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Summary: It is realized that force exerted at the two ends of an inerter is proportional to their relative acceleration between them. Generally, a mechanical inerter has much smaller mass than a conventional mass damper when identical inertial force is attained due to its mechanical characteristics. In this study, a novel active control system named active inerter damper (AID) is proposed to mitigate seismic response of buildings which is composed of a mechanical ball‐screw inerter, a servo‐hydraulic actuator, sensors, and a digital controller. Compared to an active mass damper, the AID requires less mass support structure and installation space in real engineering practice. In this paper, two force tracking controllers for the AID system are proposed, designed, and validated in the laboratory first which aim to impose control force on buildings accurately because force tracking performance of an active control system is extremely crucial to its seismic control performance. Afterwards, shake table tests of a three‐story steel specimen with an AID system are conducted to validate the feasibility of AID control application for buildings. The control force is computed from a machine learning‐based controller that utilizes acceleration feedback directly from the steel specimen. Experimental results demonstrate that force tracking performance of the AID system is satisfactory. Meanwhile, the AID system mitigates seismic response of the steel specimen successfully and effectively. [ABSTRACT FROM AUTHOR]

Seismic responses of high-rise buildings are dominated by the first few vibration modes; therefore, high-floor responses contain long predominant vibration periods. However, it may not be achievable to investigate the seismic performance of nonstructural facilities at high levels of high-rise buildings in the laboratory by using seismic shake tables because of the actuator stroke limitation. In this study, an advanced control strategy that incorporates a transfer system with modern control algorithms is proposed for shake tables to replicate high-floor responses of high-rise buildings subjected to earthquakes. First, design diagrams are proposed to determine the parameters of the transfer system. Then, a set of friction pendulums is adopted as the transfer system for the proof-of-concept stage. A mathematical model for the set of friction pendulums is developed for numerical studies prior to real experimental validation. Three linear controllers and three nonlinear controllers are designed and synthesized to verify the feasibility and applicability of the proposed strategy. Finally, the friction pendulum set is installed on a uniaxial shake table to replicate the roof responses of a 34-story building subjected to historical earthquakes. Experimental results demonstrate the proposed control strategy successfully replicates floor responses of the high-rise building that cannot be achieved formerly. [ABSTRACT FROM AUTHOR]

Damage assessment in postearthquake reconnaissance of civil structures has traditionally relied upon the judgment of experienced site inspectors. In a step toward eliminating the need for on-site inspections, this paper presents a method for automatic postdisaster structural damage assessment of reinforced concrete (RC) structures. The method uses digital image correlation to automatically detect cracks in RC structural elements and correlates the analyzed crack distributions to a damage index using fractal dimension. The method is applied in this study to track the progression of damage in a planar RC shear wall and a cylindrical RC containment vessel tested in a laboratory under reversed cyclic loading. The results from the proposed damage index are compared with quantitative and qualitative damage indices that have been used in the past to evaluate damage levels in RC structures. The results demonstrate the ability of the method to measure crack distributions and automatically correlate them to a damage index. The method is also applied to an RC shear wall tested under an actual earthquake ground motion record using hybrid simulation to evaluate its performance in a more realistic damage assessment scenario. The results show that the method is able to track the progression of damage to an RC structural element in a realistic earthquake damage scenario. Based on the results, damage grades are proposed that can be used to relate the automatically computed damage index to a specific damage level. The results show great promise for the automatic damage assessment method and is a first step towards automated postdisaster damage assessment of RC structures using digital image correlation. [ABSTRACT FROM AUTHOR]

• Essential real-time hybrid simulation (RTHS) technique has been developed for the active inerter damper (AID) system on flexible specimens. • Three force acquisition methods have been proposed and applied to RTHS, and their effects on RTHS accuracy have been investigated thoroughly. • Two control methods for AID have been validated through RTHS, and the results are cross compared and discussed. • A surrogate model has been trained and replaced the state feedback controller in RTHS successfully which has many potential applications in structural active control. Active structural control has been recognized as an intelligent method to mitigate seismic vibrations of structures by generating superior supplemental damping in structural engineering studies. Recently, active inerter damper (AID) that consists of an inerter and an actuation system has been evolved from active mass damper. AID has advantages of small volume and light weight because of the mechanical properties of inerter that amplify the inertial force by numerous times the mass of the inerter; therefore, installation of an AID system becomes simple in real engineering applications. However, it is difficult to validate seismic control performance of a multi-story specimen with an AID system in structural laboratories limited by capacity of testing facilities. In this study, real-time hybrid simulation (RTHS), which combines experimental testing with numerical simulation is applied to evaluate the control performance of the AID system. A 10-story shear building is numerically simulated as a benchmark building controlled by the AID, which is physically driven in the structural laboratory. A modal linear-quadratic regulator (LQR) with optimized weighting matrices is designed for generating the desired control force for the AID. Meanwhile, a surrogate model of the modal LQR is trained and implemented for comparison purpose. In addition, two force tracking controllers are implemented to reproduce the desired control force through the AID. Furthermore, three approaches for acquiring the achieved force of AID are proposed and employed to feedback the control force to the numerical model for completing the RTHS loop. Finally, mitigation of seismic response is compared and discussed methodically based on the RTHS results. This study suggests the most appropriate RTHS technique for evaluating the control performance of buildings with the AID system. [ABSTRACT FROM AUTHOR]

Shaking table testing has been regarded as one of the most straightforward experimental approaches to evaluate the seismic response of structures subjected to earthquake ground motions. Therefore, reproducing an acceleration time history accurately becomes crucial for shaking table testing. In this study, a control framework for uniaxial shaking tables is proposed which incorporates a feedback controller into a weighted command shaping controller. It implements through outer-loop control in addition to the conventional existing proportional-integral inner-loop control. The model-based command shaping controller which considers the control-structure interaction can be designed to shape either displacement or acceleration references. The weightings for the shaped displacement and acceleration can be calculated by a linear interpolation algorithm which considers the dominant frequency of the desired acceleration time history as well as the correlation between the displacement and acceleration responses of the shaking table. Accordingly, the weighted combination of the shaped displacement and acceleration generates the control command to the shaking table. On the other hand, the feedback controller deals with the system uncertainty and modeling error. Loop-shaping design method is adopted to synthesize the feedback controller. Finally, the control framework is verified by several shaking table tests with and without a flexible specimen. Experimental results demonstrate the performance and robustness of the proposed control framework for shaking table test systems. [ABSTRACT FROM AUTHOR]

SUMMARY Real-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. [ABSTRACT FROM AUTHOR]