demolition feb 04
TRANSCRIPT
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Demolition within UrbanDemolition within Urban
EnvironmentEnvironment
Lecture Notes prepared byRaymond Wong
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Demolition work is one of the mostDemolition work is one of the mostdangerous operations in construction.dangerous operations in construction.
Reasons/causes:Easy to cause injury to human workers due to thedifficulty of accessing into or working inside a
building which is under demolition.Falling of smaller objects or debris from thedemolishing building.
Falling of partially demolished structure.Collapse of unstable structure due to originalstructure being disturbed.
Employing inappropriate methods to demolsih
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Reasons/causes (continued):Collapse of heavy demolition equipment due toinadequate support of the partially demolishedstructure.Collapse of the partially demolished structure due to
the accommodation of large amount of uncleareddebris.Congested site environment that easily cause
damages to human workers, or to the third partiesand their properties that are situated nearby thedemo1ition site.
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Difficultaccess for
workersentering intoa building
underdemolition
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Further examplesof difficult accessin demolition jobs
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Partially demolished structure
is hazardous and may easilycollapse and create accident
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Heavy machinery used indemolition may have riskof collapse due toinsufficient support.
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Accommodation of toomuch debris duringdemolition can imposeintolerable loading tothe disturbed structure
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Typical congesting neighbour-hood condition for demolishingsmall buildings within urbanenvironment
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HK Building Department has imposed very strictHK Building Department has imposed very strict
control to any form of demolition works by thecontrol to any form of demolition works by theuse of approval & consent procedure.use of approval & consent procedure.
1. Authorized person (AP) should be appointed tosubmit application for approval of the demolition,which includes an appraisal report with a methodstatement proposed for the demolition.
2. Building Department will approve the work subjectto the satisfying of all precautionary measures
pursuant to the Building (Demolition works)Regulations, hoarding and covered walkways or any
other conditions as required.
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3. After approva1 is obtained, another 2 stageconsent procedure are still required before startingthe actual demolition.
4. Stage 1 is to obtain the consent for carrying out all precautionary/temporary works which include thehoardings, covered walkways, scaffolding, catch
fans, dust screens and shoring etc.5. In case the provisions in Stage 1 is completed and
to the satisfaction of the Building Department,Stage 2 of consent for the actual demolition can beapplied.
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In the appraisal report, the followingIn the appraisal report, the followinginformation should be includedinformation should be included
1. Structural survey of the building to be demolished2. Photographic record of the site and its adjacent
buildings, slopes and retaining structures.
3. The overall height of the structure above groundlevel and the proximity to adjoining buildings.
4. Information on the type of building, its strudura1support system, the principal materials of itsconstruction, the degree of deterioration and theeffect of demolition etc.
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Demolition PlanDemolition Plan
Forming part of the submission information, theDemolition Plan should include:
a) A set of drawings showing :- the location of the building to be demolished
- other existing structures and facilities in vicinity b) Proposed methods of demolition.
c) Proposed shoring and precautionary measures foradjacent buildings
d) Proposed shoring and protection for the buildingto be demolished
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Catch fan
Typical dust screen and fans provision to protect buildingand minimize disturbance to
public during demolition
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Provision of Hoarding as a
protection to public
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Provision of Hoarding as a protection to public
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Provision of Fence
and screen to preventfalling of debris andgetting out of dust
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Detail of protectionscaffold, screen and
catch fan
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Common ways to get rid of thedemolished debris to controlthe falling of the debris into a
pre-determined vertical shaft
formed on the floor slabs
Shaft for fallingof debris
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Temporary props erected tosupport heavy equipment
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Typical sectioning/sequencing arrangementof work duringdemolition demolishfrom exterior inward
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Typical sectioning/
sequencing arrangementof work duringdemolition demolish
from one side to theother side of building
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Protection measures to publicProtection measures to publicduring demolition processduring demolition process
The following concerns related to the protectionand safety of general public or their propertiesshould be provided in the demolition process
1. Overall structure of the adjacent buildings
(stability).2. Party walls and external walls of adjacent
buildings (sealing and waterproofing)3. Foundations of other buildings which may be
affected.
