Real-time Hybrid Testing Research Articles

Real-time hybrid testing with equivalent force control method incorporating Kalman filter

Summary The equivalent force control (EFC) method has been developed for real-time hybrid testing to replace the numerical iteration of implicit integration with a force-feedback control loop. With this control loop, the EFC method can also compensate for the time delay in real-time hybrid testing. However, the delay compensation effect of the EFC can be influenced by factors such as noises in the measured displacement. This paper discusses the influence of the measurement noises on real-time hybrid testing with the EFC. The Kalman filter is proposed to filter the noises in the measured actuator displacement for improved performance. A higher proportional gain in the PID controller, which improves the effect of time delay compensation of the EFC method, can be allowed without losing stability when incorporating the Kalman filter. A series of real-time hybrid tests were conducted, and the results validated that the EFC method with Kalman filter can effectively compensate for the time delay. Copyright © 2015 John Wiley & Sons, Ltd.

Numerical assessment of step-by-step integration methods in the paradigm of real-time hybrid testing

Real-time hybrid testing (RTHT) involves virtual splitting of the structure into two parts: physical substructure that contains the key region of interest which is tested in a laboratory and numerical substructure that contains the remaining part of the structure in the form of a numerical model. This paper numerically assesses four step-by-step integration methods (Central difference method (CDM), Operator splitting method (OSM), Rosenbrock based method (RBM) and CR-integration method (CR)) which are widely used in RTHT. The methods have been assessed in terms of stability and accuracy for various realistic damping ratios of the physical substructure. The stability is assessed in terms of the spectral radii of the amplification matrix while the accuracy in terms of numerical damping and period distortion. In order to evaluate the performance of the methods, five carefully chosen examples have been studied - undamped SDOF, damped SDOF, instantaneous softening, instantaneous hardening and hysteretic system. The performance of the methods is measured in terms of a non-dimensional error index for displacement and velocity. Based on the error indices, it is observed that OSM and RBM are robust and performs fairly well in all the cases. CDM performed well for undamped SDOF system. CR method can be used for the system showing softening behaviour. The error indices indicate that accuracy of OSM is more than other method in case of hysteretic system. The accuracy of the results obtained through time integration methods for different damping ratios of the physical substructure is addressed in the present study. In the presence of a number of integration methods, it is preferable to have criteria for the selection of the time integration scheme. As such criteria are not available presently, this paper attempts to fill this gap by numerically assessing the four commonly used step-by-step methods.

C107 中間階免震建築物のMR回転慣性質量ダンパーによるセミアクティブ制御(OS5 建設構造物の耐震・免震・制振2)

The dynamic characteristics of mid-story isolated buildings and seismic response reduction due to a semi-active control system were investigated using a three-lumped-mass model that simplified the sixteen story building with an isolation layer in the sixth story and that model. A semi-active control method using a rotary inertia mass damper filled with magnetorheological fluid (MR fluid) was proposed. The damper shows both mass amplification effect due to rotational inertia and variable damping effect due to the MR fluid. The damping force is controlled by the strength of the magnetic field that is applied to the MR fluid. It is determined by using the electric current, which is calculated by the proposed semi-active control method based on the velocity of the isolation layer relative to the layer just underneath it. Real-time hybrid tests using an actual damper and simulations using a building model were conducted to check the damper model; the test results were in good agreement with the simulation results. The simulation results suggest that the response displacement of the structure above the isolation layer is significantly reduced, without increasing the response acceleration of the entire structure against near-fault pulse and long-period ground motions. The proposed semi-active control using an MR rotary inertia mass damper was confirmed to be effective for mid-story isolated buildings.

Analysis of delay compensation in real-time dynamic hybrid testing with large integration time-step

With the sub-stepping technique, the numerical analysis in real-time dynamic hybrid testing is split into the response analysis and signal generation tasks. Two target computers that operate in real-time may be assigned to implement these two tasks, respectively, for fully extending the simulation scale of the numerical substructure. In this case, the integration time-step of solving the dynamic response of the numerical substructure can be dozens of times bigger than the sampling time-step of the controller. The time delay between the real and desired feedback forces becomes more striking, which challenges the well-developed delay compensation methods in real-time dynamic hybrid testing. This paper focuses on displacement prediction and force correction for delay compensation in the real-time dynamic hybrid testing with a large integration time-step. A new displacement prediction scheme is proposed based on recently-developed explicit integration algorithms and compared with several commonly-used prediction procedures. The evaluation of its prediction accuracy is carried out theoretically, numerically and experimentally. Results indicate that the accuracy and effectiveness of the proposed prediction method are of significance.

