Rehabilitation and strengthening of existing structures

REHABILITATION AND STRENGTHENING
OF EXISTING STUCTURES
1
• INTRODUCTION
2
• REPAIR TECHNIQUES
3
• UNDERPINNING
4
• CAUSES OF DAMAGE EXISTING MASONARY
BUILDINGS

INTRODUCTION
 Repair: To bring back the position of the structure to its
previous condition so it gives performance same as
previously. It doesn’t cover the strength aspect of the
structures.
Some examples of repair…….
Decoration of structure,Painting,WhiteWashing
 Checking the wiring of building
 Replastering of any wall if required
 Repairing of damaged flooring
 Repair of door and window
 Checking or repairing of pipe line connections, gas line
connections and plumbing serveries.

INTRODUCTION
Rehabilitation : Rehabilitation of a building means
returning a building or a structure to a useful state by
means of repair, modification, or giving strength to
structure.
It is related to the strength aspect of structures.
 To Bring back the position and condition of the structure
by considering the strength aspect.
Some of the examples of Rehabilitation…
 To fill the wide cracks using some suitable material
 Injecting epoxy like material in to cracks in walls ,
columns , beams, etc.
 Removal of damaged portion of masonry and
reconstructing it using rich mortar mix.

INTRODUCTION
 Retrofitting:
It is the modification of existing
structures to make them more resistant to
seismic activity, ground motion, or soil
failure due to
earthquakes.

INTRODUCTION
When is Seismic Retrofitting Needed ?
The two circumstances are:-
Earthquake damaged buildings, and Earthquake-
vulnerable buildings(with no exposure to severe
earthquakes)
Some examples of retrofitting ………
 Increasing the lateral strength by reinforcement or by
increasing wall areas or the numbers of walls and
columns
 Giving unity to the structure by providing a proper
connection between resisting elements.
 Avoiding the possibility of brittle modes of failure by
proper reinforcement and connection of resisting
members.

REPAIR METHODOLOGY
 Evaluation
 Relating observation to causes
 Selecting methods and materials
 Preparation of drawings and specifications
 Selection of a contractor
 Execution of the work
 Quality Control

MATERIALS FOR CRACK REPAIR
The various materials used for repairs of
cracks are:
 Cement Slurry
 Cement Mortar
 Epoxy resin

CRACK REPAIR TECHNIQUES
 Epoxy-injection Grouting
 Routing and Sealing
 Providing additional Reinforcement
 Prestressing steel
 Grouting

 Epoxy-injection Grouting
Cracks as narrow as 0.002 in. (0.05 mm) can be
bonded by the injection of epoxy. The technique
generally consists of sealing the crack on exposed
surfaces, and injecting the epoxy under pressure.
Epoxy injection has been successfully used in
the repair of cracks in :
 Buildings
 Bridges
 Dams and other types of concrete structures.

The general procedure are given below:
Clean the cracks: The first step is to clean the cracks that
have been contaminated.
 Contaminants such as oil, grease, dirt, or fine particles of
concrete prevent epoxy
 Contamination should be removed by vacuuming or
flushing with water or other specially effective cleaning
solutions.
Seal the surfaces:
 Surface cracks should be sealed to keep the epoxy from
leaking out before it has gelled.
 A surface can be sealed by applying an epoxy, polyester,
or other appropriate sealing material to the surface of the
crack and allowing it to harden.

Inject the epoxy: Hydraulic pumps may be used for injection. The
pressure used for injection must be selected carefully. Increased
pressure often does little to accelerate the rate of injection. If the
crack is vertical or inclined, the injection process should begin by
pumping epoxy into the entry port at the lowest elevation until the
epoxy level reaches the entry port above.
For horizontal cracks, the injection should proceed from one end
of the crack to the other in the same manner. The crack is full if
the pressure can be maintained. If the pressure can not be
maintained, the epoxy is still flowing into unfilled portions or
leaking out of the crack.
Remove the surface seal: After the injected epoxy has cured, the
surface seal should be removed by using hammer.

