Bolt Tension Research Articles

Experimental determination of the tightening coefficient of bolts according to the din standard

The use of slip-critical connections is very common in the design of critical steel structures and is seen as an effective way to transfer the force in conditions of dynamic loading. The limit state of the connection occurs when the calculated shear stress is reached, which depends on the friction coefficient of the contact planes and the value of the clamping force, equal to the bolt tension stress. In order to ensure the necessary bolt tensioning force, it is necessary to know the bolt tightening coefficient, because according to the current understanding of the slip-critical connection performance, the designed functioning of the bolt connection is ensured when the bolt tensioning force arising at the necessary torque value is achieved. Otherwise, the actual work of the connection will be different from the calculated, because only a given tension force provides the estimated bearing capacity of the bolted connection with friction planes. This article focuses on tensile testing of a bolt and determining the tightening factor of a bolt made of high-strength10.9 M14 steel. The tightening factor is determined with strain gauges by measuring the relative strain of the bolt when the nut is tightened. This method requires specialized equipment and a test bench and can be used in the study of bolt performance in the absence of a certificate or the need to verify or clarify the available data. The results show that the proposed method can provide a stable determination of the coefficient value. The examined bolts were made according to the German standard DIN931, strength 10.9 size M14x220, nuts according to the German standard DIN934, strength 10 size M14. An Instron 1000HDX tensile testing machine was used to plot the performance of the bolt steel. Nut tension control was determined with the use of NOGRAU NTW24-034R torque wrench, and bolt elongation control with FLA 5-11 strain gauges and National Instruments data acquisition system. On the basis of the conducted research, a method for determining the tightening factor of high-strength bolts has been tested and proposed. The proposed method of determining the tightening factor of a high-strength bolt can be used in research work and allows to determine the coefficient in the absence of an appropriate certificate or the need to clarify (verify) the stated value of the coefficient.

Experimental and theoretical investigation of prefabricated separated core tube flange column connection joint

This paper suggests a separated core tube flange connection column joint to ensure the horizontal shear performance of box section steel columns at the flange connection to meet the performance requirements of column-to-column connection in high-rise buildings and the effective connection of steel columns at the joints. Low cycle reciprocating loading tests were conducted on three specimens with different parameters (separated core tube and stiffeners) to study the seismic mechanical performance of the connection and the finite element analysis (FEA) of separated core tube column connection joint was performed. The result of the experimental study shows that the separated core tube connection joints have fuller hysteresis curves and higher energy dissipation performance, as well as less high-strength bolt tension at the same interlayer displacement angle. This investigation provides experimental evidence of the deformation compatibility of the separated core tube connection. The mechanical properties of the separated core tube connection is basically the same as that of the welded connection, which can realize the rigid connection of the steel box section column. According to the numerical simulation, the failure mode and mechanism of the connection were obtained. Based on the results of tests and the finite element numerical model, further analysis to the rotational performance of the separated core tube flange connection joint in elasto-plastic phase and yield-hardening phase is carried out, and a three-stage bearing capacity calculation theory of the joint in the seismic process is proposed, which was verified by the test and FEA.

Tension and interaction resistance of austenitic and duplex stainless steel bolts

The current design rules in EN 1993-1-4 for non-preloaded stainless steel bolted connections under pure shear and tension are essentially based on the regulations for carbon steel bolted connections. Furthermore, the load bearing behaviour under combined tension and shear (category A + D bolted connections) was adopted from EN 1993-1-8 as well. Recent research activities within the German IGF research project “Load-bearing capacity of bolted connections loaded in shear and tension made of stainless steel M12 to M36” (P 1386/IGF-No. 20651 N) showed that stainless steel bolting assemblies behave different. Herein, systematic experimental investigations and an extensive literature review into the shear, tension and interaction resistance of stainless steel bolts were conducted. Furthermore, reliability analyses according to EN 1990, Annex D were accomplished to prove the partial safety factor of γM2 = 1.25 for connections made of stainless steel bolting assemblies. The results regarding the shear resistance have already been presented in a former paper in this journal. In these investigations, it could be shown that an increase of the tension resistance Ft,Rd with k2 = 1.0 is in principle possible following the normative regulations of EN ISO 3506-1 regarding the minimum ultimate tensile strength as well as North American ANSI/AISC 360 and Australian Standard AS 4100. Furthermore, a new interaction approach for both unthreaded and threaded part of the bolt lying in the shear plane could be proposed which has statistically been verified for all property classes with γM* < γΜ2 = 1.25. The new regulations have already been implemented in the current revision of EN 1993-1-4. The background for the new regulations is presented in this contribution.

