Bolt Stress Research Articles

Temperature-compensated acoustoelastic measurements of the stress in bolts

Temperature is an important factor influencing the results of non-destructive acoustoelastic measurements of the internal stress in objects like bolts owing to its impact on the elastic modulus of the material. However, conventional methods that seek to obtain the temperature field of the measurement object independently suffer from high complexity and low accuracy. The present work addresses this issue by developing a method that eliminates the influence of temperature on the acoustoelastic measurements of stress in bolts based on the time interval between the head and coda waves of ultrasonic signals. The origin of coda waves in rod-shaped objects is investigated theoretically, and this understanding is applied for analyzing the relationship between the temperature and internal stress of the object and the time interval between the head and coda waves of ultrasonic signals. The analysis demonstrates that the observed time interval is related to temperature and stress in accordance with a linear relationship with the velocity of the longitudinal wave and the rod diameter. Finally, the obtained relationship is applied within an acoustoelastic measurement model to eliminate the influence of temperature from the measurement results.

Mechanical Properties of Fully-Grouted Bolts Support Based on Compression Tests of Anchored Rock Mass

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 PFC2D (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.

A novel experimental method for bolt stress distribution during the assembly process

Bolt fasteners play a crucial role in modern engineering equipment, and understanding the stress distribution in the bolt during the assembly process is essential for enhancing its reliability. However, traditional experimental methods based on the principle of photoelasticity may not accurately reflect the actual assembly process and engineering materials. To address this issue, a novel experimental approach is proposed in this paper, which utilizes optical fibers to measure stress in the bolt during the assembly process. By affixing an optical fiber to the inside of the bolt and employing the optical frequency domain reflectometry (OFDR) technique, the axial stress distribution in the bolt can be obtained. In addition, the concept of an axial force gain factor is introduced to establish the relationship between the maximum axial force and preload. It is found that the calculated maximum axial force of the bolt is approximately 1.4 to 1.5 times the preload. The experimental results show that the stress distribution obtained through the proposed method is consistent with conventional photoelasticity experiments. Furthermore, a comparison with previous studies validates the accuracy of the experimental findings. The experimental approach presented in this paper can realize the real-time measurement of bolt stress distribution, which is of great significance for engineering application.

Influence of the Diameter Size on the Deformation and Failure Mechanism of Shield Precast Segmental Tunnel Lining under the Same Burial Depth

With the development of large-diameter shield tunnels, how to realize effective security and stability control of shield tunnel lining has become a significant research topic. This paper investigates the deformation and failure mechanism of lining large diameter shield tunnels in depth and discusses the deformation characteristics and influencing factors of the lining of the shield tunnel with various diameters through the software of finite element analysis ABACUS. A set of models with varying diameters is built under identical stress conditions in order to maintain control over the variable. The utilization of the elastic–plastic model is observed in the application of bolts and rebar. The utilization of the Concrete Damage Plasticity model has been taken into account for the concrete lining. For the sake of comparison, the crown displacement of the shield tunnel, strain in tension and compressive zones, bolt stress and strain, deformation and intemal force distribution around the shield tunnel, and cracks in the tension zone, are carefully studied. An in-depth analysis is conducted to elucidate the variations in damage evolution mechanisms across linings of different sizes, within the framework of plastic hinge theory. The results indicate that the convergence deformation of large-diameter tunnel lining increases significantly during loading compared with that of small-diameter tunnel. Moreover, the probability of brittle failure is higher in big-diameter shield tunnels compared to small-diameter tunnels, indicating that these larger tunnel structures are more prone to suffering geometric instability.

Stress relaxation assessment of high-temperature bolts under combined biaxial loads: Theory and simulation

Estimating bolt stress within high-temperature bolted connection systems is crucial for determining bolt preload and assessing bolt assembly integrity. This work proposes a theoretical model for estimating high-temperature bolt load under combined tension, bending, torque, and shear loads, considering the characteristics of bolt stress distribution and relaxation. To assess the model's accuracy, finite element analysis was employed to examine the impact of various creep parameters and load combinations on bolt stress relaxation. The results indicate that the introduction of bending moments, torque, and shear loads accelerates axial stress relaxation in bolts. Under a high-temperature load for 300,000 h, the stress relaxation predicted by the theoretical model aligns well with the results from finite element analysis.

