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During pipeline construction and operation, the occurrence of surface dents presents a critical concern, primarily arising from factors such as pipeline installation and geological forces exerted upon the pipeline, particularly in the form of rock protrusion. These dents pose a significant threat to the pipeline's safe functionality and have the potential to diminish its load-bearing capacity. Presently, China's oil and gas pipelines predominantly employ X80 high-grade steel. It is noteworthy that prior research into the ultimate load capacity of dented pipelines has largely centered on medium and low-grade steels. The implications of these findings for the suitability of the X80 pipeline remain inconclusive. Consequently, it is imperative to undertake a comprehensive investigation into the load-bearing capacity of high-grade steel pipelines with dent defects. In addition to internal pressure, variations in the pipeline's transported medium, ambient temperature fluctuations, soil displacement, and other factors introduce additional loading effects, including bending moments and axial loads. These supplementary loads introduce latent hazards to the pipeline's operational safety. Hence, this research endeavors to investigate the ultimate load-bearing capacity of X80-grade dented pipelines under the influence of typical loading conditions and to identify pertinent factors that affect this capacity. Finite element analysis (FEA) is deployed to study the behavior of the dented pipelines under typical loads. Failure criterion for ascertaining the ultimate load is proposed and verified by the comparison to test results. Furthermore, the impact of varying dent sizes on the ultimate load capacity of X80-grade dented pipelines is examined. These findings serve as a robust foundation for the safety assessment of dented pipelines, ensuring the sustained safe operation of these vital infrastructures. [ABSTRACT FROM AUTHOR]

High-filled cut-and-cover tunnels (HFCCTs) provide an ideal solution for reclaiming usable land in northwestern China due to the unique landforms of the Loess Plateau. To improve the safety and minimize the cost of such tunnels, most current methods focus on load reduction or a soil arching effect to reduce the earth pressure on cut-and-cover tunnels (CCTs). Although optimizing the design of HFCCTs is an important topic, very few studies have focused on modifying the cross-section of CCTs to improve their design. The modifications of cross-sectional design were proposed, and the vault optimization factor, F, was introduced. The optimal cross-sectional design of a CCT was determined using the finite element method. The experimental results verify that changes to the cross-section of a CCT’s lining structure can both reduce the required thickness of the CCT’s structure and increase the allowable backfill height above the CCT. The optimization is accomplished by modifying the cross-sectional design of a CCT to minimize the bending moment and allow the CCT to carry a more axially compressive load. [ABSTRACT FROM AUTHOR]

To further improve the transportation level of China's high-speed railway, it is urgent to research on the key technology of speed in for the existing 250 km/h high-speed railway. The track structure directly bears the train load, the adaptability of the track after the train speed increase is an important factor affecting the safe and stable operation of the train. Based on the field investigation, finite element analysis, numerical calculation and other methods, this paper studies the adaptability of ballasted track, ballastless track and designed track superelevation, and the technical conditions for the speed-increase track of 250 km/h high-speed railway are put forward. The main conclusions are as follows: the speed increase of ballasted track lines will cause the increase of dynamic indexes of the fastener and track bed, which will reduce the service performance of structures; the speed increase of ballastless tracks will cause the increase of the longitudinal and transverse bending moments of track slab and concrete base slab, and the longitudinal bending moment of track slab in subgrade section increases the most, which is 4. 7 kN · m/ m; considering the safety margin, the reinforcement of track slab and concrete base slab in the subgrade, bridge and tunnel sections meets the requirements of strength and crack width; after the speed increases, the track design curve superelevation should be adjusted to meet the requirements of minimum curve radius and transition curve length under different speed levels; after the speed increase, attention should be paid to the drainage of track slab structure, track smoothness, etc., and the relevant requirements of the current specifications should be satisfied. [ABSTRACT FROM AUTHOR]

• The wooden drum-tower exhibits poor ductility, and the premature withdrawal of tenon-mortise joints in components adjacent to the failure zone is a triggering factor for the collapse of the structure. • After component failure, the structure undergoes internal force redistribution. The beam in the failure zone is forced to bear tension, bending, and torsion simultaneously, leading to the failure of the tenon-mortise joints. At the moment of mortise-tenon joints failure, the columns within the failure zone gradually tilt under the influence of gravity, eventually leading to progressive collapse. • The failure of mortise-tenon joints in the failure zone is characterized by compression deformation of the tenon in the transverse direction and splitting of the mortise edges. Non-collapsed structure tilts as a whole, with slight detachment of tenon heads and uplift of column bases. The drum-tower belongs to the category of towering structures, and the overall collapse is a common accident in such structures. In order to study the anti-collapse performance of drum-towers, this research used the bottom floor of a wooden drum-tower in the southwest China as a prototype, designing and producing a 1/3 scale structural model. The sudden-column-removal (SCR) method was employed to simulate the structural collapse process, observe collapse characteristics, and analyze the dynamic response of the structure. A finite element model was established, and on the basis of verifying its accuracy, a parameter expansion analysis was conducted. The study indicates that the ductility of wooden drum-towers is relatively poor, and the pulling out of mortise- tenon joints in adjacent components in the failure area is a primary factor for the progressive collapse of the structure. Due to the redistribution of internal forces, the load-bearing status of beams in the failure area changes, experiencing tension, bending moment, and torsion simultaneously, leading to the pulling out, compression, and splitting of mortise-tenon joints. After the failure of these joints, the structure undergoes progressive collapse under the influence of gravity. The dimensions of mortise-tenon joints and the friction coefficient have a significant impact on the anti-collapse performance of the structure. Larger dimensions and friction coefficients result in slower structural damage and more stable structural response. Among these factors, increasing the depth of mortise-tenon joints has the most significant effect. [ABSTRACT FROM AUTHOR]

