Shaking Table Control Research Articles

Influence and compensation of connection characteristics on shaking table control performance

When testing earthquake simulation shaking tables, it is commonly assumed that the test load, table, and actuator are integrated, which differs significantly from the actual situation and negatively impacts the accuracy of system waveform reproduction. This paper simplifies the connection between the three as a spring-damping model for simulation modeling. The effects of different load mass, different connection intrinsic frequency, different connection damping ratios, and other factors on the control performance of the system are analyzed, and based on the results of the analysis, a method to improve the effects of the connection characteristics on the performance of the system, called flexible connection reaction force compensation algorithm, is proposed. Resonance peaks caused by flexible connections reduce the effective bandwidth. To broaden the bandwidth and enhance system stability, the paper introduces a flexible connection force compensation algorithm based on a multi-parameter control algorithm to compensate for the interaction force caused by the connection characteristics. This compensation strategy expands the effective bandwidth, eliminates resonance peaks, improves the waveform correlation coefficient (CC), and reduces the root-mean-square error (RMSE).

Multi-parameter identification of earthquake simulation shaking table based on BP neural network

Since the model parameters of the shaking table exist in a non-linear form, this leads to distortion of the reproduced waveforms and can even lead to bias in the ground vibration test results. Therefore, the selection of the controller is particularly critical. Multi-variable (MVC) controllers are often used in shaking table control, to improve the control effect of MVC controllers. In this paper, a multi-parametric (BP-MVC) controller based on BP neural network is proposed. The BP neural network is applied to the multi-parameter (MVC) controller to identify the shaking table model, adjust the parameters in real-time, accelerate the convergence speed, and reduce the system error. The simulation results show that the correlation coefficient (CC) of the BP-MVC controller is greater than 0.985, and the root-mean-square error (RMSE) and mean absolute error (MAE) are less than 0.04 and 0.25, respectively, in a nonlinear, time-varying hydraulic system. This suggests that the BP-MVC controller has a better control performance and parameter adaptivity, which can provide a reference for the subsequent ground vibration tests.

Disturbance rejection control of shaking table based on adaptive-model-based state estimator

Real-time hybrid simulation (RTHS) is an important method for the seismic testing of building structures. This method requires high control accuracy for the waveform reproduction of a shaking table. An active disturbance rejection control (ADRC) method is introduced to control the shaking table in this research. In view of the difficulty of parameters setting caused by the large deviation of the extended state observer (ESO) to the state estimation of the shaking table, a model-based adaptive state estimator (AMSE) is designed that uses the model information to estimate the state, and introduces an adaptive strategy to dynamically compensate for the amplitude and phase deviation of the model. The total disturbance is observed by the ESO. Additionally, an AMSE-based ADRC is proposed to achieve high-precision seismic waveform reproduction. The separation principle of the designed system is proved by the Routh–Hurwitz criterion, and the pole assignment bandwidth method is proposed to improve the control performance of the system by flexibly assigning the controller poles. Finally, the shaking table experiments are designed for different specimens. These experiments verify the advantages of the proposed method for state estimation and parameter setting and can effectively improve the stability and control accuracy of shaking table control.

Enhancements of Nonlinear Substructuring Control for Shake Table Experiments on Severely Damaged Structures

This study introduces enhancements for nonlinear substructuring control (NLSC) to achieve simultaneous control of acceleration and displacement in shake table substructuring experiments with severely damaged structures. Although shake table control is greatly affected by a specimen placed on its top and its nonlinear characteristics, accurate control, even with nonlinear characteristics, is essential for experimental purposes. The NLSC was developed for a dynamically substructured system (DSS) scheme involving nonlinear substructures, and its first application to a shake table experiment was performed on a one-storey steel frame. In the experiment, NLSC realised simultaneous control of table acceleration and displacement with a slight nonlinear characteristic within the frame, although its performance degraded as the nonlinearity became stronger. To address this degradation issue, this study introduces two techniques for enhancing NLSC shake table substructuring experiments. One is a composite filtering technique to minimise noise-contaminating displacement data fed back to the table control so that the error feedback action in NLSC can be fully utilised. The other involves a new linear model that is assumed to be more highly damped than the actual system to enhance the stability robustness of NLSC against nonlinear characteristics. After a series of numerical examinations, this study experimentally examined the enhancements on actual shake table experiments using a steel frame. Using the NLSC with the enhancements, a substructuring experiment was successfully conducted; moreover, the NLSC realised simultaneous control of the table acceleration and displacement with nearly 100% accuracy, even with severe nonlinear characteristics.

