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Rope details

Rope details#

Steel#

Steel-wire rope#

  • Wire is a metal thread.

  • Several wires are combined into a strand.

  • Strands are bound together around a core to make a rope.

If this is the end-product, then it typically referred to in combination with its construction and/or material. For example a “wire rope”, “steel-wire rope”.

  • A typical product is the 6x36 IWRC (Independent Wire Rope Core )

image-20230530125058469

Cable-laid rope#

The same steps are repeated to create a cable-laid sling or grommet.

The ropes are now used as strands and are referred to as unit-ropes and the end product is cable-laid rope.

In general terms, cable is used to refer to a strong rope.

Pictures#

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6x36 Wire rope with steel core (Independent Wire Rope Core)

Cable laid wire rope (sling/grommet)

Synthetic Fiber#

Synthetic ropes are ropes assembled from synthetic fibers (as opposed to natural fibers).

Examples are nylon, polyester, HMPE (high modulus polyethylene). Dyneema and Spectra® are brand names and are specific types of HMPE.

The stiffness of synthetic rope can be very complex and is influenced by creep, temperature, loading frequency and more. The deformation can be both viscous as well as elastic (viscoelastic). DAVE can give some estimates for the stiffness but these should be treated with caution and should always be verified.

Physical properties estimation#

To perform a rigging calculation the physical properties (diameter, length, MBL, weight and stiffness) of rigging have to be known.

Purpose is to derive realistic default properties of a cable from its make and known properties.

MBL, diameter, weight and stiffness#

Ideally the physical properties of a sling or grommet are obtained from the manufacturer and verified using tests.

In absence of this, for example because slings still have to be manufactured, DAVE can provide an estimation of of the physical properties based on manufacturer information, the standard, the EN13414 standard and research.

The following table lists the build-in relations between the physical properties.

Independent Wire Rope Core
(6x36 Wire Rope)

Cable laid wire

HPME (“dyneema”)
note 6

\(d\) : diameter, [mm]

\( \sqrt (MBL / 0.064)\)
Note 1

from MBL via table
Note 2

\( \sqrt (MBL / 0.064)\)

MBL [t]

\(0.064 \cdot d^2\)\(128 \cdot 10^6 \cdot A_s\)
note 4

from d via table
Note 2

\(0.0064 * d^2\)

\(A_s\) Area [m2]

\( {0.68 \cdot \pi \over 4} ({d_s \over 1000})^2\)

\( {7 \over 9} {0.68 \cdot \pi \over 4} ({d_s \over 1000})^2\)
note 3

weight [kg/m]

\(7850 \cdot A_s\)

\(7850 \cdot A_s\)

\(0.000419 \cdot d^2\)

EA [kN]

\(128 \cdot 10^6 \cdot A_s\)
note 4

\(80\cdot10^6\cdot0.785 \cdot d^2\)
or
\(0.6 \cdot 128 \cdot 10^6 \cdot A_s\)
note 5

\(30\cdot9.81\cdot MBL[t]\)

Notes:

  1. There are various sources for factor 0.064 used for IWRC

  2. The diameter/SWL relation as informatively given in annex G of BS EN 13414-3:2003+A1 :2008 / EN 13414-3:2003+A1 :2008 (E) ; combined with diameter based the safety-factor (\(SF = 6.33 - 0.022 \cdot d\)) as given in the same code this yields a relation between diameter and MBL.

  3. The factor 7/9 follows from 7 subropes and a diameter of 3 subropes

  4. Supplier data and PAPER

  5. The additional factor 0.6 accounts for the reduction in stiffness considering full-slip conditions (\(E{full-slip}/E_{steel}\)) of the subropes. This theory is applicable for large loads and results in a lower stiffness than for low loads [ref: PAPER].

    From IWRC to cable laid wire is essentially the same step as from steel rods to IWRC. It makes sense to apply the \( E_{full-slip} / E_{steel}\) conversion again. This factor is between 0.48 and 0.71, 0.6 was used as a reasonably conservative value.

    Extract from paper

    DNV recommends values with the same order of magnitude depending on the configuration:

    • DNV 16.2.6.13 : E = 25kN/mm2 and A = 0.785xd2 in combination with a 1.25 SKL for 4-sling lifts using matched pairs of wire single laid slings

    • DNV 16.2.6.13 : E = 80kN/mm2 and A = 0.785xd2 for indeterminate 4-sling lifts using four single laid slings of un-equal length

  6. These values are general estimates based [FRT] and supplier info. [FRT] uses roughly EA = 25*MBL, this value is conservatively increased to 30.

References:

DAVE#

In DAVE it is recommended to use the SlingGrommet or RiggingString nodes to model slings or grommets. When using SlingGrommet or RiggingString nodes user can select “estimate” to automatically estimate the wire properties using the relations above.

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