Structural steels are the variety of steel customarily used for construction such as buildings, bridges and as reinforcements to concrete. The form, shapes, and size of structural steels are dependent on the specific function that it will be used on. There are several standards that must be followed when producing structural steels; these standards also include the specifications for the steel’s mechanical properties, chemical composition, specific cross section and shape profile (American Institute of Steel Construction np).
Structural steels have various chemical elements which give its properties. It is very important that the components in making structural steels are given focus since these are what make the steel reliable and useful. The following are the major elements used in manufacturing structural steel:
Carbon deemed as the most important element contained in steel; it gives lower ductility and higher strength. Thus, structural steels must have carbon content of 0.15%-0.30%, otherwise, the strength may be jeopardized.
Manganese is commonly combined with carbon and is contained at 0.50%-1.70%; it is a necessary element as it conglomerates with sulfur and oxygen during the steel’s hot rolling process.
Vanadium is generally contained at 0.02%-0.15% and gives the structural steel an increase in the fracture toughness; its percentage differs and is specific for various ASTM grades and function.
Aluminum on the other hand acts as a deodorizing material and it is a component which gives a “fine-grained crystalline microstructure” to the steel; combined with silicon, fully-skilled or semi-skilled steel may be produced.
Chromium increases the corrosion resistance of structural steel and is mostly present in considerably small amounts; it is usually combined with copper and nickel to reinforce the corrosion resistance. For stainless steel which is known as the “18-8”, it means that the components are 18% nickel and 8% chromium.
Copper also gives the same properties as that of chromium which is contained at 0.2%.
Nickel which also gives corrosion resistance also develops the fracture toughness of structural steel. This in turn gives the steel its improved behavior in low temperatures. The percentage of nickel added in making the structural steels also varies with the grade; a A588 grade structural steel contains 0.25%-1.25% while ASTM A514 has nickel ranging from 0.30%-1.5%
Columbium is an element used to increase the strength of structural steels and is most commonly used for HSLA steels.
Silicon is also used as a deoxidizer like aluminum and usually contained at 0.4%.
Sulfur and phosphorus on the other note are chemicals which are considered to be undesirable components in structural steel production. Both are being strictly monitored to be only contained at not more than 0.04%-0.05% since they reduce the ductility and stimulates segregation in the internal matrix of steel.
Lastly, there are other elements present in trace amounts such as titanium, nitrogen and boron which complement the aforementioned elements to increase their effects on structural steel production.
The process of producing structural steels comes in two different ways as of today. One way is using an Electric Arc Furnaces or EAF steel mills which generally produce wide-flange sections, channels as well as angles, all of which are under the hot-rolled category of structural steels. The other one is through a Basic Oxygen Furnace or BOF wherein Hollow Steel Sections or HSS are produces with numerous rolls of steel sheets. Plate steels which are very popular are created or fashioned from EAF or BOF.
For the Basic Oxygen Furnace, it uses coke (processed coal) and iron ores to produce rolled steel sheets and steel plates. The iron ore is melted inside a furnace fire blasted with the coke and then is transported into a ladle. Chemical pretreatment is used to process the molten iron and is then subjected to the basic oxygen furnace through a steel scrap. Inside the BOF, the entire mixture with the addition of oxygen is then melted together. The molten mixture is then cooled and poured into another ladle for it to be fashioned in plates or sheets. The process being efficient and effective has an average of 25% recycled materials.
On another note, the Electric Arc Furnace employs the use of scrap metal or steel as its starting material. Usually, scrap steels coming from industrial waste, automobiles and appliances are scavenged and melted using gigantic electric furnace. To achieve a good metallurgical balance, foreign materials are removed from the molten steel through the introduction of chemical additives. The molten steel is then poured into “beam blanks” or molds which are specific for the desired shape. The blanks are then cooled then subjected again to heat then are passed on through numerous rollers to ensure that the product is of great form and specified precise shape. The steel beams being sturdy and of great quality go through cutting machines and are again cooled and furnished to be shipped. The process of EAF is more efficient and effective compared to the BOF with an average of 90% reprocessed content.
Structural steels can be classified in several ways and one of which is mainly based on their chemical composition:
High- strength quenched and tempered alloy steels have yield stress of 90 to 100 ksi and is made to undergo heat treatment to increase the strength. There are only few of these types such as A514 that are only available in plate form.
High-strength, low alloy steels is one of the most advanced types of steel. With the addition of other chemicals, the strength of this type of structural steel ranges from 42ksi-65ksi.
Carbon-manganese steels have both manganese and carbon as its chief component aside from iron. It is widely used due to its satisfactory ductility as well as strength. It is usually known to be mild structural or carbon steels. Carbon steels are less expensive compared to the other two and has a yield stress of more than or equal to 36ksi.
