ABSTRACT
Demolition of a building means tearing down or falling down of a building with
the help of equipments or explosives. This seminar report deals with how a
demolition work is to be performed safely and also elaborates
different steps involved before and during the execution of a demolition
process. The various steps involved before the demolition process includes
surveying, removal of hazardous materials, preparation of demolition plan,
stability report and the precautionary safety measures to be taken. The main
equipments used for these demolition activities are sledge hammer, excavators,
bulldozers, wrecking balls etc. and main explosives used are dynamites and RDX.
When explosive are used for the demolition, it is known as Implosion.
CONTENTS
ACKNOWLEDGEMENT
ABSTRACT
1. INTRODUCTION
1. INTRODUCTION
2. DEMOLITION
3. STEPS
BEFORE
DEMOLITION
3.1
Surveying
3.2 Removal of hazardous
materials
3.3 Preparation of
plan
3.4 Stability
report
3.5 Safety
measures
4. METHODS
OF
DEMOLITION
4.1 Non-explosive
demolition
4.2 Explosive
demolition
5. CONCLUSION
6. REFERENCES
LIST OF FIGURES
Fig 1. Sledge
hammer
Fig 2.
Excavator
Fig 3.
Bulldozer
Fig 4. Crane with wrecking
ball
Fig 5. High reach
excavators
Fig 6. Demolition of a chimney
in Germany
1. INTRODUCTION
We know every structure is designed for a life period. The existence of the
structure after the service life period is very dangerous to its occupants and
surrounding buildings .The building act usually contains provisions that enable
local authorities to control demolition works for the protection of public
safety and to ensure adjoining premises and the site are made good on
completion of the demolition. A notice of conditions is issued that require
certain works to be undertaken to achieve these aims. Where demolition of a
building takes place, the owner must inform the council. Greenhouses,
conservatories, prefabricated garages and sheds do not require permission to be
demolished. Usually if the building to be demolished has a volume of less than
1750 cubic feet (49.56 cubic meters), then permission is not required to knock
it down.
2. DEMOLITION
Demolition is the process of tearing down or falling down of a building after
its life period with the help of some equipments or any other method. When
explosives are used for this then the demolition process are called as an
implosion. Every civil engineering structure is designed for a life period.
After that the existence of a structure is very dangerous. So removal of such
structures with proper safety measures has got great importance. There are
different steps involved before and during the time of a demolition activity.
They are described as follows.
3. STEPS
BEFORE DEMOLITION
The different steps before the execution of a demolition process are:
1. Surveying
2. Removal of hazardous materials
3. Preparation of plan
4. Stability report
5. Safety measures
3.1 Surveying
Surveying means study of different parameters of the structure and its
surroundings. There are two types of surveying are mainly conducted. They are
A. Building surveying
B. Structural surveying
A. Building surveying
It includes,
(a) Record Drawings
Prior to the Building Survey, the existing record plan, including layout
plan showing adjoining properties, pedestrian walkway, roads and street, etc.
shall be retrieved.
(b) Survey Items
The Building Survey shall cover the following:
(1) The construction materials;
(2) The existing use and, if possible, the past uses of the building prior
to demolition;
(3) The presence of wastewater, hazardous materials, matters arising from
toxic chemicals, flammable or explosive and radioactive materials, etc. and
possible presence of materials which can
contribute to air pollution and soil contamination;
(4) Potential dangerous areas, e.g., abnormal layouts, presence of enclosed
voids, and non- ventilated light wells which may trap obnoxious gas at the
bottom;
(5) Adjoining properties and site conditions, such as the existence of
slope and retaining wall, wall supporting ground, illegal structures, bridges,
underground railway and its above ground structures, including entrances,
vent shafts, distribution substations, traction substations, plant
rooms, overhead railway structures, surface track sections, overhead cables or
guy wires, and other utility Service connections;
(6) Drainage conditions and possible problems on water
pollution, flooding and erosion, especially on sloping sites and water
receiving bodies;
(7) Shared facilities with adjoining building, including common staircases,
party walls, and possible effect on it, such as self-enclosed walls to the
adjoining buildings, during demolition;
(8) Hoarding and covered walkway requirements;
(9) Adjoining pedestrian and vehicular traffic conditions;
(10) Available headroom, clear spaces and distance of building from lot
boundary which may affect the loading operation and transportation of building
debris during demolition;
(11) The sensitivity of neighborhood with respect to noise, dust, vibration
and traffic impact.
(12) Available site area to allow on-site sorting of building debris; and
(13) Street furniture such as fire hydrant, parking space/meters, street
light, street sign and hawkers’ stalls which could be affected by the
demolition project.
