ASCE requirements for dual system 1

[Groszni]

hello eng tips,
im designing a dual system which is contains special moment frame and shear wall, on ASCE it said that the moment frame has to capable restraint the 25% seismic force. does it mean the base shear of the moment frame > 25% total base shear ? what if the moment frame doesnt meet the requiremnet( base shear of mf < 25% total base shear) ?

 

[mike20793]

If your moment frame doesn't take 25% of the base shear, then you must use the seismic factors (R, Cd, omega) for the single system rather than the dual system.

Edit: You also have to design for the lowest R value between the two systems. I believe it's mentioned in the code, but I cannot recall which section off the top of my head.

 

[Deker]

Dual systems require two sets of analyses. The first is for 100% of the base shear with all frames and walls included. Since your frames and walls attract load based on their relative stiffness, the total shear in the frames will likely be less than 25% of the base shear. The second analysis is for 25% of the base shear with frames only (walls excluded from the model). For this analysis the frames only need to be designed for strength, not drift. See 2015 NEHRP Recommended Seismic Provisions (FEMA P-1050-1) section C12.2.5.1 for more information.