DEMOLITION OF BUILDINGS
DEMOLITION OF BUILDINGS
25.1.1. Dismantling - The term “dismantling” implies carefully taking up or down and removing the building materials without damaging them. The articles dismantled shall be lowered to the ground and not thrown. Dismantling work shall cover complete removal of the existing structure or part of a work including all relevant items as indicated or as directed, clearing the site, sorting out useful materials and stacking them as described, and disposing of the unserviceable materials.
25.1.2. Demolition - The term “demolition” implies breaking up the components of the structure building and then taking the components up or down. This shall consists of demolishing whole or part of work including all relevant items as indicated or as directed, clearing the site, sorting our useful materials and stacking them as directed and disposing of the unserviceable materials and rubbish as directed. The removal of overlaying or adjacent materials, if required for demolition of the structure shall be separately indicated.
Unless otherwise specified, the building/structure shall be dismantled/ demolished up to 450 mm below ground level.
25.1.3. Serviceable and unserviceable materials
Inventory- Before dismantling/demolition operations are undertaken by the contractor, inventory of all materials, fittings and fixtures (except hidden materials) which are considered useful shall be made and signed by the engineer and the contractor, wherever the operations are entrusted to a contractor.
Serviceable materials - Any material which is in the opinion of the engineer could be refused or otherwise useful will be considered as serviceable.
Unserviceable materials - Any material declared by the engineer are not serviceable shall be considered as unserviceable.
A register shall be opened at the work site to show day-to-day account of the turn out of salvaged materials. The register shall also indicate whether dismantled materials are properly stacked or wasted.
The contractor shall be reasonable for the safe custody of serviceable materials until handed over to the engineer’s representative or incorporated in the work and a written receipt for the same obtained.
25.2. Hazards in demolition.
Demolition of any structure is, inherently, more hazardous than the construction or erection of the same. From the point of view of safety, the conditions usually encountered while dismantling a structure, whatever its magnitude, do not lend themselves to the degree of control possible in the construction operations, where more stable conditions are generally obtainable. It is all the more imperative; therefore, that adequate attention is paid to planning and execution of demolition work, in its various stages, so as to minimize the risk of accidents and injuries to the personnel engaged in demolition operations.
25.2.1. It has therefore become necessary to lay down certain safety procedures, which along with a planned programmer could ensure adequate safety, particularly with the involvement of management, supervisors and workers.
25.2.2. The demolition work shall be preceded in such a way that:
- It causes least damage and nuisance to the adjoining building and the members of the public ; and
- It satisfies all safety requirements to avoid accidents.
25.2.3. Section 1 deals with all aspects on construction planning, management and safety and this section will therefore confine itself to procedures and safety precautions for demolition and dismantling of buildings.
Before beginning the actual work of demolition, a careful study shall be made of the structure, which is to be pulled down and also of its surroundings. This shall include the following: -
The manner in which the various parts of buildings are supported and how far the stage by stage demolition would affect the safety of the adjoining structure;
A definite plan and procedure of demolition work shall be prepared, taking into account the loads on various structural parts and their supports ;
Before commencement of each stage of demolition, the supervisor shall brief the workmen in detail regarding the safety aspects to be kept in view ;
Ensure that the demolition conditions do not, at any stage, enhance the nuisance value of demolition work on the use of adjacent buildings ;
No structure or part of the structure or any floor or temporary support or scaffold, side wall or any device for equipment shall be loaded in excess of the safe load bearing capacity, in its then existing condition ; and
Stairs and stair railings, passage ways and ladders shall be left in place as long as possible. These should be maintained in a safe condition.
25.4. Precautions and protective measures before starting demolition work
25.4.1 The following precautions and protective measures shall be taken before commencement of demolition work:
On every demolition job, danger signals shall be conspicuously posted all around the structure and all doors, openings giving access to structures shall be kept barricaded or manned except during the actual passage of workmen or equipment. However provision shall be made for at least two independent exits for escape of workmen during any emergency.
