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50 views61 pagesPrefrab. Construction
Uploaded by
Anandlal RCopyright
© © All Rights Reserved
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Available Formats
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/ 61
en
2.1. GENERAL
The design of precast concrete elements involves understanding the method of fabrication, the implicit constraints,
as well as the various aspects that facitate the arection and assembly of these elements on site. Salient guidelines
for the design of precast concrete elements can be found in the Singapore Code of Practices namely CP 68° and
CP 81’. In addition to the design and detailing of pracast olaments, its important to carry out design checks on
the overall building stability and robustness of the complete structure as recommended in these codes. The design
should also consider the manufacture, transportation, hoisting and temporary stability of the element and of the
structure during construction.
To achieve good auality precast coner.
design stage
t© elements, itis important to consider the following aspects during the
‘+ Dimensions and Shape of Precast Elem + Mould Design
+ Concrete Constituents + Joints and Connections
+ Reinforcement + Lifting and Handing Devices
2.2. DIMENSIONS AND SHAPE OF PRECAST ELEMENTS
‘The optimal dimensions of tho precast elements largely depend on the
-apacity ofthe lifting cranes at the fabrication yard and site as well as
transportation limitations. It is however, a good practice to design for the
largest possible size to minimise jointing and handing, Integration of different
elements, such as the beam-wall system, mul
dimensional units can be adopted to enhance dimensional controls ang
construction auaiity
1 columns and three
Where possible, plan fo
appropriate repetition and
standardisation in the
dimensions and shape of the
elements, which 's desirable
for economic of scale and
quality assurance, Fewer
mould changes will facta
the production schedule anc
hence reduce construction
time. Nevertheless, precast
elements in particular the
facade and wall panels, can
be designed and mocifiet
from the typical mould in
profiles for greater variations as wel as to maximise mould usage.
However, care should be taken in the design to consider some forms of
strengthening for panels with significant openings or narrow segment at
the side of the openings, to prevent cracking or spaling of the elements
during installation
Figure 2.2 Multtier columns
Figure 2.1 in
ed beam and wall panels
siffere
Refer to Singopore Code of Paste for St
Use of Concrete
P65; Part 1:19
"foter to: Singsoore Code a Practice for Preeas
ote Sib ana Wal Panels CP 8: 190 2 PRECAST CONCR!
IENTS | DESIGN
2.3. CONCRETE CONSTITUENTS
Depending on the design requirements, a variety of concrete strangths and characteristics can be used to achieve
‘optimum performance required of the precast concrete elements. The relevant
are listed in Table 2.1
dards for concrete constituents
‘Table 2.1 Relevant standards for concrete constituents
Concrete Mix cP ss.
cPat
88 288
gS
ment.
Concrete mix which is composed of portland cement and water
together with fine and coarse aggregates, should be designed to
achieve the desired workability during concreting, and the durability
fand strength recuired of the final precast elements. In general, the
mix should achieve a concrete strenath of minimum 10 Nimmo
more at ealy stage for demoulding an higher production etficiency.
Cement 3826
(Ordinary partiand cement and blended cement are commonly used
in precast concrete production. High alumina cement should not be
Used as it may cause substantial loss in concrete strength and
durability in warm, humid concitions.
Aggregates ss3i
‘Tho maximum size of the coarse aggragates should be established
in th design. Tho size shouls be compatible with the minimum
dimension and usage of the precast elements. As a general guide,
the maximum agpragate size should not be greater than the speciied
cover to reinforcement or tendons, For machine-extruded concrete
such as hollow core slabs, whereby the concrete mix is forced
through rotating augors and steel formers to create the voids, fine
aggregates have to be carefully graded. To achieve quality product,
the sizo of the coarse aygrogates should be loss than 18 or 20 mm,
depending on the element dimension and machinery typ.
