The document discusses seismic retrofitting techniques aimed at enhancing the earthquake resilience of existing structures. It highlights various retrofitting methods, such as adding shear walls, steel bracings, and base isolation systems, along with their advantages and disadvantages. The document emphasizes the importance of retrofitting for historic buildings and essential structures, as well as the need for updated design codes and optimization techniques in this field.

1. Seismic Retrofitting Techniques & Rehabilitation

2. Introduction
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• Seismic retrofitting is a collection mitigation technique for earthquake engineering.
• It is the modification of existing structures to make them more resistant to seismic activity, ground motion,
or soil failure due to earthquake.
• It is of utmost important for historic monuments, areas prone to severe earthquakes and tall or
expensive structures.
• The retrofitting techniques are also applicable for other natural hazards such as tropical cyclones,
tornadoes and severe winds from thunderstorms.
• Retrofitting proves to be a better economic consideration and immediate shelter to problems
rather than replacement of building.

3. Need of Retrofitting
• The two circumstances are:
 Earthquake damaged buildings, and
 Earthquake-vulnerable buildings(with no exposure to severe
earthquakes)
• Nearly 5,00,000 earthquakes occur every year around world among
which about 1,00,000 are felt and the rest occur nearly constantly
almost anywhere.
• Large number of casualties occur in buildings due to earthquake.
Reasons may be;
Inadequate design
Poor construction and maintenance
Lack of resources
Inadequate knowledge and awareness
Inadequate safety implementation
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4. Need of Retrofitting in Existing Earthquake Vulnerable
Buildings
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• 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;
• Important buildings whose services are assumed to be essential just after an
earthquake like hospitals;
• Buildings, the use of which has changed through the years; Buildings that
are expanded, renovated or rebuilt.

5. Basic Concept of Retrofitting
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The aim is at :-
Upgradation of lateral strength of the structure;
Increase in the ductility of the structure
Increase in strength and ductility

6. Earthquake Design Philosophy
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• 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. Objectives of Retrofitting
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• Public safety: The main goal is to protect human life, ensuring that the structure will not collapse
upon its occupants or passer-by and that the structure can be safely exited.
• Structure serviceability: The structure is to serve good serviceability while being subjected to
vulnerable earthquakes.
• Structure functionality: Primary structure undamaged and the structure is undiminished in utility
for its primary application.
• Structure unaffected: The level of retrofit is preferred for historic structures of high cultural
significance.
• Therefore, the aim is to upgrade the lateral strength of the structure and to increase the
ductility.

8. To Retrofit or
not?
• Retrofitting should be adopted when the evaluation of the building indicates that the strength
available before the damage was insufficient and restoration alone will not be adequate in future
quakes.
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SEISMIC LOAD CAPACITYVERSUS RISK
OF BUILDING COLLAPSE

9. Retrofitting Techniques
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10. Adding shear wall
• Used for 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, however it may cause in the appearance.
• Increase the lateral strength, ductility and stiffness of the building substantially.
SHEAR WALLS
10
Global Retrofitting Techniques

11. Adding Infill wall
 Masonry infills contribute significant
lateral stiffness, strength, overall
ductility and energy dissipation capacity.
 The structural load transfer
mechanism is changed from frame
action to predominant truss action.
 The frame columns now experience
increased axial forces but with
reduced bending moments and shear
forces.
 When infills are non-uniformly
placed in a building, cause soft storey
effect, short-column effect, torsion and
out-of-plane collapse.
 Hence, seismic code tends to discourage such constructions in high seismic regions
.
BRICK MASONRY INFILLW
ALL
RETROFITTING 11

12. 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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13. Adding Wing Wall or Buttress
• To increase lateral strength, ductility and stiffness of structure.
• The wing wall are placed on the exterior side of an existing frame.
QUADRAELEMENTRY SCHOOL, CANADA 13

