Bolt Tension Research Articles

Impact of Carbon Fiber‐Reinforced Polymer Sheets and Bolt Diameter on the Seismic Performance Enhancement of Steel Beam‐Column Joints

ABSTRACTBeam‐column joints are pivotal for ensuring the resilience of prefabricated steel structures under various loading conditions. Following the major earthquakes of the 1990s, semi‐rigid bolted connections emerged as a promising alternative to traditional welded connections. This study investigates a fully prefabricated Intermediate Beam‐Column Joint (IBCJ) with extended endplates, renowned for its excellent seismic resistance. While significant progress has been made in existing research, there is still a need to thoroughly examine the tension capacity of IBCJs concerning bolt size and explore the potential of Carbon Fiber‐Reinforced Polymer (CFRP) sheets to enhance joint performance under seismic loading. Using the finite element method, this research evaluates the performance of IBCJ under both monotonic and cyclic loading conditions. After validation with experimental data, the study examines various bolt diameters to assess their tension capacity, ductility ratio, secant stiffness, and energy dissipation capacity. The findings indicate that larger bolts exhibit higher ultimate capacities and reduced deformation at failure. Additionally, the study investigates the optimal placement and configuration of CFRP sheets, identifying the backside of the endplates as the most effective location. The application of CFRP significantly enhances bolt tension capacity by up to 1.2 to 1.3 times, demonstrating its potential in reducing bolt failure risk and improving structural reliability under seismic conditions. The superior performance of CFRP‐strengthened bolts can play a crucial role in the design and retrofitting of prefabricated steel structures, potentially contributing to the improvement of existing standards and practices of seismic enhancement of IBCJ.

Analysis of relaxation characteristics of multi-bolted connections under the transverse cyclic load

A modeling method under lateral cyclic loading is proposed for the complex multi-bolt connection loosening problem. Firstly, the thread stress surface is divided into n small sectors, and the self-relaxation mechanical model of multi-bolt connection is established considering the interaction between bolts. Secondly, the self-relaxation model is solved by MATLAB software and compared with Nassar model to verify the correctness of the model. Finally, considering the influence of different bolt number, hole clearance and connection spacing, the relaxation characteristics of multi-bolt connection are studied. The results show that during the loosening process, the bolt head undergoes a bending-sliding-bending cycle process, and the bolt tension shows a wave downward trend. When multiple bolts are connected, the number of loosening cycles decreases linearly with the increase of hole clearance. With the equidistant increase of bolt connection spacing, the number of bolt loosening cycles shows a decreasing trend. Compared with the number of bolts, the change of bolt hole clearance and connection spacing is more likely to affect bolt loosening.

Progressive bearing failure analysis and strength prediction method for the initial assembly and tensile process of composite bolted joints

Composite bolted joints have extensive application in aerospace and marine equipment. Failure analysis and strength prediction are crucial steps in the design of composite bolted joints. This study proposes a method that can accurately analyze the progressive bearing failure and static strength of composite bolted joints under different initial assembly parameters. This method first obtains an accurate initial assembly state based on the high-fidelity finite element model with detailed thread structure. Then it uses this as an input to analyze the progressive bearing failure process and the bearing strength value. Using the above method, the formation and evolution mechanism of the tightening yielding phenomenon during the assembly process are analyzed. And the influence of the two key assembly parameters, washer type and initial bolt tension, on the bearing strength of composite bolted joints is analyzed. The experimental results verify the effectiveness and accuracy of the simulation methods and results.

An ultra-thin bolt tension sensor and online monitoring system: For application in hydropower plant unit

An ultra-thin bolt tension sensor and online monitoring system: For application in hydropower plant unit

Physics Informed Gaussian Process for Bolt Tension Estimation

Bolted joints are fundamental components in many engineering applications. Therefore, the need for monitoring their tension over their life span is an essential for securing their integrity. Modelling of the dynamics of a bolt has shown success through Euler-Bernoulli beam theory where a relationship of boundary conditions and tension allows determining the changes in the modal parameters. However, the widespread adoption of this approach has faces challenges, as obtaining high-fidelity data for bolts under all tension phases is often unfeasible in practice, particularly for those in low tension. Nevertheless, merging data and prior physics knowledge can provide practical constraints for bolt tension estimation in areas lacking observational data. This study establishes its foundation by developing a stochastic model for bolt tension estimation through the integration of bolt data-driven and physics-based predictions using Gaussian Process Regression (GPR). The core concept of this approach involves predicting data observations through a stochastic simulation using a physics-based model, particularly in scenarios where observational data is absent. The proposed methodology is validated with experimental data to critically evaluate its performance.

