Problem:

Why saddle support reactions are 0.00 in an AutoPIPE Vessel output report?

Example:

For saddle calculation Case 3 - Operation Int.Max.P. (Normal Wind) (1 D + 0.6W)  .saddle 1 is fix saddle , saddle 2 is a sliding saddle . the Horizontal Reactions (Longitudinal) force for saddle 2 shall be zero, because the fix saddle take the force , why saddle 2 have the same reaction force bur negative with saddle 1 by program calculation, Please explain the reasons .

Solution:

In short, AutoPIPE Vessel considers that the bolted base plate prevents only displacements but not rotations, it is an articulation. So, the longitudinal moment at the base is zero.

See Youtube video link for detailed saddled calculation explanation:

https://www.youtube.com/watch?v=hZ_5G6qdzMU

You will have a better understanding on how saddle reactions are calculated, saddle is sliding does not mean it has 0 longitudinal reaction, the reaction will be 0 only if saddle mount is frictionless which is rarely the case, and also in this case there is a friction (0.3) so there will be reaction.

Also if one saddle has reaction there will be a counter reaction with opposite sign for the other saddle to maintain static equilibrium. The video will explain everything,  time 24.08 onwards discusses case with friction.

Just an additional comment, when the saddle is sliding, the force is zero, but before sliding, the opposite force is applied on the saddle, the sliding saddle (and the shell) must be designed to sustain this transitory force which is a function of the friction factor.

See Also

AutoPIPE Vessel

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