High-Performance Seismic Retrofit of Soft-Story Wood-Framed Buildings Using Energy Dissipation Systems

Many multi-story buildings have a structural weakness due to large openings in their perimeter walls and to a lack of interior walls at the ground level. The open condition results a ground story that is significantly weaker and more flexible (softer) than the upper stories. In addition, if the flexible wall lines of the ground story are irregularly distributed in plan, torsional response is triggered, adding to the soft-story effect. During earthquake shaking, these soft-story buildings are prone to damage, including pancake-like collapse in some severe cases. In this study, a high-performance retrofit is investigated wherein an energy dissipation system is incorporated within the soft story of wood-framed buildings. The system consists of damping devices that are installed in parallel with the narrow wall piers of the flexible wall lines using scissor-jack bracing to amplify the damper motion. The analysis indicates that the energy dissipation system is effective in dissipating a significant portion of seismic input energy, thus reducing inelastic energy dissipation demand on the wood framing system within the soft story. In addition, through strategic placement of the damping devices (location and magnitude of damping), the story drifts and seismic forces within the upper stories can be controlled while simultaneously minimizing torsional effects, especially within the soft story.