three mass modeling of an elevated water tank

Hello everyone

I am working on time history analysis of three mass modeling of elevated water tank. I have already calculated the parameters of spring mass model and done modeling in Staad. I have some doubts and queries which I am posting. If someone can edit my Staad file then it would be very helpful. Please help me in this.

Actually I want to know what I have done is correct or not so I am telling you what I have done along with my doubts.

1. I have lumped the water mass as impulsive mass, convective mass and rigid mass and applied them at their respective heights. I have also lumped the mass of rigid diaphragm and applied it at the center of the top beam.
2. Since I have lumped the masses so I have defined the density of all the members as 0 but I need to provide the section sizes else it will show the error. Since I was not able to understand how to apply spring in Staad so I have calculated the equivalent section from the stiffness value.

For lateral stiffness of column I have used K (staging) = 12EI/L^3

For stiffness of impulsive and convective masses I have used K = AE/L (Is this correct?)

3 ERRORS:

1. Zero on diagonal in Jacobi iteration (How do I fix this?)
2. A problem has been encountered for fixing the modes ( For this when I am taking higher dimension to model impulsive stiffness, these errors no longer disappear but for impulsive mass my dimensions are small. I have also tried to define lower value of E so that I can get high value of section but this error still pops up}
3. Errors in solver

Now I am getting 9 warnings

1. Zero stiffness error: This is occurring at the node at which I have defined rigid mass of water. I made this node as master node. Will there be any effect in the analysis results due to this error? How can I fix this?
2. When I am checking for multiple structures I am getting 5 structures. How do I merge it in to a single structure ?Though I am getting the results but I am not sure if all the loads are being considered or something is ignored
3. Master/Slave equations are not properly considered in the time steady solution. How to fix it?

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