The document discusses the importance of seismic retrofitting to enhance the safety and resilience of buildings against earthquakes. It outlines various retrofitting techniques such as base isolators, supplementary dampers, tuned mass dampers, slosh tanks, and active control systems, emphasizing their role in protecting human lives and preserving structural integrity. Additionally, it highlights specific IS codes related to earthquake-resistant design and retrofitting standards.

1. SEISMIC RETROFITTING OF BUILDINGS
Today, many countries are the victims of severe earthquakes resulting in the
loss of lives of human being, animals, destruction of buildings, and many more.
So, it is high time for the civil engineers to take this issue as a serious matter and
they must think of some alternatives of saving human lives as well as wildlife.
WHAT IS SEISMIC RETROFITTING?
Seismic, by the word itself means something relating to earthquakes or
vibrations of the earth and its crust. It happens due to some disturbances below the
earth’s crust which cannot be seen.
Seismic retrofitting is the modification of existing structures to make them
more resistant to seismic activity, ground motion or soil failure due to earthquakes.
There are several techniques which have come forward nowadays by which an
existing structure can be modified and make it less prone to earthquakes.
It is important to keep in mind that there is no such thing to make a structure
fully earthquake proof but seismic performance can be greatly enhanced through
proper initial design or subsequent modifications.

2. Common seismic retrofitting techniques fall into several categories:
1. Base Isolators.
2. Supplementary dampers.
3. Tuned mass dampers.
4. Slosh tank.
5. Active control system.
WHAT IS THE NEED FOR SEISMIC RETROFITTING OF BUILDINGS?
The need for seismic retrofitting in existing buildings can arise due to the
following reasons:
 Buildings not designed according to the codes of practice.
 Deterioration of strength of the buildings.
 Not considering the safety of buildings while construction.
UNIQUENESS:-
The impact of earthquake is sudden with little or no warning to make
preparations against damages and collapse of structures. The common seismic
retrofitting techniques have evolved very fast and have changed the belief of
people that buildings can be made earthquake proof with proper modifications and
thereby saving human lives. Seismic retrofit strategies have been developed in the
past few decades following the introduction of new seismic provisions and the
availability of advanced materials like fiber reinforced polymers, fiber reinforced
concrete and high strength steel.
AIMS AND OBJECTIVES:-
1. Public safety: The goal is to protect human life, ensuring that the structure
will not collapse upon its occupants or passerby.
2. Structure survivability: The goal is that the structure, while remaining safe
may require extensive repair but not replacement.
3. Structure functionality: Primary structure undamaged and the structure is
undiminished in utility for its primary application.
4. Structure unaffected: A high level of retrofit is preferred for historic
structures of cultural significance.

3. BASE ISOLATORS:-
Base isolation is one of the most powerful means of protecting a structure
against earthquake forces. It is meant to enable a building to survive a potentially
devastating seismic impact through proper initial design or subsequent
modifications.
Tomb of Cyrus is said to be the oldest base-isolated structure in the world.
Base Isolation system consists of the following:
1. Isolation units 2. Isolation components
Isolation units:- They consist of shear or sliding units. They are intended to
provide the decoupling effect to a building. The first evidence of architects using
the principle of base isolation for earthquake protection was discovered in
Pasargadae, a city in Iran in 6th century BC.
Isolation components:- These are the connections between isolation units and
their parts having no decoupling effect of their own.

4. How do base isolators work?
Base Isolation is a technique developed to prevent or minimize damage to
buildings during an earthquake. So far it has been used in New Zealand, India,
Japan, Italy and the USA. When a building is built away (isolated) from the
ground, resting on flexible bearings or pads known as base isolators, it will move
little or not at all during an earthquake.
How are base isolators constructed?
They consist of basic components-a lead plug, rubber and steel, which are
generally placed in layers.
Rubber: - The rubber provides flexibility. At the end of an earthquake, the rubber
bearings will slowly bring the building back to its original position which takes
months to happen.
Lead: - Lead has plastic
property. During an earthquake,
the kinetic energy of the
earthquake is absorbed into heat
energy as the lead is deformed.
Steel: - If layers of steel are
used with rubber, the bearing
can move in the horizontal
direction but is stiff in the
vertical direction.

