Artificial boundary condition methods provide a simple and efficient approach for simulating wave propagation and dynamic behavior in unbounded soil for soil-structure interaction (SSI) analyses. While commonly used spring-dashpot boundaries are easy to implement, their neglect of frequency-dependent dynamics at the soil's truncated boundaries often limits accuracy. Dynamic impedance functions offer a more precise representation of these frequency-dependent effects. However, stable identification of rational approximation models for dynamic impedance remains a significant challenge in SSI systems. Recent studies reveal that even stable rational approximations of the soil alone may cause instability once coupled with the superstructure-an issue yet to be resolved. This study first presents a stability analysis method for SSI systems based on gain margin, uncovering that the instability of the coupled system arises from rational approximation model identification errors, which induce low-frequency negative damping. To counter this issue, we proposed an enhanced identification method, which introduces a frequency-domain optimization framework with positive phase constraints, effectively mitigating the negative damping and suppressing phase distortion while preserving model accuracy. The proposed method is validated through numerical simulations and time-domain analysis, demonstrating its ability to maintain the stability of SSI systems without compromising their physical fidelity. The proposed phase-constraint identification method addresses a critical gap in the stable modeling of semi-infinite soil systems and enhances the reliability of SSI simulations in earthquake engineering.

Under strong earthquake loading, the stability of rock slopes situated near seismic faults is influenced by the seismic waves’ incident angle and pre-existing structure’ distribution. In this paper, a dynamic simulation model of rock slopes containing non-persistent pre-existing structure was established using a coupled finite difference–discrete element method (FDM–DEM) to investigate the rock slopes’ dynamic response and failure modes subject to obliquely incident shear waves (SV). A viscoelastic artificial boundary is introduced to enable accurate seismic wave input, allowing for the investigation of how varying incidence angles and pre-existing structure properties influence the dynamic behavior of the slope. The result indicates that tensile failure of rock bridges acts as the main initiating factor for slope instability, ultimately facilitating the development of a large-scale sliding surface once pre-existing structure becomes connected. For different seismic wave incidence angles, the slope exhibits patterns of minor deformation, overall failure, and local failure, with the overall failure occurring at an incident angle of 5–15°. In addition, the pre-existing structure distribution pattern affects internal stress transmission and crack propagation paths within the slope, but the difference in dynamic response among those models is not obvious. This work offers valuable theoretical insights into evaluating the rock slopes’ seismic stability in strong earthquake regions.

Real-Time Hybrid Simulation (RTHS) is an efficient structural dynamic testing technique that models the well-understood components as numerical substructures, while obtaining the response of the unknown dynamic characteristics through physical testing. Offline RTHS, a recently introduced iterative substructure interaction method, decouples numerical simulation from physical loading over time, enhancing the flexibility of solving complex models and performing multi-specimen tests. However, this method faces challenges in iteration stability and convergence speed, limiting its application in certain dynamic systems. To address these issues, this study proposes a Global Model-based Numerical Substructuring (GMNS) approach, which integrates known information from the physical specimen with the rest of the system into the numerical substructure, retaining only the uncertainties of the physical specimen as the physical substructure. Simulation results demonstrate that GMNS effectively enhances iteration stability and convergence speed in both actuator-based and shake-table-based offline RTHS systems. Further validation was performed through a Tuned Mass Damper (TMD) seismic mitigation test. The experimental results indicate that GMNS significantly enhances the critical stability mass ratio, increasing it from less than 2.7% to over 10%. Furthermore, under a TMD mass ratio of 2.5%, it reduces the number of iterations required to achieve a relative iteration error below 0.1 from more than 7 to only 2.

