Chapter 5
Cables
This chapter is devoted to analysis of cables under fixed loads of different types.
Among them are concentrated loads, uniformly distributed load along the hori-
zontal line and along the cable itself. Important formulas for analysis of the cable
subjected toarbitraryloads are derived; they allow determining thechangingof re-
actions, internal forces and shape due by any additional live loads. Relationships
between the thrust, internal forces and total length of a cable are established. The
influence of elastic properties of a cable is discussed.
5.1 Preliminary Remarks...................................................
The cables as the permanent members of the load-bearing structures are used exten-
sively in modern engineering. Some examples of cabled structures are as follows:
suspension bridges, anchoring systems of different objects such as guy-rope of the
masts, sea drilling platforms, stadium covering, cableways, floating breakwaters,
light-vessel, etc. Cables are also used as the temporary guys during erection of the
structures. Suspension bridge is shown in Fig.5.1.
Cables are made from high-strength steelwires twisted together, and present a
flexible system, which can resist only axial tension. The cables allow cover very
large spans. This may be explained by two reasons. (1) In axial tension, the stresses
are distributed uniformly within all areas of cross section, so the material of a ca-
ble is utilized in full measure; (2) Cables are made from steel wires with very high
ultimate tensile strength (Š1; 860MPa, while for structural steel ASTM-A36
Š 400 MPa). Therefore the own weight of a load-bearing structure becomes rela-
tively small and the effectiveness application of cables increases with the increasing
of the spans. Modern suspension bridges permit coverage of spans hundreds of me-
ters in length.
A cable as a load-bearing structure has several features. One of them is the verti-
cal load that gives rise to horizontal reactions, which, as in case of an arch, is called
a thrust. To carry out the thrust it is necessary to have a supporting structure. It may
be a pillar of a bridge (Fig.5.1) or a supporting ring for the covering of a stadium.
The cost of the supporting structure may be a significant factor in the overall cost of
the whole structure.
I.A. Karnovsky and O. Lebed,Advanced Methods of Structural Analysis,
DOI 10.1007/978-1-4419-1047-95,cSpringer Science+Business Media, LLC 2010
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