A Technical Paper On

“Implosion of Structures”

Submitted To

NIRMITEE 2005

ByAnkit Jain

Email: - ankitjain04@yahoo.co.uk

Sinhgad Technical Education Society’s

Sinhgad College of EngineeringVadgaon Budruk, Pune

“Implosion of Structures”

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Author: Ankit Jain, Sinhgad College of Engg. Pune, Email: - ankitjain04@yahoo.co.uk

Abstract

With increase in population, society demands vertical growth of structures and removal of those structures, which

hampers the growth and is not capable of accommodating the burgeoning population. Besides this, with due to

consideration to the safety reason and to avoid expensive retrofitting, which is nothing but a temporary remedial

measure, old structures must be replaced.

This technical paper introduces us to different techniques of demolition and implosion in specific. Prime intention of

this paper is to introduce civil engineers to Implosion technique of demolition.

Introduction

Demolition is an activity in which construction process is reversed that is the building or part of it is

disassembled and removed. Today structures are carefully dismantled and not demolished.

Demolition has evolved since its inception, form wrecking ball to explosives. During its evolution it

has become faster and safer and more cost effective.

Need for demolition

As a civil engineer why should I demolish a structure? This is the first question that comes in our

minds. A civil engineering structure has an in built life of 50 to 200 years. Structure needs extensive

restoration work after its design period. Structures also get damaged during natural calamities like

earthquake, cyclone etc. It is very costly to repair this kind of structure.

In light of this it is advisable to go for complete reconstruction of the structure. This brings in

current best technologies in construction in place of the older techniques. For this to happen we

need to bring down the structure, we need to demolish the structure.

DEMOLITION METHODS

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Wrecking Ball

Swinging balls made up of solid metals is used. Momentum of these swinging balls impart

tremendous amount of energy on concrete which it cannot withstand and hence breaks into pieces,

thus bringing down the structure.

Hydraulic breaker

Hydraulic force is used to crush concrete between some kind of teething mechanism. This weakens

the structure and causes collapse of structure. Demolition is carried out floor by floor.

Expansive material (Non Explosive technique)

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This is a non explosive type of demolition. Some chemical materials expand on mixing with certain

types of chemicals. These expanding chemicals provide great amount of swelling pressure. The

pressure is so intense that it overcomes concretes compressive strength. This technique is a very

clean non messy type of technique causing no type of pollution (noise, dust)

Demolition by explosives (Implosion)

Explosives are used to assist demolition of a building.

The act of imploding, or precisely controlling the exploding of a building from within, may only

require a few seconds to physically place the building on the ground is known as implosion.

Planning

However, several months of careful planning must be accomplished before an implosion can be

done. In addition, depending upon size, the actual preparation of the building may take several

weeks. Careful, precise planning with all parties involved in the process is mandatory in insuring a

successful implosion.

Demolition Method

Feasibility studies should be undertaken by the construction manager to examine the cost

effectiveness of imploding compared to the wrecking ball method. In some cases, the wrecking ball

method will be considerably cheaper. Factors which influence these costs will be building size,

asbestos abatement, type of construction, proximity to other buildings and thoroughfares, and

exposure of the general public to the building during demolition, all potential sources of liability.

Owners may choose implosion as a method by which to lessen exposure to the local press and

media when buildings have historical or sentimental significance to the community. Implosion may

also be chosen when costs are found to be comparable to or even more expensive then the wrecking

ball due to the convenience associated with the implosion process.

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Permissions and Regulatory Requirements

The construction manager must immediately begin the process of managing a demolition once this

method has been chosen by the owner. Early on, local governmental officials must be involved in

the planning process. The construction manager must call meetings with officials of agencies which

include, but are not limited to, the following: Building regulations, police, utilities, fire, public

works, air pollution control, and the natural resources departments. The officials must be directly

involved in the planning and coordinating process as each will be affected to one degree or another

by the implosion. In most locales, building regulation officials will also require a demolition permit.

Asbestos abatement permits will also be required if asbestos is present in the structure. The media

may also become involved at this point at the discretion of the owner. In some cases the media are

not notified until a day before the implosion, in order to limit spectators around the job site.

Pre Blast Precautions

The construction manager must also arrange for pre-seismic and post-seismic surveys around the

site. Pre- and post implosion video-surveys should be made of adjacent structures, sidewalks,

basements, sewer and water lines, and on exterior skins and roofs of adjacent buildings. This could

eliminate any liability claims after the implosion. Also, owners of adjacent and area businesses

should be notified of the date and time of the implosion, and what is being done to protect their

structures. In some cases, plywood barriers are constructed and placed between the site and the

businesses as a precautionary measure. Semi-trailers have also been utilized as a protective barrier,

but are used primarily as a psychological boost for the adjacent owners.

Preparation of Building For Implosion

The building itself is prepared for implosion by basically removing the contents of the building,

salvageable fixtures, and non-load bearing partitions in the basement and lower level floors.