Mechanical behavior of the extended end-plate connections of a portal frame with various retrofitted constructions under loading

With the mounting number of photovoltaic power generation panels on roofs, the proliferation of heavier cranes, the addition of interlayers, and extreme weather conditions, the loads imposed on portal frame structures have observably increased, resulting in a strong demand for retrofitting. However, there remains a dearth of quantitative assessment regarding the efficacy and superiority of retrofitting techniques for beam-column connections with a bolted extended end plates (BCCBEEPs). Given that the retrofitting process cannot be characterized by complete unloading, it is crucial to accurately comprehend the impact of preload on retrofitting. In this study, finite element models (FEMs) of BCCBEEPs with seven different retrofitted constructions were established and validated against experimental results, and their mechanical behaviors were thoroughly compared and analyzed. Moreover, the influence of the preload level on the retrofitted BCCBEEPs was explored. The analysis results reveal that: excessive reinforcement of the component was found to shift the weak link to the connection, making the bolts more prone to failure and reducing energy dissipation capacity and ductility. Compared to an un-retrofitted connection, the carrying capacity of the PSPF retrofit measure, for which steel plates were pasted on the inside of beam flange, was found to be increased by a maximum of 38%. However, the energy dissipation capacity was decreased by 39%, the bolt tension was increased by 61%, and the prying force was increased by 58%. Importantly, not only components, but also connections, must be strengthened. Excessive preloads can lead to increased vulnerability at connection areas of retrofitted connections, especially in cases of over-reinforcement. The higher the preload level, the greater the reduction in bearing capacity, which could potentially fall below that of an un-retrofitted connection. When the preload level reached 80% of the strength of un-retrofitted connection, compared to the no-preload connection, the PSPF measure experienced a decrease of 18% in carrying capacity, a reduction of 31.8% in ductility, an increase of 14% in bolt tension, and a rise of 27% in end plate prying force. Therefore, when the preload level exceeds 20%, it is advisable to accurately assess the impact of the preload on the retrofit before implementation.

ВПЛИВ РАДИАЛЬНОГО НАТЯГА БОЛТІВ НА ХАРАКТЕРИСТИКИ НДС МОДЕЛЕЙ З'ЄДНАНЬ ЕЛЕМЕНТІВ КОНСТРУКЦІЙ ЛІТАКА

To study the effect of radial bolt tension on the VAT characteristics of the bolted connection elements of aircraft structures, calculations are carried out using the finite element method, which is based on experimental verification using a model of the bolted connection design with tension. The constructed model is verified by the test of bolted connections, based on the reliability of the three-dimensional model of elastoplastic analysis by the finite element method. A model of the analysis of the influence of the design parameters of the bolted connection for six different tension values was created. A comparative analysis of the influence of different tension values on the nature of the VAT distribution, the initial stiffness and the load-bearing capacity of the bolted connection design was carried out. The results of the study showed that the stress distribution and their concentration can be changed when applying the appropriate fit with tension. At a tension value of 1.5 % of the bolt diameter, the initial stiffness and bearing capacity increase by 14.1 % and 9.33 %, respectively.

Vision-based detection of bolt tension considering non-rotatory loosening via a new calculation method of bolt flexibility coefficient

Bolted joint is widely used in construction, vehicle, aerospace, and other engineering fields. Bolt tension is the most important performance index of bolted joints. The whole life cycle monitoring of bolt tension without contact and damage can be realized by vision-based method. The existing methods indirectly predict the change of bolt tension by calculating the rotary angle of the nut. This kind of method can judge the loosening caused by nut rotation but cannot deal with the non-rotary loosening. At the same time, the relationship between nut rotation angle and loosening must be obtained through calibration experiments. This paper proposes a vision-based method to measure the change of bolt tension considering the non-rotary loosening by detecting the change of bolt elongation. Based on VDI2230 and finite element analysis, a new calculation method of bolt flexibility coefficient is proposed. The experimental results show that this method can measure the change of bolt tension with high precision in the process of tightening and loosening.

