Demolition of

Structures.

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By: Chintan Varia

Pratik Sureja

Akshay Kasundra

Why DEMOLITION is DANGEROUS?

Demolition work is one if the most dangerous operations in

construction.

REASONS/CAUSES:

1. Easy to cause injury to human workers due to the difficulty of accessing into or working inside a building which is under construction.

2. Falling of smaller objects or debris from the demolishing building.

3. Falling of Partially demolished structure.

4. Collapse of unstable structure due to original structure being disturbed.

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Why DEMOLITION is DANGEROUS?

5. Collapse of heavy demolition equipment due to inadequate support of the partially demolished structure.

6. Collapse of the partially demolished structure due to the accommodation of large amount of un-cleared debris.

7. Congested site environment that easily cause damage to human workers, or to the third parties and their properties that are situated nearby the demolition site.

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DEMOLITION PLAN

Forming part of the submission information, the DEMOLITION Plan should include:

a) A set of drawings showing:

the location of the building to be demolished other existing structures and facilities in vicinity.

b) Proposed method of DEMOLITION.

c) Proposed shoring and precautionary measures for the adjacent buildings.

d) Proposed shoring and protection for the building to be demolished

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DEMOLITION PLAN

e) Proposed methods of handling and disposing of the demolished materials.

f) Proposed sequence of carrying out work.

g) Detail of equipment used, with methods of raising, lowering or supporting the equipment.

h) Structural calculation to justify the proposal.

i) Proposed arrangements for site supervision.

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Catch Fan

Typical dust screen and fansprovision to protect buildingand minimize disturbance topublic during demolition

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Provision of Hoarding as aprotection to public

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Shaft for falling of debris

Common ways to get rid of thedemolished debris – to controlthe falling of the debris into apre-determined vertical shaftformed on the floor slabs

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Debris shaft formed by openingtemporarily cut on floor slab

Debris collection area at groundfloor under the debris shaft

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Temporary props erected tosupport heavy equipment

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Erection of shoring to supportaffected structurea) Basement demolition (left)b) A nearby retaining wall (right)

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Typical sectioning/sequencing arrangement ofwork during demolition –demolish from exteriorinward

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Typical sectioning/sequencing arrangement ofwork during demolition –demolish from one side tothe other side of building

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Typical layoutarrangement in small andmedium sized buildingunder demolition

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Typical layoutarrangement insmall and mediumsized buildingunder demolition

METHODS OF DEMOLITION

GENERAL CONCERNS:

The choice of choosing a demolition method depends on a number of factors such as the project conditions, site constraints, sensitivity of the neighborhood and availability of equipment etc.

In general, top down methods are applicable for most sites, particularly for those situated in busy urban areas. Other mechanical methods applied from the outside of a building lines, demotion by hand held tools or the cut and lift process may be a safe solution.

For structural projections such as balconies, canopies and verandahs extending beyond the building lines, demolition by hand held tools or the cut and lift process may be a safe solution.

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METHODS OF DEMOLITION

There are various methods of DEMOLITION of structures.

1. Demolition by human operatives.

2. Deliberate Collapse method.

3. Using of applied pulling / pushing forces.

4. Using of wrecking ball.

5. Use of powered plant or demolition machine.

6. Using saw cut method.

7. By Implosion (explosive).

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DEMOLITION BY HUMAN OPERATIVES

This method particularly suitable for use in smaller site with congested space where larger machine cannot be employed.

In this case, human operatives are used in the demolition process using simple electrically or pneumatically powered tools such as picks, hammers, wire cutters or hand driven hydraulic jacks etc. to carry out the demolition of individual elements.

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Typical demolitionarrangement done byhuman operatives

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Typical demolitionarrangement done byhuman operatives

Slab with the sidesdisconnected readyfor dismantle

21Typical demolitionarrangement done byhuman operatives

Worker breakingdown larger piece ofstructure which wasdemolished bypulling/pushingmethod.

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A number ofworks where

humanoperative isunavoidable

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Working conditionand behavior ofhuman operatives

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of

DEMOLITION

DELIBERATE COLLAPSE METHOD

DEMOLITION by deliberate collapse consists of systematic removal, or weakening of the key structural elements to induce the collapse of the structure.

