Retrofitting: Upgrading of certain building systems (existing structures) to make them more resistant to seismic activity.

1. RETROFITTING
OF
BUILDINGS
Submitted by:
Mr. Yash Kumar
Submitted to:
Department Of Civil Engineering

2. CONTENTS
 Introduction
 Need of retrofitting
 Goals of retrofitting
 To retrofit or not ?
 Steps of retrofit
 Condition assessments of buildings
 Materials used for retrofitting
 Classification of retrofitting techniques
 Retrofitting of RCC buildings
 Conclusion
 Appendix

3. INTRODUCTION TO RETROFITTING
 Actions that improve the strength and other attributes of the integrity of a structure or a
member with respect to seismic forces.
 Sometimes, the terms ‘seismic rehabilitation’, ‘seismic upgradation’ and ‘seismic
strengthening’ are used in lieu of ‘seismic retrofit’.
 It is intended to mitigate the effect of future earthquakes.
 Retrofit is done before the occurrence of the earthquake (as a preventive measure) in an
undamaged building, while rehabilitation is done in a building that is already damaged.

4. NEED OF RETROFITTING
The need for seismic retrofitting can arise due to any of the following reasons:
 Building not designed to code.
 subsequent updating of code and design practice
 Subsequent upgrading of seismic zone
 deterioration of strength and aging
 modification of existing structure
 In India, almost 85% of total buildings are non-engineered buildings made up of
earthen walls, stone walls, brick masonry walls, etc. These buildings are more
vulnerable.

5. GOALS OF RETROFITTING
 To increase the lateral strength and stiffness of the building.
 To increase the ductility and aims to avoid the brittle modes of failure.
 To increase the integral action and continuity of the members in a building.
 To eliminate or reduce the effects of irregularities.
 To enhance redundancy in the lateral load resisting system. This aims to eliminate the
possibility of progressive collapse.
 To ensure adequate stability against overturning and sliding.

6. TO RETROFIT OR NOT ?
A decision depends on many factors. Lifeline buildings, such as hospitals must necessarily
be retrofitted, in view of their extreme importance.
But should the aim of retrofit be to raise this capacity to 100 percent
• For lifeline buildings such as fire stations, hospitals, power stations, telephone
exchanges, television stations, radio stations, railway stations, air ports;
• Important service and community buildings such as schools, cinema halls, multiplexes,
marriage and other assembly halls, the capacity should be raised to 100 percent

7. STAGES OF RETROFITTING
Selection of the
objective of retrofit
Reviewing initial
considerations
Obtaining
information of the
building
Seismic evaluation
Decision to retrofit
or demolish
Selection and
design of retrofit
strategies
Verification of the
retrofit scheme
Construction
Maintenance and
monitoring

8. CONDITION ASSESSMENT OF BUILDINGS
 Condition assessment describes the process of assessing the actual condition of a structure in
relation to the requirement. It indicates whether the structure is satisfactory, or, whether
repair and rehabilitation are necessary.
 Condition assessment includes the following steps:
1. Initial inspection and appraisal.
2. Review of documents.
3. Detailed investigation.
4. Reporting and recommendations.
 Visual Inspection
Concrete
cracks, spalling, staining, disintegration of the surface, honey-combing, exposed
reinforcement
Steel
corrosion, Stress concentration, crippling or buckling, Bowing, misalignment,
deformation, twisting, Cracks in welds, missing bolts / rivets

9.  Detailed Investigation
1. Obtaining the properties of the structural materials used in the building.
2. Determining the type and disposition of reinforcement in building.
3. Locating deteriorated material and other defects.
A number of tests are available to study the condition of the material in a structure:
Non-
Destructive
Tests
• Rebound Hammer test
• Thermal methods
• Radiography
• Electromagnetic techniques
• Stress wave propagation method
Intrusive
Tests
• Core test
• In-Situ Shear test
• Flat-Jack test
• In-Situ Permeability

10. MATERIALS USED IN RETROFITTING
MATERIALS
Epoxy
Resins
Epoxy
Mortar
Quick
Setting
Cement
Mortar
Shortcrete
Micro-
Concrete
Fibre-
Reinforced
Concrete
Fibre-
Reinforced
Polymer
Ferro-
cement

11. CLASSIFICATION OF RETROFIT TECHNIQUES
 Local Retrofit Strategies
 Global Retrofit Strategies
• Global Retrofit Strategies: To provide increased lateral stiffness and strength to the
building as a whole. And, to ensure that a total collapse of the building does not occur.
• Local Retrofit Strategies: To avoid failure of the components, and also thereby enhance the
overall performance of the structure
• More than one combination of local and global retrofit strategies is possible.
• The structural engineer must work out an appropriate, practically and economical
solution.

