This document provides an overview of demolition of buildings. It discusses the history of demolition using explosives from the 13th century onwards. The objectives of demolition are to prevent damage to the neighborhood, allow for repairs or new construction. Key steps before demolition include surveying, removing hazardous materials, and safety planning. Demolition sequence involves a top-down approach starting with roofs and working towards foundations. Common demolition methods are ball and crane, pressure bursting, and building implosion using strategic explosive placement.

1. A Seminar on DEMOLITION OF
BUILDINGS
Presented by: Syed Naireen Zeib
38-CE-14

2. Contents
 Introduction.
 History.
 Objectives.
 Steps before Demolition.
 Demolition sequence.
 Methods of Demolition.

3. INTRODUCTION
 Demolition is bringing down the building and
other structures safely.
 The demolition of structure with the help of
explosives is called as implosion.
 The main objective for demolition may be
the age of the structure.
 Methods of demolition depends upon the
type of structure, height and surrounding
structures.

4. Image showing Demolition of a building

5. HISTORY
 Historians generally agree that the first
true "explosive" was black powder, which
was developed around the 13th century.
 The first recorded use of black powder for
demolition purposes appears to have
occurred in the early 1600s, when quarries
in Hungary began using it for rock blasting.

6. HISTORY cont..
 Black powder was put to use in the tin
mines of England, and Switzerland adopted
blasting technology for road construction.
 Throughout the 1930s, structural explosive
demolition was overseen by engineers
working directly for large dynamite
manufacturers.

7. OBJECTIVES
 Prevention damaging the neighbourhood
environment.
 Repair of damaged structures.
 Construction of other structure at that
previously constructed site.
 Provides safety for the occupants in the
building.

8. STEPS BEFORE DEMOLITION
1. Surveying
2. Removal of hazardous
materials
3. Preparation of plan
4. Safety measures

9. DEMOLITION SEQUENCE
 All cantilevered structures, verandas and features
attached to the external walls shall first be demolished
prior to demolition of main building.
 When demolishing the roof structure, all lift machine
rooms and water tanks at high level shall be demolished
in “top down” sequence to the main roof level. Floor
beams shall be demolished in the order of cantilevered
beams, secondary beams and then main beams.
 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.

10. DEMOLITION SEQUENCE cont..
 Demolition of the floor slabs shall begin at mid span
and work towards the supporting beams.
 Floor beams shall be demolished in the order of
cantilevered beams, secondary beams and then main
beams.
 Wire and winch shall be used to secure the cross
beam to other structural members.
 The concrete is first broken away at both ends near
its column supports to expose the reinforcement.
 Reinforcement shall be then cut to partially drop the
beam and the brought down with wire.
 Secure the column by wire and winch.

11. DEMOLITION SEQUENCE cont..
 Pre-weakening at the bottom of column:
1. Break away the concrete to expose the reinforcing
bars.
2. Cut the reinforcing bars at the exterior half of the
column. Cutting shall be performed immediately
prior to pulling.
3. Pulling down the column in a controlled motion.

12. METHODS OF DEMOLITION:
1. Ball and crane:
 This is one of the oldest and most commonly used methods for building
demolition. A crane uses a wrecking ball, weighing up to 6120 kg, which is
either dropped onto or swung into the element to be demolished. Wrecking
ball at rest.
 The ball is made from forged steel,which
means the steel is not cast into a mould
in a molten state. It is formed under very
high pressure while the steel is red hot
(soft but not molten) to compress and to
strengthen it.
 Concrete members can be broken into small Swinging the wrecking ball
pieces, but secondary cutting of reinforcing may be necessary.

13. 2. Pressure bursting:
 Pressure bursting can be used in cases where relatively quiet, dustfree,
controlled demolition is preferred.
 Both mechanical and chemical pressure
bursting split the concrete, either with a
splitting machine operating on hydraulic
pressure provided by a motor in the case of
mechanical bursting, or through the insertion
of an expansive slurry into a pre-determined
pattern of boreholes in the case of chemical bursting.
 The split concrete is then easily Pressure bursting removed, either by hand or by
crane.
 Both methods work by applying lateral forces against the inside of holes drilled
into the concrete.

14. 3. Building implosion:
 In the controlled demolition industry, building 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. Despite its terminology, building implosion also
includes the controlled demolition of other structures, such as bridges, smoke
stacks, towers, and tunnels.
 Building implosion (which reduces to seconds a process which could take
months or years to achieve by other methods) typically occurs in urban areas
and often involves large landmark structures.
 Numerous small explosives, strategically placed within the structure, are used
to catalyze the collapse. Nitroglycerin, dynamite, or other explosives are used
to shatter reinforced concrete supports. Linear shaped charges are used to
sever steel supports. These explosives are progressively detonated on supports
throughout the structure. Then, explosives on the lower floors initiate the
controlled collapse

15. CONCLUSION
 It can be concluded that
demolishing/imploding the building
structure will prove very useful, economical
and quickest for reconstruction.
 Leads to a safe and controlled demolition
for the occupants and neighbourhood.
 Development in techniques allows rapid
demolition with no harm to the
environment.

16. THANKYOU