**6. Steel bridges**

Widely used in different structural forms around the world steel bridges provide large span lengths for highway and railway bridges. With its strength, ductility, rapid construction, and compressive and tensile strengths of 370 N/sq. mm steel had advantages over other construction materials. It has higher strength in both tension and compression than concrete, and has strength to cost ratio and stiffness to weight ratio. Strength, ductility, toughness, weldability, weather resistance, chemical composition, shape, size, and surface characteristics are important properties of structural steel for designing and construction of steel bridges [7].