Numerically disturbed shake table experimentation to examine nonlinear signal-based control

This study introduces a numerically disturbed experimentation to address the shake table control degradation commonly observed in shake table experiments. This degradation is caused by nonlinear characteristics, such as seismic damage, in the experiments; however, observing such nonlinear characteristics is a major purpose of these experiments. In the proposed numerically disturbed experimentation, a structure is numerically simulated, and its structural responses are fed back as the disturbance signal to the table in the physical domain via real-time interaction. This enables us to examine the control performance of a shake table with a structure, without having to place an actual structure on it. This experimentation is beneficial in cases wherein new control methods are applied for shake table control because the control performance can be examined safely and efficiently under various structural conditions by using numerical simulations. The proposed experimentation was applied to the shake table control examination of nonlinear signal-based control (NSBC), which has a nonlinear signal feedback action for nonlinear structural dynamics, as well as inversion-based control (IBC), which is a common feedforward method. In the numerically disturbed experiments, NSBC accurately realized a seismic acceleration record on the shake table with severe nonlinear characteristics, whereas IBC exhibited control degradation due to nonlinear characteristics. Similar results were obtained using actual shake table experiments with a steel structure. Therefore, the proposed numerically disturbed experimentation can be an alternative to shake table experiments using structures.

Nonlinear backstepping hierarchical control of shake table using high‐gain observer

AbstractShake table testing is a common technique used to examine the responses of structures under dynamic loads. Shake table is often regulated using linear controller, such as proportional‐integral‐derivative (PID) controller. However, traditional PID control cannot consider inherent nonlinearities in the structural and control systems. In this paper, a series of novel backstepping control methods, which consider the nonlinearities in the structural and control systems, have been developed. In addition, high‐gain observers, which can provide highly accurate estimation of the shake table displacement, velocity and acceleration, are also developed. The proposed backstepping control methods and high‐gain observers are implemented in a hierarchical framework, where the high‐level backstepping controller generates the command signal for the low‐level controller to execute. A total of four hierarchical backstepping control methods, including the acceleration‐based backstepping hierarchical control (ABHC), the ABHC with high‐gain observer (ABHCO), the displacement‐based backstepping hierarchical control (DBHC) and the DBHC with high‐gain observer (DBHCO), have been implemented. Detailed parameter studies have been conducted to identify the optimized parameters for the proposed hierarchical backstepping control methods. The proposed control method is verified through a series of shake table tests. The experimental results show the ABHC, ABHCO, DBHC and DBHCO can all achieve high‐performance shake table control, especially with superior acceleration tracking over the traditional PID control. Overall, ABHCO achieves the best tracking performance for displacement, velocity and acceleration.

Acceleration‐based sliding mode hierarchical control algorithm for shake table tests

