Design Of Bolted Joints Research Articles

Analytical model for cyclic behavior of cold-formed steel bolted connection frames considering local buckling

Cold-formed steel (CFS) structures are increasingly popular in the construction industry due to their high strength-to-weight ratio, ease of fabrication, and cost-effectiveness. This study focuses on the development of a detailed mathematical model to accurately simulate the cyclic behavior of CFS moment-resisting bolted connection frames, particularly considering the local buckling of connected frames. Bolted joints are preferred in thin-walled CFS structures over welded joints due to their ease of installation and adaptability in seismic design, relying on slip and bearing mechanisms of bolts to accommodate inelastic deformations and dissipate energy during seismic events. The proposed model incorporates these mechanisms and validates them against experimental data and refined finite element analyses. Significant findings highlight the importance of the balanced number and arrangement of bolts in preventing excessive bolt slip and premature buckling. This research provides a robust analytical tool for optimizing bolted joint designs in CFS bolted connection frames, contributing to safer and more resilient CFS structures in seismic regions. The model’s computational efficiency further enhances its practicality for engineers and researchers.

ANALYSIS OF REINFORCED BOLTED JOINTS IN HIGH-CAPACITY SILOS

ABSTRACT: This paper presents an analysis of the mechanical performance of bolted joints used in silos for storing bulk materials. In particular, we investigated the effectiveness of three types of bolted joints: one without reinforcement, one with angular reinforcement, and one with squared reinforcement. Our analysis involved the use of the finite element analysis sub-modeling technique, which allowed us to construct a large finite element model with shell elements and a sub-model with solid elements. By analyzing the stress state of each joint, we were able to determine the contact state and contact pressure of the bolted joint. Our findings showed that bolted joints reinforced with triangular and square plates were effective in maintaining contact pressure, even under high-pressure conditions. This study provides valuable insights into the design of bolted joints used in silos, which can help ensure their reliable and safe operation. Keywords: bolted joints, high-capacity silo, FEA sub-modeling.

АНАЛІЗ РОЗПОДІЛУ КОНТАКТНИХ НАПРУЖЕНЬ У ДВОЗРІЗНОМУ БОЛТОВОМУ З'ЄДНАННІ КОМПОЗИТНИХ ТА МЕТАЛЕВИХ ЕЛЕМЕНТІВ

Bolted joining technique is the dominant joining method for CFRP load-carrying structures in aircraft. However, the weak point of such structures are the areas located in the vicinity of the fastener holes, which are the areas of increased stress concentration. In addition, drilling the holes results in structural discontinuities due to cutting material fibers. Among all failure modes of composite bolted joint, bearing failure is one of the most common type of damage. This failure is caused by the local compressive stresses acting normal to the contact surface, that leads to delamination of material due to insufficient strength of matrix. Therefore, it is extremely important to optimize the design of composite bolted joints in order to enhance the entire composite structure. To increase the load-carrying capacity of the composite joint structural parts and protect the hole walls from damage, a method for installing titanium bushing with glue into the holes of composite plate is proposed. The paper presents the results of numerical analysis of the impact of stacking sequence on the distribution of contact stresses in a double-shear bolted joint of composite plate to steel cover plates. Using the finite element method and ANSYS Workbench 2019 R3 software, a three-dimensional finite element model of a double-shear bolted joint was created, which enables to analyze the impact of the stacking sequence on the distribution of contact stresses at the bolts to titanium bushings interface in the case of uniaxial tension of the middle composite plate at the level of tensile stresses in the gross section of 100 MPa. The obtained result explains the fundamental difference in the behavior of composite and metal materials: due to the change in the orientation and sequence stacking, the stiffness of the composite element of the joint changes, which affects the ovalization of the holes and the level of local deformations of the bushings, which in turn leads to a change in the maximum contact stresses and their concentration. By optimizing stacking sequence, it was possible to reduce the level of maximum contact stresses by 1.1 times. At the same time, the degree of unevenness of the distribution of contact stresses decreased by 1.21 times. The optimal stacking sequence was one in which 37.5% of the fibers oriented at an angle of 0°, 50% of the fibers oriented at angles of ±45°, and 12.5% of the fibers oriented at an angle of 90°

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.

