Bolt Stress Research Articles

Study on the long-term performance of shield tunnel passing through the gas-bearing strata

When the shield tunnel passes through the gas-bearing strata, gas and water leakage may occur depending on the sealing performance of the segment joints. This process involves the complex multiphase seepage flow phenomenon in unsaturated soil. In this study, a fully coupled solid-liquid-gas model of the GIL Utility Tunnel was established to investigate the influence of the high-pressure gas on the mechanical properties of the tunnel segments and joints. The constitutive model of the Extended Barcelona Basic Model was implemented to simulate the effect of the seepage process on soil deformation. The results show that significant upward displacement occurred in the gas reservoir and its overlying strata, and the maximum displacement reached 30 mm. In addition, during the leakage of the gas and the water, an increase in the average soil effective stress was observed. It would induce a reduction in the suction and expansion of the yield surface. The tunnel tended to be stable from 20 years onwards, thus the soil deformation due to the water leakage only occurred at the early stage. In addition, the joint opening under the most unfavorable internal force combination was 0.69 mm, and the corresponding bolt stress was 119.5 MPa, which is below the yield limit. The results of this study help to understand the influence of high-pressure gas on tunnel safety and the sealing performance of the joints.

Contact stress induced by the rotation of a rigid bolt bonded to an elastic body

Torsional deformation of an elastic half-space containing a vertical cylindrical cavity caused by a rotation of a bonded rigid bolt with a long shank is studied in this article by employing Weber integral transforms and integral equations. In the limiting case of the infinite shank, we suggest two different techniques reducing the problem to the regular integral equations of the second kind, which permit efficient solutions in distinct ranges of geometric parameters and allow us to derive a highly accurate approximate analytic solution of the problem for any values of the parameters. Almost exact approximations are suggested for the stress concentration at the edge of the bolt head. In the case of a bolt with a long finite shank, relationships between the torque and the angle of twist of the bolt are derived by utilizing solutions obtained for the bolt with the infinite shank as asymptotic approximations. The effect of the geometric parameters is investigated providing insight into the behavior of the bolt and contact stress in dependence on the bolt head radius and the length of the shank.

Experiment and numerical modelling of a demountable steel connection system for reuse

Currently, steel reuse is only a marginal practice. To facilitate deconstruction and efficient reuse of steel components, an innovative connection system was proposed. This system adopts a ‘Block Shear Connector (BSC)’ that allows beam length to be standardised and suitable for a wide range of different sizes of the supporting members within the same planning grid. This paper presents the experimental and numerical studies of a beam-to-beam connection using BSCs. The BSC used was made from a standard universal HE / UC section and was bolted to the beams by using partial depth end plates. The experimental results provided the shear resistance, moment-rotation, failure behaviour, demountability and reusability of the steel components. Further numerical simulation conducted investigated the effect of some key parameters (steel strength, thickness of BSC web, thickness of BSC flange, initial bolt stress) on the behaviour of the connections. The results obtained highlighted the demountability of this innovative bolted connection system and the reusability of structural components.

Influence of material and geometry parameters on the adhesive stress and strength of anchor bolts for thick FRP laminates

Adhesive bonded anchor bolts have the potential to apply high local loads to fiber reinforced polymer (FRP) composites by standard screw connections with little manufacturing effort. However, because of different geometry and material properties the stress distribution within the adhesive layer varies from conventional lap joints. In this study the influence of these properties on the stress distribution within the adhesive and the load bearing capacity of the anchor bolt are analyzed. A numerical parametric study is performed to determine the influence of substrate geometry parameters as well as adhesive and laminate material properties on the stress distribution. The results show that there are characteristic effects on the adhesive stresses of anchor bolts in FRP laminates such as: the non-homogeneous distribution along the circumference, the influence of the in-plane shear stiffness G12 of the laminate and the interaction between the overlap length and the cross section. In addition, the impact of geometry parameters on the load bearing capacity of the joint with a glass fiber-reinforced polymer (GFRP) laminate under tensile load is experimentally determined. Damage types of the joint are described and failure modes defined. In case of the used ductile adhesive the load bearing capacity shows to be directly proportional to the anchorage length. Further, the results determined a dependence of the failure mode and the load bearing capacity on the cross section of the laminate.

