The duration of ground motion can significantly influence the cumulative damage and failure levels of structures, but its impact on structural response is inadequately considered in current seismic design. To explore the effect of ground motion duration on structural damage, this study employs a spectral matching method combined with wavelet transform to select 115 ground motion records of varying durations from the Japan strong-motion database (K-NET). Earthquake damage spectra under two different restoring force models were calculated, and a comprehensive analysis was conducted on the effects of ground motion duration, yield strength reduction factor, structural natural period and other factors on the structural damage spectrum. Additionally, 585 natural earthquake records of varying durations and different site conditions were selected from the Pacific Earthquake Engineering Research Center (PEER) database. Taking into account the combined influences of ground motion duration, yield strength reduction factor, structural restoring force model, and site conditions, a damage spectrum prediction model was developed using a differential evolution algorithm. Compared with existing prediction models, the proposed model reduces relative errors by more than 40%, which offers improved accuracy for predicting damage spectra that consider the effect of duration. The results of this study provide valuable insights for structural seismic design and damage assessment when considering the impact of ground motion duration.

This study investigates the influence of ground motion duration on the damping reduction factor through response spectrum analysis of single-degree-of-freedom systems with various damping ratio levels. The significant duration (D_S5-95) is chosen as the measure for ground motion duration. By using 84 pairs of long-duration (LD) and short-duration (SD) spectrally equivalent records, the effect of ground motion duration is decoupled from the acceleration spectral shape. The average damping reduction factors for the LD and SD sets are calculated within the range of natural periods from 0 to 6 seconds at different damping ratio levels. The effects of damping ratio, natural period, and D_S5-95 on the damping reduction factor are quantitatively analyzed. A nonlinear regression model is proposed to account for the influence of ground motion duration on the damping reduction factor, with the regression parameters provided. The results indicate that, for a linear single-degree-of-freedom system, the influence of ground motion duration on the damping reduction factor depends on the natural period and damping ratio. In the short-period range, D_S5-95 has no significant effect on the damping reduction factor、However, in the long-period range, the damping reduction factor tends to decrease as D_S5-95 increases.

Existing studies have shown that near-fault impulsive ground motions have a significant impact on the seismic performance of concrete gravity dams. However, current research on the vulnerability of concrete gravity dams under near-fault ground motions remains limited, and most studies use a single response parameter as the performance indicator, which makes it difficult to comprehensively characterize the seismic performance of gravity dams. Taking a certain engineering concrete gravity dam as an example, this paper establishes a unified plastic damage model of the dam-foundation system. Multiple measured near-fault impulsive and non-impulsive ground motions are selected. Then, it calculates the comprehensive damage index of the gravity dam is calculated using the method of efficacy coefficient combined with the modified weighting model. A logarithmic probability seismic demand model is established for PGA (peak ground acceleration) and three single indices including accumulated base sliding, relative displacement of the dam crest, and overall damage index, as well as a comprehensive response index. By combining the criteria for dividing damage levels for each index, vulnerability curves are obtained. The paper compares the characteristics of near-fault ground motion pulses and the influence of single and comprehensive response indices on the seismic performance of concrete gravity dams. The results indicate that the probability of concrete gravity dams experiencing minor, moderate, and severe damage under near-fault impulsive ground motions is higher than that under non-impulsive ground motions. Evaluating seismic performance using a single index may lead to overestimation of the dam's seismic resistance under certain PGAs. Using a comprehensive damage index as the performance indicator for evaluating the probability of damage and ultimate seismic capacity of gravity dams is more reasonable.

The near-fault velocity pulse-like earthquake ground motions usually cause more severe damage to building structures. To analyze the seismic responses of the reticulated shells with seismically base-isolated substructures subjected to near-fault velocity pulse-like earthquake ground motions, three sets of ground motions are applied to a double-layer cylindrical steel reticulated shell supported by seismically base-isolated reinforced concrete frame structure. The first group consists of 22 near-fault velocity pulse-like ground motions with a distance of 5~10 km and a pulse period of 0.7~3.2 seconds, the second group includes 22 corresponding ground motions without velocity pulse, and the third group is based on the second group, considering the near field amplification coefficients given in GB/T 51408—2021 Standard for seismic isolation design of building. Through incremental dynamic analyses, the dynamic responses of the structure under the three groups of ground motions are compared. The results show that the velocity pulse has a significant amplification effect on the isolation layer displacements, the inter-story drifts, the axial forces, the base reaction forces of the reinforced concrete supporting structure, as well as the maximum nodal displacements and the member axial forces of the reticulated shell. Moreover, when only adjusting the intensity of the ground motions, the near field amplification coefficient can not effectively account for the influence of velocity pulse on the dynamic responses of the base-isolated reticulated shell with supporting structure. The conclusions of this study can provide a basis for the seismic isolation design of the base-isolated reticulated shell-supporting structure in high seismic intensity areas near fault zones.

