When starting the elastic analysis of a model with a dynamic load or when starting a model analysis , the error below appears:
The error can be caused by a lack of stiffness/too many degrees of freedom. The lack of stiffness can be in the cross-sections, the material(s), the supports or the internal boundary conditions (hinges).
- Verify the stiffness properties of the elements: check if the sections and material properties are well defined. If an element has no stiffness, it shouldn’t be modelled in Diamonds.
- If you want to run an modal analysis on a 2D structure, make sure the translation and rotation in the third direction are prevented.
- Regarding hinges: if N bars meet in a node (neglect tie rods), and you want no moment to be transferred in that node, you should apply a hinge to N-1 bars. Not to N bars. If you apply a hinge to N bar, you’re making a mechanisme (throught the eyes of Diamonds).
- The amount of eigen modes/ eigen frequencies that can be found equals the nomber od degrees of freedom in the structure. If you make a system with 8 degrees of freedom, you can calculate 8 eigen frequencies. If you’d ask 10, Diamonds will give an error.
So what you could do, is ask less eigen frequencies. The minimum is 2.
This error can also be caused by a malfunction in the load groups.
- Remove all load groups besides Self-weight and Seismic.
- Regenerate the combinations and calculate the structure using only those two load groups.
- If this calculates, define the load groups again one by one. Regenerate the combinations and calculate the structure between each addition.
- If a model contains 2 (or more) independant structures, make a Diamonds-file for each structure.
2 structures are independent if there is no connection between them. For example: the column and the porch below are not conntect to each other, thus independant. It is better to make one Diamonds-file for each structure if you want to do a modal analysis for them.
- In the analysis settings of the modal analysis, try with an concentrated (lumped) massmatrix.
- Diamonds doesn’t accept $\varphi$ equal to zero for the self-weight. If you don’t want the self-weight to contribute to the mass for the modal analysis, set $\varphi$ to 1 and the density of materials to 0.001kg/m³. That’s the lowest value for the density that Diamonds will accept.