Multi-stage Performance Upgrade of Steel Moment Frames by Post-tension Connections

Numerous studies have been conducted on self-centering seismic lateral force resisting systems, the consequences of which have resulted in removing many ambiguities regarding the use of such systems in retrofitting the existing frames. The present study evaluated the new approach of improvement of multi-stage performance using such systems. Due to the significant costs of running the whole retrofit project in one stage, as well as some issues such as the impossibility of stopping the use of all floors in some of the existing buildings, multi-stage improvement can be considered as a good suggestion. In this regard, a part of the floors are retrofitted in the first stage and the next stage of improvement are then implemented by spending less budget and time. Accordingly, the execution of the first stage leads to an enhancement in the frame performance to an appropriate extent. In addition, the measuremets taken in the stage are a part of final retrofit project. In the present study, PUF and PEF coefficients were introduced and utilized to select the most appropriate pattern for applying post-tensioned connections in different floors. After analyzing frames, a model was proposed for the multi-stage improvement of each frame by selecting the appropriate pattern using post-tensioned connections in the floors. In the first stage of the suggested plan, for 3-, 6-, and 10-story frames the performance improvements were 15.3, 11.4, and 8.5%, respectively.