Acmintures $8320
Chemical admixtures ray be acked io enhance the performance of
‘he concrete mix by redilcing the required water content of to
accelerate the rate of early strength development. ts recommended
teacarty out tral mixes to determine the optimum design propartion
of admixtures to be added to concrete mix. Approptate methods
of batching and concreting should be used to ensure correct dosage
50 35 to avoid any detrimental effects on precast concrete elements. PRECAST CONCRETE ELEMENTS | DESIGN
2.4, REINFORCEMENT
Apart from concrate constituents, procast concrete elements are often reinforced using wolded wire meshes, bars
or prostrossing tendons to achiove the required structural capacity. Thay are required to be designed to most the
crack control, loading capacity and construction load requirements, The relevant standards for reinforcement and
prestressing tendons are listed in Table 2.2,
Table 2.2 Relevant standards for reinforcement and prestressing tendons
tems. Sons
Welded Wire Meshes $532
Stee! Reinforcement 382
ressing Tendons 88475, cP 65
In designing the reinforcement layout, itis important to also consi presence of other cast initems such as
pipe sleeves or electrical fixtures. The layout design should be simplified wherever possible, to avoid congestion
which may affect the conerate quality due to poor compaction and loss of conerote cover.
Figure 2.3. Potential congestion at connection where there are reinforcement bars and cor
When the projecting reinforcing bars that are requir
‘may pose storage and handling problem. In this respect, tis good practice to adopt mechanical counlers or spice
system to provide for the structural continuity needed.
for lap splicing PRECAST CONCRETE ELEMENTS | DESIGN
Figure 2.4 Long projecting bars may pose storage and handling problems
Figure 28 Use of splice sleeve system in place of long projecting reinforced bars PRECAST CONCRETE ELEMENTS | DESIGN
2.5. MOULD DESIGN
Moulds ean be made of any suitable materials including steel, timberlplywoad, glass
reinforced concrete (GRC) or a combination of these. The selection of the mould
materials will dopend an the number of usage, required surface finish type
and quality as well as the shape complexity ofthe pracast elements.
Locally, stoe! mould is proferre
the steal plate thickness adopted for mould dosign and fabrication varies from a
minimum of 4.8mm to mm, which ean be used up to 50 ~100 times with proper
cate and maintenance. Besicles, the mould should be designed to allow for anproprate
placing and compaction of the concrete. Adequate numbor of braces, ties and struts
should be provided for proper casting and hardening of the conerete. A minimal
number of demountable parts will hp to ensure good maintenance of dimensional accuracy during reduction as
‘wall as to facilitate easy assombly and dismantling. To enhance cost competitivenass, adjustable mould should bo
adopted where possible, for greater flexibility and variety in the production of precast concrete elements.
‘owning to its robustness and precision. In general
Fig 2.6 Example of adjustle
mould for the precast beam
and colurmn production
igure 2.7 Adequate bracing is required for better dimensional controls
Figure 2.8 Examples of battery moulds anc mechanised vertical moulds used for wall elements PRECAST CONCRETE ELEMENTS | DESIGN
moulds or mechan)
roduction of standard elements such as refuse chutes and paray
vertical moulds can be used for better quality and productivity,
2.6. JOINTS & CONNECTIONS
Joints and connections must be designed to adequately transfor the loads from a precast concrete element to the
supporting structure or to an acjacent element te form the structure, They have to meet the design and performance
criteria such as strength, ductility, fre resistance, durabilty and stability. Apart from these structural requirements,
siderations should be given to the production and erection process of the elements, To achieve a pra
ion, the following items should be considered in the design
due
Standarcise tha joint and connection types and details
Avoid congestion a joints
Avoid penetration of farms
Allow for production and erection tolerances
Plan for easy assembly and accessibility
Accompilation of conne
Precast Concrete Hand
or Landed Residential Development in Singapore
ion and jointing details commonty used can be found in other BCA publications - “Structural
00k", “Bulldable Solutions for High-Rise Residential Development” and "Buildable Solutions
Recommendations on watertightness details and workmanship standards for external wall can be obtained from
CA's Good Industry Practices on Waterproofing for External Wall
Figure 29 Examples of joints and connections between different precast elements PRECAST CONCRETE ELEMENTS | DESIGN
2.7. LIFTING AND HANDLING DEVICES
In procast concrete construction, lting and hanaling devices are roquired and placed within the elements to facitate
the demouling, handling and erection processes. The type, number and location of these temporary lifting and
handling devices play an impartan: role, in ensuring that the precast elomants are not excessively stressed during
Iting operation and befora jointing works commenced. The factors to be considered are as follows:
Capacity ofthe lifting and handling devices.
