Bolt Pretension Research Articles

Development of self-centring beam-to-column joints with large-dimensional SMA buckling-restrained plates

This paper presents an innovative self-centring (SC) beam-to-column joint (BCJ) design that utilises shape memory alloy (SMA) plates. The proposed SMA-SC-BCJ is constructed through a straightforward approach using large-scale SMA plates to concentrate inelastic deformation and achieve SC capability. This paper first introduces the components and configuration of SMA-SC-BCJ, followed by the development of a refined finite element model for simulations. Validation against previous experiments verifies the model accuracy in capturing joint behaviour. The analysis shows SMA-SC-BCJ exhibits desirable flag-shaped hysteretic behaviours with excellent SC capability, achieving approximately 92 % recovery alongside moderate energy dissipation. Substantial inelastic deformation localises in the SMA fuse plate due to joint rocking, with minimal plastic strain around the rocking centre. Parametric studies on shear element construction, bolt pretension levels and beam gap distances provide additional insights into the joint design. The proposed design meets the objectives for a minimal-damage beam-to-column joint with simple construction. The SMA-SC-BCJ design recommendations are presented on the basis of performance assessments, elucidating the effectiveness of the system. This work contributes an innovative seismic-resistant joint solution that advances the emerging practices towards resilient structures.

Optimization of small coal pillar width and control measures in gob-side entry excavation of thick coal seams

This study introduces an innovative optimized bolting support system specifically tailored for gob-side entry excavation in thick coal seams at a coal mine in southwestern Shandong, China. Employing theoretical analysis, numerical simulation, and field measurements, the research focuses on examining the failure characteristics of surrounding rock during gob-side entry excavation. The key innovation lies in the development of a 5-meter optimal coal pillar width, ensuring balanced stress distribution and structural integrity. Additionally, a lag time of at least 46 days between gob-side entry excavation and the upper working face retreat is recommended to mitigate roof subsidence and surrounding rock deformation. The optimized bolting support system, featuring increased bolt pretension, utilization of high-strength steel strips, and reinforcement of weak points, effectively reduces deformation of the roadway surrounding rock, meeting support requirements for normal production. This novel approach successfully addresses the support challenges in thick coal seam gob-side entry excavation, enhancing mining safety and resource recovery rates.

Frictional Axial Resistance of Clamped Split Pocket Mechanism Steel Structural Joint: An Experimental Study

The Clamped Split Pocket Mechanism (CSPM) prefabricated joint system was developed for a single-story steel instant house, designed to be compact and rapidly constructed without modifying the end of the beam and column element member. The CSPM bolted joint system was proposed as an optimal solution for post-disaster housing, especially after earthquakes. Despite its potential, the frictional tensile resistance behavior of the CSPM bolted joint system has not been previously studied, necessitating experimental investigation. This study examined the frictional tensile resistance behavior of the CSPM joint system by monitoring the effective friction coefficient under axial tension force. The experiments considered both the strong and weak axes of the joint and utilized two configuration types of specimens (L and T) with varying bolt pretensions of 2.5, 5, 7.5, and 10 kN. Results indicated that the effective friction coefficient of the CSPM bolted joint system ranged from 0.19 to 0.26, correlated to bolt pretension. Increased bolt pretension resulted in larger surface deformation of the split pocket, triggering a not uniform frictional tensile resistance across the steel surfaces of the split pocket joint. From this study, the achieved effective friction coefficients could guide the design of minimum pretension forces for clamps in prefabricated steel instant houses. Doi: 10.28991/CEJ-2024-010-09-07 Full Text: PDF

Sealing rubber ring design based on machine learning algorithm combined progressive optimization method

