6. Demolition Lecture 11.ppt - CEng 6108 Building Industrialization and Maintenance DEMOLITION Addis Ababa University AAiT School of Civil and

6. Demolition Lecture 11.ppt - CEng 6108 Building...

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Unformatted text preview: CEng 6108 Building Industrialization and Maintenance DEMOLITION Addis Ababa University AAiT School of Civil and Environmental Engineering Abebe Dinku, Prof. (Dr.-Ing.) May 2016 Demolition and Dismantling The importance of demolition and dismantling industry within the building and civil industry cannot be overemphasized, but sadly is all too often overlooked. It is important to refer to the demolition and dismantling industry and not demolition in isolation as there are clear and distinct differences. Demolition Demolition means to destroy or knock to pieces. This means that the components cannot be used again in their present form. The word dismantle means to take pieces carefully so that they can be used again. Demolition is one of the more dangerous sections of the construction industry, and yet that fact is the one to which the least taught is given when planning a project. Demolition (contd.) Demolition and dismantling are important construction business sector, mainly in the developed World. The Second World War and major destruction of large areas of urban development in the large cities promoted the growth of the industry. The National Federation of Demolition Contractors in the UK was established in 1941. Demolition (Contd.) The European Demolition Association was founded in 1976. Associations ensures that the client can be safe in the knowledge that the work will be carried out in a safe, efficient and economical manner by fully trained employees who are supervised by experts, using the most up-to-date methods and techniques of demolition Planning and statutory requirements The client and the professional The contractor Parties in demolition industry The Contractor Institute of demolition engineers Clients Other stakeholders: like insurance companies, financiers, and the public Tender procedure – Required information 10 Common Misconceptions about the Demolition Industr Misconception 1 Demolition contractors primarily implode, or "blow up" buildings. Fact Implosions account for less than 1 percent of all demolition work. 2 Demolition contractors destroy Demolition contractors are instrumental in many structures thatthe should be Industry achieving the goals of preservationists. 10 Common Misconceptions about Demolition saved. 3 Demolition contractors don't participate in the nation's recycling effort. The demolition industry was salvaging building elements and materials for reuse long before it was the "ecological thing to do." 4 Demolition contractors unnecessarily overcrowd landfills with debris. The industry is reducing its use of landfills in favor of recycling. 5 Demolition is an unsophisticated business. A safe and successful demolition project requires a working knowledge of both construction and the law. 6 The methods of demolition never change. Demolition practices today are not only quicker, but safer and more cost-effective. 7 One demolition contractor is basically the same as the next. Don’t tell that to the owner who has had the misfortune of dealing with an inexperienced contractor. 8 Demolition is dangerous business. In the hands of professionals, the danger is controlled. 9 Demolition is expensive. Commercial demolition work generally costs less than 2 percent of the replacement Planning before demolition The type of ground the structure erected Condition of roof truss Walls Staircases, balconies, cornices Prestressed concrete and multi storey structures Basements, cellars Wells and springs Planning before demolition (contd.) Storage tanks Structures known to be dangerous Lightning conductors Original plans Signs of bench mark Street closures or traffic diversions Planning before demolition (contd.) Public services: – Check where to locate drains, electricity, gas, water, telephone, etc. – Arrangements should be made for diversion, removal or where they have to remain, for protection, and for any pipes connected to foul sewers to be sealed off – A temporary water supply will often be needed so that spraying, to keep down dust can take place Planning before demolition (contd.) Statutory requirements: – The client should notify the local authority – Where demolition work could affect other property, the owner of the building must notify the other owners so that full agreement can be reached on matters of support, protection, disturbance, etc. Planning before demolition (contd.) On site general precautions: – Hoardings should be erected around the site with a minimum height of 2.5m – Windows should be taken out before work starts to avoid damage by broken glass. Window frames should be left in to help maintain wall strength. Planning before demolition (contd.) – Windows, doors and other openings should be boarded – Internal lift entrances should be boarded – Access to all areas where flooring has been removed should be barred with at least one