Seismic retrofitting design method for steel CBFs based on the energy-ductility model

A simplified seismic retrofitting method uses only one parameter (equivalent energy) instead of multiple pa-rameters (strength and stiffness) was presented. Reserve parameters, including reserve strength and reserve stiffness, of BRBFs were developed. The relationship between the equivalent energy (E) and the reserve pa-rameters was established. The ductility responses (mu) of the BRBF and CBF structures under a series of ground motions were calculated and compared. All acceptable parametric combinations of the BRBF for CBF retrofitting were obtained by taking the ductility response of the BRBF less than that of the CBF as the criterion. Then, the equivalent energy and ductility response were combined, and the results were fitted as the E-mu model, which is an easy-to-use equation. The seismic reinforcement design method of CBFs retrofitted with BRBs based on the E-mu model was proposed, which is a direct method without any nonlinear time-history analysis. Finally, the method was applied to a 6-story retrofitted braced frame structure project, and the results showed that the method proposed in this paper is accurate and applicable in seismic retrofitting design.