Search Results (524)

This paper reports on experimental investigations of a preloaded asymmetrical multi-bolted connection under operating conditions. At the beginning of the tests, the bolts were preloaded in a predetermined optimal order, in three passes, monitoring the bolt force values by means of a calibrated measuring system with strain gauges. The main tests were carried out on an Instron 8850 testing machine. The connection was subjected to sinusoidal loads with amplitudes of 10 kN and 20 kN at various frequencies. The data obtained was collected and recorded using prepared measurement pathway components, and then processed in MATLAB/Simulink R2018b. The observed measurement results are depicted in graphs displaying the distribution of forces in bolts as a function of cyclically varying operating loads. We have demonstrated that the forces in bolts also vary cyclically relative to their initial preload values. Due to the asymmetry of the connection, this variation was different for individual bolts. The results show bolt force deviations within ±2% and confirm the stability of the connection under cyclic operating loads. The presented results complement the database of experimental results, on the basis of which we will validate the systemic approach to modelling multi-bolted connections. Full article

This study proposes a design method for a novel bolted endplate rigid connection between circular concrete-filled steel tube (CCFT) columns and wide-flange (WF) steel beams, with particular emphasis on the parametric behavior governing joint performance. Based on the preliminary quasi-static tests, finite element simulations are conducted to evaluate the flexural behavior and failure mechanisms under beam-end maximum moment, followed by an extensive parametric study examining the effects of square tube dimensions, high-strength grout, and column axial load. The numerical results show that the wall thickness of the square steel tube significantly affects grout indentation. A 60% reduction in wall thickness led to a 503% increase in indentation. In contrast, variations in tube dimensions, grout strength, and column axial load within the studied range caused less than a 16% change and did not influence the flexural performance. These results indicate that the constraints on tube dimensions and axial load may be relaxed. The proposed connection effectively overcomes the limitations of conventional CCFT-to-beam joints, including unfavorable stress transfer, complex detailing, and construction inefficiency, by modifying the load-transfer mechanism and reducing the demand on tensile-critical welds, thereby enhancing ductility. Based on the parametric findings, a design method is established, and theoretical analysis confirms that the proposed connection satisfies the stiffness requirements for fully rigid connections. Future quasi-static tests with different member sizes are recommended to validate these findings. Full article

This study investigates the influence of out-of-plane beam skew on the cyclic performance of column-tree steel moment connections. Utilizing validated finite element (FE) models against experimental data, the cyclic responses of various configurations were evaluated under the AISC cyclic loading protocol up to a story drift ratio of 0.05 rad. Skew angles of 0°, 10°, 20°, and 30° were examined across three representative beam depths. The results demonstrate that all configurations satisfy the AISC 341 acceptance criteria for Special Moment Frames (SMFs), maintaining at least 80% of the plastic moment capacity (0.8 M_p) up to a 0.04 rad story drift ratio. However, the introduction of beam skew resulted in a gradual reduction in energy dissipation capacity, with the total dissipated energy decreasing by 2.9–8.9% at a 30° skew. Notably, the inelastic energy component was more sensitive to the skew than the frictional components, exhibiting a maximum reduction of 15.4%. While out-of-plane skew disrupted the symmetry of stress triaxiality and plastic strain at the beam-to-column interface, the overall fracture susceptibility was not significantly exacerbated up to 30°. Furthermore, column twisting remained within a negligible range (below 0.5°), and its impact on global stability was limited. Despite the general stability, a premature bolted splice failure was observed in deep beam configurations at a 30° skew during the 0.05 rad drift cycles. Based on these findings, it is concluded that column-tree connections with an out-of-plane skew up to 30° are viable; however, a design limit of 20° is recommended for deep beam configurations to ensure structural integrity under extreme cyclic demands. Full article

By applying nonlinear vibration-to-sound modulation technology to bolt loosening detection, this paper proposes a new experimental setup and signal-processing method. A linear swept-frequency signal is used to excite low-frequency vibrations, while a fixed-frequency sine wave is used for high-frequency ultrasonic excitation. First, a fractional Fourier transform is applied to the vibration-acoustic modulation signal to transform it into the optimal fractional domain where the energy of the swept-frequency signal is concentrated; next, the swept-frequency signal undergoes a masking filter, and the filtered signal is transformed back to the time domain; finally, the time-domain signal is transformed back to the frequency domain, and the amplitudes of the sum and difference frequency components of the high-frequency signal are extracted as damage parameters. The effectiveness of this method in bolt loosening detection was verified through bolt connection tests, with the applied tightening torque ranging from 10 to 30 N·m. This method is simple to operate and highly robust, making it a reliable approach for detecting the degree of loosening in bolt connections. Full article