The dynamic interaction between water and cylindrical structures can significantly affect the dynamic responses and properties of offshore structures. Among the key factors, the free-surface boundary condition plays a crucial role in determining the hydrodynamic forces on cylinders, leading to frequency-dependent added mass and damping effects. Although the dynamic responses of the cylinder can be readily obtained using frequency-domain methods, their computational efficiency is much lower than that of the time-domain methods, and they are not well suited for nonlinear structure analysis. To address this, this study proposes a time-domain substructure method for simulating water–cylinder interaction considering the boundary condition of free surface waves, where the frequency-dependent added mass and added damping are equivalently represented by a spring-dashpot-mass model in time domain. The results indicated that the calculation efficiency of the proposed method has improved by approximately two orders of magnitude compared with the frequency-domain finite element method. Moreover, the water–cylinder interaction can markedly influence the seismic responses with small mass ratios, whereas its effect on wave-induced responses becomes negligible when the wave period exceeds 5 s. The effects of the free-surface boundary condition on the wave responses of the cylinder can be generally negligible, except when the wave period approaches the natural vibration period of the cylinder. In addition, its influence on seismic responses can be ignored when the damping ratio of the cylinder exceeds 0.02.

Offline real-time hybrid testing (RTHT) offers a simplified approach to structural dynamic testing by coordinating boundary conditions through offline iterations of the global time history, eliminating the need for realtime computation and delay compensation which are required in traditional online RTHT. Despite its advantages, the limitations and challenges of offline RTHT have received limited attention in existing research, hindering its further development. This study addresses these gaps by focusing on the stability and efficiency of offline RTHT iterations. Firstly, a transfer function-based analysis method was developed, providing stability criteria and efficiency metrics. Using this method, the intrinsic iteration stability and efficiency of offline RTHT were investigated across three typical systems. Simulation results indicated that offline RTHT is most effective for systems with damping-type physical substructure and less suitable for those with inertia-type substructures. The proposed analysis method was further applied to predict the iteration stability of a practical offline RTHT on a TMD-structure system. The predicted critical stability aligned closely with experimental results, demonstrating the method's reliability in capturing the actual performance of offline RTHT.

This study investigates the seismic response and failure mode of a pile-structure system in a liquefiable site by employing a numerical simulation model combined with the shaking-table results of a soil-pile-structure dynamic system. The pile and soil responses obtained from the numerical simulations agreed well with the experimental results. The slopes of the dynamic shear-stress-shear-strain hysteretic curves at different positions also exhibited a decreasing trend, indicating that the shear strength of the soil in all parts of the foundation decreased. The peak acceleration of the soil and pile was not clearly amplified in the saturated sand layer but appeared to be amplified in the top part. The maximum bending moments appeared in the middle and lower parts of the pile shaft; however, the shear forces at the corresponding positions were not large. It can be observed from the deformation mode of the pile-group foundation that a typical bending failure is caused by an excessive bending moment in the middle of the pile shaft if the link between the pile top and cap is articulated, and sufficient attention should be paid to the bending failure in the middle of the pile shaft.

The stability analysis of real-time hybrid test (RTHT) is crucial for the division of numerical and physical substructures, performance evaluation of loading system controllers, and feasibility judgment of RTHT systems. Existing stability analysis methods involve the parameter identification and numerical modeling of physical test systems. In contrast, an RTHT involves conducting a physical test on the hard-to-model part. Therefore, it is difficult to accurately model the physical substructure as well as the loading and acquisition systems. In this study, an RTHT stability prediction method based on the measured dynamics of the physical test system was developed, which avoid the tedious numerical modeling of the physical test system. The effectiveness of the stability prediction method was verified through numerical simulation and the experimental testing of a multi-degree-of-freedom shaking table RTHT. The experimental results showed that the accuracy of the developed stability prediction method was higher than that of the model-based stability prediction method by 35.1 %. The stability prediction method developed in this study simplifies the stability analysis of RTHT and will help determine the feasibility of test in advance.

