Reinforcement function and its types

WHAT IS REINFORCEMENT? 

Reinforcement is one type of material which is used in construction. It’s one type of bar that provide ductility to any structure member like Columns, beams, slabs, etc. Reinforcement has ductile behavior which increase strength of building and give sign. 

re/in force/ment. Three distinguished parts of a word. If you cast a concrete slab without steel rods, it will collapse. When the slab is casted with steel rods, it stands and can take considerable load. Introduction of steel rods (technically called bars) to increase its load carrying capacity is called reinforcement. 

The reinforcement in concrete may be simple bar or series of bars, bend to a given schedule which known as bar schedule and tied according to the reinforcement drawings with stirrups.  The normal diameters of bars used at
site are 6, 10,12,16,20, 25 and 32 millimeters 

What is the function of reinforcement in concrete? 

There are varying reinforcements in concrete nowadays. The purpose of reinforcement are mainly because of three reasons: Economy, Structural Integrity and Aesthetics 
Economy and Aesthetics 
1. Without reinforcements, required cross sectional area of concrete could be so massive which affects both aesthetics and economical areas. Whereas having reinforcements, one can suit to a desired cross-sectional area of structures by compensating the “would-be” concrete cross sectional areas thru reinforcements. 
Structural Integrity 
2. Concrete is good in resisting compression stress but not in tensional forces. Reinforcement like steel bars will strengthen this weak area of concrete to carry the loads. 

3. It takes the tensile stresses developed sure to loading conditions, as concrete is not good in tension with minimal tensile strength (flexural stress) 

4. It gives ductility to the structure 

5. It prevents the catastrophic failure of the structure, provided the reinforcement provided in not less than nominal requirement of the structure to be designed 

6.Overall it gives the stability to the structure without which the structure would not have served the purpose for which it would be designed. 

TYPES OF STEEL REINFORCEMENT BARS? 

There are four types of steel reinforcement bars that are used in construction: 

1.Mild Steel Plain Bars 

As opposed to other types, these bars do not have ribs on its surface. It is commonly used for small projects with a tight budget since they’re cheaper to come by yet do not bond well with concrete. Its tensile strength is about 40,000 psi. 

Grades in mild steel bars 

1. Mild Steel Bars 

  • Mild steel bars grade-I designated as Fe 410-S or Grade 60. 
  • 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 

2.Cold Worked Steel Bars 

These bars look similar to hot rolled deformed bars, although it is worked by rolling the steel at room temperature. Due to its working, these bars are less pliable and work best to improve straightness and low-tolerance projects. It has a tensile strength of 60,000 psi. 

3.Prestressing Steel Bars 

These bars are composed of multiple wires (called tendons) ranging from 2 to 7 strands. It is best known for its versatile composition and impressive tensile strength. This material is often paired with prestressed concrete found in bridges and concrete slabs in buildings. It has a tensile strength of around 250,000 to 270,000 psi. 

Keep in mind that, while steel reinforcement bars improve the integrity of concrete structures, it is not perfect. Concrete is a porous material that produces moisture and salt. These can seep through and erode the steel bars’ strength over time. As a construction material, it is expensive and difficult to handle due to its weight. It can also melt in high temperatures, which can be mitigated by tying the steel instead of having it welded. 

4. Deformed Steel Bar 

Deformed steel bars have ribs, lugs and indentation on the surface of the bar, which reduces the major problem that is faced by mild steel bar due to slippage and good bonding is achieved between concrete and rebar. The tensile properties is higher compared to other rebars. These bars are produced in sections from 6 mm to 50 mm dia. 

TYPES OF DEFORMED STEEL BARS- 

1.THERMO MECHANICALLY TREATED BARS 

2. HIGH STRENGHT DEFORMED BARS 

1. TMT Bars (Thermo Mechanically Treated Bars) 

Thermo Mechanically Treated Bars are hot treated bars that are high in strength used in reinforced cement concrete (RCC) work. It is the latest induction in the MS steel bars with superior properties such as strength, ductility, welding ability, bending ability and highest quality standards at international level. 

Fig 3: Deformed TMT Steel Bar 

2. High Strength Deformed Bars 

High strength deformed bars are cold twisted steel bars with lugs, ribs, projection or deformation on the surface. It the extensively and majorly used for reinforcement purposes in a construction. These bars are produced in sizes or sections from 4 mm to 50 mm in diameter. 

Deformed HSD Steel Bar

Fig 4: Deformed HSD Steel Bar 

SOME REASON FOR USING REINFORCED CONCRETE 

1. Reinforced concrete has high fire and weather resistance. 

2. Reinforced concrete is versatile and can be formed into almost any shape. required for construction. 

3. Reinforced concrete has very low maintenance costs. 

4. Reinforced concrete is weather treated and resistant to damp conditions; this is why it is the material of choice for dams, piers and footings. 

5. Reinforced concrete is more cost effective than equivalent steel structures. 

6. Reinforced concrete requires less skilled Labour when erecting a large structure. 

COMMON FAILURE MODES OF STEEL REINFORCED CONCRETE. 

Reinforced concrete can fail due to inadequate strength, leading to mechanical failure, or due to a reduction in its durability. Corrosion and freeze/thaw cycles may damage poorly designed or constructed reinforced concrete. When rebar corrodes, the oxidation products (rust) expand and tends to flake, cracking the concrete and unbounding the rebar from the concrete. 

TWO PHYSICAL CHARACTERSTICS GIVE REINFORCED CONCRETE ITS SPECIAL PROPERTIES. 

  1. The coefficient of thermal expansion of concrete is similar to that of steel, eliminating large internal stresses due to differences in thermal expansion or contraction. 
  1. When the cement paste within the concrete hardens, this conforms to the surface details of the steel, permitting any stress to be transmitted efficiently between the different materials. Usually, steel bars are roughened or corrugated to further improve the bond or cohesion between the concrete and steel. 

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