14. Wall Thickening Techniques
• Increase the thickness by adding bricks,
concrete and steel reinforcement.
• It can bear more vertical and horizontal loads.
• Does not cause sudden failure of the wall.
RETROFITTING BYALUMINIUM FLATAT
UJJAYANTAPALACE,AGARTALA, TRIPURA
14

15. Mass Reduction
• In this process removing one or more
storey of building as shown in the
figure.
• Decrease the load at foundation.
• Increase the life and strength.
MASS REDUCTION BY REMOVING ONE STOREY
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16. Base Isolation
• Isolation of superstructure from the foundation is known as base isolation.
• It is the most powerful tool for passive structural vibration control techniques.
• Isolates building from ground motion lesser seismic loads, hence lesser damage to the structure,
minimal repair to the structure.
• Building can remain serviceable throughout construction.
• Does not involve major intrusion upon existing superstructure.
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17. Concept of Base Isolation
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 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

18. Types of Base Isolations
Base isolation systems which uses Elastomeric Bearings
Base isolation systems with Sliding System
Fig: Elastomeric Isolators
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19. 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
 A layer with low horizontal stiffness is introduced
between the structure and the foundation.
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Fig: Steel Reinforced
Elastomeric Isolators

20. Sliding Base Isolation Systems
It is the second basic type of isolators.
This works by limiting the base shear across the isolator interface.
Fig: Metallic Roller Bearing
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21. Spherical Sliding Base Isolators
• The structure is supportedby bearing pads that have curved surface
and low friction.
• During an earthquake, the building is free to slide on the bearings.
Fig: Spherical Sliding Base Isolator 24

22. Friction Pendulum Bearing
These are specially designed base isolators which works
on the principle of simple pendulum.
It increases the natural time period of oscillation by
causing the structure to slide along the concave inner
surface through the frictional interface.
It also possesses a re-centering capability.
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Fig: Cross-section of Friction Pendulum Bearing

23. 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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24. 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.
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25. Seismic Dampers
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• Seismic dampers are used in place of structural elements, like diagonal braces, for controlling
damage in structures.
• It partly absorbs the seismic energy and reduces the motion of buildings.
• Types of mass dampers:
1. Viscous dampers (energy is absorbed by silicon-based fluid passing between piston-
cylinder arrangement),
2. Friction dampers (energy is absorbed by surfaces with friction between them rubbing
against each other), and
3. Yielding dampers (energy is absorbed by metallic components that yield).

26. ENERGY DISSIPATION DEVICES
WORLD’S LARGEST
TUNED MASS DAMPER
(SPHERE) IN TAIPEI 101
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27. Jacketing (local retrofitting techniques)
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• Most popular method for strengthening of concrete building elements like as beams, columns and
beam-column junctions.
• Purpose for jacketing:
To increase concrete confinement
To increase shear strength
To increase flexural strength
• Materials to be used:
1. Steel plates
2. Steel reinforced concrete
3. Fibre Reinforced Polymer (FRP wrap)
I. Carbon fibre reinforced polymer (CFRP)
II. Glass fibre reinforced polymer (GFRP)
• FRP wraps increase the seismic energy absorption capacity of the structual elements.

28. Concrete jacketing
 involves addition of longitudinal bars, closely spaced ties, anda layer of concrete.
 The jacket increases both flexural strength and shear strength of concrete .
 The usual practice consists of first assembling the jacket reinforcement cages,
arranging the formwork and then placing the concretejacket.
 But it is cost effective.

29. Concrete jacketing
 Concrete jacketing disadvantages-
1.Cost effective
2.Requires intensive labour
3.Detailing of steel in the form of digital collars
4.Incrases Dimensions ofstructure
5.Incrases weight ofstructure

31. Steel Jacketing
 Steel jacketing refers to encasing the member with steel plates and filling the gap
with non-shrink grout.
 The jacket enhances both flexural strength and shear strength of concrete.
 Steel jacketing disadvantages –
 1.Complicated working procedure.
2.Inner surface corrosion .
3. Heavy weight.
4.C/S increases.

