Seismic retrofit of special truss moment frames using viscous dampers

The special truss moment frame (STMF) is known to provide higher lateral stiffness with relatively less weight as compared to conventional moment resisting frames. In this study the seismic performance of STMF was investigated by fragility analyses and the results were compared with the performance of special moment resisting frames. Then seismic retrofit scheme was proposed by installing a viscous damper in the special segment to meet enhanced seismic performance objective. The required amount of additional viscous damping was determined based on the nonlinear static procedure provided in the ASCE/SEI 41-10. The analysis results showed that the STMF showed larger stiffness and strength but smaller ductility compared with the moment frames, which resulted in similar seismic fragility in both structures. The seismic performance of STMF with viscous dampers in the special segments turned out to meet the desired target performance, and the effect of adding viscous dampers in the seismic fragility was most significant in the complete damage state.