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James M Ricles - One of the best experts on this subject based on the ideXlab platform.
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adaptive time series compensator for delay compensation of servo hydraulic actuator systems for real time Hybrid Simulation
Earthquake Engineering & Structural Dynamics, 2013Co-Authors: Yunbyeong Chae, Karim Kazemibidokhti, James M RiclesAbstract:SUMMARY Hydraulic actuators are typically used in a real-time Hybrid Simulation to impose displacements to a test structure (also known as the experimental substructure). It is imperative that good actuator control is achieved in the real-time Hybrid Simulation to minimize actuator delay that leads to incorrect Simulation results. The inherent nonlinearity of an actuator as well as any nonlinear response of the experimental substructure can result in an amplitude-dependent behavior of the servo-hydraulic system, making it challenging to accurately control the actuator. To achieve improved control of a servo-hydraulic system with nonlinearities, an adaptive actuator compensation scheme called the adaptive time series (ATS) compensator is developed. The ATS compensator continuously updates the coefficients of the system transfer function during a real-time Hybrid Simulation using online real-time linear regression analysis. Unlike most existing adaptive methods, the system identification procedure of the ATS compensator does not involve user-defined adaptive gains. Through the online updating of the coefficients of the system transfer function, the ATS compensator can effectively account for the nonlinearity of the combined system, resulting in improved accuracy in actuator control. A comparison of the performance of the ATS compensator with existing linearized compensation methods shows superior results for the ATS compensator for cases involving actuator motions with predefined actuator displacement histories as well as real-time Hybrid Simulations. Copyright © 2013 John Wiley & Sons, Ltd.
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evaluation of a real time Hybrid Simulation system for performance evaluation of structures with rate dependent devices subjected to seismic loading
Engineering Structures, 2012Co-Authors: Cheng Chen, Yunbyeong Chae, James M Ricles, Theodore L Karavasilis, Richard SauseAbstract:Real-time Hybrid Simulation is a viable experiment technique to evaluate the performance of structural systems subjected to earthquake loads. This paper presents details of the real-time Hybrid Simulation system developed at Lehigh University, including the hydraulic actuators, the IT control architecture, an integration algorithm and actuator delay compensation. An explicit integration algorithm provides a robust and accurate solution to the equations of motion while an adaptive inverse compensation method ensures the accurate application of the command displacements to experimental substructure(s) by servo-hydraulic actuators. Experiments of a steel moment resisting frame with magneto-rheological fluid dampers in passive-on mode were conducted using the real-time Hybrid Simulation system to evaluate the ability for the Simulation method to evaluate the nonlinear seismic response of steel frame systems with dampers that are intended to enhance the response of the structure. The comparison with numerical Simulation results demonstrates that the real-time Hybrid Simulation system produces accurate and reliable experimental results and therefore shows great potential for structural performance evaluation in earthquake engineering research.
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experimental evaluation of the seismic performance of steel mrfs with compressed elastomer dampers using large scale real time Hybrid Simulation
Engineering Structures, 2011Co-Authors: Theodore L Karavasilis, James M Ricles, Richard Sause, Cheng ChenAbstract:Real-time Hybrid Simulation combines experimental testing and numerical Simulation, and thus is a viable experimental technique for evaluating the effectiveness of supplemental damping devices for seismic hazard mitigation. This paper presents an experimental program based on the use of the real-time Hybrid Simulation method to verify the performance-based seismic design of a two story, four-bay steel moment resisting frame (MRF) equipped with compressed elastomer dampers. The laboratory specimens, referred to as experimental substructures, are two individual compressed elastomer dampers with the remainder of the building modeled as an analytical substructure. The proposed experimental technique enables an ensemble of ground motions to be applied to the building, resulting in various levels of damage, without the need to repair the experimental substructures, since the damage will be within the analytical substructure. Statistical experimental response results incorporating the ground motion variability show that a steel MRF with compressed elastomer dampers can be designed to perform better than conventional steel special moment resisting frames (SMRFs), even when the MRF with dampers is significantly lighter in weight than the conventional MRF.
