Structural Strengthening with Displacement and Direction Dependent (D3) Viscous Damper Using Aftershocks –Shaking Table Study
Buildings can have post-earthquake residual deformations. Aftershocks or subsequent earthquakes can induce further displacements, increasing the probability of collapse and affecting nearby buildings. In particular, the likelihood of increased displacement in the direction of residual displacements may exceed 50% due to P-Δ and other effects. Structural modification or devices can mitigate further movement in the direction of residual displacements. However, many such devices provide resistive forces in both directions, which can negate their benefits. There is thus a need for smart devices, which can modify their response behaviour during an earthquake to manage the risks due to residual displacements and further improve structural performance during aftershocks. This paper presents shake table testing of a 1/2 scale, two-story steel frame building with an initial 0.7% residual deformation from a prior earthquake. This structure was strengthened using two passive D3 dampers, which resist only motion away from the desired central structural position. The D3 viscous damper has an amount of out of phase action based on the residual deformation changing the neutral position of the structure, but not the device. This out of phase action can passively change during an earthquake to ameliorate and help restore structure recanting. The overall results show the simultaneous reduction of peak and residual drifts are available with the D3 viscous damper in the main shock and subsequent aftershock ground motions. The proposed device offers the adaptability of semi-active devices in an entirely passive device design, providing a unique retrofit opportunity.