Bolt axial stress measurement method based on ultrasound multi-feature fusion

ABSTRACT There exist issues of ill-adaptability and low-accuracy in ultrasonic bolt stress measurement based on acoustic elasticity and scattering attenuation. Therefore, a bolt axial stress measurement method based on ultrasound multi-feature fusion is proposed in this paper. Firstly, ultrasound characteristic parameters based on the theory of acoustic elasticity are extracted, including the difference of time-of-flight (TOF) and the longitudinal wave attenuation coefficient in polycrystalline materials within the Rayleigh scattering range. Then, following the dimension reduction principle, the difference of TOF, attenuation coefficient, and clamping length are chosen as the input feature vectors for the fusion model. Subsequently, the SVR model is employed to establish a multi-feature fusion model for bolt axial stress measurement. Calibration and measurement experiments are conducted using the constructed experimental platform. Comparative analysis between the traditional measurement methods and the proposed method reveals that the SVR model can adapt to measurements of bolts with different lengths, overcoming the limitations of traditional methods. Furthermore, the measurement results of different fusion algorithms show that SVR yields significantly lower average relative errors in the measurement of the three bolts (3.35%, 4.44%, and 4.48%) compared to BP and RBF algorithms. This indicates higher measurement accuracy and immunity to low-stress effects.

Study on dynamic stress variation of head cover bolt during transient operation of pump turbine

Abstract The head cover bolt is an important connecting part of pump turbine, if it is damaged, it will affect the operation safety of the unit and the power station. During the transient process, such as start-up and load rejection in extreme case, the head cover bolt is subjected to complex load action, and its stress also changes, and extreme cases may occur. The dynamic stress level of the bolt will have a certain influence on its fatigue life, therefore, in order to further study the dynamic stress level and variation law of the bolt, this paper relies on a pumped-storage station, the dynamic stress of the head cover bolt during the start-up and load rejection is measured, and the pressure pulsation between the head cover and the runner and the bladeless zone are collected synchronously. Through the data analysis, the bolt dynamic stress level and variation law and the correlation between stress and pressure fluctuation under the power generation and pumping conditions are summarized.

Research and Application of High Efficiency Pressure Relief Technology for Ultra-high Pressure Hydraulic Slotted Coal Seam

In order to solve the technical problem of efficient pressure relief of the impact coal seam, the principle of ultra-high pressure hydraulic slit relief and anti-impact technology is expounded, and the ultra-high pressure hydraulic slit device with working pressure up to 100MPa is selected as the pressure relief equipment of coal seam. The field test of high-efficiency pressure relief by ultra-high pressure hydraulic slotting in impact coal seam was carried out. The test showed that the slotting radius of No.3 coal in Tangkou Mine could reach 1.5m under the condition of 100MPa slotting pressure. The stress variation in seam area and large diameter drilling area is compared and analyzed. The stress in seam area decreases significantly by 40%. The stress of bolt (cable) and the deformation of surrounding rock in the slit area are investigated. Compared with the large-diameter pressure relief area, the increase value of bolt is lower and the increase value of cable is significant in the hydraulic slit test area. The technical benefits of hydraulic slotting and large-diameter drilling are summarized and compared. The engineering quantity of drilling with ultra-high pressure hydraulic slotting is reduced by 60%, and the coal output is 2.5 times of that of large-diameter drilling. The large-diameter drilling provides limited pressure relief space for coal seam, but the ultra-high pressure hydraulic slotting technology can effectively increase the deformation space in the coal body and reduce the elastic energy stored in the coal pillar, so as to achieve a good pressure relief effect. The field test shows that compared with large diameter drilling, ultra-high pressure hydraulic slotting technology has remarkable effects of pressure relief, shock absorption and shock prevention.

