Seismic retrofitting involves modifying existing structures to increase their resistance to seismic activity like earthquakes. It is important for historically significant buildings, areas prone to earthquakes, and tall or expensive structures. Retrofitting techniques can strengthen structures by increasing lateral strength, ductility, and strength-ductility. Some common retrofitting methods include adding new shear walls, steel bracing, base isolation, and column jacketing. Column jacketing involves wrapping columns with steel, reinforced concrete, or fiber-reinforced polymers to improve shear and flexural capacity. The selection of a retrofitting technique depends on factors like the structure type, material condition, cost, and effectiveness for the situation.
2. Introduction
Earthquake creates great devastation in terms of life, money
and failures of structures.
We know that earthquake is a important field of study from
long time.
Seismic Retrofitting is a collection mitigation techniques for
Earthquake Engineering.
It is utmost importance for historic monuments, areas prone
to severe earthquake and tall or expensive structures.
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 cyclones, severe winds from thunderstorms.
The seismic retrofitting gives improvements to an existing
buildings and increasing the global capacity of the building.
4. When is Seismic Retrofitting
Needed?
The two circumstances are
Earthquake damaged buildings, and
Earthquake-vulnerable buildings(with no exposure to
severe earthquakes)
The performance objectives are
• public safety
• Structure survivability
• Structure functionality
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;
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 that are expanded, renovated or rebuilt.
Buildings, the use of which has changed through the
years.
6. 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.
Basic Concept of Retrofitting
Up gradation of lateral strength of the structure;
Increase in the ductility of the structure
Increase in strength and ductility
7. 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.
8. FLOW OF RETROFITTING PROCESS
Drafting of retrofitting plan
Performance requirements of existing structure
Inspection of existing structure
Performance verification for existing structure
if ok continue and use of the structure
if not determination use of the structure
through retrofitting
if no restriction on use of structure
if yes go for selection of retrofitting
method
Implement retrofitting work and use of structure.
10. 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 placed
at the exterior of the building.
Additional shear wall
11. 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
13. 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.
Base isolated structures
14. Jacketing (Local Retrofitting Technique)
Most popular method for strengthening of building
columns
Types-1. Steel jacket, 2. Reinforced Concrete jacket, 3.
Fiber Reinforced Polymer Composite(FRPC) jacket.
Purpose for jacketing:
To increase concrete confinement
To increase shear strength
To increase flexural strength
15. STEEL JACKETING
Addition of steel often applied in the form of plates or
jackets.
Local strengthening of columns has been frequently
accomplished by jacketing with steel plates.
Advantage of steel include that it does not add significant
weight to the structure in comparison with concrete and it
saves on construction time(no curing).
The main disadvantage of this type are linked to
construction issues steel can be labor intensive and it
require heavy equipment‘s to handle thousands of tons
and as well as having a more difficult maintenance.
17. REINFORCED CONCRETE JACKETING
Reinforced concrete jacketing can be employed as a
repair or strengthening scheme.
There are two main purposes of jacketing of columns:
(i) Increase in the shear capacity of columns
(ii) To improve the column's flexural strength
Using concrete sections the other methods developed are
section enlargement
shot Crete
fiber reinforced cement composites
18. SHOT CRETE
Larger development in section enlargement is shot Crete.
It is a concrete or mortar pneumatically projected at high
velocities.
Main advantages are reduction of construction time and
cost.
Main disadvantage is it require special attention and good
quality product.
These include placing thick sections in layers using of a
blow man to help reduce rebound and requiring quality
control.
20. FIBER REINFORCED PLASTIC METHOD
FRP composites present significant advantages over a
traditional confinement techniques .
The cross section dimensions of the column do not
increase, which permits compliance with architecture
restraints.
The mass of the column does not increase; which means
the seismic behavior of the building remains unchanged.
Due to light weight of FRP materials implies that the
installation procedure is faster, easier, less dangerous for
the operator.
21. Fiber-reinforced plastic bonding method:
A construction method in which glass fibers, carbon
fibers, aramid fibers or other continuous fiber materials
(continuous fiber sheets, etc.) are bonded to the outside of
the concrete section, bonding to the existing members to
form a composite configuration, after which an organic or
other material coating is applied on top, both to prevent
the entry of carbon dioxide, chloride ions, moisture etc.
and to provide the necessary performance improvement.
This method is used for bridge decks and almost all other
concrete members.
22. Fiber-reinforced plastic jacketing
construction method:
A method in which continuous fiber sheets or other
fiber materials are placed continuously around the
entire periphery of existing column members, etc.
with insufficient load-carrying capacity, bonding to
the existing members to form a composite
configuration in order to achieve the required
performance improvement. This method is used for
bridge piers, etc.
23. DIFFERENT TYPES OF FIBERS
GLASS FIBERS:
• glass fibers have been commonly used for 50 years in the
aeronautical industry given their very high strength to
weight ratio.
• They also used in wind turbine blades and in the field of
naval engineering.
• E-glass or Electrical glass is the most widely used glass
fiber because of its low cost of production.
CARBON FIBERS:
This is mainly used for old structures that may have been
damaged by earthquakes, chemical environment etc.
24. ARMID OR KELVAR
These fibers are less used as regards applications for civil
engineering and retrofitting of structures.
These fibers gives best strength to weight ratio.
Main disadvantage of these are inadequate compressive
strength.
Column without wrapping
27. SELECTION OF STRENGTHING METHOD
Now a days old existing buildings with less load carrying
capacity are usually strengthen by the application of a suitable
strengthen method.
There is a possibility of selecting a strengthen method with out
comparing for the most efficient method.
The recommended strengthen method should be relatively
more economical, efficient and time saving.
There are numerous strengthen methods available, each of
which has its own advantages and disadvantages.
Ex:-steel jacket strengthening is not suitable in marine
environment due to corrosion.
But steel jacketing yielded a good result for the columns
designed for gravity loads with out any earthquake design.
