Advantages of steel structures :
Following are different advantages of steel structures.
Steel structures are very reliable. They are reliable because of consistency and uniformity in properties. Their quality is controlled better because they are manufactured in factory. They have large elasticity and ductility. If different specimens of same type of steel are tested in laboratory for yield stresses, ultimate tensile strength and elongation, then the results are almost same for each specimen as compared to other materials like concrete and wood. As steel is truly homogeneous and elastic material, so it satisfies most of the assumptions involved in the derivation of analysis and design formulas and the results obtained are reliable. This may not be the case in concrete structures because concrete is a heterogeneous material, due to cracking and non linearity of stress-strain relationships.
- Industrial behavior:
Rolled steel sections are manufactured in factories. The members are cut and prepared for assembly in factories. The members are joined at the site by installing rivets or bolts or by welding different components. Sometimes part of the structures are also assembled in the factories. In steel structures there is a great adaptation to prefabrication. Prefabrication is to fabricate parts of a factory so that construction mainly of assembling and uniting standardized parts. Due to this, manual errors reduce greatly, the speed of construction increases and the total cost reduces.
- Lesser construction time:
Because on the industrial behavior of steel construction, progress of this work is very fast and the total cost reduces. These structures can be put to use earlier. Because of less labor cost and the benefits obtained from the early use of building, make the construction economical.
- Light weight and high strength:
Dead loads are the bigger part of the total loads. The high strength of steel per unit weight means that the dead loads will be smaller. When the dead load reduces, the underneath members become still smaller due to less weight acting on them. This fact is of great importance for long-span bridges, tall buildings, and for structures having poor foundations. A factor ( C ) can be defined as the ratio of the density of a material to the stress it can carry is one of the least for steel.
- Uniformity, durability and performance:
Steel is a very homogeneous and uniform material. Hence it satisfies the basic assumptions of most of the analysis and design formulas. The properties of steel do not change so much with time if it is properly maintained. But the properties of concrete structures are considerably modified with time. Hence steel structures are more durable and their performance is considerably good as compared to concrete structures.
Steel follows Hooke’s law up to fairly high stresses. The stress produced remains proportional to the strain applied. The steel sections do not crack or tear before ultimate load and hence the moment of inertia of a steel structure can be calculated. The moment of inertia obtained for a reinforced concrete structures are rather indefinite.
- Ductility and warning before failure:
Ductility may be defined as
The property of material by which it can withstand extensive deformation without failure under high tensile stresses is said to be its ductility.
Mild steel is a very ductile material. The percentage elongation of a standard tension test specimen after fracture can be as high as 25 to 30 %. This elongation gives visible deflections or evidence of expected failure in case of overloads. The extra loads may be removed from the structures to prevent collapse. Even if collapse does occur time is available for occupants to vacate the buildings.
In structural members under normal loads, high stress concentrations develop at various points. The ductile nature of the usual structural steels enables them to yield locally at those points.
- Additions to existing structures:
Steel can be added to the existing steel structures easily. Connections between new and existing structures can be employed very effectively. New bays or even entire wings can be added to existing steel frame buildings, and steel bridges may often be widened.
- Possible reuse:
Steel sections can be reused after a structure is disassembled.
- Scrap value:
Steel has a scrap value even though it is not reusable in its existing form.
- Water-tight and air-tight constructions:
Steel structures provide completely impervious construction and structures like reservoirs, oil pipes, gas pipes, etc., are preferably made from structural steel.
- Long span construction:
High-rise buildings, long span bridges and tall transmission towers are made up of structural steel. Industrial buildings up to a span of 90 meter can be designed by plate girders or trusses. Bridge spans up to 260 meter are made with plate girders. For truss bridges, spans of 300 meter have been used.
- Temporary construction:
Steel structures are always preferred for temporary structures. During war, army construction are mostly made out of structural steel. The structures may be disassembled by opening few bolts, component parts are carried to new places and the structure is easily reassembled.
Reference : Steel structures by Zahid Ahmad siddiqi and Muhammad ashraf