(c) Hazardous Materials
(1) Unless the Building Survey reviews that no obvious hazardous material
is present in the building, the Authorized Person shall cause proper sampling
and testing for the hazardous materials;
(2) In the case when hazardous materials e.g., asbestos containing
materials, or petroleum, are present, they shall be removed and
cleaned/disposed of according to the
statutory requirements administered by the Environmental Protection
Department, Fire Services Department, Labour Department and any
other Government Departments.
(3) In the case when the site has previously been used to store chemicals,
and other dangerous goods, soil contamination assessment shall be required at
pre-demolition stage and/or post-demolition stage; and
(4) In the case when the site has previously been used to store explosives,
special procedures to ensure no explosives remain on site will be required.
B. Structural surveying
(a) Record Drawings
Prior to the Structural Survey, the existing record layout, structural framing
plans and structural details shall be studied. The Registered Structural
Engineer shall check the presence of unusual detailing that may cause abnormal
structural behavior during demolition, e.g., upward anchor of tensile
reinforcement in cantilevered structures. If existing record plans are
available, these plans shall be used as reference and preferably be brought
along with the Structural Survey.
(b) Survey Items
The Structural Survey shall cover the following:
(1) The structural materials used;
(2) The original structural system employed in the design;
(3) The method of construction;
(4) Any dilapidation and degree of deterioration on any structural
elements;
(5) The structural conditions of adjoining structures and its shoring which
may be affected by the proposed demolition work;
(6) The presence of continuous structures that may be truncated by the
demolition;
(7) The structural system and structural conditions of basements,
underground tanks or underground vaults;
(8) The presence of exposed bracing or possible presence of covered
bracing;
(9) The nature of walls, whether it is block wall, reinforced concrete
walls, load bearing walls or partition walls;
(10) Cantilevered structures such as canopies, balconies, or other forms of
architectural features; and
(11) Any fixtures to the building such as signboard, sun-shading devices.
(c) Special Structures
The Structural Survey shall review the following:
(1) The correctness of structural information available;
(2) The presence of any unconventional structural elements which may
require special attention and well-defined modification procedures;
(3) The possibilities of structural modification to enable efficient
demolition traffic during demolition; and
(4) Any limitation on shoring and other temporary supports.
(d) Investigation and Testing
In the case when no structural details are available, the structural survey
shall include on site measurement and retrieve any structural framing as much
as practicable, performing tests and exposing some key structural elements to
facilitate checking on existing structure. This will allow the development of
procedures that ensure the stability of the building at all stages during
demolition.
3.2 Removal of hazardous materials
If
hazardous materials, such as asbestos containing materials, petroleum
contamination and radioactive contamination, exist in the building, further
investigation and removal of such hazardous material or contamination by
specialist shall be referenced.
Asbestos Containing Material
Specialists shall be employed to take samples and cause such samples to be
tested for asbestos containing material. In the case when asbestos containing
material are discovered, specialist contractor shall be employed to remove such
asbestos containing material. The asbestos waste should be handled, stored and
disposed of as chemical waste in accordance with the Waste Disposal Ordinance
and Waste Disposal (Chemical Waste) (General) Regulation.
Soil Contamination Material
In the case when possible soil contamination material is present,
specialist shall be employed to prepare soil contamination test proposal and
submit such proposal to the Environmental Protection Department for comment.
Upon agreement by the Environmental Protection Department, and completion of
the tests, a Soil Contamination Assessment shall be submitted to the
Environmental Protection Department for acceptance. In the case when remedial
works are required, the remedial proposal shall be submitted to the
Environmental Protection Department for approval prior to implementation of
such remedial works.
3.3 Preparation of plan
A Demolition Plan shall include the following:
(1) A plan showing:
(a) The location of the building to be demolished;
(b) A detailed topography of the site and its surrounds together with
ground level contours and sections of the slopes and ground supported by the
building where appropriate;
(c) Details of ground removal and/or backfilling; and
(d) The distances from the building to be demolished to its adjacent
buildings, streets, structures and significant street furniture.
(2) A layout plan of all floors of the building to be demolished, with
adequate sections, showing:
(a) The occupancy usage of the floors;
(b) The structural support systems;
(c) Principal materials of construction;
(d) The condition of the building e.g. the degree of deterioration; and
(e) The relationship of the building to be demolished with neighboring
properties affected by the demolition, which include all adjoining buildings
and unauthorized structures, shared staircases, party walls, truncating
continuous frames, slopes, retaining wall, overhead cables, guy wires
and underground utility services.
