Hi,

I have just started my career in Pipe Stress. I have some basic questions. I shall be obliged, if some form member(s) kindly throw some light on them.

a) If we are providing a support stiffness, in place of the default rigid stiffness, the restraint load should be , in the direction of the restraint, equal to stiffness times displacement.From Caesar II output, when I am checking the restraint load, I am finding that it does not match the product of the stiffness and the displacement at that point. For example, I have used a Z restraint at a location with the stiffness value of 1200lb/in. The displacement at the point in Z direction is 0.01in.The restraint Z load should be 0.01* 1200=12Ib.This is not the output load. Kindly explain why.


2)I think Caesar is a Finite element Analysis program using standard Beam Elements.My question is, when we generate the stiffness matrix, from element stiffness matrix to global stiffness matrix, we add the stiffness elements at interconnecting node points.Now, stiffness is added this way only when the springs are in parallel. Why in Piping Ystems, the springs should be in parallel always? For example, I think, the stiffnesses of elements on one side of a bend will all be in series and the stiffnesses of all the elements after the bend will again be in series, however these two set of stiffnesses will be in parallel. In Pipe stress programes, how the springs in series and parallel are assembled to mathe matically model the real physical system?


Regards

Baburao

a) Something else is going on at the restraint - for example friction.

b) In series or in parallel has nothing to do with it (because the program doesn't understand these concepts). The stiffnesses are added based on they system degrees of freedom.

Baburao,

For your second question:

Springs will be in series or parallel will depend upon whether they have one/more than one point of fixity. The individual elements at the points of intersection ( nodes) are not having the same point of fixity, so they are in parallel. The program which does a matrix addition to compute the global stiffness matrix from the elemental one,does not follow the series/parallel concept,but the physical aspect of the problem is automatically taken care of by the rule of matrix addition.

Hope this answers your question.

Regards

Anindya Bhattacharya