Pei-Ching Chen

Large‐scale multi‐axial loading structural test equipment (LMLSTE) is a very important tool to evaluate the seismic capacity of complex structural systems and components. This promotes the continuous development of LMLSTE and implementation all over the world. The structural test techniques are also developed together with LMLSTE. The two complement each other and promote each other. This study provides an overview of the current development of LMLSTE: basic components, principles of operation, performance indicators, as well as its applications in structural tests. To introduce the developmental context of LMLSTE, they are discussed separately into four categories: multi‐axial sub‐assemblage testing (MAST), load and boundary condition box (LBCB), pressure‐shear machine, and multi‐usage structural testing (MUST) system. The key technical challenges in LMLSTE are summarized, including coordinated control of multi‐axial with different stiffness, multi‐input and multi‐output decoupling control, actuator redundancy constraints, and accurate force measurement. Finally, the potential LMLSTE are presented.

The seismic resilience has become a critical concern for power systems for high-impact, low-probability disasters such as severe earthquakes. In order to enhance seismic resilience for power systems, a novel protective device, the Passive Over-Current Trip (POCT), has been designed in this paper. In the design, the POCT integrates a fuse and a mechanical switch, able to trigger the breaker to interrupt the circuit to ensure effective protection. The POCT has the trip-free feature as it fulfills its protective function without the need for an electric relay requiring a continuous power supply. The proposed POCT provides an immediate and reliable solution for the protection in high and ultra-high voltage applications. To validate the effectiveness of the proposed POCT, shockproof and tripping tests were conducted. A seismic test waveform from the Fukushima earthquake that occurred on March 11, 2011 was used to test POCT. Under such a severe earthquake, no structural or mechanical damage on the associated components in the POCT was found. Also, the POCT is also in compliance with IEEE 693 standard. Finally, various tripping tests show that the POCT can operate within 18 ms when a fault occurs in a power system, which is much shorter than that of a typical high-voltage fuse.

Real‐time hybrid simulation (RTHS) provides an effective approach for assessing structural responses under dynamic excitation. However, performing RTHS with a complex nonlinear numerical substructure is challenging, as computations must be completed within predefined time steps. In this study, a RTHS framework which contains a rate‐dependent experimental substructure and a nonlinear numerical substructure has been proposed and verified. An OpenSees model was constructed to simulate a three‐story, one‐bay steel building with viscous dampers at each floor and was used to generate the training dataset through a large number of nonlinear time‐history analyses. A Recursive Long Short–Term Memory (LSTM) neural network model was trained to predict the nonlinear structural responses using ground acceleration and time‐delayed damper force located at the first story. Hence, the Recursive‐LSTM model served as a surrogate model for the numerical substructure, implicitly incorporating delay compensation for the experimental substructure. After the training was completed, offline testing was performed to realize the stability of the RTHS framework. Then, online RTHS with a virtual damper taken as the experimental substructure was conducted to further confirm the feasibility and accuracy. Afterwards, a nonlinear rotary fluid viscous damper (RFVD) was fabricated as the actual experimental substructure, whose dynamic response was not considered in training the Recursive‐LSTM model. Finally, RTHS with the RFVD was completed successfully and stably, demonstrating the capability of a well‐trained Recursive‐LSTM model to serve as a nonlinear numerical substructure incorporating constant delay compensation for RTHS. The potential of the proposed RTHS framework is worth further studies in the future.

External displacement control (EDC) is essential to a structural test in which a servo‐hydraulic actuator is connected to the specimen through loading fixtures, steel plates, and bolts in order to ensure that the specimen deformation meets the predefined displacement profile accurately. However, external displacement transducers for actuator feedback control could be detached from the specimen due to concrete spalling or steel buckling, leading to potential risks associated with actuator control stability and safety. In this study, image‐based displacement feedback control of actuators for structural testing is proposed and validated, which provides a noncontact approach to measure specimen deformation. In the proposed control scheme, a high‐speed camera is used to capture the images of a feature on the specimen during the test. The specimen deformation is calculated by using the captured images through online image processing and analysis. The actuator controller utilizes the calculated displacement as the feedback signal for displacement control. Finally, the proposed control scheme is validated in the laboratory. Two types of loading protocols are adopted for experimental validation including quasi‐static cyclic testing and dynamic loading testing. Experimental results demonstrate that the proposed image‐based displacement feedback control of the actuator completes quasi‐static cyclic tests and dynamic loading tests successfully and stably with satisfactory displacement tracking performance. The proposed method provides an alternative for EDC in a structural test.

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.

The building mass damper (BMD) system, which incorporates the concept of a tuned mass damper into a mid-story isolation system, has been demonstrated as an effective system for suppressing structural vibration due to earthquakes. The BMD system separates a building into a substructure, a control layer and a superstructure. By applying well-design parameters, the seismic responses of the superstructure and substructure of a building can be mitigated simultaneously. However, merely limited design parameters have been verified by shaking table testing because it is difficult to construct several sets of specimens with limited research funding. Therefore, real-time hybrid simulation (RTHS) may become an alternative to conduct parametric studies of the BMD system efficiently and economically. In this study, the BMD system is separated into a numerical substructure and an experimental substructure. The experimental substructure includes the control layer and the superstructure of the BMD system installed on a seismic shake table while the substructure is numerically simulated. Then, substructuring method of the BMD system is derived and the stability analysis considering the dynamics of the shake table is performed to realize the potential feasibility of RTHS for BMD systems. The stability margin is represented as an allowable mass ratio of the experimental substructure to the entire BMD system. Finally, RTHS of a simplified BMD system has been conducted to verify the stability margin in the laboratory. Phase-lead compensation and force correction are applied to RTHS in order to improve the accuracy of RTHS for the simplified BMD system.