Walkways and passageways shall be provided for the use of the workmen who shall be instructed to use them and all such walkways and passageways shall be kept adequately lighted, free from all debris and other materials.
Where in any work of demolition it is imperative, because of existing danger, to ensure that no unauthorized person shall enter the site of demolition outside working hours, a watchman shall be employed. In addition to watching the site he shall also be responsible for maintaining all signs, notices, lights, barricades, etc. During nights, red lights shall be placed on or about the barricades.
The power on all electrical service lines shall be shutoff and all such lines cut or disconnected at or outside the property line. The only exception would be any power lines required for the demolition work itself. Prior to cutting of such lines, the necessary approval of the Authority shall be obtained.
All mains and meters of the building shall be removed or protected from damage.
All gas, water, steam and other service lines shall be shutoff and capped or otherwise controlled at or outside the property line.
If a structure to be demolished has been partially wrecked by fire, explosion or other catastrophe, the walls and damaged roofs shall be shored and braced suitably.
Construction sheds and toolboxes should be so located as to protect workers from injuries of falling objects, wall, etc.
A warning device should be installed in the area to be used to warn the workers, in case of danger.
Screens shall be placed, where necessary, to prevent flying pieces from injuring the fellow workmen.
No demolition work shall be carried out during storm or heavy rain.
No demolition work shall be carried out at night specially when the building or structure to be demolished in an inhabited area.
All necessary safety appliances shall be issued to the workmen and their use explained. It shall be ensured that the workers are using all the safety appliances while at work. The safety appliances should be as follows:
- Safety helmets as per IS: 2925-1984 ;
- Goggles made of celluloid lens to be worn at the time of demolition of floors, walls, tearing of plaster, etc., specially when equipment like jack hammers are used for demolition work, to protect the eyes from flying pieces, dust, dirt, etc. that may be blown up by wind.
- Leather or rubber gloves worn during demolition of RCC work or removing steel work, where the hands of workers are likely to be injured.
- Safety belts while working at higher level to prevent falling from the structure.
First-aid equipment shall be available at all demolition works of any magnitude. Also, by prior arrangement, a qualified doctor is available at call.
When there is a possibility of fire breaking out, appropriate portable first-aid fire appliances (see IS: 2190-1992) shall be kept at hand.
The removal of a member may weaken the side wall of an adjoining structure and to prevent possible damage, these walls shall be supported until such time as permanent protection is provided. In case of any danger is anticipated to the adjoining structure, the same shall be got vacated to avoid any danger to human life.
Ladders, when used, shall conform to IS: 3696 (Part 2)-1991. Ladders or their side rails shall extend not less than 1.0 m above the floor or platform to which the ladder gives access. All ladders shall be secured against slipping out at the bottom and against movement in any direction at the top.
All exterior wall openings which extend down to the floor level shall be barricaded to a height not less than 1 m above the floor level. All floor openings and shafts not meant as material chutes shall be floored over and endorsed with ground rails and toe boards.
All existing fixtures/services required during demolition operations shall be well protected with substantial covering to the satisfaction of the Authority.
When demolition is to be done by mechanical means such as weight ball and power showers, the following additional precautions are necessary:
- The area shall be barricaded for a minimum distance of 1 ½ times the height of the wall ;
- While the mechanical device is in operation no workmen shall be allowed to enter the building being demolished ;
- The device shall be so located as to avoid falling debris; and
- The device when being used shall not cause any damage to adjacent structure, power line, other services, etc.
25.5. Protection of the public
25.5.1 Protection of the public before and during demolition is important and the following points should be kept in mind;
Every sidewalk or road adjacent to the work shall be closed or protected. All main roads, which are open to the public, shall be kept open to the public clear and unobstructed at all times.
Children and public shall be kept out of the building and the adjoining yards.
