The equipment used in the precast concrete industry/
construction may be classified into the following categories:
a) Machinery required for quarrying of coarse and fine aggregates;
b) Conveying equipment, such as belt conveyors, chain conveyors, screw conveyors, bucket elevators, hoists, etc;
c) Concrete mixing machines;
d) Concrete vibrating machines;
e) Erection equipment, such as cranes, derricks, hoists, chain pulley blocks, etc;
f) Transport machinery, such as tractor-cum-trailers, dumpers, lorries, locomotives, motor boats and rarely even helicopters;
g) Workshop machinery for making and repairing steel and timber moulds;
h) Bar straightening, bending and welding machines to make reinforcement cages;
j) Minor tools and tackles, such as wheel barrows, concrete buckets, etc; and
k) Steam generation plant for accelerated curing.
In addition to the above, pumps and soil compacting machinery are required at the building site for the execution of civil engineering projects involving prefabricated components.
Each of the above groups may further be classified into various categories of machines and further to various other types depending on the source of power and capacity.
11.2Mechanization of the Construction and Erection Processes
The various processes can be mechanized as in any other industry for attaining the advantages of mass production of identical elements which in turn will increase productivity and reduce the cost of production in the long run, at the same time guaranteeing quality for the end-product. On the basis of the degree of mechanization used, the various precasting factories can be divided into three categories:
a) With simple mechanization;
b) With partial mechanization; and
c) With complex mechanization leading to automation.
11.2.1 In simple mechanization, simple mechanically operated implements are used to reduce the manual labour and increase the speed.
11.2.2 In partial mechanization, the manual work is more or less eliminated in the part of a process. For example, the batching plant for mixing concrete, hoists to lift materials to a great height and bagger and bulldozer to do earthwork come under this category.
11.2.3 In the case of complex mechanization leading to automation, a number of processes leading to the end-product are all mechanized to a large extent (without or with a little manual or human element involved). This type of mechanization reduces manual work to the absolute minimum and guarantee the mass production at a very fast rate and minimum cost.
11.2.4 The equipment shall conform to accepted standards as listed in Part 7 'Construction Management, Practices and Safety' of the Code.
12 PREFABRICATED STRUCTURAL UNITS
For the design and construction of composite structures made up of prefabricated structural units
and cast in-situ concrete, reference may be made to the good practice [6-7A(4)].
For design and construction of precast reinforced and prestressed concrete triangulated trusses reference may be made to the good practice [6-7A(5)].
For design and construction of floors and roofs using various precast units, reference may be made to the good practice [6-7 A(6)].
For construction with large panel prefabricates, reference may be made to good practice [6-7 A(3)].
For construction of floors and roofs with joists and filler blocks, reference may be made to good practice [6-7A(7)].
Annexa
(Foreword) COMMON DEFECTS AND REMEDIES
A-I As defects in precast concrete elements result in direct and indirect cost in terms of rectification and construction time, it is worthwhile to ensure that they are produced and handled in a way to avoid/reduce
such incidences. Table 4 illustrates some of these common defects, their causes and preventive measures.
Table 4List of Common Defects and Recommended Measures (Clause A-I)
Sl No.
