Bridges in the early days were made of stone, wood and concrete. As time passed and with the arrival of steam train, bridges were required to carry heavier weights and needed a makeover. This led to the usage of iron in the next generation of bridges. However iron is susceptible to corrosion and ultimately failed to become the ideal material for bridges. Next came in steel.
Steel has now become an essential part of modern day bridges and comes in a variety of forms. Steel is strong, can flex without fracturing and has a long life, even in the harshest conditions. It can be used to build bridges of any length because of its durability, strength and ease of maintenance.
Steel incorporated in bridge construction can be divided into a number of categories:
The cheapest of steels available out there for constructional purposes is carbon steel. It is more stiff than strong. Carbon steel has stress value of around 250 N/sq mm and can be easily welded together into bigger structures.
High Strength Steel
Addition of various other materials to a particular element results in alloys. Alloys have better mechanical properties compared to pure materials. High strength steel results from the addition of alloying elements to basic steel. Also these require special welding techniques as well.
Weathering steels are made from alloys that result in high strength and increased resistance to atmospheric corrosion. Under suitable environments the steel forms a layer of rust ‘patina’ on the surface that prevents it from further corrosion and increases its lifespan up to 120 years!
Heat Treated Carbon Steel
Heat treated carbon steel has the highest strength which is derived from the heat treatment after rolling namely normalization or quenching and tempering. Heat treated carbon steel can be welded with normal welding techniques.
Stainless steel is the most recent form of steel incorporated in bridge construction and probably the most strong and durable. Due to its high mechanical resistance and anti-corrosion properties, the entire bridges are now made out of this one material.