If the structure to be demolished is more than two-storied or 7.5 m high, measured from the sidewalk or street which cannot be closed or safely diverted, and the horizontal distance from the inside edge of the side walk to the structure is 4.5 m or less, a substantial side walk shed (see Fig. 1) shall be constructed over the entire length of the sidewalk adjacent to the structure of sufficient width with a view to accommodating the pedestrian traffic without causing congestion. The sidewalk shall be lighted sufficiently to ensure safety at all times.
A toe board at least 1 m high above the roof the shed shall be provided on the outside edge and ends of the sidewalk shed. Such boards may be vertical or inclined outward at not more than 45 degree.
Fig 1 Typical sketch of sidewalk shed
Except where the roof of a side walk shed solidly abuts the structure, the face of the sidewalk shed towards the building shall be completely closed by providing sheeting / planking to prevent falling material penetrating into the shed.
The roof of the sidewalk shed shall be capable of sustaining a load of 730 kg/m2. Only in exceptional cases, say due to lack of other space, the storing of the material on a sidewalk shed may be permitted in which case the shed shall be designed for a load of 1 460 kg/m2. Roof of sidewalk shed shall be designed taking into account the impact of the falling debris. By frequent removal of loads it shall be ensured that the maximum load, at any time, on the roof of the shed is not more than 600 kg/m2. The height of the sidewalk shed shall be such as to give minimum clearance of 2.4 m.
Sidewalk shed openings, for loading purposes, shall be kept closed at all times except during actual loading operations.
The deck flooring of the sidewalk shed shall consist of plank of not less than 50 mm thickness closely laid and deck made watertight.
All members of the shed shall be adequately braced and connected to resist displacement of members or distortion of framework.
When the horizontal distance from the inside edge of the sidewalk to the structure is more than 4.5 m and less than 7.5 m, a sidewalk shed or fence may be built or in their place a substantial railing shall be constructed on the inside of the sidewalk or roadway along the entire length of demolition side of the property with movable bars as may be necessary for the proper prosecution of the work.
Where workers entrances to the building being demolished are not completely protected by sidewalk sheds, all such entrances shall be protected by canopies extending from the face of the building to a point not less than 2.5 m from it. In such a case, overhead projection shall be at least 0.6m wider than the building entrance or opening and every canopy shall be as strong as the sidewalk shed.
25.6. Sequence of demolition operations
The sequence of demolition shall generally be as given below:
(1). The demolition shall always proceed systematically storey by storey in descending order and the demolition of upper floors shall be completely over before any of the supporting members or other important portion on the lower floor is disturbed. No unnecessary work shall go on below when the demolition is in progress above. When some work is to be done at the lower level, adequate protection shall be provided for all the workmen so engaged.
(2). The requirements of (a) shall not prohibit the demolition of structures by sections, if means are taken to prevent injuries to persons or damage to property.
(3). Roofs (or floors), generally, be demolished first before demolishing the supporting walls structural elements.
(4). All glazed sash, glazed doors and windows etc., shall be removed before the demolition of roofs and walls starts. All fragile and loose fixtures shall be removed. Lath and loose plaster be stripped off throughout the entire structure. This is advantageous because it reduces glass breakage and also eliminates a large amount of dust producing material before more substantial parts of the building are removed.
25.7. Demolition of floors
For demolition of floors the following procedure may be followed:
(1). A slit in width not exceeding 300 mm shall be cut at the first stage for the entire length of the slab along which it spans (see Fig. 2). The opening shall thereafter be increased to the desired width by suitable installments.
Fig 2 Demolition of reinforced concrete floors
(2) Planks of sufficient strength not less than 50 mm thick and 250 mm wide shall be provided at a spacing not greater than 0.4 m. These planks shall be so placed as to give workmen firm support to guard against any unexpected collapse.
(3) Stringers of ample strength shall be installed to support the planks where necessary and the ends of stringers shall be supported by floor beams, girders and not by floor slab alone.
(4). When floors are being removed, no workmen shall be allowed to work in the area, directly underneath and such area shall be barricaded to prevent access to it.
