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With the large-scale construction of urban rail transit viaducts in China, the noise problem caused by trains traversing these sections has become increasingly prominent and a key technical challenge that restricts the sustainable development of rail transit. There are two main noise sources when trains pass on rail transit viaducts, namely, wheel-rail noise (WRN) and bridge-borne noise (BBN). However, most of the existing rail transit viaduct noise prediction models consider only a single noise source. In this study, a total noise prediction model incorporating both WRN and BBN was established using the finite element method (FEM), the boundary element method (BEM), and statistical energy analysis (SEA). The viaducts of Wuhan Metro Line 2 were selected as the research object, and noise tests of trains passing on the viaducts were carried out to validate the total noise prediction model. Based on the validated model, the spatial distribution characteristics and attenuation laws of the total noise were investigated, along with the influence of train speed on the total noise. The results show that the prediction model accurately simulated the total noise caused by trains passing on viaducts. When a train passed on the viaduct at a speed of 60 km/h, the total noise near the viaduct reached 88 dB(A) and decreased with the increase in the distance; at 120 m from the track centerline, the total noise decreased to less than 57 dB(A). As the distance increased, the total noise diminished across the entire frequency spectrum. Notably, low-frequency noise decayed at a slower rate than high-frequency noise. As the distance from the track centerline doubled, the total noise decreased by about 4.23 dB(A). The total noise increased with train speed. When the train speed doubled, the total noise at 30 m and 120 m from the track centerline increased by 6.32 dB(A) and 5.96 dB(A), respectively. The reason for this phenomenon is that the wheel-rail forces increase with the increase in train speed. This study will have important guiding significance and scientific value for the sustainable development of urban rail transit. [ABSTRACT FROM AUTHOR]

With the widespread construction of the subway in the Chinese mainland, the environmental vibration caused by subway operation has attracted increasing attention. Train-induced environmental vibrations can cause structural deformation, uneven settlement of line foundations, and tunnel leakage, affecting the structural safety of lines and foundations. This research focuses on a segment of the Nanchang Metro Line 3, which has been chosen as the subject of investigation. A numerical model was developed to analyze the subway train-induced environmental vibration, employing the finite element method (FEM). Utilizing a numerical model, an investigation was conducted to examine the impact of train speed on the subway train-induced environmental vibration, the train-induced environmental vibration transmission characteristics were analyzed, and the control effects of vibration reduction tracks on train-induced environmental vibration were discussed. Train-induced vibration tests were also conducted on Nanchang Metro Line 3 to verify the control effects of various vibration reduction tracks. The results indicate that the subway train-induced environmental vibration rises as the train speed goes up, and the vibration peaks always appear around 63 Hz. When the train speed doubles, the Z-vibration level increases from about 5.1 dB to 5.9 dB. Subway train-induced environmental vibration shows a fluctuating decreasing trend with increasing distance from the centerline of the tunnel. The Z-vibration level reaches its maximum 4 m away from the centerline of the tunnel. Compared with the embedded sleeper, the vibration-damping fastener exhibits a vibration reduction effect of about 9 dB to 18 dB, the rubber vibration-damping pad exhibits a better vibration reduction effect of about 16 dB to 24 dB, and the steel spring floating plate exhibits the best vibration-damping effect of about 18 dB to 28 dB. The calculated Z-vibration levels are basically consistent with the measured values, indicating the accuracy of the calculated results of the control effects of the vibration reduction tracks. [ABSTRACT FROM AUTHOR]

Spinel type manganese oxide MnO2⋅0.5H2O (H1.6Mn1.6O4) is considered one of the most promising precursors for lithium-ion sieves due to its high theoretical lithium adsorption capacity (72.3 mg/g), and is suitable for selectively extracting lithium from high magnesium lithium ratio brine. In this paper, the powdery lithium-ion sieve precursor Li1.6Mn1.6O4 was prepared by two-step urea-assisted hydrothermal method combining with solid phase method, and the effects of urea/Mn ratios on the adsorption performance of lithium-ion sieves were explored. The results show that as the ratio of urea to Mn increases to 40, the particles tend to acquire a cubic morphology. Moreover, desorption of lithium during the acid leaching of the precursor becomes more favorable. The lithium-ion sieve pellets were prepared by the anti-solvent precipitation method. According to the calculated selectivity coefficient, the separation order by the pellets in the mixed solution is Li+ Na+ > Mg2+ > Ca2+, demonstrating the lithium-ion sieve has a high selectivity to lithium. The adsorption kinetics of lithium-ion sieve pellets in a solution containing lithium illustrates a chemical adsorption mode. [ABSTRACT FROM AUTHOR]

