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Chapter: Civil : Prefabricated Structures : Joint In Structural Members

Factors infuenceing standardization

The following are the advantages of standardization. 1. Easier desing - Elimiation of unnecessary choices. 2.Easier manufacture - Limited number of variants. 3.Easier erection and completion - Repeated use of sepcialised equipment.



The following are the advantages of standardization.

       1. Easier desing

Elimiation of unnecessary choices.


2.Easier manufacture

Limited number of variants.


3.Easier erection and completion

Repeated use of sepcialised equipment.


Factors infuenceing standardization:-


1. The most rational type of member for each element is selected from the point of production from the assembly serviceability and economy.


2.   The number of types of elements will be limited and they should be used in large quantities.


3. To the extent possible the largest size to be used which results in less no of joints.


4. The size and no of the prefabricates is limited by the weight in overall dimension that can be handled by the handling and erection equipment and by the limitation of transportation. Hence it is preferable to have all the and transporting complete assemblies or sub-assemblies to the construction site where the structure is to be located. The term is used to distinguish this process from the more conventional construction practices of transporting the basic materials to the construction site where all assembly is carried out.


The term prefabrication also applies to the manufacturing of things other than structure at a fixed site. It is frequently unused when fabrication of a section of a machine or any movable structure is shifted from the maid manufacturing site to another location, and the section is supplied assembled and ready to fit. It is not generally used to refer to electrical or electronic components of a machine, or mechanical parts such as pumps, gearboxes and compressors which are usually supplied as separate items, but to sections of the body of the


machine which in the past were fabricated with the whole machine. Prefabricated parts of the body of the machine may be called 'sub-assemblies' to distinguish them from the other


components. Contents


1.     The process  and theory of prefabrication


2.     History


3.     Current uses


4.     Advantages of prefabrication


5.     Disadvantages

6.     Off-site fabrication


7.     See also


8.     External Links.


The process and theory of prefabrication


An example from house-building illustrates the process of prefabrication. The conventional method of buildings a house is to transport bricks, timber, cement, sand, steel and construction aggregate, etc, to the site, and to construct the house on site from these materials. In prefabricated construction, only the foundations are constructed in this way, while sections of walls, floors and roof and prefabricated (assembled) in a factory (possibly with window and door frames included), transported to the site, lifted into place by a crane and boiled together.


Prefabrication is used in the manufacture of ships, aircraft and all kinds of vehicles and machines where sections previously assembled at the final point of manufacture are assembled elsewhere instead, before being delivered for final assembly.


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. Prefabrication avoids the need to transport so many skilled workers to the construction site, and other restricting conditions such as a lack of power, lack of water, exposure to harsh weather or a hazardous envioronment are avoided. Against these advantages must be weighed the cost of transporting prefabricated sections and lifting them into position as they will usually be larger, more fragile and more difficult to handle than the materials and components of which they are made.


'Loren' Iron House, at Old Gipostown inMoe, Australia


Prefabrication has been used snce ancient times. For examples, it is claimed that the world's oldest known engineered roadway, the Sweet Track constructed in England around 3800 BC, employed prefabricated timber sections brought to the site rather than assembled on-site.


Sinhalese kings of ancient Sri Lanka have used prefabricated buildings technology to erect giant structures, which dates back as far as 2000 years, where some section were prepared separately and then fitted together, specially in the Kingdom of Anuradhapura and Kingdom of Polonnaruwa.


In 19th century Australia a large number of prefabricated houses were imported from the united Kingdom.


The method was widely used in the construction of prefabricated housing in the 20th century, such as in the United Kingdom to replace houses bombed during World war II. Assembling sections in factories saved time on-site and reduced cost. However the quality was low, and when such prefabricated housing was left in use for longer than its designed life, it acquired a certain stigma.


The Crystal palace, erected in London in 1851, was a highly visible example of iron and glass prefabricated construction, it was followed on a smaller scale by Oxford Road Railway station.


The most widely used form of prefabrication in building and civil engineering is the use of prefabricated concrete and prefabricated steel sections in structure where a particular part or form is repeted many times. It can be difficult to construct the formwork required to mould concrete components on site, and delivering wet concrete to the site before it starts to set requires precise time management. Pouring concrete sections in a factory brings the advantages of being able to re-use moulds and the concrete can be mixed on the spot without having to be transported to and pumped wet on a congested construction site. Prefabricating steel sections reduces on -site cutting and welding costs as well as the associated harards.


Prefabrication techniques are used in the construction of apartment blocks, and housing developments with repeated housing units. The quality of prefabricated housing units had increased to the point that they may not be distinguished from traditionally built units to those that live in them. The technique is also used in office blocks, warehouses and factory buildings. Prefabricated steel and glass sections are widely used for the exterior of large buildings.


Detached houses, cottages, log cabin, saunas, etc. are also sold with prefabricated elements.





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