Using Risk-based Robustness Index for Seismic Improvement of Structures

Nowadays, there are numerous indexes and parameters to review the seismic performance of improved structures. Response modification factor, fragility curves, ratio of different input energies to the structure affected by earthquake, maximum displacement and etcetera. are among these parameters, and most of these parameters are reviewed non-probabilistically. On one hand, since robustness index according to risk shapes probabilistically by reviewing uncertainty parameters of critical events and considering all existing parameters, it can be a beneficial index for reviewing the performance of improved structures. In this article, at first the robustness index is introduced according to risk analysis and one of its unique features is using percentage and amount of progressive collapse in it. After the considered robustness index, it has been used in reviewing the performance of a 4-story building of steel bending frame improved in two separate modes of concentrically brace frame and buckling restrained brace and a method has been suggested to obtain all effective parameters in intended robustness index. Ultimately, by reviewing this index for primary structure and improved structures, their behaviors have been compared and its results have been reported.