Strain-Sensing Mechanism and Axial Stress Response Characterization of Bolt Based on Fiber Bragg Grating Sensing

The anchoring quality of bolts is related to roadway safety and the surrounding rock stability. Due to the limitations of conventional monitoring methods in capturing strain, there still exists a gap in the real-time perception of the mechanical properties of bolts at the micro-scale. This paper proposes a new approach to detecting bolts’ anchoring qualities based on the fiber Bragg grating sensing principle. Moreover, it studies the strain transmission mechanism between the surface-bonded fiber Bragg grating and the bolt. A fiber-optic monitoring test platform of anchor bolt anchoring quality is built. The full-length anchor bolt’s strain evolution law and axial force distribution characteristics are studied during the pull-out test. The study results have shown that the theoretical value of the fiber strain transfer coefficient can be used to calculate the strain of the bolt. The bolt pull-out test verified the accuracy of using the fiber Bragg grating bolt axial force characterization equation to estimate the bolt stress. On the other hand, the correlation between the bolt axial force and the fiber Bragg grating monitoring value follows an exponential pattern. This study provides an important basis for improving the understanding of a bolt anchoring mechanism and the stability control of a roadway’s surrounding rock.

Failure analysis of a new-type shield tunnel based on distributed optical fiber sensing technology

The dislocation of circumferential joints in shield tunnel has serious safety impact on subway operation. A new-type shield tunnel with dowel was used to limit the dislocation of circumferential joints of the tunnel in Chengdu Metro. In this paper, the prototype segmental experiment is carried out to analyze the shear performance of circumferential joint of tunnel with the dowel. The optical fiber sensing technology is used to investigate the deformation characteristics and crack propagation law of concrete. And the change laws of the dowel, bolt and rebars in segment are obtained in detail. The research shows that segments with the assembled dowel have its particular failure mode in the shear process. The dowel significantly changes the stress of concrete, bolt and rebars. The research results provide a theoretical basis for the application and promotion of the new segment structure.

Simulation Study on Mechanical Characteristics of Rock Bolt in Rock Mass with Bedding Separation Based on the Nonlinear Bond Slip Relationship

The mechanical equation on the mechanical characteristics of rock bolt in rock mass with bedding separation is established, based on the bond slip relationship of anchoring interface by the load transfer method. The validity of the numerical simulation is verified by the analytical solution of mechanical equation, when the bond slip relationship is linear. Further, the nonlinear bond slip relationship of anchoring interface is input into Flac3D by FISH. The mechanical characteristics of rock bolt are studied with the single and multiple bedding separation by numerical simulation. The results show that the axial force and the interfacial shear stress distribution curves on both sides are symmetrically distributed with the single bedding separation in rock mass, when the bedding separation is located in the center of the anchoring segment. When the bedding separation positions are not located in the center of the anchoring segment, the bedding separation value at different positions versus the axial force curves shows a single peak distribution. The axial force of rock bolt is mainly controlled by the side with the shorter anchoring length. Compared with the single bedding separation in rock mass, the additional stress of rock bolt occurred by the multiple bedding separation will superimpose each other. This paper leads to a better understanding for the load transfer mechanism for grouted rock bolt systems in rock mass with bedding separation and provides a reference for scientific support design and evaluation method.

In-depth residual stress analysis considering manufacturing process and cyclic loading of bolts

Although bolts are considered to be a well-established structural element, only general statements on the influence of the different manufacturing processes on the fatigue life are available. Detailed investigations of the in-depth residual stress path and the residual stress stability under cyclic loading have not yet been carried out. A challenge in determining the residual stresses is the complex geometry of the thread and the expected residual stress state with steep gradients close to the surface.This paper examines the influence of the manufacturing process of the main two process types on the residual stress state. The focus lies on the residual stress and material state of high tension bolts (HT) rolled before heat-treatment (RBHT) and rolled after heat-treatment (RAHT) both with hot-dip galvanization (tZn). To get detailed information about in-depth residual stresses, neutron diffraction is used. In addition, the residual stress stability under cyclic loading is examined.For the first time, in-depth residual stress distributions are determined on unloaded and loaded RAHT M 36 and RBHT M 24 bolts, tZn, grade 10.9. The results show that RAHT bolts in the unloaded state have compressive residual stresses below the surface in the thread root in the magnitude of −225 MPa. In the case of RBHT bolts, low residual stresses are present at the surface in the magnitude of −160 MPa. The different progression of the residual stresses is associated with the manufacturing process.Loaded RAHT and RBHT bolts exhibit different stress characteristics. In the loaded state, RAHT bolts have residual compressive stresses on the surface, while RBHT bolts have residual tensile stresses. This may be one reason for the significantly longer fatigue life of RAHT bolts compared to RBHT bolts.

