Bolt Preloading Research Articles

Study on the mechanical properties of prefabricated assembled cover arch reinforcements in tunnels

The prefabricated assembled cover arch reinforcement method offers rapid construction and high quality, effectively addressing the challenges of cast-in-place cover arch reinforcement used in tunnel linings in mountainous areas of China. This study investigated the mechanical performance of prefabricated assembled arches in tunnels through model tests and numerical simulations. The results indicate that joint opening and deflection, as well as their change rates, increase with eccentric distance. There is a roughly linear relationship between joint opening and deflection with increasing load. At an eccentric distance of + 0.2 m, the peak stress appears on the outside of the joint, with a valley on the inside, and stress concentration at bolt holes. The application of bolt preloading enhances the joint’s stress performance. Furthermore, the stiffness of the lining and soil significantly impacts the mechanical response of the cover arch, with peak stress mainly observed at the foot of the cover arch and the handhole of the joint.

Thermal and Structural Performance Analysis of Piezoelectric Acceleration Sensor

Thermal and structural piezoelectric acceleration sensors are complicated and affected by many factors, especially when the sensor works in different temperature environments, its performance and structure will be affected to some extent. In this paper, the interference contact model of piezoelectric sensor is established with the method of bolt preloading, and the finite element analysis is carried out under different interference quantities. Moreover, based on the bolt preload model, the loading method of temperature load is studied, and the structural thermal adaptation characteristics of the sensor under the conditions of -70℃, -50℃, 0℃, 120℃, 160℃ and 200℃ are analyzed. Based on these thermal deformation and thermal stress analysis at different temperatures, the thermal adaptation characteristics of the sensor are analyzed. The normal operating temperature range of the sensor is -50℃ -120 ℃, and the structural parameter of the sensor (the thickness of the base) is optimized, so that the operating temperature of the sensor can reach 200℃. Ability to analyze.

Study on Preload of Bolted Connections in Pitch Bearing Based on Vibration Modal Analysis

In wind turbine systems, bolted connections are frequently subjected to gravitational and centrifugal loads transmitted by the blades during operation. This can lead to the attenuation of bolt preloading, resulting in bolt loosening or uneven loading, which in turn affects the service life of the generator unit. Therefore, the study of bolt preloading variations is crucial. However, there are numerous factors influencing bolt preloading, and the existing techniques struggle to precisely assess bolt preloading. This paper proposed a bolt preloading evaluation technique based on the hammer modal method. Focusing on the 42CrMo4 bolted connection of a pitch bearing, a test platform for bolt preloading assessment is constructed. Hammer modal tests are conducted under various preloading forces. By combining finite element modal analysis, the correspondence between preloading changes and the bending frequencies and modes of the bolted connection is obtained. The research illustrated that with changes in bolt preloading, variations occur in coherence, phase, and natural frequencies of frequency response functions. The fundamental correlation between bolt preloading and the second-order bending frequency can be utilized to assess changes in preloading. Furthermore, the applicability of this method has been validated, offering a reference for evaluating bolt preloading.

Numerical Analysis of Fracture Behaviour for Cracked Joints in Corrugated Plate Girders Repaired by Stop-Holes.

The efficient crack eliminated stop-hole measure was proposed to repair and reduce the stress concentration associated fracture risk of the corrugated plate girders by setting it at the critical joint of flange plate with tightened bolts and gaskets under preloading. To investigate the fracture behaviour of these repaired girders, parametric finite element analysis was conducted, focusing on the mechanical feature and stress intensity factor of crack stop-hole in this paper. The numerical model was verified against experimental results first, and then the stress characteristics due to the presence of crack open-hole were analysed. It was found that the moderate-sized open-hole was more effective than the over-sized open-hole in the reduction of stress concentration. For the model with prestressed crack stop-hole through bolt preloading, the stress concentration was nearly 50% with the prestress around open-hole increased to 46 MPa, but such a reduction is inconspicuous for even higher prestress. Relatively high circumferential stress gradients and the crack open angle of oversized crack stop-holes were decreased owing to additional prestress effects from the gasket. Finally, the shift from the original tensile area around the edge of the crack open-hole that was prone to fatigue cracking to a compression-oriented area is beneficial for the reduction of stress intensity factor of the prestressed crack stop-holes. It was also demonstrated that the enlargement of crack open-hole has limited influence on the reduction of stress intensity factor and crack propagation. In contrast, higher bolt prestress was more beneficial in consistently reducing the stress intensity factor of the model with the crack open-hole, even containing long crack.

