Traditional Bolt Research Articles

High pre-tension reinforcing technology and design for ultra-shallow buried large-span urban tunnels

Due to the thin overlying formation of ultra-shallow buried large-span urban tunnels, the surrounding rock can be easily loosened and damaged after excavation. High prestressed anchoring support can improve the self-bearing capacity of the surrounding rock. However, traditional bolts often undergo necking fracture after the yield stage and strengthening stage, and the designed pre-tension is low, generally not exceeding 50 % of the yield strength of the bolt. To this end, our research group developed a new NPR bolt. After comparing the mechanical properties of the NPR bolt and the traditional bolt, the high strength, high elongation, and high prestressed properties of the NPR bolt are revealed. Subsequently, the constitutive relationship of the CABLE element in FLAC3D is modified, and the constitutive model of the NPR bolt is established, which can describe the whole process of bolt. Furthermore, a numerical comparison of prestressed control for ultra-shallow large-span tunnels is carried out. Compared with non-prestress, when the prestress of bolt reaches 100 kN, the area of tensile stress zone and plastic zone of surrounding rock are reduced by 79.6 % and 73.7 %, respectively. At the same time, the settlement of surface and roof is reduced by 66.7 % and 64.1 %, respectively. The control mechanism of the prestressed NPR bolt support is explored, and the design method for ultra-shallow large-span tunnels is proposed. The field application and monitoring results show that the surface and roof settlement of the tunnel supported by NPR bolts are 3.2 mm and 6.3 mm, respectively. The safe and effective stability control of the tunnel surrounding rock is achieved.

Step by step and combined supporting technique with allowable deformation + limiting shape for soft rock roadway

Aiming at the difficult problems of the large deformation in weakly cemented soft rock roadways, the reasons of large deformation are analyzed for roadways in Hongqingliang coal mine. On this basis, the principle of step by step combined support technology based on allowable deformation + limiting shape for weakly cemented soft rock roadway is proposed, and the optimal support parameters of step by step combined technology are determined by FLAC3D. Step by step combined support technology includes the primary support of anchor bolt + anchor cable + initial shotcrete and the secondary support of U-shaped steel shed + filling flexible material behind shed + control of key parts. The comparative analysis on the site shows that the deformation rate and final deformation amount of the surrounding rock after the step by step combined support are less than those of the primary support, and the deformation of the surrounding rock can be controlled effectively after the secondary support is added. Step by step combined support is superior to the traditional bolt + anchor cable combined repair in terms of economy and efficiency. The optimal construction period of each working procedure of the step by step combined technology is 28 days after the completion of the first support, and the step by step combined support based on allowable deformation + limiting shape is an effective way to control the surrounding rock of soft rock roadway.

Bolt loosening monitoring with passive wireless-based smart washers

Ensuring sufficient preload of bolted connections is crucial for maintaining the safety of railway operations. Accidents resulting from loose bolts caused by inadequate preload are a recurring concern. Traditional bolt preload detection methods suffer from reliability issues and bulky equipment requirements. To address these challenges, this study proposes a novel solution utilising passive wireless measurement systems. However, the communication effectiveness of these systems can be significantly impacted by the surrounding metal environment. This research introduces an intelligent clover washer design to mitigate the adverse effects of eddy currents induced by the metal environment. The design incorporates a new clover antenna and washer structure, effectively reducing the influence of the metal environment and improving the communication quality. The proposed design has undergone comprehensive prototyping, simulation and experimental verification. The results demonstrate a significant improvement over the traditional circular antenna and washer combination under similar conditions. Specifically, the sensing distance of the new clover washer is enhanced by 60% and the stable communication distance is improved by 75%. The experimental results highlight the ability of the new clover smart washer to generate a stronger spatial magnetic field and exhibit reduced susceptibility to the metal washer, thereby enhancing communication effectiveness.