\Woight and shape of the procast elements,
Strength of the concrete at the time of lifting
Position of any opening or cut-out in the pracast elements.
Rigging arrangomont
Type of lifting clutch, hook or shackle used for handling and installation
Figure 2.10 Lifting and handling devices are requited to facilitate the erection process PRECAST CONCRETE ELEMENTS | DESIGN
Lifting anc handling devices can be prestressing strands or cable loops projecting from the elements, coll threaded
inserts or proprietary lifting devices. Prostrossing strands or cable loops should be designed with adequate safety
factors before use. Reinforcing bars unless specifically designed, should not be used as lifting loops as they are
susceptible to breakage during hoisting operations in view oftheir low ductility.
Where possible, these lifting and handling devices should be placed at locations thal requit little or ne patching
after use. If they are required to be located on the fin'shed face of architectural component such as facade wall
panels, it willbe good to provide recesses. These recesses can then be filled up with proper grout after instalation
le achieve better wall finishes,
Citing
a eng
Pos poe
eres
ee ee
iting
Hepat
Figure 2.11. Differant types of deviens for lifting operation and temporary support
Figure 2.12 Provision of iting anchor with recess former for bette finishes.
Itis @ good practice to adopt proprietary lifting devices that come with specified design load capacity for safe and
efficiont handling. These devices normally come with proper accessories to form recesses, which can be easily
patched up after installation, rication Process
3.1, GENERAL
Before fabrication, shop drawings of individual precast elem
following information
‘are required to be prepared and detailed with the
* Project location, reference number of elements, and their locations with respect tothe building layout and elevation
+ Dimensions of elements, centre of gravity, weight and concrete volume
* Locations of all reinforcing steal, castin items for connection, Ifting and bracing
ations of embedded items such as service conduits, blockouts and recesses as well as openings
+ Jointing and interfacing details between elements
+ Watertightness details at joints
* Architectural details and treatments where applicable
1h requitements should be resolved before
Any discrepancies among the architectural, structural and produ
confirming these drawings for fabrication to minimise abortive works.
Generally, there are two main types of precast concrete elements, namely precast reinforced concrete elements
and precast prestress:
concrete elements
+ Consist of reinforcement bars andjor
‘welded wire meshes within the elements
to provide the tensile strength and
resistance against cracks
+ Examples are facade walls, beams,
columns, slats, refuse chutes, stircases
‘and parapet walls
Deena
crore
Conere
rgonents of @ bulking
that are prefabricated in precast
Yard ar site, They are tobe installed
<0 the’ final postion in the buldng
uring construction
+ Consist of prestressing tendons within the
Reda) slements to provide a predetermined force
Concrete Elements needed to resist external loadings and
cracks
‘+ Common examples are hollow core slabs,
beams and planks
Figure 2.1. Types of precast concrete elements
0 "AST CONCRETE ELEMENTS | FABRICATION PROCESS
"
In fabrication, most ofthe precast concrate elements are produced using the normal wet casting method. However,
for hollow core slabs and wals, dry casting process or extrusion method is ado
3.2. NORMAL CASTING PROCESS FOR PRECAST REINFORCED OR PRESTRESSED
CONCRETE ELEMENTS
Table 2.1 highlights some of the good practicas recommended for normal wet casting of precest concrete elements
Table 3.1 Nor
con
1. Assembly of mould “+ Check the level and flatness of the base mould bafore assembling
the mould for panel casting,
Ensure that the dimensions of mould ae within the specified tolerances. [ETE ELEMENTS | FABRICATION PROCESS.
ie
2. Mould cleaning and preparation
Form oil or mould release agent should be applied eveniy over the
mould surfaces,
Check that the joints and edges of the mould, belts, steppe
de props and rubber seal are intact and properly secured!