4. Public roadway and traffic.
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Stiffening frame to strengthenan exposed party wall
Strengthening of party wall ofadjoining building after demolition
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Timber raking shore as a temporarysupport to adjacent building
Shoring support to adjoining building after demolition
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Method of demolitionMethod of demolition
General ConcernsThe choice of choosing a demolition method depends
on a number of factors such as the projectconditions, site constraints, sensitivity of the
neighbourhood and availability of equipment etc.In general, top-down methods are applicable for most
sites, particularly for those situated in busy urban
areas. Other mechanical methods applied from theoutside of a building may be suitable for projectsthat have sufficient clear spaces.
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Method of demolitionMethod of demolition
General Concerns (continue)For structural projections such as balconies, canopies
and verandahs extending beyond the building lines,demolition by hand held tools or the cut and lift
process may be a safe solution.Each site has its specific features and conditions. The
method, including detail procedures, shall be
designed to accommodate the specific projectrequirements. In general, demolition should bedone in the reverse order of construction.
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Method of demolitionMethod of demolition
Demolition by human operatives
This method particularly suitable for use in smallersite with congested space where larger machinecannot be employed.
In this case, human operatives are used in thedemolition process using simple electrically or
pneumatically powered tools such as picks,hammers, wire cutters, welding cutters or handdriven hydraulic jacks etc. to carry out the
demolition of individual elements.
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Typical demolitionarrangement done byhuman operatives
Typical demolition
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Typical demolitionarrangement done by
human operatives
Slab with the sidesdisconnected readyfor dismantle
Method of demolitionMethod of demolition
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Method of demolitionMethod of demolition
Deliberate collapse method
Demolition by deliberate collapse consists ofsystematic removal, or weakening of the keystructural elements to induce the collapse of thestructure.
However, when applying this method, several precautions should be observed, such as:Sufficient distance of collapse should be providedCollapse procedure should be carefully designedso that there is no pre-mature collapse or collapseout of the anticipated area.
Control height of building structure to becollapsed
Method of demolitionMethod of demolition
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Method of demolitionMethod of demolition
Using of applied pulling/pushing forcesConnecting structural members are disconnected first
allowing part of the remaining structure to bedragged down by the use of some pulling/pushingequipments such as powered jack, winchingmachine, pulley systems, pushing arms, powered
blocks or from the pull/push of a hydraulicexcavator.
However, a firm base in the demolishing building isrequired such as basing on an undisturbed corewall or a strong column section for the applyingof the pulling/pushing force.
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Demolition of an
external wall by pull-down methodusing pully
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Demolition of anexternal wall by pull-down method using
excavator arm
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Disconnectedexternal wall readyto be pulled down
by an applied force
Demolition done byapplying a pulling force toa portion of structure
Remain fragments from pulled-down structure to be removed afterward
Method of demolitionMethod of demolition
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Method of demolitionMethod of demolition
Using of wrecking ball -The use of wrecking ball method requires a craneequipped with a steel ball. The destruction of the
building is caused by the impact energy of thesteel ball suspended from a crawler crane.The wrecking ball can be operated outside or inside a
building. In case the process is operated inside a building, sufficient clearance from the buildinginterior should be made first (by having the
interior portion of the building demolished)This method also demands experienced operators in
order to handle the wrecking ball and control the
demolition sequence in a safe manner.
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Swing action ofwrecking ball
Vertical drop ofwrecking ball
Method of demolitionMethod of demolition
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Method of demolitionMethod of demolition
Use of powered plant or demolition machine -The principle of demolition by machine is typicallythe same as the top-down manual method, except thatmost of the demolition begins with the lifting of themechanical plant on to the building top floor.
Powered plant such as crawler mounted breakinghammer are used in the demolition process andexcavating machines with bucket are used in theremova1 or handling of the demolished materials.However, due to the weight of these machines, theyshould be properly supported such as by the use ofsteel props no matter in still or in operating condition.
