Short Bolts Research Articles

A refined energy ratio method based on ultrasonic echoes for measuring short bolt axial stress

Ultrasonic stress measurement methods play an important role in measuring bolt axial stresses. Traditional Time of Flight (TOF) approaches have accuracy limits when applied to short-bolt stress measurement. This paper proposes a Refined Ultrasonic Echo-based Energy Ratio (RUEER) method for bolt stress measurement that considers internal nonlinear scattering attenuation effects, transmission-reflection effects at the interface area, and energy loss in the transition region. The ultrasonic wave inside the stressed bolt is decomposed into different components to better evaluate the energy attenuation of ultrasonic echoes. The proposed method is verified with stress measurement experiments. Results show that the average error of the proposed RUEER method is less than 2.5% for different bolts and clamping lengths. Through comparative testing, the accuracy of the proposed method demonstrates improved performance over the TOF and Energy Attenuation Method (EAM). Additionally, the RUEER method is more robust to variations in equipment performance than the TOF method.

Measurement of axial stress in high-strength short bolts using ultrasonic attenuation

Based on the scattering attenuation theory of loaded polycrystalline metals, a bolt axial stress measurement method using ultrasonic echo attenuation is proposed for the problem that the conventional time of flight (TOF) method is difficult to measure the stress of high-strength short bolts. Firstly, the attenuation coefficients of body-centred cubic crystalline materials in the Rayleigh scattering range are described, and the mathematical model between the ratio of the peak of the two bottom echoes and the axial stress of the bolt is further derived. Then, the effects of the transducer wafer diameter, mounting eccentricity and bolt thread on the ultrasonic signal were analysed by finite element simulation, to provide a strategy for transducer selection and mounting. In addition, a magnetic ring clamping device was designed to ensure a tight fit between the transducer and the bolt, and to improve the alignment of both. Finally, a bolt axial stress ultrasonic measurement system was built, and a comparison experiment between TOF method and attenuation method was conducted to predict the axial stress of bolts. The experimental results shown that the average percentage measurement error of the attenuation method proposed in this paper is 4.42%–5.76% lower than that of the conventional TOF method, which is more suitable for measuring the axial stress of bolts.

Mechanics mechanism of slab-type short bolt composite structure for repairing cracked lining under compression shear

In order to repair the tunnel linings with compression-shear cracks under small eccentric compression, the use of slab-type short bolt composite structure to repair tunnel cracks is proposed in this paper through the method of model test and numerical simulation. From the perspective of the component, the mechanics mechanism of repairing the lining with shear cracks in the slab-type short bolt composite structure is studied. The model tests for repairing small eccentric compressive components with the slab-type short bolt composite structure were designed and carried out, and the ultimate bearing capacity and load-strain curves of the components were obtained, which were matched in the numerical simulation. The form of the slab-type short bolt composite structure is determined, and the model is established by using ABAQUS finite element software to study the design parameters. The influence laws and recommended values of three design parameters, namely, the thickness of repairing steel plate, the strength grade of the short bolt, and the bolted depth of short bolt, on the ultimate bearing capacity of components are obtained. The issue of repair timing during the field application of slab-type short bolt composite structure is studied, and the difference in component load-deformation curve between “pre-peak repair” and “post-peak repair” of the composite structure is clarified to give the suggested latest repair time.

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.

Study on Shear Performance of Short Bolt Interface in ECC–Steel Bridge Deck Composite Structure

Aiming at the problem that orthotropic steel bridge deck and bridge deck pavement are prone to fatigue damage, Engineered Cementitious Composites (ECC) bridge deck pavement is used to replace concrete or asphalt in flexible bridge deck pavement. In order to deeply explore the shear resistance of the short stud interface in the ECC–steel composite structure and provide theoretical support for the practical application of the project, 16 static push-out tests were completed. The effects of stud diameter, height and arrangement spacing on the shear capacity of the medium and short ECC studs were studied. The failure modes, load–slip curves, load–strain curves and interface gap width curves of the components were analyzed. The test results showed that the shear force of the medium and short ECC bolts mainly produces two failure modes, bolt shearing and bolt root weld shearing, while the ECC plate has a local crushing area at the interface bolt root position, and no large cracks occur in other areas. The shear capacity of short bolts is significantly affected by the diameter of the bolts, but is less affected by the height and spacing of the bolts, and increases with the diameter of the short bolts. The length of the stud has an important influence on the stress on the surface of the ECC board. The longer the stud, the greater the tensile stress on the ECC surface. The shorter the peg, the more prone to eccentric compression the ECC plate is, and the longer the peg, the more prone to axial compression it is.