Mechanical testing and numerical simulation of intelligent terminal structure of rockbolt used as a deformable support and for safety monitoring in rock engineering

The nonlinear mechanical behavior perception and deformation control of engineering rock masses are crucial technical challenges in the fields of underground engineering support and safety monitoring. An intelligent terminal structure (ITS) of rockbolts was designed for deformable support systems and safety monitoring in rock engineering applications. It is a type of device installed at the end of a traditional bolt. The ITS comprises two key components: a memory tooth and a yielding ring. This study introduces the design principle of an ITS in deformable rockbolt support systems. It proposes design parameters for the ITS in relation to the deformations encountered by engineering rockbolts. Tests were conducted to measure the ultimate bearing capacity and deformation of the ITS under pull-out conditions. The results demonstrate that the ITS of rockbolt undergoes deformation in the form of elongation as opposed to conventional bolts. Furthermore, finite element numerical simulations were conducted to investigate the mechanism of interaction between the memory tooth and yielding ring of the ITS. The numerical simulation results are consistent with the experimental results. The load capacity of the yielding ring exceeded that of the memory tooth. The field test results indicate that the dilatation of the surrounding rock mass causes ITS deformation in the diversion tunnel. The axial stress load exerted on the rockbolt is transferred to the ITS, leading to memory tooth breakage and compression deformation of the yielding ring. This mechanism allows the load and deformation of the surrounding rock mass to be reflected. The ITS not only serves as a deformable support system but also plays a significant role in monitoring the stress and deformation of the rock mass.

Group combined failure in tension of extended hollo blind bolts using numerical finite element method

The structural hollow sections (SHS) have several advantages comparing with the open sections. However, the application of the SHS in the industry is limited due to the traditional bolt connection and cannot be used for the SHS as the inaccessibility to the inside of section. Several blind bolt systems were developed to overcome this problem and the EHB is the modified version of one of the blind bolt systems.This project aims to investigate the behaviour of the Extended Hollo-bolt (EHB) connection under combined failure mode with a focus on the influence of the bolt pitch distance by using test data and Finite Element (FE) models and to propose an analytical model for the connection. The EHB connection is between a SHS column filled with concrete and a beam made of an open section. Two rows of EHB were embedded in concrete filled SHS and tested under tension.FE models were created and validated by tests data and they were used to investigate the aforementioned aims. It is found that pitch distance has a significant influence on the strength of the connection as increase of the pitch distance increases the strength of the connection until a critical value. An analytical model was also proposed for the connection.

Research on Non-contact Bolt Preload Monitoring Based on DIC

Bolt preload is a key parameter of the reliability of bolt connection. Traditional bolt preload detection generally uses torque wrench or high-precision strain sensor. In this paper, a new method of non-contact preload monitoring is realized by measuring the digital image of bolt elongation. A bolt tensile test device is designed, and the results of laser triangulation and three-dimensional point tracking are compared with those of optical measurement. The embedded load cell is used to monitor the bolt preload. The test results of M18 bolts with different bolt lengths and grades are evaluated. and it is found that the test values are close to the theoretical calculation, which can be used to predict the pretightening force.

Study on the Style Design and Anchoring Mechanism of Enlarged Head Anchors

To resolve insufficient traditional bolt supports due to the complexity of geological conditions, the optimal design of an expanded head bolt was investigated by using theoretical calculations and experiments. The results show that the drawing capacity of an expanded head bolt is affected by the bearing capacity of front and rear ends, side bearing capacity, and side friction resistance. For a circular anchor bolt, stepped anchor bolt, and semi-ellipsoidal anchor bolt, with an increase in the front section’s radius, the lateral friction resistance of the inner anchor section is gradually shared by the bearing force of the front end of the inner anchor section; the bearing effect of the front end of the inner anchor section is enhanced; and the pulling performance of the anchor bolt is enhanced. Therefore, the pulling force of the circular anchor bolt is at the maximum, followed by the stepped anchor bolt, and the semi-ellipsoidal bolt is at the minimum. The increase in the rear section can provide greater lateral friction resistance and end-bearing force. Compared with cylindrical enlarged head anchors, the circular, stepped, and semi-elliptic enlarged head anchors have a smaller front section but a larger rear section, and the reduction in the front section’s bearing capacity is less than the increase in the side bearing capacity and rear-end bearing capacity; thus, the cylindrical bolt has the lowest pulling force. Compared with the front radius, the back radius has more influence on the drawing ability of the enlarged head anchor. The longer the inner anchorage section, the larger the distribution range in the compression zone that is formed in the soil body and the smaller the range in the tension zone that is formed in the rear. The increase in the length of the inner anchorage section is conducive to improving the reinforcement effect of the soil in front of the anchorage section in the bolt. Therefore, this parameter plays an important role in the redistribution of the soil in front of the force. The ultimate pull-out force of a circular table-shaped tensile bolt is the highest, followed by the stepped bolt, and the semi-elliptic bolt comes in third, with the cylindrical bolt exhibiting the lowest pull-out force; the circular table-shaped enlarged head anchor constitutes the best style design.

