Recommended Diaphragm Type for Concrete Flat Plate

[dtmilad]

My question is regarding the modeling of lateral resisting system for 7 stories concrete building, the building preliminary geometry are as follows :

Floor system => Flat plate 18 cm

Lateral System => Concrete Columns (20 cm x 90 cm) , Shear Wall (20 cm Thick)

The lateral system I am intending to use is diaphragm concrete slab which is transferring the forces to columns and the shear wall.

Site parameters : Design wind speed 42 m/s , Seismic design category : B (s1 = 0.08 , Ss = 0.25)

My question is which type of diaphragm modeling I shall used , the options I have are :
Flexible diaphragm
Semi-rigid diaphragm
Rigid diaphragm

Also, in the ACI 318 there are no specifications for the diaphragm in the case of seismic design category B , However, I don't have any beams in the floor so shall I apply the conditions in chapter 21 for Structural diaphragms (ACI 318-2011 - 21.11) which are intended for SCD D,E,F

 

[hokie66]

Rigid.

It doesn't appear that you have much in the way of shear walls to grab onto, because of the way the stair wraps around that core. So the 900 columns will have to do the job.