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tracking error based servohydraulic actuator adaptive compensation for real time Hybrid Simulation
Journal of Structural Engineering-asce, 2010Co-Authors: James M Ricles, Cheng ChenAbstract:Real-time Hybrid Simulation combines experimental testing and numerical Simulation by dividing a structural system into experimental and analytical substructures. Servohydraulic actuators are typically used in a real-time Hybrid Simulation to apply command displacements to the experimental substructure(s). Servohydraulic actuators may develop a time delay due to inherent actuator dynamics that results in a desynchronization between the measured restoring force(s) and the integration algorithm in a real-time Hybrid Simulation. Inaccuracy or even instability will occur in a Hybrid Simulation if actuator delay is not compensated properly. This paper presents an adaptive compensation method for actuator delay. An adaptive control law is developed using an error tracking indicator to adapt a compensation parameter used in the proposed compensation method. Laboratory tests involving large-scale real-time Hybrid Simulations of a single degree of freedom moment resisting frame with an elastomeric damper are conducted to experimentally demonstrate the effectiveness of the proposed adaptive compensation method. The actuator tracking capability is shown to be greatly improved and exceptional experimental results are still achieved when a good estimate of actuator delay is not available.
Khalid M Mosalam - One of the best experts on this subject based on the ideXlab platform.
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theoretical evaluation of Hybrid Simulation applied to continuous plate structures
Journal of Engineering Mechanics-asce, 2016Co-Authors: Ahmed A Bakhaty, Sanjay Govindjee, Khalid M MosalamAbstract:AbstractHybrid Simulation is a popular experimental technique whereby only part of a system is physically realized and the remainder is modeled in a computer with a set of actuators and sensors to connect the two subsystems. While the methodology is common, it lacks a theoretical structure that ensures users are getting valid Simulation results of the entire system. Further, little attention has been paid to distributed mass systems and those that do not have a beam/column like topology. This work examines three basic issues: (1) an abstract geometric scheme is proposed by which one can reason about Hybrid Simulation systems and their underlying errors; (2) systems with distributed mass are explicitly considered; and (3) the model system utilized in this study has a distinctly nonbeam/column like system, namely, a Kirchhoff-Love plate with a continuous one-dimensional Hybrid system interface. It is demonstrated that such systems are generally viable only below the first fundamental frequency of the system...
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enhancement of real time Hybrid Simulation on a shaking table configuration with implementation of an advanced control method
Earthquake Engineering & Structural Dynamics, 2015Co-Authors: Selim Gunay, Khalid M MosalamAbstract:Summary This paper presents the implementation of Three Variable Control (TVC), an advanced control method, to the existing Hybrid Simulation (HS) system at the University of California, Berkeley. Motivation, background, and implementation of the TVC are explained together with modifications in the existing HS system. An application, which consists of the real-time HS of electrical disconnect switches on a shaking table configuration, demonstrates successful implementation of the TVC. The presented application also covers other HS-related features, namely employment of a three-dimensional analytical substructure, real-time HS-compatible operator-splitting integration method, and an efficient equation solver for faster computations. Copyright © 2014 John Wiley & Sons, Ltd.
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seismic performance evaluation of high voltage disconnect switches using real time Hybrid Simulation ii parametric study
Earthquake Engineering & Structural Dynamics, 2014Co-Authors: Selim Gunay, Khalid M MosalamAbstract:SUMMARY This paper presents the results of a parametric study that consists of real-time Hybrid Simulation tests of electrical insulator posts on a smart shaking table. A companion paper presents the details of the development and validation of the real-time Hybrid Simulation system used for conducting the tests of this parametric study. The purpose of the parametric study presented in this paper is 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. Copyright © 2013 John Wiley & Sons, Ltd.
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seismic performance evaluation of high voltage disconnect switches using real time Hybrid Simulation i system development and validation
Earthquake Engineering & Structural Dynamics, 2014Co-Authors: Khalid M Mosalam, Selim GunayAbstract:SUMMARY This paper presents the development and validation of a real-time Hybrid Simulation (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. A companion paper presents and discusses a parametric study for a variety of geometrical and material configurations of these switches using the developed RTHS system. Copyright © 2013 John Wiley & Sons, Ltd.