Prediction model for bearing surface friction coefficient in bolted joints based on GA-BP neural network and experimental data

A method has been developed to quantify the bearing surface friction coefficient in bolted joints based on the mechanics of the tightening process. By measuring the surface topography under different tightening torques, a strong correlation between the variation of the microscopic topography and the friction coefficient was revealed. The friction coefficient initially decreases and subsequently increases due to surface wear and microstructural transformations. A genetic algorithm (GA) and backpropagation neural network (BP) were employed to create a predictive model, optimizing network parameters for enhanced learning efficiency and accuracy. The experimentally validated GA-BP prediction model forecasts friction behavior with a maximum relative error of 3.57 %, offering valuable insights for the design and optimization of bolted joints.

A Software for Optimum Design of Laterally Loaded Bolted Joints

Bolted joints, which are one of the detachable joining methods, are used extensively. The reliability of bolted joints is extremely important for the strength and life of the system. The determination of the number of bolts to be used in a system, the position and other data of the bolt requires very serious design and engineering studies. In this study, the design and optimization of bolted joints subjected to lateral forces are performed. For this purpose, a software has been developed in C# programming language. The software visually guides the user and asks a minimum number of questions to the designer and all other parameters are calculated by the program. The visual design of the program was done in Visual Studio environment. The graphic designs used in the software help the user to enter correct data. When the program is run for bolted joint under lateral loading, the user only enters the number of plates and force as input. Although the program performs its calculations between 1.5-2 factor of safety, it is possible to change it according to the characteristics of the design. The program developed in the light of these inputs calculates the appropriate bolt diameter, number, material and dimensions of the plates for the designed joint according to the optimum design options. The design options determined by the program are also presented to the designer visually. With the developed software, the user workload is minimized by determining the optimum options of bolted joints according to the minimum amount of user input. This resulted in significant savings in the time spent in design and engineering calculations. The user-friendly interface provides an easy and visual use. The results obtained by the program were also solved manually to check the reliability of the program.

Analysis of the mechanical behavior of bolted joints with slotted-in steel plate considering the move path of rotation center for single-layer timber reticulated shell

The mechanical behavior of the bolted joints with slotted-in steel plate plays an important role in maintaining the stability of single-layer timber reticulated shell, yet methods to estimate the mechanical behavior of the bolted joints still remains to be improved. Assuming that the ductile failure of the bolted joints and the compressive failure of the glulam beam end occurred, the move path of the rotation center was obtained through theoretical derivation and used to determine the ultimate moment and rotational stiffness of the bolted joints. The equations for calculating the ultimate moment of the bolted joints were derived based on the European Yield Modes, t. Moreover, employing the beam on elastic foundation theory, a simplified equation of slipping stiffness was obtained and used to calculate the rotational stiffness. Experimental investigations on bolted joints for single-layer timber reticulated shell were conducted to verify the accuracy of the proposed theoretical methods. The results showed the rotational stiffness and ultimate moment obtained from theoretical calculation were consistent with the results of experimental tests. Furthermore, by calculating the move path of the rotation center, it was found that the rotation center started from the geometrical center of bolts at earlier loading stage and moved towards the compressive region of the glulam beam end with the increase of the external force. And the moment-rotation curves predicted by the linear model was in good agreement with the moment-rotation curves obtained from experimental tests, showing a convenient and reliable way to the design of bolted joints for single-layer timber reticulated shell.

Fastening solutions on composite structures: Progressive damage analysis of a unique bolted joint design for single-lap CFRP laminate

This study tested a unique assembly method using single and multi-body sleeves with carbon fiber-reinforced plastic (CFRP) to improve load-carrying capacity in single-lap joints. Advanced techniques were implemented into FE code to simulate progressive material degradation behavior. Ti6-4 bolt, insert, and washers with AISI 304L sleeve joint were conceptually designed to keep bolt and nut together with less relative motion. Failure indices were reduced by 16–54%, damage initiation force was improved by 8–40%, and inter-plate clamp loss was reduced by 18% compared to the sleeveless design. Lateral load-carrying capability of joint and inter-plate clamp load significantly improved.

