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1. PRESENTED BY GUIDE: Dr . NEETHU URS, Professor
ADITYA BIRADAR DAYANANDA SAGAR COLLEGE OF ENGINEERING
1DS20CV005
SIESMIC RETROFITTING OF EXISTING STRUCTURES:
“TECHNIQUES AND CASE STUDIES”
TECHNICAL SEMINAR
DAYANANDA SAGAR COLLEGE OF ENGINEERING
An Autonomous Institution affiliated to Visvesvaraya Technological University, Belagavi,
Shavige Malleswara Hills, Kumara swamy layout Bangalore – 560111

2. Introduction
Earthquake creates great devastation in terms of life, money
and failures of structures.
Earthquake Mitigation is an important field of study from a
long time now.
It is of utmost importance for historic monuments, areas prone
to severe earthquakes and tall or expensive structures.
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3. Seismic Retrofitting
Definition
It is the modification of existing structures to make them more
resistant to seismic activity, ground motion, or soil failure due
to earthquakes.
The retrofit techniques are also applicable for other natural
hazards such as tropical cyclones, tornadoes, and severe winds
from thunderstorms.
When is Seismic Retrofitting Needed ?
The two circumstances are:-
Earthquake damaged buildings, and
Earthquake-vulnerable buildings (with no exposure
to severe earthquakes)
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4. Retrofit Performance Objectives
Public safety only: The goal is to protect human life, ensuring that the
structure will not collapse upon its occupants or passersby, and that the
structure can be safely exited.
Structure survivability: The goal is that the structure, while remaining safe
for exit, may require extensive repair (but not replacement) before it is
generally useful or considered safe for occupation. This is typically the
lowest level of retrofit applied to bridges.
Structure functionality: Primary structure undamaged and the structure is
undiminished in utility for its primary application.
Structure unaffected: This level of retrofit is preferred for
historic structures of high cultural significance.
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5. Need of Retrofitting in Existing
Earthquake Vulnerable Buildings
Buildings have been designed according to a seismic code, but the code
has been upgraded in later years;
Buildings designed to meet the modern seismic codes, but
deficiencies exist in the design and/or construction;
Essential buildings must be strengthened like hospitals, historical
monuments and architectural buildings;
Problems faced by Structural Engineers are :-
Lack of standards for retrofitting methods
Effectiveness of each methods varies a lot depending upon parameters like
type of structures, material condition, amount of damage , etc.
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6. Basic Concept of Retrofitting
 Upgradation of lateral strength of the structure;
 Increase in the ductility of the structure
 Increase in strength and ductility
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Earthquake Design Philosophy
Under minor but frequent shaking, the main members of the building that carry
vertical and horizontal forces should not be damaged; however building parts that do
not carry load may sustain repairable damage;
Under moderate but occasional shaking, the main members may sustain repairable
damage, while the other parts of the building may be damaged such that they may even
have to be replaced after the earthquake; and
Under strong but rare shaking, the main members may sustain severe (even
irreparable) damage, but the building should not collapse.

7. Classification of Retrofitting Techniques
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8. Some Conventional Approaches
Adding New Shear Walls
 Frequently used for retrofitting of non
ductile reinforced concrete frame buildings.
 The added elements can be either cast‐in‐place
or precast concrete elements.
 New elements preferably be placed at the
exterior of the building.
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 Not preferred in the interior of the structure to
avoid interior mouldings.
Fig:Additional Shear Wall

9. Adding Steel Bracings
 An effective solution when large openings are required.
Potential advantages for the following reasons:
⚫higher strength and stiffness,
⚫opening for natural light,
⚫amount of work is less since foundation cost may be minimized adds
much less weight to the existing structure
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Fig: RC Building retrofitted by steel bracing

