Seismic design of buildings with basements or parkades (NBCC 2020)

[EngDM]

Hey all, I'm certain that most of the Canadian practitioners here haven't fully dove into 2020 since it isn't enforceable yet, but I believe the 2015 handles the equivalent static method the same.

Anyways, when taking the heights hi, hn, hx the code defines these as being above base i=0. Does this mean that the basement slab elevation is considered as your base elevation when distributing your forces to your floors? If I am interpretting this incorrectly, has anyone designed anything where base was not at grade? What kind of building was it?

What about buildings on stilts? Is base considered the main floor as far as earthquake goes, and the assumption is that the stilts will move with the ground, and all momentum is generated with respect to top of stilt?

 

[KootK]

I would say that the seismic base is most often assumed to be the ground floor slab level. That said, there can be a fair bit of nuance to this as described in this excellent article on the subject: Link.