Flow of seismic lateral forces

[Akeee]

Hello guys,
I have a question about how the seismic lateral load flows in the structural elements. Seismic force is a mass force and the most of the mass in concentrated in the slab plan. So first when earthqueake comes the inertial forces (seismic forces) will "drag" the slab opposite to ground motion. Now because of this, because the slab have an offset (displacement) from the slab above the columns/wall will tend to rotate and how the beams will rotate to and how and much depends on the stiffness ration between those two. I think this is the logic flow but i always had in mind that the beams tend to rotate first and rotate column not the other way around. If i am wrong please tell me or any adittional info will help me, thank you.

 

[DaveAtkins]

I have always thought the slab-on-grade and foundations move WITH the earthquake, and the inertia of the upper floors and roof prevent them from moving with the earthquake, thus causing seismic lateral force.

DaveAtkins

 

[KootK]

Similar to Dave, I think that the key is to recognize that there are no external seismic forces on the superstructure. There's only imposed relative displacement as a result of the superstructure's inertia preventing it from travelling in unison with the ground and substructure.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.