Seismic Lateral Force Distribution

[dursunlutfu]

Hi Folks,

My question is about the lateral distribution of seismic force for a 2-story wood framed residential building.
Info about the building : The front portion of the ground floor has a roof at a level which is almost 2 feet higher than the second flor of the house. I am planning on dragging the roof diaphragm of the front portion of the ground floor to the 2nd floor diaphragm at N-S Direction. At E-W direction there are walls which can be used as shear walls for the roof diaphragm at the front portion of the building. So when calculating the total weight of the building, I am planning on including the load of the roof of the front portion of the ground floor to the second floor but here when everything gets tricky. I am also planning on finding the seismic force at E-W direction for the roof of the front portion of the ground floor by only including the weight of the roof and the base shear of the house.
I am wondering if this approach is logical or not and I am wondering if you guys have encountered a situation like that ..
Is there a specific reference for this type of an issue ?

Thanks !!

 

[Agent666]

I cannot really visualise the entire situation (A sketch says a thousand words), but consider it like this:-

Seismic force distribution throughout a level is proportional to the mass distribution at that level, attribute your forces based on the distribution of mass, determine the force attributed to each level/roof, etc based on the height, mass, period and vertical distribution of forces required by your code. If the roofs are at a different level then determine the forces based on that height above ground, rather than lumping this mass at the floor level below or above.

Ensure there is a load path for each level/roof force to the lateral load resisting system (via diaphragms or bracing), and eventually to the foundations and ground.

 

[dursunlutfu]

Thanks a lot ! @Agent666