Retrofitting of existing buildings with buckling restrained braces based on distribution of plastic energy demands

This study presents a simplified method for designing buckling restrained braces (BRBs) based on the distribution of plastic energy demands along the structure’s height (EP,i) of main structure. The demand EP,i is the metric that incorporates the structural force, deformation, and the number of hysteretic loops. Consequently, it is easy to know which stories exhibit the highest levels of deformation. EP,i at each story can be converted to equivalent BRB energy by assuming a simplified bilinear behavior, hence facilitating the assessment of the required size of the BRB,i. The plastic energy method (EP‐M) is investigated through the seismic retrofit with BRBs of three existing steel moment-resisting buildings of 3-, 9-, and 20-stories, whose seismic performance is evaluated through nonlinear dynamic analysis using near-field and far-field seismic ground motions. The efficiency of the EP‐M is evaluated using a damage parameter, defined as the ratio of plastic energy demand to input energy (EP/EI). The distribution of inter-story-drift and EP,i over the building height are also examined. Furthermore, this study presents an optimum BRB configuration to minimize inter-story-drifts and column axial forces. The main conclusions are that EP‐M achieves uniform damage distribution and reduces seismic demands compared to traditional force design method.