Large-Scale Nonlinear Viscous Damper Model Characterization for Applications Towards Improving Seismic Performance of Steel Buildings

Abstract eng:
Passive damping systems can improve the seismic performance of buildings by reducing drift and inelastic deformation demands on structural system through energy dissipation. This paper investigates the hysteretic behaviour of large-scale nonlinear viscous damper and develops a damper model for design and numerical simulation applications. Three large scale nonlinear viscous dampers with a force capacity of 1470 kN and maximum stroke of +/-124 mm were characterized. The characterization tests were conducted in the laboratory by applying a ramped sinusoidal displacement excitation to the damper, with various combinations of loading frequency and displacement amplitude to cover a wide range of excitation velocities and displacement amplitudes. The test results show that the dampers do not behave as purely viscous devices; rather, a nonlinear stiffness behavior was detected, causing a phase difference between the damper force and velocity. Shear thinning behavior was identified in the force-velocity loop, i.e. with the same amplitude, the damper viscosity decreases with an increase in damper velocity. The force-deformation hysteretic response under low excitation frequency was found to be more elliptical than the response under high excitation frequency, which signifies a damper nonlinearity with an increase in the excitation frequency. In addition, it was observed that the dampers have a frictional behavior when the excitation frequency approaches zero. Furthermore, sloppiness inherent in the damper pin connection to structural members was detected. As the damper behavior is frequency dependent, its effect on dynamic properties of the structural system equipped with dampers will be demonstrated in this paper, and its effectiveness in improving seismic performance of structural system will be discussed. In order to predict the hysteresis behavior of the damper under seismic loading conditions, this paper proposes a nonlinear Maxwell material model with a frictional component and nonlinear flexibility to damper friction and connection sloppiness to simulate realistic mechanical behavior of the damper. The model shows good agreement with the experimental results from damper characterization tests. The model was further validated through real-time hybrid simulation testing of a large-scale three-story steel structure equipped with nonlinear viscous dampers. With this model, the seismic responses of the damper and structural system are shown to be accurately predicted.

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