With all the types of steel available, why do designers prefer to use structural steel over the others? One is that structural steels can help make the construction speed faster. Structural steels can be fabricated in shops or plants with a good construction tolerance making the productivity in construction a lot higher. Structural steel is only of its type which produces the least waste of a construction site and has that tolerance easily maintained for integration together with several building systems. In addition, with the use of structural steels, projects are less costly. Based on statistics, the leading cost-efficient material is structural steels for over 30 years already.
Moreover, structural steel is aesthetically appealing given its natural finish; nobody can ignore the fact that its strength and slenderness catches the interest of minimalists. Also it is very advantageous to use structural steel especially for architects since they can exercise more their creativity and come up with sleek designs. Structural steel entitles both its designer and user both functionality and style. There are structural steels which can be rolled and event bent so as to meet the non-symmetric designs the client wants to.
Structural steel also has an outstanding strength that can accommodate 50,000 pounds of compressive or tensional stress in every square inch which is a great leap compared to standard steel which can only accommodate 12000 to 15000 pounds of compressive stress and 3000 to 5000 pounds per square inch of tensional stress. Likewise, it is a strong but light material making the building more light, therefore, cost effective and less extensive (OneSteel Market Mills np).
Furthermore, structural steels are sustainable being the most recyclable construction material all over the globe. Structural steels are comprised, surprisingly, of 88% recycled materials; hence, it is easier for it to be recycled as well when time comes its functionality declines. Moreover, it is somewhat ecofriendly ever since 1990 with a carbon footprint reduced to 47% already. Fortunately, the manufacturing of structural steel continues to be leading a cleaner environment with a decrease of 30% energy consumption for the past thirty years already. The manufacturing also uses make-up water conserving our potable resources of water. The make-up water used is looped to recycle and use it for other batches (Cengage Learning np).
All of the structural steels made when the functionality is over can be recycled s100%, therefore, it can therefore be concluded that it produces almost zero waste. The director of AISC also stated that “Rather than utilizing land for quarrying operations to provide aggregates or as landfills for construction material waste, structural steel is emptying salvage yards allowing that land to be used for other purposes.”
Another in the numerous advantages of employing structural steels is that it is greatly modifiable. This only means that whenever there is a need for change in the design or requirements, your ordered structural steel and money would not be put into waste. Structural steels are very flexible and strong that when there is a need to increase loads or even changes in the mechanical equipment to be used, structural steels can readily adapt to the changes; only few modifications are needed.
One great example of a scenario where structural steels can be said as modifiable is that a building constructed with only 32 stories was overlooked to be more beneficial if it stands higher. Luckily, that building in Chicago was made of structural steel; hence, the addition of another 24 stories is as easy as it was. During the construction of the a24 floors, the lower 32 floors were still being used simultaneously. Really, the structural steels are that strong and reliable. What is also great about structural steels is that it is predictable. The strength of the steel is already known unlike in the other types of steel wherein you would know its strength and capability only when the other reinforcement materials are added. With the existing standards of the American Society for Testing and Materials (ASTM) was met by the structural steel, even exceeding the tolerances needed for a construction material (MIT Dpartment of Civil and Environmental Engineering np).
Last but not the least is that it is readily available. In the United States settings, the production of structural steel is very high since companies are already estimating the market; the structural steel had already gained its popularity in the 2000 and had a breakthrough of 8 million tons production during 2007. Most of the manufactured structural steels way back in 2007 was in hot-rolled form. There were also 6 million structural steels manufactured in the form of wide flange sections and a great number of 800,000 tons were manufactured in excess to accommodate the increasing demand. As for the recent times, the structural steel industry is greatly expanding in different parts of the world as it continues to be popular with its great properties; functionality, cost-effective, aesthetically-appealing and very flexible. Indeed, the structural steel is one of the most desired material for construction of houses, bridges, commercial buildings and the like (Fletcher EasySteel np).
Works cited:
American Institute of Steel Construction : “Structural Steel Solutions” Web. <https://www.aisc.org/content.aspx?id=3792>
Cengage Learning “Properties of Structural-Steel Shapes” Web. <http://www.cengage.com/resource_uploads/downloads/1111136025_277030.pdf>
Fletcher EasySteel “Structural Steel Properties and Design Chartbook” Web. <http://www.easysteel.co.nz/site_files/8545/upload_files/EasysteelStructuralPropertiesbook(1).pdf?dl=1>
MIT Dpartment of Civil and Environmental Engineering “Chemical Composition of Structural Steels” Web. <http://web.mit.edu/1.51/www/pdf/chemical.pdf>
OneSteel Market Mills “Hot Rolled and Structural Steel Products”. Web. <http://www.cim.mcgill.ca/~paul/hotrolled.pdf>
Where Structural Steel is Used and Advantages of Using Structural Steel