Experimental studies on slip friction device using symmetric friction connections

The use of friction-based energy dissipater is rapidly growing in seismic active zones to avoid interruptions and costs resulted from local or global damage to buildings due to severe earthquakes. Well designed and detailed friction devices using symmetric friction connections (SFCs) are often considered as an efficient way to dissipate energy for not only their stable hysteretic behaviour and low strength degradation but also the comparable assembling cost to that of conventional construction. The sliding commences when the designed sliding shear force is achieved, which relates to the contact surface’s Coefficient of Friction (CoF) and the total amount of clamping force. This paper reports 15 quasi-static testing of a slip friction device utilizing SFC clamped by two grade 10.9 M20 black finished high strength structural steel bolts in a single row. Shims using brass, aluminium, high strength steel, semi-metallic brake pads and copper-iron alloy were tested. Results show that all five shim materials tested can provide a stable hysteretic behaviour under a cumulated sliding distance of more than 4000 mm. The effect of installed bolt tension, loading rates and bolt-bearing mode are also discussed. Given the stable hysteretic response and the low strength degradation observed, the proposed slip friction device can be considered as a low damage energy dissipater.

Design and Analysis of a Compact Hydraulic Bolt Tensioner

In equipment like high pressure vessels, there will caps on which loads of the order of several thousands of tons acts. Such caps require a huge number of big-diameter bolts, often M70 to M150mm in diameter. Each bolt will be subjected to a tremendous amount of force, on the order of 300 tons. The use of hand-operated wrenches to apply such a load is deemed out. When a high number of bolts are tightened on the flange, the applied load is lost owing to friction at the clamping surface and the applied load is not uniform. It is advised that a hydraulic bolt tensioning system be used to address these drawbacks. The device operates at a pressure of 1500 bar, which is extremely high. Therefore, the equipment must be designed to ensure the device’s compactness and safety. Bolt tensioners are used to tighten bolts and studs in a variety of important applications. These devices would be imported. It was proposed in this work that a small hydraulic bolt tensioner be designed and analysed using both theoretical and finite element analysis (Non-liner static analysis). The required boundary conditions and applied pressure were computed. The tensioner’s design was optimized to assure its safety and compactness.

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.

Seismic performance of bolted flange splicing joints for CFST columns

Bolted connections are suitable to be applied in prefabricated structures and seismic resilient structures. A series of bolted flange splicing joints were proposed for square concrete-filled steel tubular columns, and six full-scale specimens with different flange thickness and flange stiffener layouts were designed and tested under cyclic loads to study the seismic performance. The stiffness, the ductility, the bolt tension forces, the strain distributions and the hysteretic behaviors of the joints were analyzed. Finite element models were established and validated by the test results, further analyzing the joint performances. According to the results, the joints with flange stiffeners or thicker flange plates could develop larger resistance, stiffness and rotational capacity. The joint yield moments would increase with the increase of the bolt diameter, the stiffener height or the stiffener thickness, and decrease when the distances between the bolts and the column walls increase. Parametric analysis of the joint was conducted, and calculation methods of the joint yield moment were proposed accordingly and validated by the test and finite element analysis results, providing satisfactory accuracy.

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.

The behaviour of anchored extended blind bolts in concrete‐filled tubes

AbstractExtended Hollo‐Bolts (EHBs) are blind bolts that have an extended bolt shank ending in an anchor nut. When used with concrete‐filled tubes, the extension and the anchor in the concrete serve to enhance significantly the performance of both connection components: bolts in tension and tube face in bending. The enhancements are a result of confining the concrete, preventing local buckling of the steel tube and allowing the blind bolt to achieve a tensile strength equal to that of standard bolt+nut fasteners. Overall, the use of the EHB results in a moment‐resisting bolted connection to hollow sections which can achieve rigid behaviour under certain configurations. This paper summarizes research work done to date on such connections at the University of Nottingham. This includes experimental, numerical and analytical modelling. The aim of the work is to provide a fundamental understanding of the behaviour of anchored blind bolt connections to concrete‐filled columns, leading to the specification of appropriate design rules that allow the use of such bolted moment‐resisting connections in practice. The work has proposed analytical models for: connection stiffness, column face‐bending strength considering both single and group behaviour of bolt rows, anchored bolts in tension and anchored bolts under combined tension and shear.