Weak axis low-damage performance of seismic resilient rocking steel column base with friction connection

Rocking column bases with friction connections are a critical technology employed in the low-damage design of steel structures. In this study, cyclic loading tests were conducted along the weak axis of the column, incorporating INITIAL, AFTERSHOCK, and REPAIR cases, with a maximum drift ratio of 3%. In the AFTERSHOCK case, both the sliding and maximum moments at the column base exhibited a significant decrease of 67% and 16%, respectively. To address the decrease in sliding strength attributed to the loss of bolt tension, Belleville Springs (BeSs) were employed, and the bolts were maintained within the elastic range. The results demonstrate that the hysteretic curves of the column base almost perfectly align in all three cases, revealing a strength loss of less than 2% and a significant enhancement in seismic resilience. This low-damage column base proves well-suited for deployment in regions with high seismic risk, especially for buildings subjected to continuous seismic excitation. A finite element analysis (FEA) model was developed to quantitatively evaluate the damage, sliding, bolt tension loss, and energy dissipation performance of the column base. Finally, a simplified flag-shaped analytical model was proposed to guide the design of such low-damage column bases, providing a basis for their integration into overall structural analyses.

Seismic Performance of U-Shaped Connection for Prefabricated Steel Plate Shear Wall

In this investigation, a U-shaped connection (U-C) was introduced for a prefabricated steel plate shear wall with beam-only connections. This design replaces a portion of shear bolts with tension bolts to enhance bolt efficiency and reduce the overall bolt count, and it is suitable for a prefabricated high-rise steel structure. Four 1/3 scale specimens were designed, and an array of performance aspects including failure modes, hysteretic behavior, skeleton curves, energy dissipation capacity, stiffness degradation, and key performance indicators were systematically investigated through a combination of quasi-static tests and finite element analyses. The results showed that the combination arrangement of tensile and shear bolts in U-C effectively reduced the usage of bolts used and reduced installation costs; under low cycle reciprocating loads, the ultimate bearing capacity and energy dissipation capacity of a beam-only-connected prefabricated steel plate shear wall with U-shaped connection (BPSW-U) had slightly decreased compared with the prefabricated steel plate shear wall with discontinuous cover-plate connection (DCPC). Nevertheless, the BPSW-U excelled in preserving the integrity of the frame beams, channeling structural plastic deformations primarily into the infilled steel plate. This design feature ensures that post-earthquake functionality recovery can be achieved by simply replacing the infilled steel plate.

Analysis and design of column splicing flange joints with different weld types

To improve the seismic performance of steel column splicing flange joints, different weld details between the column and the flange plate were proposed in this study, and four full-scale specimens were designed and tested under cyclic loads. Finite element analysis was conducted to further check the joint performances and the weld behaviors. The hysteresis behaviors, yield moment, ductility, bolt forces, energy dissipation, stress and strains were analyzed. The parametric analysis, with finite element models validated by test results, was conducted, discussing the influences of the weld details, weld geometries and flange openings. According to the results, three of the four different weld details developed different advantages on ductility or energy dissipation capacity, bolt tension distribution, stress or strain distributions. Larger weld leg size would increase the resistance of the bolted flange splice joint, but may also cause weld residual stress and prying force. The reduction of flange opening can improve the stiffness and yield moments of the Type B flange joints. Formulas for the yield moments of the joints with recommended weld types were proposed and validated by both test and numerical analysis results, and additional formulas to check weld details were proposed for seismic design of bolted flange joints in prefabricated steel structures.

New design approaches for tension, shear and interaction resistance of carbon steel bolts

More economical and statistically verified design approaches for carbon steel bolts are presented based on an extensive literature review and own systematical experimental investigations into the tension, shear and interaction resistance of carbon steel bolts conducted at the Institute for Metal and Lightweight Structures of the University of Duisburg-Essen, Germany. Herein, reliability analyses according to EN 1990, Annex D were carried out and confirmed that an increase of the reduction factor to k2 = 1.0 for the tension resistance Ft,Rd is in principle possible. Regarding the shear resistance of carbon steel bolts, simplified but more economical shear coefficients a independent of the position of the shear plane are proposed. Finally, newly design equations for the interaction resistance of carbon steel bolts are proposed, which are in line with the new interaction formulations developed by Stranghöner/Abraham and implemented in prEN 1993–1-4 and abZ/abG Z-30.3-6 for stainless steel bolts. The new interaction concept provides a more economical design compared to EN 1993–1-8/prEN 1993–1-8 and serves to harmonise the European design rules between carbon and stainless steel.

