An Introduction to Prefabricated structures

CE6016 -
Prefabricated
Structures
Mrs. SOFIARAJESH
Asst Prof - Civil Dept - AAA College of Engineering and Technology

Syllabus
Need for prefabrication
Principles
Materials
Modular Coordination
Standardization
Systems
Production
Transportation
Erection
Unit I - Introduction
This Presentation
Definition
Need for Prefabrication
Advantages & Disadvantages
Limitations
Uses
Principles of Prefbrication
Methods of Prefabrication
Classification
Standardization
Production system
Prefabrication process
Manufacturing
Stacking
Handling
Transporting
Erection
Machines for hoisting

Prefabrication
Prefabrication is the practice of
assembling components of a structure in a
factory or other manufacturing site and
transporting all assemblies or sub-assemblies to
construction site where the structure is to be
located.

Need for Prefabrication
Speedy Construction - No curing period
Effect Economy
Improve quality
Durable structure with less maintenance
Aesthetic finish
Further expanses easy

Advantages
Self supporting Readymade components –
does not need formwork, shuttering, and
scaffolding.
Construction time is reduced.
 Quality control is easy.
Time exposed in Bad weather and hazardous is
minimized.
Less wastage -or wastage / scrap can be
recycled
On site congestion can be minimized
Moulds can be reused.

Disadvantages
Very Skilled crew
Careful handling of components
Leakages at joints
Heavy duty cranes and precision
measurement to place in position
Very costly when the factory is very far
away from the site.

Limitations of Prefabrication
Very Costly
Uneconomical for smaller projects
Transportation difficulties
Safety of Crane and other support system has to
carefully considered.
Difficulties in transportation of vary large
components
Waterproofing joints

Uses
The following are the uses of introducing the prefabrication system:
Prefabricated components speed up construction time, resulting in lower labor costs;
Prefabrication allows for year-round construction;
Work is not affected by weather delays (related to excessive cold, heat, rain, snow,
etc.);
The mechanization used in prefabricated construction ensures precise conformity to
building code standards and greater quality assurance;
There are less wasted materials than in site-built construction;
There is less theft of material/equipment (and less property damage due to
vandalism);
Materials are protected from exposure to the elements during construction;
Worker safety and comfort level are higher than in site-built construction;
Computerization of the production process permits a high degree of customization,
at an affordable cost;
Quality control and factory sealing and design can ensure high energy efficiency; and
Cost savings through prefabrication can reduce the income required to qualify for a
high ratio mortgage by up to one third compared to a conventionally built home of the
same size

Prefabrication principles
 To give safety in structural system
 To design the building as an aesthetic one
 To effect economy in cost
 To improve in quality as the components can be
manufactured under controlled conditions.
 To speed up construction since no curing is necessary.
 To use locally available materials with required
characteristics.
 To use the materials which possess their innate
characteristics like light weight, easy workability, thermal
insulation and combust ibility etc


Two methods of prefabrication
- Plant prefabrication
- Site prefabrication

Classification of prefabrication
Small prefabrication
Medium prefabrication
Large prefabrication
Partial prefabrication
Open system prefabrication
Closed system prefabrication
Total prefabrication
Cast –in-site prefabrication
Off- site prefabrication

Standardization
Standardization is the repeated production of standard sizes and
or layouts of components or structures which may occur on site
or off site.
Example
Modular Bathroom, Standard kitchen cabinet, prison cell etc.

Advantages
Advantages of standardizing prefabricated components are under:
Easier in design as it eliminates unwanted choices
Easier in manufacture as there are limited number of variants.
Makes repeated use of specialized equipment in erection and
compilation easier and quicker.

Factors influencing Standardization
•To select the most rational type of member for each element
form point of production , assembly, serviceability and economy.
•To limit the no. of types of elements.
•To use large size of elements so as to reduce no. of joints.
•To limit size so as to manage overall weight to handle the
component during its stacking transportation and erection.

Prefabricated systems
Major systems are:
•Large panel system
- Longitudinal wall system
- Cross wall system
- Combined system.
•Structural Frame system
•Lift panel system ( Column slab system)
•Mixed system.
It can also be categorized as
- Open prefabricate system
- Closed prefabricate system

Aggregate system
Stand System
Line up System (conveyor belt system)
Production systems

Prefabricated Structures - Process
Manufacturing process
(on the production site)
Stacking the components before shipping
Transportation
(to the construction site)
Erection (on the construction site)

An Introduction to Prefabricated structures

Machineries used for handling
skids Gantry girder
Fork lifts
Mobile
crane

Stacking during transport and
storing the components
Precautions to be taken while Storing
the Components

Stacking – Dos and Don’t s
•Stacking method and packers for support spacers vary according to the type of precase
elements.
•Horizontal stacking – beams , slabs and columns
•The storage support position for beams and slabs – within 300 mm from the lifting
points

Do not use more than two support points in particular pack for prestress
elements like hollow core slab

The packers or support spacers should not be misaligned as shown

Wall panels should always be stored vertically and braced in position by
A - frames or racking systems

Different storage and stacking
examples

Erection
Erection and Installation of components on site: Requires proper
attention and skill to prevent the elements from developing erection
and handling stresses

Temporary strengthening of panels with opening is necessary

The lifting points should be designed and located to limit the bending moments
within the beam element.
As a general guide , they should be located at about one fifth of the beam length
measured from the edge.

Wherever necessary multiple lifting points can be designed and located to
minimize undue stresses within the slab elements, in particular for slender
panels such as precast planks.

Columns are usually
first handled in
horizontal position.
Slings are attached to
the inserts at the top
to facilitate the
rotation of the
elements to vertical
position before
hoisting and placing to
their designated
location

Machines used for hoisting
- A derrick is a lifting device composed at minimum of
one guyed mast, as in a gin pole, which may be
articulated over a load by adjusting its guys. Most
derricks have at least two components, either a guyed
mast or self-supporting tower, and a boom hinged at its
base to provide articulation.
The most basic type of derrick is controlled by three or
four lines connected to the top of the mast, which allow
it both to move laterally and up and down. To lift a load,
a separate line runs up and over the mast with a hook
on its free end, as with a crane.
Guyed Derrick Crane

Cranes
Climbing cranes
Portal cranes
Tower cranes
Mobile cranes

An Introduction to Prefabricated structures

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