Design of a Quick-Pressing and Self-Locking Temporary Fastener for Easy Automatic Installation and Removal

In the traditional pre-joining technology of aircraft panels, bolts are generally employed for pre-joining. Due to the length and width of panels, bilateral manual operations are required to operate bolts. In this case, there are problems such as low work efficiency, unstable quality, cumbersome operation, and inconvenient installation-removal. This paper takes a temporary fastener with one-side installation-removal as a research object and conducts in-depth research on three levels of quick-pressing: unloading, stable self-locking, and easy automatic installation. Firstly, by coordinating the ratchet and the spring, the restoring force of the spring is used to make the cylindrical top-rod rotary and realize the telescopic function to achieve quick loading and unloading of fasteners; subsequently, through the cooperation between the buckle and the spring, loading and unloading self-locking is attained; afterwards, through the threaded joining and the same cylinder design between the external profile components, the convenience of fasteners for automatic transportation is realized. When assembling two thin-walled parts of the aircraft, only continuous one-side pressing of fasteners is needed to carry out the tightening and unloading work, namely, one-pressing installation and one-pressing removal, which could solve the problems caused by the bilateral operation of traditional bolts and part tolerances. After the application of the fasteners into the pre-joining process of aircraft panels, the experiment results have shown that this temporary fastener provided a good clamping effect, could be quickly and efficiently installed and removed by continuous one-pressing, and avoided the problems of complexity and high cost for pre-joining processes.

Shear behavior of large studs and novel bolted connectors in steel-UHPC composite beams

With the gradual application of ultra-high performance concrete (UHPC), steel-UHPC composite bridges produce higher interfacial shear, which require larger diameter studs to avoid the group-stud effect of abundant small studs and accelerate the construction. Considering welding problems of larger studs, bolted connectors could be an alternative and benefit the replacement of composite bridges. The traditional bolted connector expressed early slip on the steel-UHPC interface due to the bolt-to-hole clearance, which reduced the composite action. To decrease the clearance, three novel bolted connectors involving a hinged bolt, a threaded-hole bolt, and a taper-sleeve bolt were proposed and tested along with large studs and traditional bolted connectors. The diameter of shear connectors ranged from 24 mm to 40 mm. Three failure modes were observed, in which the failure of the studs was significantly influenced by the welding quality. The shear capacities of the novel and traditional bolts with the same diameter were similar and unrelated to the bolt-to-hole clearance. The novel bolted connectors did not exhibit an early slip in load-slip curve and their stiffness was maximum 4.1 times that of the traditional bolt. The shear capacity and stiffness of shear connectors increased with their diameter. Six equations for predicting shear capacity and five equations for the shear stiffness of shear connectors were evaluated, the ductility of the studs and bolts were also assessed. The hinged bolt was evaluated to have a better comprehensive shear performance than other bolted connectors.

Parametric Study of the Numerical Model of a Bolted Connection of Steel Structure for Photovoltaic Panels.