Investigation of CFRP-Countersunk Bolted Assembly Fatigue Damage under Three-Point Bending via Experimental and Numerical Analysis

In this research, the fatigue damage behavior under three-point bending of a composite joint incorporating a single countersunk fastener is investigated. Firstly, a self-developed fatigue test system was set up to test the fatigue characteristics of CFRP-countersunk bolted assembly under the displacement amplitude cycles of 103 to 106 to study the formation and expansion rule of damage and cracks. It found two typical damage processes, both of which involve some formal interface damage between fiber and matrix. Based on the experiment, a finite element fatigue damage analysis on this assembly was carried out according to the Hashin failure criterion. The simulation result shows an identical fatigue damage location and fatigue life with the experimental phenomenon. Moreover, it predicted the final fatigue life of the specimen under 10 hz cyclic loading with 1 mm displacement and 10 Nm bolt preloading. This research provides guidance for the engineering fatigue issues of single-bolted joint composite connection structures and provides a reference for the corresponding technical specifications formulation.

Behavior of high-strength demountable bolted shear connectors in steel-concrete girders with prefabricated slabs

Composite structures with prefabricated concrete slabs and bolted shear studs can enhance the effectiveness and sustainability of construction. In this research, non-shrinkage cement grout is proposed to be filled between high-strength fully threaded bolt shear connectors and a prefabricated slab. Six static push-out tests are performed with different bolt dimensions and different pretension forces on the bolts to study the behavior of bolted shear studs. Finite element models for bolted shear connectors using ABAQUS/Explicit solver are developed, and they matched well with experimental results. Moreover, a Parametric study is conducted to investigate the effects of grout strength, bolt diameter, length-to-diameter ratio, bolt preloading, and bolt material type on the performance of shear connectors. Finally, the results of the parametric analysis are compared to the current design codes and previous researches and more precise equations for predicting the capacity and stiffness of bolted shear studs are proposed.

Influence of cyclical hygrothermal aging on mechanical response and structural durability of composite bolted interference-fit joints

The paper deals with the long-term performance and durability of composite bolted interference-fit joints subjected to harsh environmental loads in flight-cycles. An accelerated cyclical hygrothermal aging spectrum with repeated temperature and moisture variation is specially designed to simulate real service condition. The single-lap composite joints with various stacking sequences, interference-fit sizes and tightening torques are aged in designed hygrothermal environments with different time duration, in which the material deterioration, stress relaxation and intrinsic frequency of joints are monitored to characterize structural evolution. Tensile tests are conducted to aged composite joints to obtain joint stiffness, bearing strength and failure modes to quantitatively evaluate their residual mechanical properties and structural degradation regulation. The results show that the moisture absorption rate presents a sharp rise and slow decent trend with a peek value of 0.213%. The aging process causes weathering phenomenon and reduces the structural benefits induced by such assembly technologies as interference fitting and bolt preloading. The reduction of joint stiffness and bearing strength exhibits a negative exponential decline trend with the growth of aging time. The matrix plasticization and interlaminar debonding are main hygrothermal damages. The safety factor of 0.7 to 0.8 is suggested on bearing strength value to reach hygrothermal aging bearing strength allowable in joint application.

Fatigue life estimation of preloaded Aluminium (Al2024-T6) aircraft fasteners using finite element method

The fatigue failure of the aircraft fasteners during service conditions are unavoidable. Most of the published research works related to fatigue life estimation of threaded fasteners have neglected the effect of bolt preloading. The present work mainly aims to determine the effect of bolt preload on fatigue life of the aircraft fasteners. High cycle fatigue analysis was carried out using FE based software on aluminium bolts of Al2024-T4 material with same dimensions under two different conditions (with and without the presence of crack). The preload of the bolt was varied based on the limiting stress value of the bolt material. In addition to the bolt preloading, cyclic load was applied to the bolt in order to determine the effect of synergetic loading on fatigue life. 3D finite element model of the bolt under the presence of crack was modelled and the crack region was meshed with singular elements. During meshing, singular nature of stresses and strains at the crack tip was considered and thus 20 node quadratic brick element was used. The static analysis of the bolt was carried out using Abaqus finite element code and the fatigue life of the bolt was determined after applying the cyclic load using Fe-safe software. The residual life of the bolt was determined for various preloads. From the numerical results, it was noted that as the magnitude of the preload increases, fatigue life of the bolt also increases significantly. This is due to the ‘spring action’ provided by the initial preload on the bolt. It is also observed that, the presence of crack at the root region significantly reduces the fatigue life of the bolt.

