modal participating mass ratio have small value

[AzzA16]

Hello everyone, I need your opinion on this case.

For the modal mass participating ratio, is it okay to have UY in mode 2 to achieve a small value? In the animation, the structural movement remains translational but becomes stiffer

 

[HTURKAK]

For the modal mass participating ratio, is it okay to have UY in mode 2 to achieve a small value?

Check for vertical irregularity. Pls look The second and third columns of Table 12.3-2.

 

[JoshPlumSE]

I wouldn't call 30% a small value. I think having the UY behavior split between modes two and 4 is an excellent reason why you would WANT to use the response spectrum method. Let's say you have moment frames at the top story and shear walls below that, this could easily result in the behavior you're seeing.

That being said, I would recommend reviewing those two modes (visually) and seeing if they make sense to you. And, that the split modes are not the result of some sort of modeling problem.