Seismic Rehabilitation of an Existing Braced Frame Hospital Building by Direct Replacement with Buckling-Restrained Braces

Buckling-restrained braces may be used for both new design and retrofit applications where increased seismic performance levels are desired relative to traditional buckling braces. As a retrofit technology, buckling-restrained braces may be used to augment strength, stiffness, or damping in an existing lateral force resisting system. In the case of the seismic rehabilitation of the steel-framed hospital building at the Department of Veterans Affairs Seattle campus, buckling-restrained braces were used as a direct replacement of the existing braced frame braces. Where possible, the new braces were connected to the existing gusset plates. This implementation technique may be applied in future rehabilitation projects where ductile details are lacking or increased performance levels are desired. This paper focuses on the unique challenges encountered during the analysis, design, and construction phases of the seismic rehabilitation. Analysis topics will include the development of buckling-restrained brace nonlinear hinge properties and the use of performance-based design techniques to verify seismic performance while minimizing demands on the existing columns and connections. Design phase topics will include brace to gusset connection design and reframing at the existing interstitial floor to allow for brace erection. Construction phase topics will focus on maintaining the continued operation of the hospital functions, which was an important consideration during the entire project.