SEISMIC RETROFITTING OF EXISTING NON-ENGINEERED
LOAD BEARING STRUCTURES IN INDIA
Background
India
is a country that is frequented by disasters almost
every year in one part or another. It witnesses much
damage, destruction, injury and loss of life. A resource
starved nation like India loses much of its scarce valuable
resources on post disaster rehabilitation. There have
been many moderate to high intensity earthquakes and
cyclones in India during the past decade.
Non-engineered
Structures
In
a developing country like India an overwhelming
majority of houses, as also the infrastructure
buildings, in towns and villages, are of non-engineered
load bearing type. These structures, especially
houses, have been traditionally built
over the past century or longer, using the locally
available materials and the locally
practiced technologies that have been most
common in the area including stone, bricks, earth, lime
and timber for walls, and clay tiles, stone or mud for
roofing supported on under-structure made of local timber
such as Teak, Acacia, Neem, Deodar, Pine and also Bamboo.
In the recently built structures one also finds a mix
of the traditional and new materials/technology such
as cement, concrete and steel. The structures have pitched
roof or flat roof, and are single story or double story.
Baring exceptions a majority of these structures are
of load-bearing type. There is, however,
little or no engineering input in to these structures,
and, the people who build them have no technical knowledge
of the construction carried out by them. Hence, these
structures are called non-engineered.
For various reasons most of these buildings have simply
not been built to withstand the forces of an earthquake
anticipated in the region.
Relationship
of Non-engineered Structures with Local Context
The
non-engineered traditional construction commonly practiced
in different areas of the country depends greatly on
the respective local context of the area. In other words
the technologies vary significantly from area to area.
These technologies have evolved and as a result have
got optimized
Significance
of Non-Engineered Construction
Non-engineered
structures like these play a major role in meeting
the basic but crucial needs of the society.
This could be better understood through looking at aspects
like (a) cost, (b) climate, (c) lifestyle and (d) economy.
One could say with fair amount of certainty that a majority
of building construction will continue to be done this
way in a foreseeable future because of the eternal resource
crunch and country’s huge population. Other technical
options have become available in the past few decades
and more will become available with time. But few will
be as viable and optimized for the rural and semi-urban
context as the options that have been in use all this
time.
Large Scale
of Vulnerability
A study
conducted by Prof. Arya, Prof. Emeritus from India Institute
of Technology at Roorkee in India based on the Vulnerability
Atlas of India 1997, in the Seismic Zone V alone there
are over 11 million housing units that are vulnerable.
Similarly in Zone IV this number could be as much as
50 million. By another count there are over 80 million
houses in the country that are vulnerable. These counts,
however, do not include the non-engineered infrastructure
buildings in towns and villages as also those built
with modern technologies but without any engineering
input. In other words the number of structures
that are vulnerable is extremely large, and the
people that are at risk may amount to as much as 50%
of the country’s population.
Performance
By Non-Engineered Structures in Recent Disasters
The
performance of non-engineered structures with a variety
of building systems and materials has been studied extensively
in the past decade. All these types of buildings that
were built without taking in to account the possible
earthquakes in the area performed badly. The reasons
for the bad performance are well known. These are (a)
poor quality of construction, which reflects the violation
of the basic rules of construction, and (b) absence
of disaster resistant features in it.
Even if a structure were to be built with good quality,
it is unlikely to withstand shaking from a strong earthquake
if special features to overcome the inherent weaknesses
of a non-engineered structure were not incorporated
in the construction. These forces could be resisted
if (a) all the elements are properly interconnected,
(b) and are secured to the walls, and (c) the roof has
elements that ensure diaphragm action.
Concept of
Retrofitting
With
a high number of structures being vulnerable it is important
that their vulnerability is tackled in order to reduce
the undue hardship and losses that the people may suffer
and the economic losses that the country may face in
the event of a major earthquake. This could be achieved
through the retrofitting of these structures. A number
of tests have been carried out in India to study the
effect of retrofitting of a variety of traditional structures.
These include those carried out by Prof. Arya at Umerga
near Latur in 1995, by Rajendra Desai of NCPDP at Latur
in 1997, and by Prof. Arya and Rajendra Desai at Radhanpur
bordering Kutchch, as well as those carried out at I.I.T.,
Roorkee. These tests effectively demonstrated that retrofitting
of the non-engineered structures with simple elements
like Ferro-Cement Belt installed at lintle or eave level,
vertical single reinforcing bar in the corners, diagonal
bracings in roof, reduction in roof dead load etc. significantly
increase the resistance of the structures to withstand
the seismic forces.
Retrofitting
Measures
For each
weakness that has been observed in an earthquake there
is a remedy in the form of a retrofitting measure. These
remedies are evolved on the basis of the information available
in a number of books and Bureau of Indian Standards (BIS)
Guidelines in India. In Gujarat since after the Kutchch
Earthquake Prof. Arya had helped evolve a set of ready
to use guidelines for the Gujarat State Disaster Management
Authority (GSDMA) that are based on the BIS Guidelines
and Codes mentioned above. These guidelines were used
extensively for the retrofitting of new houses that were
not built as per the government guidelines and also for
the existing infrastructure buildings in the quake affected
parts of the State.
Economics
& Advantages of Retrofitting
The
past experiences with the economics of retrofitting
show that the retrofitting index (or
the ratio of the cost of retrofitting over the total
cost of new construction) is as low as 5%.