Simulation of large-scale numerical substructure in real-time dynamic hybrid testing

A solution scheme is proposed in this paper for an existing RTDHT system to simulate large-scale finite element (FE) numerical substructures. The analysis of the FE numerical substructure is split into response analysis and signal generation tasks, and executed in two different target computers in real-time. One target computer implements the response analysis task, wherein a large time-step is used to solve the FE substructure, and another target computer implements the signal generation task, wherein an interpolation program is used to generate control signals in a small time-step to meet the input demand of the controller. By using this strategy, the scale of the FE numerical substructure simulation may be increased significantly. The proposed scheme is initially verified by two FE numerical substructure models with 98 and 1240 degrees of freedom (DOFs). Thereafter, RTDHTs of a single frame-foundation structure are implemented where the foundation, considered as the numerical substructure, is simulated by the FE model with 1240 DOFs. Good agreements between the results of the RTDHT and those from the FE analysis in ABAQUS are obtained.

Real-Time Dynamic Hybrid Testing Coupling Finite Element and Shaking Table

In this article, a Simulink simulation block with the finite element function is developed on the basis of S-function and implemented as the numerical substructure of real-time dynamic hybrid testing. Thereby, a real-time dynamic hybrid testing system coupling finite element calculation and shaking table testing is achieved. Using the developed system, a shear frame mounted on the soil foundation is tested, in which the shear frame is simulated as the physical model and the foundation is simulated as the finite element model with 132 degrees of freedom. Several cases of the dynamic behavior of soil-structure interaction are studied.

Grid-based recording and replay architecture in hybrid remote experiment using distributed streaming network

We present a grid-based system that enables researchers in civil engineering to conduct hybrid remote experiments as well as to record and replay these experiments. The system has been designed for Real Time Hybrid Testing Facility in the Korea Construction Engineering Development (KOCED) project and has been implemented based on the Open Service Grid Architecture (OGSA) and the Open System for Earthquake Engineering Simulation (OpenSees) for modeling and computational simulation on structural systems. Users can access the system with a Java client for data visualization and video monitoring through an Internet portal using a web browser. The system runs on a network of distributed NaradaBrokering streaming servers and exploits RFT and GridFTP for reliable file transfer. The main contribution of this paper is that we propose an scalable grid-based recording and replay architecture for remote experiment using distributed streaming network that can scale to support a growing large number of clients simultaneously. We also evaluate the performance of the proposed extensible architecture of distributed servers with mathematical modeling as well as simulations to show how it scales to cope with a growing large number of clients at the same time.

Real‐time hybrid testing of a smart base isolation system

SUMMARYReal‐time hybrid testing is a very effective technique for evaluating the dynamic responses of rate‐dependent structural systems subjected to earthquake excitation. A smart base isolation system has been proposed by others using conventional low‐damping isolators and controllable damping devices such as magnetorheological (MR) dampers to achieve specified control target performance. In this paper, real‐time hybrid tests of a smart base isolation system are conducted. The simulation is for a base‐isolated two‐degrees‐of‐freedom building model where the superstructure and the low‐damping base isolator are numerically simulated, and the MR damper is physically tested. The target displacement obtained from the step‐by‐step integration of the numerical substructure is imposed on the MR damper, which is driven by three different control algorithms in real‐time. To compensate the actuator delay and improve the accuracy of the test, an adaptive phase‐lead compensator is implemented. The accuracy of each test is investigated by using the root mean square error and the tracking indicator. Experimental results demonstrate that the hybrid testing procedure using the proposed actuator compensation techniques is effective for investigating the control performance of the MR damper in a smart base isolation system. Copyright © 2013 John Wiley & Sons, Ltd.