3. Fixing of rebars/castin tems /
prestressing strands
Cheek thatthe rebar size, spacing and lap length are in accordance
withthe drawings. CRETE ELEMENTS | FABRICATION PROCESS
n process. Enno
+ Rebars, 3s, corrugated sleeve pipes, recesses, liting hooks
land inserts must be correctly positioned and properly secured
+ Use of fabrication rig ean help to ensure the accuracy of rebars fixing
and spacing CONCRETE ELEMENTS | FABRICATION PROCESS
ie Eno
of rebars /castiniterns /
rossing stands conta)
+ Whore needed, tack welding
nt number of spacers with the
tnd secured to achieve the req
cover duting
‘+ For precast prestressed concrete element such as planks, the sand
hauling should only be carried out when the form release agent has.
fed to a certain degree that will not contaminate the strands PRECAS!
CONCRETE ELEMENTS | FABRICATION PROCESS.
Fabr
Seed
4. Final inspection before casting
Cerin
Check an verify that all details comoly with drawings.
It is good to check the base mould level again before casting, in
paricular for site precasting where other concur
have shited the mould level
Site activites may PRECAST CONCRETE ELE!
ENTS | FABRICATION PROCESS
i Sr
5. Conereting
+ Conduct slump test in compliance with SS 78 to assess the workability
lof the concrete mix before placing the canerete to the mau
+ The drop height of concrete mix should nat exceed more than Im,
+ Proper vibration and compaction should be cari
rote congestion areas.
¢ out in particular, in
+ Form viorator ean be used for slender and thin elements
‘+ Maintain the required thickness by use of screed. PRECAST CONCRETE ELEMENTS | FABRICATION PROCESS
ie ery
5. Conereting (cont'd) + Use of power trowel j float is recommended for smoath surface
‘+ Observe adequate curing time and desired environment.
‘+ Concrete cubes should be subjected tothe same curing conditions as
et |
—
7, Demoulding + Depending on the anchor length of inserts and type of preva
for e.g, thin flor slabs, the mnimum conerete strength requred may
higher to overcome the suction and frictional forces during
ddemoulding,
‘+ Cube tests should be conducted to verify the concrete strength of
clements before demoulding
+ As 2 general guide, ensure that the concrete strengths attained for
reinforced precast elements and presivessed precast elements are
minimum 10 Nimm* or 25 Ninm* respectively.
+ Loosen and remove all bolts & pins and end and side mould forms
before iting.
+ For prestressed elements, cut strands before lifting INCRETE ELEMENTS | FABRICATION PROCESS
Fabrication process Enno
8. Final inspection / Transfe
yard
to storage,
Finishing works before delivery to site
+ Check the concition of the finished product,
+ Verity the ertical dimensions.
~_
+ Proper identification markings should be placed on elements showing
the location, mamber type, size, weight and erientation a per shop
drawing.
+ Chea elements have achieved 75% of thelr design concrete
strength before delivery to site for erection,
1" PRECAST CONCRETE FLEMENTS | FABRICATION PROCESS
1°
1g Process (Extrusion Method) for Precast Hollow Core Elements
to produce hollow core slab of wall panels. Table 3.2 highlights
rusion method of precast hallow core panels.
3.3. Dry Cast
The dy casting or extrusion method is mainly use:
some of the good practices recommended for dry casting o:
‘Table 3.2 Dry Casting Fabrication Process
Fabrication process ron
1. Base mould cleaning and ‘+ Check that the base mould is clean and free from debris and old
preparation mortars
the extrusion machine including the vibrator are in good
‘+ Form release agent used should have ant-rust properties and be
relatively ary after application so that the strands will not be
contarnin hould be applied eveniy over the mould surfaces PRECAST CONCRETE ELEMENTS | FABRICATION PROCESS
Fabrication process Enno
2. Prostressing strand hauling and
tensioning
+ Check the strand size, spacing an:
+ Strand hauling shouldbe carried out only when the release agent hes
dried toa degree that it will nat contaminate the strands,
“+ Before concreting, check machine setting for concrete cover and panel
thickness.