In recent years, real-time hybrid testing (RTHT) has been applied for the dynamic testing of high-speed trains running on bridges. A guarantee of stability for the RTHT system is essential to achieve a safe and reliable result. However, the inherent time-varying characteristics of the vehicle-bridge coupled system pose challenges to RTHT stability prediction. This study aims to develop a stability prediction method specifically tailored for time-varying RTHT system. Firstly, the vehicle-bridge coupled RTHT was modelled using a discrete state–space representation with a comprehensive consideration of the time-varying vehicle-bridge interaction and the dynamics of the shaking table. Subsequently, a time-varying stability criterion was derived from the periodic time-varying state matrix, forming the basis for a relative stability prediction method. The validity of the proposed method was confirmed through simulations and experiments employing a single-axle interaction within the vehicle-bridge coupled RTHT system. The coupled system consisted of a quarter-car model and simply supported beams were used as an example to evaluate the stability and accuracy of the time-varying RTHT. The results showed that the stability increased with increasing vehicle speed. Reducing the pure time delay of the shaking table improved both stability and accuracy. Increasing the effective frequency of the shaking table improved the accuracy but may reduce the stability of the RTHT.

This paper presents the residual flexural capacity of reinforced concrete beams under combined actions of corrosion and elevated temperatures. 17 concrete beams were manufactured and accelerated corrosion tests were conducted to obtain corrode concrete beams. After fire tests according to ISO 834 standard fire, each specimen was subjected to a four-point bending test. The results showed that corrosion led to premature failure of concrete beams. During fire tests, corrosion-induced cracks accelerated heat transfer in the concrete. Slight corrosion had little effect on the yield and ultimate load of concrete beams. One hour fire exposure had little effect on the load bearing capacities of slightly corroded or uncorroded beams. But when the corrosion degree exceeded 0.1, the load bearing capacities decreased by up to 31%. Increasing the concrete cover thickness significantly improved the load bearing capacity of corroded concrete beams. When the degree of corrosion of tension bars exceeded 0.069, energy dissipation capacities decreased significantly as much as 21%. The longer the fire exposure time was, the greater the decrease in energy dissipation. The conclusions obtained in this paper can provide a theoretical basis for the evaluation of residual performance of corroded concrete structures after exposure to fire.

In the field of rock mechanics, the study of void shape on the mechanical properties and fracture mechanisms of sandstone is crucial for the progression of rock engineering practices. In this study, PFC3D is utilized to conduct numerical simulations of uniaxial compression on intact rock and brittle rocks containing five different shapes of voids (including circular, inverted U-shaped, trapezoidal, rectangular, and square). By employing acoustic emission and moment tensor inversion techniques, the microscopic fracture mechanisms of rocks with different void shapes are revealed. Our key findings reveal: (1) The PFC3D’s Soft-Bond Model is adept at simulating acoustic emissions with high accuracy, facilitating an authentic reproduction of the uniaxial compression process in sandstone, including the nonlinear compaction stage. (2) The presence of hole defects markedly undermines the structural strength and deformability of the sandstone, with circular holes having minimal impact, whereas rectangular holes exert the most significant detriment. (3) A thorough analysis of fracture mechanisms demonstrates that specimens with hole defects primarily undergo initial tensile, remote cracks, V-shaped notch, and shear fractures, with shear fractures being pivotal in leading to specimen failure by rapidly evolving into macroscopic fractures that merge with V-shaped notches. (4) Acoustic Emission (AE) analysis highlights the distribution of tensile stress around the upper and lower extremities of the holes and shear stress along the left and right sidewalls, establishing shear stress as the dominant factor in the failure of specimens with hole defects.

Multiple tuned mass dampers (MTMD) are widely used to mitigate structural seismic response. With the emergence of more and more high-rise buildings, various MTMD design methods applicable to multi degree of freedom (MDOF) model have been developed. However, the existing MTMD design methods for MDOF models often involve complex optimization algorithms. In order to simplify the MTMD design while effectively reducing the seismic response of the structure, this paper proposes an explicit frequency domain transfer function, theoretically showing the mechanism of decomposing the seismic mitigation of MDOF model into simultaneous seismic mitigation of multiple modes, and developed a theoretical design method of MTMD, so that the dynamic parameters and position of each TMD can be directly obtained based on the developed explicit design formula. A benchmark model was used as an example to verify the seismic mitigation performance. It is shown that the developed multimodal control MTMD design method achieves 22.25% reduction rate of acceleration and 18.5% reduction rate of displacement with 3% mass ratio.

