Check this article on the sign of the results after response spectrum analysis and different options to work with them.

In this case study, the equivalent lateral forces acting on a 4 story residential reinforced concrete building is determined using the procedures described in International Building Code 2018 (IBC 2018).

In this case study, the equivalent lateral forces acting on a 4 story residential reinforced concrete building is determined using the procedures described in the 1997 Uniform Building Code (UBC 97).