Check that concrete grade used is according to design specications.
‘+ Conduct slump test to ensure adequate workabilly ofthe concrete
Check that the elams-on vibrate provide good compact
20 PRECAST CONCRETE FLEMENTS | FABRICATION PROCESS
Fabrication process Enno
3. Conereting cont'al + Cory out visual inspection ofthe surface finish to ensure there is
serious defect like honeycomb, dimensional changes, cracks etc
+ Stop operation to investigate if serious defect detected
4, Curing + Protect the hollow core panels with
rapid moisture loss and shrinkage cracks,
paulin oF canvas to prevent
+ Observe adequate curing time and desired environment
+ Concrete cubes should be subjacted tothe samo curing conditions as
the elements
"
a PRECAST CONCRETE ELEMENTS | FABRICATION PROCESS
Fabrication process Enno
5. Detensioning of strands
6 Final inspection / Transfer to storage
yard
+ Cube tests should be conducted to verity the conerete strength
‘+ Check that the concrete has attined the designed transter stength
fof minimum 35 Nimm’ or as sporified before detorsioning
led water holes at the bottom of panels should be between
10 ram to S00 mm fromm the end of the panels.
‘+ Ensure that dimensions of the hollow core panels mest the design
that proper identi
and tracing.
jon markings are in place for easy retrieval
‘+ Check for possible slippage of strands at both endl of hollow core
panels. The values of allowable slippage should meet the design
+ Check if there are any major cracks along the element section,
+ Plugging of holow coro openings with plastic caps before transfering
tw storage yar.
“+ Check tnat the elements have
loved 75% of their design
strength before delivery to site for erection, 4.1. DELIVERY
Delivery of precast elements should be planned according to the general erection sequence to minimise unnecessary site
ge and handling. Where possible, its des transport the precast elements into a manner which they can be
lifted directly for erection or storage without much change in orientation and sequence. For example, wall panels can be
‘ransported using A-Frame type taller in upright pos'ton
Precast elements should be loaded and delivered with proper supports, frames, cushioning and tie-downs to prevent in
transit damage. Adequate pecking or protection to the edges of precast elements should also be provided to minimise
tisk of damages during ta
Figure 4.1. The manner of delivery will depend on the type, dimension and weight of the precast elements
24 PRECAST CONCRETE ELEMENTS | DELIVERY, HANDLING AND STORAGE
Fa
Pera rae a
ret eioet peeing
cua Lae)
perro)
Berita
Cushion packing should be provided to
prevent damage to the edges of precast
Epis
eA
Damages can be commonly found at the
‘contact areas between the precast
ei antate
Figure 42 Pro
damages to precast concrete elements
reer
packer to secul
the precast
tac
Petia ety
PSS
Perea eres
pepe eerie
ion measures such as the use of cushion packing or polythene wrapping can be used to minimise PRECAST CONCRETE ELEMENTS | DELIVERY, HANDLING AND STORAGE
Figure 4.2 Precast elements should be adequately fixed and secured ta pre-emat mevernent or accidental spillage during
transit
4.2. HANDLING
The handling process mainty involves the removal of the precast elements from the mould, transportation to the
storage yard, loading and unloading operation and erection of thase elements at the job site. Different sets of lifting
points and castin devices will have to be used for various handing stages.