Utilities are disconnected, and the building itself is wrapped in a chain link fence. Testing of

concrete is done to ascertain on site strength of it. This is done with the help of NDT (Ultrasound

test, Impact hammer test). Also test blasting of selected columns is carried out to ascertain in situ

concrete strength and to determine amount of explosives to be used per column. Structural columns

are drilled for explosive charges which are loaded approximately twenty-four hours prior to the

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scheduled blast time. The demolition contractor is generally responsible for the preparation of the

building as part of the contractual agreement.

Risks Management

Columns are wrapped with meshes and geosynthetic materials so as to contain the flying debris.

Explosives used per columns are carefully computed. A berm of earth and demolition debris is

placed against the first floor in order to contain flying debris during the blast. Protective sheathing is

provided on neighbouring building so as to protect them in case some debris fly and impact it.

Falling debris creates mini earthquake which if not managed properly can cause damage to

neighbouring buildings. For this building is allowed to fall in a sequence so as to channelize energy

into ground at different time intervals. Security guards patrol the premises after the building has

been loaded.

Timing of Blasting

Ideal weather conditions for the blast are a light breeze and a cloud ceiling minimum of 1500-2500

feet. Low cloud ceiling levels will present dispersal of dust, so normally a blast will be postponed

for low ceiling levels or thunderstorms. Blast times are normally set up very early on a Saturday or

Sunday morning to lesson inconveniences to the general public, especially if main thoroughfares

have to be temporarily closed. Police departments help with crowd control and safety barriers prior

to and during the blast.

Cleaning

Immediately following the implosion, construction and City Street cleaning crews will clean and

water down the adjacent street, removing any dust or debris. Depending on the situation, most roads

are open within one to two hours. Cost of the city street cleaning crews is charged directly to the

owner via the construction manager.

Waste Management

Debris removal from the site is usually contacted on a per cubic yard basis by an excavating

contractor. During this time, an owner may chose to recycle aluminium, copper, and steel to the

area reclamation centre. All combustible and non-combustible materials must be discarded in

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accordance with local, state, and federal laws. Every year, the disposal of construction debris and

trash becomes more of an expense and problem to the contractor. Careful planning, prior to an

implosion, can actually help to reduce expenses of debris removal.

Test Blasting of Columns

Drilling holes for placement of explosives Wrapping of column with geosynthetics

Blasting of column and containment of

debris

Blasted columns Section. Exposed steel mesh

can be seen

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Types of structures that can be imploded

Smoke stacks Residential Buildings

Steel Towers

Cooling Towers

Stadiums Hotels

Bridges

CASE STUDY

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KINGDOME IMPLOSION

This particular structure was located in Seattle, USA. This structure use to house a football stadium.

It was constructed in 1976 at the cost of 67 million dollars. It was imploded on March 24 2000 at

8.50 am on Sunday. In place of this stadium a new stadium was to be constructed. Following are

some of specifications of this structure.

COMPONENTS VALUE

Site Area 23.9 acres

Building Area 9.34 acres

Roof Area 7.85 acres

Height 250 feet

Width 660 feet

Volume 67 million cubic feet

Structural Steel used 443 tons

Concrete used 52800 cubic yards

Explosives 445 tons of dynamite

Pre demolition Preparation 3 months

Time taken for implosion 16.8 seconds

Cost of Implosion 430 thousand dollars

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Implosion Procedure

The roof of the Kingdome is the largest concrete dome in the world, spanning 660 feet. It is held up

by a balance of pressure between its inner and outer rings. The compression ring in the middle

anchors the tops of the ribs, while the encircling tension ring keeps the ribs' bases in place.

 

    The key to the implosion is to release this pressure by breaking the ribs in the middle. When this

happens, most of the structure will collapse inward. The strategy is to take down the dome in a two

step fashion.

Step 1:

    Small explosions in the first three sections will fracture the concrete in the ribs, columns, and

supporting tension ring. The flexible rebar that runs through the concrete will remain intact. As the

heavy concrete roof drops, the rebar will act like ropes pulling the columns down and toward the

centre.

 

Step 2:

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    As the first sections fall, the next three sections will be detonated and collapse, bringing the

centre compression ring down with them.

 

 

Step 3:

    Gravity takes over and brings the dome down in a pile of rubble placed under the structure to

absorb some of the impact of the roofs heavy landing.  The entire process estimated to happen in

approximately 20 secs, proves successful! 

 

Risk management

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Concrete slabs were placed at bottom of dome to reduce the impact of falling debris but then

also an earthquake of magnitude 2.3 was measured.

Explosives were placed inside columns 24hours prior to blasting.

Neighboring buildings were wrapped with protective plastic sheathing.

Safety zone was clearly demarcated and cleared off people, vehicles.

Sirens were blown 15 minutes prior to blasting.

Conclusion

It is seen that implosion is a superior technique of demolition than wrecking ball and hydraulic

breakers. It costs less for a multistoried structure. It is fast and causes least discomfort to the

neighbors. Various kinds of pollutions are limited only for a brief period of time. It is safer for

workers. Therefore this technique is recommended for modern redevelopment of cities.

BIBLIOGRAPHY

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Websites

www.Howstuffworks.com

www.Findarticles.com

www.historylinks.org

www.implosionworld.com

www.home.earthlik.com

www.seattlepi.com

www.seattletimes.com

www.phillyblast.com

www.usgs.gov

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