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Demolition by the help ofmechanical plant pneumatic
breaker and bucketedexcavator
Lifting the
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Lifting themechanical
equipment to topof building
Building before demolition
Demolition using top-down method using machines
Demolition using properly proppedexcavating/breaking machine
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excavating/breaking machine
Demolition using top-down method using machines
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Demolition using top-downmethod using machines
typical floor cycle andmachine movement
Moving down of the breakingmachine to the lower floor
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Demolition using top-down
method using machines typical floor cycle and
machine movement
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Demolition using top-downmethod using machines
typical floor cycle and
machine movement
Demolition of 2-way
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floor slab using
mechanical breaker
Demolition of floor should be started from the middle
Safe practice Demolition
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Using manual method
Safe practice Demolitionof cantilever slab
Using cut and remove method
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Method of demolitionMethod of demolition
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Method of demolitionMethod of demolition
Using saw cut method
This method is suitable for alteration and additionalworks where accuracy is important and restrictionon noise and vibration is required.
It can be used to cut concrete slab and wall elementsinto segments or for the forming of openings,
breaking into existing structure like a basement,servicing tunnel, flyover, or other part of aninhabited building in the process of alteration orrenovation works.
Method of demolitionMethod of demolition
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Method of demolitionMethod of demolition
Using saw cut method (continue)
Saw cutting can be done using the followingmethods:
wire saw cutting
diamond core stitch drilling
disc saw
Set-up and mounting of the
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Set up and mounting of thesaw dis on wall
Demolition using dis saw cutting
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An openingformed on floorfor the insertionof a steel prop
Demolition using diamond core
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Demolition using wire sawing
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Disc saw
Demolition using saw-cut and drill method forthe diversion of a storm water discharge culvert
Method of demolitionMethod of demolition
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Using cut and lifting method
Cut and lifting involves the initial cuttingof the structure into individual pieces or
segments, and then lifting the pieces bycrane onto the ground for furtherdemolition or hauling away.
Special precaution should be made whenapplying this method for demolition suchas:
weight of the cut segment may causeextra loading to the remaining structure
lowering of the segment can bedangerous Lowering of segment from a
footbridge after dismantled by saw-cut
Method of demolitionMethod of demolition
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Method of demolition
Using of hydraulic clamp or robotic breaker
S pecially designed breaking/cutting machines,usually track mounted, are used to demolish
some smaller structural elements such as thinwalls, stairs, slab or parapet etc. when usingthis kind of equipment, planning for accessingthe machines into the working spot is essential.
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Demolition usinghydraulic clamp or
robotic breaker
Method of demolitionMethod of demolition
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By implosion (explosive)
If using this method to demolish a building, contractorshould carry out a comprehensive risk andenvironmental assessment on the effect of implosionon the neighbourhood.
A detail demolition design is also important, whichshould cover:Method to pre-weaken the structure (e.g. demolish someload taking structures)Placement of explosiveTime-delay design to allow the building to collapseunder control director and location
Method of demolitionMethod of demolition
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By implosion (continue)charges of explosive are placed within the fabric ofstructure and detonated to cause partial orcomplete collapse. Competent explosivespecialist is required when demolition is to bedone by using explosive.
There are numerous types of explosives for use forvarious types of demolition (sometimes includingnon-explosive agent). Consideration such as thespacing and depth of explosive to be located, the
amount of explosive to be used, or the degree offragmentation required in order to control the boundary of demolition etc., are requiredthroughout the planning and operation process.
Removal of demolished material or debrisRemoval of demolished material or debris
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Demolition will generate huge amount of debris. Thesafe and effective removal of such constructionremains will be a prime concern in the operation.
In this case, before and during demolition, thefollowing provision should thus be provided:
Overall debris disposal planningTraffic routing for debris handling and vehicularaccess etc.Adequate number of chutes for debris disposalSorting of non-structural materials such as
timber and metal for recycling.
