Stones were the first materials to be used for pylons, but nowadays, materials such as steel and concrete are mostly being used. Pylons of suspension bridges transmit the loads from the main cable to the ground through the foundations. However, wires are sensitive to wind loads and the construction period is longer than wires constructed using the PWS method. This method has the advantage of reducing the size of the anchorages. Wires are formed in strand units at the construction site and constructed as main cables. The AS method uses the cable Hauling system to construct cables in wire units. Since parallel cables have greater strength than structural steel, the cross-sectional area of the cables is reduced, and thus, secondary stresses, manufacturing errors, and the amount of main cables are significantly reduced.Ĭable construction method is mainly divided into Air Spinning method (hereinafter referred to as AS method) and Prefabricated Wire Strand (hereinafter referred to as PWS method). In general, tensile strength of 1,600 ~ 1,800MPa is used for the main cables, but recently, cable steel wires for bridges with tensile strength of 2,200MPa have been developed. The main cables used in suspension bridges are tension members, such as ropes, wires, chains, etc., that cannot resists bending or compression, and can only support axial tension. However, truss girders have large drag due to their heavy weight and long span.
Furthermore, the top and bottom layers of the girder can be used by taking advantage of the height. Truss girders can increase the torsional stiffness of suspension bridges by raising the vertical height of the girder and installing horizontal lower bracings. One example in which plate I-girders were used is the Tacoma Narrows Bridge, which is famous for its collapse due to aerodynamic instability. Truss girders are proposed for stiffening girders because plate I-girders are disadvantageous with regards to aerodynamic stability. In the past, I-girders were mostly used for stiffening girders, but later they were developed into truss structures due to aerodynamic stability problems, and most recently been developed into box-shape cross-sections. Furthermore, since the stiffening girders are supported by cables, aerodynamic stability is required. Stiffening girders of suspension bridges are longitudinal structures that support or distribute vehicle loads.
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