When running a static incremental analysis, the analysis stops automatically with a stiffness ratio of 0.0% even though no hinges have yielded. What is the reason?
Although it appears that no hinges have yielded, the analysis actually stops because yielding has occurred, resulting in a very low stiffness ratio. Here is a more detailed explanation
[Image-1] Automatic Termination
The message shown above indicates that the analysis was automatically terminated, reaching step 54, where the stiffness ratio became 0.0%. However, if you examine the results, you will notice that only steps up to 53 are displayed, as shown below
[Image-2] Deformed Shape
In midas Gen's Pushover analysis, reaching a stiffness ratio of 0.0% in a step often leads to divergence, resulting in unrealistic results at the divergent step. Therefore, when the stiffness ratio becomes 0.0% and the analysis is automatically terminated, the results only display steps up to the current step minus one. In reality, although the analysis was performed up to step 54, the results show data up to step 53, indicating that yielding occurred at step 54, causing the stiffness ratio to become 0.0%.
To further clarify this explanation, consider the following:
In a load increment analysis, the current stiffness ratio represents the stiffness as a percentage. In the initial state, it is 100%, and in the ultimate state where stiffness is completely lost, it becomes 0.0%. When the stiffness ratio reaches 0.0%, it signifies a limit state where the analysis cannot proceed further in the load increment analysis. Therefore, since reviewing the analysis with load increment analysis becomes difficult, a displacement increment analysis is performed for a more thorough examination. When performing the analysis using displacement increments, the following results are obtained.
[Image-3] Displacement Increment Analysis Results
[Image-4] Existing Model Results (Load Increment, Automatic Termination)
[Image-5] Displacement Increment Analysis (Hinge Yielding in the Reduced Internal Force)
As can be seen from the results of the displacement increment analysis above, it is evident that in the existing model, the external force (internal force) suddenly drops at the point where the analysis was automatically terminated in the load increment analysis.
Due to the reasons mentioned above, it can be concluded that the analysis was automatically terminated during the load increment analysis.