2622 Basic Feature of Wire Cable

A wire cable has to be composed of a large number of single wires to meet the strength requirement. A certain number of wires is often shop-assembled to form a prefabricated strand, subsequently at the site as basic elements for the final cable by being bundled into generally a circular cross-section.

Cable strands are classified into the wire rope formed by helically twisted wires and the parallel-wire strand (PWS), as shown in Table 26.2. A strand rope is manufactured by further twisting spiral rope strands around a single straight core strand. Mechanical properties of a cable go down in order of the PWS, the spiral rope, and the strand rope (see Table 26.3), while order of ease of handling is the reverse. Due to the inferiority of mechanical properties, the strand rope is rarely used in bridge cables. Stay cables used in cable-stayed bridges have more diversity as will be mentioned in the next section.

The cables in a cable-stayed bridge are all inclined. The actual stiffness of such an inclined cable is lower than that of the cable material itself because of sag due to its own weight. The equivalent Young's modulus of an inclined cable is expressed by

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