Seismic collapse margin of steel frame structures with symmetrically placed concentric braces

This paper focuses on the seismic collapse assessment conducted on the steel frame structures with symmetrically placed concentric braces using collapse margin ratio (CMR). The main issue with concentrically braced frames (CBFs) is the existence of a vast number of possible combinations in their topology. Therefore, selecting the most efficient group of retrofit schemes (RS), regarding the overall performance index (PI) of the structure requires a simple and quick method of brace manipulation, specifically, removal and/or addition, and a series of basic symmetrical principles in the retrofitting process. However, identifying the optimal RS for new or existent structures requires an evaluation of the optimal CMR value and the retrofitting cost as well. The influence of both cross-section and configuration type of the bracing system provides new insights into the collapse margin. Finally, this paper points out new parameters that should not be neglected in the retrofit design of bracing systems for steel frame structures.