Thursday, October 31, 2013

Different types of iron rods used in construction

An iron rod is a length of iron that is mainly used in heavy construction projects. Reinforced concrete is intertwined with iron rods, also called rebar, to strengthen the tension of the build. An iron rod can be purchased with or without a ribbed design. Construction-grade iron rods are primarily used in construction or building projects, but a wrought-iron rod can be used in various types of decorative art projects.
Iron is one of the 92 basic elements that are considered "natural," meaning they're not manmade; iron is identified by the symbol "Fe" and has an atomic number of 26. It is hardly ever found in a pure iron form, though there have been pure iron meteorites found. Iron is usually mined in the form of an oxidized or sulfide form of iron ore. The iron ore has to go through a process of reduction to be transformed into a pure metallic state. This reduction process basically takes the oxygen out of the ore and makes it pure.
Wrought iron is a fibrous metal that is soft and easily worked. It has a grainy look, almost like wood. The word "wrought" basically means “worked.” Blacksmithing is a form of iron and steel work that uses what is called a forging process. Forging is started by heating the wrought-iron rod or steel and then working it with a hammer and other tools to bend, cut and flatten the iron rod to a desired shape.
Wrought iron is produced by using a process known as smelting. The operation of smelting involves heating the iron ore with charcoal. At a proper temperature, the charcoal mixes with the oxygen and rises out of the iron as a gas. The remaining iron and slag are then removed while still hot. They are worked with a hammer, which works the iron into a consistent mass and forces out the slag.
Wrought iron is so expensive to produce that it is no longer made on a large scale; true wrought iron is now primarily used in conservation to keep historical sites authentic, and the iron is formed from recycled scrap. Most items considered wrought iron in the early 21st century are actually made of mild steel. It is still called wrought iron because it is still worked by hand. Before the switch to mild steel, wrought iron was used to make nails, rivets, chains, nuts, bolts and ornamental iron work.
Mild steel bars (as per IS: 432, part-I -1982)
Mild steel bars are used for tensile stress of RCC (Reinforced cement concrete) slab beams etc. in reinforced cement concrete work. These steel bars are plain in surface and are round sections of diameter from 6 to 50 mm. These rods are manufactured in long lengths and can be cut quickly and be bent easily without damage.
 Deformed steel bars (as per IS: 1786-1985)
As deformed bars are rods of steels provided with lugs, ribs or deformation on the surface of bar, these bars minimize slippage in concrete and increases the bond between the two materials. Deformed bars have more tensile stresses than that of mild steel plain bars. These bars can be used without end hooks. The deformation should be spaced along the bar at substantially uniform distances. 
To limit cracks that may develop in reinforced concrete around mild steel bars due to stretching of bars and some lose of bond under load it is common to use deformed bars that have projecting ribs or are twisted to improve the bond with concrete. These bars are produced in sections from 6 mm to 50 mm dia.
In addition the strength of bonds of deformed bars calculated should be 40 to 80 % higher than that of plain round bars of same nominal size. And it has more tensile stress than that of plain round bars of same nominal size.
Cold twisted deformed (Ribbed or Tor Steel Bars) bars are recommended as best quality steel bars for construction work by structural Engineer.

Various Grades of Mild Steel Bars

Reinforcement bars in accordance with standard IS No. 432 part-I can be classified into following types.   
1) Mild Steel Bars: Mild steel bars can be supplied in two grades 
     a)Mild steel bars grade-I designated as Fe 410-S or Grade 60 
     b) Mild steel bars grade-II designated as Fe-410-o or Grade 40
2) Medium Tensile Steel Bars designated as Fe- 540-w-ht or Grade 75
Grade II Mild steel bar are not recommended for use in structures located in earth quake zones subject to severe damage and for structures subject to dynamic loading (other than wind loading) such as railways and highways bridges.
Every lot or consignment of mild steel bars brought at the site of work should be tested in laboratory before use in the work. However for small work one can use mild steel bars on the basis of verifying tests results made by manufacturer in his own laboratory; which are available with supplier. 
Some of manufacturers stamped MS bars grade with their make /name and also give certification of test and grade. On the basis of the above information you can store mild steel bars grade-wise at the site of work.

Steel Bars for RCC Work 

All finished steel bars for reinforced work should be neatly rolled to the dimension and weights as specified. They should be sound, free from cracks, surface flaws, laminations, rough, jagged and imperfect edges and other defects. It should be finished in a work manlike manner. 

General precautions for steel bars in reinforcement
  • Steel bars are clear, free from loose mil scales, dust and loose rust coats of paints, oil or other coatings which may destroy or reduce bond strength.
  • Steel bars should be stored in such a way as to avoid distortion and to prevent deterioration and corrosion.   
  • Steel bars should not be clean by oily substance to remove the rust.
  • The bar is bent correctly and accurately to the size and shape as shown in drawings. 
  • If possible, the bar of full length is used.
  • Overlapping bars do not touch each other and these should be kept apart with concrete.
  •  The overlap if given should be staggered.
  • The cranks in the bar at the end should be kept in position by using spots.
  • The steel bars should not be disturbed while lying cements concrete.
  • Required cover under steel bars should be given before laying the cement concrete.  
  • No over lap is given in the bar having a diameter more than 36 mm, if required, the bar should be welded.
Weight of Different Steel Bars
When we want to purchase Mild steel members from the market, the shopkeeper quotes the price of steel members in weight. 
When any type of steel members for use in house construction is required, we calculate the length of steel member in feet or meter but we are ignorant about the weight of steel.  
Here are details of weight per meter for various types of steel members:-
This will help us for estimated weight and cost. It will also help at the time of purchase to avoid pilferage in weight.

Pest Control

Periodic cleaning of every nook and corner helps control pests.
Hire a fumigator once in six months. Yellow Pages has a list of pest control companies.

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