Presentation on Prefabricated Structures & Prefabrication – Concept, Components & Advantages
– by Priyaranjan Behera
Concept of prefabrication?
Prefabrication is the method of construction which includes assembling components of a structure in a manufacturing or production site, transporting complete assemblies or partial assemblies
to the 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.
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.
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 Casting, Curing, Transportation 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.
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.
Prefab Building Components
Some of the prefabricated components are as explained below
Columns: – 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.
Beams: – 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. Methods of connecting beams and columns are
- A precasting 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 insitu concrete to complete the joint. This is as shown in the figure.
Waffle 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
Advantages And Disadvantages
- 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.
- 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.
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.