Experimental study of fully bolted joint composed of inner cruciform core and outer sleeve

To realize the ring truss of the long-span cable dome assembled by bolting, this paper proposed an innovative fully bolted joint which is composed of inner cruciform members superposed by angle steels and outer sleeves. It is the internal and external connections that achieve the mechanical performance of this fabricated joint the same as that of the welded joint. The joint has several advantages such as efficient construction, convenient assembly and disassembly and resource conservation. To study the mechanical property of the novel joint, three specimens were designed for low cycle reciprocating loading tests. Particularly, the failure mode, hysteresis performance, skeleton curve, stiffness degradation, ductility, bolt tension, strain distribution and energy dissipation capacity of the specimens were analyzed. According to the results, the hysteresis curves of the specimens were plump, and this joint had excellent stiffness and bending resistance, which was similar to the welded joint. In addition, the internal cruciform members cooperated with the bolts on the flange and played the role of the second line of defense, to ensure the bearing resistance and stiffness of the joint.

Comparative study on fracture characteristics of carbon and stainless steel bolt material

Bolt fracture often limits the ultimate strength and deformation capacity of bolted connections and leads to overall joint failure. Therefore, the prediction of structural collapse under extreme loads necessitates the incorporation of a reliable fracture model that reflects the observed structural response of bolts. This paper reports a comprehensive experimental and numerical study into the structural behaviour, ductility and fracture characteristics of Grade A4–80 austenitic stainless steel bolts and carbon steel 8.8 bolts in tension, which are commonly used as fasteners in bolted connections. Tensile tests were performed on smooth material coupons machined from both bolt grades to obtain the material response. Thereafter, tensile tests were performed on notched specimens from both grades, allowing the fracture characteristics to be studied over a range of stress triaxialities and the development of an equation relating the plastic strain at fracture to the stress triaxiality. 2D axisymmetric and 3D advanced finite element models were calibrated against the experimental results and damage propagation parameters. The developed numerical models are shown to perfectly replicate the observed experimental behaviour of the tested bolt materials under predominantly tensile loading, including fracture. Both experimental and numerical results confirm the superior ductility of A4–80 bolts over their 8.8 counterparts.

接着接合を併用した一面せん断高力ボルト接合部の耐力評価

Adhesive bonding has been increasingly used for seismic retrofit and repair recently. However, the interaction between bolt and bonding joints is not clear in detail. This study focuses on the hybrid joint method using adhesive bonding and high-strength bolts for the single-shear lapped joint to improve joint strength. Three experimental parameters, with or without adhesive, bonding area, and bolt tension, were adopted. The results show that the connection strength can be effectively increased by adhesive. Moreover, the effective adhesive area and strength evaluation formulas are proposed through the cohesion failure behavior.

Anchor Behavior of One-Side Bolt with Flip-Top Collapsible Washer

With the development of blind bolts that can be installed from the outer side of a section, the application of steel pipe hollow sections in prefabricated structures has become possible. The novel one-side bolt with a flip-top collapsible washer (FTW-OSB) is proposed, which can fold the washer at the end of the bolt to achieve a simple and efficient installation. Firstly, the components and installation process of the FTW-OSB are introduced. Additionally, axial tensile tests were carried out on three types of new bolts, and the failure mode, load–displacement curve, and ultimate capacity were analyzed. Based on this, the finite element model was verified, and through a series of finite element parameter analyses, the influence of washer size and construction, the friction coefficient, and the contact surface size on the new bolt were analyzed and optimized. The results show that the L-shaped washer can prevent washer rotation and has better anchoring performance than the I-shaped washer. The washer thickness, height, and upper contact surface size are the key factors affecting the anchoring performance of the FTW-OSB bolt. Among these factors, when the washer thickness increases from 0.1 d0 to 0.3 d0, the ultimate capacity and initial stiffness of the FTW-OSB bolt increase by 136.5% and 100.3%, respectively. The lower contact surface size and friction coefficient can be ignored. The failure model of the FTW-OSB is mainly washer shear failure and bolt tension failure. By effectively adjusting the washer thickness, side wall height, and upper contact surface size, shear failure of the washer can be avoided and an anchoring performance can be achieved that is the same as that of the same type of 10.9-grade ordinary high-strength bolt.

An improved 3D model of composite bolted joints with detailed thread structure and progressive damage analysis of realistic tightening process

Bolted joint is a common connection method in composite structure assembling. The initial assembly state has a significant influence on the subsequent performance. To realize the simulation of the assembly process of composite bolted joints, an improved 3D model is proposed. This model considers the detailed thread structure and can be used to simulate the realistic tightening process. The relationship between the tightening torque and bolt tension is analyzed and the effect of the friction coefficient on the value of the tightening coefficient is analyzed using this model. A new fitting model for the nonlinear pressure distribution state on the outer surface of the composite laminates during the assembly process is proposed. And a quantitative analysis and prediction method of the nonlinear pressure distribution state is established. Finally, the effects of bolt tension and washer type on initial assembly damage are analyzed and experimentally verified.

