Search Results (17)

Titanium alloy TC4 countersunk head bolts (CHB) are widely used in spacecraft structures, but the research on CHB does not receive enough attention at present. There are still some more opportunities worthy of in-depth research, such as insufficient research on CHB of high-strength fasteners for aerospace applications, an insufficient combination of CHB simulation tests with real working conditions, and inspection and testing methods. In this study, through the combination of finite element simulation and experiments, the working conditions of the CHB connection structure bearing tensile load and CHB screwing were analyzed, and the requirements of the CHB connection structure and installation of CHB were optimized. Based on the single-bolt tensile simulation, the working conditions of multi-bolt connection structures under eccentric load and single-bolt composite laminate connection structures under tensile load were analyzed. Meanwhile, the structure of CHB was further optimized, and the simulation analysis model of the CHB tightening process was established. The research shows that the larger fixing bolt countersunk angle θ₁ and the smaller countersunk fillet radius r, the better the ultimate bearing capacity of the connection structure will be. When the countersunk bevel angle of pressure plate θ₂ was greater than or less than 100°, the clamping force–angle slope will decrease, while when θ₂ was smaller, it will have a greater influence on the slope. The coaxiality Φ had little influence on the slope around the allowable tolerance range (0.3 mm), but the influence on the slope becomes greater when it exceeds the tolerance range. The research results provide a reference and basis for the layout of CHB and the use of composite materials in aerospace connection structures. Full article

A novel hydraulically actuated uniform clamping flange connection mechanism is proposed to address the long-standing challenges in high-pressure natural gas flowmeter calibration, including cumbersome bolt-by-bolt assembly/disassembly, high leakage risk, and severe non-uniform gasket contact pressure associated with conventional multi-bolt flanges. Unlike traditional discrete bolt loading, the proposed mechanism generates a continuous and actively adjustable circumferential clamping force via an integrated hydraulic annular piston, ensuring excellent sealing uniformity and rapid installation within minutes. A high-fidelity transient finite element model of the hydraulic clamping flange assembly is established, incorporating the nonlinear compression/rebound behavior of flexible graphite–stainless steel spiral-wound gaskets and one-way fluid–structure interaction under water hammer loading. Parametric studies reveal that reducing the effective clamping area to below 80% of the original design significantly intensifies stress concentration and compromises sealing integrity, while clamping force below 80% or above 120% of the nominal value leads to leakage or component overstress, respectively. Under steady 10 MPa pressurization, the flange exhibits a maximum stress of 150.57 MPa, a minimum gasket contact stress exceeding 30 MPa, and a rotation angle below 1°, demonstrating robust sealing performance. During a severe water hammer event induced by rapid valve closure, the peak flange stress remains acceptable at 140.41 MPa, while the minimum gasket contact stress stays above the critical sealing threshold (38.051 MPa). However, repeated water hammer cycles increase the risk of long-term gasket fatigue. This study introduces, for the first time, a hydraulic uniform-clamping flange solution that dramatically improves sealing reliability, installation efficiency, and operational safety in high-pressure flowmeter calibration and similar temporary high-integrity piping connections, providing crucial technical guidance for field applications. Full article

Recently, the problem of climate change caused by the increase in greenhouse gases has become a major issue, and the importance of eco-friendly energy is increasing worldwide. The installation of PV systems is increasing, and they are being installed in areas adjacent to users. Nevertheless, the concerns relevant to safety problems, such as grounding modules to prevent electric shock accidents, should be addressed. This study examined the effectiveness of applying grounding clips for PV module installations. When the grounding clip was applied, it showed approximately 6.7% improvement compared to the resistance value of the existing grounding wire. The grounding performance and construction convenience of the technology applied with the new grounding clip were verified by a comparison with the existing conventional grounding wire. For manufacturing the clips, a mold with a 32° cone angle and a height of 3.5 mm was used, and a fastening torque of 225 kgf∙cm was found to achieve satisfactory grounding resistance values compared to the conventional approach. Using a power tool and expanding it to nine modules (=5.56 kWp), the clip installation process took 585 s, which succeeded in reducing the installation time by approximately 38.1% compared to the 945 s taken using wires. Moreover, the module could be installed and grounded with only a two-step process of installing the module and fastening it with bolts, increasing the installation economy. Full article

