2. DEMOLITION OF BUILDINGS
Necessity of demolition
Old building for further period can not be put
in use
Structural changes required
Modernization – old building to new building
Development of city – expansion of buildings
Structural failure – repair work not possible
Expansion or extension of buildings
3. Safety aspects
Number of accidents in building industry
to men at site is extremely high
Reduce the number of accidents
Better supervision and organization
( Safety rules, guide, insurance etc..)
4. General precautions during
demolition
Supervision aspects:
Many men in demolition work are not
conversant with structural stability
Guidance in this regard should be
continuous
Supervision should be entrusted to
experienced person
Supervisor has to examine the plan and to
make his own survey
5. Contd..
First service connections are to be
disconnected by appropriate authority or
under their direction
All windows and doors boarded up to use
Internal entrances to lift shafts should be
barricaded
Artificial lighting and ventilation provided
Safety helmets, belts, gloves etc..- provided
9. Contd..
Approaches of flooring should be barricaded
Balconies and cantilevers cut down first
Stone or concrete staircase used once they
have been disturbed
Staircase should be kept free from debris
Timbers removed to be stacked carefully
Glass windows should be removed first
On completion of day work – stable condition
Adequate hoisting facilities to be provided to
remove trusses, girders or beams
10. Sequence of demolition
Disconnect the services and made safe over
the whole site to be demolished
( EB, Water,Gas, Telephone , Television)
Demolition proceeds in the reverse order of
construction
Strip out roof coverings, fittings, pipe work and
all non structural parts
Roof trusses and timbers should be lifted down
All rubble and debris should be lowered to
ground and cleared to avoid build up
11. Demolition process of roof truss
o Dismantling the trusses in reverse order – erection
o No indiscriminate cutting should be allowed
o The structure should be braced or shored
o Roof claddings should be removed and lowered to
the ground
o The truss supported by a crane or rope
o For truss with large span brace the tie with heavy
timber or girder splinted along the components
o The truss is lowered to the ground & dismantled
21. Catch platform
Provided with sufficient strength while
demolishing exterior walls of multistory
buildings.
Injury may not be workers below
Debris should not be dumped at the
catch plat form
25. Lowering, removal and disposal of
materials
Debris should not be dropped
Lowered either by container rope and tackle
or chute
Chute provided >45˚ to horizontal should be
closed on all four sides except for open
Top of chute protected with guard rail
Debris removed at the earliest – space
provided
26. Methods of demolition
1. Demolition by hand
2. Pulling down by wire rope
3. Mechanical demolition
a) Demolition ball
b) Pusher arm machinery
4. Deliberate collapse
5. Explosives
6. Other methods
27. 1. Demolition by hand
Adopted for the highest and most inaccessible
section of the work
Prior to breakdown by machinery for complete
buildings
Tools like chisel, hammer, crow bar, pneumatic
drills, hand saw, power saw
30. 2. Pulling down by wire rope
For masonry and brick structures
All timbers, pipes, beams and lintels to be
removed by this way
Unsuitable for long members
A wire band is set around a portion of brick
work
Dragged by tracked vehicles
Cut into the BW, causing it to collapse
32. 3. Mechanical demolition
(a) Demolition ball
Used for large brick work structures –RC
buildings, mass concrete, RC slabs etc.