Selim Gunay - One of the best experts on this subject based on the ideXlab platform.
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enhancement of real time Hybrid Simulation on a shaking table configuration with implementation of an advanced control method
Earthquake Engineering & Structural Dynamics, 2015Co-Authors: Selim Gunay, Khalid M MosalamAbstract:Summary This paper presents the implementation of Three Variable Control (TVC), an advanced control method, to the existing Hybrid Simulation (HS) system at the University of California, Berkeley. Motivation, background, and implementation of the TVC are explained together with modifications in the existing HS system. An application, which consists of the real-time HS of electrical disconnect switches on a shaking table configuration, demonstrates successful implementation of the TVC. The presented application also covers other HS-related features, namely employment of a three-dimensional analytical substructure, real-time HS-compatible operator-splitting integration method, and an efficient equation solver for faster computations. Copyright © 2014 John Wiley & Sons, Ltd.
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seismic performance evaluation of high voltage disconnect switches using real time Hybrid Simulation ii parametric study
Earthquake Engineering & Structural Dynamics, 2014Co-Authors: Selim Gunay, Khalid M MosalamAbstract:SUMMARY This paper presents the results of a parametric study that consists of real-time Hybrid Simulation tests of electrical insulator posts on a smart shaking table. A companion paper presents the details of the development and validation of the real-time Hybrid Simulation system used for conducting the tests of this parametric study. The purpose of the parametric study presented in this paper is 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. Copyright © 2013 John Wiley & Sons, Ltd.
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seismic performance evaluation of high voltage disconnect switches using real time Hybrid Simulation i system development and validation
Earthquake Engineering & Structural Dynamics, 2014Co-Authors: Khalid M Mosalam, Selim GunayAbstract:SUMMARY This paper presents the development and validation of a real-time Hybrid Simulation (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. A companion paper presents and discusses a parametric study for a variety of geometrical and material configurations of these switches using the developed RTHS system. Copyright © 2013 John Wiley & Sons, Ltd.
Shirley J. Dyke - One of the best experts on this subject based on the ideXlab platform.
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parametric identification of a servo hydraulic actuator for real time Hybrid Simulation
Mechanical Systems and Signal Processing, 2014Co-Authors: Yili Qian, Amin Maghareh, Shirley J. DykeAbstract:Abstract In a typical Real-time Hybrid Simulation (RTHS) setup, servo-hydraulic actuators serve as interfaces between the computational and physical substructures. Time delay introduced by actuator dynamics and complex interaction between the actuators and the specimen has detrimental effects on the stability and accuracy of RTHS. Therefore, a good understanding of servo-hydraulic actuator dynamics is a prerequisite for controller design and computational Simulation of RTHS. This paper presents an easy-to-use parametric identification procedure for RTHS users to obtain re-useable actuator parameters for a range of payloads. The critical parameters in a linearized servo-hydraulic actuator model are optimally obtained from genetic algorithms (GA) based on experimental data collected from various specimen mass/stiffness combinations loaded to the target actuator. The actuator parameters demonstrate convincing convergence trend in GA. A key feature of this parametric modeling procedure is its re-usability under different testing scenarios, including different specimen mechanical properties and actuator inner-loop control gains. The models match well with experimental results. The benefit of the proposed parametric identification procedure has been demonstrated by (1) designing an H ∞ controller with the identified system parameters that significantly improves RTHS performance; and (2) establishing an analysis and computational Simulation of a servo-hydraulic system that help researchers interpret system instability and improve design of experiments.
