Usually those steps relate to added eccentricity in seismic cases. If you open your load patterns, I would assume you have X load, X +e, X-e, where the e is your code required eccentricity.
That would explain why displacements may differ as well.
Correct, it relates to the eccentricities in the defined static earthquake load cases, if you view the base reactions, you should see that the Fx, Fy, Fz, Mx & My are all the same, Mz varies with eccentricity. If you have set 0.1 for the eccentricity and checked positive, central and negative eccentricty, the 3 load steps relate to each of these eccentricities.
thanks for the reply , one more question why does Mz varies if the eccentricities are in x and y axis ?
Also shouldn't the moment value for X load should be lower than X +e, X-e ?
No, My is the moment about the global y-axis caused by Fx. Likewise Mx is the moment about the global X axis driven by Fy. These moments don't change cause Fx & Fy get applied at the same z-offset from the base of the structure. Mz is the twist about the global Z-axis by the Fx & Fy being applied at different x & y positions on the building