Numerical analysis of reinforced concrete columns strengthened with sleeve wedge bolts and a self compacting concrete layer

With the development of technology in the field of structural analysis, it has now become possible to computationally model more complex structures, each with its own peculiarity, such as those with structural reinforcement. With regard to the non-linear analysis of structural elements in reinforced concrete, the Finite Element Method is ideal, since it is only possible with the use of computational resources. For columns subjected to flexion compression, elements that are highly susceptible to second-order effects and which have as an important function the global stability of buildings, software for numerical analysis, such as ATENA, become especially applicable for the study of behavior structural of these elements. Marques et al. (2015) carried out a study on the performance of columns reinforced through casing with self-compacting concrete and wedge bolts applied to prevent slipping between these materials. Based on this study, then, in this work, 5 numerical models were developed in the ATENA software: PO, PR, P150-18, P150-26 and P75-50. The first two are references (original column and reference column, respectively), while the others are reinforced, whose nomenclature distinguishes them in terms of the quantity and disposition of wedge bolts on the compressed face of the element. The relationships and parameters that allowed the analysis of the models were: rupture load versus displacement, specific strains in longitudinal reinforcement, cracking and stresses in wedge bolts at failure. Good results were obtained, both with regard to the variation between the experimental results and those obtained numerically, and for the performance of the structural reinforcement technique, which represents the reliability of the computational modeling and the adopted methodology. The variation between such results respected the 15% limit established by the comments of the ACI 318 (2011) standard, with the exception of the PO, and the reinforcement technique, in turn, resulted in the growth of the initial strength of the column in its original condition (PO). The present study allows, therefore, to guarantee and disseminate the application of numerical simulation for the analysis and design of reinforced concrete elements.

Monitoring and Analysis of Deformation Evolution Law of Fault Activation Caused by Deep Mining in Shizishan Copper Mine, China

In order to study the deformation evolution law of fault activation caused by deep mining in Shizishan Copper Mine, China, a monitoring system for fault activation slip is designed and implemented on the basis of the field investigation of footwall fault activation of the main orebody in the mining area. The displacement and stress of the fault are monitored by the multipoint displacement meter, bolt stress meter, and borehole stress meter. According to the measured results, the activation deformation laws of fault F2, fault F3, and fault F4 during deep continuous mining are analyzed in detail. The results show that, when the influence range of underground mining spreads to the fault, the increase in the additional tensile stress on the fault plane will reduce the shear strength of the fault and increase the slip of the fault. When the shear stress exceeds the shear strength of the fault plane, the shear failure of the fault plane occurs, the rock mass on both sides of the fault loses stability, and the fault becomes active; when the orebody in the deep sublevel 14 and sublevel 15 were continuously stoped, the development of the mining influence area to fault F2 leads to fault F2’s activation. When stoping the orebody in sublevel 16, fault F3 also activates. With the continuous downward mining of the deep part, the slip amount increases continuously. The fault activation sequence is from fault F2 to fault F3, and then to fault F4.

Effect of rolling angle on segment cracking and damage of shield tunnel - field investigation and modelling

Based on a curved shield tunnel, this study classified the grades of segment cracking and damage during the construction and counted the segment cracking and damage. Combined with the data of tunnelling parameters, the significance of segment cracking and damage factors was analysed by the ordered multi-classification logistic regression method. Furthermore, the refined finite element numerical model was established to study the damage mechanism of the segment under the rolling angle. The results indicate that the analysis results of numerical simulation correspond to the field phenomena, which confirms that the rolling angle is a critical factor affecting the segment disease. The total stiffness of the segment attenuates significantly after torsion. When the torque is 43580.17 kN·m, the maximum longitudinal bolt stress connecting the segment out of the shield shell and the segment in the shield shell reaches 619.6 MPa, close to 640 MPa of the bolt yield stress.