(5) The demolition of the floor in question shall be started only after the surrounding area for a distance of 6 m have been entirely cleared of persons, and the debris and other unnecessary material removed.
(6) Planks used for temporary protection shall be sound and at least 50 mm thick. They shall be laid close together with ends overlapping at least 100 mm over solid bearing to prevent tipping under load.
25.8. Demolition of walls
The following procedure shall be followed when demolishing walls:
(1) While walls or sections of masonry are being demolished it shall be ensured that they are not allowed to fall as a single mass on the floors of the building so as not to exceed the safe carrying capacity of the floor; wherever practicable, they may fall away from the floors on to catch platforms. Overloading of floors shall be prevented by removing the accumulating debris through chutes or by other means immediately. The floor shall be inspected by the Authority before undertaking demolition work and if the same is found incapable of carrying the load of debris, necessary precautions shall be taken to prevent any unexpected collapse of the floor.
(2) Walls shall be removed part by part. Stages shall be provided for the men to work on, if the walls are very thin and dangerous to work by standing over them.
(3) No section of the wall whose height is more than 15 times the thickness, shall be permitted to stand without lateral bracing unless such a wall is in good condition and was originally designed to stand without such lateral bracing or support.
(4) Structural or load supporting members on any floor shall not be removed or cut until all the storeys above that floor have been demolished and removed.
(5) Before demolishing any interior or exterior wall within 3 m of the opening in the floor immediately below, such opening shall be substantially planked over, unless access is denied to workmen to that portion of the floor immediately below the opening, in the floor of the storey being demolished, where any debris passing through the opening may fall.
(6) In framed structures, the frame may be left in position during demolition of masonry work. Where this is done all beams, girders, etc., shall be cleared of all loose materials as the demolition of masonry work progresses downward provided it is still strong enough to stand as an independent structure.
(7) Walkways shall be provided to enable workmen to reach or leave their work on any scaffold or wall. Such walkways shall neither be less than 3 planks wide, nor less than 0.8 m in width.
(8) After completion of each days work, all walls shall be left stable to avoid any danger of getting overturned.
(9) Foundation walls which serve as retaining walls to support the earth or adjoining structure, shall not be demolished until such an adjoining structure has been under pinned or braced and the earth removed by sheet piling or sheathing.
25.8.2. Catch platforms
Catch platforms shall be provided in case of demolition of exterior walls in multi-storey buildings. The following details may be considered:
(1) Catch platforms shall generally be provided for multi-storeyed buildings more than 20 m high to prevent injuries to the worker and to the public when exterior walls are being demolished.
(2) Such platforms shall be constructed and maintained not more than three storeys below the storey from which the exterior wall is being demolished. When demolition has progressed to within three storeys of ground level, catch platforms will not be considered necessary.
(3) Catch platforms shall not be less than 1.5 m in width measured in a horizontal direction from the face of the structure and shall consist of outriggers supported not more than 3 m apart. Planks shall be laid tight together, without openings between them and the walls. Catch platforms shall be provided with a continuous solid parapet along its outer edge of at least 1 m height. The parapet may be constructed with the same material as the platform.
(4) Catch platform shall be capable of sustaining a live load of not less than 610 kg/m2.
(5) Catch platforms shall neither be used for storing of materials nor dumping of materials.
25.9. Demolition of different types of structures and elements
Structures may be dealt with as masonry, concrete, steel and timber. The structures or their elements shall be dealt with as below, in addition to other requirements as applicable.
25.9.2. Masonry structures
18.104.22.168. Jack Arches – Where tie rods are present between main supporting beams, these should not be cut until after the arch or series of arches in the floor have been removed. Particular care should be exercised and full examination of structure be made before the demolition is commenced (see Fig 3). The floor should be demolished in strips parallel to the span of arch rings (at right angles to the main floor beam).