In this paper, a GPU-accelerated explicit nonlinear mode superposition method (ENMS) is proposed for real-time computation of large-scale bridge structures with local nonlinearities, especially non-linear dampers. This method treats the non-linear damping force as an external load, decouples linear equations of motion at each discretized time step by using the mode superposition method, and solves them by using an explicit step-by-step integration method. In this way, this method avoids the iterative solution to the equations of motion, and significantly improves computational efficiency with the fast mode superposition method. In view of the decoupled equations, a GPU is utilized to accelerate the computation, thereby further improving the computational efficiency. Numerical simulation studies on a large-span cable-stayed bridge show the followings: For a large multi-degree-of-freedom structure with local nonlinearities, this method can be used to conveniently and accurately solve dynamic responses with the parameters exported from Midas Civil. For an exponential Maxwell model of viscous dampers, the dichotomous method is able to accurately solve the damping force, providing a better solution to the problem of modeling non-linear dampers. The GPU acceleration can significantly improve the computational efficiency of the explicit non-linear mode superposition method.

In order to explore the specific causes of fastener bolt looseness and elastic strip loosening on the already built and operational rail transit lines, and to prevent similar problems from recurring on newly-built rail transit lines, this study combines with the actual situation of two rail transit elevated bridges in a certain city. Taking the failure analysis of U-beam fasteners as the breakthrough point, it explores the causes of fastener failure of ballastless track through field tests and vehicle-bridge coupling vibration simulation methods. Then, focusing on the vibration characteristics of the ladder sleeper structure and the comparison of vibration reduction and isolation effects between damper fasteners and the ladder sleeper structure, and applying the principles and methods of dynamic flexibility and energy flow, it analyzes the mechanism of factors affecting the vibration frequency of the track structure through a series of diagrams, and interprets the vibration mechanism of the track structure. The vibration effects are analyzed based on the measured and simulated data. The contribution of wheel wear to vibration is analyzed by measuring the vibration acceleration caused by vehicles in different operating years. Based on the field test, finite element simulation and vehicle-bridge coupling vibration calculation, the contribution of main girder section to vibration is analyzed. The contribution of track structure to vibration is analyzed by measuring the vibration acceleration of fasteners in different intervals; Based on the vibration field test of rail-crossing bridge, the mechanism analysis of the factors affecting the vibration frequency of rail structure is carried out with the vehicle-bridge-rail coupling vibration analysis program, and the vibration variation law is explored when the stiffness of fasteners and the stiffness of under-pillow damping pads are changed. The research results show that wheel wear, bending-torsion coupling effect of beam and vibration isolation of ladder sleeper are important potential factors that constitute fastener diseases of rail transit lines. The vibration reduction and isolation effect of ladder sleeper track structure is good, and the vibration of rail and ladder sleeper is significantly affected by the stiffness of fastener, while the vibration of bridge is significantly affected by the stiffness of damping pad. Proper reduction of fastener stiffness can significantly reduce the vibration of ladder sleeper. The research results can provide a reliable basis for improving the vibration research of rail transit bridge fastener system and provide design reference for related projects.

Considering the 3D wave effect of soil and the kinematic soil-pile interaction, the seismic response of end-bearing single piles to vertically incident P-wave excitation is studied. The vertically incident P waves are modelled as the time-harmonic longitudinal displacement of the bedrock, and the governing equations of soil are established by considering both the longitudinal and radial displacements of the surrounding soil. The displacements of the surrounding soil are assumed as the summation of the free-field and scattered displacements, and subsequently the expression of the soil frictional force actingon the pile due to its motion is obtained. The pile is assumed to be a one-dimensional Euler bar. By substituting the soil frictional force into the governing equation of pile, the analytical solution of the seismic response of the pile under the action of vertically incident elastic P waves is obtained by considering the continuity conditions at the pile-soil interface and the boundary conditions at the top and bottom of the pile. The solution obtained is compared with existing studies to verify its validity. Finally, based on the obtained solutions, the effects of the main pile-soil parameters on the seismic amplification factor of the pile top, the kinematic response factor, the displacement of the pile, the frictional force of the soil and the kinematic Winkler parameters of the surrounding soil are investigated. The results show that: the resonance behavior of the pile-soil system occurs under the vertically incident P-waves, and the resonance behavior is particularly obvious at the first-order resonance frequency of soil layer. The pile slenderness ratio and pile-soil modulus ratio have significant effects on the seismic amplification factor of the pile top and kinematic response factor. The displacement of pile decreases significantly with the decrease of pile slenderness ratio or the increase of pile-soil modulus ratio. Compared with longer and softer piles, shorter and stiffer piles are subjected to a higher friction force of surrounding soil under seismic excitation. The influence of the pile slenderness ratio on the kinematic Winkler parameters is particularly prominent, and the kinematic Winkler parameters decrease significantly with the increase of the pile slenderness ratio, while the influence of the pile-soil modulus ratio is relatively small. The study can provide theoretical support for the seismic analysis and design of piles.