board to indicate danger Planning before demolition (contd.) – Stone balconies and stone cantilever projections should be cut off before the main demolition starts – All external metal staircases or ladders should be carefully inspected before use – Once disturbed, stone staircases should not be used at all since they can no longer be regarded as safe access Planning before demolition (contd.) – Staircases should be kept free from debris – Timber, taken out during demolition work, should have any projecting nails and screws flattened or removed – Check personnel protection: safety boots, helmets, goggles, safety belts, …etc Planning before demolition (contd.) – Strict control should be exercised over the burning of rubbish since flames fanned by a breeze can easily get out of hand – Explosives must be properly stored – etc. Starting the work of demolition The contractor can now proceed to start the work of demolition The type of structure to be demolished will determine the method which is adopted Normal order of demolition/dismantling: – Any material value is removed, – stripping and removal of internal fixtures and fittings, Starting the work of demolition (contd.) – roof covering, – roof timbers, – Superstructure Demolition contractor has to complete his work on time to avoid monetary penalty Code of practices on Demolition Codes of practices give recommendations on best practices. They include, among others: – Insurance requirements – Statutory notices – Safety and convenience of third parties – Supervision – Excavation, – Etc. Demolition Management Building demolition management involves planning, design and implementation, Deals with its unique issues, such as decisionmaking on alternatives to conventional building demolition, and the handling and disposal of demolition waste. Building demolition promotion strategies Planning For Demolition The key to the safe and efficient demolition of a structure is planning. The safest method of demolition is that which proceeds in the reverse order to construction. Demolition workers must constantly assess the strength, stability and weak points of partially demolished structures The Work-plan Of Demolishing Should Include the following: Technique and method of demolition to be adopted. Sequence of work operations. Estimate of time to complete each stage. Plant and equipment to be used, Method of moving plant around the site Proposed access and egress to demolition site Precise details of any pre-weakening of the structure, Nature, extent and location of public protection required, barricades, scaffolding, nets, gantries and signage. Type and location of bracing and shoring to be used, for temporary support and retaining of ground. Arrangements for isolation/disconnection of services. (Some services may need to continue to supply the worksite, e.g., water and temporary power supply.) Demolition Techniques Various types of demolition techniques are available in the demolition industry The most common techniques used for demolition of structures are Hand demolition and Hand-held percussion tools Demolition by pusher arm Demolition by wire rope pulling Ball and crane Diamond sawing and cutting Hydraulic Pusher Arm Hydro demolition Blasting Bursting Machine-mounted pneumatic and hydraulic breaker – – – – – – – – – – – – – – Criteria For Selection Of Demolition Techniques Client specification; Location and accessibility; Shape and size of the structure; Stability of the structure; Presence of hazardous material; Time constraints; Degree of confinement; Transportation consideration; Extent of demolition; Structural engineers’ approval; Financial constraint; Recycling considerations; Environmental considerations; and Health and safety. Plant And Equipment Used In Demolition – During the planning process, the number and types of plant and equipment to be used should be determined and documented in the work plan. – The type of plant and equipment will be determined by the method of demolition adopted. – Plant and equipment used on demolition sites must be used and maintained in accordance with the manufacturers’ recommendations and only operated by appropriately competent persons Some Of The Common Types Of Plant Used On Demolition Sites include: Excavators; Cranes; Bulldozers; Front end loaders; Trucks; Jackhammers; Non powered hand-tools (E.G. Hammers, sledge hammers, picks and shovels); Powered hand-tools Demolition Techniques for conventional structures Hand demolition – It is normally carried out by operators using manually operated or portable tools such as shovels, pneumatic hammers, drills etc. Crane and lifting appliances are often used to supplement and provide a means to support and lower structural numbers while they are being cut and lower to the ground. – Whenever practicable, all demolition material should be lowered to the ground by means of properly constructed chute. Access to partially demolished areas should be prevented at all times when work is not taking place for the sake of safety. Hand demolition (contd.) – Debris should only be allowed to fall freely where the horizontal