Real-time hybrid simulation (RTHS) results from the integration of numerical modeling with experimental testing of structural systems. In substructured RTHS tests, a reference structure may be partitioned into two or more substructures to save cost and space. Researchers may choose to model the elastic and less critical structural components numerically, while physically testing the components where appropriate numerical models are lacking. The dynamic characteristics of the numerical and physical substructures are combined by imposing the boundary conditions calculated from the numerical model in the physical substructure and returning measured physical forces back to the numerical model. To date, the majority of RTHS have been focused on substructuring with a single boundary point, physical substructure, and actuator. A multiaxial real-time hybrid simulation (maRTHS) framework was recently proposed, also using a single boundary point and physical substructure. However, for many practical engineering and research applications, more than one boundary point and physical substructure is necessary. Challenges to direct extension of the previously proposed maRTHS strategy to multiple boundary points include incorporation of a larger number of degrees of freedom in the physical experiment, robustness to coupling through the hybrid simulation when using multiple boundary points, and problems introduced by out-of-plane 3D motion. After presenting the analytical constructs of the proposed framework, these issues are explored, and a validation study is introduced involving a multispan curved bridge. This RTHS experiment employs two load and boundary condition boxes (LBCBs) with 12 actuators to assess the scalability of the proposed maRTHS framework to accommodate multiple LBCBs at multiple boundary points. Out-of-plane behaviors of this RTHS experiment are intrinsic. Further, both mechanical coupling present between the actuators for motions in Cartesian coordinates and the coupling introduced through the numerical structure in the RTHS are present. Nonetheless, the decoupled model-based control strategy performed well for both the linear and nonlinear structural responses. These results demonstrate the promising nature of the proposed maRTHS framework for investigating complex and nonlinear structural systems.
Cables are prone to vibration due to their low inherent damping characteristics. Recently, negative stiffness dampers have gained attentions, because of their promising energy dissipation ability. The viscous inertial mass damper (termed as VIMD hereinafter) can be viewed as one realization of the inerter. It is formed by paralleling an inertial mass part with a common energy dissipation element (e.g., viscous element) and able to provide pseudo-negative stiffness properties to flexible systems such as cables. A previous study examined the potential of IMD to enhance the damping of stay cables. Because there are already models for common energy dissipation elements, the key to establish a general model for IMD is to propose an analytical model of the rotary mass component. In this paper, the characteristics of the rotary mass and the proposed analytical model have been evaluated by the numerical and experimental tests. First, a series of harmonic tests are conducted to show the performance and properties of the IMD only having the rotary mass. Then, the mechanism of nonlinearities is analyzed, and an analytical model is introduced and validated by comparing with the experimental data. Finally, a real-time hybrid simulation test is conducted with a physical IMD specimen and cable numerical substructure under distributed sinusoidal excitation. The results show that the chosen model of the rotary mass part can provide better estimation on the damper's performance, and it is better to use it to form a general analytical model of IMD. On the other hand, the simplified damper model is accurate for the preliminary simulation of the cable responses.
This paper presents an updated perspective on semi-active control strategies for civil applications, with special attention on recent developments for magneto-rheological (MR) dampers. A brief overview of control strategies is presented, and then benchmarks studies on semi-active control strategies using MR dampers are presented for further comparison of their effectiveness in terms of satisfying seismic performance objectives.