Effect of Assembly Uncertainties on Shock Propagation Through a Bolted Joint Under Impact Loading

Abstract Bolted joints have been widely used in engineering structures because of their advantages of simplicity, economy, and assembly. However, material nonlinearities, interface nonlinearities and uncertainties in the assembly process will lead to the dynamic response to become very complex. This work investigated the effect of assembly uncertainties on shock propagation through a bolted lap joint under impact loading. The object of the study was a bolted lap joint subjected to separate Hopkinson pressure bar (SHPB) test. First, a high-fidelity finite element model of the bolted lap joint was developed, and the model was validated by comparing with the experimental results. The error between simulation and experimental results prompted the necessary to consider the uncertainty effect. Then, the effects of multiple uncertainties were considered to identify important input random variables related to the impact response of the joint. The results showed that the slip between the connected parts has the most significant effect on energy dissipation and stress wave propagation. Finally, useful conclusions for the design of bolted joints were obtained from the computational results and discussions.

Prediction of contact stress in bolted joints using the Polynomial Chaos-Kriging model

Bolted joints are one of the most widely used forms of connection. As the weak link, its contact stress directly influences the mechanical properties of a structure. In this work, Polynomial Chaos-Kriging (PCK) surrogate model is adopted to predict the contact stress in bolted joints. Firstly, a Finite Element (FE) model of the bolted joint is established using a parametric modeling method. On this basis, the stress datasets for the contact area of the plate are obtained. Subsequently, the generated stress datasets are imported into the PCK surrogate model for training and validation. Maximum axial stress and influence coefficient are used to conduct the characterization analysis of the contact stress. Results show that the PCK surrogate model is suitable to predict these two parameters. In the case that compressive stress does not exist in all contact areas, quantitative analysis of the contact stress can be further carried out by using this model. The main influencing parameters of contact stress are extracted according to the correlation analysis results. The trained PCK surrogate model can be used as an alternative to finite element analysis for the prediction of contact stress. Design of bolted joints can also be achieved by the parametric control using this model.

Experimental investigation of textile reinforced concrete thin-wall panel bolted connections

Textile Reinforced Concrete (TRC) is a composite material that combines fine-grained concrete with textile fibers to create a new building material with improved mechanical properties. TRC, an innovative thin-wall precast panel construction solution, offers excellent tensile strength, crack resistance, and durability. The behavior of bolted joints in textile-reinforced concrete thin-wall panels was experimentally studied in this research. The investigation focused on three types of connections: moment joints, shear joints, and half-box connections. The study aimed to examine the structural performance of these joints under different loading conditions and identify the failure modes. Ten specimens were tested, and the results were analyzed to determine the relationship between applied load and joint behavior. This research provides valuable information for the design and optimization of bolted joints in textile-reinforced concrete thin-wall panels.

Degradation and failure analysis of bolted joints under transverse loading

There are a huge number of bolted joints used in engineering applications. However, unreasonable design and use may lead to degradation and failure of the connected structure. Herein, finite element analysis method is used to investigate the influence of various factors on the mechanical properties of bolted joints. To simulate the actual assembly and loading process, different analysis steps were considered, given as: tightening step, initial lose step and the loading step. In the loading step, transverse load is applied to obtain the force-displacement curve. Structural parameters, i.e. clamping force, effective clamp length and assembly clearance, and coefficients of friction of all the contact surfaces are considered in the finite element analysis. The results showed that the performance of the bolted joint under transverse loading exhibits different stages, and this agrees well with the results of our previous experimental results. Through the analysis of the force-displacement curves, the characterization parameters for the mechanical properties of the bolted joint can be extracted, such as curve form, tangential stiffness, slip distance, transverse load threshold, etc. The characterization and evaluation of the mechanical properties integrates the process from design to service, which helps to provide reference for the reliability design and performance improvement of bolted joints.

