DEMOLITION OF BUILDINGS
I.INTRODUCTION
Demolition is the process of destroying down or dismantling or collapsing down of large buildings after its useful life period. The process of demolition is carried out with the help of some equipment or other methods with legal procedure followed by the consent of the local authority. We know that every structure is designed for a specific life period generally from 70 to100 years. The existence of the structure after the service life period is over is very dangerous to its occupants and surrounding buildings. The purpose of demolition is to prevent the accidental collapse of any part of the building and to ensure safety of workers, public and neighboring properties.
Demolition work is one of the most important operations in construction engineering field. If demolition activity is not done carefully it may result into severe consequences. The various causes of consequences of demolition of buildings are as follows -
To avoid these consequences from demolition work, it is necessary to understand complete process of demolition of building.
II. DEMOLITION OF BUILDINGS
Demolition is the tearing-down of buildings and other structures. Demolition contrasts with deconstruction, which involves taking a building apart while carefully preserving valuable elements for re-use. Demolition methods can vary depending on 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. Times saving methods are more expensive than the slower ones.
2.1. Pre-planning of demolition activity
The different steps before the start of a demolition process are -
2.1.1. Surveying of Site
Study of different parameters with different views of the structure and its surroundings with structural point of view is carried in surveying. The two types of surveying which are mainly conducted are building surveying and structural surveying.
2.2.2. Removal of hazardous materials
Before starting demolition of building hazardous materials if any, such as asbestos containing materials, petroleum contamination and radioactive contamination, etc exist in the building are removed. Further investigation and removal of such hazardous material or contamination by experts shall be done.
2.2.3. Preparation of plan for demolition work
Demolition Plan and strategy is prepared which includes the following -
2.2.4. Required stability report
The Stability Report shall include the following parts -
III. METHODS OF DEMOLITION
The demolition sequence will depend on things like the type of construction, location, and demolition methods selected. Buildings and structures should generally be demolished in reverse order to their construction, that is, by „sequential demolition?. The different methods of demolition are as below –
3.1. Demolition of building by Top Down- Manual Method
Manual methods are carried out top down, proceeding, in general, from the roof to ground. The particular sequence of demolition may vary, depending on site conditions and structural elements to be demolished.
3.1.1. Demolition of Cantilevered Structures and Balconies
Cantilevered structures, balconies and canopies may project out of the building over the pedestrian footpath or in some cases over a portion of the traffic lane. Figure 1.Illustrates the demolition of cantilevered slab. The general sequence of dismantling cantilevered slabs and beams are described in the following –
Figure:. Demolition of cantilevered RCC slab (Manual method)
3.1.2. Demolition of Floor Slabs
Reinforced concrete floor slab shall be demolished by gradually breaking away the concrete. The reinforcement shall remain and be cut off after the concrete is broken away.
Figure: Demolition of slab
3.2. Demolition of building by Top Down- 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 from the area within reach of the rope or tie wire. The concrete shall be broken away first before the cutting of reinforcement. Alternatively the reinforced concrete slab may be cut by saw cutting. Demolition sequence would be as shown in following figures.
3.3. Demolition of building 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. Recommended techniques for the wrecking ball operations include
3.4. Demolition of building by 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 weight. Implosion are discussed in the following -
IV. PROTECTIVE PRECAUTIONS FOR DEMOLITION
Safety precautions must be taken to safeguard persons working on the site and members of the public who are in the vicinity, as well as to protect property likely to be affected by the demolition.
4.1. Precautions regarding Machinery / Equipment
The following precautions should be taken regarding machinery/ equipment -
4.2. Precautions regarding Scaffolding
The following precautions should be taken regarding scaffolding -
4.3. Precautions regarding Public Safety
The following precautions should be taken regarding public safety -
4.4. Precautions regarding Worker Safety
The following precautions should be taken regarding worker safety -
V. PROBLEMS IN DEMOLITION OF BUILDINGS
The problems which may arise while carrying out the building demolition are as follows -
Demolition of buildings involves various demolition activities which cause influence on the environment which ultimately give rise to pollution.
VI. CONCLUSIONS
It is concluded that before carrying out any demolition works, building survey must be done carefully, so that it may not cause any severe damage to the environment, public and adjacent properties around the building which is to be demolished. Any type of building to be demolished, its method depends upon various factors such as site condition, type of structures, age of building, height of building and economy and most important its location with presence of its surrounding with its structural stability. Controlled demolition of building is necessary to ensure safety of both the workers and the surroundings so as to cause least amount of injuries and accidents. Explosive or implosion demolition is the most preferred method for safely and efficiently demolishing the larger structures which requires a very high precision. The procedure of demolishment should be carried out with the aim of minimizing the risks of causing damage to persons and properties of the public, endangering the health and safety of site personnel and damaging the neighborhood environment.
REFERENCES
IS Codes For Demolition and Dismantling
Demolition and Dismantling
IS 1200: 1974 Part-18 : Method of measurement of building and civil engineering works- demolition and dismantling
IS Codes for Safety
IS 818:1968 (Reaffirmed-2003) : Safety and healthy requirements in electric and gas welding and cutting operations.
IS 3696:1987 Part-1:Safety Codes of scaffolds and ladders- Scaffolds.
IS 3696:1991 Part-2:Scaffolds and Ladders - Codes of Safety - Ladders.
IS 3764:1992:Codes of safety for excavation work.
IS 4081:1986:Codes of safety for blasting and related drilling operation.
IS 4130:1991:Safety Codes for demolition of buildings.
IS 5916:1970:Safety Codes for construction involving use of hot bituminous materials.
IS 6922:1973:Structural subject to underground blasts Codes of practice for safety and design of structure subject to underground blast.
IS 7293:1974:Safety Codes for working with construction machinery.
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