In this study, a progressive optimization method combining machine learning and optimization method is proposed and applied to seal structure design. The method is divided into two stages to select the optimal design gradually. So as to find the best design scheme meeting the design requirements. For optimal design, numerical calculation method is commonly used, but hard to evaluate the optimal solution. In this work, a series of numerical model considering the effect of super elastic material about O-ring study the waterproof performance behavior of a rubber seal. K nearest neighbors (KNN) of machine learning algorithms applied to the simulation data to predict the appropriate bolt pretension classification. Furthermore, use TOPSIS method to optimize the groove depth of 30 N bolt pretension classification. By using the TOPSIS method to consider the stress of the rubber component, optimization analysis is conducted to find the optimal design. Results show that the dual optimization method can quickly predict the best design scheme. Through the experiment, a prototype test under the condition of IPX7 verify the method. The design scheme selected by this method meets the waterproof grade requirements. There are no water stains on the surface of the O-ring and inside the motor. This paper provides a fast optimization design method for the design of sealing structure.

Experimental and numerical study on behavior of demountable T-shaped bolt shear connectors in sustainable composite beams

This paper proposed a new type of demountable T-bolt shear connector to improve the disassembly efficiency of composite beams and realize the sustainable of the structure components. The shear behavior of nine groups of push-out specimens was experimentally investigated through monotonic loading push-out tests. The finite element analysis (FEA) models were validated against the test results, specifically in terms of the load-slip responses and failure modes of the T-bolt shear connectors in these push-out specimens. The obtained results show that all the specimens have no obvious deformation and cracks in the steel beam and RC slab. The separation between the slab and the steel beam is no more than 1 mm, indicating that the anti-lifting ability is excellent. Moreover, parametric analysis demonstrates that increasing the bolt pretension of the T-shaped shear connector and the friction coefficient between the bridge gasket and the steel beam significantly enhances the initial stiffness and ultimate strength of the shear connectors. However, the shear behavior is relatively insensitive to variations in the channel thickness and bolt grade. Based on regression analysis, a load-slip mechanical model has been proposed. This model accurately describes the mechanical properties of this type of shear connector, providing a theoretical foundation for the application of demountable composite beams.

Impact of anti-corrosion coatings and maintenance on high-strength bolt friction connections in C4 marine environment

High-strength bolt friction connections (HSBFCs) in steel constructions often employ exterior anti-corrosion coatings, and some connections in steel bridges extend these coatings to their friction surfaces. However, previous studies on HSBFCs have overlooked the influence of external anti-corrosion coatings and coatings on friction surfaces. This research investigates the impact of internal and external anti-corrosion coatings on shear performance through experimental testing. Shear tests were conducted on 43 connections under 17 different conditions, varying the presence of anti-corrosion coatings on friction surfaces and external coatings, including conditions of construction and maintenance. Calibration tests revealed varying anti-slip coefficients: sandblasted surfaces measured 0.44, below specification; epoxy zinc-rich primer coatings measured 0.27; and alcohol-soluble inorganic anti-rust primers measured 0.50, both meeting or exceeding specifications. Simulated C4 atmospheric corrosion environments and dry-wet alternating copper accelerated acetic acid salt spray tests were performed. Results indicate predictable indoor corrosion acceleration and significant shear capacity degradation (4.9 % to 19 %) despite external coating use. Coatings on friction surfaces delayed degradation, while external anti-corrosion coating effectiveness declined post-construction and maintenance. Analysis shows shear capacity degradation in unprotected connections was 1.5 to 1.8 times higher than protected counterparts, attributed to reduced anti-slip coefficients and bolt pre-tension loss.

Simulation study on acoustic performance of Tonpilz piezoelectric transducers

Abstract The Tonpilz configuration of transducers is recognized for its capability to generate high-power acoustic emissions at relatively lower frequencies, which is a prevalent setup in sonar systems. Comprising a frontal radiating element, a rear casing, and a piezoelectric ceramic ring sandwiched between them and affixed by a central bolt, this study delineates the inclusion of bolt pretension impact. The investigation assesses the structural and acoustic ramifications of the transducer’s frequency response. These findings indicate the commendable acoustic performance of the transducer.