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real time Hybrid Simulation from dynamic system motion control to experimental error
Earthquake Engineering & Structural Dynamics, 2013Co-Authors: Nestor Castaneda, Shirley J. DykeAbstract:SUMMARY Real-time Hybrid Simulation (RTHS) has increasingly been recognized as a powerful methodology to evaluate structural components and systems under realistic operating conditions. It is a cost effective approach compared with large scale shake table testing. Furthermore, it can maximally preserve rate dependency and nonlinear characteristics of physically tested (non)structural components. Although conceptually very attractive, challenges do exist that require comprehensive validation before RTHS should be employed to assess complicated physical phenomena. One of the most important issues that governs the stability and accuracy of an RTHS is the ability to achieve synchronization of boundary conditions between the computational and physical substructures. The objective of this study is to propose and validate an H∞ loop shaping design for actuator motion control in RTHS. Controller performance is evaluated in the laboratory using a worst-case substructure proportioning scheme. A modular, one-bay, one-story steel moment resisting frame specimen is tested experimentally. Its deformation is kept within the linear range for ready comparison with the reference closed-form solution. Both system analysis and experimental results show that the proposed H∞ strategy can significantly improve both the stability limit and test accuracy compared with several existing strategies. Another key feature of the proposed strategy is its robust performance in terms of unmodeled dynamics and uncertainties, which inevitably exist in any physical system. This feature is essential to enhance test quality for specimens with nonlinear dynamic behavior, thus ensuring the validity of the proposed approach for more complex RTHS implementations. Copyright © 2012 John Wiley & Sons, Ltd.
B F Spencer - One of the best experts on this subject based on the ideXlab platform.
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validation of model based real time Hybrid Simulation for a lightly damped and highly nonlinear structural system
Applied and Computational Mechanics, 2020Co-Authors: Amirali Najafi, B F SpencerAbstract:Hybrid Simulation (HS) is a cost-effective alternative to shake table testing for evaluating the seismic performance of structures. HS structures are partitioned into linked physical and numerical substructures, with actuators and sensors providing the means for the interaction. Load application in conventional HS is conducted at slow rates and is sufficient when material rate-effects are negligible. Real-time Hybrid Simulation (RTHS) is a variation of the HS method, where no time-scaling is applied. Despite the recent strides made in RTHS research, the body of literature validating the performance of RTHS, compared to shake table testing, remains limited. In the few available studies, the tested structures and assemblies are linear or modestly nonlinear, and artificial damping is added to the numerical substructure to ensure convergence and stable execution of the Simulation. The objective of this study is the validation of a recently proposed model-based RTHS framework, focusing on lightly-damped and highly-nonlinear structural systems; such structures are particularly challenging to consider using RTHS. The boundary condition in the RTHS tests are enforced via displacement and acceleration tracking. The modified Model-Based Control (mMBC) compensator is employed for the tracking action. A two-story steel frame structure with a roof-level track nonlinear energy sink (NES) device is selected due to its light damping, high nonlinearity, and repeatability. The complete structure is first tested on a shaking table, and then substructured and tested via the RTHS method. The model-based RTHS approach is shown to perform similar to the shake table method, even for lightly-damped and highly-nonlinear structures.
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feedforward actuator controller development using the backward difference method for real time Hybrid Simulation
Smart Structures and Systems, 2014Co-Authors: Brian M Phillips, B F Spencer, Shuta Takada, Yozo FujinoAbstract:Real-time Hybrid Simulation (RTHS) has emerged as an important tool for testing large and complex structures with a focus on rate-dependent specimen behavior. Due to the real-time constraints, accurate dynamic control of servo-hydraulic actuators is required. These actuators are necessary to realize the desired displacements of the specimen, however they introduce unwanted dynamics into the RTHS loop. Model-based actuator control strategies are based on linearized models of the servo-hydraulic system, where the controller is taken as the model inverse to effectively cancel out the servo-hydraulic dynamics (i.e., model-based feedforward control). An accurate model of a servo-hydraulic system generally contains more poles than zeros, leading to an improper inverse (i.e., more zeros than poles). Rather than introduce additional poles to create a proper inverse controller, the higher order derivatives necessary for implementing the improper inverse can be calculated from available information. The backward-difference method is proposed as an alternative to discretize an improper continuous time model for use as a feedforward controller in RTHS. This method is flexible in that derivatives of any order can be explicitly calculated such that controllers can be developed for models of any order. Using model-based feedforward control with the backward-difference method, accurate actuator control and stable RTHS are demonstrated using a nine-story steel building model implemented with an MR damper.
