The severe earthquake that struck Nepal on April 25, 2015, claimed almost 9,000 lives, many thousands more were injured, and 600,000 structures in Kathmandu and other nearby towns were either damaged or destroyed. The staggering figure of structural damages forces us to believe that it is not the earthquake that kills but poorly built buildings.
Throwing more light on the importance of using earthquake resistant steel in construction is the fact that the majority of buildings in India successfully weathered the impact of Nepal earthquake. According to industry experts, the key differentiating factor between India and Nepal was the use of high-quality TMT bars. Despite India being bracketed under Seismic Zones III, IV & V, the awareness to use earthquake-resistant materials in construction only grew after the tragic Latur earthquake in 1993.
TMT Steel Bars have become the gold standard when it comes to earthquake-resistant construction in the country. Let us explore:
Good quality TMT bars exhibit high:
Focussing on the earthquake resistant properties, elongation and ductility of TMT bars play a crucial role as high energy is generated on a structure during an earthquake. And, to retain structural integrity it is essential that a ductile material absorbs this energy without breaking itself.
Earthquake Resistant Structure
TMT bars owe their excellent ductility and elongation characteristics to their structure. The bars possess a strong external martensite surface and a soft ferrite-pearlite core. Irrespective of the manufacturing process, these characteristics remain unchanged. During an earthquake, the core of the steel bar allows the action of mild tilting and the exterior surface bringing it back to its original position. Adding to this ductility, the elongation property ensures inelastic strains are better accommodated during seismic activity and also aftershocks.
Quality of steel bars and its mechanical properties like yield strength, elongation percentage are highly important in determining the flexural capacity and post-yield behavior of a reinforced member during an earthquake.
Rib formation is a crucial factor to consider when handling earthquake resistant TMT bars. It decides the bar’s reinforcement to concrete. Owing to the high compressive strength and low tensile strength of concrete, it becomes essential to reinforce it with steel
Which TMT grade provides real earthquake resistance?
Different grades of TMT steel bars like Fe-415, Fe-500, Fe-550, and Fe-600 are available in India as specified by BIS. Each of these grades come with their own strengths and limitations. Studies have showcased the difficulties associated with using higher strength grades like Fe 500, Fe 550.
Theoretically, Fe 415 and Fe 500S appear to have earthquake resistance properties. But when considered practically, Fe415 outperforms the latter. The right mix of ductility and tensile strength makes it the best choice for construction in seismically active regions. High ductility of the bars enables the building to withstand both dynamic and seismic loads well.
As suggested in IS 13920:1993, buying Fe415 steel grade is the right choice to build earthquake-resistant buildings.