Applies To
Product(s):	AutoPIPE
Version(s):	ALL;
Area:	Analysis
Date Logged & Current Version	June,2025 24.00.02.243

Problem:

How does AutoPIPE compute the missing mass response when the modal analysis option is selected in missing mass combination method? 

 

Solution:

AutoPIPE calculates the missing mass at the cutoff frequency specified in the Modal tab of the Dynamic Analysis dialog. By setting the missing mass combination dropdown to 'Modal', AutoPIPE will apply missing mass to the flexible responses using the same method that is selected in the Modal Combination dropdown. For example, by selecting 'Modal' in the M. Mass Combination dropdown, and 'Ten Percent' in the Modal Combination dropdown, provided the Missing Mass option is checked, both flexible and rigid responses will be modally combined using the ten percent method. The example below for instance uses SRSS to combine missing mass in both analysis sets, such that both results should be exactly the same. 

As accurately stated in the help documentation:  
The rigid response (missing mass response) is treated as any other mode and combined with flexible modes according to Modal combination option chosen.

 

Question:

How is the Missing Mass Response (Rigid Response) combined with the Modal Response (Flexible Response) when the Modal and Following options are selected?

 

Answer:

When the Modal method is selected as the missing mass combination approach, the missing mass (rigid) response is integrated with the modal (flexible) response using one of the following modal combination techniques: 

1. 1. 1. SRSS
      2. Grouping
      3. Ten Percent
      4. Double Sum
      5. Signed Double sum 
      6. Signed CQC
      7. Absolute CQC

See Also

Dynamic "Response Spectrum" Analysis

Bentley AutoPIPE