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Steel is the most preferred metal for the construction of large structures such as bridges, single storey industrial buildings, and some residential buildings.
There are three main types of steel construction – conventional steel fabrication, bolted steel structure construction and light gauge steel structure construction.
STRENGTH
Most steel construction is done with a type of steel called mild steel. Mild steel is a material that is immensely strong.
Take a circular bar of steel 1 inch / 25mm in diameter. If you were to attach this bar securely to your ceiling, you could hang from it 20,000 Kg (which is 20 tons), or any one of the following:
‐ 18 Honda City Cars
‐ 2 and a half African Elephants
‐ 1 and a half London City Routemaster Double-Decker Buses
This immense strength is of great advantage to buildings.
FLEXIBILITY
The other important feature of steel framing is its flexibility. It can bend without cracking, which is another great advantage, as a steel building can flex when it is pushed to one side by say, wind, or an earthquake.
PLASTICITY OR DUCTILITY
The third characteristic of steel is its plasticity or ductility. This means that when subjected to great force, it will not suddenly crack like glass, but slowly bend out of shape. This property allows steel buildings to bend out of shape, or deform, thus giving warning to inhabitants to escape. Failure in steel frames is not sudden - a steel structure rarely collapses. Steel in most cases performs far better in earthquake than most other materials because of these properties.
However one important property of steel is that it quickly loses its strength in a fire. At 500 degrees Celsius (930 degrees F), mild steel can lose almost half its strength. This is what happened at the collapse of the World Trade Towers in 2001.
Therefore, steel in buildings must be protected from fire or high temperature; this is usually done by wrapping it with boards or spray-on material called fire protection.
WHERE STEEL FRAME STRUCTURES ARE USED
Steel construction is most often used in
‐ High rise buildings because of its strength, low weight, and speed of construction
‐ Industrial buildings because of its ability to create large span spaces at low cost
‐ Warehouse buildings for the same reason
‐ Residential buildings in a technique called light gauge steel construction
‐ Temporary Structures as these are quick to set up and remove
WEIGHT OF STEEL FRAME STRUCTURES
Steel structures weigh 60% lesser than concrete.
This may be surprising to know that if you weigh 2×4 square feet piece of wood and 2×4 square feet piece of steel, the steel would weigh more due to its density. However, when steel is used in framing, the design of beam will cause it to be lighter than a structurally sound wooden/concrete beam design.
Steel is light in weight as compared to timber/concrete, which makes it easier to transport and hence, reduces fuel costs and quicken project schedules.
This low weight of steel frame buildings means that they have to be firmly bolted to the foundations to resist wind forces, else they could be blown away like deck umbrellas!
ADVANTAGES OF STEEL STRUCTURES
Steel structures have the following advantages:
‐ They are super-quick to build at site, as a lot of work can be pre-fabricated at the factory.
‐ They are flexible, which makes them very good at resisting dynamic (changing) forces such as wind or earthquake forces.
‐ A wide range of ready-made structural sections are available, such as I, C, and angle sections
‐ They can be made to take any kind of shape, and clad with any type of material
‐ A wide range of joining methods is available, such as bolting, welding, and riveting
DISADVANTAGES OF STEEL STRUCTURES
Steel structures have the following disadvantages:
‐ They lose strength at high temperatures, and are susceptible to fire.
‐ They are prone to corrosion in humid or marine environments.