강 뼈대 구조물의 다자유도 실시간 하이브리드 동적 실험

하이브리드 실험은 수치해석 모형과 물리적 부분구조 모형사이의 상호작용을 통하여 구조물의 거동을 예측하는 실험법이다. 본 연구에서는 지진하중 재하 시 1경간 2층 강 뼈대 구조물에 대한 다자유도 하이브리드 실험을 수행하고 유효성을 확보하는데 그 목적이 있다. 이를 위해 전용 하이브리드 수치해석 프로그램인 FEAPH을 개발하였으며, 최적화된 시스템을 구축하였다. FEAPH은 고정 반복법(Fixed iteration)과 병렬화(Parallelization) 기법을 적용하여 순차적 해석에서 발생되는 비효율적 연산을 개선하였다. 또한, 종전에 데이터 통신과 부분구조물과 해석프로그램간의 인터페이스를 간략화하여 하이브리드 시스템 구성을 최적화 하였다. 그 결과, 입력 가진시간(30초) 대비 약 10%의 실험시간이 소요되었다. 시스템의 신뢰성을 검증하고 선형실험과 강 뼈대 구조물의 동적거동을 예측하기 위해 비선형 실험을 수행하였으며 수치해석과의 변위응답이력은 거의 일치 하였다. 그러나 최대변위에 대한 응답은 다소 차이를 보였으며, 이는 재료 비선형성에 대한 해석상의 오차와 영구변형에 의해 발생한 것으로 판단된다. 따라서 적절한 재료 비선형 모델과 알고리즘의 개선이 이루어지면, 실시간 하이브리드 시스템은 구조물의 동적거동을 예측하는데 유용하게 활용될 것이며, 추후 진동대 실험을 대체할 수 있는 효과적인 실험 방법이 될 것으로 판단된다. The hybrid test is one of the most advanced test methods to predict the structural dynamic behavior with the interaction between a physical substructure and a numerical modeling in the hybrid control system. The purpose of this study is to perform the multi-directional dynamic test of a steel frame structure with the real-time hybrid system and to evaluate the validation of the results. In this study, FEAPH, nonlinear finite element analysis program for hybrid only, was developed and the hybrid control system was optimized. The inefficient computational time was improved with a fixed number iteration method and parallel computational techniques used in FEAPH. Furthermore, the previously used data communication method and the interface between a substructure and an analysis program were simplified in the control system. As the results, the total processing time in real-time hybrid test was shortened up to 10 times of actual measured seismic period. In order to verify the accuracy and validation of the hybrid system, the linear and nonlinear dynamic tests with a steel framed structure were carried out so that the trend of displacement responses was almost in accord with the numerical results. However, the maximum displacement responses had somewhat differences due to the analysis errors in material nonlinearities and the occurrence of permanent displacements. Therefore, if the proper material model and numerical algorithms are developed, the real-time hybrid system could be used to evaluate the structural dynamic behavior and would be an effective testing method as a substitute for a shaking table test.

Comparative Studies of Semiactive Control Strategies for MR Dampers: Pure Simulation and Real-Time Hybrid Tests

This paper presents comparisons of the performances of three semiactive control algorithms for use with multiple magnetorheological (MR) dampers. The three controllers are (1) the clipped-optimal controller, (2) the decentralized output feedback polynomial controller, and (3) the simple passive controller. These controllers use different types of inputs to calculate control signals for the MR dampers, based on different control mechanisms. To investigate the advantages of each controller, a three-degree-of-freedom steel moment-resisting frame, designed using a performance-based design methodology, was developed. The performance was investigated by using four different earthquakes utilized during the design of the building frame. Comparisons of the controllers’ performance were carried out in terms of reduction in the maximum interstory drifts, displacements, absolute accelerations, and control forces. Real-time hybrid tests were carried out to validate these comparisons.

Introduction of Shaking Table Test of Rigid Frame Bridge Model

To investigate the seismic response of long-span rigid frame bridges with high-pier, the shaking table test of a 1/10 scaled rigid frame bridge model is introduced in this paper. Details about test equipment, model design, test arrangement, input ground motion waves and test principle are provided. The response of bridge model under the seismic excitation included the uniform excitation and the multi-support excitation is observed. The influence of the soil-structure interaction on the bridge is considered through the real-time dynamic hybrid testing method. The impact effect for different ground motion input during the test is discussed. The influence of multi-support excitation, soil-structure interaction and impact effect on structural seismic responses are studied based on the test results. The isolation effectiveness and the damping effect are discussed as well.

