HSD Steel Bars (High Strength Deformed Bars)

High strength deformed bars IS: 1786-1985 are steel bars which are provided with lugs, ribs, projection or deformation on the surface and are produced in form of cold twisted deformed bars. These bars are extensively used for reinforcement purposes in a construction. Due to ribs or projections on the surface, these steel bars minimize slippage in concrete and increase the bond between two materials i.e. between cement concrete and steel bars.

The deformed bars have more compressive and tensile stress than that of mild steel plain bars. High strength deformed bars have improved anchorage; therefore they can be used without end hooks or bent up ends of bars. This reduces labor for fabrication of steel reinforcement. The deformation is spaced on bar at uniform distances. These bars are produced in sizes or sections from 4 mm to 50 mm in diameter.

Generally cracks develop in reinforced concrete around mild steel bars due to stretching of bars, loss of bond under the load. To minimize this problem, deformed bars having projecting ribs or twisted surface which improves the bond with the concrete should be used in RCC work.

Features of HSD Bars

Low carbon value: HSD Bars have lower carbon level, resulting in good ductility, strength and welding ability.
Superior bonding strength: HSD bars are well known for their excellent bonding strength when used with concrete.
Welding capability: Since these bars have lower carbon content, they have 100% welding capability than conventional bars.
High tensile strength: HSD bars feature high tensile strength. They offer great asset in construction process, where a lot of bending and re bending is required.
Wide application range: These bars have wide application range like in building residential, commercial and industrial structures, bridges, etc.
Satisfactorily malleability, minimum weight and maximum strength and suitable for both compression and tension reinforcement.

Process of production of bars

The main process for production of bars is hot rolling followed by cold twisting. Latest technological advances in the field of micro-alloying of steel and thermo-mechanical treatment process have resulted in the production of deformed bars as reinforcement for use in cement concrete in three grades namely Fe 415, Fe 500 and Fe 550.

The strength of bonds of deformed bars
In addition, the calculated strength of bonds of deformed bars should be 40 to 80 % higher than that of plain round bars of same nominal size. Tor steel possesses the strength of 1.5 to 2.0 times of mild steel in compression as well as in tension, whereas it costs only 10% more than mild steel.

Deformed steel bars have minimum 0.2% proof stress or yield stress in N/mm square. Proof stress is the stress at which non proportional elongation equal to 0.2% of the original gauge length takes place. Hence deformed steel bars are very economical to use in RCC work. Structural Engineer recommends cold twisted deformed (Ribbed or Tor Steel Bars) bars as they are best quality steel bars for construction work.

Mechanical properties of high strength deformed (HSD) steel bars for concrete reinforcement

Property	Grade of Steel
	Fe415 Fe500 Fe550
0.2% proof stress/ yield stress minimum N/mm square	415.0 500.0 550.0
Elongation, percent minimum on Gauge length 5.65 VA where A is the cross sectional area of the test piece	14.5 12.0 8.0
Tensile strength, minimum, N/ mm square	10% more than proof stress but not less than 485, 8% more than proof stress but not less, than 545, 6% more than proof stress but not less than 585

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