Demolition methods and its sequence

S.RANJITH KUMAR
GRDUATE,CONSTRUCTION
ENGINEERING MANAGEMENT,
MEENAKSHI SUNDARARAJAN
ENGINEERING COLLEGE.
DEMOLITION

UNIT V DEMOLITION
Demolition Techniques, Demolition by
Machines, Demolition by Explosives,
Advanced techniques using Robotic
Machines, Demolition Sequence,
Dismantling Techniques, Safety
precaution in Demolition and
Dismantling.

WHAT IS DEMOLITION?????
 Demolition means dismantling, razing,
destroying or wrecking any building or
structure or any part by pre-planned and
controlled methods.
 Demolition is the tearing-down of buildings and
other structures

WHY DEMOLITION????
 The structures which have already passed
their design life need to be reconstructed,
for safety and operational requirements.
 The old structures need to be demolished
for replacement by new structures.
 Small structures can be demolished by
manual methods but machinery and
advanced techniques are required for
demolition of bigger structures.
 Advanced techniques are also required
for faster demolition and demolition in
confined areas.

DEMOLITION SEQUENCE
Demolition sequence shall be determined based on
Actual site conditions, Restraints, The building layout,
The Structural layout and its construction.
In general, the following sequence shall apply:
1)UTILITIES disconnection.Electricity,plumbing water
lines,drainage conections etc..
2)All cantilevered structures, canopies, verandahs
and features attached to the external walls shall first
be demolished prior to demolition of main building
and its internal structures on each floor
3)When demolishing the roof structure, all lift machine
rooms and watertanks at high level shall be
demolished in “top down” sequence to the main
roof level

DEMOLITION SEQUENCE
3)Demolition of the floor slabs shall begin at mid span and
work towards the supporting beams.

4) Floor beams shall be demolished in the order of
cantilevered beams, secondary beams and then
main beams.
5) Non-load bearing walls shall be removed prior to
demolition of load bearing walls.

Columns and load bearing walls shall be
demolished after removal of beams on top.

If site conditions permit, the first floor slab
directly above the ground floor may be
demolished by machine standing on ground.

DEMOLITION METHODS
Demolition methods can vary depending on the
following
 The area where it will be held on
 Time available
 The building material
 The purpose of the demolition and
 The way that debris is going to be disposed.
Time saving methods are more expensive
than the slower ones.
If noise, dust, and vibrations are to be
restricted, it will add to the cost of demolition.

MANUAL METHOD
Manual methods are carried out top down,
proceeding, in general, from the roof to ground.
The sequence of demolition may vary, depending
on
1. site conditions and
2. structural elements to be demolished.

 For reinforced concrete buildings, jack
hammers are commonly used to break
down the concrete.
 Oxy-acetylene torch could be used to
cut the reinforcements.
 The reinforcements shall remain until all
the concrete connecting to or supported
by the reinforcement is broken away or
when its support is no longer required.
 In congested areas, these features could
have critical impact on the safety of the

 Demolition of these features shall
be performed with extreme
caution.
 If rope or tie wires are used to pull
down the structural elements, the
pulling wire must be at least 4
times stronger than the anticipated
pulling force.
 In addition, workers shall be
shielded from the rope or tie wires.
The rope or tie wire shall be

DEMOLITION BY MACHINES
 The sequence of demolition
by machine is typically the
same as the top down
manual method, except that
most of the demolition is done
by mechanical plant.
 The demolition begins with
the lifting of the mechanical
plant on to the building top
floor.
 When rope or tie wire is used
for pulling, the workers shall
be protected or stay away

 Adequate propping shall be installed at
floor levels below the working floor to safely
support the operation of the mechanical
plant.
 The movement of the mechanical plant
shall only be within the propped area. The
propped areas shall be suitably marked.
 The movement of the mechanical plant
shall be prohibited within 2 m of the
building edge, within 1 m of any floor
openings or any cantilevered structures.

 The mechanical plant shall be lifted onto
the roof of the building by the use of
mobile crane or other appropriate means
as approved.
 The machine shall descend down to the
next floor by means of a ramp. The ramp
may be a temporary structure or other
appropriate design.
 The slope of the ramp shall be no steeper
that 1.75 to 1 or as recommended by the
machine manufacturer.
 As an alternative, the machine may also be

DEMOLITION BY HYDRAULIC
RUSHERS
 The crusher attachment breaks the
concrete and the reinforcement by the
hydraulic thrust through the long boom arm
system.
 The hydraulic crusher can be operated from
the ground outside the building. This
method is also suitable for dangerous
buildings, silos and other industrial facilities.
 The operation shall have a minimum clear
space of ½ the building height as a safety
zone for the falling debris.
 The excavator shall operate on firm ground
that can support the machine during the
crusher operation.
 Each section of the structure shall be