However, when applying this method, several precautions should be observed, such as:

1. Sufficient distance of collapse should be provided.

2. Collapse procedure should be carefully designed so that there is no pre-mature collapse or collapse out of anticipated area.

3. Control height of building structure to be collapsed.

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of

DEMOLITION

USING OF APPLIED PULLING / PUSHING FORCES

Connecting structural members are disconnected first allowing part of the remaining structure to be dragged down by the use of some pulling/pushing equipment such as powered jack, winching machine, pulley systems, pushing arms, powered blocks or from the pull/push of a hydraulic excavator.

However, a firm base in the demolishing building is required such as basing on an undisturbed core wall or a strong column section for the applying of pulling/pushing forces.

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USING OF APPLIED PULLING / PUSHING FORCES

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27Disconnectedexternal wall readyto be pulled downby an applied force

Remain fragments frompulled-down structure tobe removed afterward

Demolition done byapplying a pulling force toa portion of structure

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of

DEMOLITION

USING OF WRECKING BALL

The use of wrecking ball method requires a crane equipped with a steel ball.

The DESTRUCTION of the building is caused by the impact energy of the steel ball suspended from a crawler crane.

The wrecking ball can be operated outside or inside a building.

In case the process is operated inside a building, sufficient clearance from the building interior should be made first .

This also demands experienced operators in order to handle the wrecking ball and control the DEMOLITION.

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Swing action ofwrecking ball

Vertical drop ofwrecking ball

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DEMOLITION

USE OF POWERED PLANT OR DEMOLITION MACHINE

The principle of demolition by machine is typically the same as the top-down manual method, except that most of the demolition begins with the lifting of the mechanical plant on to the building top floor.

Powered plant such as crawler mounted breaking hammer are used in the demolition process and excavating machines with bucket are used in the removal or handling of the demolished materials.

However, due to the weight of these machines, they should be properly supported such as by the use of steel props no matter in still or in operating condition.

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Demolition by the help ofmechanical plant – pneumaticbreaker and bucketedexcavator

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Close-up view of thepneumatic breaking machine

33Lifting themechanicalequipment to topof building

Demolition using top-down method using machines

Building before demolition

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Moving down of the breakingmachine to the lower floor

Demolition using top-downmethod using machines –typical floor cycle andmachine movement

35Some more examples of mechanical means to demolish

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of

DEMOLITION

USING SAW CUT METHOD

This method is suitable for alternation and additional works where accuracy is important and restriction on noise and vibration is required.

It can be used to cut concrete slab and wall elements into segments or for the forming of openings, breaking into existing structure like a basement, servicing tunnel, flyover, or the other part of an inhabited building in the process of alteration or renovation works.

Saw Cutting can be done using the following methods:

1. Wire Saw Cutting

2. Diamond Core Stitch Drilling

3. Disc Saw

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WIRE SAW CUTTING38

WIRE SAW CUTTING39

DIAMOND CORE STITCHING DRILLING40

DIAMOND CORE STITCHING DRILLING41

USING DISC SAW42

Set-

up

an

d m

ou

nti

ng

of

the

saw

dis

on

wal

l

Demolition using disc saw cutting

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Using core and drill method todemolish a pedestrian subway

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DEMOLITION

USING IMPLOSION (EXPLOSION)

If using this method to demolish a building, contractor should carry out a comprehensive risk and environmental assessment on the effect of implosion on the neighborhood.

A detail demolition design is also important, which should cover:

1. Method to pre-weaken the structure (e.g. demolish some load taking structures)

2. Placement of explosive

3. Time-delay design to allow the building to collapse under control director and location

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USING IMPLOSION (EXPLOSION)

Charges of explosive are placed within the fabric of structure and detonated to cause partial or complete collapse. Competent explosive specialist is required when demolition is to be done by using explosive.

There are numerous types of explosives for use for various types of demolition (sometimes including non-explosive agent). Consideration such as the spacing and depth of explosive to be located, the amount of explosive to be used, or the degree of fragmentation required in order to control the boundary of demolition etc., are required throughout the planning and operation process.

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USING IMPLOSION (EXPLOSION)46

DEMOLITION BY ONE LEVEL AT A TIME47

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