Removal of demolished material & debrisRemoval of demolished material & debris
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Debris created by demolition is usually collected toone or two pre-arranged shafts in the building andthe debris are allowed to fall or drop freely from
the shafts, by the push of a bulldozer or alike,down to a safe debris collecting areas for furtherdeposal. Since the accommodation of a certain
amount of debris is expected, the areas around theshaft should be properly fenced or propped so thatthe extra weight of the debris can be taken up.
Accommodation of debris is often dangerous for theymay impose extra load to the floor or wall (ifleaned against onto). Debris should be cleared
away the structure at the earliest possible.
F l d li h d t i l h ti
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For larger demolished materials, such as a sectionof a beam or column member, they can behoisted down using steel rope, lifting arms orwinch etc.
If the site area is large enough or where situationallows, a section of building may be demolished
first. The area vacated can be used for thehandling of the debris. In this case, a mobilecrane may be employed to lower the debrisusing a bucket or skip.
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Portion of the buildinginterior being cleared out fordebris handling purposes
Collected metal and other
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Collected metal and other
valuable scrape for recycle
Demolition for special structureDemolition for special structure
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The following structure should require veryspecial attention during demolition:
Precast elementsPrestressed elementsCantilever structureHigh headroom or Large-spanned elementsStructural elements under special jointing
arrangement (e.g. hinged or pin-jointed)Composite or steel structure
Demolition for special structureDemolition for special structure
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pp
The following structure should require veryspecial attention during demolition (continue):Hanging structuresTransfer plate and deep beams
Special floor structures - waffle floor, flat slabArches, trusses or girders structures
Cladding or curtain wall
Demolition for special structureDemolition for special structure
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The following facilities or buildings should requirevery special attention during demolition:
Buildings located in contaminated siteBuildings used as oil or dangerous goods storage
Marine structuresUnderground structures (tunnel, basement orfoundation)Soil retaining structures
Disconnection of utilities servicesDisconnection of utilities servicesbefore demolitionbefore demolition
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before demolitionbefore demolitionThe following utilities should be properly sealed or
disconnected before the commencement ofdemolition:Electricity and gasGas and water supply
Vent shaft or any underground accessDrainage and sewage systems
Majority of these utilities services are locatedunderground and can hardly be seen visually. Adetail survey should be done before hand to ensure
they are found and disconnected.
Environment concerns in demolitionEnvironment concerns in demolitionDemolition is a dirty and dangerous process In view
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Demolition is a dirty and dangerous process. In viewof ensure such works are done properly withoutcausing any unnecessary interference to general
public, the following areas of environmentalconcern should be noted.The proper recycle or disposal of the constructionwasteTreatment of harmful material (e.g. asbestos orcontaminated waste)
Control of dust generationControl of noiseControl of waste water (including rain water
carrying large amount of mud running out from site)
Other precautions to be notedOther precautions to be noted
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1. When handling the debris, continual spraying ofwater onto the debris can help suppressing thecreating of dust.
2. Better work coordination should be maintained toensure no worker is working inside the building
when the debris is being pushed down from thedebris shafts.3. Secure all the partially demolished structures by
prop, wire or bracing etc. to ensure the areas aresave and will not fall down, at least temporary, andhurt the workers who is working around.
4. When a building is attached to other buildings
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4. When a building is attached to other buildingsnearby, the structure to be demolished should first
be detached from the adjoining structure by handdemolition techniques.
5. Very special attention should be made to anydemolition work that is carried out along the
external perimeter of building for the falling ofobjects may cause great casualty to third party
below.