60188 The coupled dynamic analysis of hydroelectric unit and powerhouse considering the bolt connection characteristics

As the increasing of the capacity and water head of the hydropower stations, the hydroelectric unit’s vibration and its induced powerhouse vibrations become a critical problem. The system of hydraulic-mechanical-electric-structural is coupled and with strong non-linear characteristics. The frame and head cover are all connected with the powerhouse pier via high-strength bolt. The paper is concentrated on the dynamic coupling mechanism and simulation model considering the bolt’s connection and load transmission characteristics. With the theory analysis and numerical simulation, the connection and transmission behaviour of the high-strength bolt would be studied and a more accurate and simple mechanical expression would be derived. The connection sliding law and dynamics modelling method of bolts are discussed. Based on the displacement-load curve of single lap and single bolt analysis it is concluded that the increasing preloading will improve the tangential bearing capacity of the bolted joint connection. Then the FEM coupling model of the lower bracket and powerhouse is established with the virtual medium method. Based on the free-vibration and dynamic response analysis the effects of the loosening of the bolt on the static stiffness of the coupling structure are discussed. The von-Mises stress’s increasing due to some of the bolt’s loosening would result to the material fatigue damage. Finally five preloading schemes of the bolts are discussed and the simulation results show that the preloading force has a greater lateral impact on the structure than on the longitudinal direction. The preloading force improves the coupling structure’s stiffness and reduces the vibration amplitude of the frame. As for the preloading force, when it is small the connection effect is not strong enough and the vibration level may be higher, so the actual preloading state should be exactly simulated. When the bolt preloading reaches 60-70% of the material yield strength, the rigid connection can be directly used in the modelling for the convenience of calculation.

Methodology for the assessment and refinement of friction-based dissipative devices

An innovative dissipative system for the seismic upgrade of historical buildings is presented. The system comprises a friction-based dissipative device able to provide energy dissipation capacity to connecting walls. To verify the compliance of the device’s initial prototype with the relevant European Standards, a testing and design methodology is developed. This optimisation approach consists of: two tests loops, to identity the dependence of the dissipative device on bolt preloading, type of fasteners, frictional interfaces and environmental conditions; and a design loop where advanced 3D modelling and analysis are used to improve the design according to the experimental results. The performance is measured by variation of effective damping. This iterative procedure singles out parameters that need improvement and allows to produce two new prototypes, differing by shape and frictional interfaces. The revised prototypes prove to deliver a reliable response to cyclic loading, containing the variation of effective damping well within code requirements, even after exposure to adverse environmental conditions.

Modeling on mechanical behavior and damage evolution of single-lap bolted composite interference-fit joints under thermal effects

This paper reports the modeling method and outcomes of mechanical performance and damage evolution of single-lap bolted composite interference-fit joints under extreme temperatures. The anisotropic continuum damage model involving thermal effects is established on continuum damage mechanics which integrates the shear nonlinearity constitutive relations characterized by Romberg-Osgood equation. The temperature-induced modification of thermal strains and material properties is incorporated in stress-strain analysis, extended 3D failure criteria and exponential damage evolution rules. The proposed model is calibrated and employed to simulate behavior of composite joints in interference fitting, bolt preloading, thermal and bearing loading processes, during which the influence of interference-fit sizes, preload levels, laminate layups and service temperatures is thoroughly investigated. The predicated interfacial behavior, bearing response and failure modes are in good agreement with experimental tests. The numerical model is even capable of reflecting some non-intuitive experimental findings such as residual stress relaxation and matrix softening at elevated temperatures.