‘Tyically, precast concrete elements are demoulded and lifted from their casting position to storage yard and delivery
to site once they reach the expected concrete strength reauired. As these elements have not gained their full
designed strength, they are generally more susceptible to damages during handling. Its therefore important to
fensure that they are handled in a way that is consistent with their shapes and sizes, to avoid excessive stresses
or damages. For elements with large openings, temporary bracing, ties or strongoacks should be provided
handling as shown in Figure 4.4
‘The handling requirements depends on th
lowing factors
+ Position of the casting mould {e vertical casting vs horizontal casting)
‘+ Minimum conerate strength of the precast elements for demoulding, delivery and erection
* Adequacy of the design reinforcement to resist handling stresses
+ Size and weight of the precast sloma!
+ Number, size and location o iting points and type of inserts/de
+ Method of iting, type af lifting equipment and crane capacity
* Support points for storage and transportation
2% PRECAST CONCRETE ELEMENTS | DELIVERY, HANDLING AND STORAGE
Figure 4.4 Temporary strengthening of panels with openings
Basically, the elements when handled must be balanced and inline with their centre of gravity. The general hoisting
methods used for different precast conerete elements are llustrated inthe following Figute 4.5 - Figure 48
Precast Beam
Note : The lifting points should be designed and located to limit the bending moments within the bear element.
‘As a general guide, they should be located at about one fifth of the beam length measured from the edge.
Figure hoisting method for beam
2 PRECAST CONCRETE ELEMENTS | DELIVERY, HANDLING AND STORAGE
Precast Wall
For wall panels itis recommended
tolft the panel in vertical position
for installation so that turning is
not required
joisting mothod adopted for
demoulaing of wall panels that are
cast horizontally
Figure 4.6 General hoisting method for wal
Precast Plank / Slab
Note : Where necessary, multiple iting points can be designed and located to minimise undue stresses within
the slab elements, in particular for slender panels such as precast planks.
Figure 4.7 General hoisting method ‘or plankslab
Ey 2
PRECAST CONCRETE ELEMENTS | DELIVERY, HANDLING AND STORAGE
Precast Column
gd
LV
Note : Columns are usually frst handled in horizontal position Slings are attached to the inserts at the top
0 facilitate the rotation of the elements to vertical position, before hoisting and placing to their designated
Figure 4.8 General hoisting methos for column
4.3. STORAGE
The storage area provided in the yard and job site should be adequate to permit easy access and handling of the
ast elements. The area should be relatively level, firm and well drained to avoid any differential ground s
re
which may damage the stored elements
iate stacking method shoul be used to store the precast concrete elements to prevent any undue stresses
and damages (see Fig 4.9 and 4.10}. Horizontal precast conerete elements such as precast slabs, planks, beams
and hollowcore panels, can be stacked and supported separately using strips of woods or battens across the full
‘width of the designated bearing points. Precast walls and tacade panels are usually stored in vertical position
supporting their own weight using racks with stabilising wall, Storage conditions can be an important fact
achieving and maintaining panel bowing and warping tolerances, More lateral support should be given to slender
panels, which are more likely to bow or warp. To minimise handling, the elements should also be stored based on
Ann
the erection sequence. PRECAST CONCRETE ELEMENTS | DELIVERY, HANDLING AND STORAGE
J
Stacking method and packers for support spacers] vary | Do not use mote than two support points in partic,
socercing to the tynes of precast elements, Horizontal | for prestressed element such as hollow core slab
stacking of slabsbeam of column units can be done with
Suitable packers or support spacers shown above. AS
2 guide, the storage support position for beams and
planks should be within 200mm from the lifting points.
x
x v
‘Tho packers or supaor spacers should pot be misaligned | Wal panels should be stored vertically and braced in
as shown, position by Aframes or a racking system.