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model based feedforward feedback actuator control for real time Hybrid Simulation
Journal of Structural Engineering-asce, 2013Co-Authors: Brian M Phillips, B F SpencerAbstract:AbstractSubstructure Hybrid Simulation is a powerful, cost-effective alternative for testing structural systems, closely coupling numerical Simulation and experimental testing to obtain the complete response of a structure. In this approach, well-understood components of the structure are modeled numerically, while the components of interest are tested physically. Generally, an arbitrary amount of time may be used to calculate and apply displacements at each step of the Hybrid Simulation. However, when the rate-dependent behavior of the physical specimen is important, real-time Hybrid Simulation (RTHS) must be used. Computation, communication, and servohydraulic actuator limitations cause delays and lags that lead to inaccuracies and potential instabilities in RTHS. This paper proposes a new model-based servohydraulic tracking control method including feedforward-feedback links to achieve accurate tracking of a desired displacement in real time. The efficacy of the proposed approach is demonstrated throug...
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Hybrid Simulation for earthquake response of semirigid partial strength steel frames
Journal of Structural Engineering-asce, 2013Co-Authors: Hussam Mahmoud, B F Spencer, Ohsung Kwon, Amr S Elnashai, David J BennierAbstract:AbstractThe behavior of semirigid partial-strength connections has been investigated through either experimental component testing or detailed three-dimensional (3D) finite-element (FE) models of beam-column subassemblies. Previous experiments on semirigid partial-strength connections were conducted under idealized loads and boundary conditions, which do not represent real situations. In addition, the developed 3D FE models are computationally expensive and have primarily been used under monotonic loadings. Evaluating the full potential of any connection requires a system-level investigation, whereby the effect of the local behavior of the connection on the global response of the structural system is considered. Moreover, the connection should be tested under realistic load and boundary conditions and/or analyzed using an accurate yet computationally affordable analytical model. This paper represents a new system-level Hybrid Simulation application aimed at investigating the seismic performance of semirig...
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geographically distributed real time Hybrid Simulation of mr dampers for seismic hazard mitigation
20th Analysis and Computation Specialty Conference, 2012Co-Authors: Sung Jig Kim, Richard E Christenson, Brian M Phillips, B F SpencerAbstract:In the field of earthquake engineering, and more generally in structural dynamics and control, experimental verification is critical. For large structural systems, full-scale experimental tests may not be economically or practically feasible. However, Hybrid Simulation (where the Simulation is partitioned into numerical and physical components), provides the capability to isolate and physically test critical components of a structure in an efficient manner, while still fully capturing the dynamic behavior of an interaction with the entire structural system. Real-time Hybrid Simulation (RTHS) conducts these tests in hard, real-time to ensure that any ratedependant characteristics of the physical component are accurately represented. Furthermore, testing at multiple geographically distributed laboratories can optimize the use of distributed resources found in the Network for Earthquake Engineering Simulation (NEES) equipment facilities. Leveraging multiple equipment sites for RTHS poses great challenges due to the hard real-time nature of RTHS and the inherent and unpredictable network delay associated with geographically distributed testing. This paper describes the framework, sensitivity analysis, and resulting tests of a series of geographically distributed RTHS successfully conducted between the University of Connecticut (UConn) and the University of Illinois (Illinois). INTRODUCTION The George E. Brown Jr. Network for Earthquake Engineering Simulation (NEES) consists of fourteen shared-use equipment sites located throughout the U.S. Among them is a variety of state-of-the-art test equipment, including large-scale Hybrid test facilities, shaking tables, geotechnical centrifuges, a tsunami wave basin, as well as field equipment and an information technology (IT) infrastructure linking these sites over high-speed internet. The National Research Council (NRC, 2004) identified research activities, involving tests at multiple equipment sites, as a major focus of the geographically distributed NEES collaboratory. In addition to collaboration and data sharing between sites, NEES was charged to develop distributed physical and numerical Simulation capabilities in order to conduct more complex experiments and Simulation tests simultaneously across multiple equipment sites. The NEES community has traditionally focused on geographically distributed multi-site, pseudo-dynamic testing, including the Multi-site Online Simulation Test (MOST) (Spencer et al., 2004) and ensuing bench-scale mini-MOST