| Applies To | |||
| Product(s): | STAAD.Pro | ||
| Version(s): | All | ||
| Environment: | N/A | ||
| Area: | Analysis | ||
| Subarea: | Dynamic Analysis | ||
| Original Author: | Bentley Technical Support Group | ||
- I have modeled a floor grid in STAADPRO. How do I calculate the natural frequency of the floor?
- The mass participation factors table only gives results for the first six modes (even if there are more than six modes). Is it possible to get it to display more than six factors?
- How can I get the Mode Shapes to be displayed on the screen? Also, how can I export the mode shape drawings to MS Word?
- How do I use the CUT OFF MODE command?
1. I have modeled a floor grid in STAADPRO. How do I calculate the natural frequency of the floor?
The best method to use to obtain frequencies of a model is the eigenvalue method. An elaborate explanation on using this method is available at the following link :
- Issue No SP-2906 (download link for SP2906.zip)
An approximate but quicker method is the Rayleigh method. The following 2 links provide details of that method.
2. The mass participation factors table only gives results for the first six modes (even if there are more than six modes). Is it possible to get it to display more than six factors?
Staad attempts to solve for the number of modes specified in the CUT OFF MODES command or 6 if the command is omitted. Since STAAD has a reasonable estimate of several additional frequencies, those accurate frequencies beyond the cut off are printed after a message (which indicates that they will not be used).
Another factor is the CUT OFF FREQUENCY command which defaults to 108 Hz. If the 7th frequency is greater than the CUT OFF FREQUENCY, then it will not be used.
Only the frequencies meeting both tests will have the Participation factors printed and used in subsequent analyses.
3. How can I get the Mode Shapes to be displayed on the screen? Also, how can I export the mode shape drawings to MS Word?
To get mode shapes to appear on the screen, first successfully analyze the structure by going to Analyze | Run Analysis and then pressing the "Run Analysis" button.
Once you have done that go to View | Structure Diagrams from the top menu and go to the "Loads and Results" tab. Select the appropriate Mode Shape from the "Mode Shape" drop down box. Press the "OK" button.
To get the modes shape results into Microsoft Word, go to File | Report Setup and then go to the "Modes" page. Select the mode you want to include in your report. To export this to MS Word go to File | Export Report | MS Word. Name the report when prompted in the "Save As" dialog box, press "OK" and then select the appropriate template.
4. How do I use the CUT OFF MODE command?
Please ensure that the CUT OFF MODE command is before the first load case and do not enter it after the PERFORM ANALYSIS command. For example,
CUT OFF Mode 7
LOAD 1 MODAL RESPONSE IN X
SELFWEIGHT X 1
*SELFWEIGHT Y 1
*SELFWEIGHT Z 1
MODAL CALCULATION REQUESTED
PERFORM ANALYSIS
*CUT OFF Mode 7
FINISH
In this example, without a CUT OFF MODE command before the PERFORM ANALYSIS, STAAD defaults to 6 modes. At the end STAAD is attempting to output the number of modes listed on the last CUT OFF MODE command.
See Also
Structural Product TechNotes And FAQs
External Links
Bentley Technical Support KnowledgeBase
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