AbstractExisting control algorithms for seismic shake table tests (STTs) generally exhibit limitations such as poor acceleration tracking for displacement control, instability that results in table drift for direct acceleration, force, or velocity control, and the lack of a theoretical justification for hybrid control. Therefore, a reliable control algorithm has become key for effective shake table control. This paper presents acceleration‐based sliding mode control (SMC) as a solution to the drawbacks of the traditional force‐based SMC; in this manner, the influence of the force of the tested structure applied on the table as well as unmodeled complex nonlinear forces, such as friction, are counteracted. An acceleration‐based sliding mode hierarchical control (ASMHC) algorithm is proposed, where the acceleration‐based SMC is used as the high‐level controller to generate the corrected acceleration command, and the low‐level controller, that includes feed‐forward and feedback control, tracks the acceleration command in real time. The high‐level controller, having zero asymptotic stability, and the low‐level controller, designed based on the system transfer function, ensure tracking stability in time and frequency domains, respectively. The proposed ASMHC algorithm was first verified by a series of bare STTs, and was then applied to a real STT of a two‐story steel structure. The experimental results show that the proposed ASMHC algorithm can achieve good tracking of displacement, velocity, and acceleration in both time and frequency domains, which ensures accurate reproduction of seismic excitation in STTs.

Real-Time Hybrid Simulation of a Single-Span Girder Bridge Using a Shake Table Coupled with an Actuator

This paper recounts a real-time hybrid simulation (RTHS) that employed a shake table coupled with an actuator to evaluate the seismic performance of a single-span girder bridge. The test specimen for this RTHS was a scaled single-span girder bridge, which was subjected to Loma Prieta excitation in the test. In the RTHS, the bridge specimen, which lacked mass on top of the bridge deck, was physically tested by a shake table and an actuator, whilst the mass on the bridge, as well as the pile foundation and the soil were modeled numerically. OpenSEES was used for numerical modeling and OpenFresco was used for the communication between the test system and numerical model. An adaptive time series (ATS) technique was employed to compensate for time delay in the RTHS. In this way, a novel bridge engineering RTHS application case composed of shake table and actuator control was presented. To validate the results of the RTHS, a shake table test (STT) of the bridge structure with full mass on the bridge deck was conducted correspondingly. Comparing the RTHS and STT results, it can be concluded that acceleration histories, bearing deformation histories, and strain histories of the selected points matched well. The application of RTHS to assess the seismic behavior of the single-span girder bridge was reasonably verified in this paper.

A Shake Table Frequency-Time Control Method Based on Inverse Model Identification and Servoactuator Feedback-Linearization

Shake tables are one of the most widespread means to perform vibration testing due to their ability to capture structural dynamic behavior. The shake table acceleration control problem represents a challenging task due to the inherent non-linearities associated to hydraulic servoactuators, their low hydraulic resonance frequencies and the high frequency content of the target signals, among other factors. In this work, a new shake table control method is presented. The procedure relies on identifying the Frequency Response Function between the time derivative of pressure force exerted on the actuator’s piston rod and the resultant acceleration at the control point. Then, the Impedance Function is calculated, and the required pressure force time variation is estimated by multiplying the impedance by the target acceleration profile in frequency domain. The pressure force time derivative profile can be directly imposed on an actuator’s piston by means of a feedback linearization scheme, which approximately cancels out the actuator’s non-linearities leaving only those related to structure under test present in the control loop. The previous architecture is completed with a parallel Three Variable Controller to deal with disturbances. The effectiveness of the proposed method is demonstrated via simulations carried over a non-linear model of a one degree of freedom shake table, both in electrical noise free and contaminated scenarios. Numerical experiments results show an accurate tracking of the target acceleration profile and better performance than traditional control approaches, thus confirming the potential of the proposed method for its implementation in actual systems.

Recent Progress on Control Techniques of Shaking Table and Array Systems in China: An Overview

Shaking table is one of the important equipments for seismic research. It can accurately reproduce the seismic wave in the laboratory to accurately study the structural response. Based on the summary of domestic shaking table and array system control algorithms, the applications of various control algorithms and their advantages and disadvantages are summarized. The development trend of the shaking table control algorithm is analyzed and explained. It can be used as a reference for research on control technology of shaking tables at home and abroad.

