Search Results (43)

To investigate the bending performance and damage characteristics of segmental joints with double sealing gaskets in large-diameter shield tunnels under high water pressure, this study established a three-dimensional high-fidelity numerical model of the segment-joint system based on the Pearl River Estuary Tunnel project. A comprehensive analysis was conducted on the mechanical and deformation behavior of large-diameter shield tunnel segmental joints under combined compressive/flexural loading. The research systematically examined the evolving relationships between bending moments, vertical displacements, and joint opening at the double-sealed gasketed joints under varying axial compression conditions, thereby elucidating the phased characteristics of joint deformation. The results indicate that the deformation patterns of double-sealed gasketed segmental joints under compressive/flexural loading exhibit pronounced nonlinearity and stage-dependent features. Both positive and negative bending moment scenarios demonstrate four distinct failure phases. Under high-water-pressure conditions, structural damage initiation consistently occurs at waterproof sealing grooves and bolt holes, regardless of bending moment direction. As loading intensifies, cracks propagate symmetrically at 45° angles from the joint interface, generating extended fracture networks, which creates additional water infiltration pathways, significantly compromising the joint’s waterproofing integrity. Full article

To enhance the waterproofing performance of segment bolt holes in shield tunnels and ensure they meet the synergistic waterproofing requirements of segment joint sealing systems, a novel sealing gasket installed at the joint interface of the segment bolt hole has been designed. Numerical analysis was employed for a parametric study of factors influencing the waterproofing performance of the new gasket. Additionally, experimental research was conducted to evaluate its waterproofing capabilities. The study’s findings indicate that the hardness, height, and width of the novel bolt hole waterproof gasket significantly influence both the closure compression force and waterproofing performance. In contrast, the inner diameter primarily affects the closure compression force with a minimal impact on waterproofing performance. Compared to traditional water-swellable gaskets used for segment bolt holes, the novel EPDM (Ethylene Propylene Diene Monomer) waterproof gasket is more effective in mitigating the effects of manufacturing defects. For double-gasket segment joint sealing systems where the waterproofing strength of the bolt hole is critical, the adoption of this novel bolt hole waterproof gasket can better satisfy the synergistic waterproofing requirements between the two sealing gaskets, thereby effectively improving the overall waterproofing capacity of the segment joint sealing system. Full article

This paper presents the results of preliminary numerical and experimental studies concerning the sealing performance of static seals (gaskets) with geometrically designed sealing surface microstructures. The concept of the microstructure, inspired by the operating principle of Tesla’s one-way valve, relies on the generation of localized flow circulation within the microchannels formed between the contact surfaces, which increases flow resistance and reduces leakage. CFD simulations were performed to assess the influence of the geometric parameters of the microstructure on the leakage rate. The numerical calculations demonstrated that introducing microstructures into the gap formed between the contact interfaces can significantly reduce leakage, with the most critical geometric parameters being the gap width between the microprotrusions, their packing density, and their height. Experimental studies confirmed the higher sealing performance of structured gaskets compared to quasi-smooth gaskets, particularly at lower contact pressures. An analysis of the effective contact surface revealed that the improvement in tightness is a result of both the local intensification of the contact pressure and the flow effects induced by the microprotrusions. The results obtained confirm that an appropriately designed surface microstructure can substantially enhance the sealing performance of flange-bolted joints, even under relatively low clamping loads. Full article

To investigate the longitudinal mechanical behavior of shield tunnels traversing soft and hard heterogeneous strata, a refined three-dimensional numerical model was developed using ABAQUS. The model includes tunnel segments, longitudinal bolts, reinforcement, longitudinal thrust, and additional loading conditions to simulate realistic mechanical responses during construction and operation. The results show that significant differential settlement occurs at the interface between soft and hard soils. Greater joint dislocation is observed on the soft soil side, while joint opening is more pronounced on the hard soil side. Compressive damage concentrates at the soil interface, whereas tensile damage is more severe in soft soil zones. The dislocation at the vault is distributed over a wider area but has a smaller magnitude than that at the arch bottom. Parametric analysis indicates that increasing longitudinal thrust enhances tunnel stiffness and reduces joint dislocation. However, it also leads to increased compressive and tensile damage due to greater trans-verse deformation. Optimizing bolt configuration, including diameter, inclination, and quantity, improves longitudinal stiffness and joint integrity, helping to reduce tensile damage and control deformation. These findings provide theoretical support for the structural design and performance optimization of shield tunnels in complex geological environments. Full article

