Prefabrication is the practice of assembling components of a structure in a factory or other manufacturing site, and transporting them to the construction site where the structure is to be located.

1. DEEKSHA MITTAL
PRATIKSHA
AGGARWAL
SHAILJA KUMARI

2. What is Prefabrication?
 Prefabrication is the practice of assembling components of a structure in
a factory or other manufacturing site, and transporting them to the construction site
where the structure is to be located.
 The method controls construction costs by economizing on time, wages, and
materials.
 Prefabricated units may include doors, stairs, window, wall panels, floor
panels, roof trusses and even room-sized components.

3. Theory
 The theory behind the method is that time and cost is saved if similar construction
tasks can be grouped, and assembly line techniques can be employed in
prefabrication at a location where skilled labour is available, while congestion at the
assembly site, which wastes time, can be reduced.
 The method finds application particularly where the structure is composed of
repeating units or forms, or where multiple copies of the same basic structure are
being constructed.
 The restricting conditions such as a lack of power, lack of water, exposure to harsh
weather or a hazardous environment are avoided.
 Against these advantages must be weighed the cost of transporting prefabricated
sections and lifting them into position.

4. What Material to Use?
 Materials that allow a large span construction shall be used.
 Actual manufactured components vary slightly when made from the specified
dimensions , thus a material shall be used which gives minimum variation.
 Economic and cost– effective materials.
 Aesthetically sound material shall be used to improve the appearance of building.
 Material must be able to take the structural loads and stresses.
 A material that can be molded to variety of shapes shall be used.
 Ease of maintenance.

5. What is the Aim of Prefabrication?
 to speed up the construction time.
 to lower the labour cost.
 to allow the year round construction.
 to ensure precise conformity to standards.
 to ensure greater quality.
 to allow less wastage of materials.
 to ensure higher worker safety and comfort level than in site- built
construction.

6. Prefabricated Building Material
 Door frames
 Window frames
 Roof slabs
 Lintels
 Ventilators
 Wall partition panels
 Compound wall panels
 Cement concrete
 Small pillars for
compound wall
 Sills
 Trusses etc.

7. Prefabricated Building Material

8. Flow of Materials, Components &
Prefabricated Elements

12. Components of Prefabrication
The preferred dimensions of precast elements according to
NBC shall be as follows:
Flooring and Roofing Scheme - Precast slabs or other
precast structural flooring units:
 Length - Nominal length shall be in multiples of 1 M;
 Width - Nominal width shall be in multiples of 0.5 M; and
 Overall Thickness - Overall thickness shall be in multiples of
0.1M.
Beams
 Length - Nominal length shall be in multiples of 1 M;
 Width - Nominal width shall be in multiples of 0.1 M; and
 Overall Depth - Overall depth of the floor zone shall be in
multiples of 0.1M.

13. Columns
 Height - Height of columns for industrial and other building 1 M; &
 Lateral Dimensions - Overall lateral dimension or diameter of
columns shall be in multiples of 0.1 M.
Walls
 Thickness - The nominal thickness of walls shall be in multiples of
0.1 M.
Staircase
 Width - Nominal width shall be in multiples of 1M.
Lintels
 Length - Nominal length shall be in multiples of 1 M;
 Width - Nominal width shall be in multiples of 0.1 M; and
 Depth - Nominal depth shall be in multiples of 0.1 M.
Sunshades/Chhajja Projections
 Length - Nominal length shall be in multiples of 1 M.

14. Types of Prefabrication
Components
The prefabricated concrete components such as those given below may be used
which shall be in accordance with the accepted standards, where available:
 Reinforced/Prestressed concrete channel unit.
 Reinforced/Prestressed concrete slab unit.
 Reinforced/Prestressed concrete beams.
 Reinforced/Prestressed concrete columns.
 Reinforced/Prestressed concrete hollow core slab,
 Reinforced concrete waffle slab/shells.
 Reinforced/Prestressed concrete wall elements,
 Hollow/Solid blocks and battens,
 Precast planks and joists for flooring and roofing,
 Precast joists and trussed girders,
 Light weight/cellular concrete slabs,
 Precast lintel and chhajjas,
 Large panel prefabricates,
 Reinforced/Prestressed concrete trusses,
 Reinforced/Prestressed roof purlins,
 Precast concrete L-panel unit,
 Prefabricated brick panel unit,
 Prefabricated sandwich concrete panel, and
 Precast foundation.

15. On Site & Off Site Prefabrication
Manufacture:
The manufacture of the components can be done in a factory for
the commercial production established at the focal point based on
the market potential or in a site-precasting yard set up at or near
the site of work.
 Factory prefabrication
Factory prefabrication is resorted to in a factory for the
commercial production for the manufacture of standardized
components on a long-term basis. It is a capital-intensive
production where work is done throughout the year preferably
under a closed shed to avoid effects of seasonal variations.
High level of mechanization can always be introduced in this
system where the work can be organized in a factory-like
manner with the help of a constant team of workmen.