Double-arch tunnels in inclined layered jointed rock masses face risks of lining cracking and collapse under bedding-inclined asymmetric stress (BIAS); however, related studies remain limited. Based on a case study of an expressway tunnel case in Zhejiang Province, a three-dimensional discrete element model of a double-arch tunnel was developed using Three-Dimensional Distinct Element Code (3DEC) (version 7.0, Itasca Consulting Group, Inc., Minneapolis, MN, USA). The impacts of joint dip angle (0–90°) and spacing (0.5–6.5 m) on deformation, BIAS evolution, and middle partition wall stability were analyzed. Key findings reveal that joint presence significantly amplifies surrounding rock deformation, with pronounced displacement increases observed on the counter-dip side. The BIAS intensity follows a unimodal distribution with joint dip angles, peaking within the 30–60° range. Increasing joint spacing reduces BIAS effects, with a 57.1% decrease in asymmetric deformation observed when spacing increases from 0.5 m to 6.5 m. The implementation of dip-side pilot excavation with the main tunnel full-face method, combined with an optimized support strategy (installing dip-side bolts perpendicular to joints and extending counter-dip side bolt lengths from 4 m to 6 m), achieved a near-unity stress ratio between tunnel sides under equivalent overburden depths compared to conventional methods. These findings offer theoretical and technical insights for optimizing excavation and reinforcement in similar tunnel engineering contexts. Full article

We systematically investigated the anchorage performance of self-drilling anchor bolts in strongly weathered dolomite through integrated field pull-out tests and FLAC3D numerical modeling. The study incorporates symmetry principles in both experimental design and numerical simulations to ensure balanced force distribution and model simplification. Experimental data collected from a slope reinforcement project demonstrated that grouting parameters of 0.8 MPa pressure and 0.8 water–cement ratio achieved an interfacial bond strength of 0.147 MPa, surpassing the recommended value by 22.5%. A modified FLAC3D pile element, calibrated against RS6-01 anchor bolt test data, exhibited improved alignment with load–displacement curves, converging to 272 kN ultimate capacity at 26.1 mm displacement. Symmetrical anchor configurations in the numerical model reduced computational complexity while maintaining accuracy in stress distribution analysis. Through orthogonal experimental design, symmetry-driven parameter optimization identified a 7 m bolt length, 30° installation angle, and 2 m spacing as the most effective configuration. This solution increased the slope safety factor by 19.98% while reducing displacements by 46–62%. The symmetry in anchor spacing and angular alignment contributed to uniform stress redistribution, enhancing slope stability. The findings highlight the synergy between symmetry principles and geotechnical reinforcement strategies. Full article

This study examined the influence of the effective embedment depth h_ef of undercut anchors and the diameter of their heads on the formation of the so-called cone failure angle α. Cone failure formation during simulated anchor pull-out tests was analyzed numerically using the Finite Element Method (FEM) with the ABAQUS software and the XFEM algorithm. The analysis was conducted for three sizes of undercut anchor heads and four embedment depths. The numerical analysis results were compared with field test results obtained during pull-out tests of anchors installed in a rock medium (sandstone). Good agreement was observed between the numerical and field test results. The results of the numerical study are highly consistent with those obtained during the field survey. Moreover, they align closely with findings from previous numerical studies conducted by members of the research team, as presented in earlier publications. For the assumed simulation and field test conditions (sedimentary rocks, gray sandstone), no clear correlation was found between the embedment depth or the anchor head diameter and the value of the cone failure angle in the initial phase of the failure zone development. This result contrasts with certain findings reported in the literature. Many existing studies on anchor bolts focus on material properties or load-bearing capacity, but lack an in-depth analysis of how anchor depth influences the geometry of the failure cone. This research addresses that gap, providing valuable insights with practical implications for design codes and safety evaluations. Full article