A ball weighs half a ton ( 500Kg) is dropped
vertically on to the structures or sides
By swinging ball – crane
Requires high standard supervision
35. (b) Pusher arm machinery
Use – extended arm and steel pad
Fitted to track vehicle in place of
excavator bucket
Machine is more controllable
Pusher arm is placed on top of section
Forward motion is applied
Hydraulic thrust mechanism used
38. 4. Deliberate collapse
Removal of certain key structural members
will cause collapse of the whole or part of
structures
Hazards operation - needs specialization
39. 5. Explosives
Most economic and quicker method
Holes are bored into various supported
sections
Explosive inserted
Charges are exploded – structures
Collapse
Breaking up on impact
42. 6. Other methods
Various machines and types of drills and
mechanical breakers
More than one or two techniques
Foundations of the buildings are broken
by using manual pneumatic breakers or
tractor mounted weight dropping breaker
45. Maintenance:
Work done to keep the Civil Engg. Structures
and Work in a condition
Enable to carry out the function for which
they are constructed
Necessity:
Prevention of damages and decay due to natural
agencies & wear / tear
Repair of the defects occurred and strengthening
46. CLASSIFICATIONS
PREVENTIVE MAINTENANCE
•Work done before defects occurred
•Damage developed stage
•Include inspection, planning & execution
REMEDIAL MAINTENANCE
• After the defects or damage occurs
• It involves finding, causes, evaluation, need and
selection of methods and implementation
ROUTINE MAINTENANCE
• Regular service / periodical maintenance
• SPECIAL MAINTENANCE: to rectify the heavy
damages, but not included in routine programme
49. Contd..
Defect of patch in plaster due to insufficient
adhesion between the plaster and base
50. Procedure
Cut the patch to a regular shape
Remove all the loose particles
Saturate the surface fully with water
When free water appears, apply mortar –
sufficiently higher than adj. structure
After 10 to 15 min – brought in level to the
adjacent surface
Thickness more – two layer
Proper curing and finishing colour
52. Procedure
Installation of dead shore above the floor
Check the suitability of opening lying floor
Holes provided for the needle beam are made
in wall – fix height
Holes are cut at a spacing of 1m to 1.5
Needle beam inserted and supported by
vertical props- braced
Make opening for doors and windows – width
20cm to 40cm strips – required open
Open provision include jambs and finish
55. Contd..
Insert precast RC lintel, props to be provided at
bottom till jambs get necessary strength
After completion of work the shores should be
removed atleast after 7 days
Loose the dead shore two days in advance
After two days needles and vertical props are
removed
56. Renewing glass panes with wooden
fillets or putty or glazing beads
windows consists of two parts
One frame fitted in the wall opening
Shutters fixed by hinges to the frame
Shutter frames contain sashes (glass inserting
frame with groove) and glass panes
The process of fixing glass with sash bars is
called
glazing
Rebates of 6mm depth on one side of sash bars to
support glass panes
57. Contd..
Glass panes are placed and in position by
means of putty, glazing beads or strips of
woods
Sash bars with glass panes are fixed on
shutters
59. Procedure
In RCC slab main reinforcement are provided in
shorter direction
In exsist. Slab mark the position of fan hook on
the slab
Chip the bottom concrete for above 300mm in
long span and 100mm in shorter span - depth :
50mm
Minimum of two rods are essential to hold the fan
hook: U type, S type ( >10mmdia - 1)
Fan hook placed and rich concrete using 10mm
chips- packed – finished - surface
60. Repair to Terrazo flooring
(Mosaic)
TYPES
Terrazo flooring laid in situ
Terrazo tile flooring
Terrazo flooring laid in situ rest on concrete base if
any repair cement slurry used on edges
Terrazo tile flooring
○ Dismantle the damage base
○ Clean the damaged surface
○ Without any damage piece reuse
○ Cement mortar strength – base – after clean
○ New tiles fixed usign mallet – leveled – curing – 7
days
61. General defects and remedies
in Mosaic flooring
Dusting on flooring :
Clean by acid wash
Polishing by machine and apply wax
Cracks:
Clean the opened joints or cracks
Fill with white cement mixed with coloring agent
Polish the total area and wax over it
Pot holes:
Chip the holes – place the mosaic chips - allow to dry – 3 days
Polish and finish by machine – wax
Structural Defects; cracks originating from the base – study the
cause – rectify the base crack first – repair the mosaic flooring
63. CRACKS:
Cracks are quite common in buildings
Cracks are developed in building component when the
stress exceeds the permissible value.
Stress could be caused by externally applied forces
(dead, live, wind, seismic load or foundation movement)
Other stress: Thermal changes, Moisture content,
chemical action.etc
66. Structural Cracks:
Due to incorrect design, faulty construction or overloading
Endanger the safety of a building
Example: Extensive cracks in RCC beam
67. Non-structural Cracks:
Due to internally induced stresses in building materials
and these do not directly result in structural weakening.
