Dynamic analysis troubleshooting

 

This chapter presents a list of basic checks to be carried out by the user when using dynamic analysis in SCIA Engineer. Part of it applies to any dynamic analysis, some is specific for seismic analysis. Additionally, some hints are provided for troubleshooting, in case some of the validation criteria are not fulfilled. Finally, a set of frequently asked questions is presented, along with explanations and solutions.

How to validate a model for dynamic & seismic analysis

• Validation of modal analysis
  • Calculation protocol
    • Sum of masses
    • Frequencies / Periods
    • Relative modal masses (modal mass ratio)
  • Visual evaluation of mode shapes
  • Specifics for seismic analysis
    • Total modal mass ratio
    • Immobilized masses
    • Local modes
  • Specifics when using reduced system analysis
• Validation of seismic analysis
  • Calculation protocol
  • Signature of results

Seismic Analysis' Do's and Don't's

• Modelization for seismic analysis - Good practices
• When should IRS analysis be used (or not)?
• Seismic load case settings
• Combinations containing seismic load cases
• Seismic modal superposition and resultants

How to...

• Perform 2^nd order sensitivity check acc. EC-EN 1998 4.4.2.2
• Include 2^nd order effects in dynamic analysis (P-delta)

Troubleshooting - common issues

• Issue: IRS: Non-associated R-node detected
• Issue: IRS: Too many eigen values requested
• Issue: the cumulated modal mass ratio is less than 90%
• Issue: incorrect sum of masses
• Issue: total base shear is not the sum of modal values
• Issue: masses are not generated from plane load generator
• Issue: Z-coordinates in results do not match with storey levels
• Issue: resultant of reactions does not match calculation protocol
• Issue: Insufficient number of non-zero masses
• Issue: mesh settings affect mode shapes - bi-symmetrical structures
• Issue: incorrect interpolated spectral acceleration
• Issue: unexplained changes of sign in seismic results
• "Issue: alternating signs in results from a linear combination"

This section is work in progress. New articles will be added here on a regular basis.
Please stay tuned...