Behavior of the damage-tolerant beam-column connection for earthquake-resilient steel frame: Experimental and numerical study

Achievement of damage concentration is key to realizing structural resilience. In this study, a replaceable damage-tolerant beam-column connection is developed and the mechanical behavior was studied through experimental study. Results demonstrated that the proposed connection achieved damage concentration within the connecting region, and the failure mode and hysteresis behavior obtained by finite element modeling matched well with the test results. Then subsequent numerical study based on the validated detailed finite element model was carried out to investigate the influence of the width and thickness of the sliding plate, the length of slotted holes, the slip coefficient and the bolt load on the seismic behavior. The parametric study results demonstrated that the length of slotted holes significantly influenced the load-deformation characteristics while the width and thickness of sliding plates affected the bearing capacity once the bearing behavior occurred. A longer slotted hole could improve the ductility and energy dissipation capacity since it delayed the local buckling behavior of the flange segment. The bending moment was enhanced with the activation of bearing action and it was mainly affected by the width of the sliding plate. The increase of the friction coefficient and bolt pretension was beneficial to the energy dissipation behavior, while it did not influence the bearing behavior a lot.

Semi-analytical modeling and vibration analysis of bolted frame structure under non-uniform pretension

Most of the frame structures in mechanical equipment are connected by bolts, and the non-uniform pretension among the bolts will have an obvious impact on the vibration characteristic parameters of the frame structure. In this paper, semi-analytical modeling and vibration analysis of a frame structure considering non-uniform pretension of bolts are carried out based on the Timoshenko beam theory and Rayleigh-Ritz method. Specifically, a method is proposed to decompose the frame structure into several substructures and model them respectively, and further the coupling springs are applied among the substructures. Through the vibration test of a beam lap structure with a bolted joint, the analytical expressions between bolt pretension and bolted joint stiffness and damping parameters are obtained. Moreover, the method of simulating the non-uniform pretension among each bolted joint is proposed. Considering the external factors such as reinforcing rib structures and flexible rod exciter, and a complete semi-analytical dynamic model of the bolted frame structure introducing the non-uniform pretension is further established. A case study is carried out on a frame structure that contains four connecting bolts with non-uniform pretension. The natural characteristics of the frame structure are solved by using the developed modeling method, and the rationality of the analysis results is verified by experiments. Based on this, the increasing trends of the resonant frequencies and the resonant response of the frame structure under different pretension conditions are analyzed from two aspects of experiment and simulation.

Study on the sealing performance of high-pressure flanges by a magnetic measurement method of bolt axial force

Under high-pressure conditions, flange sealing often fails due to inadequate bolt pre-tension, leading to unstable pressurization or leakage. Assessing the integrity of high-pressure flange sealing presents challenges, constrained by operational conditions, complex equipment integration, and associated costs. This study introduces a method to evaluate flange sealing using magnetic measurements of bolt axial forces. A novel device developed using the magnetoelastic method efficiently and conveniently measures these forces under various internal pressures. The results show a linear relationship between magnetic signals and bolt axial forces at nominal pressures, whereas excessively high pressures cause anomalous changes in magnetic signals, indicative of bolt plastic deformation. Finite element simulation analyzed the changes in bolt axial force and gasket contact stress due to internal pressures, leading to an empirical formula that correlates these variables under varying pressures. The study also explored the impact of uneven pre-tensioning and gasket material on sealing contact stress. A sealing contact surface model, established based on actual roughness profile parameters, enabled the simulation and formulation of an exponential relationship between contact stress and sealing clearance. This foundation facilitated the creation of a leakage prediction model that incorporates bolt axial force parameters, thus enabling a quantitative assessment of flange sealing performance. This research provides a practical approach to evaluating the sealing performance of operational high-pressure flanges.

The Investigation of Various Flange Gaps on Wind Turbine Tower Bolt Fatigue Using Finite-Element Method

Upon careful examination, numerous wind turbine collapses can be attributed to the failure of the tower bolts. Nowadays, the Schmidt–Neuper algorithm is extensively accepted in wind turbine tower bolt design. It is not advisable to utilize the finite-element method, notwithstanding the effect of the flange gap. To quantitatively investigate the influence of flange gaps on bolt fatigue, a nonlinear finite-element model of a flange segment incorporating bolt pretension and contact elements is herein proposed. Three distinct types of flange gaps are defined intentionally. It is possible to determine the nonlinear relationship between the wall load and bolt internal force. The fatigue damage of bolts was thus computed using the obtained nonlinear curve. Comparing with the results with those of Schmidt–Neuper method revealed the bolt fatigue damage is susceptible to a specified flange gap.