Numerical simulation models for pile group-superstructure in liquefiable and non-liquefiable sites were established. The validity and reliability of the numerical model are verified by the shaking table test results. Based on the cross-correlation analysis of superstructure acceleration-pile bending moment and soil displacement-pile bending moment obtained from the tests, the coupling law of kinematic and inertial interaction and its influence on pile failure modes were discussed combined with the numerical simulation results. The results shown that the effect of kinematic interaction on piles were greater than that of inertial interaction in both types of sites, but coupling mechanisms of kinematic and inertial interaction were different. For the liquefiable site scenario, the middle part of piles was prone to bending failure and the kinematic interaction was the main reason for it. For the non-liquefiable site scenario, the inertial interaction had an obvious influence on the pile failure occurred at the pile top. The results of parameter analysis shown that the mass of the superstructure was the most important parameter of inertial interaction in the liquefiable site. Parameters of inertial interaction would affect the vibration of the superstructure in the non-liquefiable site, but the influence on pile bending moments was not obvious.

The dynamic pile-soil interaction in a liquefied site was investigated by means of numerical simulation and shaking table tests in this study. Based on the results from the shaking table experiment, the cross-correlation analysis of the soil displacement-pile bending moment and superstructure acceleration-pile bending moment was performed to study the influence of kinematic interaction and inertial interaction on the seismic response of piles. A relatively reasonable and accurate finite difference numerical analysis model of liquefiable soil-pile group-superstructure dynamic system was established. Through numerical simulation, the understanding of kinematic interaction and inertial interaction in the shaking table test was verified. The mass, damping and period of the superstructure were selected as variables to carry out parameter analysis to further study the influence of inertial interaction on the pile-structure failure mechanism. The results show that the influence of kinematic interaction on the pile was much greater than that of inertial interaction. The mass of the superstructure was the most important parameter of inertial interaction, and dynamic characteristics of the superstructure also had an effect on inertial interaction. The effect of inertial interaction on the part near the pile tip was more significant, indicating that the failure near the pile tip is closely related to inertial interaction.

Tuned liquid damper (TLD) is a typical passive device to control structural response under wind and earthquake excitation. At present, TLD is often used to control single-mode of structure. Hence, the design theory of TLD is often based on single-degree of freedom (SDOF) system in frequency domain, which is hard to accurately evaluate seismic performance of TLD-installed multi-degree of freedoms (MDOFs) with consideration of higher mode. In this work, a frequency domain transfer function for TLD controlled MDOFs system is established through the concept of substructure to evaluate overall seismic performance of TLD-installed MDOFs. The accuracy of the transfer function is verified by real-time hybrid testing. Using this transfer function, the effect of TLD on the seismic performance of MDOFs was discussed in frequency domain by parametric analysis. The analytical results indicated that, based on the design theory for single-mode, the TLD with large mass ratio cannot enhance the seismic performance effectively comparing with small mass ratio. In order to improve the control efficiency of relatively large mass TLD, a design method for multi-mode control is established based on the developed frequency domain transfer function. The simulation results showed that, with same TLD mass, the multi-mode method performed smaller structural acceleration response and similar displacement response relative to the single mode method.

