Thesis-2013-Khan.pdf (3.34 MB)
Structural characteristics of various types of helically wound cables in bending
thesis
posted on 2014-02-17, 11:41 authored by Sajjad W. KhanThe primary aim of this research was to investigate the bending behaviour of helically
wound steel cables of various types (i.e. normal spiral strands, sheathed spiral strands
and locked coil cables) in the presence of friction and to propose more efficient
computational models for their analysis under combined tension and bending.
The proposed model fully takes into account interwire contact forces both in the
radial direction (point contact between wires in different layers) and hoop direction
(line contact within the wires in the same layer). Extensive theoretical parametric
studies have been undertaken on a variety of cable constructions covering a wide
range of geometrical and material parameters. Explicit formulations have been
developed for the smooth transition of the bending stiffness from no-slip to full slip
regimes, as a function of cable curvature. Based on these formulations, it is now
possible to calculate the relative displacements of the wires, as well as the tensile,
bending and hoop stresses in the individual wires of the cable. Furthermore, bending
stiffness of the cable is shown to decrease by a factor of 2 to 16, depending upon the
friction coefficient between wires and the type of cable construction. Wherever
possible, the theoretical results have been compared with experimental results from
the available literature and are found in very good agreement with them.
A simple method for the determination of the bending stiffness of large diameter
multi-layered cable has been developed. The simplified method is further shown to
provide estimates of the bending stiffness which are very close to those calculated by
the original theory, allowing hand calculations for an easier use in industry.
The proposed formulations have been extended to cater for the effects of external
hydrostatic pressure on sheathed spiral strands in deep water applications. These
forces are shown to have a great influence on the pattern of interwire contact forces
and hence the interlayer slippage between the wires in the strand. Numerical results
have been obtained and analysed for three different 127 mm diameter strands with
lay angles of 12°, 18° and 24° respectively, experiencing a wide range of external
hydrostatic pressures of 0 to 2,000 metres. The significant increase in normal contact
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force between wires is shown to suppress the slippage of wires in the cable. However,
the no-slip and full slip values of the effective bending stiffness of the cable is shown
to be independent of the level of hydrostatic pressure.
A theoretical model is also proposed for estimating wire kinematics, pattern of
interwire slippage, contact forces as well as the flexural rigidity of locked coil cables
with outer layers made of shaped wires. In order to validate this model, numerical
results are reported for two different locked coil cables. It is shown that the shaped
wires in the outer layers of locked coil cables play an important role in the
distribution of contact forces, slip initiation and cable unwinding.
Funding
Higher Education Commission of Pakistan
History
School
- Architecture, Building and Civil Engineering
Publisher
© Sajjad Wali KhanPublication date
2013Notes
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.Language
- en