Numerical Study on the Dynamic Response and Damage Cumulative of Bolt-Supported Cavern under Adjacent Cyclic Explosion

Adjacent cyclic explosions significantly impact the stability of underground anchored caverns. Based on the similar model test of the vault explosion of the anchored cavern, the dynamic analysis finite element software ANSYS/LSDYNA(18.0) was used to establish a model of the straight wall side explosion of the underground anchored cavern and conduct a numerical simulation. When the total amount of explosion load is the same, we compared the stress time history curve, displacement time history curve, tunnel wall displacement, and circumferential strain curve of the surrounding rock in the underground anchored cavern (under both a high-level single-side blast and a low-level cyclic side blast). We obtained the dynamic response rules of the surrounding rock. By comparing the damage evolution process of the surrounding rock in the two situations, the damage accumulation law of the surrounding rock was analyzed. At the same time, the axial stress distribution characteristics of underground anchor cavern anchors under the action of cyclic explosion were studied. The findings demonstrate that when the total level of blast load adjacent to the cavern is the same, the displacement and circumferential peak strain of surrounding rock and the axial stress of rock bolt in the high-level single explosion are greater than those in the low-level cyclic explosion. However, compared to a single explosion, the rock mass suffers more damage in the cyclic explosion. This study will provide engineers with information that will assist them with a better understanding of the cumulative damage mechanisms of surrounding rock, as well as the stress characteristics of rock bolts under dynamic loads near the explosion site, which will be used to design underground caves with anti-blast features.

A novel constitutive law of confined grouted rock bolt under pull-out load based on a fully nonlinear bond-slip model

Rock bolts are widely applied in deep underground excavations for rock reinforcement. Here, a constitutive model that quantifies the pull-out load-displacement relationship of the grouted rock bolt has been developed though theoretically analyzing the load transfer behaviour along the bolt-grout interface. An improved nonlinear continuously yielding criteria was employed as a bond-slip model where the role of confining pressure playing in slip was accounted. The performance of the proposed constitutive model was demonstrated by comparing with three sets of laboratory pull-out tests on the fully grouted rock bolts under different confining pressure levels (including a short-encapsulated pull-out test designed in our laboratory). The input parameters in the model were determinable within the laboratory environment. The analytical simulation results of pull-out load-displacement performance, the axial stress in the rock bolt and shear stress along the bolt-grout interface agreed well with the laboratory data. We also found that the confining pressure significantly affects the critical embedment length and the higher the confining pressure, the shorter the critical embedment length. The findings enrich the understanding on the mechanical properties of grouted rock bolts and hence aid the rock engineers in rock reinforcement design in underground excavations.

Performance of Engineered Cementitious Composites (ECC) in shield tunnel segmental joints: A comparative study with ordinary reinforced concrete

Shield tunnel segmental joints are traditionally vulnerable, limited by their tensile capacity and susceptibility to cracking. Engineered Cementitious Composites (ECC) offer a promising solution due to their superior tensile strength, exceptional crack resistance, and remarkable toughness. However, the application of ECC in tunnel segment joints remains unexplored. To address this gap, this paper conducted comprehensive full-scale tests of ECC segmental joints versus ordinary reinforced concrete (RC) segmental joints. It investigated mechanical responses including material behavior, deflection, joint action, bolt strain, crack development, and failure modes. Results revealed that: (1) ECC joints provided a 33.97 % higher stable bearing capacity and a 50 % increase in initial cracking strength compared to RC joints. (2) ECC joints excelled in crack control, maintaining crack widths below 0.2 mm, while RC joints experienced significant cracking with widths exceeding 1 mm. (3) In terms of toughness, ECC joints surpassed RC by 66 % in the elastic stage and 123 % in the normal serviceability stage, with 96 % higher ductility. (4) ECC joints significantly outperformed RC joints in bolt stress uniformity and concentration, achieving a 43.21 % reduction in average bolt stress. (5) Regarding multi-scale mechanical effects, ECC joints increased the toughness and strength advantage over RC by more than 45 % in the elastic phase. These results reveal the potential of ECC in significantly enhancing the durability and resilience of shield tunnels, particularly in harsh environments subjected to high ground stress or seismic activities.

