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
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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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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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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