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Strength of a Building

INFRASTRUCTURE development is the backboneof nation’s growth. A major contribution to In-dia’s infrastructure has come from growth in theconstruction of residential/commercial buildings

and high rise. In the demand for making such build-ings safer,builders as well as individuals are focusingmore on the quality of material used.Steel is the keyraw material used in India’s predominantly RCC con-struction.

Reinforced concrete construction (RCC) is thedominant construction method adopted in India ow-ing to advantage of economy in designs,corrosion re-sistance and fire proofing properties.Reinforced con-crete structure comprises of bonding steel andconcrete together to withstand induced forces.

Thermo mechanically treated rebars (TMT re-bars) impart strength and ductility to RCC structure towithstand various kinds of loads impacting a building.These days a lot of focus is given in designing struc-tures that have high earthquake resistance.TMT barshave high fatigue resistance to Seismic loads due toits higher UTS/YS ratio.This makes them most suitablefor use in earthquake prone areas.Usage of TMT hasenabled economy in design,construction of high ris-ers with improved earthquake resistance along withadded advantage of superior weldability,corrosion re-sistance,ductility and durability.

In India, steel demand is approximately 75mntonnes.Out of this around 23mn tonnes are for TMTBars alone making it single largest consumed steelproduct.However when we examine the supply side,the demand of 23 mn tonnes is roughly met by 7mntonnes from primary steel producers and remaining16mn tonnes from secondary steel producers. SAIL,Jindal Steel and Power Ltd (JSPL) , JSW, Tata Steel,RINL are the primary steel producers in the countryproducing steel using virgin iron ore.The extensivemetallurgical process of producing steel followed byrolling the clean steel in modern rolling mills leads toproduction of superior quality steel with uniform andconsistent properties. On the other hand, the sec-ondary steel producers follow a less modern andsometimes questionable set of processes and tech-nologies making the reinforced bars susceptible tosub-standard quality. Unfortunately, many housebuilders and common folks are not aware of differ-ence between the two kinds of producers and arealso not clear on quality parameters that one ought tolook for while buying TMT bars which are viewedmore as a commodity product.

The difference between product quality of pri-mary and secondary steel producers is mainly on twocounts. One is the raw material used and second isthe rolling process adopted.Primary steel producersprocess virgin iron ore through extensive metallurgi-cal operations followed by refining technologies thatmake steel clean and free from inclusion and harmfultramp elements such as sulphur and phosphorous.Secondary steel producers on the other hand primar-ily use steel scrap as their core input and convert itinto TMT rebars. Further the scrap used is mostlynon-homogeneous,non- segregated and of inferiorgrade having high level of tramp elements. Thechemical composition of re-bars thus produced is in-consistent leading to non-uniform physical propertieswhich hampers the strength, ductility and elonga-tion of steel.Secondly, the automated rolling processand control on heat treatment procedures adopted byPrimary steel producer enables them to produce ultra-high strength TMT rebars with lean and precisechemistry free from harmful impurities.TMT rebars soproduced have tight and controlled size tolerance,better rib pattern to ensure bonding with concrete,higher UTS/YS ratio and less carbon equivalent toimpart superior weldability.Whereas the rolling millsfound in the secondary steel producer category arenot so automated and in some cases downright anti-quated and lacking in various critical processes suchas heat treatment which leads to non-uniform prod-uct properties potentially putting the constructionin harm’s way.

Jindal Steel and Power Limited (JSPL) have setup one of the most modern and state of the art steelrolling plant in Jharkhand. The TMT rebars producedhere are technically advanced and are vastly superiorfrom the rest owing to a combination of ultra-cleansteel that is rolled in world’s most advanced MOR-GAN MILL deploying SIEMENS state of the artHYQST technology for thermo mechanical treat-ment. The quality standards of rebars produced inthis mill surpass the requirements of Bureau of In-dian Standards (BIS).

Jindal Panther TMT reinforcement bars instrength grades Fe500D & Fe500S have enhancedphysical, chemical and mechanical properties ascompared to the bars in strength grade Fe500.