The freeze-thaw cycle (FTC) is one of a major factors leading to the damage of reinforced concrete (RC) structures in severely cold regions. The seismic performance evaluation of FTC-damaged RC beam-column connections is critical to the assessment of structural safety. However, the studies on the seismic performance evaluation of FTC-damaged RC beam-column connections under severe cold environments are still scarce. In this study, the influences of freeze-thaw cycles (N) and axial force ratio (n) on the seismic performance of RC beam-column connections are deeply investigated. Based on the test results, a calculation model of the shear force-strain envelope curve of RC connections that integrates the effects of the inhomogeneous temperature field distribution and axial compression ratio was established. The results show that with the increase of NFTC_s, the bearing capacity of the RC connections and the shear bearing capacity of the core area decrease, while the ductility, shear strain γ, and shear deformation to the total deformation Δ_PZ/Δ gradually increase, and after 300 freeze-thaw cycles, Δ_PZ/Δ is up to 21.90%. The established shear force-distortion calculation model for the FTC-damaged RC core area can accurately calculate the shear force V_jh and shear distortion γ. The mean error of both the shear force V_jh and shear distortion γ does not exceed 20%, and the standard deviation does not exceed 0.1. Furthermore, the precision of V_jh is slightly higher than that of γ. The shear skeleton curve calculation model established can be used to evaluate the seismic performance of FTC-damaged RC beam-column connections under earthquake actions.

The geotechnical isolation system based on glass beads and sand cushion (referred to as GSI-GBSC) has exhibited good seismic isolation performance on a one-story masonry building, but its effectiveness for two-story or higher rural buildings remains not determined. This study carried out a shake table test on a 1/4-scale model of a two-story masonry building. The first model was a two-story brick masonry structure without seismic isolation (the non-isolated model), and the second model was a two-story brick masonry structure equipped with the GSI-GBSC seismic isolation system (the isolated model). The acceleration and displacement responses of the two models were evaluated and compared, and compared with the results of the one-story rural building test conducted in previous studies. The results indicate that the glass-bead-sand-pad layer in the GSI-GBSC seismic isolation system tends to slip and slide, resulting in relative slippage between the foundation soil and upper structure of the isolated model. This ultimately reduces the seismic response of the upper structure. Under different peak acceleration input conditions, the upper structure of the isolated model was observed to move predominantly in a horizontal direction. In contrast, the displacement response of the non-isolated model increases as peak acceleration input values increase, leading to an increasing gap between horizontal displacement peaks in each layer. Furthermore, it was found that inter-story deformation in the isolation model is significantly reduced. Specifically, when peak acceleration input values are 0.2 g and 0.4 g respectively, it was observed that acceleration responses at top structures were 28% and 36% lower in comparison to those from non-isolated models. In summary, it can be concluded that while GSI-GBSC isolation system demonstrates good effects on one-story and two-story rural masonry structures, however, increasing weight and height-to-width ratio will reduce its effectiveness.

As a typical slender structure, solar towers, which have been widely applied in recent years, are highly prone to significant vibrations under wind loads. Based on a 228.5 m-high solar tower, the wind-induced vibration control performance of Tuned Liquid Dampers (TLDs) was studied by wind tunnel tests. Firstly, a 1∶200 full aeroelastic test model of the solar tower was designed and fabricated, and the corresponding optimal parameters of the TLD were analyzed. Then, a miniature and multi-container TLD was designed for the aero-elastic test model, and wind tunnel tests for the model, both with and without the miniature TLD, were conducted respectively. Wind-induced responses of the tower, including top acceleration, displacement, base shear force and moment were measured. It was found that significant vortex-induced vibrations occurred within the range of the design wind speed (33 m/s). The results showed that wind-induced responses of the tower could be significantly suppressed by the TLD both in the cross-wind direction and the along-wind direction. With the installation of the TLD, the peak values of the top acceleration and displacement in the cross-wind could be reduced by 56.3% and 53.5%, respectively, and the corresponding reduction ratios for the base shear force and moment were 58.7% and 56.5%. At the design wind speed, the peak crosswind top acceleration and displacement were reduced by 48.4% and 40.3% , respectively, and the peak base shear force and bending moment were reduced by 65.4% and 45.5%.