Modal analysis rel.masses and Lin rel.

[Stilie87]

Hi!

Question 1: I am running modal analysis in a multi-story building to do seismic analysis.

However it seems impossible to get the relative masses over 90 percent!. What is the reason for this? It seems OK in Y-direction, but not X.

Question 2: Is it preferable to add linear releases to walls and slab connections? And is this the correct way to approach it?

[Rafal.Gaweda]

1. Send us model
2. Interesting releases ffff on bottom of walls.

[Stilie87]

1. Model link: http://www.filedropper.com/byggbeptest

2. What do you mean? Is this the Wrong approach? The shear walls are pinned in the bottom.

[Rafal.Gaweda]

2. What do you mean? Is this the Wrong approach? The shear walls are pinned in the bottom.

I do not know what you mean by pinned but ffff means all dofs are free (released) => bottom of the wall not connected to slab

[t.sautierr]

Rafal is telling you that your walls are not connected each other, neither with the slab.

there not rease for such releases and it will create a mechanism. 

the only interessting releases :

Foundation level : possibly rotation is free if you design your foundation this way

Edge of slabs : rotation is free if you decide, Rx/Ry free if you have got an expansion joint with a slidding support (watch that there is always some friction between slab and support even if it is considered fully released)

[Rafal.Gaweda · Accepted solution]

Question 1: I am running modal analysis in a multi-story building to do seismic analysis.

However it seems impossible to get the relative masses over 90 percent!. What is the reason for this? It seems OK in Y-direction, but not X.

On the file you sent you have to run at least 45 modes.