In the face of the reality that unexpectedly mobilized the governments of most central European countries (including Poland), the development of renewable energy sources (RES) seems to be an important direction. Therefore, both wind parks and solar farms will be constructed at double speed for energetic independence. This urgency makes the market of producers of structures for mounting solar panels also need to adapt quickly to the new situation. New constructions adapted to quick assembly with the use of nutless screw connections seem to be one of the best solutions. These structures must not only be easy and quick to install but also durable, which makes the connections resistant to cyclical loads. The speed of assembly of the substructure can be achieved precisely with the help of nutless connections, but their durability should be carefully analyzed. This article presents parametric analyses of the numerical model of this type of connection. The selection of appropriate numerical models for simulation is of key importance in the fatigue strength analysis of bolted connections. This article investigates two different models used in numerical fatigue analyses performed in the Abaqus FEA and FE-Safe program, namely, traditional bolt with nut and innovative self-tapping nutless bolt. Extended parametric analyses of both numerical models were carried out, which ultimately allowed optimization of the fatigue capacity of the connection.

Improvement on the Key Element of Flexible U‐Shaped Steel Support and Its Field Applications

In China, there are a significant numbers of soft rocks roadways in underground coal mines. The roofs of these roadways are generally highly fractured, and traditional bolt installation does not provide sufficient supporting capacity. Hence, U‐shaped steel support has gained popularity, and the key influential factor of steel support is the lock unit between its mechanical structures. The commonly used two‐slotted splint lock unit can experience eversion and splitting and resulted in overall instability. To overcome the limitation, a “surface snap‐in” lock unit was developed. Based on experimental results, it was found that the relationships of bearing capacity and deformation of two lock unit types were similar under same loading conditions. The ultimate bearing capacity of surface snap‐in lock unit was lower than the two slotted splint unit. Although, its overall stability and flexibility were better. On the other hand, screw bolts of both unit types exhibited increase or decrease with the compressional deformation of steel support. The maximum stress along the screw bolt of two‐slotted splint lock unit was 1.6 to 1.8 times of the surface snap‐in lock unit. Based on the findings, the combination of two lock unit types was proposed and used at Peigou coal mine. Results show that the proposed design can effectively manage the roadway deformation while preventing the steel support damage. This in turn can reduce the associated supporting cost as the steel support can be recycled.

Experimental study on steel plate shear walls with novel plate-frame connection

The bolt connections between frame and infill steel plate in steel plate shear wall (SPSW) are relatively weak, and their deformation around the holes of steel plate or fishplate induced by tension field effect causes difficulties in replacing the damaged infill steel plates. This paper proposes a novel plate-frame connection for thin SPSWs. The proposed connection, consisting of a fishplate with large holes, steel angles with standard holes, and bolts, is able to achieve a multi-stage force transfer mechanism. Two failure criteria of the proposed connection were defined, followed with shear test of the novel connection. Three SPSW structure specimens with various thicknesses of steel plate and plate-frame connections were tested. Finite element models for SPSW structure with novel connections were developed and verified by the test results. The influence of thickness of infill steel plate on the seismic performance and connection slippage of SPSW structure was evaluated. The results show that the novel plate-frame connection is convenient to install in SPSW as the precision requirement of bolt holes in traditional connection is mitigated. The SPSW structure with the novel connection exhibits similar seismic performance as that in the traditional bolts-connected SPSW structure. With the plastic deformation of angle steel at the latter stage, the load bearing and energy dissipation capacities of SPSW structure are increased by 0.83% and 5.4% as compared with those of the SPSW with the traditional bolt connection, respectively. The multistage stress model and two-stage failure criterion can accurately predict the failure of the plate-frame connection.

The mechanism of decrease in bearing capacity and performance evaluation of the yielding bolt in coal mine

AbstractWith the increase of the coal mining depth, the surrounding rock shows characteristics of high stress and large deformation. However, the traditional bolt could not adapt to this surrounding rock environment and become invalid due to low elongation. In order to solve the problem, the new type of yielding bolt has been designed. It could release the deformation energy of the surrounding rock through its yielding pipe. However, few studies have been reported on the mechanism in bearing capacity decrease of the yielding pipe. Furthermore, the evaluation of the yielding bolt was not fully understood. Under such a background, a numerical model of the yielding model was established. According to the numerical simulation, the mechanism of the decrease in the bearing capacity of the yielding bolt is that the buckling occurs at different positions of the yielding pipe, making the material stiffness matrix turn negative, and the bearing capacity decreases significantly. Also, the performance of the yielding bolt could be evaluated from the use efficiency of the yielding pipe, the plastic strain characteristics of the components of the yielding bolt, and the energy absorption law. The evaluation results indicated that: (a) the deviation of the yielding pipe's Mises stresses was within the range of 1.0%‐4.0%. The stresses were distributed evenly, and the material use efficiency was high; (b) only the yielding pipe occurred the plastic failure during the yielding process, and other components were at the elastic stages. After the yielding, the yielding bolt was still effective for support. (c) The yielding pipe could absorb energy smoothly, which is helpful for the stability of the yielding bolt.