Figure 4.9 General guidelines on stacking method of precast elements
Fr eet oes
31 Figure 410 Different storage and stacking requirements for diferent precast elements PRECAST CONCRETE
MENTS | DELIVERY, HANDLING AND STORAGE
Figure 4.11 Examples af improper storage and stacking methods
‘The storage area atthe jo site should areferably be close to the locations where the precast elements are to be installed
to minimise the risk of damage by handing
Figure 4.12 Procast concvot
should profe
near ther final position for
easy handling
ments
be stored
2 5. Installatio
5.1, GENERAL
Proper planning and preparatory works are required before the actual erection of precast concrete elements to
ensure efficiant and qualty instalation. The following items should be carefull planned
. 1d and sequence of assembly and erection
. 1d of providing temporary supports
+ Provision for final steuctural connections and joint details
Erection tolerances
Handling and rigging requirements
Prior to the instllati
checks isted in Table 6.1
of the precast concrete elements, itis important to consider the following work items and
Table 5.1 Pray
ratory works items and checklists
= Check for site accessibllty for the delivery of precast elements
* Check delivery checklist for corroct type, quantity and panel identiicatic
* Check for adequate crane capacity and working clearance for hoisting of precast concrete elements
‘Conduct samole measurement to confirm
the accuracy ofthe critical dimensions
st concrete elements and openings
'* Conduct visual inspection on concrete
finishes and check for any major defects PRECAST CONCRETE ELEMENTS | INSTALLATION
‘+ Check the locations and conditions of iting inserts before hoisting
+ Check on the accessibility of unloading point and storage area’
* Check that the storage area is of hard, level, clean and well drained ground
* Store the precast elements where required using "First In First Out” principle according to the delivery schedule
and erection sequence
™ ONCRETE ELEMENTS | INSTALLATION
5.2. INSTALLATION OF VERTICAL PRECAST COMPONENT
The method a Cf installing the precast wall panels (which is also applicable to other vertical components)
tlined in Table 6.2
Peer
cers
nee line and offset tine | + Check the accuracy of the offset lines.
mine the position of the
precast elements to be instaled. | + Chack the shim plate level and stability
+ For vertical precast component, check the positions and aignmen:
lof the starter bars before hoisting for installation.
1.2. Provide level pads (or shim plates)
for setting the level of the
elements. Set the level pads in
position using non-shrink mortar.
b
1.3.For precast external wall
column, fix the compressiole
form or backer rod on the outer
perimeters of wall PRECAST CONCRETE ELEMENTS | INSTALLATION
2.1. Lift and ig the panel to its
location with the
Use of wire ropes.
2.2. Adjust the panel to position and
‘secure it with diagonal props.
SS
+ Check the hoisting condition of the precast oloment.
+ Check alignment and verticalty of the panel. If necessary, aust the
temporary propaing to achieve the level and position of the precast
+ Check the staiity of the.
cable
leasing the hoisting
=<
36 PRECAST CONCRETE ELEMENTS | INSTALLATION
2
Pe
3a
32,
33,
routing work
Prepare and apply non-shrink
‘mortar to seal the gaps along the
boattom edge othe inner sie of
the panel
For corrugated pine sleeve or
splice sleeve connection, prepare
fand pour non-shrink grout or
proprietary grout into the sine
inlets provided.
Keep the installed panels
Lnsisturved for atleast 24 hours,
Good
+ Check that the joint width between panels are within design
allowances before grouting
i
+ Non-shrink grout used atthe interface with the precast elements
should preferably be free flowing and self comoacting in nature so
{2 fo ensure good compaction at the joint and to minimise the risk
of cracking.
‘+ Non-shrink grout should be prepared in accordance with the
specifications.
+ Check that all horizontal joints are properly sealed.
+ Collect sample test cubes ofthe grout mix used fr critical elements
such loading bearing walls or testing PRECAST CONCRETE ELEMENTS | INSTALLATION
Installation sequ
4, Joint casting and sealing
4.1. For panels with cast in-situ joints,
install the jon rebars as required.
4.2. Sot up forms for the casting of
the vertical joint.
43, Carty out concrete casting
44, Remove forms atter sufficient
concrete strength has beon
achieved,
45, For joints between facade walls
or between external columns
‘with beams or walls elements,
approved sealant and grout will
be installed at later stage,
cy
46. For panel with welded
connecton, place the connecting
plate between the panels and
carry out welding as per design
requirement.
+ Tho joint rebars should be correcty placed in accordance with the
dosign specifications.
