500D AND 550D TMT BARS – THE IDEAL CHOICE FOR MODERN CRITICAL INFRASTRUCTURE PROJECTS

With increasing need for critical infrastructure projects and high rise construction in India 500D and 550D TMT bars are the ideal choice.

Here is a look at why they are the most suitable option for construction grade steel.

Fe500 grade vs Fe500D grade of TMT bars as defined by IS: 1786

Fe500 and Fe500D are types of TMT steel bars. “Fe” stands for Iron out of which the TMT bars are made. The figure “500” implies the minimum yield stress in MPa.

The letter “D” in Fe 500 D implies ductility which means that the steel bars have a higher percentage of elongation.

The structures which require more ductility are skyscrapers, stadiums, fly-overs, airports, malls, multiplexes, dams, etc. that demand “D” grade TMT bars.

Fe500 and Fe 500D have the same 0.2 percent proof stress/yield stress (Min) whereas the tensile strength is increased by 2 percent. Tensile strength (Min) for Fe 500 is 545 MPa and for Fe 500D it is 565 MPa.

As per IS:1786, Fe500 contains S+P 0.105% collectively and individually 0.055% each. Fe500D contains S+P 0.075% collectively and individually 0.04% each. The elongation norm for Fe500 is 12% and Fe500D is 16%.

From the chemical composition point, Fe 500D has 0.25% Carbon (max) as compared to 0.30% (max) in Fe 500. Also the maximum percentage of Sulphur and Phosphorus are lower in Fe 500D.

Fe500D with lower quantities of carbon, sulphur and phosphorous, helps in preserving the steel and resisting earthquake shocks in future.

Elongation of TMT bars and the strength of the rods on applying tension / force is higher in the D variant of the rods. These enhanced mechanical properties of the D grades TMT bars allow elevated resistance of the bars to natural calamities and also better resistance under stress.

Salient applications of “D” grade of TMT bars

“D” denotes Ductility, which means these bars are highly seismically resistant – hence they are preferred in earthquake zones 3, 4 & 5. They give guaranteed elongation well above 16 %. The 500“D” grade has balanced mechanical properties of higher ductility which is most suitable for bridges, dams, high-rise apartments (skyscrapers), industrial structures, flyovers, wind mills, earthquake prone zones, mountain bridges, railways bridges, structures such as airports, ports, hospitals, cantilever structures, tunnels or concrete roads, statues and other load bearing structures.

500D or 550D grade TMT bars are preferred for building critical infrastructure in the country for some specific properties of these bars:

Resistance to earthquakes: TMT bars are resistant to earthquakes due to their soft pearlite core. They can bear seismic and dynamic loading. TMT bars have high fatigue resistance to seismic loads because of high ductility and therefore they are widely used in earthquake prone areas.

Flexibility and Bending capacity of the bars: TMT bars have excellent bending capacity. Due to their flexibility, they can be moulded into different shapes by bending them up to any extent which is great for modern style architectural designs.

High Elongation property: TMT bars are completely earthquake resistant because of their elongation property. In fact they can elongate up to 50% more than the original length without compromising on the measurements which helps to save on the construction as well.

Resistance to corrosion and rust: TMT bars are corrosion free and have a moisture resistant property hence they can be used in constructions along sewage drains and where they may be exposed to water as well as salinity in the groundwater.

Fire resistance: The fire safety of a structure is one of the primary concerns for engineers and residents. TMT bars boast of high thermal stability and can resist temperatures ranging from 400 to 600 °C. Thus, they are perfect for resisting fire and provide safety.

Fatigue Resistance: A unique feature of TMT Bars are their High Fatigue Resistance on dynamic loading on account of the high strength of the surface layer.

Weldability: TMT Bars with low carbon equivalent content can be used for butt/ lap and other weld joints without reduction in strength at the weld joints.

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