distance from the point of fall to the public high way or an adjoining property is greater than 6.0 m or half the height from which the debris is dropped whichever is greater. In all other cases a chute or skip should be used. – Hand demolition is used on restricted sites, is labor intensive and tends to be slow and laborious. Hand demolition Powered hand-tools Demolition Techniques for conventional structures (contd.) Demolition ball – A method of progressive demolition carried out by swinging a weight or demolition ball, suspended from a lifting appliance such as crane; against the fabric of the structure. Three techniques can be used. Vertical drop Swinging in line with the jib Slewing Demolition ball (contd.) – Whichever method is used a skilled operator is essential. Demolition ball techniques should not be used on buildings over 30m high since the fall of debris is uncontrollable. Attached buildings should be separated from the adjoining structure by hand demolition to leave a space of at least 6.0m or half the height of the building whichever is greater. This method is highly dangerous unless a very experienced crane operator is used. – Not recommended when the retention of components is essential. Slow and laborious when used on reinforced concrete. Demotion ball kicking a wall Demolition ball Demolition Techniques for conventional structures (contd.) Pusher arm demolition – A method of progressive demolition using a machine fitted with a steel pusher arm exerting a horizontal trust on to the building fabric. The height of the building should be reduced by hand demolition if necessary to ensure that the height above the pusher arm doesn’t exceed 1.0m. – Where these method of demolition is adopted in connection with attached buildings, the structure to be demolished should first be detached from the adjoining structure by hand demolition. Demolition by pusher arm Demolition by high reach arm Demolition Techniques for conventional structures (contd.) Deliberate collapse – This is the removal of key structural members causing complete collapse of the whole or part of the building. – Expert engineering advice should be obtained before this method is used. – It should only be used on detached isolated buildings on reasonably level sites so that the safety to personnel and equipment can be carefully controlled. Deliberate collapse Demolition Techniques for conventional structures (contd.) Pulling by wire ropes – Only steel wire ropes should be used and the size should be adequate for the purpose but in no case less than 38mm circumference or 25mm in diameter. – The rope should be firmly attached at both ends and the pulling tension gradually applied, and the pulling devices should be located at a distance not less than one and half time that of the structure being demolished. – A well –anchored winch or heavy vehicle should be used to apply the pulling force, greater care being taken to ensure that the winch or the vehicle does not lift off its mounting, wheels or tracks. – This method is another form of demolition by deliberate collapse. Demolition Techniques for conventional structures (contd.) Explosives – This is a specialist method where charges of explosives are placed with in the fabric of the structure and detonated to cause partial or complete collapse. – This technique should never be attempted with out the advice and supervision of competent explosive specialist. – There are numerous types of explosives available, and the explosive operator should have a certificate of competence in the use of explosives for demolition and civil engineering works. Demolition by blasting Demolition by blasting Demolition Techniques for conventional structures (contd.) There are important points about explosives the operator should know:– Laws related to storage of explosives – Laws related to conveyance of explosives – Characteristics of the explosives – Simple electrical terms, electrical circuits and their functions, how to avoid short – circuits – Safe methods of handling explosive Demolition Techniques for conventional structures (contd.) – Simple electrical term, electrical circuits and their functions, how to avoid short, circuits – Safe methods of handling explosives – Safety of other persons on site and the public – Knowledge of the effects of explosive – How to drill holes for explosives – procedures to be adopted in an emergency ,etc Demolition Techniques for conventional structures (contd.) Demolition by explosives differs from most other types of blasting in as much as one rarely has a second chance to experiment. As in most cases, it is a once only situation. The hazard caused by an incorrectly positioned charge can have disastrous effects and leave a structure in an unsafe condition. Demolition by explosives (contd.) There are two obvious advantages of this type of demolition. Speedy removal of the structure and safety of other operators in as much as no one need be in the immediate area of demolition and the work can then be carried out by remote control from a safe distance. The disadvantage of this type of demolition is three