A novel integrated compensation method for actuator dynamics in real-time hybrid structural testing

SUMMARY Real-time hybrid structural testing is a novel method that is gaining acceptance for examination of civil engineering structures. This method facilitates testing of an unknown physical component coupled with an analytical model of the remainder of the structure. A primary challenge in performing real-time hybrid testing to accurately reproduce the behavior of the complete system is the appropriate compensation of actuator dynamics. Accounting for the magnitude roll-off while also reducing the time lags to a minimal value is critical to ensure both accuracy and stability of a real-time hybrid structural test. Here, a new compensation scheme is proposed that integrates the best features of two commonly used approaches. The proposed method, simply called integrated compensation, uses online delay estimation to improve on the performance of inverse compensation method for problems in which the effective time delay is not constant over the frequency band of interest. Two real-time experiments are conducted to examine the capabilities of the approach for achieving good displacement tracking. Both experiments focus on the use of a device as the physical component. One experiment uses a linear spring as the physical component, and one uses a controllable, nonlinear damping device. The actuator displacement tracking results are compared with the results using other compensation approaches. The results from these experiments demonstrate that the proposed integrated compensation method is very effective and suitable for real-time hybrid testing using a device as the physical component. Copyright © 2012 John Wiley & Sons, Ltd.

Development of Software and Hardware Architecture for Real-Time Dynamic Hybrid Testing and Application to a Base Isolated Structure

Real-Time Dynamic Hybrid Test (RTDHT) is a promising experimental testing technique, which combines numerical simulation and experimental testing of physical specimen in a complementary and efficient way. However, taking advantage of both numerical and experimental capabilities requires facing issues related to both environments. In this article, the design and implementation of a RTDHT hardware and software architecture is presented. Issues related both to the numerical model and to the experimental setup are discussed; this is done from a general perspective, as well as referring to a base isolated structure which represents the implemented case study.

Seismic performance of structures incorporating magnetorheological dampers with pseudo-NEGATIVE STIFFNESS

SUMMARY Pseudo-negative stiffness control is a control scheme that is aimed to track, in a passive energy dissipation fashion, a target spring force with negative stiffness when possible. In this study, it is proved that systems with pseudo-negative stiffness control have the property of homogeneity even though they are nonlinear systems. The harmonic response analyses reveal that the pseudo-negative stiffness reduces the resonant frequency of the system. Seismic response spectrum analyses show that both acceleration and displacement can be reduced with the pseudo-negative stiffness control when the structural period is long and damping level is not high. Pseudo-negative stiffness control of a five-story base-isolated structure incorporating magnetorheological damper is studied through analytical and real-time hybrid test methods. The results show that displacement and acceleration responses with pseudo-negative stiffness control are lower than those with passive-off control and isolator alone, whereas the displacement response with pseudo-negative stiffness is greater than the passive-on control. Copyright © 2011 John Wiley & Sons, Ltd.

