Steel remains the material of choice for long-span bridges where concrete’s weight-to-strength ratio makes it impractical or uneconomical. Modern steel bridges utilize weathering steel (Grade S355J2W or ASTM A588) to eliminate painting maintenance, high-strength grades (S460 or Grade 50 and above) to reduce structural weight, and fracture-toughness certified plates for primary tension members where failure would be catastrophic. Box girder bridges use steel plates welded into closed rectangular sections that combine excellent torsional stiffness with high bending resistance. Cable-stayed and suspension bridge decks use orthotropic steel deck plates — fabricated assemblies of deck plate, longitudinal stiffeners, and transverse cross-girders — that minimize dead weight while providing the required structural stiffness.