ProtaStructure : How to check singularity or large deformation warnings during Building Analysis

How to check singularity or large deformation warnings during Building Analysis

It’s very important to know how to check the validity of the model especially if there are errors or warning messages appearing during building analysis.  



The warning are also record in the "Analysis Model Echo" report accessible by going to "Drawings & Reports" ribbon > "Report" dropdown menu. 

Matrix singularity warning means the joint stated is unstable or mechanism has developed which may lead to large deformation (i.e. deformation larger than 1m). Hence these two warnings are likely to be related. 

Here are some reasons of instability :
  1. Floating members, example : 
  1. beam just hanging in the air without proper support
  2. hanging transfer columns without a proper transfer beam supporting it
  1. Too many hinges applied to members, example : 
    1. Columns that are hinged at both ends with no incoming beams (column will collapse when lateral load is considered)
    2. Fixed end of cantilever beam hinged (will collapse)
    3. Free end cantilever beam hinged (not required)
Alert
We do not recommend hinging concrete column as its fixity is important for lateral load transfer and stability of the structure generally, even under gravity loading. Further, column is constructed monolithically with other concrete members and its actual behavior is unlikely to be a true hinge.  As such, exercise extreme care when deciding to hinge a concrete column at any end (never both ends at the same time). 
The general procedure to check for these instabilities are outline below :  
  1. If you receive singularity or large deformation warning during building analysis, print it out (click Print).   
  2. Allow the analysis to run to completion
  3. Click on Analytical Model icon in "Analysis" top ribbon Post Analysis to check the actual analytical model and the results graphically. 
  4. Use the “Find” icon to find the node/joint  (example shown below)  

  1. You can use the “Filter” command to filter to the floor concern to have a less cluttered view
  2. You can also switch on “Label” = member label in the Elements Tab to identify the actual member label

  1. It is very meaningful to look at the deflection of the model by clicking “Displacement” in the Results tab
  1. If there large deformation, the default scale may not show clearly the actual deflection
  2. Click Increase or Reduce Scale to improve visualization
  3. Alternatively, in the View Settings, expand the “Displacement” folder and manually override the scale by unchecking “Auto Scale” and then manually key in the “Scale”
  1. To show the actual displaced value, click “R” = Resultant or the components “x”, “y” or “z”
  2. Click Animation to animate the deflection to better visualise how the structure deforms.
  3. If the displacement is too big or unexpected, then it’s not meaningful to look at the forces as the model is unstable or wrongly set up. 
  4. After verify the displacement, then it’s meaningful to inspect the forces by activating “Diagrams” in the Results tab.  

After identifying the cause of instability or large deformation, go back model to rectify the members as required.
Idea
Users can refer to the tutorial video for detailed guidance to deal with singularity or large deformation warnings : How to Detect Modeling Errors with Sparse Solver? | ProtaStructure 

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