The shear wall is not to be designed in isolation. As per code, dual system is one in which (a) Wall + Frame take 100% of eq load, and (b) Frame itself is capable of taking 25% of eq load.
Hence to design it in STAAD, the following procedure may be adopted.
1. Model the structure in STAAD incl. shear walls. Apply the loads, standard load combinations. Perform analysis.
2. Find Vb (Base shear) in each direction from staad output. Also, find out Vbsw as sum of reactions of shear wall supports. For each direction you have to compare Vbsw to Vb. If Vbsw is less than 75% of Vb, the standard load combinations can be used in design of wall and frame. However, if Vbsw is more than 75% of Vb, the standard combinations will result in frame taking less than 25% of Vb. Hence, additional load combinations specifically for frame design have to be created.
Vb =1000 kN, Vbsw=800 kN.
Frame alone should take 25% of 1000 = 250 kN. But for the eq load, frame is taking only 200 kN. Hence, for the frame design, load combinations should have EQ load factor increased by 250/200 = 1.25 times.
Hence, load combinations for shear walll are
1.5 DL + 1.5 EL
0.9 DL + 1.5 EL
1.2 DL + 1.2 LL + 1.2 EL
and load combinations for frame are
1.5 DL + 1.875 EL
0.9 DL + 1.875 EL
1.2 DL + 1.2 LL + 1.5 EL