12. RETROFITTING OF RCC BUILDINGS
LOCAL Techniques
Concrete Jacketing,
Steel Jacketing
Fibre-Reinforced polymer (FRP)
sheet wrapping.
GLOBAL Techniques
Addition of Infill Walls
Addition of Shear walls or wing
walls or Buttress Walls
Addition of Steel Braces
Addition of Frames
Reduction of Irregularities and
Mass
Energy Dissipation Devices & Base
Isolation

13. • To increase the lateral stiffness of a storey.
• Addition of infill walls in the ground storey is a viable option to retrofit
buildings.
• Due to the ‘strut action’ of the infilled walls, the flexural and shear forces and
the ductility demand on the ground storey columns are reduced.
ADDITION OF INFILL WALLS

14. • To increase lateral strength and stiffness of a building.
• Usually the shear walls are placed within bounding columns, whereas wing
walls are placed adjacent to columns.
• And, the buttress walls are placed on the exterior sides of an existing frame.
• For a buttress wall, the new foundation should be adequate to resist the
overturning moment or uplift pressure.
ADDITION OF SHEAR WALL OR
WING WALL OR BUTTRESS WALL

15. Addition of shear wall Addition of Buttress wall
Addition of wing wall

16. • It can be inserted in a frame to provide lateral stiffness, strength & ductility.
• The braces can be added at the exterior frames and for an open ground storey,
the braces can be placed in appropriate bays with least disruption of the
building use.
• Since, the braces are connected to the frames at the beam-column joints, the
forces resisted by the braces are transferred to the joints in the form of axial
forces
ADDITION OF STEEL BRACES

17. Addition of steel braces

18. • Addition of infill walls, shear walls or braces can alleviate the deficiency of soft
or weak storeys.
• Discontinuous components such as floating columns can be extended up to the
foundation.
• Although partial demolition can have impact on the appearance of the
building, it can be an effective measure to reduce irregularity.
• The mass can be reduced through demolition of unaccounted additional
storeys, replacement of heavy cladding or removal of heavy storage.
REDUCTION OF IRREGULARITIES
AND MASS

19. • Base Isolation
• A base isolation system decouples the superstructure from the seismic ground
motions. The objective is to prevent the superstructure of the building from
absorbing the earthquake energy.
• The principle is to introduce flexibility at the base of a structure in the
horizontal plane, while at the same time introducing damping elements to
restrict the amplitude of the motion caused by the earthquake.
• The role of a energy dissipation device is to increase the absorption of seismic
energy in the structure.
• Friction dampers
• Metallic dampers
• Viscoelastic Dampers
• Viscous Dampers
BASE ISOLATION AND ENERGY DISSIPATION DEVICES

20. ADDITION OF INFILL
WALLS
• Merits
• Increases lateral
stiffness of a storey
• Can support vertical
load if adjacent
column fails
• Demerits
• May have
premature
• Does not increase
ductility
• Increases weight
ADDITION OF SHEAR,
WING WALLS OR
BUTTRESS WALL
• Merits
• Increases lateral
strength and
stiffness
• May increase
ductility
• Demerits
• May increase design
base shear
• Stresses
concentrated near
the walls
• Need adequate
foundation
ADDITION OF BRACES
• Merits
• Increases lateral
strength and
stiffness
• May increase
ductility
• Demerits
• Connection of
braces to an existing
frame can be
difficult
ADDITION OF FRAMES
• Merits
• Increases lateral
strength and
stiffness
• May increase
ductility
• Demerits
• Needs adequate
foundations
Comparison Of Global Strategies

21. Pall Friction Dampers
• Proposed by Pall and Marsh (1982).
• It can be located at the intersection
of cross bracings in frames.
• When loaded, the tension brace
induces slippage. Consequently, the
four links force the compression
brace to slip.
• Energy is dissipated in both braces
and prevent slippage

22. Metallic Dampers
• Proposed by Tyler (1995), and
fabricated from round steel bars.
• Energy is dissipated by inelastic
deformation of the rectangular steel
frame in the diagonal direction of the
tension brace.
• These dampers are stable, long-term
reliable, and good resistance to
thermal conditions.
• These dampers have been used in
New Zealand & Italy.

