Spectrum Load Case, Base pressure

Hi,

I modeled a PLATE MAT  foundation using plates, Option Y, and the subgrade module.

I am using various load cases including earthquake (Spectrum Load Case).

However I found a contradiction when looking at Base Pressure results, specifically

some nodes show Negative base pressure values, but when I look at the corresponding node displacements (Y) they 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 would like to know if there are some restrictions or specific issues when using Spectrum Load case along with

Mat Plate option Y and reaction modulus.

Also, any explantion of the difference between  Node Reaction (direction Y) and Base Pressure will be much appreciated.

Many thanks for any help. I am stuck on this naive issue.

Best regards,

Parents Reply
  • Owing to the very nature of response spectrum analysis, the response quantities like displacements, support reactions, base pressure etc. are all positive. Since the signs are lost, it is not possible to determine whether a node is moving up or down by looking at the results. So when such results are combined with results from other load cases like gravity loads the signs do not really mean anything.  



    Answer Verified By: desideratus 

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