Fracture simulation of a demountable steel-concrete bolted connector in push-out tests

Many bolted connectors were proposed for use in steel-concrete composite structures over the past few decades. This is because using bolted connectors could make the assembly and disassembly of steel-concrete composite structures more convenient and reusing the dismantled structural components could also improve structural sustainability. Lots of static and fatigue experimental tests on steel-concrete bolted connectors were conducted but detailed finite element simulations including fracture of bolted connectors were rarely reported. This paper presents a series of simulations of a demountable steel-concrete bolted connector in push-out tests, which was proposed and reported by the authors of this paper before. Damage models of bolt and concrete materials are incorporated in the simulations to better understand the behaviour of the bolted connector and the failure mode of the push-out tests. Direct tension tests on bolts are simulated to calibrate the stress-strain relationship of bolt material and assumed pure shear tests on bolts are modelled to validate the fracture criterion used in the simulations. Results of modelling push-out tests indicate that the friction force at the steel-concrete interface accounts for a part of shear resistance of the bolted connector in push-out tests conducted. The load-slip curves and the fracture of bolts in push-out tests can be approximately predicted by incorporating damage models of bolt and concrete materials and considering an appropriate friction coefficient. The effects of concrete damage model, clearance in bolt hole, and pretension of short bolt on the shear performance of the bolted connector are discussed at last.

Analysis of Cooperative Control Effect of Pressure Relief and Long Bolt Support for Deep Roadway Under Strong Mining Disturbance of Adjacent Working Face

The stability of mining roadways is pivotal to safe mining in deep underground coal mines. In order to control the stability of mining roadways in deep mines, this paper studies the cooperative control effect of pressure relief and long bolt support for deep roadway under strong mining disturbance of adjacent working face in Wenjiapo Coal Mine in West China. The numerical calculation software FLAC3D was used to simulate the distribution law of the displacement, stress and plastic zone around the roadway under the disturbance of excavation and working face mining with three support schemes: “short bolt + long cable”, “long bolt + short cable”, and “long bolt + short cable + drillholes and cutting grooves pressure relief”. The results show that extending the length of bolt can ensure the supporting effect while reducing the consumption of anchor cables in the roof, and can reduce the roadway floor heave by 5.5%. Moreover, the peak lateral pressure of the roadway is reduced by 12.5%, the peak value is shifted to the depth by 6 m, and the floor heave of the roadway is reduced by 36% when the countermeasures of pressure relief in the ribs and floor are adopted. This indicates that the schemes of pressure relief and long bolt support has a significant beneficial effect on decreasing the high stress environment and controlling the deformation of roadway.

A Reliability Study of Joints with Bolts Designed with Threads Excluded but Installed with Threads Not Excluded

This paper presents a reliability and probability study focusing on connections using relatively short bolts that in a companion paper have been shown to have the potential to have been designed with threads excluded from the shear plane and then subsequently installed with the threads not excluded from the shear plane. After an introduction outlining the background of the shear strength and associated design of joints in various editions of the AISC Specification, the paper presents a structural reliability analysis as well as a probability study using Monte Carlo simulations, and then finally a discussion of additional considerations and mitigating factors associated with this potential problem. Calculated reliability coefficients and probabilities of failure are tabulated for joints using two diameter groups of 120-ksi bolts (from ? in. to 1 in. and from 1? in. to 1¼ in.) and for joints using 150-ksi bolts. The paper provides an evaluation of the reliability of joints with bolts that have been designed with the threads excluded from the shear plane but installed with the threads not excluded from the shear plane. Although it is recommended that future designs involving short bolts be based on the assumption that the threads are not excluded from the shear plane, this study provides a measure of the reliability of structures that have already been constructed with bolts designed assuming that the threads were excluded but installed with the threads not excluded. The results show that the reliability of joints in this class is dependent on the grade and size of the bolts used, on the length of the joint, and on which edition of the AISC Specification was used for design. It was found that some joints in this class still meet the AISC target reliability for connections, and that many joints meet the AISC target reliability for members.

