Selecting the Mode Shapes

Go to the Selection of Modes tab next. It controls which modes are taken into account for the spectral analysis.

Modes Shapes for Spectral Analysis

In the table, all 33 modes that were calculated for the modal analysis load case (LC5) are listed (see the Factors for Effective Modal Masses image). They are all activated by default. At the end of the table, you can see the overall sums of the ratios between M_eff,i and ∑ M: 90.6% for f_meX and 93.7% for f_meY.

Use the button to deactivate all modes less than 1% and, thus, deselecting minor relevant modes.

Deselecting Modes According to Criterion

As a result, you will notice that the limit of 1% ('0.01' in the box to the right of the button) produces ratios for f_meX falling below the 90% rule. The limit must be adjusted: Enter 0.001 to reduce the limit manually.

Adjusting Criterion to Fulfil Requirement

The ratio between M_eff,i and ∑ M now is 0.905 for f_meX and 0.936 for f_meY. 26 modes are sufficient for the analysis instead of 33.