I have a one story building approximately 230'x230' with steel braced frames, pretty symmetric layout. I am puzzled by results of Response Spectrum Analysis. When acceleration is in on X-direction, there is sizable total base shear (more than 60% of X direction base shear) in the perpendicular Z-direction. Does this make sense? Shall the sum of support reactions in Z-direction be zero, when there is no acceleration and external force in Z-direction? Otherwise equilibrium does not hold in the Z-direction.

Thank you very much for your responses.