 Hydraulic
shears
 Pulverizers
 Grapple

DEMOLITION BY WRECKING
BALL
 The wrecking ball application
consists of a crane equipped
with a steel ball.
 The destruction of the building is
by the impact energy of the steel
ball suspended from the crawler
crane. The wrecking ball
operates outside the building.
 This method is suitable for
dilapidated buildings, silos and
other industrial facilities.
 However, the operation requires
substantial clear space. The
application also demands high
level skill operators and well-

 The balling of each section of the
structure shall proceed from top to
bottom.
 Recommended techniques for the
wrecking ball operations include (1)
Vertical Drop -free falling of the wrecking
ball onto the structure and (2) Swing in
line - swinging of the ball in-line with the
jib.
 A second dragline will normally connect
to the ball horizontally to control the ball
motion.

 The jib or boom shall be operated with no less than 3
m above the portion of the structure being demolished.
 Clear space for operation between the crane and the
structure being demolished shall be ½ of the height of
structure, with additional distance between crane and
boundary wall for maneuverability.
 High strength wire shall be used to allow pullout of
the wrecking ball from potential traps.
 To minimize the dust impact on the surrounding
area, the structure to be demolished shall be pre-
soaked with water before demolition. Water spraying
shall continue on the structure during demolition.
 The operation shall not be performed adjacent to
overhead power lines. The site shall be entirely
fenced off to forbid public access.

IMPLOSION
 Implosion is the strategic
placing of explosive
material and timing of its
detonation so that a structure
collapses on itself in a matter
of seconds, minimizing the
physical damage to its
immediate surroundings.
 The technique weakens or
removes critical supports so
that the building can no longer
withstand the force of gravity
and falls under its own

 The explosives are just the trigger for
the demolition. It's gravity that brings the
building down.
 Explosives are loaded and progressively
detonated on several different levels of
the building so that the building structure
falls down on itself at multiple points.
 When everything is planned and executed
correctly, the total damage of the
explosives and falling building material is
sufficient to collapse the structure entirely,
so cleanup crews are left with only a pile

 In order to demolish a building safely, each
element of the implosion must be studied
ahead of time. This is done by a blasting
expert.
 The first step is to examine architectural
blueprints of the building to determine how
the building is put together.
 Next, the building is surveyed to study about
the support structure on each floor.
 Based on this data and drawing from past
experiences with similar buildings, the expert
decides what explosives to use, where to
position them in the building and how to time

 The main challenge in bringing a building down is
controlling which way it falls. Ideally, a blasting
crew will be able to tumble the building over on
one side, into a parking lot or other open area.
This sort of blast is the easiest to execute, and it
is generally the safest way to go.
 Tipping a building over is something like felling a
tree.
 To topple the building to the north, the blasters
detonate explosives on the north side of the
building first, in the same way a tree would be
chopped into from the north side if it is to fall in
that direction. Blasters may also secure steel
cables to support columns in the building, so that

 Sometimes, a building is surrounded by structures that
must be preserved. In this case, the blasters proceed
with a true implosion, demolishing the building so that it
collapses straight down into its own footprint (the total
area at the base of the building).
 The basic idea in implosion is to think of the building as
a collection of separate towers.
 The blasters set the explosives so that each "tower"
falls toward the centre of the building.
 When they are detonated in the right order, the toppling
towers crash against each other and all of the rubble
collects at the centre of the building.
 Another option is to detonate the columns at the centre
of the building before the other columns so that the
building's sides fall inward.

 Generally speaking, blasters will explode
the major support columns on the lower
floors first and then a few upper stories.
 In a 20-story building, for example, the
blasters might blow the columns on the first
and second floor, as well as the 12th and
15th floors.
 In most cases, blowing the support
structures on the lower floors is sufficient for
collapsing the building, but loading columns
on upper floors helps break the building
material into smaller pieces as it falls. This
makes for easier cleanup following the blast.

Columns are fully loaded with
explosives

Blasting machines
 Traditional
rack-bar
and
 Modern
electronic
control box

The Scudder Homes in Newark,
N.J., blasted in 1996

ADVANCED TECHNIQUES USING
ROBOTIC MACHINES
 There is a different, specialized approach
to every demolition project.
 Identifying the project’s unique
requirements and selecting the right
machine to ensure the work is done is a
safe and efficient manner.
 Robotic machines meet these unique
challenges.
 We have large high reach equipment that
has the capability to reach some very high
and awkward areas.
 Smaller Robotic demolisher machines to
get into those tight spots and if a project
has some tricky or confined spaces we
have robotic equipment on hand to get the

ADVANCED TECHNIQUES USING
ROBOTIC MACHINES

SAFETY PRECAUTIONS
 Demolition
 Dismantling
.