Monitoring the safety status of service bolts in mining roadways.

To monitor the safety status of the bolts in coal mining roadways in real time, the safety and stability of the bolt support structure were evaluated. Based on the conventional support bolts used in the field, a fiber Bragg grating (FBG) sensor and medium materials were selected. Through theoretical analysis, the bolt tension, and FBG temperature tests, the strain transmission mechanism of the FBG bolt was analyzed, and it was ensured that the developed FBG bolt could accurately measure the strain of the bolt. In the field test, FBG bolts were arranged on the positive and negative sides of the mining roadway to accurately monitor the safety status of the bolts in service in real time, and the force characteristics of the bolts monitored by the FBG sensor were analyzed to obtain the maximum axial force of the positive and negative bolts. Thereafter, the safety status of the roadway bolt was evaluated. The results show that the positive side bolts axial force change is significantly greater than that of the negative side bolt; with the working face advancing to a distance of 60 m from the bolt as the dividing line, the positive side bolts axial force grows slowly before this, after which the axial force increases rapidly. The locations of the roadway where the positive and negative bolts are most affected by mining are determined, and roadway support and prevention measures for this location should be conducted in time. The safety status of the bolts is evaluated and monitored as follows: the positive side No. 2, No. 3, No. 5, and No. 6 bolts have reached the failure state, the positive side No. 4 bolt is in a dangerous state, the positive side No. 1, negative side No. 8 and No. 9 are in an abnormal state, and the negative side No. 7, No. 10, No. 11, and No. 12 are in a normal condition. This research has laid a technical foundation for the real-time monitoring of the bolt support of the mining roadway and the assessment of the safety status of bolts.

Deformation Analysis of Surrounding Rock of Deep Roadway by the Fluid Structure Coupling Model with MIDAS-GTS

In order to verify the universal applicability of the fluid structure coupling model to the analysis requirements of deep tunnels under the MIDAS-GTS geotechnical simulation environment, the study, together with several mining enterprises, carried out verification and analysis on the measured data of 107 deep tunnels in recent years. The reference group selects the mean value of the analysis results generated by the analysis model using the preferred nonfluid structure coupling model in the MIDAS-GTS environment. Finally, it is confirmed that the fluid structure coupling model group data have significant advantages over the reference group data within the buried depth of 550 ∼ 1450 m and the tunnel cross-sectional area of 45 ∼ 102 m2. Finally, it is considered that the fluid structure coupling model has universal applicability within the analysis range. It is suggested that, in the future work, for example, when the tunnel construction project within the above analysis scope needs to carry out the simulation analysis of roof displacement and anchor bolt tension, the fluid structure coupling model should be directly selected as the analysis model.

Coupling effects with vibration-based estimation of individual bolt tension in multi-bolt structures

Recent work with various single-bolt experimental setups has shown promising results for applying a vibration-based bolt tension estimation procedure. To estimate tension, the novel procedure models a bolt’s transverse vibrations with a single Euler–Bernoulli beam. The present work investigates the applicability of that novel approach when a structure contains more than one bolt. The principal question is if the vibrational response obtained from excitation of a specific bolt, mounted in a structure with other similar bolts, can still roughly be modeled as an independent single-bolt system, or if the other bolts affect the vibrational response in an undesirable way. To determine if the novel single-bolt approach is applicable, it is necessary to gain insight into possible coupling phenomena. For this, a two-bolt problem is investigated, modeled both as a coupled two-beam Euler–Bernoulli model and numerically with FEM software, and with experimental testing of two real bolts mounted in the same structure. It is found that strongly coupled bending vibrations, with in-and out-of-phase modes, only occur when tension and boundary stiffness in the two bolts are very close to identical. When the bolts have different boundary parameters, the coupling is weak, and the two bolts can roughly be treated as two independent single-bolt systems. In both situations, it is actually possible to estimate bolt tension and boundary stiffness based on measured transverse natural frequencies using a single-bolt beam model.

