Seismic Loading and Flexible Diaphragms

[ChiEngr]

Hello,

I am wondering about the following condition. Say you have a single story building with a flexible roof diaphragm. I understand that the seismic forces will be transferred to the surround lateral force resisting elements in accordance with tributary area. However, what if the center of mass does not align with the centroid of the roof structure. Would you then analyze the diaphragm as a simple beam spanning between LFRS elements with a resultant "point load" not concentrated at midspan?

 

[KootK]

Yup, exactly right.

 

[ChiEngr]

Thanks, KootK.

A follow up question: Do you include the tributary weight of walls into the center of mass of the diaphragm?

 

[KootK]

Yup.