Hi,
I am sending again a question that I posted in another thread
communities.bentley.com/.../415756
Because I think I didn't described the issue well enough
I modeled a steel structure supported by a PLATE MAT foundation using Option Y and the subgrade module.
I made dynamic analysis (modal analysis), and I found a contradiction when looking at Base Pressure results, specifically
some nodes show Negative base pressure values and the corresponding node displacements (Y) show negative values,
in the same way the Node Reactions (Y) show negative values, so I do not understand why this is happening.
Notice that I am no using Y COMPRESSION option but just Y for the Mat Plate
I am uploading the .std file using the secure uploading option that this site offers, however if there is another
fast way to get help do not hesitate to give me advice.
Many thanks in advance for any help on this becuase I urgently need to find a solution for this,
Best regards,
I answered this question in my post
Talking specifically of your model, the load combination case 106 includes couple of response spectrum load cases 1 and 2. For cases like these, the displacements ( and all other response quantities ) are devoid of signs because of the modal combination methods used. So when you are combining these with responses from other static cases, depending on the load combination factors and their signs that are used for the various loads in that combination, the eventual response could be positive or negative. A negative value for such a combination does not mean that the node is displacing in the negative Y direction. In fact, you cannot conclude about the direction of movement of the node when you are doing a response spectrum. It could go either way. The basic idea of doing a response spectrum analysis is to get the maximum response and then do a positive and a negative combination with the gravity cases, so that you are covered for the worst effect. Also stress plots do not mean anything for a response spectrum load case as the responses that you are getting at adjacent nodes in the mat are not at the same instant of time but these are individual maximums.
Answer Verified By: desideratus