Soil-structure interaction (SSI) can potentially compromise structures that are subjected to seismic excitation. In recent years, real-time hybrid testing (RTHT) has been used to study soil-structure interaction. However, a very simple soil model has been adopted in existing hybrid testing, which cannot simulate nonlinear effects in a soil-foundation system under vigorous seismic shaking. To study the stability and accuracy of RTHT for nonlinear SSI and to evaluate the dynamic impact of soil nonlinearity on an SSI system, real-time hybrid shaking table testing was performed based on full-state control via simulation (FSCS), in which the soil-foundation system was simulated using a macroelement model. The results demonstrate that FSCS-controlled RTHT is an effective approach for investigating nonlinear SSI. The nonlinear characteristics of the numerical substructure had little influence on the stability and accuracy of RTHT for nonlinear SSI systems, but the nonlinear characteristics of the soil had a positive effect on the structural seismic response. An effective dynamic testing method was proposed for the SSI studies.

In modern actuator technology, shape memory alloy actuator (SMAA) has the characteristics of high strain stress, high power-weight ratio, and high degree of freedom, SSMA is gradually applied in aerospace, automobile industry, robot, biological medicine, and other fields. However, high precision position control based on high-frequency pulse width modulation technology leads to the radiated EMI problem. This paper proposed a novel application of spread spectrum technique to reduce radiated EMI for SMAA, the ANSYS MAXWELL simulation of different SMA conductive circuits confirms the radiated EMI generated by the PWM modulation technology, Furthermore, through power spectral density analysis, it is concluded that random frequency modulation technology has less electromagnetic radiation interference than fixed frequency PWM modulation technology. Finally, the laboratory prototype verifies the conclusion that the method proposed in this paper has less electromagnetic radiation interference.

Stability prediction is a key step to implement a real-time hybrid simulation (RTHS) testing successfully. There are two kinds of stability prediction methods based on continuous and discrete transfer function. In the family of continuous transfer function based methods, the numerical and physical substructures are seen as continuous systems together with loading system. In discrete family, all subsystems in RTHS are regarded as discrete systems. Actually, in a real RTHS, the numerical substructure is discrete; the physical substructure is continuous. Meanwhile, the signal coordination is needed to balance the sampling interval between numerical solution and physical loading, which is ignored in the reported methods. In order to predict the stability of RTHS system more accurately, this work develops a discrete-continuous stability analysis method through the concept of gain margin, which can consider the performance of numerical substructure, physical substructure, loading system and signal coordination comprehensively. And the accuracy of the method is verified by SIMULINK simulation and experimental testing. Based on shaking table and actuator RTHS systems, the performance of continuous and discrete methods is compared with the proposed method analytically. The results show that the discrete method and continuous method have slight influence on the stability prediction with a small integration step (e.g 1 ms). However, with the increase of integration step, compared with the discrete-continuous method, the discrete method and continuous method may overestimate or underestimate the stability of a real RTHS system.

The tuned liquid dampers (TLD) technology is a feasible and cost-effective seismic design. In order to improve its efficiency it is fundamental to find accurate models describing their dynamic. A TLD system can be modeled through the Housner model and its parameters can be estimated by solving a nonlinear state estimation problem. We propose a robust extended Kalman filter which alleviates the model discretization and the fact that the noise process is not known. We test the effectiveness of the proposed approach by using some experimental data corresponding to two classical seismic waves, namely the El Centro wave and the Hachinohe wave.

To protect endangered birds, a bird song classification model combining a bi-directional long and short term memory neural network (Bi-LSTM) and a dense convolutional network (DenseNet) is proposed. The main operations are as follows: Step 1: Classify, filter and extract various features such as Mel frequency cepstrum coefficients and dump them into TFRecord as input data for the model. Step 2: Build the Bi-LSTM-DenseNet network; use the cross-entropy loss function to tune the network structure; use the softmax classifier to classify 20 bird species, and save the trained model and weights. Step 3: Test the model performance using a test set. Experimental analysis of 14,311 audio files showed that the average accuracy of the Bi-LSTM-DenseNet network model for the detection of hawks, western ruffed grouse, crested wheatears and red-throated divers was 91.1%, 92.7%, 91.4% and 92.6%, respectively; the average accuracy for all bird species detection was between 90% and 93%. The average accuracy of this model was found to be significantly higher than that of other common neural networks in control experiments.