Stiffness Calculation Method and Stiffness Characteristic Analysis of Bolted Connectors

At present, few scholars have studied the effect of surface roughness on assembly stiffness. The influence of the joint surface stiffness on the overall stiffness is neglected. In this paper, a new method for calculating the stiffness of bolted joints is presented. The effect of joint surface stiffness on the overall stiffness is considered. Firstly, the relationship between load and displacement between cylinder and cylinder (including the joint surface with certain roughness) is studied, and the stiffness characteristic expression of the joint surface is obtained; the results are compared with the traditional stiffness calculation theory, and then, the influence of bolt connection surface on bolt connection is studied and compared with the stiffness calculation results of traditional bolt connection. The results show that the theoretical model presented in this paper is more practical.

Supporting characteristics analysis of constant resistance bolts under coupled static-dynamic loading

To study the tensile mechanical properties of constant resistance bolts, the RFPA (Rock Failure Process Analysis) statics software is used to perform a uniaxial tensile test on a constant resistance bolt. The numerical test results show that the plastic strain value is 12 times the magnitude of the elastic strain. During plastic deformation, the fluctuation in the stress magnitude is relatively stable, indicating that the bolt has good constant resistance characteristics. The numerical test results are in good agreement with the laboratory test results of M.C. He, and the accuracy and reliability of the numerical test method are verified. Therefore, the RFPA software with coupled static-dynamic loading is further adopted to study the supporting effects of traditional bolts and constant resistance bolts under coupled static-dynamic loading. The numerical comparison of the test results show that the constant resistance bolts can effectively control the deformation amount and rate of the laneway surrounding rock, reduce the total and rate of increase in the accumulated acoustic emissions, decrease the stress on the units in the model and protect the stability of the laneway. This paper verifies that a constant resistance bolt has better impact resistance mechanical properties than those of a traditional bolt and provides an effective way to control rock burst and soft rock that is prone to large deformation damage.

Shear behavior of lap connection using one-side bolts

Experimental and numerical investigations on the basic shear behaviors of the lap connections connected by the threaded-fixed one-side bolts were presented. The threaded-fixed one-side bolt in the connection was clamped by internal threads on the wall of a bolt hole, instead of the traditional nut. 36 test specimens with different thicknesses of screwed shear plate and different bolt pre-tension forces were conducted. The failure mode of the shear connection obtained from tests were perfectly consistent with those predicted by EC3-1-8 design equations and the ultimate shear predicted resistance was conservative compared with the test result, both of which differed by 4.6%. A finite element model was built and verified to further investigate effects of the thickness of base plate and the bolt diameter on the shear behavior of the lap connection. The simulated results concluded that the bolt would tilt if the thickness of base plate was smaller than the bolt diameter. The lap connection using the threaded-fixed one-side bolts and the traditional bolts with nut were compared. Difference in the ultimate shear resistance is 0.24% as only the bolt shear fracture failure occurred, however, difference in the ultimate shear resistance is 2.5% as the bolt shear fracture accompanied by the bolt tilting occurred. This paper proved that the screwed shear plate could replace the traditional nut in engineering applications.

