Multi-axial real-time hybrid simulation

Real-time hybrid simulation (RTHS) is an alternative to shake table testing for studying the seismic behavior of structural systems. RTHS divides a structural system into numerical models and experimental components. The numerical substructure contains the finite-element model of the well-understood components of the structure. The highly nonlinear and numerically burdensome components are physical tested in one or distributed laboratory settings. The numerical modeling and physical substructuring combined, serve to create a more cost and space efficient testing method. The real-time feature of RTHS implies that the physical specimen is loaded at real velocities to account for nonlinear and rate-dependent material behaviors.

For a realistic replication of seismic conditions in test labs, multi-axial RTHS capabilities are needed. Therefore, multi-axial boundary conditions are necessary in the physical specimen, which requires multiple actuators. Such boundary conditions suffer from significant dynamic coupling between the actuators. Kinematic transformations are necessary to operate each actuator to achieve displacements in the desired degree-of-freedom. Furthermore, appropriate compensation must be provided for the actuator dynamics, otherwise stability problems are likely to occur during the RTHS experiment.

Robust and high performance control of shake tables

Shake tables are used to study the behavior of structures under earthquakes. To do this, shake tables must reproduce historical/synthetic ground motion accelerations. Accurate reproduction means that important characteristics of the ground motion are captured during experiments. Shake tables however have inherent properties, which add unwanted dynamics to the desired earthquake time history.

Systematic control techniques are thus adopted to compensate for the unwanted behavior by manipulating the signal sent to the shake table. Ideally, a more authoritative controller will result in improved tracking between the command and measured executed accelerations of the shake table. However, increases in the control authority tend to cause stability issues.

The goal in this research is the development of a shake table compensation method with tracking and stability properties, that builds on existing techniques.

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RTHS and Shake table testing of a steel frame with a nonlinear energy sink device

A vast body of literature currently exists on the developments in the RTHS domain, including advancements in numerical computation, actuator compensation, and multi-axis implementations. Despite the progress made, the research on comparisons between the RTHS and shake table testing methods is limited.

The goal in this research is the evaluation of a two-story steel frame with a roof-level nonlinear energy sink (NES) device via the RTHS and shake table methods. In the RTHS implementations, the two-story frame is numerically modeled while the nonlinear energy sink device is physically tested. Different boundary condition control techniques are explored in the RTHS experiment. Lastly, several performance indicies are introduced and the outcome of the two test methods are compared.

A NES device operates in a similar manner to a tuned mass damper. By optimizing the nonlinearity of NES device, energy is more effectively absorbed from building structures. In addition, a wider frequency bandwidth is targeted via an NES device.