檩条设计问题

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Regarding the Zero-stiffness problem, Basically, at any node of the structure you can have six degrees of freedom viz. Translation in X direction, Translation in Y direction, Translation in Z direction, Rotation about X axis, Rotation about Y axis, Rotation about Z axis and they are named as degrees of freedom 1,2,3,4,5,6 respectively. Since you have specified those members to be TRUSS members, that type of specification leads to all the members having only axial degree of freedom and having no capacity in shear, bending and torsion. If you look into the warnings, then you will see that the instability occurs in FZ, MY and MZ directions. Obviously, those members do not have the capacity to resist the translation in Z direction and the rotation about Y and Z axis (i.e. third, fifth & sixth degree of freedom) i.e. the specification leads those degrees of freedom to be zero. When the program runs the analysis, it calculates the displacement vector through matrix inversion (shown as triangular factorization during Run Analysis) and if it encounters zero value of matrix, it becomes infinite during matrix inversion. So, the zero stiffness in the corresponding direction comes up. I would request you to have a look at the following links for details on this warning on Zero stiffness. These links would lead you the specific FAQ in our web page which is a pop-up box. So, please ensure to disable your pop-up blocker in order to view the contents of the above links, or press "Ctrl" when you click on the link.