demolition feb 04

8/12/2019 Demolition Feb 04

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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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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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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



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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



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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



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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



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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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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.



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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



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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



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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



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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



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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



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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



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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 )

demolition feb 04

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