Common Defects
Possible Causes
Recommendations
Remedial Measures
(1)
(2)
(3)
(4)
(5)
i)
Dimensional deviation:a) Variation in the dimension of precast elements would affect the joint alignment between these elements when erectedb) Precast slab element may warp due to insufficient concrete strength at lifting or improper storage condition
a) Mould forms may not be sufficiently rigid to maintain specified tolerances during concrete placementb) Precast elements may not have gained sufficient concrete strength when demouldedc) Top surface finish of precast elements may not be properly levelled and troweled during production which result in differential thicknessd) Precast elements (especially slender wall or slab panels) may be subjected to undue stress and deformation when they are not properly
a) Regular check on the dimensions and rigidity of mould forms before casting operations.As a general guide the recommended thickness for steel mould are:1) 4.5 mm - up to 50 castings2) 6 mm - up to 100 castings3) 9 mm - up to 200 castingsMould forms conditions will deteriorate with time and usage. They should be repaired, stiffened or replaced when neededb) Cube tests should be conducted to ascertain the concrete strength of
a) For minor deviation, corrective measures such as surface grinding, trimming/hacking and skim coat application can be appropriately used to remedy the situationb) Precast elements that are not within acceptable tolerance limits and have significant effects on the structural integrity or architectural performance should not be used
PART 6 STRUCTURAL DESIGN - SECTION 7 PREFABRICATION, SYSTEMS BUILDING AND MIXED/COMPOSITE CONSTRUCTION: SECTION 7A PREFABRICATED CONCRETE
Table 4(Continued)
(1)
(2)
(3)
(4)
(5)
supported during storage
elements before demoulding.c) Spreading and levelling of concrete placement using appropriate tools such as screederd) Precast elements should be properly stored and stacked at designated points using suitable support spacers and frame rack system
ii)
Cracks
a) Precast elements may not have gained sufficient concrete strength before demouldingb) Cracks may have occurred during initial lifting due to friction between the elements and the casting mould formsc) Thickness of the precast elements may be too thin (70 mm or less) and flimsy for safe demoulding and handlingd) Cracks may have occurred during erection due to lack of planning and provisions given to the precast panel geometry, crane rigging configuration and location of openings
a) Proper curing method, curing time and temperature should be maintainedb) Cube tests should be conducted to ascertain the concrete strength of elements before demouldingc) Appropriate form release agents should be used and uniformly applied onto the mould surface to minimize frictiond) Sectional thickness of precast elements should be increased to accommodate demoulding and handling stressese) Proper handling techniques should be adoptedf) Sufficient lifting points should be used to minimize over-stressing on certain areasg) Additional reinforcing bars should be placed around the opening and odd cornersh) Temporary stiffeners for openings should be provided during erection
a) All cracks should be examined by a qualified engineer to determine if they present a structural problemb) Depending on the locations and seriousness of the cracks, different repair methods can be used to make good the affected precast elementsc) Hairline cracks (not more than 0.3 mm) can be repaired by cutting V-groove of specified minimum depth along the crack-lines, followed by patchingd) For surface cracks (more than 0.3 mm) or through cracks, epoxy injection method should be used to ensure that the cracks are completely bound and filled with epoxy
iii)
Chip-off and damages
a) Chip-off at panel edges are usually caused by the hard bearing at supports or excessive force exerted on the elements when handlingb) Improper storage method
a) Precautions should be taken to avoid damaging the elements in the course of placement on vehicle, travel to site and during the unloading operation. Bearing pads should be used to cushion the contact areas from damageb) The storage area should be relatively flat and dryc) Precast elements should be properly stored and stacked at designated points using suitable support spacers and frame rack systemd) The casting slab or mould form should be thoroughly cleansed, levelled to achieve a smooth surfacee) The coverage of form release agents should be
a) Remove all loose concrete and wash off any dust or dirt in the affected areab) Apply bonding agent to affected concrete surfacec) Welded wire mesh can be included to provide support for the patch mix concrete or groutd) Patch mix composition or grout should be consistent with the strength requirements of the adjacent concretee) Formwork is to be put up where necessary to contain the patch mix or groutf) Protect the affected
Table 4(Continued)
(1)
(2)
(3)
(4)
(5)
adequate and uniformly applied onto the mould surfacef) Spacers of the correct sizes should be used and well secured to maintain the concrete cover required during castingg) Lifting inserts and concrete strength of elements should be of adequate capacity for the intended lift. Use lifting proprietary products for safe and efficient handlingh) Lifting inserts or hooks should be inspected for proper location. They should be fastened to specified depth prior to concrete placement
area from any disturbance during curing period