Fuzzy-Sliding-Mode Supervisory Control of a Seismic Shake Table with Variable Payload for Robust and Precise Acceleration Tracking

ABSTRACTPrecise tracking of the earthquake acceleration profile in the presence of uncertainties is a challenge for the shake table control design. Design and implementation of a fuzzy-sliding-mode super- visory controller for an electric seismic shake table with variable payload is addressed in this paper. The proposed controller contains two layers including a proportional–integral loop and a fuzzy-sliding-mode supervisory controller. The controller is then implemented in the shake table and its performance is evaluated. The test results reveal successful performance of the proposed controller at robust tracking of some harmonic and seismic excitations in the presence of parametric uncertainties.

Generalised formulation of composite filters and their application to earthquake engineering test systems

SummaryThis paper addresses the problem of generating unmeasured kinetic data—and/or providing improvements in existing data—for the enhancement of performance characteristics of earthquake engineering test systems, such as shaking tables, reaction walls and other custom‐made test rigs. The approach relies upon the use of composite filters (CF), a method of data fusion that was originally conceived via transfer function formulation. The current work generalises the CF concept and extends its formulation into the state‐space domain, thereby providing a wider basis for application to test systems and their controllers, including those of a multivariable (coupled, multi‐axis) nature.Comparative simulation studies of shaking table control are presented that demonstrate the design techniques for state‐space CF and also their effectiveness for signal synthesis, noise suppression and performance improvement. Specific examples include the use of CF for displacement demand signal generation, velocity feedback generation and acceleration control. In each case, the essential principles behind CF—output signals with zero bias and zero drift—are consistently upheld. Copyright © 2017 John Wiley & Sons, Ltd.

Real-time hybrid simulation of a shear building with a uni-axial shake table

Recent investments in earthquake engineering research have produced an array of experimental equipment and testing capabilities worldwide. Laboratories are often equipped with shake tables, ranging from uni-axial tables to six-degree-of-freedom tables to multiple table arrays. These tables are capable of providing interface boundary conditions for substructure real-time hybrid simulation (RTHS). In the simplest case, the lower stories of a shear building are simulated numerically while the upper stories tested experimentally. Even this simple case reveals the challenges of RTHS using shake tables. Shake tables are highly nonlinear devices, making modeling and control a challenging task. Furthermore, the mass of the test specimen is typically large relative to the capacity of the table, leading to substantial coupling of the table and specimen dynamics. These challenges are exacerbated by the loop of action and reaction between numerical and experimental components in RTHS. Any delay or lag in the realization of the desired table trajectory and measurement of the base shear can introduce inaccuracies and instabilities into the loop. This research investigates the challenges of RTHS using shake tables through a simple uni-axial shake table and shear building specimen. A model-based shake table control approach is successfully implemented for online acceleration tracking. A Kalman filter is used to reduce measurement noise in the RTHS loop without introducing phase lag. Numerical and experimental substructures with low damping are selected to demonstrate the robustness of the proposed framework for a challenging RTHS scenario. Even for shake tables with large control-structure interaction and structures with low damping, the proposed framework is robust, reliable, and uses readily available equipment, providing a new experimental tool for laboratories with modest experimental testing capabilities.

Development of high‐performance shake tables using the hierarchical control strategy and nonlinear control techniques

SummaryConventional shake tables employ linear controllers such as proportional‐integral‐derivative or loop shaping to regulate the movement. However, it is difficult to tune a linear controller to achieve accurate and robust tracking of different reference signals under payloads. The challenges are mainly due to the nonlinearity in hydraulic actuator dynamics and specimen behavior. Moreover, tracking a high‐frequency reference signal using a linear controller tends to cause actuator saturation and instability. In this paper, a hierarchical control strategy is proposed to develop a high‐performance shake table. A unidirectional shake table is constructed at the University of British Columbia to implement and evaluate the proposed control framework, which consists of a high‐level controller and one or multiple low‐level controller(s). The high‐level controller utilizes the sliding mode control (SMC) technique to provide robustness to compensate for model nonlinearity and uncertainties experienced in experimental tests. The performance of the proposed controller is compared with a state‐of‐the‐art loop‐shaping displacement‐based controller. The experimental results show that the proposed hierarchical shake table control system with SMC can provide superior displacement, velocity and acceleration tracking performance and improved robustness against modeling uncertainty and nonlinearities. Copyright © 2015 John Wiley & Sons, Ltd.