Structural behavior of large anchor bolts used for sign-support structures

Anchor bolts are commonly used to tie sign-support structures to their concrete base through a double-nut moment connection. Over the past decade, loose anchor rod nuts have proven to need frequent attention, incurring significant cost, while endangering the safety of sign-support structures. In particular, connections tightened with the current pre-tensioning specifications are found to have been loosened within only a year (if not sooner) after installation. Considering this long-standing issue, the objective of this study is to investigate the structural behavior of large anchor bolts used at the base of sign-support structures and evaluate the parameters that influence the rod tightening and loosening process most. For this purpose, a set of Skidmore-Wilhelm bolt tension calibrator tests were performed on different sizes of bolt that had been lubricated with various methods. The tests were to evaluate the effects of the lubrication method on the tightening process. In addition, a sign-post structure removed from the field was tested in the laboratory to study the bolt behavior when it was subjected to the lateral load. Finite-element models were then developed and calibrated using the data collected form the laboratory test. A parametric study was conducted on the calibrated model to understand the effects of key contributing factors, such as level of tightening preload, variation of preload level, washer size, and grip length, on the tightening and loosening process. The investigations determined that the current tightening process can generate a stress concentration in the rod in the range of 30 ksi, which was 55% of the rod's yield strength. The clamping force was also noted to experience a significant reduction during the first few cycles of loading (i.e., up to 20 cycles), beyond which further reduction was minimal. The outcome of this study directly helps choose a preload level that ensures adequate tightening, while avoiding permanent damage to the rod. This is critical for preventing or alleviating the issue of nut loosening.

Study on the Effect of Blasting Vibration on Rock Bolt and Shotcrete

The blasting tunneling construction method is often used in the underground engineering projects such as tunnels, coal mines roadway, chambers and so on, rock bolt and shotcrete support is used. Although the blasting construction method has many advantages, but also will be accompanied by adverse effects. Blasting vibration of blasting construction not only to the surrounding environment, building (structure) and other adverse effects, but also on the support of the underground project itself has a negative impact. In order to discuss the impact of blasting vibration on shotcrete and rock bolt support in the process of blasting tunneling of roadway, a certain amount of explosives is detonated in the hole of the working face, the finite element software ANSYS/LS-DYNA was used to establish the numerical calculation model, through time history analysis calculation, the distribution law of the vibration velocity on the shotcrete surface along the section and the variation law of the longitudinal tension and compression stress of the rock bolt are obtained. The results show that the blasting vibration produced by blasting tunneling has a great influence on the shotcrete at the shoulder, but little influence on the axial force of the rock bolt.

Experimental validation of the formulation for maximum socket depth estimation of non-reduced strength bolts

The analytical formulation introduced for the estimation of the maximum depth of the socket of the bolts that have a shaft diameter smaller than the diameter of the socket was validated with experimental studies. The maximum socket depth of a chosen representative bolt calculated by the analytical formulation for weight reduction was verified experimentally. Bolts with varying socket depths were manufactured through cold forging method and bolt tension tests were carried out on quasi-static tension test machine. Results showed that experimental predictions were in good agreement with the results taken from developed analytical model. The critical depth of the socket calculated using the analytical formulation was 3.2% more secure compared to the experimental results. As a result, the validity of the analytical formulation to calculate the critical socket depths of bolts with smaller shaft diameter than socket diameter was confirmed by experimental studies.

Numerical Analysis of Cold rolled structural steel angle sections subjected to tension members

Finite element method is a precise and flexible technology for predicting the performance, load conditions of a structure, mechanism or process. During the tests, the structural behaviour was used to build a FEM, especially for the nonlinear analysis. As the failure approaches, angles under tension exhibit non-linear behaviour. Everything is constructed, including the static structural component and all of its modules. Like ANSYS MAPDL modules (Mechanical Ansys Parametric Design Language). Build geometry, define materials, generate mesh, apply load, solving the model, and reviewing the results are all part of the static analyses of FEA. In order to determine the various structural investigations of a single or double section, a number of models have been developed. There were 72 specimens used in the analysis; they were modelled by bolt tensioners that were attached to the specimen. In order to calculate equivalent stress, equivalent elastic strain, and total deformation of single angle and double angle sections, equivalent stress, elastic strain, and total deformation of single angle and double angle sections were examined. In order to find out the ultimate load-carrying capacity of the single angle specimens and double angle specimens, a non-linear static analysis was done. The findings from the experiments, computational codes, and worldwide investigations into load capacity tension members are detailed in the paper. Failure modes are observed, too. In an ANSYS simulation using a numerical model, which used the ANSYS angle algorithm, researchers discovered that experimental and international codes values closely match each other.