10. Some Conventional Approaches (Contd.)
Jacketing (Local Retrofitting Technique)
 Most popular method for strengthening of building columns
 Types-1. Steel jacket, 2. Reinforced Concrete jacket, 3.
Fibre Reinforced Polymer Composite(FRPC) jacket
 Purpose for jacketing:
⚫To increase concrete confinement
⚫To increase shear strength
⚫To increase flexural strength
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Fig: Column Jacketing
Fig: Beam Jacketing

11. Retrofit of Structures using Innovative
Materials
Current research on advanced materials has mainly concentrated
on FRP composites.
Studies have shown that externally bonded FRP composites
can be applied to various structural members including
columns, beams, slabs, and walls to improve their structural
performance such as stiffness, load carrying capacity, and
ductility.
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12. Base Isolation (or Seismic Isolation)
Isolation of superstructure from the foundation is known as
base isolation.
It is the most powerful tool for passive structural vibration
control technique
Fig: Base Isolated Structures
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13. Concept of Base Isolation
Significantly Increase the Period of the Structure and the Damping so
that the Response is Significantly Reduced.
Fig: Spectral Response for a
Typical Base Isolation System
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Types of Base Isolations
Base isolation systems which uses
Elastomeric Bearings
Base isolation systems with Sliding System
Fig: Elastomeric Isolators

14. Elastomeric Base Isolation Systems
This is the mostly widely used Base Isolator.
The elastomer is made of either Natural Rubber or Neoprene.
The structure is decoupled from the horizontal components of the earthquake
ground motion. Alayer with low horizontal stiffness introduced
between the structure and the foundation.
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Fig: Steel Reinforced
Elastomeric Isolators

15. Advantages of Base Isolation
Isolates Building from ground motion
 Lesser seismic loads, hence lesser damage to the structure.
 Minimal repair of superstructure.
Building can remain serviceable throughout construction. Does not
involve major intrusion upon existing superstructure.
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Disadvantages of Base Isolation
Expensive
Cannot be applied partially to structures unlike other retrofitting
Challenging to implement in an efficient manner
Allowance for building displacements
Inefficient for high rise buildings
Not suitable for buildings rested on soft soil.

16. Seismic Dampers
Seismic Dampers are used in place of structural elements, like
diagonal braces, for controlling seismic damage in structures.
It partly absorbs the seismic energy and reduces the motion of
buildings.
Types:-
 Viscous Dampers (energy is absorbed by silicone-based fluid
passing between piston-cylinder arrangement),
 Friction Dampers (energy is absorbed by surfaces with friction
between them rubbing against each other), and
 Yielding Dampers (energy is absorbed by metallic components
that yield).
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17. Viscous Dampers
Fig: Cross-section of a Viscous Fluid Damper
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18. Tuned Mass Damper(TMD)
It is also known as an active mass damper (AMD) or harmonic absorber.
It 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 tall
buildings.
Fig: TMD in Taipei 101 35
Taipei 101 has the largest TMD sphere in the world and weighs 660 metric
tonnes with a diameter of 5.5 metre and costs US$4 million (total structure
costs US$ 1.80 billion).
Fig: TMD in Taipei 101