A New Axial Stress Measurement Method for High-Strength Short Bolts Based on Stress-Dependent Scattering Effect and Energy Attenuation Coefficient.

The accurate estimation of axial stresses is a major problem for high-strength bolted connections that needs to be overcome to improve the assembly quality and safety of aviation structures. However, the conventional acoustoelastic effect based on velocity-stress dependence is very weak for short bolts, which leads to large estimation errors. In this article, the effect of axial stress on ultrasonic scattering attenuation is investigated by calculating the change in the energy attenuation coefficient of ultrasonic echoes after applying axial preload. Based on this effect, a stress-dependent attenuation estimation model is developed to measure the bolt axial stress. In addition, the spectrum of the first and second round-trip echoes is divided into several frequency bands to calculate the energy attenuation coefficients, which are used to select the frequency band sensitive to the axial stress changes. Finally, the estimation model between axial stress and energy attenuation coefficients in the sensitive frequency band is established under 20 steps of axial preloads. The experimental results show that the energy attenuation coefficient in the sensitive band corresponds well with axial stress. The average relative error of the predicted axial stress is 6.28%, which is better than that of the conventional acoustoelastic effect method. Therefore, the proposed approach can be used as an effective method to measure the axial stress of short bolts in the assembly of high-strength connections.

Methodology of Leakage Prediction in Gasketed Flange Joints at Pipeline Deformations.

The paper presents the proposal of a leakage prediction method in flange joints, after pipeline deformation, based on FEM (Finite Element Methods). The stages of developing the design are discussed, and a complex, multi-stage method of applying the loads is presented in detail. Moreover, the gasket material data obtained in experiments were used. The paper also presents the results of calculations on a non-uniform stress distribution in the radial direction of the gasket. In addition, it has been shown that the deflection of the pipeline with a minor displacement causes an increase in the diversification of the circumferential pressure of the gasket, and also has a significant influence on the determination of the actual state of stress to which the gasket is subject. Moreover, it was found that the distribution of contact pressure on the deflection of the pipeline has a significant influence on the level of leakage. The results of tests are compared to the results of the numerical calculations of the stress in bolts. By comparing the bolt tension changes obtained by numerical and experiment analyses, it has been shown that the assumptions made in developing the numerical model are correct.

ZnO piezoelectric coatings used for the ultrasonic excitation of longitudinal-transverse waves and their application for smart bolts

The accurate measurement of the prestress for bolt has been intensively investigated in recent years. Many research studies have been conducted to improve the accuracy of prestress measurement using ultrasound techniques; in particular, the real-time prestress of bolt can be obtained without the requirements to calibrate the original load when ultrasonic longitudinal and transverse waves are applied simultaneously. However, there are few studies that have focused on ultrasonic transducers that can generate longitudinal and transverse waves simultaneously. Furthermore, research on coatings deposited directly on the top of the bolts for the excitation of longitudinal and transverse waves has not been reported. ZnO coating is widely used for the ultrasonic transducer due to its excellent piezoelectric property and stable structure in high temperatures. Therefore, it is an outstanding candidate for the excitation of both longitudinal and transverse waves and has a good application prospect in the field of bolt prestress measurement by ultrasonic sound wave with high accuracy. In this paper, ZnO piezoelectric coatings were deposited on (100)-oriented Si substrates by radio frequency sputtering techniques. The morphology, structure, and echo signal characteristics of the coatings were characterized by SEM, AFM, XRD, and ultrasonic measurement instruments. The experimental results showed that Ar/O2 ratio and deposition position exhibited significant effects on the excitation waveform of the ZnO piezoelectric coating. When the Ar/O2 ratio reduced to 1:3, the coating could excite both transverse and longitudinal waves. However, when the deposition position gradually moved away from the sputtering center, the transverse wave gradually enhanced. The coating could excite a pure transverse wave when the sample was at the edge of the effective sputtering area, which showed that the type of the excitation wave and the relative intensity of each wave could be well controlled by the Ar/O2 ratio and deposition position. These research results have a good application prospect in bolt stress measurement.

