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Setting up a rigging design analysis

Setting up a rigging design analysis#

Design of a rigging goes hand in hand with a rigging analysis. The design is often updated based on the outcome of the analysis. This is the (in)famous “design cycle”. DAVE is designed to make these design iterations as quick and fun as possible.

Design sketch#

In DAVE the “design” part typically starts with:

  • Defining the object that needs to be lifted

  • Defining the liftpoints on it

  • Loading the crane, hoist and lifting beams

  • Configuring the lifting beam configuration (grommet protectors, trunnions etc)

  • Moving all these objects to their approximate relative positions

  • Creating the rigging items between liftpoints, lifting beams and hook(s)

The steps above define the approximate lifting arrangement. The nodes that were introduced in the previous sections are created especially for this.

Refine,#

The next step is to fine-tune and optimize it. This involves:

  • leveling the lifted object by:

    • changing the (relative) hook elevations for dual-crane lifts

    • optimizing the lengths of new-buy slings and grommets

    • adding or removing shackle

    • selecting different slings, grommets or shackles from available stock.

  • checking if the the required strength (MBL) is sufficient by:

    • calculating the occurring loads

    • defining global safety factors and DAF

    • defining local (partial) safety factors for slings and grommets

The rigging analysis node is there to assist with these tasks as well as to define the data required for the final step

Rigging-analysis node#

The purpose of the rigging analysis node is to assist with optimizations of the design.

Rigging Analysis Node

Rigging analysis report#

For efficient engineering it is therefore important to get feedback quickly.

Design rigging

  • Rigging items

  • MBLs, lengths, number of shackles

Rigging analysis

  • Lifting heights

  • Lifted object tilts

  • Tensions in rigging items

Rigging analysis report

  • Run variations cases

  • Reporting

What is defined where?

What

Where

Remarks

Dual crane

Hoists

Node

Tilt axis of lifted object

Node

Hook height difference

Section

Friction

Local/global friction definition per sling/grommet

Section

Angle threshold for inclusion in friction load-cases

Section

TODO

Rigging item factors

Bending factor

Node

use tags

Partial safety factors (DNV)

Node

Use coefficient of utilization \(z_p\) instead (IMCA, Eurocode) using user defined interpolation table (note 1)

Node

Lifted object

CoG inaccuracy factor or envelope

Node

Global factors - general

Weight contingency factor

Node

Dynamic application factor

Node

Global factors - rigging system specific

Skew load factor

Node

override skew factor with variations

Section

Yaw effect factor (dual crane)

Node

Replace skew factor with length variations

Section

Length variation as factor of diameter

Section

Matched pairs

Section

Alternative calculation of rigging item working-load limits#

Warning

Deviates from the DNV method

Some companies calculate the WLL according to in-house rules. To cater to that, the DAVE rigging module offers an alternative way to determine the working load limit of slings and grommets.

The formulation is as follows:

\(F_{allowed}\) = \(g \cdot\) MBL/ (\(\gamma_r \cdot z_p\)) [kN]

where:

  • MBL = minimum breaking load [t]

  • \(g\) = gravitational constant [kN/t] \(\approx 9.81\)

  • \(\gamma_r\) = reduction factor

  • \(z_p\) = coefficient of utilization

Values provided for lifting, consequence, material and wear_and_application factors are not used in this calculation.

Just like in the DNVGL analysis the reduction factor is the maximum of:

  • bending factor

  • termination factor

Note that the definition of the termination factor (which is user-provided) may be different.

Coefficient of utilization#

The coefficient of utilization is defined as a function of the rope diameter of the item. This function is provided by the user in the form of an interpolation table. The function stays constant outside the defined range.

Example#

The typical formulation \(z_p = 4 - 0.018d\) with \(2.25 \le z_p \le 3.33\) is equivalent to the following table:

diameter [mm]

coefficient of utilization

<37

3.33

37

3.33

97

2.25

>97

2.25

which can be entered as:

\(z_p\) = 3.33, 2.25

d = 37, 97

The formulation from the Eurocode or BS (section 5.3.2) can be entered similarly.

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