고정반복법에 의한 암시적 HHT 시간적분법을 이용한 철근콘크리트 골조구조물의 실시간 하이브리드실험

고정반복법에 의한 암시적 HHT 시간적분법을 이용하여 3층 3경간 철근콘크리트 골조구조물을 수치해석모형과 물리적 분구조모형으로 나누어 실시간 하이브리드실험을 실시하였다. 물리적 부분구조모형으로는 1층 내부 비연성기둥 1개소가 선택되었고, 수치해석모형에 일축 방향의 지진하중을 시편이 심한 손상에 의하여 파괴에 이를 때까지 작용시켰다. 비선형 유한요소해석 프로그램인 Mercury가 실시간 하이브리드실험을 위하여 새로이 개발 및 적용되었다. 실험결과는 물리적 부분구조모형의 상부 수평방향 층간변위비를 OpenSees에 의한 수치해석시뮬레이션과 진동대실험의 그것과 비교하였다. 본 실험은 가장 복잡한 실시간 하이브리드실험 중의 하나이고, 하드웨어, 알고리즘 그리고 모형에 대한 기술적인 내용을 본 논문에 자세히 설명하였다. 수치해석모형의 개선, 물리적 부분구조 모형 접선강성행렬의 유한요소해석 프로그램에서의 평가 그리고 하중기반 보-요소의 요소상태결정의 연산시간을 줄이기 위한 소프트웨어의 개선이 이루어진다면 실시간 하이브리드실험과 진동대실험결과의 비교는 권장할 만하다. 그리고 "지진과 같은 동적하중하의 복잡한 구조물의 수치해석시뮬레이션"이라는 목적을 위하여 실시간 하이브리드실험은 동적하중에 대한 실험적 검증을 점진적으로 수치해석모형으로 대체하기 위한 저비용-고효율 실험법으로서의 가치를 충분히 가지고 있다고 할 수 있다. A real-time hybrid test of a 3 story-3 bay reinforced concrete frame which is divided into numerical and physical substructure models under uniaxial earthquake excitation was run using a fixed iteration implicit HHT time integration method. The first story inner non-ductile column was selected as the physical substructure model, and uniaxial earthquake excitation was applied to the numerical model until the specimen failed due to severe damage. A finite-element analysis program, Mercury, was newly developed and optimized for a real-time hybrid test. The drift ratio based on the top horizontal displacement of the physical substructure model was compared with the result of a numerical simulation by OpenSees and the result of a shaking table test. The experiment in this paper is one of the most complex real-time hybrid tests, and the description of the hardware, algorithm and models is presented in detail. If there is an improvement in the numerical model, the evaluation of the tangent stiffness matrix of the physical substructure model in the finite element analysis program and better software to reduce the computational time of the element state determination for the force-based beam-column element, then the comparison with the results of the real-time hybrid test and the shaking table test deserves to make a recommendation. In addition, for the goal of a "Numerical simulation of the complex structures under dynamic loading", the real time hybrid test has enough merit as an alternative to dynamic experiments of large and complex structures.

Response to ‘Discussion of paper “Real-time hybrid testing using the unconditionally stable explicit CR integration algorithm” by Cheng Chen, James M. Ricles, Thomas M. Marullo and Oya Mercan’ in Earthquake Engineering and Structural Dynamics 2009; 38:23-

Earthquake Engineering & Structural DynamicsVolume 41, Issue 5 p. 1065-1067 Author's Reply Response to ‘Discussion of paper “Real-time hybrid testing using the unconditionally stable explicit CR integration algorithm” by Cheng Chen, James M. Ricles, Thomas M. Marullo and Oya Mercan’ in Earthquake Engineering and Structural Dynamics 2009; 38:23–44 Cheng Chen, Corresponding Author Cheng Chen [email protected] School of Engineering, San Francisco State University, San Francisco, CA, USA Cheng Chen, School of Engineering, San Francisco State University, San Francisco, CA, USA. E-mail: [email protected]Search for more papers by this authorJames M. Ricles, James M. Ricles [email protected] Civil and Environmental Engineering, Lehigh University, Bethlehem, PA, USASearch for more papers by this author Cheng Chen, Corresponding Author Cheng Chen [email protected] School of Engineering, San Francisco State University, San Francisco, CA, USA Cheng Chen, School of Engineering, San Francisco State University, San Francisco, CA, USA. E-mail: [email protected]Search for more papers by this authorJames M. Ricles, James M. Ricles [email protected] Civil and Environmental Engineering, Lehigh University, Bethlehem, PA, USASearch for more papers by this author First published: 16 September 2011 https://doi.org/10.1002/eqe.1160Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Volume41, Issue525 April 2012Pages 1065-1067 RelatedInformation