A friction-strip hybrid damper with multi-phase energy dissipation mechanism: Cyclic test and numerical verification

By combining the frictional and plastic energy dissipation modules (FEDM and PEDM), a novel multi-phase friction-strip hybrid damper (MFSHD) is proposed in the current study. The theoretical analyses demonstrate that, when applied in a self-centering structure, the MFSHD is able to provide higher strength, secondary stiffness and energy dissipation and maintain the self-centering capacity compared with conventional friction dampers. A series of quasi-static tests was conducted on the MFSHD to evaluate the effects of different parameters on the hysteresis performance of the MFSHD. The results showed that increasing the strip number or the bolt pre-tension force could both improve the mechanical performance of the MFSHD. The MFSHD with sandglass-shaped strips had a better performance than that with I-shaped strips. In the MFSHD with lower slipping displacement, the PEDM was activated earlier and provided higher strength, stiffness and energy dissipation, whereas its low-cycle fatigue life was reduced. The numerical analyses based on the model validated by the test results showed that the self-centering braced frame substructure equipped with the MFSHD exhibited hysteresis behavior in consistency with the theoretical model. The superior performance of the MFSHD compared with conventional friction dampers was verified numerically.

Hybrid joints consisting of pre-tensioned bolts and a bonded connection—The influence of adhesives on the load-bearing capacity

This study explores the intricate mechanics of hybrid joints, which combine prestressed bolts and adhesive bonding, with a focus on increasing the joint capacity of steel structures. Despite their potential, the fundamental behaviour of these joints is not fully understood. The research focuses on unravelling the load-bearing capacity of these hybrid joints, emphasising the influence of the adhesive properties. The unique manufacturing process, involving the pre-tensioning of bolts while the adhesive is uncured, introduces additional dependencies not present in conventional adhesive joints. Analysis of the mechanical and physical properties of five adhesives provides key insights into the mechanics of load transfer and failure modes in hybrid joints, providing a comprehensive understanding. The study shows that load transfer occurs through micron-thin adhesive layers, highlighting the significant influence of adhesive properties on joint performance. Epoxies emerge as the top performers, with 2.5 times the average friction joint and more than five times the average bonded joint capacity, indicating their superiority in hybrid joint applications. Hybrid joints show significantly less variation than adhesive and friction joints, underlining their consistency and reliability in structural applications. When comparing hybrid and bonded joints with the same adhesive (SW7240), the variance was suppressed to one seventh by the application of preloaded bolts, with practical implications for design values based on quantiles. The study establishes correlations between joint strength and adhesive properties, emphasising the critical role of Young's modulus and tensile strength. It also finds that the elongation of hybrid joints at break is almost entirely dependent on load capacity, with viscosity having a lesser effect. Fracture surface investigations provide insight into the failure modes of hybrid joints, highlighting differences from those observed in frictional or purely bonded joints. This comprehensive study, combining experimental campaigns and in-depth analysis, provides valuable insights into the intricate relationships between joint capacity and adhesive properties in hybrid joints. The findings guide the selection of appropriate adhesives and provide the basis for the development of accurate load prediction methods, unlocking the full potential of hybrid joints and overcoming the limitations of conventional joining techniques in steel structures. Further research is encouraged to investigate the influence of adhesive class, post-tensioning stability and the nuanced mechanics of load transfer in these innovative joints.

