The case for steel
Commodity prices are tricky. They are the most volatile of international prices. Usually caused by disturbances in demand and supply, the volatility of commodity prices makes price forecasting difficult.
Last month, prices of steel fell by 3-5% or Rs 1,000-1,500 a tonne due to a steep decline in raw material costs. Overall, steel prices have declined a marginal 0.51% last couple of months and the commodity has seen 9% decline in four months, due to weak demand from consumer industries.
Ashwani Kumar, vice-president, sales & marketing, Jindal Steel & Power Ltd, says, “Steel prices are dynamic in nature and governed by the fluctuation in raw material prices, international prices and rupee appreciation/depreciation. It’s also cyclic in nature. This year, price will depend on raw material prices and government policy on coal and iron ore. We feel that prices will be stable basis on demand.”
Gautam Suri, director, Interarch Building Products, says, “The weak pricing happened due to lots of regional players coming into the industry; we are very pleased and appreciate the fact that the consumers are getting ahead of the price sensitive market and are considering companies providing better and quality products.”
The building segment in India is presently dominated by concrete. It has been slow to adopt the global construction practices, even in the metropolitan cities. Structural steel usage in the building segment in India is presently driven by exception rather than practice. Penetration of structural steel in overall buildings segment is currently very low. However, this trend has seen a change over the past 4-5 years as developers are realising the advantages of using structural steel in building segment, particularly high rise buildings.
There’s been a marked increase in the use of steel in housing and residential building sector last decade. What has aided in the growing appreciation is the performance benefits that arise from the off-site nature of the construction process, which is particularly important in urban or mixed-use buildings. Off-site steel construction technologies improve the final quality of the building and its speed of construction, and can lead to additional points under the Code for Sustainable Homes.
Considering the direction in which population density in metro cities is moving, it’s not possible to opt for horizontal construction, and comfortably spread out real estate is hard to find. Buildings are getting taller, and most importantly, it’s pertinent that construction happens faster. The use of steel in high-rise buildings comes into vogue.
Over the years, structural steel in India has come to be widely accepted and realised for the umpteen benefits it has to offer to the modern construction sector. A case in point are the PEB buildings that have been proving its mettle in several diverse sectors like automotive, public sector, oil & gas, power, retail, hospitals and hotels, to name a few. Structural steel buildings or PEBs are addressing parameters including aesthetics, environment friendliness and longevity of life-span with an assurance given product innovation and technology advancement.
Interarch Building Products offers structural steel engineered aimed for speed of construction due to in plant fabrication, tight construction tolerances, and minimum site wastage; lower project cost, compared to conventional construction materials; limitless aesthetic possibilities can be shaped in any form; design flexibility for any application; high strength to weight ratio; ease of design; sustainable; modifiable/expandable; and space efficient due to larger spans and efficient member sizes.
Building tall with steel also allows more floors per total height of the building. This is due to the fact that the building structure in steel is lighter and more efficient, and has beams that are not required to be as deep as those of concrete to support the floors. The ability to have lighter sections, allowing the same load bearing capacity per floor, allows space for almost 1.5 extra floors in the same overall external height of the building.
One of the main reasons steel is used in so many construction projects is its durability — it has the highest strength-to-weight ratio as compared to any other building material, making it ideal for buildings both large and small. In addition to being one of the most durable materials available, steel products are also good for the environment. It is one of the few metals that is continuously recyclable, and any steel product that you use likely contains at least 25% recycled steel. The recycling process does not break down or weaken steel, making it an ideal choice for continuous reuse.
Kumar of Jindal Steel & Power says that steel has been used as a construction material for commercial buildings since a long time. Prior to that, cast iron was used as a construction material. “But it was found that structural steel beams set in concrete enabled construction of tall buildings that were more fire resistant and more structurally sound than cast iron. Since then, steel (an alloy made by combining iron and carbon) has not only become the best building material for commercial construction but closely tied to the economic health of any country.”
Steel is today being used in different projects, including construction of roads and rails, building infrastructure such as bridges and buildings, construction of modern architecture from skyscrapers and airports to residential homes and parks. Even buildings that are constructed using some other material (such as concrete) are often reinforced with steel beams.