Do not endanger the safety of a building
Look unsightly or create an impression of faulty work or a
feeling of instability.
Ex: Vertical cracks in long compound wall due to thermal
expansion
69. Other Cracks
Hair cracks:
Fine random cracks in the surface of structures are
called hair cracks
Usually hair cracks are less than 1mm width and seen
mainly on top surface
Shrinkage cracks:
Shrinkage cracks occur when concrete members
undergo restrained volume changes, it results
volumetric drying or thermal effects .
Plastic shrinkage cracks are immediately visible on
fresh concrete surface.
70. Factors influencing cracks
• Differential settlement of soil
• Shrinkable clays or expansive soils
• New construction bonded with old construction
• Filled up earth
• Vegetation
• Thermal expansion
• Differential strain
• Drying shrinkage and thermal contraction
71. Differential settlement of soil
Shear cracks in buildings due to large differential
settlement of foundation
Unequal bearing pressure under different parts of
structure
Bearing pressure on soil exceed SBC of soil
Low factor of safety in the design of foundation
72.
73.
74. Shrinkable clays or expansive soils
Clay swell on absorbing moisture and shrink on
dry
Building cracks due to change in moisture
Shrinkable clay also called as expansive soil
76. New construction bonded with old construction
Newly constructed portion undergoes settlement
Unsightly cracks occur at junction of new and old
construction
77. Filled up earth
Building constructed in site with low and deep filling under
the floors in plinth level
If the filling is not well compacted, due to moisture entry
the soil may cause settlement and cause cracks in floor
78. Vegetation
Fast growing trees very near to compound wall, cause
cracks in walls due to expansive action of roots under
the foundation
Plants take root grow in fissures of walls because of
seeds from bird dropping cause severe cracking of wall
81. Thermal Expansion
Cracks start from DPC level and travel upward and
pass straightly through masonry
Make adequate provision for expansion joints
82.
83. Differential Strain
Vertical cracks below openings in line with
windows jambs
Due to shear caused by differential strain below
the opening
Crack at junction of masonry wall and RCC
columns
86. Drying shrinkage and thermal contraction
Horizontal cracks in window lintel or sill level
due to pull exerted on the wall by the slab
because of drying shrinkage and thermal
contraction
87. Chemical Reaction
Chemical reaction increase in volume of materials
and internal stresses are setup which may result in
outward thrust and formation of cracks.
The material gets weakened
Due to sulphate attack, carbonation in cement,
corrosion of reinforcement and alkali aggregate
reaction
91. General precautions to prevent
cracks in buildings
Bricks should be well burnt, don’t use very strong mortar
(cement content) and do plastering after curing and
drying
Bricks after taken from kilns to be exposed for at least 2 –
3 weeks
Season the timber
Mortar for parapet 1:1:6 (cement: lime : sand) and use
good bond
Plastering should be deferred( late plaster in after BW) as
much possible and made discontinuous at job by
providing V - groves
92.
93.
94.
95. General precautions to prevent
cracks in buildings
Adequate expansion joint must be provided for all types
of buildings
Provide slip joint or expansion joint between old and
new buildings
Mortar joints in brick masonry should be raked to 10mm
depth
96. General precautions to prevent
cracks in buildings
Cover to reinforcement as per IS456-2000
Provide water proof apron all round the
building on shrinkage able clay
Filling soil should be good and done in layers
of 25mm thick then each layer watered and
well rammed
Do not grow trees too close to buildings
97. Common cracks in buildings
• Horizontal cracks
• Vertical cracks
• Diagonal cracks
• Transverse cracks
98. Horizontal cracks in masonry
and plaster
In load bearing wall structure, roof slab under
goes alternate expansion and contraction due to
heat and cooling, shear crack occurs in cross
walls
To prevent this cracks , provide insulation/ cover
on top or slip joint at support
102. Horizontal Cracks in in a wall at
supports due to excessive deflection of
a slab of large span
When a slab or beam ( large span) undergoes
deflection, when the load on supporting wall is small,
horizontal crack appears in the supporting wall.
