This parts of the structure as a whole.

This paper introduces us to steel structures, their common structural shapes, the EU standard for these structures, the comparison with other types of structures(like concrete structures). There are many type of steel structures around us. It is obvious that the material used for these kind of structures are steels which may be classified by chemical composition, tensile properties.  Structural steel is mostly known for skyscrapers, large agriculture buildings and garage. Why do we use steel structures, where do we use them and why are steel structures more popular nowadays are the most asked questions in these days. And in this paper we will try to give for each question an answer.

What is Steel Structure?!
         Across the world, in almost every city stands an unique building or a statue. We call them differently, landmarks. They are precious to the respective cities and countries because they show a part of their history.  Beyond history, we appreciate them for their structure and only a few of us may know that at the base of most of these landmarks stands a steel structure. 
           It is defined as a metal structure which is made of structural steel components connected to each other to carry loads and provide full rigidity. These steel structures are a very important part of the following buildings we will mention in this paper. 
          They involve sub-structures and structural members which are physically distinguishable parts of the structure as a whole. These kinds of structures are popular among engineers because they are durable and can hold a lot of weight and because of the ability to choose among different types of steels like non-alloy steel or stainless steel. 
          Also we find this kind of material in various shapes and sizes so we can select the right part for the specific building. In other words, steel structures has made our job a lot easier.

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Advantages and Disadvantages of Steel Structures. 
        Steel it is very used mainly because is very affordable , versatile and durable. Despite being one of the most durable materials, steel is also good for environment because it is one of the very few materials which is continuously recyclable. Also, because it is made of partially recycled material and it is used in buildings which aim to last very long, the steel structures are pretended  to be more cost-effective than other buildings which are made with other materials. All these good things lead to making steel structures very used nowadays. 
            Steel structures have very advantages. Starting from the high strength that the steel provides to the uniformity of it since the steel doesn’t change its properties as appose to concrete. Elasticity is also an advantage and steel undergoes the Hooke’s Law very accurately. Also being very strong and flexible, steel framed structures are great in hurricane or cyclone prone regions.  What is the most important thing in steel structures is that they can be prefabricated in large sections.  
             As everything that is present in our world, even steel structures have their own  disadvantages. Being susceptible to corrosion when exposed to air, water and humidity, the structures must be painted periodically. Since it conduct heat, steel  has very small resistance against the fire. Steel is a very strong solid and it cannot be mold in any direction and also it is very heavy so it is expensive to transport.  

Most Famous Steel Buildings In The World.

         There are some famous steel structures that are very attractive for people for example : Eiffel  tower,  the Brooklyn Bridge, Burj Kalifa, The Empire State Building etc. All these mentioned buildings (except Brooklyn Bridge) are classified as skyscrapers. This means that structural steel  is used for very high structures and this makes the steel one of the most stable and strong material for buildings.
         Most famous buildings in the world are steel structures. There are buildings that are known for their super heights, sculptures that connect nations, and bridges that span the widest rivers all around the world. Yet, we forget that the most of the world’s iconic structures would not have been possible without steel.
           Let start with Tapei 101 Tower in Taiwan. The known building is half a kilometer tall and it is proof of strength and longevity of steel. Tapei 101 Tower has 61 elevators and is considered as one of the Seven Wonders of Engineering by the Discovery Channel.                                                                                             
            Also the Eiffel Tower is another well-known steel structure. It  is the most recognized and the most famous landmark around the world. For some years it was the highest steel structure till the built of Chryslers Building. Since 1889(for the World’s Fair) till these days, this building is a very touristic place   Shun Hing Square Tower in China is still the largest steel building holding the record for being constructed at a pace of four floors every 9 years.                                                                                              
              The Beijing National Stadium known differently as The Bird’s Nest stadium. It took five year to complete this structure and there are used 42,000 tons of steel. It is known as the largest steel structure in all over the world. Steel structures aren’t only for high building but also for bridges. The most famous are The Brooklyn Bridge was the first steel –wire build in 1869. It took a decade to complete it and it is still at the top 10 list. Another famous bridge is The Sydney Harbour Bridge whose total steelwork weights approximately 99,000 tones.

Categories of Steel Structures.
There are three general categories in which structures can be divided:
1. Framed Structures
2. Shell type Structures
3. Suspension type Structures

Framed Structures

This category is the most typical building construction. The high-rise building usually  is composed of beams and columns, either stiffly connected or having simple end connections along with diagonal bracing to provide stability. Even though a high-rise building is 3D it is usually designed to be much rigid in one direction that the other.

Shell-type structures 

It is obvious that the main characteristics of this type of structure is the shell. It is formed in that way because it main function is to carry big weights. With that as the main duty of it, we see shell-type structures in specific products. Some of them are storage bins, tanks, containment vessel and hulls of ships. While dealing with shell-type structures, we often see a framed structure too which is used in conjunction with the shell. In other words, they act together with a framework. The aircraft body is an example for this case.

Suspension-Type Structure

In this type of structure, the most supporting elements are the tension cables.  Suspension bridge is the most common structure of this type. It is quite common to find a subsystem  holding a framed structure like in the stiffening truss for the suspension bridge. Since this method is way more efficient in to carrying load, these structures are being used a lot lately.

Types of steels

          As we mentioned before in today’s world we have a lot of to choose from any material needed. In the case of steel, they can be classified in many ways like the production method, finishing method, form, quality, composition, microstructure etc. But the most fundamental and the most important at the same time is by their composition. We arrange them to two major categories: alloy and stainless. We are going to compare them by their materials and their importance.

           Alloy steel is called that way because it has had an amount of one or more alloying elements like manganese, silicon, nickel, titanium, copper, chromium, and aluminium. Of course this amount of alloy elements is at a specific level. This is an unique characteristic of alloy steel. As for the importance of it, this product is widely spread in different workplaces and preferred by workers because of their economical cost, easiness to find, easiness to process and good mechanical properties. All of them are combined with each other. Alloy steel is very cheap since there is widely spread and the market provides a lot of it. On the other hand, it is able to find it in every metal supermarkets since there is a high demand for it. People’s job is a lot easier to work with it because of its good mechanical properties. For example this kind of steel is much more responsive to heat and mechanical treatments than standard carbon steel. So it is easier to shape them and to edit them in the way we need to.

            Another type of steel is stainless steel. As the alloy steel that we mentioned before, this also has its own importance. When it comes to corrosion resistance, this product is the most important of all. What makes it unique is the existence of chromium. Also, by having structural properties of carbon steel, stainless steel is extremely useful for many projects we may have. There exists some issues about this material. First of all, it is very hard to find which makes it more expensive than alloy steel and second, not all types of stainless steels are easily welded, which means that it is hard to work with some of them. Austenitic and ferritic stainless steels are more preferred than martensitic steels or duplex stainless steels. That is because they have reduced amounts of chromium and other alloying elements, which makes those more weldable.