For retrofitting to be most advantageous it must be
done in a proactive manner. In other words it is best
if done before a disaster strikes. This would help save
lives and losses, and prevent suffering. Thus far in
India the approach to retrofitting, what ever little
that has been carried out, has been retroactive. The
past disasters show that retrofitting has not been a
priority for most concerned parties. It has been observed
that many house owners, donor agencies, and, at times,
even government agencies want to demolish the structures
that are little damaged or absolutely undamaged. But
that proposition has been expensive, inconvenient and
time consuming. Instead, the option of repair and retrofitting
is faster, economical, and helps retain the
conveniences that were created in the existing
structure, be it a house or an infrastructure building.
It is indeed the most economical option that one could
exercise for ensuring one’s long-term safety.
The option of building anew, although effective, involves
the cost of (a) dismantling the existing structure,
(b) carting of debris and, finally, (c) the cost of
reconstruction. With the rapidly escalating costs the
expenditure involved may be several times that of what
was spent when the structure was first built. On the
other hand, retrofitting costs a tiny fraction of it.
Yet another important advantage of this option is its
in-built flexibility. Of the several
different measures that need to be applied one has a
choice to apply
One or a few measures at a
time to a part of the structure or,
One or a few measures to the
whole structure, or
All the options to the whole
structure in one go.
Thus
one could take a decision based on the
(a) availability of funds,
(b) availability of time, and finally
(c) the convenience, while ensuring the technical
soundness of the overall scheme.
Possibility
of phasing in retrofitting of the whole structure
greatly increases the accessibility of this
option.
Hurdles in
Application of Retrofitting Measures to Non-Engineered
Structures
There
are several hurdles in the large scale application of
retrofitting in the country, be it in the urban area
or in rural. These could be listed as follows.
Few engineers understand the
technicalities of a variety of load-bearing systems
used in the country. Most of them consider them
un-scientific, archaic, unreliable, un-safe, out
of fashion and not modern. As a result in the event
of making a choice between preserving a load bearing
structure through repair & retrofitting versus
building it anew, the choice falls on the later.
Decision by an engineer to
recommend retrofitting, which is essentially a low
cost option, is dictated at times by its economic
attractiveness to the engineer whose advise is sought
.
In the aftermath of a disaster
the over abundance of funds tends to result in to
the exclusion of this option in the favor of a more
expensive option of dismantling and reconstruction.
House owners, in general, are
ignorant about it and they lack confidence in it.
Hence, they do not readily opt for it and invest
their own funds.
The building artisans and contractors
do not possess the necessary skills and knowledge,
nor do they understand the economics of it.
There have been training programs
for masons and engineers in the past in many areas
of the country. Most of them have been classroom
programs. It is vital that the training is carried
out in the field.
Most training programs have
been “one shot deals”. But this is simply
not enough to begin work on one’s own. Much
follow-up and refresher training is needed to prevent
mistakes and the false sense of security that such
wrong work may create.
Necessary materials such as
welded wire mesh (galvanized or otherwise), 16 gauge
GI wire, low shrink grout etc. are not available
in most places. In other words the delivery system
for retrofitting simply does not exist and needs
to be created.
Need of the
hour
It
is recognized around the world that retrofitting of
the existing buildings is the most viable option for
ensuring the long term safety of the most number of
people against future disasters. Since, in a developing
country like India bulk of the houses and infrastructure
buildings are non-engineered and are executed in the
informal sector, the focus of promoting this option
must be aimed primarily towards the people at large
including building artisans. The technical community,
however, does have a marked influence on the psyche
of the people and the artisans. Hence, the efforts of
promotion must also focus on the technical community.
The following is a list of things that ought to be taken
up for the large scale promotion of the option of retrofitting.
Education of Engineers
Engineering curriculum
addition/revision – Since the education
curriculum lacks the vernacular systems of
construction the engineers coming out of the
colleges are totally ignorant about them.
Load bearing building systems are also absent
from curriculum of most colleges. On the other
end the education over emphasizes the RCC
and steel construction. As a result for most
engineers these are the only legitimate construction
systems worth using. Everything else is useless
and must be discarded.
Continuing education
– The practicing engineers also need
to be exposed to the vernacular systems and
ways to retrofit them.
Impart Visibility through demonstration of retrofitting on actual
buildings in various locations.
Public Awareness campaign for creating felt-need among the people is a crucial step in evolving the
delivery system for retrofitting.
Confidence Building Program could be organized tailor made for different
audiences such as those from construction industry,
common man, policy makers, children etc. need to
be taken up
Training of Petty Contractors
and Building Artisan – This forms
the most important link in the whole delivery system.
After all for a common man the mason and the petty
contractor are the “engineers” that
help him build his house
Clear and Positive
Government Policy – The government
invests the most amount of money in construction,
as well as in the post disaster relief and rehabilitation
work. Hence, the government must have a policy that
promotes retrofitting to minimize future losses
The synergistic effect of
all these programs on a sustained basis could bring
the desired results in a foreseeable future.
By
Rajendra Desai, Hon. Jt. Director
National Centre for Peoples’ Action in Disaster
Prepreadness, (N.C.P.D.P.)
103 Antariksh, Panjarapol Char Rasta, Near Polytechnic,
Ahmedabad 380015, GUJ. India
Tel/FAX: 091 79 2630 8843, E-Mail: [email protected]