Model‐based multi‐metric control of uniaxial shake tables

SUMMARYShake tables provide a direct means by which to evaluate structural performance under earthquake excitation. Because the entire structure is mounted on the base plate and subjected to the ground motion in real time, dynamic effects and rate‐dependent behavior can be accurately represented. Shake table control is not straightforward as the desired signal is an acceleration record, while most actuators operate in displacement feedback for stability. At the same time, the payload is typically large relative to the capacity of the actuator, leading to pronounced control‐structure interaction. Through this interaction, the dynamics of the specimen influence the dynamics of the shake table, which can be problematic when specimens change behavior because of damage or other nonlinearities. Moreover, shake tables are themselves inherently nonlinear, making it difficult to accurately recreate a desired acceleration record over a broad range of amplitudes and frequencies. A model‐based multi‐metric shake table control strategy is proposed to improve tracking of the desired acceleration of a uniaxial shake table, remaining robust to nonlinearities including changes in specimen condition. The proposed strategy is verified for the shake table testing of both linear and nonlinear structures. Copyright © 2013 John Wiley & Sons, Ltd.

Direct Acceleration Feedback Control of Shake Tables with Force Stabilization

This study presents a new strategy for shake table control that uses direct acceleration feedback without need for displacement feedback. To ensure stability against table drift, force feedback is incorporated. The proposed control strategy was experimentally validated using the shake table at the Johns Hopkins University. Experimental results showed that the proposed control strategy produced more accurate acceleration tracking than conventional displacement-controlled strategies. This article provides the control architecture, details of the controller design, and experimental results. Furthermore, the impact of input errors in shake table testing on the structural response is also discussed.

Simulink Application in Structural Vibration Control and Simulation

This paper mainly introduces the application of simulink in structural vibration control and simulation. It introduces the method and procedure of using simulink to establish the control simulation program.Thus obtained, for the establishment of whole shaking table control system and the simulation of control system, simulink has unique advantages, it is the best software for the research and development of the shaking table control system.

Method of Compensation Control for Shaking Table

This paper presents the defects existing in shaking table control including the overshoot of displacement under low-middle frequency input using three variable parameter controls, the narrow bandwidth resulting from the performance of servo-valve and low accuracy of seismic wave reproduction because of specimen and table interaction. The effects of these factors on the stability and control accuracy of shaking table are discussed, and then the reasons of these problems existing are analyzed. The aim of this paper is to improve the stability and control accuracy of shaking table, thus, some corresponding strategies for compensation control are proposed. And a series of shaking table tests with one-story frame and two-story frame for verifying the validity of compensation control algorithm are performed.

Shaking-Table Control Taking Account of Reaction Force (Two-Degree-of-Freedom Controller Design of Shaking-Table Acceleration Control)

Shaking-Table Control Taking Account of Reaction Force (Two-Degree-of-Freedom Controller Design of Shaking-Table Acceleration Control)

High-fidelity Tracking Control of Electric Shaking Tables

This paper proposes a design method of tracking control for electric shaking tables via the stochastic optimal control theory with preview action based on a third-order model with respect to the jerk, acceleration, velocity and displacement of the table. The reaction force caused by the dynamic motion of a test structure subjected to seismic disturbances can be regarded as a random disturbance for the shaking table. The mission of our tracking controller is accurately to reproduce the earthquake ground motions using the derived third-order model and the preview information of the displacement of the ground motions. An augmented discrete-time stochastic system of an incremental state and an incremental tracking error corresponding to the shaking table is constructed. This system is subject to the sum of the reaction force of the test structure and its derivative which is modeled by a white Gaussian noise. Combining this system with a command generator for making the preview information, a stochastic optimal tracking control based on the noisy observation data is constructed for the resultant system.