Advancement of Conventional Anchor Support System through Use of NATM and NMT Approach for Underground Drift Stability

In present scenario underground mines of Central India is using conventional supporting with anchoring/boltingsystem to supports the excavated haulage road and cross cut. In case of geologically disturbed areas concretingwith girders is the main support. In routine formations short bolts suffice the purpose. These conventionalmethods specially concreting is time consuming and hampers productivity. Application of NMT (NovergianMethod of Tunneling) and NATM (New Austrian tunneling method) will give the advancement in the supportsystem. Application of both the method will reduce support erecting time and thus the cyclic operation ofmining can be accelerated. The cross-section area of Under drift will 6m x 3m, 4 m x 3 m, 3m x 3, etc.Conventional concrete support for the area may have required 15 days (5 R-mt span). The same was done byshotcreating with NATM/NMT in just 5 days (5 R-mt span) including lowering of machine and materials.Ingeologically stable formations applicationof long bolt, short bolt, and anchorage through cable was found toprovide requisite support tothe excavated drift.Rock Mass Rating of Bieniawskiand Barton’s Q system supportcalculation methods have been used to calculate support requirementsfor haulage as well as cross cut drifts.

Numerical investigation on flexural performance of retrofitted tunnel lining with short bolts and steel-plate

To establish the flexural performance of a retrofitted anchor-bolted steel plate reinforced structure as a cast-in-place tunnel lining, we conducted a numerical analysis using bend-compression tests. The current rehabilitation structure involves the combination of a long bolt and an H-shaped steel girder. However, installing the long bolt is complex and can damage the waterproof structure. Furthermore, the H-shaped steel girder can intrude into the tunnel clearance. To overcome these limitations, we replaced the existing long bolts and H-shaped steel girder structure with girders using short bolts. The developed numerical model was validated against the experiment model based on the failure pattern, load-deflection, and load-strain results. Three initialised cracks of different depths were considered and produced on the beams. The numerical results unveiled the flexural-tensile failure pattern and demonstrated significant enhancements in flexural capacity, stiffness, and ductility. The proposed short anchor-bolted steel plate system is a viable option for repairing cast-in-place tunnel linings.

Stability Analysis and Support Control for a Jointed Soft Rock Roadway Considering Different Lateral Stresses

The stability of coal mine roadways in jointed soft rock masses is an important issue for safe and efficient mining production in underground mines. Taking a main haulageway of a coal mine in Guizhou Province in China as the research background, the instability failure caused by large deformation of a roadway in a cracked rock mass was analysed, and its support control measures were put forward. First, the stability of the surrounding rock was evaluated by field investigation on the failure characteristics and statistics for the development of joints and fissures in the surrounding rock. Second, the corresponding numerical model was established by using FLAC3D software, and the influence of the lateral pressure coefficient λ on the plastic zone and principal stress were analysed quantitatively. In addition, the evolution process of the plastic zone over time was summarized. Furthermore, the key points of the reinforcement plan and support parameter design were provided on the basis of the technical approach for deformation control of the surrounding rock of the roadway. The original supporting scheme was optimized step by step, and the combined supporting scheme with “short bolt, long anchor cable and two-step grouting shell” serving as the main concept was put forward. Finally, the results of numerical calculation and field practice showed that the optimized scheme could effectively restrain the local deformation in the plastic zone of the surrounding rock of the roadway. The overall deformation was in a controllable range. In addition, the reinforced anchor cable was anchored to the deep part of the surrounding rock, ensuring the safety and stability of the roadway.