The operational reliability of Emergency Diesel Generators (EDGs) is paramount for the safety of nuclear power plants. This study investigates the fretting wear mechanism on the non-working back-face of connecting rod big-end bearings—a critical failure mode that can lead to catastrophic engine damage. A synergistic approach was employed, integrating theoretical pressure calculations, on-site strain measurement experiments, and high-fidelity non-linear finite element analysis (FEA). The results demonstrate that while the theoretical design back-face pressure ranges from 8.1 to 10.1 MPa, the actual pressure is highly sensitive to bolt preload. A 16.2% attenuation in preload (from 550 kN to 461 kN), common during maintenance cycles, causes the interfacial pressure to drop to 6.9 MPa, falling below the recommended safety threshold of 7 MPa required to inhibit fretting. Furthermore, comparative experiments reveal that used bearings exhibit significantly lower and less uniform radial pressure retention compared to new bearings, even when physical dimensions appear compliant. Dynamic FEA indicates that peak inertial loads induce an out-of-roundness (DOR) of 0.295 mm, triggering a transition from a “partial slip” to a “macro-slip” regime at the interface. The findings confirm that the coupling of preload attenuation and loss of bearing elasticity drives the fretting process, providing a theoretical basis for optimized maintenance and selective assembly strategies. Full article

To explore the stress-bearing characteristics of the “inner tensioned steel ring–segment–surrounding rock” composite structure in TBM (Tunnel Boring Machine) pressurized water conveyance tunnels, a 3D refined finite element model for this composite structure was established, with the Class V surrounding rock section of the TBM pressurized water conveyance tunnel in the Rongjiang-Guanbu water diversion project selected as the research subject. The effects of the internal water pressure, surrounding rock type and tunnel burial depth on the mechanical properties of the composite structures are studied. The findings demonstrate that reinforcing the tunnel structure with an inner tensile steel ring can effectively constrain tunnel deformation, diminish the tensile stress of segments and the extent of tensile zones, and enhance the bearing capacity of the composite structure. Under the effect of internal water pressure, the compressive stress of segments, vertical deformation, joint opening degree, stress of connecting bolts, stress of the inner tension ring, and stress of anchor rods all exhibit a reduction compared to the scenario without internal water pressure. Under the combined action of external water–soil pressure and internal water pressure, variations in surrounding rock types lead to respective increases of 37.16%, 15.75%, and 15.12% in the stress of connecting bolts, segment joint misalignment, and anchor bolt stress. As the tunnel burial depth increases, the stress of connecting bolts and the vertical deformation of segment and the joint misalignment of the pipe segment increase by 140%, 107% and 60.61%, respectively. In addition, under the combined action of external water and soil pressure and internal water pressure, the load-sharing ratios of the surrounding rock, pipe segment, inner tension ring and anchor rod are 34.87%, 34.59%, 21.59% and 8.95%, respectively, and the load-sharing ratio of the inner tensioned ring is 85.80% higher than that observed in the absence of internal water pressure, indicating that internal water pressure effectively enhances the load-sharing performance of the inner tensioned steel ring. In the composite structure, the load-sharing ratio of surrounding rock decreases as the surrounding rock class increases (from Class III to Class V). Under the same load condition, the load-sharing ratio of Class III surrounding rock is 7.14% higher than that of Class V. As the tunnel burial depth increases, the inner tensioned steel ring and anchor rods function more prominently as reserve-bearing components. When the tunnel burial depth reaches 71 m, the load-sharing ratio of the inner tension steel ring and anchor rod increases by 19.91% and 55.72%, respectively, compared with that of the buried depth of 31 m. The research results can provide a theoretical reference for the lining design and late reinforcement measures of similar tunnel projects. Full article

Threaded fasteners and tapping joints are essential for the structural integrity and leak-proof performance of subsea systems subjected to high external pressure, aggressive corrosion, and complex cyclic loading. This study presents a comprehensive, systematically structured review of experimental, analytical, and numerical investigations of nut–bolt and threaded connections used in deep- and ultra-deepwater applications. The literature is classified based on governing performance parameters, including thread engagement mechanics, preload retention, fracture behavior, corrosion–fatigue interaction, material evolution, and environmental effects such as hydrostatic pressure and thermal gradients. Experimental observations are critically synthesized with finite element modeling to interpret stress distributions, failure mode transitions, and sealing reliability. A comparative material selection framework is developed by linking conventional carbon steels with advanced alloys such as duplex stainless steels, titanium, and nickel-based materials for long-term subsea service. The novelty of this review lies in the development of an integrated, design-oriented framework that unifies engagement optimization, preload control, fracture modeling strategies, material selection, and environmental coupling into a single engineering interpretation for subsea fastening systems, which has not been collectively addressed in previous studies. The presented synthesis provides direct application guidelines for improving the design, analysis, and operational reliability of subsea bolted joints. Full article

