SAP2000 Vertical Modal Period 1

[Mgut_j]

Hi, I am doing some studies regarding the vertical component of a response spectrum and am wondering, if the SAP2000 program takes in account the vertical component (Z axis) in the calculation of the Period shown in the Modal Analysis display.

 

[driftLimiter]

Yes you can solve for mode shapes and frequencies in the vertical direction. Although for most structures this is a very stiff set of displacement modes so you may need to solve many many load shapes to get sufficient modal mass participation in this direciton.

 

[Mgut_j]

It required almost 50 cases to reach 0.9 modal mass participation; but if I would be solving in the vertical direction, would the Period shown in the modal analysis take in account its vertical component in the calculations?

 

[driftLimiter]

So I'm not exactly clear on your question but here are my thoughts.

This output indicates you have solved for 3 directions of mode shapes. You have identified that over 90% modal mass participation has been achieved in the Z direction.

Understand that each mode shape SAP solved for has some mass participation in each direction. For most uncoupled modes, you will have one direction with a significant mass participation and a very small (near zero) mass participation factor in the other two directions. If your structure has more coupled mode shapes than you will see significant mass participation factors in more than one direction.

If your trying to identify the predominate modes in the vertical direction....

You would do well to go through the UX column and find column indicating the modal mass participation for each mode shape. The mode shapes with the highest magnitude of mass participation in the vertical direction would be the predominate modes in that direction.