Hydrodynamic Load and Parametric Design of Grouted Clamp Used on Offshore Jacket

Abstract The reliability and safety of offshore platform are an important research aspect in marine engineering. The jacket platform is mainly used for oil development and submarine drilling, and the long-term work in the marine environment will be subjected to different loads, which will lead to the damage of the structure part of the offshore platform. It affects the structural strength of the platform. For the repair of jacket damage, grouted reinforcement technology is adopted, which has the advantages of simple underwater installation and low cost. The reinforcement technology of the grout hoop has been applied to the engineering projects abroad, but the stress and serialization design of the hoop in the marine environment need further study. This paper will combine the ocean current and wave force to carry out the research of underwater work and prevent loosening, and put forward the parametric design method for the specific size of the hoop. Two types of experimental models are designed: short bolt form clamp and long bolt form clamp. The mechanical experiment of the long bolt clamp is carried out, and the relationship between the slipping force and the bolt preload is analyzed, so as to verify the theoretical analysis.

Stability Analysis of Bolts Reinforced Rock Jointed Slope by Considering the Transverse Effects

The fully grouted bolt is a convenient, effective, and economic technology for slope reinforcement. A new nonlinear Hoek-Brown strength reduction method based on the characteristics of a jointed rock mass is proposed. By analyzing the change in slope failure mode, effects of the bolt head, spacing, inclination, and arrangement on the stability of the slope are investigated. Results show that the shear strength of the bolted structure is contributed by the axial force and transverse shear force. The transverse shear force of bolts increases the slope stability and improves the bolt bearing capacity; the bolt head is important in determining the failure mode and factor of safety of a bolted slope, while the size and material parameters of the bolt head are not important when the size of the bolt head is sufficiently large. The vertical bolt spacing has a nonlinear effect on the slope safety factor, and the failure mode of the slope changes from deep sliding to partial deformation along the joint surfaces with increase in the bolt horizontal spacing. With increase in the bolt inclination angle, the safety factor first increases and then decreases, and the maximum safety factor occurs when the bolts are placed horizontal or perpendicular to the slip surface. The slope safety factor decreases with decrease in the bolt length. An optimal design of longer bolts at the bottom and shorter bolts at the top is recommended. A shear zone forms from the intersection of two joints to the slope surface in the upper part of the slope.

Threaded Fastener Locking With Safety Wire and Cotter Pins

This paper presents test results and analyses of safety lock wire and cotter pins with castellated nuts used as locking features in threaded fasteners. These mechanical components are used to secure hardware in aerospace and other applications as well as to assess whether a fastener has been tampered with. Tests are performed on aerospace threaded fasteners. Locking moments up to safety lock wire and cotter pin failure are measured. Calculations of locking moment to failure are provided and compared to measured results. For fasteners with safety lock wire, the angle of turn with applied moment is measured and computed. For fasteners with cotter pins and castellated nuts, the angles of turn from clearances and applied moment are computed. Since both safety lock wire and cotter pin with castellated nut applications result in some angle of turn, analysis for loss of preload with angle of turn is developed. Calculations show modest loss in preload for typical angles of turn for long bolts, but a significant loss of preload is found for short bolts.

Investigations of Support Failure and Combined Support for Soft and Fractured Coal-Rock Tunnel in Tectonic Belt

The structural integrity of coal and rock tunnel affected by structural belts is generally poor, and the fracture development leads to the failure of support. Therefore, in this study, the tunnel deformation characteristics and deformation control technology were conducted using a combination of field investigation, laboratory experiment, theoretical analysis, field test, and other methods based on the Mukong coal mine. First, field investigations show that the main structural support failure often starts from some key parts associated with weak strengths, and the deformation is basically unevenly distributed. For this, the structural plane of tunnel rock mass was investigated and the internal structural deformation of the surrounding rocks was also monitored through the peepholes. In addition, point-load strength test was also conducted. Field observations and testing results show that rock fissures in the tunnel are well developed and a large loose circle will be formed after excavation. According to Barton Classification Q value and rock mass rating value, the mining tunnel stability falls into the category of Class V, i.e., the surrounding rock is poor or extremely poor. Finally, the support principles concerning surrounding rock stability control technology were proposed. The core idea is using support reinforcement repeatedly for several times until both internal and external load-bearing capacities of the surrounding rock are met. For the support reinforcement, a test with combined support scheme was conducted, including short bolts, long anchor cables, and U-steel brackets. Monitoring results of site application show that the proposed scheme contributes to the long-term stability of tunnel surrounding rock.