23. Visco-elastic Dampers (VED)
• Proposed by Aiken and Kelly (1990).
• It has been used in structures where
the damper undergoes shear
deformations.
• A typical VED consists of viscoelastic
layers bonded to steel plates.
• When mounted to a structure, shear
deformations and consequently energy
dissipations take place when relative
motions occurs.

24. Fluid Viscous Dampers
• Proposed by Constantinou and Symons
(1992).
• These dampers possess linear viscous
behavior and are relatively insensitive to
temperature changes.
• It is filled with silicone oil, consists of a
steel piston and an accumulator.
• The force in the damper is generated by a
pressure difference across the piston head.
The reduction in volume causes a
restoring force, which is prevented by the
accumulator.

25. Tuned Mass Dampers (TMD)
• It consists of a mass, which moves relative to
the structures and is attached to it by a
spring.
• It reduces the vibration of a system with a
comparatively lightweight component so
that the worst-case vibrations are less
intense.
• When the structure vibrates, it excites the
TMD and the kinetic energy is transferred
from the structures to the TMD and is
absorbed by its damping component.

26.  ATC Tower Delhi Airport (New Delhi) — a 50-ton tuned mass damper installed just
beneath the ATC floor at 90m.
 Statue of Unity (Gujarat) - a 400-ton tuned mass damper located at the chest level of Sardar
Patel statue.
 Taipei 101 skyscraper — Contains the world's largest and heaviest tuned mass dampers, at
660 metric tons

27. • It involves addition of a layer of
concrete, longitudinal bars and
closely spaced ties. The jacket
increases both the flexural strength
and shear strength of the column.
• To increase the flexural strength, the
additional longitudinal bars need to
be anchored to the foundation.
• If the jacket is only partially around
the existing column, the new bars can
be welded to the existing bars.
• It involves drilling holes in the
existing beam. But drilling holes for
the stirrups at closing spacing
damages the beam.
CONCRETE JACKETING

28. Concrete jacketing of column Concrete jacketing of beam

29. • It refers to encasing the column
with steel plates and filling the
gap with non-shrink grout.
• If the shear capacity needs to be
enhanced, the jacket is provided
throughout the height of the
column. .
• Circular jackets are more
effective than rectangular
jackets.
• The plates are attached to the
tension face of a beam to
increase the flexural strength,
whereas they are attached to the
side face of a beam to increase
the shear strength.
STEEL JACKETING

30. Jacket with batten plates Jacket at top and bottom

31. • FRP has desirable physical
properties like high tensile
strength and corrosion
resistance.
• These are thin, light and
flexible.
• In retrofitting a column with
FRP sheets, there is increase in
ductility due to confinement
without noticeable increase in
the size.
• The FRP should be oriented
horizontally, perpendicular to
the axis of a column.
• The increase in thickness of
the wrapping improves the
strength and ductility.
FIBRE-REINFORCED POLYMER
SHEET WRAPPING

32. CONCRETE JACKETING
• Merits
• Increases flexural & shear
strengths and ductility
• Easy to analyse
• Good compatibility
• Demerits
• Size of member increases
• Anchoring of bars involves
drilling of holes in the
existing concrete
STEEL JACKETING
• Merits
• Increases shear strength
and ductility
• Minimal increase in size
• Demerits
• Needs protection against
corrosion and fire
• Use of bolts involves
drilling in the existing
concrete
FRP SHEETS WRAPPING
• Merits
• Increases shear strength
and ductility
• Minimal increase in size
• Rapid installation
• Demerits
• Needs protection against
fire
Comparison Of Local Strategies

33. CONCLUSION
• To determine the actual condition of the building.
• To identify the deficiencies of the building
• The compatibility of deformation should be ensured by proper detailing of the connections.
Importance of condition assessment
• When a building is severely deficient for the design seismic forces, it is preferred to select a
global retrofit strategy. If deficiencies still exist in the members, local retrofit strategies are
to be selected.
• To be selected after careful considerations of the cost and constructability.
• Any overstressed member has to be identified.
Selection of a retrofit strategy
• Retrofit aims at overcoming the deficiencies of an existing building.
• The quality of construction cannot be overemphasized. And, any sort of patch work will be a
wasted effort.
Quality of construction

34. APPENDIX
 Retrofitting overview
 Epoxy inject for crack repairing
 Fibre-reinforced polymer sheet wrapping
 Base Isolation
 Friction Damper
 Fluid Viscous Damper
 Tuned Mass Damper

35. Thank you…
Created By:
Mr. Yash Kumar