demonstrations, pre-NEESR zipper frames project (Leon, et al., 2004), and Multi-site soil-structurefoundation interaction test (Elnashai et al., 2008). RTHS has been proposed to fully capture strain, damping, and inertial effects by computing each numerical integration time step of the experiment in exactly that amount of time (Nakashima, 1999; Dimig, 1999; Horiuchi et al., 1999a; Darby, 1999; Blakeborough et al., 2001; and Williams and Blakeborough, 2001). In RTHS, the dynamics of the testing system and numerical integration scheme are critical to ensure stability of the test and accuracy of the end results (Horiuchi, et al., 1999b; Nakashima 2001; and Zhao, et al., 2003; Mercan and Ricles, 2007). The major challenge with geographically distributed, or multi-site, RTHS is the accommodation of large communication time delays present in sending data over large distances – including the internet. Modern local controllers and Hybrid Simulation algorithms typically run at a rate of around 1000 Hz (1 msec). Recent multi-site tests conducted between the NEES facilities at Lehigh University and the University of Illinois (Illinois) encountered network time delays in one direction (geographically located approximately 1200 km apart) of 25-50 msec (Kim et. al, 2011). Due to this large delay, testing in real-time (which would allow for testing rate dependent physical components) cannot be accomplished with traditional methods and algorithms. This paper presents the framework used to successfully conduct geographically distributed RTHS tests and presents the experimental results of a two-story, seismically excited shear-frame building with an MR damper located between the ground and first story. The MR damper is physically tested at UConn. Analytical results that examine the sensitivity of geographically distributed RTHS to an increase in the network delay, and uncertainty in the models of the physical specimens used to compensate for the network delay will also be presented. It is shown that less than 5% error can be achieved with the network delays commonly observed between UConn and Illinois with a modestly accurate model of the physical specimen. The analytical results are confirmed with a series of RTHS experiments. PROPOSED FRAMEWORK A Smith prediction-based approach is adopted to accommodate the communication time delay present in multi-site testing, while maintaining the deterministic requirements of hard real-time Simulation numerical integration. A schematic for the proposed geographically distributed real-time, geographically distributed Hybrid test framework is shown in Figure 1. An external excitation (e.g. ground motion) is applied to the numerical component. As shown in Figure 1, the external excitation elicits a response from the numerical component, which in turn results in excitation of the physical component. The excitation of the physical component is achieved using test equipment, such as actuators or a shaking table. The test equipment is typically controlled in closed loop fashion, not depicted in Figure 1, which ensures that the commanded displacement is accurately realized by the equipment. In turn, the motion of the physical component results in a reaction force, which is fed back into the numerical component. If the numerical and physical components are geographically distributed, then associated time delays τ1 and τ2 are added to the Simulation. To compensate for the network time delay, a Smith predictor is added to the Simulation. Figure 1. Proposed Geographically Distributed RTHS Framework. It should be noted that the physical component block has been highly simplified for this depiction. The physical component has been the focus of a great deal of research in RTHS. A variety of approaches have been proposed to improve actuator control, and minimize the effects of actuator dynamics. This is often viewed as an apparent time delay – adding anywhere from 1-2 msec, to upwards of 20 msec of time delay in the closed loop RTHS. Early approaches focused on eliminating the apparent time delay, including the polynomial extrapolation approach (Horiuchi et al., 1999) and a least-squares extrapolation approach (Wallace et al., 2005). More recent approaches have begun to address frequency dependent actuator dynamics through inverse compensation (Chen and Ricles, 2010) as well as using accurate models of actuator dynamics for model-based actuator control (Carrion and Spencer, 2007; Phillips and Spencer, 2011). For this research, an inverse compensation technique was implemented, reducing the apparent time delay from actuator dynamics to approximately 10 msec. As previously identified, the critical aspect in geographically distributed testing is the large communication time delay that occurs passing displacement and force data between the Simulation coordinator and remote sites. The network time delays are observed to be on the order of 20-100 msec and could be larger, depending on the geographic distance and Internet speed between sites. To accommodate the communication time delays, a Smith-prediction based algorithm can be employed (Lin and Christenson, 2007). A modified formulation of the Smith predictor is employed, where a single Smith predictor is located at the Simulation coordinator site. Ground motion Numerical component (Structure) Physical component 1 τ 2 τ ( ) t x