(3) A plan showing the structural arrangement and construction of all
unconventional structural elements, such as prestressed concrete structures,
precast concrete members, stressed skin structures, steel framed structures,
hangers, hanging ties, trusses or Vierendeel girders, deep beams, long span beams
(greater than 10m), arches, transfer plates, transfer girders, earth retaining
or basement structures, buildings which also act as earth-retaining structures
supporting adjacent ground, flat slabs, hollow block ribbed slabs and large
cantilevered structures;
(4) A plan showing the procedure for the demolition of the building;
detailed sequence of demolishing particular structural members; and the method
of demolition to be adopted including the restrictions on the use of any
particular type of equipment;
(5) In the case when powered mechanical plants and equipment are used, a
plan showing the route of movement of powered mechanical plants and equipment
including the method of lifting mechanical plant, where necessary, onto the top
floors of the structure; any structural alterations required to
suit the demolition, e.g. temporary strengthening to suit early removal of
any ground floor/or cockloft structure to facilitate vehicular movement at
ground floor, or strengthening of deteriorated key structural members; and any
shoring, temporary supports and/or floor propping required;
(6) A plan showing all precautionary measures for the protection of the
public including hoardings, covered walkways, catch platforms, catch fans,
scaffolding, protective screens and safety nets;
(7) A plan showing the proposed shoring and precautionary measures for all
affected adjacent buildings, slopes, retaining structures and services at each
stage of the demolition works;
(8) A plan showing the proposed shoring and temporary support to be
provided to the building to be demolished;
(9) A plan or descriptive notes on the proposed methods for handling and
disposal of debris including
(a) The permissible temporary accumulation of building debris at upper
floors and at ground floor;
(b) Method of handling demolished building debris;
(c) The routing and movement of debris from each floor to on grade holding
area prior to leaving the site;
(d) Means of transportation of debris off the site;
(e) Time and frequency of debris disposal off site;
(f) Record scheme on the tonnage of each truck load, truck license plate,
driver’s name, trip tickets and location of dump site;
(g) The site supervisory personnel responsible for the debris management system;
and
(h) A temporary parking layout for mobile machines and trucks, if
necessary;
3.4 Stability report
According to Building (Administration) Regulation, the Demolition Plan
must be accompanied by a Stability Report with supporting calculations. The
Stability Report shall include the following parts:
(1) A report on the stability of the building to be demolished during all
stages of demolition;
(2) In the case when powered mechanical plants or equipment are used, a
report on the stability of the building with supporting calculations to
demonstrate that the use of the plants and equipment will not render inadequate
the margin of safety of, or cause damage to any building, structure, street,
land and services;
(3) In the case when powered mechanical plants or equipment are used,
structural calculations for all temporary supports and bracings;
(4) A report on the stability of neighboring buildings, adjoining
properties.
(5) In the case when temporary or permanent supports are required to these
neighboring buildings, adjoining properties, and party walls, structural
calculations for these temporary and permanent supports; and
(6) A report with calculations demonstrating that the demolition work will
not render inadequate the margin of safety of, or cause damage to any building,
structure, street, land and services.
3.5 Safety measures
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. At present, the
Construction Industry Training Authority has organized relevant training
courses for site supervisors/foremen and plant or equipment operators.
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 utilized in demolition sites. The safety
requirements given in the Factories and Industrial Undertakings (Electricity)
Regulations shall be adhered to.
Fire
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. The Construction Site (Safety) Regulations
require the contractor to maintain in good condition and free from defects all
fire fighting appliances provided in such construction site.
Occupational
Health
The health of workers on site shall be properly protected in accordance with
the relevant subsidiary regulations of the Factories and Industrial
Undertakings Ordinance and the Occupational Safety and Health Ordinance with
particular attention to the following areas:
(A) Exposure to Dust;
(B) Chemical Exposure;
(C) Heat Stress and Ventilation;
(D) Noise Exposure;
(E) Medical and First Aid Facilities;
(F) Sanitation; and
(G) Occupational Diseases.
Emergency Exit Requirements in Demolition Sites
Emergency exits shall be provided during building demolition. In case of any
emergency evacuations, the emergency exit will serve as a lifeline for
transportation of injured workers. A minimum of one exit route shall be
maintained and designated as the emergency exit at all times during the
demolition. Adequate lighting and fire extinguishing equipment shall be
provided. Emergency exit shall be properly protected, free of obstruction, and
properly marked with exit signs or other indications to clearly show the route.
All workers shall be informed about the exit route.