BACK ANALYSIS AND STABILITY PREDICTION OF SURROUNDING ROCK DURING EXCAVATION OF THE SHUANGJIANGKOU UNDERGROUND POWERHOUSE

The underground powerhouse of the Shuangjiangkou hydropower station is one of the largest caverns under construction in China, and its stability during construction is crucial for safe construction. To study the stability of the surrounding rock during excavation, the displacement and stress of the surrounding rock were monitored by multi-point displacement meters and bolt stress meters. Based on the monitoring data, the elastic modulus, Poisson’s ratio, friction angle, and cohesion of surrounding rock were inversely analyzed by the PSO-BP algorithm. Then, the back-analyzed parameters were used to simulate the subsequent excavations and predict the stability of surrounding rock during the following construction. The analysis results show that the surrounding rocks were generally stable during the initial four stages of excavation, and the main factors affecting their stability were blasts and unfavorable geological structures, including the lamprophyre vein and the F1 fault. These unfavorable geological structures also significantly decrease the mechanical parameters of surrounding rock as demonstrated by back analysis, and the stability prediction results show that the omnibus bar cave and the tailrace tunnel were at the greatest risk of instability during the subsequent excavations. This study provides a practical analysis for engineering excavation of the underground caverns.

Parametric Finite Element Study on FREEDAM Beam to Column Joints with Different Details of the Haunch Slotted Holes

Parametric Finite Element (FE) simulations were performed to investigate the ultimate flexural of different configurations of friction steel beam-to-column joints equipped with FREEDAM (free from damage) dampers. The main aim of this study was to compare the effectiveness of friction dampers featuring either single or multiple slotted holes, examining how these variations influence the behavior of the joint and the devices under seismic loads. In particular, the ultimate behavior of the connection (i.e., when the device reaches its maximum stroke) was investigated to characterize the involvement of the bolts in shear, the bearing of the plates, and the yielding of the supporting components. The analysis of bolt stress states revealed significant differences influenced by the number of bolts and slots. The FE models were calibrated against the experimental results obtained within the FREEDAM RFCS Project. These insights contribute to the design and performance evaluation of steel beam-to-column joints with FREEDAM connections, in particular the detailing of the haunch slots, laying the groundwork for future research and applications.

Numerical Analysis of Ground Surcharge Effects on Deformation Characteristics in Shield Tunnel Linings

To investigate the deformation characteristics of shield tunnel linings under ground surcharge, finite element software was employed to create a detailed three-dimensional model of the staggered assembly of the shield tunnel lining. This model includes components such as precast concrete segments, reinforcements, and joints (comprising bent bolts, washers, and bolt sleeves). Additionally, the model accounts for interface frictions between segments and the interactions between different rings. The reliability of the numerical model was verified based on the results of a full-scale model test. Additionally, the model accounts for interface frictions between segments and the interactions between different rings. Changes in tunnel convergence, joint tensioning, bolt stresses, reinforcement stresses, and concrete crack development were systematically analyzed. The results indicate the following: (1) the deformation mode of the lining structure under ground surcharge resembles a “transverse ellipse”. Joints located near the haunch opened along the outer arc, while those near the vault and bottom opened along the inner arc. The restraining effect of the bolts on joints opening in the inner arc was greater than that on the outer arc. Notably, when the opening of the inner arc reached 4.9 mm, the bolt stress escalated to the yield strength of 640 Mpa. (2) Under larger loads, the lining structure’s joints are susceptible to greater deformation, resulting in the tensile yielding of local reinforcement within these joints. (3) Cracks predominantly occur near the haunch, vault, and bottom of the lining structure, with the central angle of crack distribution ranging between 70° and 85°.

Phased Array Ultrasonic Method for Robotic Preload Measurement in Offshore Wind Turbine Bolted Connections.

This paper presents a novel approach for preload measurement of bolted connections, specifically tailored for offshore wind applications. The proposed method combines robotics, Phased Array Ultrasonic Testing (PAUT), nonlinear acoustoelasticity, and Finite Element Analysis (FEA). Acceptable defects, below a pre-defined size, are shown to have an impact on preload measurement, and therefore conducting simultaneous defect detection and preload measurement is discussed in this paper. The study demonstrates that even slight changes in the orientation of the ultrasonic transducer, the non-automated approach, can introduce a significant error of up to 140 MPa in bolt stress measurement and therefore a robotic approach is employed to achieve consistent and accurate measurements. Additionally, the study emphasises the significance of considering average preload for comparison with ultrasonic data, which is achieved through FEA simulations. The advantages of the proposed robotic PAUT method over single-element approaches are discussed, including the incorporation of nonlinearity, simultaneous defect detection and stress measurement, hardware and software adaptability, and notably, a substantial improvement in measurement accuracy. Based on the findings, the paper strongly recommends the adoption of the robotic PAUT approach for preload measurement, whilst acknowledging the required investment in hardware, software, and skilled personnel.

