Effective seismic weight of the structure 1

[compe_ad]

For calculating the base shear of the structure which has shear walls on all four sides, do we exclude the weight of the shear walls parallel to the seismic force applied? For diaphragm forces (ASCE 12.10-1) mentions to include the weight tributary to the diaphragm. I think exuding the parallel shear walls makes more sense for calculating diaphragm design forces. My understanding it we should include all four shear walls (just half of its height based on lumped mass) for calculating base shear and exclude parallel shear walls for calculating diaphragm design forces. Do you guys do the same? Can you guys provide the reason as well?

 

[strucbells]

I found this a confusing thing to grasp as an EI, especially for 1 story buildings that are often done with shortcut conservative methods in practice.

SK Ghosh has an explainer that covers this topic:

https://www.skghoshassociates.com/b...-seismic-weight-what-do-you-include-and-when/

 

[compe_ad]

Thank for sharing. I read that but it doesn't explicitly states the right way to do it.

 

[driftLimiter]

You are on the right track with this.

The diaphragm only sees the load from out of plane walls.
The shearwalls however need to carry the full base shear.

This is well exemplified in Design of Wood Structure by Breyer.

For me this step is too time consuming, I usually just lump all of the seismic mass into the diaphragm and design the diaphragm for that. If I am have trouble with a diaphragm then I might go back and remove the weight from in plane walls.