Existing support systems for thermal pipeline trenches often fail to meet the specific needs of narrow strips, tight timelines, and short construction periods in urban environments. This study introduces a novel recyclable, non-embedded support system composed of corrugated steel plates, retractable horizontal braces, angle steel, and high-strength bolts designed to address these challenges. The system’s effectiveness was validated through prototype testing and optimized using Abaqus finite element simulations. The research hypothesizes that this new support structure will enhance construction efficiency, reduce installation costs, and provide adaptable and sustainable solutions in urban trench applications. Prototype tests demonstrated that the proposed support had maintained safety and stability in trenches of 2 m and 3 m depth under a 58 kPa load and rainfall, as well as the 4 m deep trenches under asymmetric loading of 80 kPa. Optimization of the proposed system included installing two screw jacks on each horizontal brace and adjusting the corrugated plates, resulting in reduced weight, improved node strength, and enhanced screw jack adjustability. Numerical simulations confirmed the optimized system’s reliability in trenches up to 3 m deep, with caution required for deeper applications to avoid structural failure. The proposed support system offers notable advantages over traditional methods by improving construction efficiency, flexibility, and adaptability while also reducing costs, ensuring safety, and promoting environmental sustainability. Its modular design allows for rapid installation and disassembly, making it suitable for projects with strict deadlines and diverse construction conditions. The findings uphold the initial hypotheses and demonstrate the system’s practicality in urban trench projects. Full article

The mechanical properties of fully-grouted bolt support are critical for the safety of support engineering works. To study the influences of factors including the bolt length and diameter, strength of the rock, and fracture angle on the mechanical properties of fully-grouted bolt support, compression tests were conducted on an anchored rock mass, considering the shortcomings of pullout tests on bolts. The discrete element software PFC^2D (4.0) was adopted for numerical simulation and analysis from two aspects, namely, the stress distribution and anchorage force supplied by such bolts. The research found that by increasing the bolt diameter and length as well as the strength of the rock, the maximum anchorage force of bolts increases. Whereas the stress distribution of all bolts increases at first and then decreases along the bolts, and there is only one peak on the stress distribution curves, which also gradually shifts to a greater depth. In a fractured rock mass, the maximum anchorage force of bolts decreases, then increases (and is minimized at a fracture angle of 45°) with the decrease in fracture angle. The influence of fractures with different angles on the stress distribution of bolts is mainly reflected in the fracture zone. The bolt stress decreases abruptly in the zone with a fracture angle of 90°, forming a valley. The bolt stress increases suddenly in the zones with fracture angles of 60° and 45°, thus forming peaks. The bolt stress does not increase or decrease suddenly in the zone with a fracture angle of 30°. Therefore, it necessitates consideration of the influences of fractures on the anchorage force and the selection of bolts of appropriate size during anchorage design. After installation, the bolt stress should be monitored for stability and early warning of anchored rock mass according to changes in the stress provided. Full article

Rock bolting is a commonly used method for stabilizing the surrounding rock in coal-mine roadways. It involves installing rock bolts after drilling, which penetrate unstable rock layers, binding loose rocks together, enhancing the stability of the surrounding rock, and controlling its deformation. Although recent progress in drilling and anchoring equipment has significantly enhanced the efficiency of roof support in coal mines and improved safety measures, how to deal with drilling rigs’ misalignment with the through-hole center remains a big issue, which may potentially compromise the quality of drilling and consequently affect the effectiveness of bolt support or even result in failure. To address this challenge, this article presents a robotic teleoperation system alongside a hybrid visual servo control strategy. Addressing the demand for high precision and efficiency in aligning the drilling rigs with the center of the drilling hole, a hybrid control strategy is introduced combining position-based and image-based visual servo control. The former facilitates an effective approach to the target area, while the latter ensures high-precision alignment with the center of the drilling hole. The robot teleoperation system employs the binocular vision measurement system to accurately determine the position and orientation of the drilling-hole center, which serves as the designated target position for the drilling rig. Leveraging the displacement and angle sensor information installed on each joint of the manipulator, the system utilizes the kinematic model of the manipulator to compute the spatial position of the end-effector. It dynamically adjusts the spatial pose of the end-effector in real time, aligning it with the target position relative to its current location. Additionally, it utilizes monocular vision information to fine-tune the movement speed and direction of the end-effector, ensuring rapid and precise alignment with the target drilling-hole center. Experimental results demonstrate that this method can control the maximum alignment error within 7 mm, significantly enhancing the alignment accuracy compared to manual control. Compared with the manual control method, the average error of this method is reduced by 41.2%, and the average duration is reduced by 4.3 s. This study paves a new path for high-precision drilling and anchoring of tunnel roofs, thereby improving the quality and efficiency of roof support while mitigating the challenges associated with significant errors and compromised safety during manual control processes. Full article

