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Ferro cement construction

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Rural Technology

In Ferro cement construction a frame of chicken wire mesh is made. A mixture of cement, sand, and water is spread over the frame. Then the Ferro cement structure is allowed to cure for 28days. Advantages of Ferro cement structures are as follows:

i) Despite the small thickness, Ferro cement structures are strong ii) Economical iii) It requires less skill to manufacture iv) Safe in earthquakes. Now a days other materials viz fiber, bamboo etc are used in place of chicken mesh to reduce the cost. Structures for strength

In this section, we will discuss commonly used arrangements to get the proper strength for construction. In nature, all animals have skeleton. They are able to take up their own weight and do movement due to skeleton. In tree trunks fibers are connected to each other using lignin. This makes wood strong. Man has learnt from nature and made use of this structure in imaginative way for their benefit. There are two different kinds of structure:

1 Skeleton type

Flexible limbs and parts of animal body are supported by a bony skeleton (frame). Similarly man has learnt to construct frame-work to support weak substances. Viz. Man has constructed trusses, beams, and columns of steel or wood, to support roof made of grass or mud-tiles. Similarly steel frames filled with concrete become stronger than either.

2 Fiber method

Fiber’s are often flexible but they are strong in tension. If the fibers are combined together by an adhesive substance then it can produce strong material. If fiber is added to brittle substances then its brittleness decreases. For example : i) Cement is brittle; to overcome that weakness asbestos is added to cement to make strong asbestos- cement sheets. ii) Plastic is breakable. If glass fiber is added to it then it turns into strong FRP. iii) Cement Mortar is easily breakable. But if thin chicken-mesh is put into mortar that makes it a strong Ferro cement. iv) Similarly, fiber is added to tar to make it into durable roof-sheet. It is not always necessary to use two or different materials to create strong objects. Strength can be obtained by arranging the same material in different ways. We can learn this from following comparisons: 1) Flat and Rod – Judge Strength of flat from all direction. Rod is strong in all direction but flat is stronger in only one direction.

3) Twisted Flat 4) Rod and hollow Tube If the diameter of cross section is same, Hollow tube is stronger than the rod. 5) Triangle and Rectangle: Between the same size of triangle and rectangle, triangle is stronger. Under load triangle will not change its shape. 6) A joint in fig 8(f) be made stronger as shown in the fig 8(g). 7) Truss Different types of trusses are shown in the figure. Different triangles are joined together to get the required shape and strength.

8) Geodesic Dome structure Architect “Buck Minster Fuller” had shown the method of constructing a geodesic dome structures. In which round building is constructed by connecting frames. In this type of construction, wall and roof are not separately constructed but both are combined in single round. In this way buildings can be constructed with large diameter without any column. Advantage of geodesic structure is as follows : · It provides the greatest strength for the least volume of weight. · The geodesic dome can withstand winds of 210 mph, while at the same time it is light and easily transportable. It can be put up in hours. · A geodesic dome can withstand cyclones and earthquakes far better than conventional buildings. The geodesic dome is the only structure that actually gets stronger, lighter in density and cheaper per square foot with size.

Low cost housing does not mean inferior or low quality housing. Many organizations worked on cutting down construction cost by using alternatives to conventional methods and inputs. It is about the usage of local and indigenous building materials, local skills, energy saver and environment-friendly options. Famous architect Laurie Baker said “a cheaper house is not just for the poor. One can cut unnecessary expenditure even while building beautiful houses’.

Intext questions

Write True or false: i) Despite smaller thickness ferrocement structure are strong. ii) Cement can withstand tensile load. iii) If diameter of cross section is same, hollow tube is stronger than the rod. iv) It is necessary to connect two different materials to create strong object. v) Geodesic domes are preferred in earthquake and cyclone prone region.

What you have learnt

In this chapter, you studied history of construction. You learnt about different types of construction. You studied different elements of RCC construction. You learnt about different ways to lay bricks. You studied basic instruments used in construction. Now you know about different structures used to get strength for construction.

Terminal Questions

1) Write reason: i) In old temples, stone columns are placed close to each other. ii) Arches are used to build big halls or bridge. iii) Triangle is more stronger than square under load. 2) Write different simple instruments used by meson. 4) Write down advantages of ferrocement construction. 5) Write down advantages of geodesic structure.

Answer to intext questions

6.1 i) False ii) true iii) false iv) true 6.2 i) Reinforced cement concrete ii) wall bearing structure, RCC structure iii) foundation iv) plinth beam v) cantilever 6.3 A B i) Spirit level Leveling horizontal level ii) Plumb Leveling vertical length iii) Red trap bonds Cooler houses iv) Spanish bond bearing wall v) Stretcher bond Single brick wall 6.4 i) True ii) False iii) True iv) False v) True suggested Activity • Observed different types of trusses used in your surroundings. Draw sketches of trusses used in old houses, poultry shed, tin roof shed, polyhouses.

Fig. 8 (f)

Fig. 8 (g )

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