The ground motion of pulse type near fault has the characteristics of higher frequency, faster speed and more concentrated energy than that of a distant site, which has serious harm to engineering structures. With abundant water resources, frequent and high-intensity earthquakes occur in Western China, and many high dams are located near fault zones. The permanent deformation and slope safety of high dams under near-fault ground motion are very important. A random pulse ground motion model is established based on the pulse ground motion records of the Jiji near fault in Taiwan Province. Finite element analysis is carried out on the Gushui 250 m grade engineering panel dam, and stochastic dynamic analysis and reliability analysis are carried out on the displacement and slope slip of the high earth-rock dam by the direct probability integral method. The results show that pulse ground motion significantly affects on the vertical deformation and slope stability of high earth-rock dams. The seismic safety and seismic capability of high earth-rock dams near faults with high seismic risk are evaluated comprehensively.

To solve the problem of a lack of theoretical guidance in the simplification process of space pipe truss structure, the equivalent bending moment of inertia of space pipe truss structure was deduced by using the knowledge of material mechanics, and the corresponding calculation formula was put forward. Based on the principle of equal torsional strain energy, the formulas for calculating the equivalent thin plate thickness of the web members and the top and bottom lateral bracing of the pipe truss were derived, and the continuous equivalent section was constructed. The formula for calculating the equivalent torsional moment of inertia of the space pipe truss structure was proposed by using the thin-walled bar theory. The cantilever method was used to verify the accuracy of the calculation formula of equivalent moment of inertia. The equivalent analysis of the tennis court of Lanzhou Olympic Sports Center was carried out. The results show that the formula for calculating the equivalent moment of inertia is reasonable, and its error is within 4% compared with that of the cantilever method. Under the action of deadweight, the errors of the maximum displacement value and the maximum stress value between the original structure and the simplified structure of the tennis court are less than 9%. The vibration modes of the first five steps of the original structure are similar to those of the simplified structure, and their errors of the natural frequency are less than 4%, so the simplified structure has high accuracy.

To achieve high-precision prediction of bridge-coupled extreme stresses, the wavelet multi-resolution analysis method is adopted to decouple the coupled extreme stresses. The decoupled low-frequency data is taken as the trend item information, where the high-frequency data is considered as the vehicle load effect information. The trend item, after subtracting its mean, is the temperature load effect information. A bivariate Bayesian dynamic linear trend model (BDLTM), which introduces a time-varying trend term, is built to predict and analyze low-frequency extreme stress. GRU neural network model is provided to predict and analyze high-frequency extreme stresses. The dynamic coupled extreme stresses are predicted. The monitoring coupled data from Tianjin Fumin Bridge is provided to illustrate the feasibility and application of the proposed BDLTM-GRU model, the accuracy of which is compared with the single BDLTM model and single GRU model for verifying the high precision of the BDLTM-GRU model.

In order to accurately reveal the impact of high-speed train operation on the vibration response of foundation, the out-of-round wheels and uneven rail surface were introduced to modify the quasi-static moving load. Based on the 2.5D finite element equation of nearly-saturated foundation, a train-track-quasi saturated foundation dynamic analysis model has been established. On this basis, the vibration response of nearly-saturated foundation under different train speeds and loads were analyzed. The results show that both of out-of-round wheels and uneven rail surface have little influence on the time history and peak value of displacement and acceleration at a low speed, whereas the vibration amplitude is significantly increased after the coupling of the two aspects. When the vehicle speed reaches the soil shear wave speed, the influence of out-of-round wheels and uneven rail surface on displacement and acceleration response gradually increases. Compared with the out-of-round wheels, rail surface unevenness has greater influence on nearly-saturated foundation vibration, and it is more sensitive to the change of vehicle speed. The pore water pressure decays rapidly within the range of 0~4 m below the center line of the track bed when the vehicle speed is low, and the pore pressure peak appears at 0.5 m below the track. After the vehicle speed increases, the peak value of pore pressure increases significantly under all kinds of modified loads, and the position of the peak value of pore pressure develops to the deeper part of the foundation under the condition of uneven rail surface and irregular wheel-rail. The vibration response of the nearly-saturated foundation under the irregular wheel-rail coupling condition is obviously greater than that under other load conditions. Therefore, the influence of out-of-round wheels and uneven rail surface should be considered simultaneously in the safety evaluation and foundation vibration response prediction of high-speed railway.

The strong surface impact loads caused by dynamic compaction and construction operations have significant implications on the surrounding environment. Traditional research methods often simplify the impact load as a triangular load for calculation. However, this simplification does not consider the energy loss during impact, leading to overestimation in the calculation results. This paper is based on the measured data from an actual dynamic compaction project. After validating the numerical method’s feasibility, a parametric analysis of key influencing factors is conducted. The paper proposes a reasonable reduction coefficient to modify the current triangular loading model. The objective is to improve the accuracy and applicability of the model for dynamic compaction projects. The calculation results indicate that the magnitude of impact energy and the soil parameters of the site are critical factors influencing the impact vibration response. It is suggested that for impact energy levels categorized as low, medium, and high, the reduction coefficients for medium-soft soil can be set as 0.85, 0.6 and 0.5, respectively. For medium-hard soil, the reduction coefficients can be set as 0.9, 0.7 and 0.6 for the corresponding low, medium, and high energy levels.