Fig 3 Demolition of Jack Arches
22.214.171.124. Brick Arches - As much dead load as possible may be removed provided it does not interfere with stability of main arch rings ; it should be noted that the load carrying capacity of many old arches relies on the filling between the spandrels. On no account should the restraining influence of the abutments be removed before the dead load of the spandrel fill and the arch rings are removed. The normal sequence of demolition shown in Fig. 4 A includes the following:
- remove the spandrel filling down to the springing line,
- remove the arch rings,
- Remove the abutments.
- Special temporary support shall be provided in the case of skew bridges.
A single span arch can be demolished, by hand, by cutting narrow segments progressively from each springing parallel to the span of the arch, until the width of the arch has been reduced to a minimum which can then collapse (see Fig. 4 B). Where it is impossible to allow debris to fall to the ground below, centering designed to carry the load should be erected and the arch demolished progressively. The design of the centering should make appropriate allowance for impact.
Where deliberate collapse is feasible the crown may be broken by the demolition ball method working progressively from the edges to the centre (see Fig 4 C).
Collapse of structure can be affected in one action by the use of explosives. Charges should be inserted into bore holes drilled in both arch and abutments. This method is the most effective for demolition of tall viaducts.
In multi-spun arches, before individual spans are removed, lateral restraint should be provided at the springing level. Demolition may be proceeded as for a single span care being taken to demolish the spandrels down to the springing line as the work proceeds (see Fig. 4 D). Where explosives are used it is preferable to ensure the collapse of the whole structure in one operation to obviate the chance of leaving unstable portions standing.
25.9.3. Reinforced concrete
Before commencing demolition, the condition and position of reinforcement and possibility of lack of its continuity should be ascertained. Demolition should be commenced by removing partitions, non-load bearing cladding, etc. and similar non-structural elements.
a) Where hand demolition methods are used, the following procedures should be used :
Fig 4 Demolition of masonry and brick arches
- Beams – For beams supporting rope should be attached to the beam. Then the concrete should be removed from both ends by pneumatic drill and the reinforcement exposed. The reinforcement should then be cut in which a way as to allow the beam to be lowered under control to the floor (see Fig. 5 A).
- Columns – For columns reinforcement should be exposed at the base after restraining wire guy ropes have been placed around the member at the top. The reinforcement should then be cut in such a way as to allow the column be pulled down to the floor under control (see Fig. 5 B).
- Walls – Reinforced concrete walls should be cut into strips and demolished as for columns (see Fig. 5 C).
- Suspended floors and roofs – Solid slabs should be demolished as described in Fig. 2. Where ribbed construction is used, the principle of design and method of construction should be ascertained before demolition. Care should be taken not to cut the ribs inadvertently.
Fig 5 Hand demolition of in-situ concrete structure
25.9.4. Precast reinforced concrete
Precast reinforced concrete units in a structure are normally held in position by the strength of the joints in-situ or on supporting walls, etc. As such before starting on demolition the joint structures or the supporting mechanisms shall be studied and understood.
In devising the following demolition sequences, due precaution shall be taken to avoid toppling over of the prefabricated units or any other part of the structure and wherever necessary temporary supports shall be provided.
25.9.5. Prestressed concrete
Before commencing of the demolition work involving such structures advice of an expert engineer should be obtained.
No beams shall be cut until precautions have been taking to prevent it from swinging freely and possibly striking any worker or equipment or any part of the structure being demolished.
All structural steel members shall be lowered from the building and shall not be allowed to drop.
Tag lines shall be used on all materials being lowered or hoisted up and a standard signal system shall be used and workmen instructed on the signals. No person shall be permitted to ride the load line.
When a derrick or hoisting equipment is used care shall be taken to see that the floor on which it is supported shall be strong enough for the loading. If necessary heavy planking shall be used to distribute the load to floor beams and girders. Overloading / overturning of the equipment shall be avoided.
