Seismic Retrofitting Techniques & Rehabilitation

Presented by,

Shuvam kumar sarkar

4th Year, Civil engineering

Jalpaiguri Government Engineering College

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Flow of presentation

What is retrofitting?

Why retrofitting is

required?

Objectives of retrofitting

To retrofit or not?

Retrofitting techniques

Some conventional approaches

Existing retrofitted structures

Conclusion

References

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What is retrofitting?

• 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.

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Why retrofitting is required?

• The two circumstances are:

Earthquake damaged buildings, and

Earthquake-vulnerable buildings(with no exposure to severeearthquakes)

• Nearly 5,00,000 earthquakes occur every year around worldamong which about 1,00,000 are felt and the rest occur nearlyconstantly 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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Objectives of retrofitting

• 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.

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To retrofit or not?

• Retrofitting should be adopted when the evaluation of the building indicates that the strengthavailable before the damage was insufficient and restoration alone will not be adequate in futurequakes.

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SEISMIC LOAD CAPACITY VERSUS RISK

OF BUILDING COLLAPSE

Retrofitting techniques

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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.

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SHEAR WALLS

Adding infill wall

• Masonry infills contribute significantlateral stiffness, strength, overallductility and energy dissipationcapacity.

• The structural load transfermechanism is changed from frameaction to predominant truss action.

• The frame columns now experienceincreased axial forces but withreduced bending moments and shearforces.

• When infills are non-uniformlyplaced in a building, cause soft storeyeffect, short-column effect, torsionand out-of-plane collapse.

• Hence, seismic code tends todiscourage such constructions in highseismic regions.

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BRICK MASONRY INFILL WALL RETROFITTING

Adding steel bracings

• An effective solution when large openings arerequired.

• Potential advantages for the following reasons:

Higher strength and stiffness,

Opening for natural light,

Amount of work is less since foundation costmay be minimized

Adds much less weight to the existing structure

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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.

11QUADRA ELEMENTRY SCHOOL, CANADA

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.

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RETROFITTING BY ALUMINIUM FLAT AT

UJJAYANTA PALACE, AGARTALA, TRIPURA

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.

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MASS REDUCTION BY REMOVING ONE STOREY

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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Seismic dampers

• 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).

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ENERGY DISSIPATION DEVICES

WORLD’S LARGEST

TUNED MASS DAMPER

(SPHERE) IN TAIPEI 101

Jacketing (local retrofitting techniques)

• Most popular method for strengthening of concrete building elements like as beams, columns andbeam-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.

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RETROFITTING AT JUNCTION BY STEEL PLATE

19RETROFITTING BY STEEL REINFORCED CONCRETE

COLUMN JACKETINGBEAM JACKETING

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RETROFITTING OF COLUMN BY CFRP WRAP

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GFRP WRAP AND WRAPPED STRUCTURE

Existing retrofitted structures in India

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UJJAYANTA PALACE, AGARTALA, TRIPURA SWET MAHAL, AGARTALA, TRIPURA

Conclusion

• 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.

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References

• 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

• IS: 13935-1993 Repair And Seismic Strengthening Of Buildings – Guidelines

• IS: 13828-1993 Improving Earthquake Resistance Of Low Strength Masonry Buildings –

Guidelines

• IS: 13827-1993 Improving Earthquake Resistance Of Earthen Buildings - Guidelines

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Thank You…

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