REPAIR BY PROVIDING EXTRA REINFORCEMENT

GROUTING
Grouting is a process of injecting mixture of
cement, sand water at high pressure in the
cracks, joints, voids etc.
Purpose of grouting:
 To strengthen the porous Concrete
 To prevent the seepage in dam and water
retaining structures
 To fill the cracks in concrete structure

GROUTING
Procedure for grouting:
Drilling of Grouting holes
For drilling grouting holes, equipment's like jack hammer, diamond drill,
shot drill etc are used. The choice of type of drilling equipment depends
upon the type of stone, size of hole and depth of hole.
Arrangement of grout pipes
Grout pipes or packer of 4 to 5 cm dia and 45 to 90 cm length are
inserted in the grout holes. The space surrounding the pipe is filled with
cement mortar. The top end of the pipe is connected to the pump.
Cleaning of cracks
Before injecting grout mixture in the cracks, it is necessary to clean the
cracks.
Inserting grout in holes
Normally grout is inserted in the holes at a pressure 0.65kg/cm2 per m
depth hole.

GROUTING
Types of grouting:
1. Consolidation Grouting:
This type of grouting is used for shallow depth grouting holes.
Normally pressure below 3 kg/cm2 is known as low pressure
grouting.
2. Stage grouting:
When thick layers are to be grouted the total thickness of layer is
divided into stages of 1m each and grouting of each layer is
carried out one by one. Grouting of upper layer is started only
after the grout in the lower layer had properly set.
3. Curtain Grouting:
 This type of grouting is done to prevent the seepage of water
below foundation of dam.

PORTLAND CEMENT GROUTING
 This type of grouting is particularly used in dams and thick walls.
 This method is effective in preventing water leakage.
 First of all clean the cracks by air jetting or water jetting.
 Flushing the crack to clean it.
 Installing grout at suitable interval and seal the crack .
 Then grout the whole area.
 Grout mixtures may contain cement and water or cement plus
sand and water,depending upon the width of crack
 Water reducers or admixtures may be used to improve the
properties of the grout.
 For large volumes , a pump is used and for small volumes ,a
manual injection gun may be used for injection of grouting.
 After the crack is filled, the pressure should be maintained to
ensure proper penetration of grout.

UNDERPINNING
 DEF: In construction, underpinning is the process
of strengthening and stabilizing the
foundation of an existing building or other structure.
 Reasons for Underpinning
• The original foundation is simply not strong or
stable enough.
• The usage of the structure has changed.
• The properties of the soil supporting the
foundation may have changed (possibly through
subsidence) or were mischaracterized during
design.

PROCESS OF UNDERPINNING
 Underpinning is accomplished by extending
the foundation in depth or in breadth so it
either rests on a more supportive soil stratum
or distributes its load across a greater area.
 All of these processes are generally
expensive and elaborate.

TYPES OF UNDERPINNING
• Mass Concrete Underpinning
• Mini-piled underpinning

MASS CONCRETE UNDERPINNING
• Also known as 'traditional underpinning, 'This
underpinning method strengthens an existing
structure's foundation by digging boxes by hand
underneath and sequentially pouring concrete in a
strategic order. The final result is basically a
foundation built underneath the existing foundation.
This underpinning method is generally applied when
the existing foundation is at a shallow depth,
however, the method still works very well even at fifty
feet deep. The method has not changed since its
inception with its use of utilitarian tools such as
shovels and post hole diggers. Heavy machinery is
not called for in this method due to the tight nature
of the boxes being dug.

MINI-PILED UNDERPINNING
 Mini-piles have the greatest value where
ground conditions are very variable,where
access is restrictive.
 Mini-piled underpinning is generally used
when the loads from the foundations need to
be transferred to stable soils at considerable
depths - usually in excess of 5.0 meters.

CAUSES OF DAMAGE OF MASONRY
BUILDINGS
 Heavy Weight and very stiff buildings, attracting large
seismic forces.
 Very low tensile strength particularly with poor mortars
 Low shear strength
 Brittle behavior in tension as well as in compression
 Weak connection between wall and wall
 Weak connection between roof and wall
 Stress connection at corners of doors and windows
 Overall unsymmetry in plan and elevation of buildings

Rehabilitation and strengthening of existing structures

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