Shear performance of a novel demountable steel-concrete bolted connector under static push-out tests

Bolted connectors could be an alternative to replace conventional welded headed studs between steel girders and concrete slabs, which may benefit prefabricated construction and replacement of concrete slabs considering the life-cycle design of steel-concrete composite structures. In this paper, a novel steel-concrete bolted connector, consisting of a short bolt, a long bolt and a coupler, is proposed. Compared with other bolted connectors, this bolted connector could render the dismantling of concrete slabs more convenient. To investigate the failure mode and fundamental mechanical behaviour of novel bolted connectors and to compare their shear performance with that of conventional welded headed studs, static push-out tests were implemented on four groups of bolted connector specimens and one group of welded stud specimens. The test results demonstrate that the failure mode of novel bolted connectors is that shanks of short bolts are sheared off directly without local concrete crushing phenomenon under couplers. The shear bearing capacity is about 0.8 times of the tensile strength of short bolts, and the peak slip of the steel-concrete interface grows as the bolt shank diameter increases. The exponential expression which generally describes load-slip curves of welded stud connectors simulates the test load-slip curves of novel bolted connectors well. The clearance between bolt shank and bolt hole has a significant effect on the shear stiffness of novel bolted connectors.

The Hungarian Wood-Based Panel Industry and its Impact on the Environment

Abstract It is well known that worldwide deforestation has a negative impact on the global environment. Forests play an important role in producing oxygen as well as retaining gases that create the greenhouse effect. Forests primarily absorb carbon dioxide, the major air pollutant released by the industrial activities. Energy production is the major source of environmental contamination. In addition to reducing CO2 emissions, another issue this industrial sector must tackle is to decrease the use of fossil fuels by substituting them with renewable, environmentally friendly energy sources. One of the answers to these challenges is the utilization of biomass as energy sources. However, biomass-based fuels include short bolts, split round-wood, pulpwood, bark and by-products of sawmilling, which are the raw materials for the wood-based panel industry as well.Wood utilization of the forest products industry has a major impact on the delayed release of carbon dioxide stored in the wood. All over the world, just as in Hungary, the wood-based panel industry mainly uses low quality wood resources and turns them into value added products. The elongation of the life cycle of low quality wood materials decreases CO2 emissions, thus significantly contributing to environmental protection. Furthermore, it is assumed that raw material demand of the wood-based panel industry could be satisfied by focusing on sustainable forest management and well-planned reforestation. Additionally, special energy-plantations may provide extra wood resources, while waste and other non-usable parts of trees contribute to the effective and economic operation of biomass utilizing power-plants. This paper summarizes the current situation of the Hungarian wood-based panel industry and discusses the effects of the panel manufacturing processes on the environment. Also, it outlines the possible future of this important segment of the forest products industry.

