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[GEN/Analysis]Abnormal Reasons and Eigenvalues in P-Delta Analysis

Question

When performing structural analysis by specifying the P-Delta option, the following message is displayed. How should this be resolved?

[Image] Warning Message

Answer

When performing structural analysis by specifying the P-Delta option, the P-Delta analysis of the structure is conducted by defining the load conditions to be considered in the formation of the geometric stiffness matrix using Analysis > P-Delta Analysis Control before running the analysis.

In order to manifest the P-Delta effect, the geometric stiffness of the members diminishes. The example structure has a span of 15m, and the beam is using an overly small section of 350X350X12X19. If excessive deformation of the structure occurs, the message 'DISPLAYMENT DZ AT NODE NO. 2 IS ABNORMAL' might appear. It is advised to modify the member's size to a section feasible for design.

[Image] Analysis Model

               

 [Image] 1st Floor Frame(Beam Section: 350x350x12x19)     

[Image] 1st Floor Frame(Changed Beam Section: 700x300x12x19)

 

Question

When considering the P-Delta effect in GEN, is it also reflected in eigenvalue analysis?

Answer

When considering the P-Delta effect in GEN, it is indeed taken into account in the eigenvalue analysis.

If the overall stiffness of the building decreases due to the P-Delta effect, the natural periods become longer. Conversely, if the overall stiffness of the building increases due to the P-Delta effect, the natural periods become shorter.

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