In-service failure of mechanically galvanised low alloy steel bolts of three 25,000 m3 bolted water tanks

Several single-lap bolted joints fastening the steel plates of three 25,000 m3 water tanks showed premature failure. Most fractured bolts were in the lower sector of the tanks.The tempered martensitic steel bolts were mechanically galvanised, and the poor quality of the galvanisation allowed the corroding agents (Cl− and SO4−2) to percolate through the Zn and Sn coating particles, finally reaching the steel surface of the bolts. Additionally, multiple 6 μm-deep intergranular pre-cracks were observed at the threads’ roots of the new bolts. During service, these pre-cracks accumulated the corrosive agents, creating numerous 10 μm-deep corrosion pits, nucleating the bolts’ environmentally assisted cracks. Microfractographic examination of the bolts featured stable growth of brittle cracks (intergranular and quasi-cleavage cracking) followed by mixed-mode cracking and a small region of ductile overload fracture. This failure sequence confirms that the fracture mechanism of the low alloy steel bolts is due to environmentally assisted cracking. Finite elements analysis investigated the effect of the bolt diameter, bolted joint design and pre-load force on the tensile stress distribution. Improvements in the bolts’ quality control and bolted joint design were discussed to prevent new failures.

Bolted Joint Preload Distribution from Torque Tightening

Abstract The purpose of this paper is to develop an understanding of how bolt preloads are distributed within a joint as each bolt is tightened in turn by the use of a calibrated torque wrench. It discusses how the order that the joints nuts/bolts are tightened can affect the final bolt preload. It also investigates the effect on incrementally increasing the bolt preload through a series of applications of the controlled torque tightening sequence. Classical analysis methods are used to develop a method of analysis that can be applied to most preloaded bolted joints. It is assumed that the static friction coefficient is approximately 15% less than the dynamic friction. It is found that the bolt preload distribution across the joint can range from slightly above the target preload to significantly less than the target preload. The bolts with a preload greater than the target preload are found to be those tightened towards the end of the tightening sequence, usually located close to the outer edges of the joint’s bolt array. The bolts with a preload less than the target preload are those tightened early in the tightening sequence, located centrally within the joints bolt array. The methods presented can be used to optimise bolted joint design and assembly procedures. Optimising the design of preloaded bolted joints leads to more efficient use of the joints.

Design and analysis of FRP composite bolted joints for space structures

Man tries to learn his surroundings by showing tendencies such as discovering, researching, asking questions, and noticing the relationships between objects. In other words, he tends to understand the world he lives in with various judgments. Therefore, it is important to raise individuals with advanced reasoning skills, mathematical thinking skills, proofing skills, problem solving skills, metacognitive knowledge, skills or qualifications. It can be said that this can only be possible with the right teaching models, methods, techniques and teachers who can use them in the most efficient way. In this context, the aim of the study is; To determine the difficulties in the preparation process for LGS, which has been implemented in our country since 2018, and the reflections of LGS on mathematics education applied in schools within the framework of the opinions of mathematics teachers and make suggestions accordingly. In the study, the screening model was adopted because it was tried to portray the thoughts of a certain group of participants on a subject. The sample of the study; It consists of 110 mathematics teachers who attended 8th grade classes in the 2018-2019 academic year. The data obtained from teachers' opinions were analyzed by content analysis method. According to this; The predominant opinion is that students have problems in understanding, interpreting, thinking and reasoning in the new examination system, however, because the textbooks and the exam are not parallel, teachers have various difficulties. In this direction, various activities can be organized to increase students' motivation and to gain reading habit. In addition, it is thought that it would be beneficial to provide teachers with in-service training for the exam.

Semi-analytical model development for preliminary study of 3D woven Composite/Metallic flange bolted assemblies

This research deals with the development of a new semi-analytical model for composite-metal eccentric tensile bolted joints of casing structures. The model is based on a direct stiffness method considering structural elements, where flanges are modeled with axisymmetric shell elements, the bolt with a beam element and contact behavior with a specific number of compressive linear springs, identified by means of convergence tests. A hybrid element is added in order to set the link between flange and bolt. Since the model is intended for the preliminary design of bolted joints including composite materials, we propose an extension of the stiffness matrix formulation of isotropic axisymmetric shell elements to orthotropic ones. This formulation is validated with respect to a 2D FE axisymmetric model. Then, a semi-analytical model is established for a casing assembly approximately corresponding to a real casing of an aircraft engine. Design criteria such as normal stress on the bolt, bending moment and axial load at a specific section of the composite flange, given by the semi-analytical model are compared to a 3D FE computation. Results are in very good agreement and the semi-analytical model offers considerable time saving where the computation time was 120 times faster than the 3D FE model. Moreover, relative error does not exceed 2% for normal stress of the bolt and 9% for the flange bending moment which is satisfactory in a preliminary design approach. However, due to the formulation of hybrid element, less accurate results were observed for axial displacement of the composite flange and it would be advisable to consider a new formulation. This will be detailed in future work. Finally, a parametric study showed the ability of the semi-analytical model to predict the physical behavior of joints and proved its usability for running optimization studies and its reliability as a preliminary design tool.