In India, most often structural steel has traditionally been fabricated on-site. This was due to the lack of infrastructure for transporting heavy sections from an off-site workshop to project site. Also one needs to consider the constraint of space at a fabrication workshop. This is exacerbated by the problem of inexpensive skilled labour. These issues can always be mitigated by pre-engineered buildings, which are fabricated in a workshop elsewhere. Alakesh Roy, managing director, Zamil Steel, says, “If fabricators and vendors can avail of complete rolled sections then production can be done at the factory. We would not require executing fabrication at the site or design. So workers can work on the site premises and build the structure. All that the fabricator will be required to do is transport the material and fit it up.”
A spokesperson for a reputed steel company says that faster and economical solutions are being achieved in recent times especially through the evolution of pre-engineered buildings and the usage of decking systems. Most industrial projects are now being completed by using rafters, purlins (C & Z types) and girts as structural materials.
Steel can undergo large plastic deformation before failure, thus providing large reserve strength. This property is referred to as ductility. Properly designed steel structures can have high ductility, which is an important characteristic for resisting shock loading such as blasts or earthquakes. A ductile structure has energy-absorbing capacity and will not incur sudden failure. It usually shows large visible deflections before failure or collapse.
Steel bars are also used to improve the bond with concrete. The concept of reinforced concrete evolved due to the fact that steel and concrete act together in resisting force. Concrete is strong in compression but weak in tension. For this reason, concrete works well for columns and posts that are compression members in a structure. But, when it is used for tension members, such as beams, girders, foundation walls, or floors, concrete must be reinforced to attain the necessary tension strength.
Kumar of JSPL says, “Steel is the best material for reinforcing concrete because the properties of expansion
for both steel and concrete are considered to be approximately the same;
that is, under normal conditions, they will expand and contract at an almost equal rate.”
Generally there are two types of steel bars available in the market: Mild steel bars; and deformed steel bars.
Mild steel bars (as per IS:432): These steel bars are plain in surface and are round sections of diameter from 6-50mm. These rods are manufactured in long lengths and can be cut quickly and bent easily without damage.
Deformed steel bars (as per IS:1786): As deformed bars are rods of steels provided with lugs, ribs or deformation on the surface of bar, these bars minimise slippage in concrete and increase the bond between the two materials. Deformed bars have more tensile stresses than that of mild steel plain bars.
Delving into the mechanics of high rise building construction, we see that the introduction of hot rolled steel sections, using higher grade steel add more strength to the building. Better steel decking as a construction material has brought about a revolution in the steel building space. Building a high rise or any multi-level building demands the use of light-weight yet strong materials.
Most high-rises have frames made of steel and concrete. Pre-engineered steel framed structures with the composite floor bring considerable economies to the overall cost of the project during its lifetime. Steel structures can have a variety of structural forms like braced frames and moment resistant frames suitable to meet the specific requirements of higher buildings. Taller buildings also face higher wind loads, and hence steel being flexible, allows the building to move and deflect with the wind forces, rather than making it rigid like concrete.
However, steel can also have certain disadvantages. Steel structures may be more costly than other types of
structures. The strength of steel is reduced substantially when heated at temperatures commonly observed in building fires. Also, steel conducts and transmits heat from a burning portion of the building quite fast. Consequently, steel frames in buildings must have adequate fireproofing.
Steel structures exposed to air and water, such as bridges, are susceptible to corrosion and should be painted regularly. Application of weathering and corrosion-resistant steels may eliminate this problem. Due to high strength/weight ratio, steel compression members are in general more slender and consequently more susceptible to buckling than, say, reinforced concrete compression members. As a result, considerable materials may have to be used just to improve the buckling resistance of slender steel compression members.
Kumar of JSPL says that any building which has been designed and built using steel as the construction material has to be governed by certain parameters ensuring the safety of that building which is of prime importance. The steel bars used in a RCC structure, have to pass certain quality checks before they are declared safe to use. In the production of these steel bars, the quality tests are performed on the bars as per certain standards. In case of TMT bars used in India, the bars have to comply with certain minimum requirements defined in IS 1786-2008. The standard defines the minimum requirements of chemical as well as mechanical properties of the bars. In addition to checking the chemical and mechanical properties of the material, the weight and surface finish of the material has to be also kept in view which should be within the allowed limits defined in the standard, as that also plays an important role in the construction process.