Steel–timber composite (STC) structures offer a sustainable and low-carbon structural solution. Steel–timber interface behavior is critical for the mechanical performance of STC structures. This paper introduces a novel connection for steel–timber composites (STC) that combines mechanical interlocking with adhesive bonding through an epoxy-bonded bolted design. Epoxy resin is injected into the timber dowel slots, followed by pre-tightening of the bolts, forming a composite dowel system where the ‘bolt–epoxy resin–timber’ components work in synergy. The load–displacement characteristics and failure modes of nine specimen groups were investigated through a series of double-shear push-out tests. The influence of a wide range of connector parameters on the stiffness, shear bearing capacity, and ductility of STC joints was systematically investigated. The parameters included fastener strength grade, thread configuration, diameter, number, and the use of epoxy resin reinforcement. The experimental results demonstrated that high-strength partially threaded bolts were crucial for achieving a synergy of high load-bearing capacity and commendable ductility, while full-threaded bolts exhibited vulnerability to brittle shear failure, a consequence of stress concentration at the root of the threads. Although screw connections provided enhanced initial stiffness through timber anchorage, ordinary bolt connections exhibited superior ultimate load-bearing capacity. In comparison with conventional bolt connections, epoxy resin–bolt connections exhibited enhanced mechanical properties, with an augmentation in ultimate load and initial stiffness of 12% and 11.8%, respectively, without sacrificing ductility. Full article

The stability of shield tunnel segmental linings is highly sensitive to the lateral pressure coefficient, especially under weak, heterogeneous, and variable geological conditions. However, the mechanical behavior of steel plate-reinforced linings under such conditions remains insufficiently characterized. This study aims to investigate the effects of varying lateral pressures on the structural performance of reinforced tunnel linings. To achieve this, a custom-designed full-circumference loading and unloading self-balancing apparatus was developed for scaled-model testing of shield tunnels. The experimental methodology allowed for precise control of loading paths, enabling the simulation of realistic ground stress states and the assessment of internal force distribution, joint response, and load transfer mechanisms during the elastic stage of the structure. Results reveal that increased lateral pressure enhances the stiffness and bearing capacity of the reinforced lining. The presence and orientation of segment joints, as well as the bonding performance between epoxy resin and expansion bolts at the reinforcement interface, significantly influence stress redistribution in steel plate-reinforced zones. These findings not only deepen the understanding of tunnel behavior in complex geological environments but also offer practical guidance for optimizing reinforcement design and improving the durability and safety of shield tunnels. Full article

In advanced structural applications—aerospace and automotive—fiber-laminated composite (FRP) materials are increasingly used for their superior strength-to-weight ratios, making the reliability of their mechanical joints a critical concern. Mechanically fastened joints play a major role in ensuring the structural stability of FRP Composite structures; however, accurately predicting their failure behavior remains a major challenge due to the anisotropic and heterogeneous nature of composite materials. This paper presents a progressive damage modeling approach to investigate the failure modes and joint strength of mechanically fastened carbon fiber-laminated (CFRP) composite joints. A 3D constitutive model based on continuum damage mechanics was developed and implemented within a three-dimensional finite element framework. The joint model comprises a composite plate, a steel plate, a steel washer, and steel bolts, capturing realistic assembly behavior. Both single- and double-lap joint configurations, featuring single and double bolts, were analyzed under tensile loading. The influence of clamping force on joint strength was also investigated. Model predictions were validated against existing experimental results, showing a good correlation. It was observed that double-lap joints exhibit nearly twice the strength of single-lap joints and can retain up to 85% of the strength of a plate with a hole. Furthermore, double-lap configurations support higher clamping forces, enhancing frictional resistance at the interface and load transfer efficiency. However, the clamping force must be optimized, as excessive values can induce premature damage in the composite before external loading. The stiffness of double-bolt double-lap (3DD) joints was found to be approximately three times that of single-bolt single-lap (3DS) joints, primarily due to reduced rotational flexibility. These findings provide useful insights into the design and optimization of composite bolted joints under tensile loading. Full article