5. SUPPLEMENTARYDAMPERS:-
A Supplementary Damping System (SDS) is essentially an energy dissipation
system that is incorporated into the design of a structure to absorb vibration
energy, thereby reducing motion.
Dampers for earthquake protection
How do the supplementary dampers work?
Supplementary damping is the most efficient and cost effective way to achieve
energy dissipation in buildings. This would inadvertently mean decreasing the
energy dissipation demand on the structural components i.e. beams/columns/slabs
thereby increasing the survivability of the building structure. Dampers are
mechanical devices that look somewhat like huge shock absorbers and their
function is to absorb and dissipate the energy supplied by the ground movement
during an earthquake so that the building remains unharmed. Whenever the
building is in motion during an earthquake tremor or excessive winds, dampers
help in restricting the building from swaying excessively and thereby preventing
structural damage. The energy absorbed by dampers gets converted into heat which
is then dissipated harmlessly into the atmosphere. Dampers thus work to absorb

6. earthquake shocks ensuring that the structural members i.e. beam and columns
remain unharmed.
Benefits:-
 Achievement of occupant comfort and safety criteria.„
 Increased design life (structural durability) through reducing structural
stress and/or fatigue.
 Decreased construction and maintenance costs. „
 Increased tenant space.
Dampers used in a building

7. TUNED MASS DAMPERS: -
A tuned mass damper, also known as
a harmonic absorber is a device mounted
in structures to reduce the amplitude of
mechanical vibrations. Their application
can prevent discomfort, damage or
outright structural failure. They are
frequently used in power transmission,
automobiles and buildings.
How do tuned mass dampers work?
Tuned mass dampers stabilize against violent motion caused by harmonic
vibration. It reduces the vibration of a system with a comparatively lightweight
component so that the worst-case vibrations are less intense. Practical systems are
tuned to either move the main mode away from a troubling excitation frequency or
to add damping to a resonance that is difficult to damp directly.
Location of Taipei101’s largest tuned mass damper

8. SLOSH TANK: -
In fluid dynamics, slosh refers to the movement of liquid inside another object
undergoing motion.
Nowadays, one of the biggest challenges that engineering faces is to reduce
structure motion due to external loadings especially in high rise buildings. Slosh
tank is one of the inventions that can be installed in different locations and levels
into a structure, in order to increase dampening (energy absorbing mechanism) and
decrease vibrations. It can either be installed on the top floor of a structure or in
some certain floors or even at each floor of a building.
Rectangular slosh tank

9. Sensors
Control Actuators
Excitation Structure Response
ACTIVE CONTROL SYSTEM: -
The use of active control systems and some combinations of active and passive
systems, so called hybrid systems, as a means of structural protection against
seismic loads has received considerable attention in recent years. Active/hybrid
control systems are force delivery devices integrated with real-time processing
evaluators/controllers and sensors within the structure. They act simultaneously
with the hazardous excitation to provide enhanced structural behavior for improved
service and safety.
An active structural control system consists of the following:
a) Sensors located about the structure to measure either external excitations, or
structural response variables, or both.
b) Devices to process the measured information and to compute necessary
control force needed based on a given control algorithm.
c) Actuators, usually powered by external sources, to produce the required
forces.
Structure with Active Control
Controller Sensors

10. LIST OF IS CODES REQUIRED FOR SEISMIC RETROFITTING:
 IS 4326:1993 – Earthquake resistant design
 IS 13827:1993 – Earthquake resistance of earthen buildings
 IS 13828:1993 – Earthquake resistance of low strength masonry buildings
 IS 13920:1993 – Ductile detailing of reinforced concrete structures
 IS 13935 – Seismic strengthening of buildings
 IS 1893 – Earthquake resistant design of structures
Submitted by – SUKANTA PAUL
Registration ID – EXS230151
Email ID – sukantapaul92@gmail.com
College – JIS College of Engineering
Stream – Civil (4th year)