment
Detailed Assessment
IIIT Hyderabad took up the work in following three phases:
A Handy Tool for Seismic Risk Assessment of Buildings
The RVS methodology (Ref 1) is referred to as a “side-walk survey” in which an
experienced screener visually examines a building to identify features that affect
the seismic performance of the building, such as the building type, seismic zone,
soil conditions, horizontal and vertical irregularities, apparent quality in masonry
and RC structures and short column etc. This side-walk survey is carried out based
on the checklists provided in a proforma specified for building category. Other
important data regarding the building is also gathered during the screening,
including the occupancy of the building and the presence of nonstructural elements
and falling hazards.
A performance score is calculated for the building based on numerical values on the
RVS form corresponding to these features. A massive exercise of collecting RVS
data of over 15000 buildings in Gandhidham and Adipur areas of Gujarat has been
carried out in the year 2009. This was executed with the collaboration of Institute of
Seismological Research (ISR) and Nirma University. This exercise has given the
range of RVS scores. However, it is not clear from the RVS score that in the event of
an earthquake what will be the performance of building. Hence it is necessary to
benchmark these RVS scores for each building category. For benchmarking,
preliminary assessment (stage 2) and detailed assessment (stage 3) are to be
carried out. It took 5 years of effort to benchmark these RVS scores to qualitative
damage estimates. Details are given below:
Similar project was taken up in Nanded-Waghala city, sponsored by Government of
Maharashtra and collaboration with NGRI. During this project preliminary
assessment was also included along with RVS. Subsequently, another project was
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taken up in Himachal Pradesh in 2013 in collaboration with TARU consultants. In this
period, more dimensions were added including building vulnerability survey which
covered five different varieties of constructions like RC Construction, Stone
masonry, Brick buildings, Earth buildings and hybrid buildings using different
construction materials. During this project “Expended energy based damage
assessment model” [6] was developed at IIIT Hyderabad and the same was linked
to the Rapid visual survey (RVS) score of a building for finding out the seismic risk
assessment. In this, the damage can be categorized under five categories as No
damage, slight damage, moderate damage, severe damage and complete collapse.
The graphs have been developed to indicate the type of damage a building will
have when subjected to a particular level of shaking which depends on the
magnitude of an earthquake. The information on level of shaking will come from
seismological inputs in a particular area. These graphs are being tested in different
areas to validate the study in future earthquakes.
0.9
Collaps e
0.8
0.7
PGA (g)
0.6
S evere dam age
0.5
M oderate dam age
0.4
0.3
S light dam age
0.2
0.1
0
60
No dam age
70
80
90
100
110
RVS Score
120
130
140
Figure 4: Damage state corresponding to RVS score of a RC building
The graph can be read as follows:
Step 1: RVS score of a building can be calculated by RVS Proforma
Step 2: Peak Ground Acceleration is decided by the area (Geographical)
Step 3: Intersection point in the graph gives qualitative estimate of damage state
of a building in the event of future earthquake.
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This will help both individual home owners to know the vulnerability and risk status
of their building and the government to know the status of built environment in a
given region. The above kind of graphs can be developed for all the building
varieties in India and can be improved depending on the size of data.
Conclusions
At a time when around 56 percent of the land area in India is earthquake prone
(with 12% of land area coming under Zone V, 18% under zone 4, 26% under zone 3,
and 44%under zone 2), it is imperative for India to develop strategies for risk
assessment and mitigation as 82 percent of the population is living in 56 percent of
the land areas. Detailed seismic risk 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 develop simpler procedures that can help to rapidly
evaluate the vulnerability and risk of different types of buildings, so that more
complex evaluation procedures can be limited to the most critical buildings.
IIIT Hyderabad has developed the graphs to indicate the type of damage a building
will have when subjected to a particular level of shaking which depends on the
magnitude of an earthquake. This will help both individual home owners to know
the vulnerability and risk status of their building and the government to know the
status of built environment in a given region.
REFERENCES
1.
BMTPC, (1997), Vulnerability Atlas of India 1997, Building Materials and
Technology Promotion Council, New Delhi
2.
BMTPC, (2007), Vulnerability Atlas of India 2007, Building Materials and
Technology Promotion Council, New Delhi
3.
IS 1893 (Part I), (2007), Indian Standard Criteria for Earthquake Resistant
Design of Structures, Bureau of India Standards, New Delhi
4.
Murty,C.V.R., (2007), IITK-BMTPC Earthquake Tips, National Information Centre
of Earthquake Engineering, IIT Kanpur
5.
MoHUAPA, (2007), National Urban Housing and Habitat Policy, Ministry of
Housing, Urban Affairs and Poverty Alleviation, Government of India, New Delhi
6.
A. Vimala and R. Pradeep Kumar (2015), “Expended Energy Based Damage
Assessment of an RC Building, Indian Concrete Institute Journal, July-Sept 2015.
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