The stiffness of connections between machine elements depends on the geometry of the product and the condition of the material from which the joined elements are made. This stiffness is also influenced by the state of the surface geometrical texture and the technological parameters during the assembly process. This study examined whether, under normal load, there is a significant change in the geometrical state of the surfaces joined by a multi-bolted connection. It was shown that by properly performing the preloading process for such a connection, loss of the elastic properties of the jointed surfaces can be avoided. The 3D images of the surfaces of the joined elements obtained as a result of the measurements can be used to model multi-bolted connections in a systemic approach. Full article

This paper proposes a novel prefabricated beam-to-column joint to increase the seismic performance and post-earthquake recoverability of steel frames, which use the shape memory alloy (SMA) bolts and replaceable steel ring dampers. The comparative analysis of the seismic behavior was conducted for three beam-to-column connection types using finite element models. The three connection types include those installed using internal SMA bolts, external SMA bolts, and external SMA bolts with novel ring dampers. In addition, the novel ring damper was analyzed separately. These analysis results indicate that the connection type installed using external SMA bolts is superior to that by internal SMA bolts for the seismic performance of beam-to-column joints. The beam-to-column joints have the best seismic performance among the three joints when equipped with the additional steel ring damper, which can be easily replaced. This ring damper can increase the energy dissipation by approximately 11% and effectively reduce the stress of SMA bolts, which can delay their failure. The increasing preload of SMA bolts and high-strength bolts has a certain positive effect on the improvement of the seismic performance. All of the three joints exhibit excellent self-centering characteristics, with residual displacements nearly at zero. The gap of replaceable ring dampers can keep the re-centering capacity and improve the energy dissipation of joints. However, the changes in the steel strength of dampers have little impact on the seismic performance. This study verifies the improvement of the replaceable ring dampers on the seismic performance and post-earthquake recoverability, providing a reference for the seismic design of resilient structures. Full article

Beam-to-column connections govern both seismic performance and post-earthquake repairability of steel moment-resisting frames. Yet direct, apples-to-apples comparisons among welded, bolted, and repair-oriented replaceable-fuse moment connections are still scarce, which hinders rational selection for resilient construction. This study conducts a unified finite-element comparison of three representative joint archetypes—W-RBS, Bolted, and Prefab-web-fuse—under monotonic and cyclic loading. Consistent moment-rotation definitions are adopted, and normalized indices are introduced to compare hysteresis shape, degradation, and energy dissipation across joint concepts with different strength scales. Component-wise plastic dissipation is also extracted to quantify damage localization and assess main-frame protection and replaceability. Results reveal clear trade-offs: W-RBS provides the highest strength and dissipation but degrades most in stiffness; the bolted joint shows pinching due to interface compliance; and the web-fuse concept concentrates inelastic demand in a replaceable segment, supporting repairability-oriented design. The proposed framework offers mechanism-based guidance for selecting steel moment connections toward resilient and repairable frames. Full article

Slewing bearing is a rotating component with high load-carrying capacity, which is an important part of the crane connecting the upper rotating parts and the lower supporting parts; therefore, it is of great significance to analyze the performance of slewing bearings. This paper establishes a theoretical model and an integrated finite element model for the mechanical performance of slewing bearings, and the results of the two show high consistency. The influences of four bearing parameters (contact angle, raceway curvature radius coefficient, rolling element diameter, and number of rolling elements) and three bolt parameters (number of bolts, bolt preload, and washer thickness) on the mechanical performance of the slewing bearing were studied, aiming to provide a reference basis for the selection and design of crane slewing bearings. Full article

