Concentrically braced frames (CBFs), eccentrically braced frames (EBFs), and more recently buckling-restrained braced frames (BRBFs), have proved being efficient seismic resistant systems with high elastic lateral stiffness as required for drift control. However, beside their advantages, CBFs, EBFs, and BRBFs suffer from low post-elastic stiffness, especially in the case of frames with non-moment resisting beam-to-column connections, due to the low post-yield stiffness of their braces. Thus, these structural systems might show significant tendency to soft storey formation during seismic events. This tendency is strongly related to the regularity of the brace over-strength distributions over the building height. Such issue has been observed even when limitations in the maximum difference in brace over-strength are satisfied. Overall, the studies available in the technical literature delineate the need to further examine the influence of the brace over-strength on the structural seismic performance as well as the effectiveness of current code recommendations. In this paper a general methodology to investigate the relation between seismic performance reduction and regularity of brace over-strength distributions is presented. The influence of brace over-strength distributions on the seismic motion are studied through gradient methods based on sensitivity computation. A range of variation of the brace over-strengths is defined and the brace over-strength patterns that are the most unfavourable for each response parameter are identified. Finally, the relationship between the brace over-strength used in the seismic design and the maximum seismic performance reduction is obtained. Results for a case study considering a realistic BRBF are presented and discussed.