Lifting Analysis

[engpes]

I am conducting a lift analysis using a linear FEA software package. The lift is a flat skid that at 4 points with a 60 deg (from horrizontal) lift angle.

The package will only calculate the stresses, deflections, etc. What I am trying to analyze is the buckling of the main skid beams being compressed axially from horrizontal force components of the slings.

Is this to be treated as a column, pineed at both ends? Can I use the same critical length in the caluclation? Do the transverse members come into play for the unsupported length?

Thanks in advance.

 

[jte]

Ummm... even a linear FEA package shouls have a linear (Eigenvalue) buckling evaluation capability.

Yes, you could treat the rails as columns and run some hand calc's. Presumably the weak axis is inthe horizontal plane - this is where the transverse members may have an influence. However, if you consider that both rails have the same loading, and may both buckle in the same direction, would you really take credit for the support provided by the transverse members?

Run the numbers without consideration for the transverse members... then start to think about what your design margin should be. If your Pcritical is greater than 10 times the actual load, its pretty straightforward. If its 1.4, that's a much harder situation to evaluate.

jt

 

[Ron]

I would treat as column with lateral load. Pinned condition, both ends.

 

[Ron]

Ps...assuming pinned condition can be used in this application.

 

[EngineerTex]

engpes,

I noticed that you had previously asked a question about fork pockets on DNV 2.7-1 skids. Assuming that your current question is also about 2.7-1 skids, remember that one of the required tests for this skid will be to remove two diagonal shackles and pull the remaining two shackles to 1.5X the MGW of the skid. In this case, transverse members will come into play, and you will definitely not be treating the skid as having pinned beams. The corners will take some (potentially large) bending loads. Your transverse and vertical members will contribute significantly to carrying the load of the 2-part pull test. The member receives both bending and compression.

Engineering is not the science behind building. It is the science behind not building.

 

[MJCronin]

eng..

How about the required use of a "spreader bar" during the lift ?

As i see it , column loadings and buckling problems within the skid structure will go away ??? Is that correct ?

I am assuming that there will only be a single lift to place the skid.

If you can control the lift enough to ensure a lift angle of no less than 60 degrees, (you do realize that 45 is more common....right ?) then you can ensure spreaders beams are used.

The cost of the spreader beams is probably less the the FEA..

My opinion only

-MJC

 

[rb1957]

is this really as simple as it sounds ? ... a skid being lifted at the 4 corners by slings inclined 60 deg ??

how much compression in the skid ? come on, this is 1st year vectors, no ?