25.9.7. Other elements
126.96.36.199. Roof trusses – Roof trusses shall be removed to wall plate level by hand methods. Sufficient purling and bracing should be retained to ensure stability of the remaining roof trusses while each individual truss is removed. Temporary bracing should be added, where necessary, to minimize instability. The end frame opposite to the end where dismantling is commenced, or a convenient intermediate frame should be independently and securely guyed in both directions before work starts. On no account should the bottom tie of a truss be cut until the principal rafters are prevented from making outward movement.
188.8.131.52. Cantilevers – A cantilever type of construction depends on the balancing superimposed structure for its stability. Canopies, cornices, staircases, balconies should be demolished or supported before the balancing load is removed.
184.108.40.206. Heavy floor beams – Heavy bulks of timber should be supported before cutting at the extremities and should then be lowered to a safe working place.
25.10. Removal of materials
Removal of dismantled materials should be done carefully; they may be thrown/lowered to the ground. The materials shall preferably be dumped inside the building. Normally such materials shall be lowered to the ground or to the top of the sidewalk shed where provided by means of ropes or suitable tackles.
25.10.2. Through chutes
Wooden or metal shall be provided for removal of materials. The chutes shall preferably be provided at the centre of the building for efficient disposal of debris.
Chutes if provided at an angle of more than 45 degree from the horizontal shall be entirely enclosed on all sides, except for opening at or about the floor level for receiving materials.
Opening for chutes shall not exceed 1.20 m in height measured along the wall of the chute and in all story’s below the top floor such opening shall be kept closed when not in use.
To prevent the descending material attaining a dangerous speed, the chute shall not extend in an unbroken line for more than two storeys. A gate or step shall be provided with suitable means of closing at the bottom of each chute to stop the flow of materials.
Chutes at an angle less than 45 degree to the horizontal may be left open on the upper side provided that at the point where such chute discharges into the chute steeper than 45 degree to the horizontal, the top of the steeper chute shall be boarded over to prevent the escape of materials.
Any opening into which workmen dump debris at the top of the chute shall be guarded by a substantial guard rail extending at least 1 m above the level of the floor or other surface on which men stand to dump the materials into the chute.
A toe board or bumper not less than 50 mm thick and 150 mm high shall be provided at each chute opening, if the required material is dumped from the wheel barrows. Any space between the chute and the edge of the opening in the floor through which it passes shall be solidly planked over.
25.10.3. Through openings
Debris may also be dropped through holes in the floor without the use of chutes. In such a case the total area of the hole cut in the intermediate floor, one which lies between floor that is being demolished and the storage floor shall not exceed 25 per cent of such floor area. It shall be ensured that the storage floor is of adequate strength to withstand the impact of the falling material.
Openings in all floors below the floor from which materials are being removed, shall be protected by standard railings and toe boards (see IS 4912: 1978) or preferably planked over if the holes are not being used for dumping materials.
All intermediate floor openings for passage of materials shall be completely closed with barricades or guard rails not less than 1 m high and at a distance of not less than 1 m from the edge of the general opening. No barricades or guard rails shall be removed until the storey immediately above has been demolished down to the floor line and all debris cleared from the floor.
When cutting a hole in an intermediate floor, between the storage floor and the floor which is being demolished, makes the intermediate floor or any portion of it unsafe, then such intermediate floor shall be properly shored. It shall also be ensured that the supporting walls are not kept without adequate lateral restraints.
Other Indian Standards on the subject of safety of workers, in addition to the handbook under preparation are as follows:
3696 (Part 1)-1987
Safety code of scaffolds and ladders Part 1 Scaffolds
4014 (Part 2)-1967
Code of practice for steel tubular scaffolding ; Part 2 Safety regulations for scaffolding
Code of safety for excavation work (first revision)
Safety code for handling and storage of building materials.
Code of safety for protective barriers in and around buildings.
13416 (Part 1)-1992
Recommendations for preventive measures against hazards at workplaces; Part 1 Falling material hazards prevention.
13416 (Part 2)-1982
Recommendations for preventive measures against hazards at work places ; Part 2 Fall prevention.
13430 : 1992
Code of practice for safety during additional construction and alteration to existing buildings.
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