PSI - Issue 84

Fabio Brancaleoni et al. / Procedia Structural Integrity 84 (2026) 1095–1102

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Leon Solomon Moisseiff with the ill-fated Tacoma. In this period, cable construction technology improved in many details, but aerial spinning remained the only technique. A final significant contribution from American industry was to occur in 1968: Jackson L. Durkee of Bethlehem Steel was the first in the world to reel parallel wire strands for the entire length of the cable. Thus, the technology of “Prefabricated Parallel Wire Strands” (PPWS) was born, with which two bridges were built in the United States—the Newport in 1969 and the Chesapeake Bay in 1973 (Birdsall, 1971). But the “spanning of America” was now complete and, again, technology developed elsewhere, in this case in Japan. 4. Suspension bridges worldwide Most suspension bridges built around the world in the second half of the twentieth century used the aerial spinning technique, with the record set in 1981 by the Humber Bridge in England, with a span of 1410 m. For the major project connecting the islands of Honshu and Shikoku in Japan, the Honshu Shikoku Bridge Authority instead acquired the patent of Bethlehem for PPWS, and with this technique—refined to allow up to 127 wires in a strand—several bridges were built, including the new record-holder Akashi Bridge in 1998, with a span of 1991 m. PPWS allows for short construction times and proves to be highly effective; is this the end of aerial spinning? No: in 1988, two bridges were erected, the Fatih Sultan Mehmet Bridge (or second Bosphorus Bridge) and the Shimotsui Seto Bridge in Japan, improving the technique in what is now called “modified aerial spinning”. Today, both technologies are adopted: e.g. the Braila Bridge in Romania, completed in 2023, used spinning, while the current world record, the 1915 Bridge over the Dardanelles, completed in 2022, with a span of 2023 m, used PPWS. 5. Evolution of wire strength In the first half of the 19th century, wires were in general drawn or wrought. The material was still iron, not yet steel, with protection provided by oils, greases, pitch, or paints. Progress was rapid, Table 1, with breaking strengths on the order of several hundred MPa. Around the middle of the century, steel wire became available, and hot-dip zinc coating techniques were perfected. The first example of the use of hot-dip zinc coated steel wires was the Brooklyn Bridge, with a breaking strength that reached 1100 MPa, a value that was soon surpassed, with the 1500 MPa of the Williamsburg Bridge in 1903. The path toward long spans was open, but it was followed by a long period in which the strength remained substantially unchanged, while the allowable working stresses were gradually refined and increased, as the ductility properties: the Storebaelt Bridge in Denmark, built in 1998, still has a breaking strength of 1570 MPa (Sluzka, 1991; Sluzka, 1993; Ono, 2018; Ono, 2019; Gimsing, 1998). However, a new impetus was maturing, driven by the involvement of new markets and technologies but, above all, by the clear need of containing the weight of the cables for very large spans, a fundamental aspect both for costs and for achieving stability against wind actions, together with the aerodynamic characteristics of the deck (Brancaleoni, 2009). In fact, up to spans of about 1000–1500 m, the weight of the deck prevails over that of the cable, but around 2000–2500 m the two tend to equalize and, for the very large spans of the future, the weight of the cables would become much greater, Table 2. The first significant progress occurred with the Akashi Bridge, with 1770 MPa, then 1860 MPa and 1960 MPa were first applied in the 2010s in South Korea, and today strengths above 2000 MPa are already applied in China, reaching up to 2200 MPa for the Zhangjinggao Bridge currently under construction, Errore. L'origine riferimento non è stata trovata. . It is believed that a stabilization should now be expected, while certainly such high mechanical properties, associated with the dimensions of the cables reached for very large spans, require careful examination of a series of behavioural aspects, always characteristic of suspension bridges but accentuated by these new achievements.

6. Evolution of cable size, transversal behaviour of compacted cables The increase in size and forces in cables leads to two primary issues:

• Regardless of the construction technique—whether aerial spinning or PPWS—once the individual strands are installed, the next step is their compaction (Gimsing, 2012), which transforms them into a single large bundle of wires. Compaction is carried out using hydraulic jacks arranged radially around the cable, with their size and power strongly dependent on the cable’s dimensions. In the compaction process, it is important to know the transverse stiffness of the wire bundle, as this affects the characteristics and stroke of such equipment.