LOW COST BUILDING

PRIFABRICATION

WHAT IS PREFABRICATION?

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

It is combination of good design with modern high performance components and quality controlled manufacturing procedures

This work is carried out in two stages, manufacturing of components in a place other than final location and their erection in position.

PREFAB CONCEPT

Prefabricated sections are produced in large quantities in a factory and then shipped to various construction sites.

This procedure may allow work to continue despite poor weather conditions and should reduce any waste in time and material at the site.

Precast concrete units are cast and hardened before being used for construction Sometimes builders cast components at the building site and hoist them into place after they

harden. This technique permits the speedy erection of structures.

DESIGN CONCEPT FOR PRECAST CONCRETE BUILDINGSThe design concept of the precast buildings is based on 1.build ability.2.economy 3.standardization of precast components.

PREFAB BUILDING COMPONENTS

Beams can vary in their complexity of design and reinforcement from the very simple beam formed over an isolated opening to the more common encountered in frames where the beams transfer their loadings to the column.

Precast Walls

Precast SLABS

Precast BEAM & GIRDERS

A hollow core slab, also known as a voided slab or hollow core plank, is a precast slab of prestressed concrete typically used in the construction of floors in multi-story apartment buildings. The slab has been especially popular in countries where the emphasis of home construction has been on precast concrete, including Northern Europe. Precast concrete popularity is linked with economical constructions because of fast building assembly, lower self weight (less material), etc.

PREFAB BUILDING COMPONENTS

A column is a vertical member carrying the beam and floor loadings to the foundation.

It is a compression member and therefore the column connection is required to be proper.

The main principle involved in making column connections is to ensure continuity and this can be achieved by a variety of methods.

Column to Column Connection Precast Columns

Precast columns

Precast concrete Stairs Steel plates supported on 2 steel beams

Precast stairs

PREFAB BUILDING COMPONENTS

METHODS OF CONNECTING BEAMS AND COLUMNS ARE A pre-casting concrete haunch is cast on to the column with

a locating dowel or stud bolt to fix the beam. A projecting metal corbel is fixed to the column and the

beam is bolted to the corbel. Column and beam reinforcement, generally in the form of

hooks, are left exposed. The two members are hooked together and covered with concrete to complete the joint.

This is as shown in the figure.

PREFAB BUILDING COMPONENTSWAFFLE UNIT FOR FLOORING / ROOFING: These are suitable for roofs / floors

spanning in two directions.

They are laid in a grid pattern.

These units are cast in moulds.

The saving achieved is not much. Also Shuttering are complicated and costly.

Time consumption for construction is less

SLAB TO BEAM CONNECTION

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

WALL TO SLAB CONNECTION

DESIGN CONSIDERATIONS

final position and loads transportation requirements – self load and position during transportation storing requirements – self load and position during storing – (avoid or store in the same

position as it transported / built in) lifting loads – distribution of lifting points – optimal way of lifting (selection of lifting and

rigging tools) vulnerable points (e.g. edges) – reduction of risk (e.g. rounded edges)

TYPES OF PRE CAST SYSTEM

1. Large-panel systems2. Frame systems3. Slab-column systems with walls4. Mixed systems

TYPES

Box-like structure. Both vertical and horizontal

elements are load-bearing. One-story high wall panels

(cross-wall system / longitudinal wall system / two way system).

One-way or two way slabs.

Components are usually linear elements.

The beams are seated on corbels of the pillars usually with hinged-joints (rigid connection is also an option).

Joints are filled with concrete at the site.

2. FRAME SYSTEMS1.LARGE-PANEL SYSTEMS

3.Lift-slab systems

partially precast in plant (pillars) / partially precast on-site (slabs). one or more storey high pillars (max 5).

up to 30 storey high constructions. special designed joints and

temporary joints. slabs are casted on the ground (one

on top of the other) – then lifted with crane or special elevators.

PLANNING TRAFFIC ROUTE How long transporter vehicle is

required? What is the required load capacity of

the transporter vehicle? What is the maximum vertical

extension of the shipment Routs on the site Is route permission required?

EQUIPMENTS

cranes: mobile crane tower crane (above 3stories)

lifting tools:spreader beams wire rope slings

rigging tools: eye bolt shakles hooks

PRE FABRICATION The Prefabrication as defined will be done in two stages Manufacturing at factory condition

and erection of components at the required location. This requires certain stages of preparation. They are

CastingCuringTransportation and erection

CASTING: Precast components are casted with controlled cement concrete in moulds of required shape and sizes. The vibrator is used to vibrate concrete and this removes any honeycombing inside the components.

PRE FABRICATION

CURING: After 24 hours of casting, the casted components are released from the mould and transported to curing tanks. Certain special components like railway sleepers where high strength is required are steam cured.

TRANSPORTATION AND ERECTION: After complete curing is done the components are transported to the site with heavy trucks and erection will be done using cranes with skilled labour force.

EXAMPLES….The hospital will feature multi-trade prefabricated racks in the corridors, anapproach that is still new in the U.S.

ADVANTAGES AND DISADVANTAGES

Advantages:

Saving in cost, material, time & manpower.

Shuttering and scaffolding is not necessary.

Installation of building services and finishes can be done immediately.

Independent of weather condition.

Components produced at close supervision .so quality is good.

Clean and dry work at site.

Possibility of alterations and reuse

Correct shape and dimensions and sharp edges are maintained.

Very thin sections can be entirely precast with precision.

LIMITATIONS size of the units. location of window openings has a limited

variety. joint details are predefined. site access and storage capacity. require high quality control. enable interaction between design phase and

production planning. difficult to handling & transporting.

SCHEDULINGsome approximate data for installation emplacement of hollow core floor slabs - 300

m2/day erection of pillars/columns - 8 pieces/day emplacement of beams - 15 pieces/day emplacement of double tee slabs - 25

pieces/day emplacement of walls - 15 pieces/day construction of stair and elevator shafts - 2

floors/day

Miami Valley Hospital Dayton,OH

EXAMPLES….

ADVANTAGES AND DISADVANTAGES

Disadvantages:

Handling and transportation may cause breakages of members during the transit and extra provision is to be made.

Difficulty in connecting precast units so as to produce same effect as monolithic. This leads to non-monolithic construction.

They are to be exactly placed in position, otherwise the loads coming on them are likely to get changed and the member may be affected.

High transport cost.

Need of erection equipment. Skilled labour and supervision is required.

CONCLUSION

The prefab components and prefab structures eliminate space and time over conventional constructions.

Although prefabrication is employed to a large extent in a wide variety of countries, in India, construction industry, in spite of its expansion continues to adopt same conventional methods.

  The root of the economic problem is the fact that the majority of the households do not have the confidence needed to construct prefab houses.

These structures are easy to erect as it is light material. This type of prefab buildings were constructed in earthquake prone areas of Lature and Gujarat.