In the era of interconnected transportation infrastructure, steel, with its superior mechanical properties, span adaptability, and styling flexibility, has become a core material for spanning rivers, lakes, and seas, and connecting urban networks. From kilometer-long cable-stayed bridges to ultra-long-span suspension bridges, steel forms the "steel skeleton" of bridges, ensuring the safe passage of millions of vehicles while embodying engineering aesthetics with its light, upright structural form. It has become a key pillar in promoting the development of a strong transportation nation.

The stability of bridge structures relies on breakthroughs in steel performance. The main beams and towers of long-span cable-stayed bridges are extensively made of Q690-Q960 ultra-high-strength structural steel, boasting a yield strength of up to 960 MPa. This allows for lightweight main beams while also withstanding cable loads exceeding one million Newtons, making bridge main spans exceeding 1,000 meters possible. For example, the steel box girders of sea-crossing bridges utilize orthotropic steel decks. Through precise welding of the steel plates and stiffening ribs, a structural system is formed that combines load-bearing and fatigue-resistant properties, capable of withstanding wave impacts and prolonged vehicle traffic, ensuring a bridge service life exceeding 100 years.

Adaptability to complex working conditions highlights the technological advantages of steel. In bridge construction in cold and high-altitude areas, low-temperature-resistant steels demonstrate excellent performance. For example, Q355GNHD weathering steel maintains excellent toughness even in extreme temperatures of -60°C, eliminating the risk of low-temperature brittle fracture. For sea-crossing bridges traversing corrosive environments, marine atmospheric corrosion-resistant steel is used. By adding alloying elements such as nickel and titanium, the steel's corrosion resistance is increased by 3-5 times, significantly reducing subsequent anti-corrosion and maintenance costs. Furthermore, the pressure-bearing components of the bridge supports utilize 42CrMo alloy structural steel. After quenching and tempering, its hardness reaches HB220-250, enabling it to withstand the vertical loads and horizontal displacements of the bridge structure over extended periods.

Technological innovation is driving the upgrading of steel applications. In modern bridge construction, high-performance steel is deeply integrated with digital construction technology. Parametric design of steel components using BIM technology allows for assembly accuracy of steel box girders to be controlled within 2mm. Modular construction, leveraging the standardized processing properties of steel, allows bridge steel components to be prefabricated in factories and assembled on-site, significantly shortening the construction cycle. Furthermore, the recyclability of steel, combined with green steelmaking processes, has reduced carbon emissions from bridge construction by over 40%, achieving the coordinated development of engineering construction and ecological protection.