103. Horizontal Cracks in a wall at supports
due to excessive deflection of a slab of
large span
To prevent this type of cracks, increase the depth of slab
or beam or adopt bearing arrangements at support and
provide groove in plaster at the junction of wall and
ceiling
104. Horizontal Cracks in brick panels of a
framed structure
When panel walls are tightly built in framed structure,
cracks formed due to shortening of columns on elastic
shortening , creep and shrinkage or due to deflection of
upper beams
To prevent, construct the panel wall as late as possible
The walls should not be constructed tightly between the
RCC frame.
Joint may be left at the soffit of beam and top of wall
108. Vertical Cracks at the bearing
of RCC beams or pillars
When RCC column is introduced in load
bearing structure for heavier loads.
If undergoes elastic shortening due to
elastic deformation and creep, resulting
vertical cracks at junction
109. Vertical Cracks at the bearing
of RCC beams or pillars
To prevent, RC column may be
adequately cured or having an air gap
between masonry and column.
Provide a groove in plaster at the
junction
110. Vertical Cracks at window
openings in multi storeys
If the building has large opening in
external wall – sill level of window
subject to less loads cause differential
stress
111. Vertical Cracks at window
openings in multi storeys
To prevent, select size and location of
openings as to avoid unequal loading
condition
112. Vertical Cracks in BW panel in Framed
structure – due to expansion of brick
When the panel walls are tightly built in
the framed structure, vertical cracks
formed
If the length of panel is more
Wall between column get compressed
due to moisture movement, elastic
deformation
113. Vertical Cracks in BW panel in Framed
structure – due to expansion of brick
To prevent, construct the panel wall as late as
possible
Movement joint between top of wall and
bottom of beam filled with compressible
jointing material
115. Diagonal Cracks in Masonry (LB)
• Occur in load bearing structure
• Brick walls, RCC roof and Floor
• From Fig Wall A carries more load
compare to wall B
• Result shear stress in cross walls
cause diagonal cracks
• To prevent – design to ensure stress in
various walls of load is uniform
116. Diagonal Cracks in Brick Masonry
wall over lintel beam
• These cracks are due to drying
shrinkage of in-situ concrete lintel
• To prevent, use low shrinkage and slump
concrete for lintels
• Use precast lintel
118. Contd..
In continuous members like long RCC
sunshade, open verandah slab, RCC railing
exposed to sun
Subjected to alternate expansion and
contraction
Structures are not allowed for free
movement result in formation of transverse
cracks at regular intervals
119. Contd..
• Endanger the stability of the structure
• Prevention:
• Break the continuity
• Provide expansion joint
• Joints provide regular intervals
• 8to12 interval for sunshades
• 6to 9m for RCC railings
• 12 to 14m for verandah slab
• Joints sealed with water bar
• sealing compound
120. Repairs
• Repair of concrete structures – vary from Cosmetic
treatment to Total replacement
• Proper investigation and by equipments, tools and
materials
• Method depends cause and extent of damage,
importance of element and its location
Stages
1. Removal of damaged concrete
2. Pretreatment of surface and treatment
3. Application of repair material
4. Restoring the integrity of individual sections and
strengthening of structure
121. Classification of crack for repair purpose
• Cracks may be - Dormant crack, Active crack and
Growing crack
• Dormant crack – caused in the past (drying shrinkage),
do not recur, remain constant repaired by filling with a
rigid material
• Active crack – not constant in width, open and close as
the structure is loaded or due to thermal and hydral
changes in the concrete
• Growing crack – increase in width due to foundation
settlement or reinforcement corrosion
123. Materials used for filling cracks
1. Epoxy primer and epoxy moldable putty – for fine or
medium crack, hairline to 15mm wide
2. Structural epoxy pouring resin – for over 15mm wide
cracks
3. Thixotropic epoxy injection resin and epoxy glass rod –
for brick work stitching
4. Fillet seal powder or Bond acryl - for floor to wall joint
filling
5. Premixed cement mortar or concrete
6. Polymer modified mortars and concrete