Initial stiffness and plastic resistance of bolted stainless steel T-stubs in tension

Building upon a previous investigation, this study reports a total of 13 experimental tests on austenitic and duplex stainless steel T-stubs subject to monotonic loading. The structural behaviour of the tested T-stub specimens, including load versus displacement (F-Δ) curves and corresponding failure modes, was obtained and is reported herein. The experimental tests were replicated by finite element (FE) analysis, and upon validation of numerical models, a comprehensive parametric study including 168 FE models was conducted to investigate the effects of key parameters such as material grade, bolt preloading, bolt diameter and flange thickness on the structural response. Based on both experimental and numerical results, the suitability of the design provisions for the determination of the plastic resistance specified in EN 1993-1-8, proposed extensions thereof by Demonceau et al. to cover T-stubs with four bolts per row for stainless steel T-stubs as well as the design method codified in Chinese code JGJ 82 were assessed. Novel design methods for the determination of the initial stiffness and the plastic resistance of stainless steel T-stubs, accounting explicitly for the observed structural response and the pronounced material strain hardening were developed. The proposed design methods lead to improved and more consistent capacity predictions and their adoption in design standards is recommended herein.

Short- and long- term loss of preloading in slotted bolted connections

One recent solution to reduce the building repairing costs, in case of exceptional or destructive seismic events, is represented by the Sliding Hinge Joint (SHJ), initially proposed by the research group of the University of Auckland in 2005. This connection typology, using slotted bolted connections in beam-to-column joints of Moment Resisting Steel Frames (MRFs), ensures a large energy dissipation capacity with negligible damage. The slip resistance of the SHJ is usually provided by Asymmetrical or Symmetrical Friction Connections (AFCs or SFCs), whose response depends on the friction coefficient of the shims and on the bolt preloading. Since the bolt forces directly affect the resistance, the control of preloading during the life-time of the connection represents a key issue for the proper functioning of the device.Within this framework, considering the lack of previous experimental works specifically devoted to the long-term response of SHJs, this paper presents the results of an experimental activity on subassemblies of friction dampers, assessing the loss of preload under service loading conditions, examining the possibility to limit the loss through different conical washer layouts (Belleville disk springs). Short-, mid- and long-term tests have been carried out in a joint experimental program carried out at the Universities of Liege and Salerno. The experimental results have been exploited to calibrate an analytical model able to predict the loss of preload over time, accounting for the influence of the external loads. The adoption of pre-set disk springs, reducing the stiffness of 1/10, shows a substantial reduction of the loss.

TESTS ON LOAD-CARRYING BEHAVIOR OF STAINLESS STEEL BOLTED T-STUB CONNECTIONS

A total of 14 stainless steel bolted T-stubs were tested under monotonic loading. The ultimate strength, failure modes and prying forces of the test specimens were obtained. The effects of the key parameters including the flange thickness, flange material grade, bolt diameter and bolt preloading were analyzed. It was revealed that the introduction of bolt preloading had little effect on the ultimate strength and failure mode, but resulted in increased initial stiffness for the T-stub specimens. The failure mode of the T-stub connections depended on both the tensile strength of the bolt and the flexural strength of the flange. The prying forces increased gradually with reduced flange thickness and bolt diameters, while the prying forces corresponding to the ultimate strength were not influenced by the bolt preloading. The test results were further compared with the strength predicted by the existing European, American and Chinese design codes. It was found that the existing design provisions were generally conservative for stainless steel bolted T-stub connections, among which the American code provided relatively better predictions. It may be attributed to the use of material tensile strength instead of yield strength.

Analysis of elastic interaction stiffness and its effect on bolt preloading

The preloading variation of bolt joint relies on the elastic interaction between tightened bolts significantly. But how to characterize the elastic interaction essentially and truly is still an intractable problem. In this article, an analytical interaction stiffness model is established through stress distribution analysis. The effect of interaction stiffness on the preload variation of tightened bolt was investigated, such as the magnitude of preload variation and the judgement of change direction of preload and the influence scope of elastic interaction was also predicted analytically and numerically. From the cliff-style interaction stiffness variation curve of typical 2-bolt joint, it was found that there was always an obvious singular point indicating no elastic interaction in a certain place between the two bolts. From comparison, the predicted results using the developed model were consistent with the FE simulations.