The mechanical method has become a new construction method for connected aisles in metro tunnels due to its advantages of fast construction speed, high safety, and minimal ground disturbance. During the tunneling process, the interaction mechanism between the composite segment and the shield cutterhead is complex. Taking Shenzhen Metro Line 8 No. 1 Connected Aisle as the research object, a 3D refined model of the shield cutterhead, composite segments and bolt system were built with Abaqus to investigate their dynamic response under cutting. The Drucker–Prager damage model and contact algorithm were introduced to describe the nonlinear behavior of the cutting process. The reliability of the numerical model was verified by concrete cutting tests and on-site Fiber Bragg Grating monitoring, and good agreements were observed. Results show cutterhead cutting first induces circumferential squeezing, then extends longitudinally with a notable time lag, and longitudinal dynamic response is much stronger than transverse. Affected by cutterhead thrust–rotation coupling, cuttable segments have larger displacement with maximum 0.07 mm, forming an asymmetric deformation zone. Ring joint opening follows “a distal attenuation of the opening amount” rule with maximum 0.018 mm, while bolt stress and displacement show “near-end concentration with gradient attenuation”, with longitudinal bolts being more responsive. Mechanical disturbance from small-shield cutting is minimal, with tunnel segment deformation, joint openings, and bolt stress all remaining well below code-specified allowable values. Numerical results show good agreement with field monitoring data of ring joint openings obtained using Fiber Bragg Grating (FBG) sensors, confirming the reliability of the simulation. The results can provide references for structural design and construction parameter optimization of composite segments in a connected aisle. Full article

The rapid development of multimegawatt wind turbines presents greater demands on the structural safety and stability of tower structures. In response, this study investigates the axial compressive behavior of steel–concrete–steel (SCS) composite towers with a low steel ratio and enhanced shear connection. The two steel plates are integrated by bolt connectors to ensure overall stiffness and effective composite action. Axial compression tests are conducted on curved tower wall members representing a 1/16 segment of the tower cross-section. Previous experimental results indicate that failure is dominated by local buckling of steel plates between adjacent connectors, highlighting the critical role of connector-induced confinement in controlling instability. Numerical models of curved composite walls are established and validated against previously published experimental results, showing good agreement in both failure modes and bearing capacity. Parametric analysis indicates that increasing the bolt diameter from 16 mm to 20 mm and 24 mm enhances the ultimate load by 3.09% and 6.58%, respectively. For the full-section tower model, reducing bolt spacing to 500 mm, 300 mm, and 250 mm increases the ultimate load by 16.33%, 20.05%, and 21.79%, respectively, compared to the bolt-free model. These results confirm that reducing connector spacing substantially enhances bearing capacity through improved confinement and delayed local buckling. A calculation method for evaluating the axial bearing capacity of SCS composite towers incorporating confinement effects is proposed, showing good consistency with both experimental and numerical data. Full article

Bolted joints are extensively used in mechanical and civil engineering structures because of their low cost, standardized design, and ease of installation and maintenance. The preload in a bolted connection is critical for ensuring joint stability and service reliability; however, preload degradation commonly occurs under complex operating conditions, particularly in environments involving sustained or cyclic vibration. To tackle this problem, this study proposes a portable, force-controllable percussion system for bolt looseness detection. The system integrates a solenoid-driven automatic percussion device, acoustic signal acquisition, onboard data-processing, and real-time visualization of diagnostic results. By adjusting the driving current of the solenoid, the percussion force can be accurately controlled, ensuring stable and repeatable excitation. Benefiting from its compact structure and low cost, the proposed system is suitable for real-time, on-site inspection of bolt looseness. Furthermore, a novel audio-processing approach based on a Siamese Capsule Network is developed to identify bolt looseness conditions. Compared with existing percussion-based techniques, the proposed method exhibits improved classification performance, especially in recognizing bolt states that are unseen during training. Exploratory experimental results validate the effectiveness of the proposed system and demonstrate its strong potential for practical engineering applications. Full article

Bolt-nut fasteners are critical components of substation equipment, and their integrity directly affects the operational reliability of power systems. In practical inspection scenarios, however, the small physical scale of bolt-nut fasteners, together with complex background structures, often obscures their discriminative visual features, making accurate automated detection particularly challenging. Reliable detection is a prerequisite for downstream tasks such as loosening identification and defect diagnosis. To address these challenges, this paper proposes YOLOv8n-ALC, an enhanced detection network built upon the lightweight YOLOv8n framework. The backbone is redesigned by integrating the AdditiveBlock from CAS-ViT and a Convolutional Gated Linear Unit (CGLU) to strengthen fine-grained feature extraction and suppress background interference without increasing computational burden. In addition, an improved Large Separable Kernel Attention (LSKA) module is introduced to expand the effective receptive field while maintaining efficiency, enabling more robust multi-scale feature representation. To further alleviate feature degradation of small bolt-nut fasteners in deep layers, a Context-Guided Reconstruction Feature Pyramid Network (CGRFPN) is employed in the neck to optimize cross-layer feature fusion and enhance localization accuracy. Experimental results demonstrate that YOLOv8n-ALC achieves an mAP@0.5 of 92.1%, with precision and recall of 93.5% and 87.1%, respectively, outperforming the baseline by clear margins. These results confirm the effectiveness and robustness of the proposed method for intelligent substation inspection and bolt-nut fastener condition monitoring. Full article