ANALYTICAL MODEL OF THE T- STUB COMPONENT IN THE END-PLATE BOLTED CONNECTION OF THE BEAM TO THE COLUMN IN TENSION

End plated connections of metal structures are quite relevant and are usually used in office, commercial, and commercial-office buildings. It is very important to be able to diagnose the real general behavior of beam-to-column connections based on their geometric and mechanical properties. Therefore, the analysis of steel structures at the modern level requires a specialist to have a thorough understanding of their work, as well as the calculation provisions laid down in current design codes. In contrast to Eurocode 3 design codes, the current Ukrainian state building regulations do not contain clear instructions on the beam to column joint calculation and do not even give a clear definition of the concept of steel joint and steel connection. It should be noted that the beam to column connection is the most responsible area that requires special attention, as it significantly affects the design scheme of the structure, as well as its economic efficiency. By using the semi-rigid connection concept, weight savings of up to 20% can be achieved. In the presented article, a simplified mathematical model of the t-stub component of the tensile zone of the semi-rigid bolted connection of the beam to the column was developed using the component method. In the given solution of the connection in the tension zone, the following components were distinguished: the flange in bending, the end of the column in bending, and the bolts in tension. All these elements were modeled from two t- stub components connected through an end plate with the help of bolts. A design scheme for determining the stress-strain state was proposed. The analysis of the exhaustion of the bearing capacity of the t- stub component was performed according to three scenarios depending on the size of its individual elements (end plate thickness, bolt diameter). The obtained results will make it possible to determine the bearing capacity with possible variations of the transition to the limit state, as well as to estimate the deformations of the considered component of the connection. Keywords: end-plate connection, mathematical model, T-stub component, bolt connection.

Identification of the torsion coefficient of bolts in slip-critical connections

Introduction. The article proposes a method for identifying the coefficient of torsion of a high-strength bolt in the laboratory environment. The coefficient is found by determining the relative deformation of a drawn bolt using load cells. This method requires specialized equipment and a test bench, and it can be used to study the behavior of bolts. The value of the torsion coefficient is necessary to ensure the appropriate bolt tension force, since according to current friction concepts of bolted connections involving high-strength bolts, the design behavior of a bolted connection is ensured by the appropriate bolt tension force, determined using the required torque. Otherwise, the actual behavior of a bolt differs from its design behavior, since only a pre-set tension force ensures the necessary bearing capacity of a bolted connection in the friction planes.
 
 Materials and methods. Specimens of bolts under study are made according to the German standard DIN931 with a strength of 10.9, and the size M14 × 220; their nuts comply with the German standard DIN934 with a strength of 10 and the size M14. Instron 1000HDX tension testing machine was used to make a diagram describing the performance of steel bolts. Nut tension was determined using NOGRAU NTW24-034R torque control key, and bolt elongation was controlled using FLA 5-11 strain gauges and the National Instruments data collection system.
 
 Results. A new method for monitoring the measurement of the torsion coefficient of high-strength bolts was tested and proposed in furtherance of the research conducted by the authors.
 
 Conclusions. As a result of testing, a change in the torsion coefficient can be evaluated depending on the torque value.

Experiment and design methodology of an IODR flange connection under bending load

A new type of inner and outer double-ringed (IODR) flange was introduced in this paper, which can make full use of the inside and outside space of circular tube and reduce the dimensions of connecting bolt and flange plate. Five groups of down-scaled IODR flanges with different flange plate dimensions were designed and tested under bending moment to study the failure mode and force-transferring mechanism. The finite element model was built to further investigate the influence of connection dimensions on the bending performance from different aspects, such as bearing capacity, location of rotation axis and bolt tension ratio. It reveals that the failure of IODR flanges occurred due to the necking of bolt. The bolt tension ratio has an insignificant change when the applied load is smaller than about 80% of bending capacity, then it tends to increase until approaching 1.0. A theoretical method for rotation axis position and bolt force was proposed considering flange geometry parameters and bolt arrangement. It was found that the obtained rotation axis positions are about 0.7r, which is smaller than 0.8r recommended in DL/T 5629–2021, meaning that the existing design method is unsafe. Based on the theoretical analyses, the design methods of flange plate, stiffener and bolt were proposed and a corresponding design process was also established.