fold. First, the storage of explosives on site when these could be stolen or tampered with; secondly, when used the damage caused by flying debris; third, the danger to other buildings caused by blast where the effects of air borne of ground –transmitted shock wave can be underestimated. Demolition Techniques for tensioned structures Strict planning of tensioned structures demolition work is essential If done improperly, building of tensioned structures would react like a bomb and explode with missiles flying in all directions could possibly having fatal effect. The problem facing demolition contractors is how to unstress the building prior demolition Structural engineers should be consulted Demolition Techniques for industrial structures Basically follows similar procedure as others Care should be taken to avoid possible hidden hazards that could cause serious injury or death as a result of toxic material and liquid being present (asbestos, chemicals, ….) Demolition Techniques for radio active structures A special focus is required in demolition of nuclear facilities when the time comes to withdraw them permanently from operational services. The main problem will be to ensure that sufficient trained operators are available when the time comes to commence the work. The other unique problem associated with such project are, removal of the nuclear radio active material and the equipment necessary, which needs further study in the future. Plants and equipment used for demolition The demolition industry has demanded for more sophisticated plant and equipment. When we are always dealing with equipment in demolition industry, we should ensure the following facts. – The machine must only be used for the purpose for which it is designed and manufactured. – The machine should be properly maintained. – The operator should be properly trained to operate the machine. – The machine should be tested and certified at proper intervals by a suitably qualified independent person. Plants and equipment used for demolition (contd.) Use of scaffolds in Demolition Scaffolds are temporary structures used also in demolition work as important as in the construction works, and it must be erected correctly and in compliance with the regulation to serve the intended purpose. The following major points should be studied when erecting scaffolds for demolition and construction as well: – The ground must be firm enough to carry the weight of the scaffold and the load the scaffold will carry. – Public foot paths and roadways must not be obstructed without a permit from the local authority, and there must be proper clearance. – Lights must be set up to warn people after dark of the presence of obstruction. Use of scaffolds in Demolition (contd.) – – – – – – All hoardings (fencing) must be sufficiently tied. Handrails and toe boards must be fitted to any platform or landing. Members on the scaffold should be property anchored and the base plates are firmly fixed. Any service near the proposed scaffold, underground or overhead, such as power lines, telephone wires, alarm system, should be checked. Any adjacent properties, public facilities such as bus, steps, should be studied. Scaffolds can be used to protect demolished material from falling to adjacent buildings or area, and underneath if they are properly constructed on working platforms and hoardings, and materials more than the reasonable limit should not be stored on the platforms. ENVIRONMENT AND DEMOLITION Environmental considerations are more important than ever to demolition projects Regulations relate to Vibrations – vibrations in the ground which disturb residents must be taken into account when preparing demolition projects Noise – Demolition work can involve substantial noise emissions. – It can disturb concentration and make speech communication difficult. – Long term exposure to excessive noise can cause permanent hearing damaged . – If the noise exposure exceeds the limit, suitable hearing protector would have to be worn Dusts – Most demolition jobs generate dust Safety requirements during demolition The following demolition safety check list should generally be employed for demolition work. A survey of the physical characteristics of the buildings should be mandatory and a written record of the survey should be kept available for inspection. – A duty should be laid on the client when inviting tenders for a contract to supply the contractor with all the information available to the client about potential hazards involving the property to be demolished. – A contractor should be under a duty not to start work until he has a certificate from the gas and electricity authorities that all known supplies have been cut off from the site except those required for the execution of the work. Safety requirements during demolition (contd.) – – – The department of the envi...
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  • Summer '19
  • Demolition, National Federation of Demolition, Institute of demolition, European Demolition Association, Demolition Industr

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