Mechanical properties of rock bolt and analysis for the full-process of sliding failure based on rock mass absolute displacement

Previous studies rarely involved the mechanical properties of anchorage system under the condition of internal absolute displacement of surrounding rock and the solution of important parameters of anchorage system. In this paper, the absolute displacement law of rock mass under the anchorage system is analyzed by the fiber grating (FBG) multi-point displacement meter and multidirectional displacement conversion formula. Based on the coordinated deformation principle for rock bolt and rock mass, the mechanical analysis model for rock bolt-rock mass system is established, and the influence rules of rock bolt length, rock bolt diameter and rock bolt preload on the internal force distribution of rock bolt is studied based on the stress analysis of full-length rock bolt in a tunnel engineering. The results show that: (1) with the increase of rock bolt length, the anchoring effect gradually enhances, but the improvement degree decreases gradually; (2) with the increase of rock bolt diameter, the anchoring effect is enhanced; at the same time, however, the shear stress of rock bolt is larger, and the possibility of rock bolt sliding also increases; and (3) with the increase of preload, the increase of “anchor length” makes the anti-sliding ability of rock bolt increase correspondingly, and the supporting effect of rock bolt increases gradually. Then the full-process analysis for the mechanical mechanism of rock bolt sliding failure and the iterative calculation method for rock bolt displacement are studied. At last, the numerical simulation for pull-out test is carried out through the finite element analysis to verify the calculation results of mechanical model, and according to the iterative operation, the two important parameters such as the interface shear stiffness K and the interface peak shear strength τ P are solved. The analysis show that the numerical simulation results are in good agreement with the mechanical model calculation. This study can provide a theoretical basis for rock bolt support technology and support structure design. • The testing and calculation methods of absolute displacement law of rock mass are analyzed by the FBG. • The analytical expressions for the axial force and shear stress of full-length rock bolt are obtained. • The full-process analysis for the mechanical mechanism of rock bolt sliding failure is studied. • The iterative calculation method for rock bolt displacement is proposed.

Experimental /numerical study of a circular rib-stiffened flange connection with inner and outer flange plates under combined bending and tensile loading

Focusing on circular rib-stiffened flange connections with inner and outer flange plates, termed inner-outer flange, the mechanical behavior of the flange subjected to the combined bending and tensile loading is experimentally studied. Four nominally identical specimens were utilized to investigate the effects of the eccentricity on the mechanical behavior. The distribution of the gap between flange plates, as well as the distribution of the bolt forces, is presented. It is found that the neutral axis would gradually approach the central axis of the flange connection, as the eccentricity increases. Moreover, provided the sufficiently strong ribs, welds, and flange plates, the capacity of the flange is found to be mainly predominated by the bolt strength. A good agreement is found in the comparison of the results obtained via the finite element analysis, the semi-analytic method (SAM) and the experimental study. It corroborates the validity of using the bolt failure assumption and the plane cross-section assumption in the SAM for approximating the capacity of the inner-outer flange. In terms of the interaction of the tensile capacity with the bending capacity, the experimental results along with those in the literature are compared with the curves defined by the codes, and suggestions for design are concluded. Yield capacity, defined as the load when the bolt stress reaches the yield strength, is recommended herein for the design of a structure under in-service condition. It is found the specifications in the current codes for the rib-stiffened flanges with a single flange plate would occasionally overestimate the yield capacity of the inner-outer flanges under the combined bending and tensile loading. Moreover, both the experimental and the numerical results show a linear load interaction curve, in terms of the ultimate capacity.