Based on the Biot’s dynamic consolidation equation and Novak’s plane strain theory, a coupled mechanical model of radially heterogeneous saturated soil and wedge-shaped pile was established under the horizontal vibration, by considering the construction disturbance effect of the surrounding saturated soil. Then, the analytical solution for the horizontal impedance of the pile head was obtained by using the potential function, Laplace transformation and variable separation methods, and the accuracy of the solution was verified by degenerating with the existing literature solutions. On this basis, the effects of the pile’s parameters and construction disturbance effect on the horizontal vibration characteristics of wedge-shaped pile are further discussed by conducting an extensive parametric analysis. The results show that: The horizontal impedance of the pile head tends to be stable when the number of pile-soil system layers reaches 100. With the increase of softening degree and range of surrounding saturated soil, the horizontal impedance of the pile head decreases, while both the horizontal displacement and bending moment of pile shaft increase. The reasonableness and reliability of the analytical model and solution proposed in this paper are verified by comparative analysis in many aspects.

To address the dynamics modeling of a single local damage fault in rolling bearings, a comprehensive approach based on Hertz contact theory has been developed.Specifically, a contact deformation retention factor is defined and a variable stiffness function using a static analysis method is proposed. This allowed us to establish and simulate a variable stiffness dynamics model for a single local damage fault in rolling bearings under radial load. The model was also experimentally validated. The research results show that when the rolling element enters the load zone its effective contact stiffness suddenly increases. Conversely, when it exits the load zone or falls into the fault position, the stiffness suddenly decreases. This change causes the contact force and contact deformation of other load-carrying rolling elements in the load zone to suddenly decrease or increase to rebalance the external load. However, this does not affect the effective contact stiffness of the rolling element itself. The effect is more pronounced for rolling elements near the center of the load zone. Additionally, these changes cause the total effective stiffness of the system to suddenly increase or decrease, leading to system vibrations. When the outer race has a fault, the change in total effective stiffness is of equal amplitude, resulting in an equal-amplitude time-domain vibration response. In contrast, when the inner race has a fault, both the change in total effective stiffness and the response amplitude are modulated by the rotation of the inner race, leading to significant variations. The proposed variable stiffness dynamics model is more consistent with reality and provides a certain theoretical basis for effective diagnosis of rolling bearing faults.

At present, the layout plan of cable force sensors for cable-stayed bridges usually selects different specifications of cables and cables with large cable forces or significant stress amplitude changes for monitoring, lacking a scientific method of cable force sensor placement. This study proposes an optimal cable force sensor placement method for long cable-stayed bridges based on sensitivity analysis, aiming to identify the structural damage in cable-stayed bridges. The proposed method is based on the sensitivity analysis of cable force to structural damage, and a genetic algorithm is used to obtain the minimum number and placement position of cable force sensors that required to identify structural damage in cable-stayed bridges. In addition, engineering experience and sensor placement habits are fully considered when determining the initial population and constraint condition of genetic algorithm. The proposed method is applied to the numerical model of the Yuxi River Bridge, and the optimal cable force sensor placement for cable-stayed bridges with the target of damage identification is realized. Moreover, the influence of sensitivity threshold on the optimal placement of sensors is discussed.

Aiming at the problem of secondary impact caused by mismatching parameters of traditional isolation system with displacement restrictor, firstly, a mechanical model of the quasi-zero stiffness (MMPDQZS) isolation system was established by using the opposed disc spring as the negative stiffness component and the repulsive permanent magnets was used to adjust the nonlinear positive stiffness. The static characteristics of the system were analyzed. Then, the mathematical model of MMPDQZS isolation system was established. The influence law of different damping parameters on the impact isolation performance of MMPDQZS isolation system was analyzed. The impact characteristics were compared and analyzed through simulation and experimental study for without and with equivalent linear displacement restrictors and MMPDQZS limiters. The results show that for any initial clearance, there is an optimal viscous damping ratio that minimizes the system’s buffer coefficient. Smaller initial clearances generally lead to better impact isolation effects. Considering different initial clearance, the damping ratio of power-law fluid damping is 0.02, the velocity correlation index obtains the optimal buffer coefficient within the interval [2.2, 2.3], and the optimal initial clearance is when the clearance is equal to 4 mm. For any initial clearance, the buffer coefficient is proportional to coulomb damping, and smaller initial clearances result in better buffering performance. Compared with the equivalent linear limit isolation system, MMPDQZS limit isolation system can not only effectively limit the relative displacement, but also greatly reduce the buffer coefficient of the system and improve its impact resistance.

Flexible structures actuated by smart materials have been widely used in the fields of underwater bionic robotics, precision medical machines, micro/nano devices, and so on. It is still a challenging task to acquire the hydrodynamic force exerted on the oscillating flexible structure by the surrounding fluid. The fluid-structure coupled dynamic equation of the MFC-actuated flexible structure is established. A cantilever-based measurement system for the hydrodynamic force is proposed, and the performance indexes are also proposed. The characteristic parameters of the force measurement device are calibrated by experiments. Then, dynamic variations of the hydrodynamic forces exerted on the MFC-actuated flexible structure at different actuation levels are acquired using the proposed system. The measured hydrodynamic forces are decomposed into two components, namely, the added mass force and the hydrodynamic damping force. Moreover, the inertia and drag coefficients in the form of Morrison’s expression are obtained. Experimental results show that the underwater oscillating amplitude of the MFC-actuated structure increases from 3.67 mm to a maximum of 4.23 mm, as the excitation frequencies increase from 2.5 Hz to the resonant frequency of 3.1 Hz. Accordingly, the measured hydrodynamic force exerted on the oscillating structure increases significantly from 86.16 to 184.83 mN. However, the hydrodynamic force stays roughly unchanged, differing by no more than 15%. The proposed method and measurement system may be helpful for the design and application of the underwater flexible structure actuated by MFC and other smart materials.