Assessment of Using of Knee Bracing in Retrofitting of Existing Steel Structures with Special Moment Resistant Frame System (Technical Note)

In this paper, non-linear behaviors of structures with special moment resistant frame were studied and possibility of using knee bracing for retrofitting of those structures was examined. For this aim, the structures that have been designed according to the second edition of Iranian seismic code (2800), were selected. Those models have 3, 5 and 7 stories. To evaluating and retrofitting of models, non-linear static analysis and capacity spectra (ATC-40) method were applied and providing of the expected performance levels in FEMA356 was studied. Results showed that the response of structures that designed according to the previous edition of code (second edition) is not compatible with the criteria of third edition. The knee bracing system was used to seismic retrofit of those structures. It would be concluded that the using of knee bracing increases lateral stiffness and improves their energy dissipating capacity. Furthermore, the results showed that the shorter knees have the highest stiffness and ductility in the structures.