6. Maintain a safe emergency access all the timeduring demolition.
Jetting water to the spotwhere demolition takes
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place
Protect by secure a freestanding external wallsection by steel ropes
Steel rope
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Fence off the vertical shaftfor the removal of debris
Maintain a safe access forworker during demolition
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Avoid letting along section of
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wall free standingwithout support
Free standingwall withoutsupport
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Safe practice Demolition of an externalcolumn by pull-down method using pull rope
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Some other very complicateddemolition cases
The redevelopment
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of the Lee GardensHotel
Various phases of basementdemolition part of the
basement being removed forconstruction of the pile capfor the future building
Continual stages of the basement demolition with theincorporation of other substructure of the future building
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The redevelopment of the Lee Gardens Hotel
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The demolition of the basement structure working at the
same time with the construction of the future building
The redevelopment of the Lee Gardens Hotel
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The redevelopment of the Hilton Hotel
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Demolition of the basement structure of the previous Hilton Hotel the
lower basement was backfilled to maintain stability of the disrupted basement structure before the commencement of the new basement
The redevelopment of the Hilton Hotel
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Demolition of the basement structure ofthe previous Garden Road Carpark
The Millennium City in Kwun Tong
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Demolition of the basement working at the same time with the building foundation
Concerns when demolishing a basementConcerns when demolishing a basement
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Basement is a soil retaining structure. If demolishednot in a proper manner, the basement and thesurrounding may collapse and cause seriousdamage both inside and outside the basement
boundary. The following concerns should be takenwhen doing the demolition work:
Careful planning of work is important (usual todemolish in smaller section and in coordinated
phases)
Proper shoring should be provided to the basementduring demolition
Concerns when demolishing a basementConcerns when demolishing a basement
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(continue)(continue)Because the upper structure has been remove, the
basement (and the soil below) may have uplifting problem.
There may have ground water problem.
Existence of old foundation structure (usuallyrequired to be removed)
Accessibility into basement (and removal ofdebris) is difficult.
An accident caseAn accident case the collapse of thethe collapse of theAsian Trade Centre atAsian Trade Centre at Yau Yau TongTong
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The Asian TradeCentre before
the collapse
Existing structure of the Asian Trade Centre
1 ld
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1. Building size:about 45m by 50m on plan and 25m high
2. Structural form:- flat slab structure with limited amount of beams on
the building edges and corners- non-load bearing reinforced concrete external wall- arranged in approx. 8m span in 5 x 6 bay grid- strength of concrete 30 N/mm 2 (judge accordingto speaker s experience)
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The site as seen after the collapse on 30.11.01 (viewing north)
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The site as seen on 30.11.01 (viewing south)
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The site as seen on 30.11.01 (viewing west)
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The site as seen on 30.11.01(viewing at J/O Sze Shan Street and Shung Shun Street)
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The damage the wreck of two out of the five breaking/excavating machines used for demolition
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The damage the 6-storey building collapsed inwardforming a heap of debris about 6m high from ground
Adjoining building Separating joint
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The damage fortunately, the collapse does not damage
the adjoining building which separated from the collapsed building by a separating joint only a few millimeter apart
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The remain a section of the external wall onthe west side of the building
The remain a portion of building
structure at the
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structure at thecorner at J/O SzeShan Street &
Shung Shun Street
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Party wall
being pullinward
Observation all the fallen columns centered inward indicatesthat the collapse orientated somewhat from the building center
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Observation with the columns basically remain intact while no trace
of floor slab can be observed in the remain indicates that the floorstructure in general is a weak source that may cause the collapse
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Observation the exposed steel bars on the cut-edges indicates thecollapsing structure fell rapidly and produced tremendous pulling force thatfail to keep the floor in position. There is no trace of floor concrete adheredto the bar, again indicates that strength of concrete may be sub-standard
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Observation further evidence of possible floor failure.
More than 3 storeys of floor slab crushed to rubble anddetached completely from the columns
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Steel prop
Observation the steel props
used as temporary support forthe positioning of the heavy breaker machines seeminsufficient for the purpose
Props shouldrest on bearing
plate rather
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pthan directlyon floor to
avoidconcentrationof loading
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Observation the accommodation of large amount of debrisabove the floor impose great loads to the structure
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End of Presentation
Please refer to the Code of Practice forDemolition of Buildings published by the
Buildings Department, HKSAR Government
(can be downloaded from the homepage of BD athttp://www.info.gov.hk/bd/english/documents/index.html )