Stress Distribution Law of Full-Length Anchorage Bolt in Rectangular Roadway

To study the evolution law of axial force and shear stress of a full-length anchorage bolt in a rectangular roadway during roadway driving and working face mining, based on the stress analysis of the bolt, considering the elastic parameters and geometric size of the bolt, the effect of a bearing plate on surrounding rock, roadway cross-section shape, roadway deformation degree, and roadway elastic parameters, elastic mechanics and mathematical analysis methods were used to establish the mechanical model describing the interaction between the bolt and surrounding rock, and the mechanical formulas for calculating the axial force and shear stress of the bolt were derived. Taking the mining roadway of 1,131(1) working face in the Zhujidong coal mine of the Huainan mining area as the engineering background, the axial force and shear stress of the bolt in the middle of the roof and side of the rectangular roadway with the advance of driving face and working face were analyzed. The mechanical model and theoretical analysis results are verified by installing force measuring bolts with the same mechanical properties as the field and observing the real axial force distribution of the bolts.

Structural Stress Characteristics and Joint Deformation of Shield Tunnels Crossing Active Faults

Fault dislocation severely threatens the safety of a tunnel structure. Formerly, researchers mainly engaged in the mechanical response of mountain tunnels crossing the fault fracture zone. In contrast, few studies have focused on the structural stress characteristics and joint deformation of the cross-fault shield tunnels. There is an apparent difference between segmental tunnels and mountain tunnels with respect to mechanical properties. In the current study, a three-dimensional numerical model of cross-fault segmental tunnels is established based on the theory of concrete plastic damage constitutive relations using the finite element program ABAQUS. The numerical calculation results are compared with the model test results for validation. Subsequently, the relevant factors affecting the mechanical response of the shield tunnel crossing the active fault are analyzed. The results illustrate that when normal fault dislocation occurs, the shield tunnel structure is initially damaged appearing in the circumferential joints, which is prone to large tension deformation. Otherwise, when reverse faulting occurs by the same displacement, the shield tunnel structure is initially damaged at the arch haunch of the segments, and the deformation of the longitudinal joints is relatively slight. Under the same fault displacement, the bearing capacity of the segmental lining subjected to the reverse fault dislocation is more significant than that of the normal fault dislocation. Both the soil elastic modulus and the vertical distance between the top of the fault and the tunnel exert a considerable impact on the structural damage of the segmental tunnels, bolt stress, and joint deformation. The fault dip angle does not affect the mechanical characteristics of the shield tunnel structure when subjected to normal fault displacement. In reverse faulting cases, with the increase of the fault dip angle, the tunnel structural failure mode transforms from the transverse compression failure of the segments to the shear failure of the circumferential joints.

A Sensing Mechanism and the Application of a Surface-Bonded FBG Dynamometry Bolt

In the present paper, a new type of surface-bonded fiber Bragg grating (FBG) dynamometry bolt is designed. It is assumed that the adhesive layer is a linear viscoelastic material and its creep mechanical behavior is expressed by the standard linear solid model. The shear strain transfer model of the surface-bonded FBG sensor is established. Additionally, the instantaneous and quasistatic strain transfer functions of the surface-bonded FBG sensor are obtained. The functions are validated by a uniaxial tensile test and a long-term constant-load tensile test. The test results show that the strain measured by the FBG sensor has a proportional relationship with the strain measured by the resistance strain gauge. Furthermore, under the fixed load for a long period of time, the strain of the FBG sensor has a tendency to drift and the strain reduction rate is about 40.5%. Finally, the field application is carried out in a mining area. It has been proved that the ground pressure online monitoring system based on the FBG sensing technology can successfully monitor the stress of the rock bolt.

Monitoring rock bolt safety based on FBG sensors

A good bolt support structure effectively enhances the strength of the surrounding rock. Bolt support monitoring provides a basis for modifying and improving the design of this structure and enables safety hazards to be identified so that safe production can continue. A bolt fiber Bragg grating (FBG) stress sensor is developed based on FBG sensor technology, providing a data-driven analysis tool for monitoring the bolt stress in the working face. Continuous dynamic monitoring of the internal force distribution in a high-precision roadway bolt support structure is achieved through strict laboratory calibration, thus enabling comprehensive safety monitoring. Furthermore, the anchor FBG stress sensor is used to analyze the real-time stress variations in a bolt support structure during excavation. The results reveal the security evolution characteristics of bolts buried in shallow bedrocks and show that the security state varies with location (i.e., the roof, roadside, apex between roof and roadside, and apex between roadside and floor) and depth.