Seismic performance of welded-bolted joint between double channel beam and CFST column

A novel welded-bolted beam-to-column joint, connecting double channel beams to concrete-filled steel tubular (CFST) columns, is proposed for a prefabricated steel structure that only need bolted assembly on site in construction. To investigate the seismic performance of the proposed joint, eight full-scale specimens were designed and tested under cyclic loads, and the joint moment resistance, stiffness, hysteretic behaviors, slipping behaviors, ductility, and and energy dissipation capacity were analyzed. Finite element models were built and validated by the test results, and the bolt tensions, the friction between slip surfaces and the bearing force on the bolt hole were further investigated by the finite element analysis. According to the results, the slip load of the bolted channel becomes larger and the hysteretic curve becomes plumper with the increase of the number or the diameter of the bolts. The increased bolt hole size showed no significant effect on the plumpness of the hysteretic curve but would increase the slip distance, thus increasing the energy dissipation capacity. Compared with the welded joints from the FEA results, the welded-bolted joints could develop larger rotation capacity, energy dissipation capacity and ultimate moment. Based on the investigations, the proposed novel joints could be designed as rigid joints. Based on the investigation, formulas of the yield and ultimate moment resistance of the welded-bolted joints were proposed and validated by the experimental results.

Dynamic Modeling and Nonlinear Characteristics of a Cracked Bolt-Disk Combined Rotor System

Abstract Different from the crack on the rotating shaft, the crack on the bolt, which is a connecting part of the bolt-disk combined rotor, is a kind of local defect. The local crack on the bolt under high pretension is always in open state, and it increases the overall vibration of the combined rotor significantly in practice. This paper studies the modeling of the crack on the bolt and nonlinear dynamic behaviors of the cracked bolt-disk rotor system. The circumferential bolts with a transverse open crack are treated as several bar elements under the assumption that each bolt has the same original tensile extension length. The cracked correction coefficient is introduced to describe the decreasing amount of bolt's tension due to crack. After this coefficient is obtained according to finite element method, the stiffness matrix of circumferential bolts with crack is built based on total potential energy. The dynamic model consists of a time-independent stiffness matrix for perfect bolts, a time-variant reductive stiffness, and an additional moment. As a result, the crack in bolt reduces rotor's nonlinear stability and leads to greater vibration and fluctuation. In addition, crack depth has much larger influence than crack location on the dynamic behaviors.

1 g Shaking table test of segmental tunnel in sand under near-fault motions

A 1 g shaking table test is conducted to investigate seismic responses of a segmental tunnel in sand under near-fault motions. The tunnel model is assembled with segments, bolts and rubber strips and embedded in a shallow sand ground. The test facility, design and preparation of the tunnel model and the sand ground, as well as selected earthquake motions, are presented in detail. Dynamic responses obtained from the experiment include accelerations of the sand ground and the tunnel model, strains of segments, diametric deformations of the tunnel section, as well as bolt tensions and rotation of radial joints. Results show that the ground fundamental frequency changes with different input motions due to sand nonlinearities, and the deformation of the segmental tunnel is concentrated on radial joints. Moreover, near-fault motions would significantly aggravate the seismic response of both the sand ground and the segmental tunnel compared to far-field motions. Physical mechanisms contributed to the observation that near-fault motions would lead to larger shear strains of ground, especially when the ground fundamental frequency decreases, are also discussed.

A Novel Test Rig for the Basic Nonlinear Characterization of Bolted Joints

The paper aims at performing a comprehensive experimental study on the peculiar properties of a bolted joint, and investigates the damping induced at different interfaces (between flanges, bolt head/nut and flange, threads) during vibrations. A novel, simplified, single-bolt system joining a two-beam structure is designed and tested. Experimental results under different boundary conditions are presented, and the influence of the harmonic excitation force, as well as the bolt tension, is investigated. The test results show how the contact interface between the clamped flanges plays an important role in terms of frictional damping provided to the system during vibration, while the contact interfaces between the head/nut and flange, and secondarily between the threads, affect the system response at a less, but not negligible, extent. The test setup and test procedure can provide a database to validate single bolt contact models to be included in a more complex structure.