19. Indian Codes for Earthquake Design
IS: 1893-2002 (part-1) Criteria for Earthquake Resistant Design of Structures (Part 1 :
General Provision and Buildings) - Code of Practice
IS: 4326-1993 Earthquake Resistant Design and Construction of Buildings – Code of
Practice
IS: 13920-1993 Ductile Detailing of Reinforced Concrete Structures subjected to
Seismic Forces – Code of Practice
IS: 13935-1993 Repair and Seismic Strengthening of Buildings – Guidelines
IS: 13828-1993 Improving Earthquake Resistance of Low Strength Masonary
Buildings - Guidelines
IS: 13827-1993 Improving Earthquake Resistance of Earthen Buildings – Guidelines
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20. Case Study : Mani Mandir Complex at Morbi, Gujarat
• The Mani Mandir complex is an important historic monument of town of
Morbi in state of Gujarat, suffering significant damage during the M7.7
Bhuj earthquake.
• The complex was modelled using finite elements and behaviour was studied
of the existing structure as well as retrofit structure
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21. Case Study : Mani Mandir Complex at Morbi, Gujarat
• Damage documentation
1. Stone slab wedged between steel joists
2. Separation of joist flanges and failure of stone slab
3. Destruction of arches in elevational elements
4. Partial collapse of Bastions
5. Openings of joints in arch
6. Diagonal cracks in walls
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22. Case Study : Mani Mandir Complex at Morbi, Gujarat
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23. Case Study : Mani Mandir Complex at Morbi, Gujarat
METHODOLOGIES FOR REPAIR, RESTORATION AND RETROFITTING
• Introducing rigid diaphragm action of slab : for improved seismic performance a rigid
diaphragm was required to be put in place at both the floor levels. The diaphragm action
was proposed by introducing diagonal bracing elements on underside of first floor.
• Enhancing strength of structure : due to poor bonding of stone masonry walls were unable
to provide adequate lateral strength. Various options were considered such as introducing
new shear walls, strengthening existing walls by shotcreting and providing base isolation.
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24. Case Study : Mani Mandir Complex at Morbi, Gujarat
METHODOLOGIES FOR REPAIR, RESTORATION AND RETROFITTING
• End pinning of wall corners: proposed to securely connect the perpendicular walls to each
other by cross pinning with stainless steel rods of 8mm and 10mm dia at every 600mm
along height.
• Introduction of horizontal reinforced bands to existing masonry walls to [rovide seismic
features and to improve their performance and ductility.
• Strengthening of Arches : based on damage 2 retrofit details had been recommended. For
movement of support and internal arches a stainless steel tie with turn buckle is proposed.
For no movement of supports keystone is tied back into wall above my means of stainless
steel rod
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25. Case Study : Mani Mandir Complex at Morbi, Gujarat
METHODOLOGIES FOR REPAIR, RESTORATION AND RETROFITTING
• Cross pinning of corridor columns: columns are made up of 3 stones interlocked by socket
system. It is proposed to hold up these stones profoundly.
• Stitching and grouting of cracks in walls : diagonal cracks are to be stitched using stainless
steel bars before the cracks are grouted
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26. Conclusion
Seismic Retrofitting is a suitable technology for protection
of a variety of structures.
It has matured in the recent years to a highly reliable
technology.
But, the expertise needed is not available in the basic level.
The main challenge is to achieve a desired performance
level at a minimum cost, which can be achieved through a
detailed nonlinear analysis.
Optimization techniques are needed to know the most
efficient retrofit for a particular structure.
Proper Design Codes are needed to be published as code of
practice for professionals related to this field.
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27. References
Agarwal, P. and Shrikhande, M., 2006, Earthquake Resistant Design of Structures, 2nd Edition,
Prentice-Hall of India Private Limited, New Delhi.
Cardone, D. and Dolce, M., 2003, Seismic Protection of Light Secondary Systems through
Different Base Isolation Systems, Journal of Earthquake Engineering, 7 (2), 223-250.
Constantinou, M.C., Symans, M.D., Tsopelas, P., and Taylor, D.P., 1993, Fluid Viscous Dampers
in Applications of Seismic Energy Dissipation and Seismic Isolation, ATC-17-1, Applied
Technology Council, San Francisco.
EERI, 1999, Lessons Learnt Over Time – Learning from Earthquakes Series: Volume II
Innovative Recovery in India, Earthquake Engineering Research Institute, Oakland (CA), USA.
Murty, C.V.R., 2004, IITK-BMTPC Earthquake Tip, New Delhi.
Siesimic Retrofitting of Mani Mandir Complex at Morbi, Gujarat, India. Alpa Sheth, R D
Chaudhari, Ejaz Khan, Divay Gupta, Malvika Saini. World conference on Earthquake
Engineering Vancouver, B.C., Canada 2004
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28. THANK YOU…
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