Abstract
This study investigates the seismic performance of an existing four-story steel frame structure in need of a retrofit using two types of retrofit methods: Steel Plate Shear Walls (SPSW) and Concentrically Braced Frames (CBF). Steel moment resisting frames are prevalent lateral load resisting frames in high seismic regions and have been the focus of intense research due to the observed beam-column fractures during the Northridge earthquake. The brittle joints of pre-Northridge steel moment frames pose life-safety issues for many existing buildings where earthquake loads govern the lateral loading case. To mitigate these issues, many such buildings are in need of retrofit to achieve an acceptable level of ductility. This paper describes the analysis and design process for a seismic retrofit using SPSWs and CBFs for a four-story steel moment frame in Los Angeles area. The performance criterion of existing frame system is determined by performing a nonlinear static “pushover” analysis to a target displacement. The seismic performance level is evaluated to compare and contrast the system’s behavior in terms of their stiffness, ductility and deformation.