Study of bolted joint axial stiffness using finite element analyses, experimental tests, and analytical calculations

The bolted joints sizing procedures shall adequately match the conditions imposed on the joint in service, to ensure high reliability designs. Therefore, this study aims to analyze the load distributions on the bolt when applying external load on bolted joints. Finite element and extensometry analyses as well as analytical calculations were performed in order to compare the magnitude of the joint overall stiffness, with respect to several available theories. The results acquired through the analytical method prescribed in the VDI 2230 standard as well as the finite element and extensometry analyses obtained great accordance. These results indicate that VDI 2230 standard adequately represents the mechanical behavior of the joint and should be used as a guideline for the reliable design of bolted joints subjected to the loading conditions of the present paper.

Interval estimation for contact stiffness of bolted joint with uncertain parameters

Bolted joints are elements used to create resistant assemblies in the mechanical system, whose overall performance is greatly affected by joints’ contact stiffness. Most of the researches on contact stiffness are based on certainty theory whereas in real applications the uncertainty characterizes the parameters such as fractal dimension D and fractal roughness parameter G. This article presents an interval estimation theory to obtain the stiffness of bolted joints affected by uncertain parameters. Topography of the contact surface is fractal featured and determined by fractal parameters. Joint stiffness model is built based on the fractal geometry theory and contact mechanics. Topography of the contact surface of bolted joints is measured to obtain the interval of uncertain fractal parameters. Equations with interval parameters are solved to acquire the interval of contact stiffness using the Chebyshev interval method. The relationship between the interval of contact stiffness and the uncertain parameters, that is, fractal dimension D, fractal roughness parameter G, and normal pressure, can be obtained. The presented model can be used to estimate the interval of stiffness for bolted joints in the mechanical systems. The results can provide theoretical reference for the reliability design of bolted joints.

분포하중을 받는 목재 적층복합재 빔의 볼트 체결 최적화 설계

Numerical analysis for various design parameters should be preceded by optimal design of composite materials. Numerous studies have been conducted on the bolting of interconnecting beams. In this study, the response surface method was applied to optimize the design of bolted joints connected by laminated wood composite beams. The response surface was created by combining the FEA code for composite analysis and the algorithm for forming the response surface. Optimization on this response surface was performed with a genetic algorithm to derive the results. The determination of the optimum bolt-hole position for the connection of composite beams is an optimization problem. Tsai-Wu composite failure index, maximum deflection, and simple von Mises stress are set as the objective functions. It has been proved that the design results of the optimized bolt-hole are superior to the design performance of the existing conventional bolt-hole position.

A global-local finite element analysis of hybrid composite-to-metal bolted connections used in aerospace engineering

Efficient bolted joint design is an essential part of designing the minimum weight aerospace structures, since structural failures usually occur at connections and interface. A comprehensive numerical study of three-dimensional (3D) stress variations is prohibitively expensive for a large-scale structure where hundreds of bolts can be present. In this work, the hybrid composite-to-metal bolted connections used in the upper stage of European Ariane 5ME rocket are analyzed using the global-local finite element (FE) approach which involves an approximate analysis of the whole structure followed by a detailed analysis of a significantly smaller region of interest. We calculate the Tsai-Wu failure index and the margin of safety using the stresses obtained from ABAQUS. We find that the composite part of a hybrid bolted connection is prone to failure compared to the metal part. We determine the bolt preload based on the clamp-up load calculated using a maximum preload to make the composite part safe. We conclude that the unsuitable bolt preload may cause the failure of the composite part due to the high stress concentration in the vicinity of the bolt. The global-local analysis provides an efficient computational tool for enhancing 3D stress analysis in the highly loaded region.