Analysis On The Status Of International Standards For Steel Wires Used In Bridge Cables

The United States is one of the earliest countries in the world to use steel wire as bridge cables. The peak of its suspension bridge construction lasted from the early 20th century to the mid-20th century. Limited by the level of steel wire manufacturing technology at the time, the carbon mass fraction of the steel wire of most suspension bridge main cables was about 0.8%, the diameter was 4.87 mm, the zinc layer thickness was 0.025 mm (equivalent to a surface mass of 180 g/m2), the free circle diameter of the steel wire was 2 m, and its minimum tensile strength was 1 480 MPa. The Williamsburg Bridge in New York uses a smooth steel wire with a diameter of 4.84 mm for the main cable; the Brooklyn Bridge uses a galvanized steel wire with a diameter of 4.67 mm. In 1968, the United States promulgated ASTM A 576-68 "Galvanized parallel steel wire cables and spiral structural cables and galvanized steel wire for on-site fabricated structural cables". This standard covers galvanized parallel steel wire cables and spiral structural cables that require or do not require pre-tensioning, and is used for prefabricated steel wire cable load-bearing components with high strength and high elastic modulus. Some chapters of the standard specify the requirements for galvanized steel wire for on-site cable fabrication. Most of the suspension bridges built in the United States after 1968 adopted this standard. The standard has been revised many times, the most recent revision being in 1998. The maximum diameter of galvanized steel wire in this standard is 4.775 mm, and the strength levels are 1 380 MPa, 1 450 MPa and 1520 MPa respectively. The standard also specifies the elongation after fracture, winding performance, coating quality and coating adhesion of the steel wire. However, there are no requirements for the fatigue resistance, relaxation resistance, torsion resistance, repeated bending performance, coating uniformity, and linearity of the steel wire.

On the other hand, prestressed steel originated in Europe in the 1920s, but was not widely used and developed until after World War II. Today, prestressed steel has been widely used in countries around the world. The United States has made prestressed steel the first of the five major metal products it focuses on developing. Prestressed steel was first used in concrete structures, and then gradually became widely used in bridges as the needs of other building components increased. Early structural experts believed that cable-stayed cables were also a type of prestressed material, so the steel wire used for cable-stayed cables in the United States generally referred to ASTM A421/A421M "Prestressed Concrete Smooth Steel Wire". This standard is mainly used for steel wires and strands with both sides of the head or the installation of clips in the prestressing industry. Although prestressed products and bridge cables have something in common, the requirements for steel wires are very different: (1) Prestressed products are basically inside bridges or structures and are in an indoor environment, while bridge cables are directly exposed to the natural environment. The corrosion environment is more severe than that of prestressed steel wires, so higher corrosion resistance is required for steel wires. (2) Due to different force modes and different positions, the live load acting on the bridge cables is greater, so the fatigue resistance requirements of the steel wire are high. (3) Bridge cables are more prone to vibration, which causes local bending fatigue of the steel wire, so the mechanical properties of the steel wire are required to be higher. (4) Bridge cables are difficult to replace or the replacement cost is high due to the difficulty of construction, so the durability requirements of the steel wire are higher. Most of the steel wires used in bridge cables are hot-dip galvanized or hot-dip galvanized aluminum alloy steel wires, so the above standards cannot be directly applied to steel wires used in bridge cables. In recent years, most cable-stayed bridges in the United States use galvanized steel strand cable systems and epoxy-coated steel strand cable systems, so the formulation of relevant standards is for steel strand products for cable stays.