Effects of bolt pre-loading variations on performance of GDL in a bolted PEMFC by 3-D FEM analysis

This study numerically investigated the effects of different bolt pre-loadings on the performance of the gas diffusion layer (GDL) in a bolted proton exchange membrane fuel cell (PEMFC). Firstly, a complete three-dimensional finite element model of a PEMFC bolted by 12 bolts with a reactive area of 5 cm by 5 cm was established using the commercial software SolidWorks. Then, a pre-loading of 1 MPa to 7 MPa on each bolt was applied, increasing in increments 1 MPa, and the corresponding deformation and stress fields of each component of the fuel cell were obtained using the commercial software ANSYS 15.0/Workbench. Finally, the effects of the bolt pre-loading variations on the performance of the GDL were discussed. The results showed that the compression ratio of the GDL increased linearly with the magnitude of bolt pre-loading, and improving the performance of the GDL. However, when the pre-loading on each bolt reached 7 MPa, the compression ratio exceeded 15%, degrading the efficiency of the PEMFC. Also, by comparing the relationships between bolt pre-loading and conductivity and porosity of GDL, in order to obtain the maximum performance of GDL, an optimum value of 4 MPa for bolt preloading was recommended.

Elastic behaviour of bolted connection between cylindrical steel structure and concrete foundation

The paper deals with bolted connection between cylindrical steel structures and concrete foundations. In the considered connection, the circular steel structure of large diameter is welded to a base plate, and then anchor bolts are used to connect the base plate to the concrete foundation. Repartition plates are also placed to ensure an appropriate distribution of the stresses from the steel parts into the concrete. The studied configuration is often met in industrial chimneys, wind towers, cranes, etc. To characterise the studied connection, an elastic model is more relevant than plastic model but no appropriate and efficient tools for the characterisation of its elastic behaviour are available in the codes and literatures.In the present paper, a complete analytical procedure is proposed to predict the elastic responses of the connection from their geometrical and material characteristics. Several effects are taken into account in the model, such as the effect of the bolt preloading, the long term effects in the concrete and 3D behaviour of the concrete foundation. The analytical results are validated through comparisons with numerical results. Numerical examples are also given to illustrate the proposed calculation procedure.

Analytical plate approach for the axial stiffness prediction of stiffened angle cleats

In this paper, a plate analytical model for the prediction of the axial stiffness of stiffened angle cleats has been dealt with. In order to support the investigation, an experimental study was carried through on pull test of stiffened angle assemblies, representing some of the common practice design possibilities for top-and-seat angle connections. Additionally, an advance 3D Finite Element model was developed to assess this investigation. The FE model includes the possibility of bolt preloading, reproducing with great accuracy the actual stiffened angle cleat behavior. An equivalent plate analytical model for the prediction of the axial stiffness has been proposed on the basis of numerical parametric studies linked with the definition of an effective width for stiffness calculations. This effective width covers the different possibilities regarding the angle widths and the bolt-to-stiffener positions. This proposal provides satisfactory results in comparison with experimental data from literature and from the tests carried out for this study. It is intended for practical design purposes of stiffened angle cleat connections, and could be used within the EC3 component approach.

Experimental Analysis of Bolted Connections: Snug versus Preloaded Bolts

The rotational stiffness of bolted connections can be properly predicted by means of the so-called “component method.” In this method, the T-stub plays a fundamental role, because it is used to compute the stiffness contribution of the most important joint components. For this reason, an experimental analysis on bolted T-stub assemblies has been performed. On the basis of this analysis, the possibility of predicting the axial stiffness of the T-stub assembly is investigated. In addition, as the joint behavior is strongly influenced by the bolt preloading, the experimental analysis has been performed applying three different levels of bolt preloading and, starting from the obtained experimental results, simple rules to take it into account are suggested. Finally, the reliability of the relationships derived from the T-stub analysis has been verified through the application of the component method to the prediction of the rotational stiffness of a wide number of tested specimens concerning extended end plate connections, both with snug-tightened and pretensioned bolts, collected in the technical literature.

A second generation EMET railgun for secondary arc studies

Since 1985 GT-Devices has been operating a pair of railguns with lengths of 0.9 m and 3.6 m, respectively. A new second-generation railgun is now being constructed to improve straightness, stiffness, sealing, and diagnostic access. The basic design consists of a steel tube with a thin lengthwise slit forming two halves in cross section with bolt preloading. The internal structure consists of split tubular G-10 compression blocks with Glidcop AL-15 rails and polycarbonate insulators formed from 90 degree tube sections. A new 0.9 m launcher of the same design is now under construction, with a 3.6 m version to follow. An upgraded electrothermal injector has been developed using modified armature injection module (AIM) hardware. Injection velocities of 2500 m/s have been attained with 1.1 gram polycarbonate projectiles for stored bank energies of 65 kJ. Injection velocities of 3000 m/s may be possible. The design details of the new railgun, injector, and diagnostics are discussed, and some initial experimental results are presented. >