On my entry at 13:30, we must first investigate what differentiates the Mathcad model from the SAP2000 model.
In the Mathcad worksheet model we assume as a simplification inextensible rods and cables that out of the geometry, and then we find that for every geometry that takes the shape of the solution in which one triangle is rotated 30 deg from the one that keeps its position we can have infinite sets of grouped tensile and compressive stresses in the members that satisfy equilibrium as long as they meet some precise proportions that depend on the dimensions of the base and length of the strut (or overall height of the outfit, if you want).
SAP2000 on the contrary is an advanced analysis program, and, partly at least, mechanical solver, and simply, as long you go within the basic understandings of the program and make a good model it is accepted by most of its users provides a reliable answer to equilibrium and other useful structural stuff. From this description and knowing that it admits property modifiers, we must expect that SAP2000 will (or at least can, with a proper model) resolve for solutions that take the final shape of the kind found through Mathcad.
But to produce such model we first than anything need make the axial rigidity of the members very big. Imagine we have rigidity enough to mimick the infinite axial rigidity of the Mathcad model to tolerance, then we can for go the obvious solution when producing the model of just using one of the geometries of the found solution, then if I set some force on, say, the retentors, wil relax it to take the values proportional that we may established through mathcad for the same geometry and that would be all. I suspect the overall high stiffness may do worrying things numerically but this is just a suspicion and we may defer it to further proof. Even so, then you may believe that the forces found are the "solution" to the structural case (within the named parameters), yet you may eventually by inspection discover what we did through the Mathcad study, that other forces, just proportional, also would be, and even if you have found "THE" one that correspond to its derivation from the unrelaxed force applied to the retentors, you might be forfeiting the other proportional answers that may also be of your interest.
This is no surprise, since we all solve everyday for just a set of hypotheses and forfeit every other understandings of the problem and secondary ways of structural response that would burden our structural design tasks.
We maybe need not to adjust ourselves just to the tight geometry of the answer, and maybe with SAP2000 we can set the case of the cables at the triangles hanging somewhat loose, whereas the retentors (to be loaded) and struts have the straight geometry. We should expect that as long the slackened cables at the triangles have the final length, and axial rigidity brings the solution of a final shape of the kind found in Mathcad, it also will find the solution, something that we also can bring to test.
Yet SAP2000 potentially at least has shown us that it needs not to abide within the hypothesis of perfect rigidity and found shapes of the Mathcad study, since it can derive solutions according to the laws of structural analysis not within these limits.
Respect the kind of error you refer to I found it when I tried to convert v15 to v14 yet since I am not SAP2000 expert, but novice, I have not found solution if it exists and maybe someone may help us in the task whilst we learn how.
Whilst you get the model working, I didn't manage to get any response till I used for all elements other than the struts the cable element; i.e., the tendon element -in whatever definition I put where the retentors are- failed to produce meaningful response, maybe because they are thought to be applied on some beam or struts or whatever other reason that for now escapes me. I inmovilized the vertices of the upper triangle in an horizontal plane (whilst allowing it to vary in position in such plane and forfeiting the lack of enough constraints that might bring the outfit in movement and so, analysis error), i.e., one node inmovilized XYZ, other YZ, and other just Z.
Everything rendered weightless one way or another.
Then I just applied a descent of temperature to the retentors, and then the solution adopted the kind of predominantly rotational displacement that we see to be consistent with the nature of the outfit. You can dump all this in just one hypotheses, even dead load case, since the members have no weight.
Respect sharing the Mathcad worksheet, I have already made in my post of 6 Aug 11 13:30. It is the wholly operative file with extension .mcd
The file is for Mathcad 2000, but, since the mathematics are simple, any of the later Mathcad 11, 12, 13, 14 or 15 should open it without any problem in the automatical conversion.