These are produced under controlled manufactur-ing process and have excellent bendability.Externalribs running across the entire length of the TMT barsgive superior bonding strength between the bar and

the concrete.They have lower percentage of Carbon, Sulphur

and Phosphorous. The low carbon content ensuressufficient ductility and superior weldability for alltypes of welding without preheating.The impuritieslike sulphur and phosphorus tend to decrease thestrength of steel in extreme weather conditions;hence a lower percent is always desirable.

Jindal Panther TMT Rebars have higher yieldstrength, superior ultimate tensile strength to yieldstress ratio,and superior percentage elongation.Thehigher yield strength of reinforcing bars allowshigher loads with the same weight of steel, result-ing in optimal utilization and cost saving. Superiorultimate tensile strength to yield stress ratio and per-centage elongation ensure better performance whenexposed to unusual events such as earthquakes,col-lisions and / or fires.

As per IS 13920:1993 (Ductile detailing of rein-forced concrete structures subjected to seismicforces - code of practice) High Strength Deformedbars produced through TMT process and havingelongation more than 14.5 percent can be used inseismic Zones 3,4,5.

It is worth mentioning that the minimum speci-fied elongation for Fe 500D and Fe 500S is 16% and18% respectively. In Fe 500S,additionally, there is anupper limit specified for yield stress (625 N/mm2)and the tensile strength must be at least 1.25 timesthe actual yield strength.The properties of FE 500S aredesigned so as to improve the performance furtherwhen greater ductility is required, as in the case ofstructures in higher seismic zones. Such a provision

also helps the structure in experiencing a strong col-umn – weak beam type of behaviour, desired inearthquake resistant design of structures.

In order to make world class TMT available to In-dividual House Builder, JSPL has taken an unusualstep of foraying into retail with the launch of JindalPanther™ TMT Rebars.

Jindal Panther is not only a premium and ad-vanced quality product but also a brand that isrewriting the commercial rules of the game throughinitiatives such as:l Well branded dealer shops uniquely identifiablethrough JSPL’s Retail Identity Programl Material sold on per piece basis to avoid wastageand any ambiguity that may occur in case of weighingl Well defined, transparent and fixed monthly pricesl Free home deliveryl Material quality backed with Test Certificates

Even within the primary producer category, JSPLuniquely stands out as the only company having endto end manufacturing process control on TMT Re-bars. JSPL is making TMT from superior quality ironore and high quality imported coal from Australia.These raw materials go through extensive metallur-gical process of cleaning, refining, casting androlling.On the other hand,some of the primary steelproducers are partially producing through what isknown as “Conversion Route”wherein the raw ma-terial (billet) is given to small re-rolling units which

convert it into TMT.This shift of control from primarysteel producers to secondary mills dilutes the qualityof the end product.

Individual Home Builders are not aware aboutthe quality parameters of TMT.As a national brandwhich is rapidly attaining leadership position in theTMT product category, JSPL stands committed to of-fering world class product as well as spreadingawareness so that the consumers are enlightenedon the subject and is able to take an informed deci-sion on their choice of TMT rebars.

TMT is at the heart and soul of construction. It isthe backbone of whole structure.More attention is re-quired while buying the TMT bars as once they areused they become irreplaceable. Little more con-sciousness, a penny more invested for the sake ofquality can lead to enhanced life and safety of yourdream house.

Buyer must take note of the following beforepurchasing rebars:l Should buy TMT Rebars of Primary Steel producersl Ascertain quality parameters in line with require-ment of BIS 1786l Ask for mill test certificate l Should buy on per piece basis to avoid wastage

Excerpts by Mr Mohan Gupta, Professor &Head, Department of Civil Engineering, BIT Durg

TMT IS AT THE HEART ANDSOUL OF A CONSTRUCTION.IT IS THE BACKBONE OFWHOLE STRUCTURE. MOREATTENTION IS REQUIREDWHILE BUYING THE TMTBARS AS ONCE THEY AREUSED THEY BECOMEIRREPLACEABLE

The choice of TMT Rebars is the key to structural soundness

JSPL’s Patratu, Jharkhand TMT Rebar Mill- The most Modern Rebar Mill in India