Construction industrialization addresses various challenges in the traditional construction industry, enabling building structures to conserve resources and enhance energy efficiency while reducing emissions. Precast shear walls involve the factory-based production of components, followed by transportation to a construction site for assembly. The method of connecting these components is crucial for precast concrete shear wall systems. Common connection methods include lap-spliced connections, post-tensioned connections, welded connections, bolted connections, and sleeve connections. However, challenges such as construction precision and technology proficiency have limited their application. In response, a novel precast concrete shear wall system utilizing angle steel connectors has been proposed. These angle steel connectors enhance the shear resistance of horizontal joints between precast concrete shear walls and the foundation, providing provisional support for specimen positioning and installation. Presently, the seismic performance of this innovative precast shear wall system under the combined actions of cyclic horizontal loads and axial pressure or tension has been extensively investigated. In practical engineering applications, precast concrete shear wall systems are often accompanied by infill walls. However, there is limited research on the seismic performance of precast concrete shear wall systems with infill walls. To address this gap, this study designed and fabricated two novel precast concrete shear walls with different infill wall constructions. One specimen featured an infill wall composed of a single wall panel, while the other had an infill wall consisting of two panels. Pseudo-static tests were conducted on both specimens under constant axial compression. Subsequently, the seismic performance and force mechanism of the two specimens were compared with the novel precast concrete shear walls without infill walls. The test results demonstrated that the specimen with two infill wall panels exhibited superior overall performance compared to the one with a single continuous infill wall panel. Furthermore, it was observed that, during the loading process, the edge columns of specimens with infill walls provided the majority of the increased load-bearing capacity, while the infill walls made a limited contribution to the overall load-bearing capacity of the structures. Full article

To explore the mechanical failure characteristics of bolted joints under different bolt installation angles and the effect of bolting on the shear strength of joints, a numerical model of structural plane anchoring with different bolt installation angles was established based on the improved Pile element, and a series of uniaxial compression numerical tests were carried out to systematically study the effects of bolt installation angle on bolts. The results show that as the bolt installation angle increases, the peak stress of the specimen is first constant and then decreases, and the elastic modulus of the specimen decreases nonlinearly. When the bolt installation angle is lower than 45°, the bearing capacity of the joints is higher. The interaction between the bolt and the specimen’s force is mainly concentrated at the intersection of the structural plane and the area where the nut gaskets are installed at both ends of the bolt. The horizontal stress is higher in the area where the nut gaskets are installed at both ends of the bolt. With an increase in bolt installation angle, the plastic zone volume of the anchored joint specimen increases linearly with an exponential function. When the bolt installation angle is lower than 45°, the plastic zone volume increases slowly, and when the bolt installation angle is higher than 45°, the plastic zone volume increases rapidly. When the bolt installation angle is small, the contribution of the bolt axial force is greater than that of the bolt shear force. In contrast, when the bolt installation angle is large, the contribution of the bolt axial force is lower than the contribution of the bolt shear force. With an increase in bolt installation angle, the contribution of the bolt axial force decreases nonlinearly, the contribution of the bolt shear force increases linearly, and the shear resistance decreases nonlinearly. The optimal bolt installation angle is about 45°, but the optimal bolt installation angle also changes constantly under the influence of factors such as bolt type, rock strength, and external load. Full article

Bolted spherical joints, due to their prominent merits in installation, have been widely used in modern spatial structures. Despite significant research, there is a lack of understanding of their flexural fracture behaviour, which is important for the catastrophe prevention of the whole structure. Given the recent development to fill this knowledge gap, it is the objective of this paper to experimentally investigate the flexural bending capacity of the overall fracture section featured by a heightened neutral axis and fracture behaviour related to variable crack depth in screw threads. Accordingly, two full-scale bolted spherical joints with different bolt diameters were evaluated under three-point bending. The fracture behaviour of bolted spherical joints is first revealed with respect to typical stress distribution and fracture mode. A new theoretical flexural bending capacity expression for the fracture section with a heightened neutral axis is proposed and validated. A numerical model is then developed to estimate the stress amplification and stress intensity factors related to the crack opening (mode-I) fracture for the screw threads of these joints. The model is validated against the theoretical solutions of the thread-tooth-root model. The maximum stress of the screw thread is shown to take place at the same location as the test bolted sphere, while its magnitude can be greatly reduced with an increased thread root radius and flank angle. Finally, different design variants related to threads that have influences on the SIFs are compared, and the moderate steepness of the flank thread has been found to be efficient in reducing the joint fracture. The research findings could thus be beneficial for further improving the fracture resistance of bolted spherical joints. Full article