Vibration
Demolition work will cause vibration to neighboring buildings or structures to
various extents, depending on the method of demolition. The most serious
vibration is caused by implosion. The effect of vibration caused by implosion
is categorized as follows:-
1. Permanent ground distortion produced by blast-induced gas pressures;
2. Vibratory settlement of foundation materials;
3. Projectile impact (i.e. blast fly rock); and
4. Vibratory cracking from ground vibration or air blast. These effects
will have to be dealt with specifically in the method statement for implosion.
For other mechanical demolition methods, the vibration effect is usually less
than some other construction processes, such as percussive piling and blasting.
In some cases, the traffic vibration caused by heavy duty tractors is more
significant than that caused by mechanical demolition. In order to identify the
actual cause and effect of vibration, Registered Specialist Contractors
(Demolition) are advised to carry out vibration monitoring during demolition.
As a general guideline, the peak particle velocities at any adjoining structure
shall not exceed 15mm/sec for prolonged vibration caused by mechanical
demolition.
Environmental Precautions
The general requirements to minimize environmental impacts from construction
sites can also be applied to demolition processes. The following sections
contain some of the procedures to be adopted:
(a) Air Pollution
Concrete breaking, handling of debris and hauling process are main sources of
dust from building demolition. Dust mitigation measures complying with the Air
Pollution Control (Construction Dust). Regulations shall be adopted to minimize
dust emissions. Burning of waste shall not be allowed. Diesel fumes generated
by mechanical plant or equipment shall be subject to the control of the Air
Pollution Control (Smoke) Regulations.
(b) Noise
Noise pollution arising from the demolition works including, but not
limited to, the use of specified powered mechanical equipment (SPME), powered
mechanical equipment (PME), such as pneumatic breakers, excavators and
generators, etc., scaffolding, erection of temporary works, loading and
transportation of debris, etc. affects the workers, and the sensitive receivers
in the vicinity of the demolition site. Silent type PME shall be used to reduce
noise impact as much as practicable. Demolition activity shall not be performed
within the restricted hours as established by EPD. Currently under the Noise
Control Ordinance, noise from the use of SPME and PME within restricted hours
is governed by a Construction Noise Permit (CNP) system.
(c) Water
The discharge of wastewater from demolition sites requires a valid discharge
license from the EPD and the application of such a license shall be made under
the Water Pollution Control Ordinance (WPCO). Effluent shall be treated to the
standards as stipulated in the license before discharge.
(d) Hazardous Materials
If removal of asbestos containing material is needed, an Asbestos
Investigation Report (AIR) shall be submitted to EPD. An Asbestos Abatement
Plan (AAP) shall be submitted at least 28 days before the asbestos abatement
work commences. The asbestos abatement works shall be carried out in accordance
with the Air Pollution Control Ordinance (APCO) and the Factories and
Industrial Undertakings (Asbestos) Regulations before demolition. Other
materials such as LPG cylinders in domestic flats, toxic and corrosive
chemicals for industrial undertakings, and any other hazardous materials have
to be identified and properly handled and removed prior to the commencement of
the demolition of the building. The management of waste must fully comply with
the Waste Disposal Ordinance. Additionally, management of waste which is
classifiable as a chemical waste must also comply with the Waste Disposal.
4. METHODS
OF DEMOLITION
There are two types of demolition
1. Non explosive demolition
2. Explosive demolition.
4.1 Non
explosive demolition
It means the demolition of a structure done with some equipment without the use
of any explosive. Different equipments used for the demolition
activity are
a. Sledge hammer
A sledge hammer, equipment used for removing a stone wall or a single column.
It consists of a long stem with a metallic head. It is used to give impacts on
the surfaces and that cause the demolition of structure. It cannot be used for
removal of large buildings.
b. Excavators and Bulldozers
Hydraulic
excavators may be used to topple one-or two-story buildings by an undermining
process. The undermining process means, erode the base or foundation, i.e., dig
or excavate beneath the foundation so as to make it collapse. The strategy of
excavation is to undermine the building while controlling the manner and
direction in which it falls. The demolition project manager will determine
where under mining is necessary so that the building is pulled into the desired
manner and direction. Safety and cleanup considerations are also taken into
account in determining how the building is undermined and ultimately
demolished.