iv)
Honeycomb and excessive pinholes
a) Poor concrete compaction due to ineffective vibration or rebars congestionb) Grout leakage along the perimeter side forms due to,1) loose or missing bolts, fixing pins2) damaged rubber gasket seal3) mould part, if defective
a) Proper compaction method should be adopted and carried outb) Concrete mix design and workability should be reviewed and adjusted when neededc) Appropriate concrete vibrator such as clamp-on form vibrator can be used to attain better compactiond) Rebar congestion can be alleviated by having larger (that is, lesser) rebars or by increasing the sectional dimensions of the elements, where possiblee) Mechanical couplers or sleeves can be used to simplify the reinforcement layout and to minimize rebar congestionf) Defective mould forms and accessories should be repaired or replaced to prevent grout leakage during concreting
a) Remove all loose concrete and wash off any dust or dirt in the affected areab) Apply bonding agent to affected concrete surfacec) Welded wire mesh can be included to provide support for the patch mix concrete or groutd) Patch mix composition or grout should be consistent with the strength requirements of the adjacent concretee) Formwork is to be put up where necessary to contain the patch mix or groutf) Protect the affected area from any disturbance during curing period
v)
Missing or wrong details such as cast-in items, architectural nib and groove details, lifting hooks, reinforcement/starter bars/blockout/corrugated pipes
a) Items may not have been included in the shop drawingb) Quality checks may not be properly in place
a) All items should be reflected in the shop drawings for production. Any changes should be made known to the production teamb) The use of checklists during inspection can help to ensure that all items specified in the drawing are included before casting
a) Certain details such as missing starter bars/ reinforcement and lifting hooks can be replaced by welding additional reinforcement bars after hacking off the concrete at the affected areab) Other items such as cast-in items, groove and blockout can be provided by chasing or chiseling out the face of the precast panels
PART 6 STRUCTURAL DESIGN — SECTION 7 PREFABRICATION, SYSTEMS BUILDING AND MIXED/COMPOSITE CONSTRUCTION: SECTION 7A PREFABRICATED CONCRETE
Table 4 — (Concluded)
(1)
(2)
(3)
(4)
(5)
applicable to pre-stressed elements only)Slippages of pre-stressing strands can be detected by visual inspection
pre-stressing strandsb) Poor compaction of concrete around pre-stressed strands
should be attained and verified by cube test results before de-tensioning of strandsb) Proper compaction method should be adopted and carried out during castingc) Concrete mix design and workability should be reviewed and adjusted when neededd) Provision of appropriate concrete vibrator to attain better compaction
from strand slippageb) Design verification should be carried out to ascertain the reduced capacity of the elements due to slippage, if adopted
vii)
Alignment
a) Inaccurate setting out and positioning of precast elements during erectionb) Deviation in the dimensions of the precast element
a) Appropriate surveying and leveling equipment should be used to achieve better alignmentb) Required alignment and level should be confirmed before permanent jointingc) Critical dimensions of precast concrete elements should be verified before installation
a) Minor adjustments of the element/panel alignment can be done during installationHowever the effects on the final alignment and deviation of the building should be evaluatedb) For minor deviations, corrective measures such as surface grinding, trimming/hacking and skim coat application can be appropriately used to rectify the precast elements before installationc) Precast elements that are not within acceptable tolerance limits and have significant effects on the structural integrity or architectural performance should not be used
The following list records those standards which are acceptable as ‘good practice’ and ‘accepted standards’ in the fulfilment of the requirements of the Code. The latest version of a standard shall be adopted at the time of enforcement of the Code. The standards listed may be used by the Authority for conformance with the requirements of the referred clauses in the Code.
In the following list, the number appearing in the first column within parentheses indicates the number of reference in this Subsection.
6073 : 2006 Specification for autoclaved reinforced cellular concrete floor and roof slabs (first revision)
9893 : 1981 Specification for precast concrete blocks for lintels and sills
10297 : 1982 Code of practice for design and construction of floors and roofs using precast reinforced/ prestressed concrete ribbed or cored slab unit
10505 : 1983 Code of practice for construction of floors and roofs using precast concrete waffle units
11447 : 1985 Code of practice for construction with large panel prefabricates
12440 : 1988 Specification for precast concrete stone masonry blocks
13990 : 1994 Specification for precast reinforced concrete planks and joists for flooring and roofing
14143 : 1994 Specification for prefabricated brick panel and partially precast concrete joist for flooring and roofing
14201 : 1994 Specification for precast
IS No. Title
reinforced concrete channel unit
for construction of floors and
roofs
14241 : 1995 Specification for precast L-Panel units for roofing