Calculation Method of Flange Bolt Preload Based on Finite Element

Flange bolt connection is one of the most important connection modes in bolt connection at present. In this paper, the finite element model of the bolt between the shell and the head flange is established to analyze the influence of different initial preload on the bolt stress state under external load. The results show that according to the bolt stress state, the range of initial preload is divided into the influence area of the external load, the influence area of the resultant force and the influence area of the initial preload. In the influence area of external load, the bending moment exerted on the bolt dominates the stress state of the bolt, and the stress state of the bolt is poor, which is not the safe value area of the initial preload；in the influence area of the initial preload, initial preloads dominates the stress state of the bolt, the average stress of the bolt section is larger, and the bolt safety is smaller, which is not the safe value area of initial preloads; in the influence area of the resultant force, the bolt has better stress state and higher safety coefficient, which is the safety value area of initial preload. The initial preload corresponding to the boundary point between the influence area of the resultant force and the influence area of the external load and the influence area of the external load is the limit of the safe value range of the bolt preload.

Shear performance of elliptical head one-sided bolt double-lapped joint with plug-in gasket

One-sided bolts are commonly used for bolted connections between closed section members to address the issue of insufficient space for nut installation. Among them, the elliptical head one-sided bolt uses the difference in length between its long and short axes. This allows the bolt head to be inserted into the elliptical bolt hole and subsequently rotated by 90 degrees, effectively achieving anchoring. But the use of elliptical bolt holes may cause some problems, such as bolt slippage and stress concentration around the bolt holes. In this paper, building upon the elliptical head one-sided bolt concept, a novel structure for one-sided bolted connection is proposed, incorporating a plug-in gasket to improve the mechanical properties of the elliptical one-sided bolted joints. Six sets of steel plate double-lapped joints, connected by elliptical head one-sided bolts and plug-in gaskets, were designed for shear resistance tests. A finite element model was designed using ABAQUS, based on the test specimen parameters. By comparing the simulation results with the experimental findings, the reinforcing effect of the gasket on joint stress was analyzed and validated. The results show that the plug-in gasket effectively resolves the excessive slippage issues and enhances the initial stiffness of the joint. Moreover, when pressure is applied to the bolt hole, the plug-in gasket reduces the stress concentration caused by the extrusion between the bolt hole and the bolt shank, thus preventing local premature failure of the bolt hole.

Influence of the temperature changes on stresses in carbon composite fastening bolts

High joint strength of composite structures can be achieved by using mechanical fasteners. The materials used for rivets and bolts have lower coefficients of thermal expansion than composites in the direction perpendicular to the reinforcement fibers. It is suspected, therefore, that temperature changes can cause stress changes in mechanical fasteners. The purpose of this study was to experimentally determine and analytically substantiate the values of stress changes resulting from a change in temperature in the range from -20 to 60°C in M8 steel bolts fastening carbon composite. The value of stress changes was estimated to be around 100 MPa, which can consequently lead to joint unsealing or plastic deformation of the mechanical fastener.

Finite element analysis on failure-yielding stresses in the wheel bolt of automobile vehicle due to operational loading conditions

Finite element analysis on failure-yielding stresses in the wheel bolt of automobile vehicle due to operational loading conditions

Analysis and design of column splicing flange joints with different weld types

To improve the seismic performance of steel column splicing flange joints, different weld details between the column and the flange plate were proposed in this study, and four full-scale specimens were designed and tested under cyclic loads. Finite element analysis was conducted to further check the joint performances and the weld behaviors. The hysteresis behaviors, yield moment, ductility, bolt forces, energy dissipation, stress and strains were analyzed. The parametric analysis, with finite element models validated by test results, was conducted, discussing the influences of the weld details, weld geometries and flange openings. According to the results, three of the four different weld details developed different advantages on ductility or energy dissipation capacity, bolt tension distribution, stress or strain distributions. Larger weld leg size would increase the resistance of the bolted flange splice joint, but may also cause weld residual stress and prying force. The reduction of flange opening can improve the stiffness and yield moments of the Type B flange joints. Formulas for the yield moments of the joints with recommended weld types were proposed and validated by both test and numerical analysis results, and additional formulas to check weld details were proposed for seismic design of bolted flange joints in prefabricated steel structures.