Shake Table Testing of a Low Damage Steel Building with 2-4 Displacement Dependent (D3) Viscous Damper

To improve seismic structural performance, supplemental damping devices can be incorporated to absorb seismic response energy. The viscous fluid damper is a well-known solution. However, while they reduce displacement demand, they can increase overall base shear demand in nonlinear structures as they provide resistive forces in all four quadrants of force-displacement response. In contrast, Direction and Displacement Dependent (D3) viscous fluid dampers offer the opportunity to simultaneously reduce structural displacements and the total base-shear force as they only produce resistive forces in the second and fourth quadrants of a structural hysteresis plot. The research experimentally examines the response of a half-scale, 2-storey moment frame steel structure fitted with a 2-4 configuration D3 viscous fluid damper. The structure is also tested with conventional viscous dampers to establish a baseline response and enable comparison of results. Dynamic experimental tests are used to assesses the base shear, maximum drift and residual deformation under 5 different earthquakes (Northridge, Kobe, Christchurch (CCCC), Christchurch (CHHC), and Bam ground motion). Response metrics including base shear, the maximum structural displacement, and peak structural accelerations are used to quantify performance and to assess the response reductions achieved through the addition of dampers. It is concluded that only the 2-4 device is capable of providing concurrent reductions in all three of these structural response metrics.

Hybrid Recentering Energy Dissipative Device for Seismic Protection

A hybrid recentering energy dissipative device that has both recentering and energy dissipation capabilities is proposed and studied in this paper. The proposed hybrid device, referred to as the hybrid shape memory alloy (SMA) recentering viscous fluid (RCVF) energy dissipation device, connects the apex of a chevron brace to an adjoining beam using two sets of SMA wires arranged in series on either side of the brace and a viscous fluid damper arranged in parallel with the SMA wires. The viscous damper is used because being a velocity-dependent device it does not exert any force that counteracts the recentering force from the SMA wires after the vibration of the frame ceases. In the numerical study, the Wilde’s SMA constitutive model is used to model the SMA wires, and the Maxwell model is used to simulate the viscous fluid damper. To demonstrate the viability and effectiveness of the proposed hybrid device, comparative studies are performed on several single-story shear frames and a series of four-story steel frames. The results show that the frames equipped with the hybrid device have noticeably smaller peak top story displacements and residual story drifts when subjected to ground motions at three different intensity levels.

Real-Time Hybrid Simulation of Viscous Dampers for Seismic Hazard Mitigation

Laboratory experiments play a critical role in earthquake engineering research for seismic safety evaluation of civil engineering structures. Real-time hybrid simulation provides a viable alternative for shake table testing to evaluate seismic performances of structures with rate-dependent seismic devices. Servo-hydraulic actuators play a vital role in a real-time hybrid simulation to maintain the boundary condition between the analytical and experimental substructures. Compensation of actuator delay is critical to minimize synchronization error from actuator delay and to achieve a successful real-time hybrid simulation. Research on how actuator delay can affect the real-time hybrid simulation involving viscous fluid damper is presented in this study. It is demonstrated that although the viscous fluid damper can help stabilize the real-time hybrid simulation with actuator delay, the experimental results need to be interpreted appropriately to evaluate the performance of viscous fluid damper for seismic hazard mitigation.