The objective of this Early-Concept Grant for Exploratory Research (EAGER) award is to explore new ideas to overcome the heuristic approaches of hybrid simulation research of the past decade. In hybrid simulation, the structure is typically idealized into several substructures, where some of the substructures are modeled analytically and the remaining substructures are physically tested and their measured responses are used in the computational algorithm for the numerical integration. This research aims at establishing the fundamentals of hybrid simulation to allow it to become a reliable method for simulation of structures and structural systems. Recent advances in computational mechanics will be used to create algorithms for hybrid simulation through an integrated approach involving both theory and experiments. In that regard, modified variational principles will be used to change the geometric structure of the governing equations for the purposes of time stepping. The research will be conducted using a verification and validation paradigm in which experiments, conducted in the George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES) and the Civil and Environmental Engineering Structural laboratories at the University of California, Berkeley, will be used to identify the correct theoretical models and algorithms for hybrid simulation by means of different test structures and a tailored experimental program. This exploratory approach brings together the two fields of hybrid testing and computational mechanics, in a synergistic fashion, aiming at the interdisciplinary advancement of the field. If successful, this work will represent a major conceptual shift from the present hybrid simulation techniques and will establish a thorough basis for hybrid simulations rooted on sound experimentation coupled with theoretical and applied multi-scale mechanics.
The structural safety of the built environment is critical to all citizens. When faced with the challenges of constructing bridges, buildings, power plants, and other infrastructure to withstand the extreme forces from earthquakes, hurricanes, and other natural disasters, engineers need to be able to test new ideas in a safe and reliable manner without having to construct full-scale prototypes. The research aims at providing engineers a robust methodology to reliably test components for new designs without having to build complete structural systems solely for test purposes, leading to safer and more reliable structures for everyone. This award also aims to train a new generation of engineers to be knowledgeable in both the theory and practice of hybrid simulation.
The project presented a novel theoretical framework and develop new approaches to overcome the current limitations of the hybrid simulation (HS) method. Moreover, improvement of the control techniques used in real-time HS (RTHS) took place. Extending the use of RTHS to infrastructure applications benefiting from the performance-based earthquake engineering methodology is one of th emajor outcomes of the project. We are able to show sharp sensitivities to control system errors. Further, we are able to show the existence of unacceptably high errors whenever excitations exceed the system’s first fundamental frequency. It is demonstrated that the investigated hybrid systems are generally viable only below the first fundamental frequency of the system. At and above the fundamental frequency of the system, there are significant and unpredictable errors. It is shown that there is a tendency to accumulate global errors at the slightest introduction of any interface matching error, but that these errors become insensitive to further increase in mismatch. It is found that the different substructures are subject to excitation at their independent natural frequencies in addition to the natural frequencies of the hybrid system. Thus, in general, one needs to check both the natural frequencies of the whole as well as sub-systems in system design. Development and validation of a RTHS system for efficient dynamic testing of high voltage electrical vertical-break disconnect switches. The RTHS system consists of the computational model of the support structure, the physical model of the insulator post, a small shaking table, a state-of-the-art controller, a data acquisition system and a digital signal processor. Explicit Newmark method is adopted for the numerical integration of the governing equations of motion of the hybrid structure, which consists of an insulator post (experimental substructure) and a spring-mass-dashpot system representing the support structure (analytical substructure). Two of the unique features of the developed RTHS system are the application of an efficient feed-forward error compensation scheme and the ability to use integration time steps as small as 1 ms. After the development stage, proper implementation of the algorithm and robustness of the measurements used in the calculations are verified. The developed RTHS system is further validated by comparing the RTHS test results with those from a conventional shaking table test. Parametric study is conducted which consists of RTHS tests of electrical insulator posts on a smart shaking table to evaluate the effect of support structure damping and stiffness on the response of disconnect switches with two different insulator materials, namely porcelain and polymer insulator posts. Various global and local response parameters including accelerations, forces, displacements, and strains are considered in this evaluation. The data obtained from the conducted tests show that the maximum insulator response corresponds to the case where the support structure frequency is close to the insulator frequency. An incorporated evaluation of all the response parameters indicates that the stiff support structures constitute the most suitable configuration for both material types of the tested insulator posts. It is also observed that support structure damping has an effect on the response of both insulator types. However, this effect is secondary compared with the effect of support structure stiffness. Implementation of TVC, an advanced control method, to an existing HS system is conducted. An application, which consists of RTHS of electrical disconnect switches on a shaking table configuration, demonstrated successful implementation of the TVC. This application also covered other HS-related features, namely employment of a three-dimensional analytical substructure, RTHS-compatible operator-splitting integration method, and an efficient equation solver for faster computations.