At present, specific earthquake motion is often used for analyzing the influence of trains on high-speed railway structure; however, the uncertainty of earthquake motion is rarely taken into consideration. In this study, on the basis of considering the uncertainty of earthquake motion, and taking a simply-supported beam with CRTS II track system and CRH2 high-speed train in China as the research objects, a finite element analysis model of vehicle-bridge coupled model was established and verified by tests. The influencing mechanism of the trains on structural response under the action of uncertain earthquake was analyzed, and the range of the influence levels of trains on seismic response of structure was calculated. The research findings show that under the effect of earthquake, the presence of trains decreases the responses of piers and bearings, while increases the response of track structure. With increasing peak ground acceleration, the effect of trains on the track structure deformation increases, while that on the bending moment of piers, shearing force, and bearing deformation all decrease. The increase in train speed will not significantly affect the seismic response of structures. The ratio of seismic response between the operating conditions with and without vehicles was kept within a certain range, so that the demand range for seismic response under the operating condition with vehicles can be approximately simplified. [ABSTRACT FROM AUTHOR]

Abstract A high-fill slope located in Zhenxiong County, Yunnan Province, China, was designed for building placement on its top platform. A reinforcement system consisting of a geogrid, front stability piles (FSPs), retaining sheets, prestressed anchors, and rear deeply buried piles (DBPs) has been used to stabilize the slope. Two typical slope sections were selected to study the high-fill slope stability and retaining mechanism of the reinforcement system. Field measurements of the horizontal displacement and strain in the piles, as well as the anchor working load, were collected and analyzed. In addition, a series of two-dimensional finite element method (FEM) analyses combined with a strength reduction technique was conducted to analyze two selected cross sections. The results show that the retaining structure behavior is closely related to the fill construction process of a high-fill slope. The deflection of the stabilizing pile increases almost linearly with the filling height in the initial stage of fill construction. The variation in the working load of the prestressed anchor shows an offset between prestress loss and increasing fill pressure. The FEM results can provide insight into the pile-soil interaction mechanism and its contribution to fill slope stabilization. The FSPs shift the sliding surface from through the slope toe to through the top of the FSPs. The anchors can reduce the bending moment by supplying additional bearing points. The DBPs can share a portion of the sliding thrust and effectively enhance the safety factor. This paper provides a reference for reinforcement system design for similar engineering projects considering high-fill slopes. Highlights • A case of reinforcement and monitoring for a high-fill slope is presented. • The reinforcement system includes two rows of piles, retaining sheets and anchors. • The behavior of the reinforcement system is investigated through field measurements. • The reinforcement mechanism is analyzed by FEM combined with monitoring. • This study provides a reference for the design of similar high-fill slopes. [ABSTRACT FROM AUTHOR]

• Tests and numerical analysis of specimens with large width-thickness ratios. • Elastic-plastic local buckling and its effects on hysteretic behaviour of beam-columns. • Design formula for bearing capacity of Q690 high strength beam-columns. To evaluate local buckling and its effect on the hysteretic performance of high-strength Q690 thin-walled H-section beam-columns, cyclic testing was carried out on four H-section columns composed of plates with a nominal yield strength of 690 MPa. Based on China's standard for the design of steel structures (GB 50010-2017), the four H-section columns are categorized as S4 and S5 sections, and the axial load ratio of the columns is 0.2 and 0.35. After the test, the failure mode, second-order effect of bending moment, hysteresis curve, bearing capacity, backbone curve, energy dissipation, ductility and stiffness degradation of the specimens were investigated. The failure mode of the specimens is elastic–plastic local buckling of the column bottom flange and web. The ductility coefficient of the specimens is 2.08–3.04, and they have certain specific deformation and energy dissipation capacities. Following this, a finite element model was established to simulate the hysteretic performance of the Q690 thin-walled H-section beam-columns. The failure mode and hysteresis curve obtained by the finite element simulation corresponded well with the tests. Based on this agreement, a parametric study was carried out to investigate the influence of the flange width-thickness ratio, web width-thickness ratio, and axial load ratio on the local buckling and hysteretic performance of H-section beam-columns. The variation trend of the backbone curve and the bearing capacity were further investigated by the finite element parametric analysis. Finally, a prediction formula for the beam-column bearing capacity was proposed based on the finite element results. The comparison with the test results shows that the proposed formula has sufficient accuracy and can be used in engineering design. [ABSTRACT FROM AUTHOR]