•HOARDING isolates the demolition
site from the public, thus preventing
unauthorized access and
trespassing.

 WALKWAYS:
Walkways shall be provided for the use of
the workmen who shall be instructed to use them
and all such walkways shall be kept adequately
lighted, free from debris and other materials.
 CATCH PLATFORMS
In demolition of exterior wall of multi-
storeyed structure, catch platform of heavy
planking shall be provided to prevent injuries to
the worker working below and to the public,
when the external walls are more than20 m in
height.

The covered walkway, in conjunction with catch
platform, provides additional protection to the
pedestrian traffic against falling debris.

PROTECTIVE
SCREENS
 Protective screen covers shall be placed, where
necessary, to prevent flying pieces from injuring the
fellow workmen.
 Bamboo scaffolds or metal scaffolds shall be used for
providing protective screens to completely enclose the
building structure for retaining dust and small debris.
 Tarpaulin and heavy duty nets shall be used to cover
the exterior face of the scaffold.
 The protective screens shall be secured to the
scaffoldings at intervals in both horizontal and vertical

TEMPORARY SUPPORTS
 Temporary supports are required to cater for the
loads due the machinery used in demolition, debris
accumulated, impact from fallen debris and lateral
loads due to the fallen debris and wind force etc.
 A suitable factor of safety shall be considered.
 They are also provided when any part of the
structure or any element being demolished is not
self-supporting (or)
 when the temporary stability of the structure or its
elements could be impaired as a result of the
demolition activities.

‘
TRAINING AND COMMUNICATION
 Demolition workers, including plant or
equipment operators, shall go through
proper job safety training and be
informed of the potential hazards by
attending training sessions as well as
on-the-job training.
 They shall be trained regarding-
 working at heights, working in
confined spaces, working with lifting
appliances, use of personal protective
equipment, handling of chemicals,
health hazards in demolition works
and safe operating zones.
 The safety concept can be

EQUIPMENT MAINTENANCE
 All equipment shall be
tested and examined before
use.
 They shall be properly
stored and maintained.
 The equipment shall be
inspected daily and results
of the inspection shall be
recorded accordingly.
 A detailed safety instruction
shall be provided to cater
for specific situations of the
project, if necessary.

ELECTRICAL SAFETY
 A properly connected
power source from a
local electric utility
supplier or a mobile
electricity generator
shall be utilised in
demolition sites.
 The safety
requirements given in
the Electricity
Regulations shall be

 All flammable goods shall be
removed from site unless they are
necessary for the works involved.
Any remaining flammable goods
shall be stored in proper storage
facilities.
 All furniture, timber, doors, etc. shall
be removed before any welding
work is performed. Fire fighting
appliances shall be provided and
maintained in working conditions.
Emergency access to site shall be
provided.
FIRE SAFETY

Vibration
 Demolition work will cause vibration to neighbouring
buildings or structures to various extent, depending
on the method of demolition, which should be
controlled by suitable monitoring. The most serious
vibration is caused by implosion.
Air Pollution
 Concrete breaking, handling of debris and hauling
process are main sources of dust from building
demolition. Dust mitigation measures, such as water
spray, shall be adopted to minimise dust emissions.
Burning of waste shall not be allowed.
 Diesel fumes generated by mechanical plant or
equipment shall be controlled.

NOISE
 Noise pollution arising from the demolition
works due the use of powered mechanical
equipment such as pneumatic breakers,
excavators and generators, loading and
transportation of debris, etc. affects the
workers, and the sensitive receivers in the
vicinity of the demolition site.
 Silent type equipment shall be used to reduce
noise impact as much as practicable.
Demolition activity shall not be performed
within the restricted hours established.

CHUTES
 Debris, waste and other materials shall not be
thrown, tipped or shot down from a height where
they are liable to cause injury to any person on or
near the site.
 Existing lift shaft, light well and openings on floor
may be used to convey debris down the building
floors.
 Areas adjacent to the openings of these features
used as a chute shall be barricaded when they
are not in use. Warning signs shall be posted to
prevent workers from entering the area.
 As an option, plastic chutes may be used inside
the floor openings and lift wells to minimise noise
and confine the falling debris.

DISMANTELING
 “Dismantle" means to take apart
something and can easily be use/built
again.
 Dismantle is usually used when you take
something apart in different pieces and
 Demolish is to damage something
beyond repair or reconstruction.They
overlap in that you are breaking
something into pieces but demolish is
mainly used when you destroy

 Example:
 Doors
 Windows
 Grills
 P.V.C pipes
 Bath fittings
 Electrical cables/wires

Demolition methods and its sequence

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Demolition methods and its sequence