(2) 4905:1968 Methods for random sampling
(3) 11447 : 1985 Code of practice for construction with large panel prefabricates
(4) 3935 : 1966 Code of practice for composite construction
(5) 3201:1988 Criteria for design and construction of precast trusses and purlins (first revision)
(6) 6332 : 1984 Code of practice for construction of floor and roofs using precast doubly-curved shell units (first revision)
10297 : 1982 Code of practice for design and construction of floors and roofs using precast reinforced/ prestressed concrete ribbed or cored slab units
10505 : 1983 Code of practice for construction of floors and roofs using precast reinforced concrete waffle units
13994 : 1994 Code of practice for design and construction of floor and roof with precast reinforced concrete planks and RC joists
14142 : 1994 Code of practice for design and construction of floors and roofs with prefabricated brick panel
14215 : 1994 Code of practice for construction of floor and roof with RC channel units
14242 : 1995 Code of practice for design and construction of roof with L-Panel units
(7) 6061 Code of practice for construction of floor and roof with joists and filler blocks
(Part 1): 1971 With hollow concrete filler blocks
(Part 2): 1981 With hollow clay filler blocks (first revision)
(Part 3): 1981 With precast hollow clay block joists and hollow clay filler blocks
(Part 4): 1981 With precast hollow clay block slab panels
PART 6 STRUCTURAL DESIGN — SECTION 7 PREFABRICATION, SYSTEMS BUILDING AND MIXED/COMPOSITE CONSTRUCTION: 7A PREFABRICATED CONCRETE
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PART 6 STRUCTURAL DESIGN
Section 7 Prefabrication, Systems Building and Mixed/Composite Construction:
7B Systems Building and Mixed/Composite Construction
BUREAU OF INDIAN STANDARDS
FOREWORD
... 3
1 SCOPE
... 5
2 TERMINOLOGY
... 5
3 MATERIALS, PLANS AND SPECIFICATIONS
... 6
4 MODULAR COORDINATION, ARCHITECTURAL TREATMENT AND FINISHES
... 6
5 COMPONENTS
... 6
6 FORMWORK SYSTEMS
... 6
7 SYSTEM AND STRUCTURAL SCHEMES
... 7
8 DESIGN CONSIDERATIONS
... 7
9 JOINTS
... 8
10 TESTS FOR COMPONENTS/ STRUCTURES
... 8
11 ERECTION
... 8
12 EQUIPMENT
... 8
13 PREFABRICATED STRUCTURAL UNITS
... 8
ANNEX A CONSTRUCTION PRACTICE FOR DECKING
... 9
ANNEX B CONSTRUCTION PRACTICE FOR CONCRETING ON DECKING
... 10
LIST OF STANDARDS
... 12
National Building Code Sectional Committee, CED 46
This Code (Part 6/Subsection 7B) covers recommendations regarding modular planning, component sizes, joints, manufacture, storage, transport and erection of prefabricated elements for use in buildings and such related requirements for systems building and mixed/composite construction.
Systems building and mixed/composite building construction, popularly referred to as pre-engineered building (PEB) construction, is an upcoming field as far as its development and use in the country is concerned. Two aspects specifically to be borne in mind are the system to be adopted for the different categories of buildings and the sizes of their components. Here the principle of modular coordination is of value and its use is recommended.
This Section was first published in 1970 and was subsequently revised in 1983 and 2005.
In the second revision in 2005, this Section, earlier named as prefabrication and systems building was renamed and restructured as follows:
Section 7 Prefabrication, Systems Buildings and Mixed/Composite Construction
7A Prefabricated Concrete
7B Systems Buildings and Mixed/Composite Construction
This Subsection 7B covering systems building and mixed/composite construction, introduced in 2005, prescribed general requirements applicable to all valid existing systems and mixed/composite constructions as also to accommodate any new system introduced in the country. The Subsection 7A covered those systems approach which predominantly uses concrete as the material for components.
In this revision of this Subsection, following modifications have been incorporated:
a) Definitions of some existing terminologies have been modified, wherever required.
b) Aspects enlisted relevant to devising systems and structural schemes, have been updated.
c) Design considerations have been reviewed and modified based on latest thinking and practices.
The information contained in this Subsection is largely based on IS 15917 : 2010 ‘Building design and erection using mixed/composite construction — Code of practice’.
All standards, whether given herein above or cross-referred to in the main text of this Subsection, are subject to revision. The parties to agreement based on this Subsection are encouraged to investigate the possibility of applying the most recent editions of the standards.
For the purpose of deciding whether a particular requirement of this Subsection is complied with, the final value, observed or calculated, expressing the result of a test or analysis, shall be rounded off in accordance with IS 2 : 1960 ‘Rules for rounding off numerical values (revised)’. The number of significant places retained in the rounded off value should be the same as that of the specified value in this Subsection.
PART 6 STRUCTURAL DESIGN — SECTION 7 PREFABRICATION, SYSTEMS BUILDING AND MIXED/COMPOSITE CONSTRUCTION: 7B SYSTEMS BUILDING AND MIXED/COMPOSITE CONSTRUCTION
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vi)
Strand slippage which exceed allowable design values (item
a) Insufficient bond strength between concrete and the
a) Required concrete strength of the precast elements