Loaders or bulldozers may also be used to demolish a building. They are
typically equipped with “rakes” (thick pieces of steel that could be an I-beam
or tube) that are used to ram building wall. Skid loaders and Loaders will also
be used to take material out and sort steel.
c. Wrecking balls
In case of buildings have greater heights (5 to 6 story)
normal excavators and bulldozers are not sufficient. In such cases
crane with wrecking balls are used to perform the demolition activity. The
wrecking balls are steel balls hanging from a steel rope which is attached to
the crane. This method is more effective only for high rise masonry
structures because of the uncontrolled backward movement of steel ball after
the impact on the wall surface. Now this method not commonly used because of
this uncontrolled behavior of wrecking balls.
d. High reach excavators
High reach demolition excavators are more often used for tall buildings where
explosive demolition is not appropriate or not possible. These excavators are
used to demolish up to a height of 300 feet. These excavators with some
attachments are also provided for some specific purposes. For example
excavators with shear attachments are typically used to dismantle steel
structural elements. Hydraulic hammers are often used for concrete
structures and concrete processing attachments are used to crush concrete to a
manageable size, and to removing reinforcing steel.
4.2. Explosive demolition
The basic idea of explosive demolition is quite simple. If we remove the
support structure of a building at a certain point, the section of the building
above the point will fall down on the part of the building below that point. If
this upper section is heavy enough, it will collide with the lower part with
sufficient force to cause significant damage. The explosives are just trigger
for the demolition. It’s gravity that brings the building down.
Demolition blasters or blasting expert (“Blasting expert” means a person who is
the holder of a valid mine blasting certificate.) load explosives 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
of rubble.
The main challenge in bringing a building down is controlling which way if
falls. There are mainly two ways to implode a building,
1. felling
like a tree
2. falling
into its own footprint Felling like a tree
1. Felling like a tree
In this the blasting crew will be able to tumble the building over on one side,
into a parking lot 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. For example to topple the building to the
north, the blasters detonate explosives on the north side of the building first
, in the same way you would chop into a tree from the north side if you wanted
it to fall in that direction . Blasters may also secure steel cables to support
columns in the building, so that they are pulled a certain way as they crumble.
2. Falling into its own footprint
Sometimes, though, 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
footprints (that means the total area of building is removed into the base of
the building). This feat requires such skill that only a handful of demolition
companies in the world will attempt it.
Blasters approach each project a little differently, but the basic idea 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, in
roughly the same way that they would set the explosives to topple a single
structure to the side. When the explosives are detonated in the right
order, the toppling towers crash against each other, and all of the rubbles
collect 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.
According to Brent Blanchard, an implosion expert with the demolition
consulting firm Protec Documentation Services, virtually every building in the
world is unique. And for any given building, there are any number of ways a
blasting crew might bring it down. Blanchard notes the demolition of the Hayes
Homes, a 10-building housing project in Newark, New Jersey, which was
demolished in three separate phases over the course of three years . “A
different blasting firm performed each phase,” Blanchard says, “and although
all of the buildings were identical, each blaster chose a slightly different
type of explosive and loaded varying numbers of support columns. They even
brought the buildings down in different mathematical sequences, with varying
amounts of time factored in between each building’s collapse.”
Explosives used
Blasters use different explosives for different materials, and determine the
amount of explosives needed based on the thickness of materials. For concrete
column, blasters use traditional Dynamite or similar explosive materials.
Dynamite is just absorbent stuffing soaked in a highly combustible chemical or
mixture of chemicals. When the chemical is ignited, it burns quickly, producing
a large volume of hot gas in a short amount of time. This gas expands rapidly,
applying immense outward pressure (up to 600 tons per square inch) on whatever
is around it. Blasters cram this explosive material into narrow boreholes
drilled in the concrete columns. When the explosives are ignited, the sudden
outward pressure sends a powerful shock wave busting through the column at
supersonic speed, shattering the concrete into tiny chunks.
Demolition of steel column is a bit more difficult, as the dense material is
much stronger. For buildings with a steel support structure, blasters typically
used the specialized explosive material Cyclotrimethylenetrinitramine, called
RDX for short. RDX – based explosive compounds expand at a very high rate of
speed, up to 27,000 feet per second (8,230 meters per second) . Instead of
disintegrating entire column, the concentrated, high velocity pressure slices
right through the steel, splitting it in half. Additionally blasters may ignite
dynamite on one side of the column to push it over in a particular direction.
5. CONCLUSION
Type of demolition method depends upon various factors such as site condition,
type of structures, age of building, height of building and economy. Anyway
controlled demolition of building is necessary to ensure safety. Explosive
demolition is the preferred method for safely and efficiently demolishing the
larger structures. Almost all major building implosions in the world are
handled by 20 well-established companies, blasting is passed on from generation
to generation.
6. REFERENCES
1. Code of
practice for demolition of buildings by Building Departments of Hong Kong in 2004.
2. Prof.
Chimay Anumba, Dr. Barbara Marino, Prof. Arie Gottfried, Health and safety in refurbishment
involving and structural instability .(Research 204)
3. Tom Harris, An article on How Building Implosions work.