With the development of industrial automation, articulated robots have gradually replaced labor in the field of bolt installation. Although the installation efficiency has been improved, installation defects may still occur. Bolt installation defects can considerably affect the mechanical properties of structures and even lead to safety accidents. Therefore, in order to ensure the success rate of bolt assembly, an efficient and timely detection method of incorrect or missing assembly is needed. At present, the automatic detection of bolt installation defects mainly depends on a single type of sensor, which is prone to mis-inspection. Visual sensors can identify the incorrect or missing installation of bolts, but it cannot detect torque defects. Torque sensors can only be judged according to the torque and angel information, but cannot accurately identify the incorrect or missing installation of bolts. To solve this problem, a detection method of bolt installation defects based on multiple sensors is proposed. The trained YOLO (You Only Look Once) v3 network is used to judge the images collected by the visual sensor, and the recognition rate of visual detection is up to 99.75%, and the average confidence of the output is 0.947. The detection speed is 48 FPS, which meets the real-time requirement. At the same time, torque and angle sensors are used to judge the torque defects and whether bolts have slipped. Combined with the multi-sensor judgment results, this method can effectively identify defects such as missing bolts and sliding teeth. Finally, this paper carried out experiments to identify bolt installation defects such as incorrect, missing torque defects, and bolt slips. At this time, the traditional detection method based on a single type of sensor cannot be effectively identified, and the detection method based on multiple sensors can be accurately identified. Full article

In this paper, a Fiber Bragg Grating (FBG) stress sensor is developed to measure the stress variation between the lower Excavation Damaged Zone (EDZ) and the upper undistributed rock. The disturbance brought by the environmental temperature can be differentially compensated with two FBGs mounted symmetrically on the spokes. Through finite element analysis, it can be known that the direct stress and shear stress are pointed at the angles of 45° and 60° on both sides of the coal mine roadway, respectively. The anchor ends of the sensors are installed into the upper undistributed rock and the bolt tails of the mine roadway with a depth of 700 m and fastened by nuts to secure the load sensing device on the surface of the rock. When the shallow foundation of surrounding rock is pressed and deformed toward the coal mining road, the structural modifications can be converted into the stress of rock bolt and the strain of spoke. Thus, the FBG mounted on the surface of the spoke receives the shift information of the Bragg wavelength. The monitoring results indicate that the FBG stress sensors are sensitive to the variation of the EDZ. During the blasting, the stress amplitude varies from 40.256 to 175.058 kPa, and the creep time changes from 21 to 74 min. The proposed method can be applied in the field of underground coal mines for safety condition monitoring of the EDZ and forecasting the coal mine roadway stability. Full article

The friction-type high-strength bolted (FHSB) T-stub connection has been widely used in steel structures, due to their good fatigue resistance and ease of installation. While the current studies on FHSB T-stub connections mainly focus on the structural behaviors under both shear and tensile force, no research has been reported on the mechanical responses of the connections under the combined effects of shear and compression. To make up for this gap, this paper presents a novel FHSB T-stub connection, which is simple in structure, definite in load condition, and easy to construct. Static load tests were carried out on 21 specimens under different shear–compression ratios, and the finite-element (FE) models were created for each specimen. The failure modes, initial friction loads and ultimate strengths of the specimens were compared in details. Then, 144 FE models were adopted to analyze the effects of the friction coefficient, shear–compression ratio, bolt diameter and clamping force on the initial friction load and ultimate strength. The results showed that the FHSB T-stub connection under shear and compression mainly suffers from bolt shearing failure. The load–displacement curve generally covers the elastic, yield, hardening and failure stage. If the shear–compression ratio is small and the friction coefficient is large, its curve only contains the elastic and failure stage. The friction coefficient and shear–compression ratio have great impacts on the initial friction load and ultimate strength. For every 1 mm increase in bolt diameter, the initial friction load increased by about 10%, while the ultimate strength increased by about 8.5%. For each 10% increase/decrease of the design clamping force, the initial friction load decreases/increases by 7.8%, while the ultimate load remains basically the same. The proposed formula of shear capacity and self-lock angles of FHSB T-stub connection can be applied to the design of CSS-enhanced prestressed concrete continuous box girder bridges (PSC-CBGBs) and diagonal bracing. Full article