Application of Fiber Bragg Grating Sensing Technology for Bolt Force Status Monitoring in Roadways

Bolts support have become a major active support method in coal mine roadways to control roadway roof failure and improve surrounding rock structure stability. The traditional bolt force status monitoring (BFSM) method has poor anti-interference performance, is easily affected by harsh downhole environments, and cannot support remote real-time monitoring. This paper presents a fiber Bragg grating (FBG) bolt force sensor that monitors the force of roadway bolts. This sensor uses a cantilever and a diaphragm as elastic elements and two FBGs bonded on the top and bottom surfaces of the cantilever as sensing elements. The experimental results indicate that the measuring sensitivity is improved by using the center wavelength difference between the two FBGs. The sensitivity is 38.79 pm/kN within the range from 0 to 150 kN, and the correlation coefficient reaches 99.98%. The engineering applications show that the FBG sensing technology can automatically acquire, and monitoring results are of great significance in roadway anchorage engineering safety and bolt support quality evaluation. Furthermore, such a sensor is also widely used in quasi-distributed measurement and long-term online monitoring of bolt force status in such fields as geotechnical engineering, tunnel engineering, and slope engineering.

Support principles of NPR bolt/cable and control techniques of large-deformation disasters

Deep mining has been paid much more attention because of the depletion of shallow mining resources. Traditional bolts could be invalid to accommodate large displacement and deformation in geomaterials. Consequently, alternative support and reinforcement bolts need to be studied and their constitutive models also need to be developed to help understanding for the complex stress-strain responses of rock masses under loadings. The effect of Negative Poisson’s Ratio (NPR) that is attributed to the swelling phenomenon along the lateral direction may appear in metal materials under tensional loadings. Thence NPR materials often have an advantage over NPR ones in mechanical behavior such as impact resistance, anti-shearing, and energy absorbed. From the characteristics of NPR materials, a series of bolt and cable supports with the effect of NPR and constant-resistance have been recently developed. We here firstly introduce the structural features of NPR support. Then the constitutive model of NPR support is presented and its corresponding equation of energy equilibrium. Its basic principle interacted on rock masses is further discussed. Finally, NPR cables are employed to support the slope of an open-pit mine. The applications show that NPR cables can ease failure within the slope and play an important role in predicting and providing early warning of slope failure, together with a monitoring system of slope stability.

Cable-truss supporting system for gob-side entry driving in deep mine and its application

In order to solve the large deformation controlling problem for surrounding rock of gob-side entry driving under common cable anchor support in deep mine, site survey, physical modeling experiment, numerical simulation and field measurement were synthetically used to analyze the deformation and failure characteristics of surrounding rock. Besides, applicability analysis, prestress field distribution characteristics of surrounding rock and the control effect on large deformation of surrounding rock were also further studied for the gob-side entry driving in deep mine using the cable-truss supporting system. The results show that, first, compared with no support and traditional bolt anchor support, roof cable-truss system can effectively restrain the initiation and propagation of tensile cracks in the roof surrounding rock and arc shear cracks in the two sides, moreover, the broken development of surrounding rock, roof separation and extrusion deformation between the two sides of the roadway are all controlled; second, a prestressed belt of trapezoidal shape is generated in the surrounding rock by the cable-truss supporting system, and the prestress field range is wide. Especially, the prestress concentration belt in the shallow surrounding rock can greatly improve the anchoring strength and deformation resisting capability of the rock stratum; third, an optimized support system of “roof and side anchor net beam, roof cable-truss supporting system and anchor cable of the narrow coal pillar” was put forward, and the support optimization design and field industrial test were conducted for the gob-side entry driving of the working face 5302 in Tangkou Mine, from which a good supporting effect was obtained.

Active Sensing Based Bolted Structure Health Monitoring Using Piezoceramic Transducers

Bolted structures are commonly used in civil infrastructure. It is important to perform bolt inspection regularly to ensure the safety of structures. Traditional bolt inspection methods are time-consuming; moreover, bulky instruments are needed in these methods. In this paper, a piezoceramic based active sensing approach is developed to perform the health monitoring of bolted structures. Surface-bonded piezoceramic patches are used as health monitoring transducers. Wavelet packet analysis is used to analyze the sensor data to extract the features that indicate bolt looseness. Based on wavelet packet analysis results, a damage index is developed to quantitatively evaluate the damage status. To verify the effectiveness of the proposed method, a bolted connection experiment with piezoceramic transducers was performed. In the experiment, the looseness of the bolt is adjusted by a torque wrench. Experimental results show that the proposed approach is effective to detect and evaluate bolt looseness.