16.  Site prefabrication
Prefabricated components produced at site or near the site of work
as possible. This system is normally adopted for a specific job
order for a limited period.
 Semi-mechanized
The work is normally carried out in open space with locally
available labor force. The equipment machinery used may be
minor in nature and moulds are mobile or stationary in nature.
 Fully-mechanized
The work will be carried out under shed with skilled labor. The
equipments used will be similar to one of factory production. This
type of precast yards will be set up for the production of precast
components of high quality, high rate of production. Though there
is definite economy with respect to cost of transportation, this
system suffers from basic drawback of its non-suitability to any
high degree of mechanization and no elaborate arrangements for
quality control. Normal benefits of continuity of work are not
available in this system of construction.

17. The transportation of precast facades.The temporary supporting props
to
hold the precast facade in
position. This prevents any
movement of the panel and
allows final adjustments to be
made.

18. The worker is laying the services
pipes and service conduits
Lifting Precast Slab into Position

19. Advantages of Using Prefabricated
Structures
 Factory made products.
 Independent of adverse weather conditions during construction.
 Reduced energy consumption.
 Environmentally friendly way of building with optimum use of materials, recycling
of waste products, less noise and dust etc.
 Cost effective solutions.
 Reduction in construction time.
 Safety in construction.
 Increase in the quality of construction.
 Reduction of construction waste.
 Demountable structures.
 Accelerated curing techniques.

20. Disadvantages of Using Prefabricated
Structures
 A small number of units required may prove to be uneconomical.
 Special connections, such as special bearings to transmit the vertical and horizontal
loads, can add cost to the system.
 Waterproofing at joints.
 Transportation difficulties.
 Large prefabricated sections require heavy-duty cranes and precision measurement
and handling to place in position.

21. Prefabrication Systems
 Open Prefabrication System
 Large Panel Prefabrication system

22. Open Prefabrication System
 It allow the pre-casted to produce a limited number of elements with a
predetermined range of product and at the same time maintaining
architectural aesthetic value.
 Inspite of many advantages of open system, its adoption experiences one
major setback. For example, joint and connection problem occur when two
elements from different system are fixed together. This is why similar
connection technology must be observed in order to achieve greater structural
performance.
 There are two categories of open prefab system depending on the
extent of prefabrication used in the construction as given in Partial and
Full prefabrication systems:
 Partial prefabrication system
This system basically uses precast roofing and flooring components
and other minor elements like lintels, chhajjas, and kitchen sills in
conventional building construction. The structural system could be in the
form of in-situ framework or load bearing walls.
 Full prefabrication system
In this system almost all the structural components are prefabricated.
The filler walls may be of brick/block masonry or of any other locally
available material.

23. Large Panel Prefabrication System
 This system is based on the use of large
prefab components. The components
used are precast concrete large panels
for walls, floors, roofs, balconies,
staircases, etc. The casting of the
components could be at the site or off the
site.
 Multistory structures are composed of
large wall and floor concrete panels,
connected in the vertical and horizontal
directions.
 Panels form a box-like structure. Both
vertical and horizontal panels are load
bearing. Wall panels are usually one story
high.
 Horizontal floor and roof panels span either
as one-way or two-way slabs. When
properly joined together, these horizontal

24. • Contains insulation, wiring, or pre-cut opening for
windows and doors
• Construction of panelized homes includes whole
walls with windows , doors, wires or outside
siding prepared in factory and erected on site.
• Depending on the wall layout, there are three
basic configurations of large-panel buildings:
1. Cross wall system
2. Longitudinal wall system
3. Two way system
Thickness of wall panels:120 mm (interior walls)
300 mm (exterior walls)
Floor panel thickness : 60 mm.
Wall panel length : room length (2.7m to 3.6m)
Precast vertical boundary wall panel
Precast wall panel
Precast wall panel

25. Process:
• Precast concrete panels are cast face-downwards in
purpose-built moulds, usually made of either timber
or fibre glass.
• A steel reinforcement cage is placed in the mould
prior to the concrete being poured.
• By inserting mats or rods in the base of the mould
different designs and effects can be created - from
false joints to intricate leaf patterns.
• Increasingly, maximum use of off-site fabrication is
being made by fixing other elements, from insulation to
entire windows, during manufacture of precast panels.
• Once de-moulded, the exposed surface of the unit
can be treated in a variety of ways - acid-etched,
smooth or coarse ground, grit or sand-blasted, rubbed or
polished.
Moulds
Different designs and
effects can be created