32. Fiber Reinforced Polymer( FRP)
 Fiber reinforced polymer (FRP) is a composite material consisting of polymeric
resin reinforced with high strength fibers.
 Composite materials are available in the form of sheets, pre-formed shapes and
bars.
 The FRP sheets are thin, light and flexible enough to be inserted.
 The fibers can be of glass, carbon, aramid.
 Glass fibers have lower stiffness and cost compared to carbon fibers.
 They are suitable in low cost seismic retrofit applications.

33. Fiber Reinforced Polymer( FRP)
 The FRP composites are useful for repair, rehabilitation and retrofit of
structures for the following reasons:
facilitate
flexible, which
drilling of concrete or
1.The FRP sheets are light and
installation. It does not need
masonry.
2.The curing time required is less
3.The sheets are thin and hence there is no marginal increase
in the size of retrofitted member.
4. The material is chemically inert and has resistance against
electro-chemical corrosion.
5. There is good fatigue strength, which is suitable for fluctuating loads.

34. External Plate Bonding
• Steel plates are attached to the surface of damaged members
forming a three phase steel composite system
• Acts as supplement to existing reinforcement.
Attachment of steel to concrete
o Adhesive connecting mechanism (glue).
o Bolting connecting mechanism.
Advantages
• Stress reduction due to the external steel plate.
• Enhances load bearing capacity.
• decreases chances of cracks and deflection.

35. Disadvantages
• Increase in dead load.
• High installation cost due to heavy weight of steel plate.
• If there is any indications of corrosion in the reinforcement
this technique cannot be used.
• Susceptible to high level of premature de-bonding.
• Chances of corrosion is high.
• Bonding between concrete and steel plate.
• Reaction between epoxy adhesive and concrete.

36. EXTERNAL POST TENSIONING.
• High strength steel strands or pre-stressing tendons are used.
• Tendons are pulled and connected to anchor points on member.
• Very much suitable for retrofitting of bridges.
Advantages
• Ability to restress, destress and exchange any external pre-
stressing cable.
• Crack free members.
• Reduce deflection.
• High fatigue and impact resistance.
• Immediate enhancing of load bearing capacity.

37. Disadvantages
• Usually requires a greater section depth.
• Exposed to environmental influences.
• Handling of the tensioning devices may be
more difficult.
• High cost.
• Prone to corrosion.
• Skilled person is needed for post tensioning

38. RETROFITTINGAT JUNCTION BY STEELPLATE
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39. 19
RETROFITTING BY STEELREINFORCED CONCRETE
BEAM JACKETING COLUMN JACKETING

40. RETROFITTING OF COLUMN BY CFRPWRAP
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41. GFRPWRAPAND WRAPPED STRUCTURE
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42. Existing retrofitted structures in India
UJJAYANTAPALACE,AGARTALA, TRIPURA
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SWET MAHAL,AGARTALA, TRIPURA

43. Conclusion
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• Seismic retrofitting is a suitable technology for protection of a variety of structures. It has matures
in recent years but the expertise needed is not available in the basic level.
• Decrease the working space of concrete structure due to extension in structural elements and affect
the appearance. Optimisation techniques are required to know the most efficient retrofit for a
particular structure.
• The main challenge is to achieve a desired performance level at minimum cost, which can be
achieved through a detailed nonlinear analysis.
• Proper design codes are required to be published as code of practice for professionals related to this
field.

44. References
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• Handbook on retrofit of building by Indian Institute of Technology Madras (Civil Engineering
department)
• IS: 4326-1993 earthquake resistant design and construction of buildings – code of practice
Buildings –
• IS: 13935-1993 RepairAnd Seismic Strengthening Of Buildings – Guidelines
• IS: 13828-1993 Improving Earthquake Resistance Of Low Strength Masonry
Guidelines
• IS: 13827-1993 Improving Earthquake Resistance Of Earthen Buildings - Guidelines