Note:Yesterday 3 workers hurt when the renovate building collapsed and hits the workers and luckly nobody died.
Continued from the last post
4.0(3).Cantilevered structure and balconies-The general sequence of dismantling cantilevered slabs and beams described the following:a).The exterior wall shall be demolished first.b).Any structure or dead load supported by the cantilevered system shall be removed prior to demolishing the cantilevered slabs and beams.c).The concrete shall be broken down gradually starting from the exterior edge of the cantilevered floor,working towards and toward its supporting beams,d).The cantilevered beams shall be demolished after demolition of the connecting floor slab.Demolition of the cantilevered beam shall be advance further than the floor slab so that the support for the slab is always maintained.
4.Exterior wall beams and columns-a).Brick wall-bricks removal shall begin from top layer downward.the work shall be carried out layer by layer with each layer not larger than 300 mm.b).The reinforced concrete framing can be dismantled by taking down the individual beams and columns separately as described below:c).Exterior beams-The exterior beams nay be demolished by gradually breaking away the concrete of by dismantling the entire beams section.i).Wire and winch or other systems shall be used to secure the cross beam to other structural members,ii).The concrete is first broken away at both ends near the column supports to expose the reinforcement.iii).Reinforcement shall be cut at one end to allow the beam to partially drop.the wire shall be safely which the beam down to the building floor in a controlled manner.iv).the dismantling would be completed by cutting the reinforcement at the remaining end,and the beam will then lift up by crane to lay its on ground.d).Exterior column-exterior column may be demolished by the following procedures;-i).The top of the column shall be first be secured to a structural member by wire or winch.ii).Pre-weakening shall be performed at the bottom of the column to reduce the pulling force and to ensure that the break occurs at the desired location.The concrete cover to reinforcement shall be first removed.Reinforcement at interior face shall be remain.Reinforcement at the exterior shall be cut immediately before pulling the column.iii).After pre weakening the column shall be pulled down by the wire and winch towards the interior and lift up by crane to lay on ground.
5.Floor slabs-Reinforcement 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.The sequence for demolition of typical floor slabs are discussed is the following:-a),Two way slab-The two way slab is supported by beams or structural members on the all four sides,Demolition of the slab shall begin in the middle of the slab and advance towards the side in all 4 directions.b). One way slab-The breaking of the concrete shall begin at the unsupport end and proceed in strips perpendicular to the supporting beam or structural member.The strip shall demolished from their centre towards the support in both directions.c).Flat slab-Demolition of flat slab shall begin at the centre of the bay between the supporting beam and proceed outwards to the columns and /or members that provide lateral support of the slab,Care must be exercised not prematurely weaken the shear capacity of the column or other supports.In general,when demolishing a column strip or part of it,adequate supports shall be provided to the strip in advance.
6.Interior beam-a).Interior beams normally supports floor slabs on the both sides.the supporting beam shall not removed until all other deads load imposed on the beam are removed,including the slabs support by beam,b).The dismantling of interior or secondary beams.
7.Interior column-Interior column may be dismantled by pre weakening at their base and pulling down by wire and winch system.The process is similar to the demolition of the exterior columns as previously described.
5.0 UNDERGROUND STRUCTURE
1.General-Demolition of footing shall be incorporated into the new foundation construction.Such arrangement may eliminate the redundancy of the temporary works for soil retention and dewatering system.
2.Demolition method-All the newly and existing footing shall be demolished by jack hammer.care must be taken to the existing footing.
3.Guideline-a).Overall stability-The stability of the building under demolition and any remaining part of it shall be maintained at all times.b).Shoring-All the remaining part of the building shall be shored at all time.c).To retained the soil from collapse during the excavation of footing.d).Do not expose or hit the remaining part of existing footing
4.Existing foundation-a).All the newly and existing footing at the concern area shall be demolished.b).All the broken concrete shall cart away from the site and not used as a filling material at any area.