Real-time dynamic hybrid testing for soil–structure interaction analysis

Simulating dynamic soil–structure interaction (SSI) problems is a challenge when using a shaking table because of the semi-infinity of soil foundations. This paper develops real-time dynamic hybrid testing (RTDHT) for SSI problems in order to consider the radiation damping effect of the semi-infinite soil foundation using a shaking table. Based on the substructure concept, the superstructure is physically tested and the semi-infinite foundation is numerically simulated. Thus, the response of the entire system considering the dynamic SSI is obtained by coupling the numerical calculation of the soil and the physical test of the superstructure. A two-story shear frame on a rigid foundation was first tested to verify the developed RTDHT system, in which the top story was modeled as the physical substructure and the bottom story was the numerical substructure. The RTDHT for a two-story structure mounted on soil foundation was then carried out on a shaking table while the foundation was numerically simulated using a lumped parameter model. The dynamic responses, including acceleration and shear force, were obtained under soft and hard soil conditions. The results show that the soil–structure interaction should be reasonably taken into account in the shaking table testing for structures.

Real-Time Hybrid Test Validation of a MR Damper Controlled Building with Shake Table Tests

Real-time hybrid testing (RTHTing) is a relatively new form of experimental testing where only the critical components of the system are physically tested while the rest of the structure is simulated. A RTHT can provide a cost-effective means for testing semiactive controlled civil structures. This paper describes the experimental validation of the RTHT facility at the University of Connecticut through comparison of RTHT results with corresponding shake table responses of a Magneto-Rheological (MR) fluid damper controlled test structure. The two-story structure has an MR damper connected between the ground and first story and is excited by ground accelerations. For the shake table tests the fully physical building model and MR damper are tested on a medium-scale shake table. In the RTHT the MR damper alone will be tested physically while the rest of the test structure and ground excitation is simulated in the RTHT control computer. The performance of the RTHT is validated by comparing the building responses and measured damper force with those from the shake table test in both the time and frequency domains.

EFFECTIVENESS OF REAL TIME HYBRID TEST IN SEMI-ACTIVE CONTROLLED BASE ISOLATION SYSTEM

In the base isolation system, when the response is controlled, it is said that the semi-active control by the variable damper is effective, because it can decrease the response displacement without raising the absolute acceleration. Authors use Magneto-rheological fluid damper (MR damper) for the semi-active control, and conducted the real time hybrid test that considers the uncertainty of modeling of the MR damper. The results of the real time hybrid test are compared with those of shaking table test and analytical simulation. Thus, the effectiveness of the evaluation of the semi-active control in the base isolation system by the real time hybrid test is verified. In this study, the optimum control theory is used for control techniques.

Real-time Hybrid Test on a Semi-actively Controlled Building Structure Equipped with Full-scale MR Dampers

The real-time hybrid testing method (RT-HYTEM) is a structural testing technique in which the numerical integration of the equation of motion for a numerical substructure and the physical testing for an experimental substructure are performed simultaneously in real-time. This article presents the quantitative evaluation of the seismic performance of a building structure installed with a magnetorheological (MR) damper using RT-HYTEM. A building model is identified from the force-vibration testing results of a full-scale five-story building and is used as the numerical substructure, and an MR damper corresponding to an experimental substructure is physically tested using a universal testing machine (UTM). First, the force required to drive the displacement of the story, at which the MR damper is located, is measured from the load cell attached to the UTM. The measured force is then returned to a control computer to calculate the response of the numerical substructure. Finally, the experimental substructure is excited by the UTM with the calculated response of the numerical substructure. The RT-HYTEM implemented in this study is validated because the real-time hybrid testing results obtained by application of sinusoidal and earthquake excitations and the corresponding analytical results obtained using the Bouc-Wen model as the control force of the MR damper with respect to input currents are in good agreement. Also, the results from RT-HYTEM for the passive -on and -off control show that the structural responses did not decrease further by the excessive control force, but decreased due to the increase of the current applied to the MR damper. Also, two semi-active control algorithms (modulated homogeneous friction and the clipped-optimal control algorithms) are applied to the MR damper in order to optimally control the structural responses. To compare the RT-HYTEM and numerical results, Bouc-Wen model parameters are identified for each input current. The results of the comparison of experimental and numerical responses show that it is more practical to use RT-HYTEM in semi-active devices such as MR dampers. The test results show that a control algorithm can be experimentally applied to the MR damper using RT-HYTEM. This article provides a discussion on each algorithm with respect to the seismic performances.