Construction of a house requires perfect planning and the sufficient strength to withstand loads of the structure and the certain natural disasters. In order to deliver such strength, the TMT steel reinforced bars are primarily used. Thermo Mechanically Treated (TMT) steel reinforced bars are known for their absolute strength and ductility. TMT is actually an innovated procedure performed on the hot rolled steel bars, which results in a strong outer martensite layer that deals the tensile strength and a soft ferrite-pearlite inner core which deals with the ductility factor. TMT reinforced steel bars are known for its Bendability.
Ductility and Bendability
Bendability is an important factor of TMT reinforced steel bar because the TMT steel bars will require scenarios where it must be bent to suit the building design. Most people are not aware of the importance of ductility in TMT reinforced steel, all they care about is the high tensile strength of the rebar. While high strength increases the capability to withstand more load of the structure, ductility determines the capacity of bending.
A Rule of Thumb, more ductility results in better bendability of the reinforced bars. TMT reinforced bars are of many grades namely Fe415, Fe500, Fe 550 and Fe 600. The numbers denote the minimum yield strength of each TMT reinforced bars. The higher grades are achieved by making slight changes in the original TMT process. This results in producing reinforced steel bars which have more strength. This higher strength is achieved by compromising the available percentage of ductility.
How does Less Ductility affect Bendability
Less ductile means the rebar is more prone to breaking, also known as Brittleness. Normally TMT reinforced bars are bent using a universal bending machine which ensures that the rebars are correctly bent rather than manually by labourers. When a less ductile reinforced bar is bent, the chances of it breaking are more than bending a reinforced steel bar with optimal ductility.
Less ductility makes the reinforced bars more susceptible to natural disasters, particularly earthquakes. As the tensile strength of the reinforced bars are increased, the ductility of the ferrite-pearlite core is gradually reduced. This makes them brittle and this causes the higher grade bars to be less supportive of the sudden underground seismic vibrations i.e earthquakes.
When it comes to bendability, higher grades does not bend easily than lower grades due to less ductility and high strength. When bent to diameters higher than the minimum specified, the internal ribs split which in turn causes the reinforced bar to break. Moreover, bending higher grade reinforced bars should be carried out very slowly without any sort of jerking and hydraulic bending machines must be used for the bending process. It is recommended that high grade reinforced bars like the Fe 500 should be preheated before bending, but this approach is not practical on construction sites.
Out of the TMT reinforced bar grades, Fe 415 is the only the grade having the optimal tensile strength and ductility. In higher grades such as Fe 500, Fe 550 and Fe 600, ductility is compromised for achieving the high tensile strength, so typically Fe 415 has more bendability than others but that doesn’t degrade the other grades. Higher grades are used for constructions according to its requirement.