An Innovative Method for the Seismic Retrofitting of Existing Steel Moment Frame Structures Using Side Plate Technology

摘要

The 1994 Northridge earthquake caused widespread damage to steel moment-resisting frames including brittle fractures of beam-to-column welded moment connections. The damage was in the form of brittle failures at the interface of the beam and column members and was detected in multi-story buildings. Improvements to these pre-Northridge existing connections are often required as part of an overall strengthening scheme, particularly when higher performance levels are desired. To improve the behavior of moment resisting connections, the SidePlate connection was designed and began to market as an alternative moment connection. The SidePlate connection technology uses a pair of parallel full-depth side plates to connect the beam to the column, thereby eliminating the traditional welded connection between the end of the beam and the face of the column flange. While the SidePlate technology has been largely used in the construction of post-Northridge buildings, its application in the retrofitting of existing buildings has been limited to date. In this paper, a new generation of SidePlate connections is proposed, which is applicable for retrofitting purposes and can improve the performance of existing steel structures. It is believed that the new technology may lead to the best way for retrofitting existing building moment frame systems instead of adding concrete shear walls and/or bracing elements. The proposed detail aims to minimize the disturbances of existing building usage situation and at the same time improves the performance of the system by increasing the rigidity of panel zone region and the stiffness of the beam segment between the column face and plastic hinge location. A case study including two multi-story steel moment frame structures was conducted to show that the proposed technology can largely upgrade the performance level of existing structures. Nonlinear analysis was performed to evaluate the vulnerability of the existing structures first, then the proposed detail was implemented to the connections, and new performance levels were obtained by means of nonlinear static analysis. The results showed that the plastic hinges are always formed in beams instead of the columns. It has also been shown that the application of the proposed details reduces the target displacement and improves the performance level of the structures. It can be concluded that depending on the performance level of existing buildings, the proposed detail might be considered as an efficient and optimized way of retrofitting those structures.