+The formwork shouldbe propery secured duting the casting operation
of the joint
+ The joint gaps should be consistent to alow for proper installation
of sealant or grout for better watertightness.
Consistent joint
1989 to for proper
sealant or grout
instalation
Sealent
application
Backer rod
38 PRECAST CONCRETE ELEMENTS | INSTALLATION
5.3. INSTALLATION OF HORIZONTAL PRECAST COMPONENT
‘The method and sequence of installing the precast slabs and beams {which is also af
omponents} are outlined in Table 5.3.
‘able to other horizontal
Table 5.3 Horizontal component installation
Installation sequenet ens
Setting out
1. Set reference ine and ofset line | * Check the accuracy ofthe offeet lines.
fo determine the required
‘ignment andlevel tthe precast | * Chock the level and stability ofthe shim pat
slab/beam elements during
instalation. + Before hoisting, check that the dimensions and alignment of
the protruding bars are within the speci
prevent any obstruction during the erec
fied toleranc
to
+ Beam elements shouldbe supported at minimum two leations
during hoisting, PRECAST CONCRETE ELEMENTS | INSTALLATION
2.2. Lift and rig the slemants to
designated location with the
use of wire ropes.
2.3. Align and check I
the required seting out before
placement of precast members
to final position
+ Balcony, planter lodge and slab should be supported at more than
tions, depending on the dimensions of the elements and
+ Itisimportant to check on the levelness of the precast elements as
‘well as between the elements bofore proceeding to do the jointing
works.
40 PRECAST CONCRETE ELEMENTS | INSTALLATION
a
2.1. For components with cast in-situ
Joints, place and lap the rebars
as required.
3.2. Set up the formwork for the
casting of the joint.
33.Carry out concrete casti
2.4, Remove forms after sufficient
fe strength hes been
ear
actices
+ The joint rebars should be corre
design specifications.
ly placed in accordance with the
+ The formwork should be properly secured during casting ofthe in-
+ Supporting beams can be designed to form part of the formwork
for the casting of joint. uality In
6.1. GENERAL
iis important to have quality inspections as part of the integral process in managing quality of precast concrete
elements. Close supervision should be provided for both critical in-process and finished works so as to achieve high
‘workmanship quality.
Quality assurance and control stats with good planning and management. Itis @ good practice to prepare an Inspection
and Test Pian, ITP (see Appendix A) whicn summarises the projects’ inspection, acceptance criteria and frequency of
inspections. Checklists for the in-process and final inspection of precast concrete elements should also be prepared
{as in Appendix B} to detail the checks required at critical stages.
Quality inspections for the in-process works are highlighted in Chapter 3 ~ Fabrication Process. This section will only
cover quality inspections for the finished precast concrote elomants delivered and erected on site,
6.2. INSPECTION OF PRECAST CONCRETE ELEMENTS
The finished precast concrete elements and works should be inspected to ensure they meet the client's requirement
and standards. Table 6.1 shows the recommended checklist fo final inspection of the precast conerete elements based
‘on CONQUAS 21 quality assessment criteria,
Table 6.1 Checkli
{or final inspection of precast concrete elements
ears
PEON CUE ea oc Re
1.1. Tolerance of cross sectional dimensions of precast elements : +10mm /-Smm
[Note : It is common to have the actual dimensions of a precast Maximum dimension
concrete element to be slightly different from its designed A, +10mm OR A, +10mm
dimensions, However, the variation n cross sections should be
within acceptable tolerances “Minium gimension
A 5mm OR A, 5mm 4“
PRECAST CONCRETE ELEMENTS | QUALITY INSPECTION.
Note: It is important to ensure that the penetration / opening for services are within tolerances for proper
connection and linkages of the M & E services.
1.3, Tolarance for langth of precast members (major dimension of unit
+ Upto 3m: + 6mm
+ 3m t0.4.5m : 4 9mm
{8m + 12mm.
tion for every subsequent 6m : + 6mm
po,
t members
Dimensional length of pre
L& 6mm for L<3m
LL 9mm for am