정하중 재하 시 실물 강성벽 일체형 철도보강노반의 성능평가

강성벽 일체형 철도보강노반의 열차하중 하에서의 성능을 평가하기 위하여 실물 단선 철도 노반과 동일한 규모인 높이*폭*길이(5m*6m*20m)의 보강노반을 건설하였다. 철도보강노반은 높이의 30~40%의 짧은 보강재와 강성벽체, 보강재 연직배치간격 30와 40cm를 적용한 특징이 있다. 경제성 및 시공성 향상을 위하여 강성벽체와 보강토체와의 일체화 연결방식을 3종류(용접형, 힌지볼트형, 굵은 철사형)로 다르게 설계하였다. 철도 설계하중 50kPa의 19.6배에 해당되는 0.98MPa (최대시험하중 5.88MN) 최대하중에 대하여 2회 정하중 재하시험을 실시하였다. 철도보강노반의 성능은 파괴에 대한 안정성, 지지력과 침하, 벽체 발생 수평변위, 보강재 발생 변형률에 대한 검토로부터 평가하였다. 실물 실대형 시험결과로부터 높이의 35% 수준의 짧은 보강재와 힌지 볼트형 연결방식을 채택한 강성벽체 일체형 철도보강노반에서 40cm의 보강재 연직간격을 적용하여도 열차 설계하중 하에서 좋은 성능을 보이는 것을 확인할 수 있었다. The Reinforced subgrade for railroad (RSR) was constructed for one way railway line with the dimension of 5 m high, 6 m wide and 20 m long to evaluate its performance under train design load. The RSR has characteristics of short length (0.3-0.4 H) of reinforcement and rigid wall, 30 and 40 cm vertical spacing of reinforcement installation. To enhance economics and constructability, three kinds of connections (welding, hinge & bolt, bold wire) were also designed to realize the integration between rigid wall and reinforced subgrade. Two times of static loading tests were done on the full size railroad subgrade. The maximum applied pressure was 0.98 MPa (the maximum test load 5.88 MN), which corresponds to 19.6 times of the design load for railroad subgrade, 50 kPa. The performance on the RSR was evaluated with the safety on the failure, subgrade bearing capacity and settlement, horizontal displacement of wall, and reinforcement strain. Based on the full scale test, we confirmed that the RSR with the conditions of 0.35 H (35% of height) short reinforcement length, hinge & bolt type connection for integration between rigid wall and reinforced subgrade, and 40cm vertical spacing of reinforcement installment shows good performance under train design load.

Mechanism and technology study of collaborative support with long and short bolts in large-deformation roadways

Common short bolts of equal length are widely used to support the roofs of roadways in coal mines. However, they are insufficient to keep the roof stable against large deformations, so docking long bolts with high levels of elongation that can adapt to large deformations of the surrounding rock have been adopted. This paper proposes a collaborative support method that uses long and short bolts. In this study, the mechanism of docking long bolts and collaborative support was studied. Numerical simulation, similarity simulation, and field testing were used to analyze the distribution law of the displacement, stress, and plastic failure in the surrounding rock under different support schemes. Compared with the equal-length short bolt support, the collaborative support changed the maximum principal stress of the shallow roof from tensile stress to compressive stress, and the minimum principal stress of the roof significantly increased. The stress concentration degree of the anchorage zone clearly increased. The deformation of the roof and the two sides was greatly reduced, and the subsidence shape of the shallow roof changed from serrated to a smooth curve. The roof integrity was enhanced, and the roof moved down as a whole. Plastic failure significantly decreased, and the plastic zone of the roof was within the anchorage range. The similarity simulation results showed that, under the maximum mining stress, the roof collapsed with the equal-length short bolt support but remained stable with the collaborative support. The collaborative support method was successfully applied in the field and clearly improved the stability of the surrounding rock for a large deformation roadway.

Time-Domain Reflectometry for the Prediction of Loblolly Pine and Sweetgum Moisture Content

Time-domain reflectometry (TDR) can be used to predict the moisture content in porous materials, including soil, and is an exciting tool that could be used to measure the moisture content in wet-stored wood. Three-rod probes with 127 mm- or 152 mm-long rods were inserted into 62 loblolly pine and 34 sweetgum saturated bolts. The bolts were air dried over a span of five weeks. TDR waveforms and moisture content were periodically recorded. In total, 534 and 482 readings were taken for the loblolly pine and sweetgum bolts, respectively. An algorithm in R was written to automatically analyze the apparent length of the TDR rods. Calibration models were developed between moisture content and X (apparent length / actual rod length). A three-parameter logistic model was developed for loblolly pine (R2=0.64) and sweetgum (R2=0.84). The process was repeated using shorter bolts and 152 mm-long rods, resulting in improved models for loblolly pine (R2=0.99) and sweetgum (R2=0.97). Overall, TDR and the algorithm written to analyze the waveforms were accurate in predicting moisture content and could be used to monitor moisture in wet-decks.