Instability Joint

Question

1. Staad_19-01-2023 .std 
 I am not sure what is causing this instability and how to fix this issue. Any advice, suggestions would be appreciated! I have attached the staad model to view. Thank you. 
 1. Instability at joint 447 
 2. ***WARNING - DIAGONAL DECAY AT JOINt 147 
 3. **WARNING-Tension/Compression did not converge after 10 iterations, Case= 4

Abhisek M · Accepted Answer

Hello HK, 
 I have 2 suggestions for your file. 
 1. As you have used tension compression spring in the model you should use Repeat Load instead of Load Combination. 
 How to convert a LOAD COMBINATION to a REPEAT LOAD 
 2. In the model you have used compression only spring in Y direction. This suggests if there is any tension in the support, the supports will be inactive. In your model due to lateral loads and vertical upward loads, a huge amout of tension is generated and the downward gravity load is not enough to suppress it resulting net tensile force in the support. As a result the whole structure is become unstable in certain load cases and combinations. You may either use NONE instead of compression only option and the file should run okay. 
 
 Or you should review the loads and try to match the boundary condition accordingly.

Abhisek M · Answer

Please refer below wiki for detailed explanation. 
 Difference Between ELASTIC MAT and PLATE MAT