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The Demolition Process for buildings and structures
The requirement to demolish or refurbish a building occurs for a variety of reasons. It is essential that the demolition process is adhered to.
Every building has a lifespan which is known as its ‘design life. An architect will design a building with perhaps a life span of 80 -100 years. When it has reached the end of its life span, it might become dangerous for habitation or to the adjacent buildings around it.
Other reasons are that new ones replace old structures. The structure has lost its stability, or it may have structural damage.
Demolition – means destruction, breaking down or removal. The Demolition of a building is the process of dismantling a structure after its life span or serviceability by pre-planning and controlled demolition methods.
Implosion – This type of Demolition is carried out by a few specialist companies in the UK
The Demolition Process for buildings and structures
The four steps in the process are
a) Surveying
b) Removal of hazardous materials
c) Preparation of plan
d) Safety measures
Surveying
Surveying means the study of different features of the building or structure and surroundings. The two types of surveying are
a) Building surveying
b) Structural surveying
1. Building Surveying
The surveying processes include
- Types material used in its construction
- Previous usage
- The presence of hazardous materials
- The condition of drainage and underlying problems with water pollution, flooding and erosion.
- Shared utilities and facilities
- Adjoining vehicular and traffic conditions
- The impact of noise, dust, vibration and traffic movements on the local community
Structural Surveying
In a structural survey, following process are carried ou
- Construction method
- The fundamental conditions of basements and underground tanks
- The skeletal system used in the design.
- The building condition
The removal of Hazardous Materials
Hazardous materials which could include asbestos could come to light as the result of a demolition survey. Specialist asbestos removal and remediation companies should be employed to remove dangerous substances from the site before the Demolition.
Demolition Plans
A demolition plan illustrates the different process involved, and they are:
- Location of the building
- The distances from adjacent buildings, roads, structures and schools
- The structural support
- Method statements for the Demolition of the building; showing the sequence of Demolition and the method of Demolition to be employed
- A health and safety plan showing all the measures for the protection of the public including hoardings, covered walkways, crash decks, and scaffolding protection screens
- Waste management plan
- Programme of the demolition process
Safety Measures during Demolition of Buildings
All the workforce will have a site induction and toolbox talk to discuss methods and environment
Fire and emergency plans are prepared and included within the health and safety induction.
As a matter, of course, measures are put in place to reduce and monitor, Dust, noise and vibration.
All the workforce wear full PPE. Occupational health checks are carried regularly for all demolition workers.
Demolition Methods
There are two types of Demolition employed for buildings and structures
a) Non-explosive or controlled demolition
b) Explosive Demolition.
1. Non-Explosive
The Demolition of the building using hand tools and machinery. It encompasses robotic Demolition using electric excavators operated from a distance.
The types of Demolition within this category are
Soft Strip
Demolition using standard or high reach excavators
Top-Down Demolition
Deconstruction
Dismantling
a) Soft strip
Usually after, or in conjunction with asbestos removal the building has floor coverings, suspended ceilings, partitions, doors, air conditioning, heating and lifts removed before the building demolition.
Work is predominantly using hand tools, and the materials are removed from the building using waste chutes, lifts or walked out manually to waste bins.
b) Standard and High Reach Demolition
Standard and High Reach Excavators are the conventional method of Demolition used of buildings. The height of the building dictates which type of machine is selected. Semi/High reach machines are used generally for buildings over three storeys. Once Demolition reaches the lower levels, the standard excavators will take over.
All excavators have an array of low noise generating attachments including
- Shears
- Crackers
- Breakers
c) Top Town Demolition
A method commonly used on Tower Blocks where the space around the building is listed. The building is scaffolded on all sides and covered in monarflex, which helps reduce Dust. The building will be checked structurally before this method
Small excavators and skids steers (Bob Cats) are lifted onto the roof by cranes. Openings made in the roof allow the construction of ramps. These allow excavators to go down onto the floor below. The excavators will then remove the roof working from below and above under controlled conditions.
The same process follows on for each floor and with waste materials removed using waste chutes, lift shafts or materials craned away in skips.
See our project at Carlton House.
d) Deconstruction
Deconstruction is the prefered method on Panel System Buildings. In the 1950s and 60’s many Council, Tower blocks constructed using large concrete panels lifted into place by cranes.
In the early sixties, Ronan Point collapsed due to a gas explosion which resulted in the buildings undergoing modifications to strengthen.
Deconstruction takes place using a crane. The panels are removed from the building in the reverse order of construction. However, the building has to undergo propping to avoid its collapse while the work is taking place.
As with top-down Demolition, scaffolding encapsulates the building and machinery lifted onto the roof.
Where space allows the Demolition can take place using high reach machines.
d) Dismantling
This process to remove old machinery and equipment before the primary Demolition takes place. Machinery is dismantled or cut into pieces.
2. Explosive Demolition
Implosion Method
Implosion is the Demolition of a building by explosives. With the removal of the foundations, the structure will collapse. This method is used mainly for large factories and power stations. Most Demolition in Towns and Cities is carried out by conventional means.
This method involves the main supports of a building, including column’s, beams and slab fixed with explosives. Once the explosives detonate, the building will collapse.
Depending on how the structure falls, there are two types of implosion:
a) Falling like a tree
The implosion makes the building fall like a tree sideways and is the most common method of implosion. Where the building has sufficient area around it available besides the building, this type of Demolition is preferred.
If there is free space available on the left side of the building the explosives are placed on the lower level of the building on the left-hand-side columns. As the explosives detonate, the columns bursts and the building will fall towards the left-hand side. Cables are tied to the building and control the direction of the fall.
b) Falling into its footprint
When there is limited space around the building, this type of Demolition selected. Explosives are placed into the floor below the middle part of the building.
These explosives are substantial as the explosion must demolish the building at once. It is a series of blasts, one followed by another. Then the building falls towards the first blasted part.
When the charges detonate, the upper part of building implodes and falls onto the lower building. The heavy load and force the lower part of the building also collapses and falls on its footprint.
Demolition Insights – Link
https://en.wikipedia.org/wiki/Demolition