This paper examines the costs associated with installing PIP (Pile-in-Pile) slip joints compared to traditional tubular joints, focusing on investment, installation processes, and long-term benefits. Previous studies have indicated that the structural performance of PIP slip joints is superior to that of traditional joints. By utilizing the frictional interfaces between conventional structural steel components and the simplest installation methods, PIP slip joints maximize structural integrity and ease of maintenance. As a result, they can lead to lower lifecycle costs, provided they are installed correctly. Quantitatively, the PIP slip joint achieved the highest internal rate of return (IRR) at 43.42%, the lowest Levelized Cost of Energy (LCOE) at 0.013589 EUR/kWh, and the shortest payback period at 2.92 years—outperforming grouted and bolted flange joints across all key financial metrics. The analysis also addresses logistical challenges and workforce requirements, highlighting that significant economic benefits can be realized when implemented appropriately. Furthermore, the PIP slip joint promotes sustainability goals by minimizing material usage, which ultimately leads to reduced carbon emissions through more efficient fabrication and installation, as well as enabling faster deployment. A comprehensive financial assessment of these joint systems in offshore wind monopiles reveals that PIP slip joints are the most cost-effective and financially advantageous option, outperforming key metrics like IRR, LCOE, and payback period due to lower initial investments and operational costs. As PIP slip joints yield a higher net present value (NPV), a shorter payback period, and a lower LCOE, they can enhance profitability and reduce financial risk, and are suitable for streamlined implementation. While grouted and bolted flange joints exhibit similar financial performance, PIP slip joints’ minimal expenditure and consistent superiority make them the optimal choice for sustainable and economically viable offshore wind projects. Full article

The paper presents the effect of the symmetric and asymmetric semi-metallic gasket core shape on the tightness level in bolted flange joints. Experimental tests, as well as numerical calculations based on the finite element method, revealed that the asymmetric gasket core provides a higher strain on the sealing graphite layer and leads to a more uniform distribution of strain on the particular ridges of the core. Furthermore, the leakage rate of the asymmetric gasket was reduced by approximately 60% compared to the symmetric gasket. It was also observed that the uniformity of pressure and strain distribution in a gasket with an asymmetric core occurs over about 80% of the gasket width. The leakage reduction effect in a flange joint sealed with a gasket with an asymmetric core was theoretically explained. As shown, the main leakage flows through the porous structure of the graphite layer, while the leakage path at the interface between the metal rough profile and the graphite layer is several orders of magnitude smaller. Full article

The joint of a shield tunnel segment is the weak part of tunnel, and the opening amount of the joint seriously affects the watertightness of the internal structure of the tunnel. In this experiment, a model was created with ANSYS, the fluid–solid coupling effect of the seawater and seabed was considered using the SuperFLUSH/2D 6.0 software, and the local site effect was considered by free-field seismic response analysis. Considering the structure and stress characteristics of the shield tunnel in conjunction with the marine area, earthquake research on shield tunnel culverts was conducted using lateral and longitudinal beam–spring models. The main focus of this article is to study the earthquake resistance of shield tunnel joints under extreme seismic excitation (SL-2) in complex marine environments. The results indicated that in the lateral analysis, under varying soil layer conditions, the diameter deformation rates for sections 1 and 2 using high-strength bolts were 1.752% and 1.334%, respectively, while the joint-opening amounts were 0.515 mm and 0.387 mm, respectively. This suggests that locations with thicker silt layers exhibit larger joint-opening amounts and are more susceptible to deformation. In the longitudinal analysis, when bolt strength varied, the maximum joint-opening ranged from 4.706 mm to 6.507 mm, and the maximum dislocation ranged from 0.625 mm to 1.326 mm. The deformation rule of the joint bolts followed the pattern that higher stiffness led to smaller deformation, whereas poorer geological conditions resulted in larger deformation. Therefore, the interface between soft and hard strata is a weak point in the longitudinal seismic resistance of the shield tunnel structure. The conclusions of this study can supplement the seismic research on shield tunnels in the marine areas of nuclear power plants. Full article

Featured with optimal power consumption, active magnetic bearings (AMBs) have been extensively integrated into turbomachinery applications. For turbomachinery components, including the rotor and impeller, their connection is generally based on bolted joints, which would easily induce excessive interface contact. As a result, the pre-tightening torque can induce modal vibrations in the rotor upon levitation. Although a notch filter can be adopted to suppress the vibrations, it should be noted that the current reported notch filters are based on fixed center frequency, making it challenging to enable high effectiveness over a broad range of rotor speeds, particularly in cases where the gyroscopic effect is significant. Herein, a modal vibration suppression based on a varying-frequency notch filter is proposed, considering gyroscopic effect and interface contact. First, the rotor–AMB system was developed, taking into consideration the bolted-joint interface contact. This modeled the effect of the interface contact as a time-varying force in the positive feedback. Secondly, the relationship between vibration frequency and rotational speed was obtained, based on simulations. Lastly, a test rig was configured to validate the performance of the frequency-varying notch filter. The experimental data confirm that the filter is capable of attenuating the modal vibrations resulting from interface contact across all operational speeds. Full article

