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Re: Lift Lug

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Lift lug design for a skid is quite different. You will be using
shackles to connect the sling to the skid. The dimensions of different
elements would be governed by the size of the proposed shackle.
Normally, the following points will govern design of lift lugs in such a
case:

1. Hole dia = 1/8(preferred) to 1/4(for large lift weights) in. greater
than pin dia (of the shackle). This facilitates insertion and removel of
pin. Also accounts for fabrication tolerance. There will be high stress
concentration at the point of contact between pin and plate, and higher
gap is not advised.

2. The edge distance from centre of hole should be at least 1.5 times
pin dia. You may be able to get a larger distance based on the size of
shackle and the size of rope to be accommodated. The quoted AISC
limitation does not apply. (There would be no eccentricity effects since
the shackle would encompass the eye plate on both sides symmetrically
(hope the sketch below makes sense!)

                                              shackle
                                        | ----------|
             ooooooooooooo |o        ========== Eye plate
             rope                    | ----------|

3. There would be a gap between the insides of the shackle and the eye
plate. This should be filled with washer plates, or, cheek plates. These
plates should be placed symmetric with respect to the eye plate, and
welded all around. Total thickness = inside width - (1/8 to 1/4 in).
This minimizes bending of the pin and increases the shear area. Normally
the holes should be bored after the cheek plates are welded, so as to
get a smooth hole.

                                                ======  cheek plate
                                            =============  eye plate
                                                ======  cheek plate

4.You can use the full available net section for tension check.

This is a common practice in offshore industry for lift lugs of even 500
tonne working load. More than one set of cheek plates can be used, but
some reviwers, particularly in Europe, may not accept that.

Normally, if you dimension your lift lugs based on shackle dimensions as
given above, you will not get a design deficiency (A36 or superior grade
steel, Crosby or equivalent shackle). We don't design a lifting lug
without knowing /determining the shackle, and always note the shackle
size and safe working load of the lifting eye in the drawing.

Hope this helps. If your situation is different, please elaborate.

Dr. M. Hariharan
Ocean Engineering Department
Engineers India Limited
New Delhi, India.

Padmanabhan Rajendran wrote:

> One of the criteria for lift lug design is to check
> the tension on the net section passing through the
> pinhole. AISC (ASD) Section D3.2 states: "For
> calculation purposes, the distance from the edge of
> the pinhole to the edge of the plate...., shall not be
> assumed to be more than 0.8 times the diameter of the
> pinhole". (Please note that in the original
> publication a factor of 1.25 was printed which was
> subsequently corrected to be 0.8 per Errata issued by
> AISC). Also, the maximum width from the edge of the
> pinhole is limited to 4 times the plate thickness.
>
> Therefore, in order to satisfy this criterion (tension
> capacity), one can increase the pinhole diameter or
> increase the plate thickness. In a design I completed
> recently, I chose to increase the hole diameter: The
> pin diameter was 2.5" and the hole diameter came out
> to be 5". The design, while technically correct,
> seemed odd because of a large hole to accommadate a
> smaller pin. Am I missing something?
>
> Rajendran
>
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