27. PRECAST
CONNECTIONS

28. •Precast boundary walls are similar to precast wall panels but are typically of smaller
sizes.
PRECAST BOUNDARY WALLS
•quite ideal for pre casting as the smaller panels
•fewer problems with handling, transportation and installation on site.
Joint details
The considerations for proper joint details in the precast boundary panels are similar
to those for precast wall panels. The design of the wall joints will include the
following considerations:
• water tightness • installation method
• structural movement • type of wall finishes
• panel sizes • weathering
• tolerance

29. Finishes
 wide range of design flexibility and innovation.
 wide range of surface finishes on the precast boundary wall design.
The most common techniques used are modeling techniques like sand
blasting, acid washing, polishing and honing, hammering and chipping to
create the required effects.
 These finishes can then be treated with appropriate protective coatings
to prevent weathering and staining problems.
A wide range of colours for precast boundary wall panel can be derived
from aggregates, cement or pigments. Aggregate can provide colour to the
final finishes.
Cement with different colours can also give the desired colour for the
boundary wall panel. Another form of colour finishes are colour and oxide
pigments.

33. Installation of wall base Precast walls are placed and propped

34. Completed view of the precast boundary panel walls

35. The precast staircases proposed here are of standard sizes with tread sizes between
225mm to 250mm and risers between 150mm to 175mm. On the other hand, steel
staircases can come in non-standard sizes to suit the architectural design.
Precast/ steel staircases can be fabricated to a range of various forms and shapes.
There are three basic staircases profiles:
• Curved
• Straight
• Spiral profile
In the case of the terrace and semi-detached houses, these staircases can be
fabricated
in three ways:
• Type A for flight only
• Type B flight and top landing
• Type C flight and base landing
The erection of the staircase can either be on the critical path or non-critical path of
the construction sequence. In each case, prefabricated staircases will result in better
quality, accuracy and productivity. The prefabricated staircases can be installed
quickly and messy, cast-in-situ works can be eliminated.
PREFABRICATED STAIRCASE

36. Precast concrete Stairs Uniquely shaped structural elements
for a sports stadium

37. There are two main methods for fixing and installing the prefabricated staircases. The
staircase can either be prefabricated together with the landing as a complete unit or
it can be prefabricated separately and installed on site. The prefabricated staircase
should be designed to ensure easily transportation and hoisting. However, in most
cases, the size and weight are usually within the manageable capacity of the cranes.
Precast Flight Cantilevered precast treads

39. Details to staircase to frame
connections

40. PRECAST
WINDOW
ELEMENTS

41. Precast Flooring
Before any system of precast concrete flooring can be considered in detail the
following factors must be taken into account:
1. Maximum span
2. Nature of support
3. Weight of units
4. Thickness of units.
5. Thermal insulation properties
6. Sound insulation properties
7. Fire resistance of units.
8. Speed of construction.
9. Amount of temporary support required.

42. • With the development of precast concrete construction techniques, precast units e.g.
floor slabs are successfully manufactured.
• Advantages:
 Construction is quick
 Sound proof
 Members are lightweight
 Does not require formwork
 No time wasted for curing of concrete
 Good thermal insulation properties
• Disadvantages:
 Requires uniform spacing of columns which can be difficult
 Great care has to be taken in construction in order for precast members to be
able to resist handling stress
 May be wastages due due to breakages in transportation to site
 Careful supervision is required during manufacturing
 Formwork for manufacturing is usually costly – only economical when
manufacturing in large scale.

43. Precast Slab
SLAB TO SLAB PRECAST CONNECTION

44. WALLPANEL CONNECTED TO IN-SITU CONCRETE

45. CONNECTION OF WALL PANELS TO COLUMNS

46. Precast walls are propped before
casting of joints – proper planning
is required for perfect alignment
The pour strip
between 2 pieces
of precast walls
are cast
Precast
wall
units
PRECAST WALLS

47. Precast planks are installed in
place
Preparation of welded mesh
and services for cast in-situ
topping
Concreting to topping

48. Precast Beams,Griders,Corbel & Nib
Reinforced concrete nib
Reinforced concrete corbel

50. Precast beam-column connection
using cleat angle

51. BEAM TO COLUMN CONNECTION

52. SLAB TO BEAM CONNECTION

54. COLUMN TO COLUMN CONNECTION

56. WALL TO SLAB

57. Precast
concrete
structure
consisting of
solid wall
panels and
hollow core
slabs.

58. FOUNDATIONS
WITH BOLTED
FLANGES
FOUNDATIONS WITH
PROTRUDING BARS
FOUNDATIONS WITH
BOLTED SOCKETS

59. Precast
Column
Precast
Beam
Precast
Decking
/Slabs
Precast
Corbel
Assembly of Precast Members