Three-dimensional analysis of steel beam-column bolted connections

Abstract The design of steel beam-column end-plate bolted connections is becoming increasingly popular owing to its simplicity of production. This requires knowledge of the full nonlinear resisting moment–rotation (M–Φ) behavior of the joint. To investigate the impact of various geometrical factors on the overall behavior of the connection, this work provides a three-dimensional finite element model (FEM) utilizing ABAQUS software. The suggested model accounts for the pretension force on the bolts, material and geometrical deviations from linearity, and the proximity of surfaces that are adjacent. The numerical model’s ability to simulate and process both the total and specific behavior of varieties of end-plate steel riveted connections is confirmed by calibrating the finite element findings with experimentally disclosed outcomes, which are reviewed in this study. The ultimate behavior was then investigated through a parametric study using the verified FEM with variations in the bolt pretension load, yield strength of the sections, and yield stress of the bolt considering the M–Φ curve. The results of the parametric study showed that as the bolt pretension load and yield stress of the column, beam, and plate materials increased, so did the connection’s moment ability. The yield tension of the bolts, however, had only a minor effect on the connection’s moment capacity.

Shear performance of high-strength bolted connections with stainless-clad steel plates in a corrosive environment

Stainless-clad (SC) steel plates offer desirable corrosion resistance at a relatively low cost, but their shear performance in high-strength bolted connections in a corrosive environment has not been fully explored. In this study, monotonic tensile tests were performed on specimens connected by normal and stainless high-strength bolts at different corrosion degrees. The results were used to determine the influence of corrosion on the slip coefficient, bolt pre-tension force, initial slip load, and ultimate bearing capacity, and a simplified method was developed for estimating the slip coefficient and initial slip load.

Development and optimization of a novel response‐amplified friction damper with different friction pairs

AbstractIn order to improve the efficiency of friction dampers, a shear‐type response‐amplified friction damper (RAFD) was proposed, which utilized a lever mechanism to amplify the shear displacement and increase the sliding distance of friction pairs. Cyclic loading tests were conducted on 12 RAFD specimens to evaluate the effects of machining processes, friction materials, loading protocols, and bolt pretension on the mechanical performance of the specimens. The results showed that the RAFD specimens with NAO and brass friction pads exhibited plump hysteresis loops, and the bearing capacity, effective stiffness, energy dissipation, and equivalent viscous damping ratio all met the stability requirements of FEMA 356 for the friction damper. Reducing the clearance between pins and holes and strengthening the hole edges shortened the plateau near zero resistances of the hysteresis loops by 75%–90%. Furthermore, combined with rotational analysis of the lever, a design methodology for the RAFD specimen was developed. Based on the response amplification factor R, key mechanical indices such as bearing capacity and equivalent friction coefficient were derived, and a theoretical hysteresis model for the RAFD was constructed, which matched well with experimental results.

Bolted shear connectors in steel–concrete composite structures: Shear behavior

The use of bolted shear connectors is of great importance to the sustainable development of steel–concrete composite structures. In this paper, an experimental program consisting of four push-out specimens is performed to investigate the effects of bolt length and fabrication method of concrete slabs on the shear behavior of single-nut embedded bolted shear connectors in terms of failure mode and load-slip response. The concrete slabs are fabricated either as cast-in-situ monolithic slabs or precast slabs with reserved pockets which will be filled with grout in the final construction stage. The obtained results demonstrate that the fabrication method based on grouting, which is commonly utilized for strengthening and retrofitting works, does not affect the behavior of the bolted shear connection. Based on the experimental observations, a finite element (FE) model of the bolted shear connection is developed, after the obtained numerical results are verified against the test results obtained in this paper and those presented in other existing literature, a parametric study is carried out to further investigate the effects of the concrete strength, bolt strength, bolt diameter, bolt pretension load, and the length-to-diameter ratio of bolt on the performance of the bolted shear connection. Moreover, based on the obtained results, a design formula is proposed to obtain the ultimate shear resistance of the bolted shear connection, and the efficacy of the proposed design formula is proved through the comparison with the test results shown in the existing literature.