The vibration characteristics of a composite bridge with constrained layer damping (CLD) were investigated using the wave and finite element method (WFEM), and the effects of the material and geometrical parameters of the CLD on the vibration reduction in the bridge were analyzed. Firstly, a numerical model for the dynamic response of a composite steel–concrete bridge using WFEM. The calculated acceleration of the bridge under the wheel–rail force obtained using this model was in good agreement with that obtained using the conventional finite element method and field measurements. Second, a segment model of the bridge with a CLD was established. The equation of motion based on the WFEM was solved to determine the dynamic response of the bridge induced by running trains. Finally, the effects of the covering area and CLD parameters on the vibration mitigation of steel–concrete bridges were analyzed. The results show that a reduction of 5–10 dB of the acceleration level of steel members in the full frequency range can be achieved by installing the CLD. A lower shear modulus of the viscoelastic core is beneficial for low-frequency vibration reduction in the bridge. However, a higher shear modulus of the damping layer is required for vibration mitigation in the high-frequency range. The vibration reduction in the composite bridge was more sensitive to the thickness of the constraining layer than to that of the damping layer. [ABSTRACT FROM AUTHOR]

Influenced by topography, geological conditions, and environmental factors, the alignment design of long‐distance tunnels frequently incorporates curved tunnel segments. When subjected to obliquely incident transverse SV seismic waves, curved tunnels exhibit more complex patterns of stress and deformation, which could become pivotal in governing the seismic safety of the tunnel compared to their straight counterparts. This paper presents a numerical simulation on the response characteristics of curved tunnels subjected to obliquely incident lateral seismic SV waves. Curved tunnels exhibit more complex deformation under oblique SV wave incidence compared to vertical incidence, with notable increases in axial tensile deformation and shear deformation, both axially and in‐plane, as the angle of incidence rises. While vertical incidence primarily induces lateral bending, oblique incidence results in bending influenced by both wave direction and incidence angle, necessitating advanced seismic design considerations for tunnel integrity. The bending moment distribution in curved tunnels under oblique incidence displays nonuniformity and localized concentration. The findings underscore the importance of considering the oblique incident angle in the design and analysis of curved tunnels for seismic safety. [ABSTRACT FROM AUTHOR]

Structure-borne noise from railway bridges has become increasingly severe due to increased train speeds and axle loads. Constrained layer damping can suppress structural vibration and noise considerably across a wide frequency range by dissipating vibrational energy via damping layer shear deformation. This paper proposes a theoretical method of calculating the train-induced vibration and noise of a constrained layer damping-enhanced railway bridge based on the train–track–bridge coupled vibration, the modal strain energy method, and statistical energy analysis. First, the vibration responses of bridge decks were obtained via train–track–bridge coupled vibration calculations. Second, the constrained layer damping subsystem modal loss factors were determined via modal strain energy analysis and converted to damping loss factors in 1/3 octave band. Third, upon substituting the vibration energies of the decks and the damping loss factors of constrained layer damping subsystems into the statistical energy analysis power balance equations, the transmitted vibration energy results from various bridge subsystems were determined by solving the referenced equations. The structure-borne noise from the bridge was finally determined by analyzing the vibratory energies of all of the bridge subsystems using vibro-acoustic theory. Numerical analysis and field measurements of vibration and noise from a three-span steel–concrete composite bridge before and after constrained layer damping installation were performed. The predicted train-induced vibration and noise agreed well with the measured results. The stringer web and flange vibration velocity levels were reduced by 10.5 dB and 6.1 dB, respectively, and the sound pressure level at a measurement point 25 m (horizontal) from the track centerline and 1.5 m off the ground decreased by 4.3 dB(A). [ABSTRACT FROM AUTHOR]

Simply supported pre-stressed concrete box-girder bridges are the most common bridge type found on high-speed railway and urban rail transit lines in China. A field experiment has been conducted on the Pixian Viaduct of the Chengdu–Dujiangyan Intercity Railway, where two kinds of simply supported pre-stressed concrete box-girder bridges with a standard span of 32 m are used, one single track and the other double track. Characteristics of the noise underneath the box-girder, far from the bridge, and near the bridge gap were measured and analyzed in the time and frequency domains during high-speed train passage, as was the vibration of the box-girder’s bottom plate. The variations of noise with distance and train speed at locations 1.5 and 9 m above ground level were measured and fitted using mathematical formulae. A simplified formula to predict near-field bridge-borne noise was proposed and verified. The peak bridge-borne noise frequency and its tonal characteristic at 50 and 63 Hz for the double-track and single-track box-girders, respectively, were interpreted in terms of bridge vibration and sound radiation efficiency, respectively. The vibration/noise transfer function and coherence were evaluated, showing that vibration resonance is more significant than acoustic coincidence and that the former is more important in terms of noise reduction. [ABSTRACT FROM PUBLISHER]