Cables are a construction of wire strands, laid (i.e. twisted) helically around a core, to form a tension member of symmetrical cross section. Cables have a high strength-to-weight ratio as the wire strands are drawn to high strengths and laid to share tensile loads efficiently. There are two fundamental cable constructions: Wire rope (“flexible construction”) and structural strand (“stiff construction”). The construction and subsequent mechanical properties are determined by the wire pattern and wire size used for the core and outer strands.
For a given strength, wire rope is larger in diameter and lower in stiffness than structural strand or solid rods, so it may not be the most cost-effective product for static, tension load-carrying structural members. However, in cases where relatively high stretch is desired, or where the cable needs to turn a sharp angle, wire rope may be the appropriate choice.
Structural strand is the cable construction most commonly used in structural applications. It offers an economical combination of strength and stiffness for static structures. As cables get larger in diameter, the number of strands increases. For instance, cables with a nominal diameter up to 3/4 inch [19 mm] have 19 strands (called 1×19), while cables of 2 inch [50.8 mm] diameter have 91 strands (called 1×91).