During the excavation process of a Tunnel Boring Machine (TBM), the cutterhead exerts significant torque on the tunnel structure, which potentially causes torsional shear deformation at segment ring joints. Thus, examining the characteristics of torsional shear deformation and the shear-bearing performance of segment joints under construction torque is crucial for the design and safety of segment structures and the construction of TBM tunnels. To achieve this, a refined finite element model of the segment joints was developed to study their torsional shear resistance under varying axial forces and with or without mortise and tenon. Furthermore, the failure modes of bolts and the damage characteristics of segment concrete during torsional shear deformation are analyzed. The results show that the load-bearing process of torsional shear deformation in segment joints consists of three stages: development of the friction at the segment interface (Stage I), development of the bolt force (Stage II), and development of the mortise and tenon force (Stage III). It is noteworthy that axial force is the primary factor in enhancing the torsional shear resistance of the segmental joints. Moreover, as the torsional shear deformation increases, the contact and compression occur between the bolts and the segment bolt holes as well as between the mortise and tenon, leading to the yielding of the bolts and the failure of the concrete at the joints. Consequently, the segment concrete around the mortise and tenon and the bolt hole is prone to cracking and crushing. To prevent shear failure of the bolts, it is recommended that the rotational angle of segment be maintained at less than 0.045°. Full article

As a weak part of the concrete tower in wind turbines, the insufficient shear capacity of vertical joints can cause the local shear failure of the tower, reduce the overall bearing capacity and stability of the tower, and lead to safety issues. At present, the splicing of tower vertical joints mainly uses epoxy resin filling and arc bolt connections. However, sometimes the concrete near the vertical joints is damaged due to compression after applying pretension to the arc bolts, which will affect the bearing capacity and stability of the entire tower structure. If other interface processes are used for vertical joint splicing, the shear performance will be directly affected. Therefore, in order to study the influence of different interface processes on the shear performance of vertical joints in concrete tower tubes, four vertical joint specimens were designed for a pull-out test under shear load and the failure mode of the specimens and the shear capacity of the vertical joint interface were analyzed and studied. The results showed that with an increase in epoxy thickness and the application of an interface chiseling treatment, as well as injecting epoxy resin into the channels, the shear performance of vertical joints could be enhanced. Finally, based on existing research and standardized design methods, the shear capacity of vertical joints in wind turbine concrete towers was predicted, which showed that the existing design methods were not yet fully applicable to the shear capacity design of vertical joints in wind turbine concrete towers with different interface processes. Further research is needed to supplement and improve them. Full article

C/SiC composites are widely used in aerospace thermal structures. Due to the high manufacturing complexity and cost of C/SiC composites, numerous hybrid joints are required to replace large and complex components. The intricate contact behavior within these hybrid joints reduces the computational efficiency of damage analysis methods based on solid models, limiting their effectiveness in large-scale structural design. According to the structure characteristic, a fractal contact stiffness model considering bonded behaviors is established in this paper. By introducing this model, it is proved that the bonded layer can affect the interface strength between plates but not the bearing strength of the specimen for the bolt/bonded hybrid joint structure. Furthermore, by introducing the strength envelope method, this paper overcomes the problem wherein the shell-fastener model cannot accurately describe the complex stress field. Validation through experimental comparison confirms that this approach can accurately predict both the failure mode and strength of multi-row hybrid joint structures in C/SiC composites at a detailed level with an error of 5.4%, including the shear failure of bolts. This method offers a robust foundation for the design of large-scale C/SiC composite structures. Full article

Contact interface is essential for the dynamic response of the bolted structures. To accurately predict the dynamic characteristics of bolted joint structures, a fractal extension of the segmented scale model, i.e., the JK model, is proposed in this paper to comprehensively analyze the dynamic contact performance of engineering surfaces and revisit the multi-scale model based on the concept of asperities. The influence of asperity geometry, dimensionless material properties, and the elastic, elastoplastic, and full plastic mechanical models of a single asperity is established considering the asperity–substrate interaction. Then, a segmented scale contact model of rough surfaces is proposed based on the island distribution function in a strict sense. The mechanical contact process of determining rough surfaces is divided into small-scale, medium-scale, and large-scale stages. Moreover, cross-scale boundary conditions, i.e., a_l1′, a_l2′, and a_l3′, are provided through strict mathematical deduction. The results show that the real contact area and contact stiffness are positively correlated with fractal dimension and negatively correlated with fractal roughness. On a small scale, the contact damping decreases with an increase in load. In meso-scale and large-scale stages, the contact damping increases with the load. Finally, the reliability of the proposed model is verified by setting up three groups of modal vibration experiments. Full article