Data-Driven Prediction Model for High-Strength Bolts in Composite Beams

In recent years, the application of artificial intelligence-based methods to engineering problems has received consistent praise for their high predictive accuracy. This paper utilizes a BP neural network to predict the strength of steel–concrete composite beam shear connectors with high-strength friction-grip bolts (HSFGBs). These connectors are widely used in bridge and building construction due to their superior strength and stiffness compared to traditional beams. A validated finite element model was used to predict the strength of HSFGB shear connectors. A reliable database was created by analyzing 208 models with different characteristics for machine learning modeling. Previous studies have identified issues with result variation and overestimation or underestimation of shear connection strength. Among the machine learning methods evaluated, the backpropagation neural network model performed the best. It achieved a goodness of fit of over 93% in both the training and testing sets, with a low coefficient of variation of 6.50%. Concrete strength, bolt diameter, and bolt tensile strength were found to be important variables influencing the strength of shear connectors. Other variables showed a proportional or inverse relationship with compressive strength, except for concrete strength and bolt pretension. This study presents an accurate machine learning approach for predicting the strength of HSFGB shear connectors in steel–concrete composite beams. The study offers valuable insights into the effects of various variables on the performance of shear connection strength, providing support for structural design and analysis.

Anti-sliding performance of parallel wire strand clamps at elevated temperatures

This study investigated the influence of temperature on the anti-sliding performance of prestressed parallel wire strand clamps (PWSCs) through experiments and numerical analyses. The ultimate anti-sliding resistance of the clamps at different temperatures was obtained through steady-state experiments, and formulae for calculating high-temperature reduction factors of anti-sliding resistance were proposed. When the temperature reaches 400 °C, the ultimate anti-sliding resistance that the cable clamps can withstand is only 20.8% of the ambient temperature. The function between the ultimate fire resistance time of the PWSC and thrusting load level was proposed under ISO-834 heating conditions through transient-state experiments. It was found that the higher the thrusting load level, the shorter the fire resistance time that the PWSC can withstand. When the load level is 0.9Ffc,20, the fire resistance time of the specimen is only 38.1% of that under 0.3Ffc,20. The bolt pretension loss process of PWSCs under high temperatures was studied through numerical simulations of steady-state experiments. At 400 °C, the pretension of the bolt was only 67.3% of that at 20 °C. On this basis, a refined calculation formula for the high-temperature bolt pretension loss was proposed on the basis of the numerical results. The findings of this research can further improve the fire resistance design of prestressed steel structures.

Laboratory and ultra-low cycle fatigue evaluation of the seismic performance of BFP connection with different amounts of pre-tension in bolts

Bolted Flange Plate Moment Connections (BFP) are one of the most practical connections, used as prequalified connections in special steel moment frames. Using three full-scale BFP connections designed according to AISC, this paper has explored the effects of bolt pre-tension levels experimentally under SAC cyclic loading protocol. The bolt pre-tension level has been defined as α coefficient to indicate the pre-tensioning level in three specimens. The bolts of the first specimen were not pre-tensioned, called snug-tightened bolts, and considered as reference connections. The bolt pre-tension levels of the second and third specimens were established in accordance with the minimum and allowable limits of AISC design code and ultimate strength of the bolt, called pre-tensioned and fully pre-tensioned, respectively. The moment capacity, total energy absorption, and strain variation of the bolts have been investigated. Meanwhile, using the ultra-low cycle fatigue failure index obtained from experimental specimens, the capacity of modeled BFP connections in finite elements has been compared with the laboratory samples in terms of failure location and connection capacity. The experimental results revealed that final resistance in BFP connections occurs in the cycle of 7% of the drift angle of SAC protocol loading, and the location of the connection failure is around the farthest hole from the column, which is consistent with the failure results from ultra-low cycle fatigue in finite element modeling for BFP connections. The measure of moment resistance in the pre-tensioned connection (Both connections were minimum pre-tensioned according to the regulation and ultimate strength of the bolt) has increased by about 50% compared to the without pre-tensioned connection. The amount of energy absorption of the pre-tensioned connection with the ultimate strength of the bolt has increased by 176% of the energy absorption capacity of the connection without pre-tensioned and 14% of the energy absorption capacity of the connection with the minimum allowable pre-tensioning of the regulation. The extent of energy absorption in the three connections was equal to 38, 92, and 105 KJ.