Bolt-ball Joints Research Articles

Damage analysis and mechanical performance evaluation of frame structures in recycling

Research on the recycling of space frame structures is beneficial to reduce the waste of resources and has important engineering application prospects. Repeated disassembly tests were carried out on a full size space frame structure with bolt-ball joints. The maximum number of cycles was 3. The test results showed that with the increase of the number of cycles, the damage of joints and tubes gradually increased, the phenomenon of false tightening increased, and the construction efficiency decreased. After three cycles, the damage of high-strength bolts accounted for 16.56 % and the damage of steel tubes accounted for 5 %. Due to the component damage and construction deviation, the deformation and stress of the structure after unloading could not be restored to that before loading. However, within three cycles, the overall displacement and stress of the frame structure under general roof loads were almost not affected by component damage and construction deviation. Furthermore, the distribution pattern of displacement and stress was independent of the number of cycles. The maximum mid-span displacement of the structure was about 80 mm and the maximum difference of the overall stress level was within 10 MPa. Finally, according to the test results, the relevant engineering suggestions for the recycling of space frame structures were put forward.

Experimental and numerical investigation on the impact response of bolt-ball joints

The densely populated space lattice structure requires reliable performance under impact loads. The bolt-ball joint serves a crucial role in connecting members at various angles, significantly contributing to the overall safety of the structure. However, there is limited literature available on the impact resistance of the bolt-ball joint. In this study, the drop hammer impact test system was employed to conduct impact tests on 11 specimens of bolt-ball joints. Comprehensive records were maintained, including the final deformation states, video recordings of the impact process, and data on impact force, displacement, and strain. Additionally, numerical simulation analysis was conducted to expand the scope of the study. Five failure modes were observed: global bending deformation, bolt fracture, local denting, coupling deformation of local denting and global bending deformation, bolt and tube fracture. When the impact applied at the bolt ball or conical head and steel tube welding positions, the impact process was categorized into three stages: inertia, global bending deformation, and elastic recovery/bolt fracture. When the impact position was the steel tube, coupling deformation and elastic recovery/ bolt and tube fracture were observed. The energy absorption during the impact test was analyzed, revealing a positive correlation between the degree of specimen failure and the proportion of energy absorbed relative to the work done by the impact force. The effects of impact velocity, impact position, bolt dimension and impact angle on the dynamic response of the specimens were thoroughly analyzed.

Study on the tensile performance degradation of bolt-ball joints after bolt-thread corrosion

Bolt-ball joints, which have been used in corrosive environments for a long time, are prone to corrosion problems, particularly in the contact area between the bolt and the ball, posing a threat to the overall structural safety. This paper established a refined finite element model of bolt-ball joints that considers the effects of bolt-thread corrosion and corrosion products using an integrated simulation method of 3D corrosion evolution and mechanical properties of steel building components. The reliability of the simulation method was verified through several tensile tests. Subsequently, the stress distribution and load-displacement curves of M20, M24, and M27 joints with varying degrees of corrosion were analyzed after tension. The results indicate that when the corrosion mass loss rate is less than 80%, the tensile failure mode of the joint is bolt rod yielding. However, when the mass loss rate of the thread reaches 80%, the failure mode is ball thread yielding. For joints with the same thread mass loss rate and section area, the bearing capacity degradation increases as the bolt diameter increases. Additionally, for joints with different cross-sectional areas of threads, the bearing capacity degradation rate is higher when the cross-sectional area of the thread is smaller. Finally, a degradation formula for the tensile bearing capacity, taking into account the corrosion mass loss rate and bolt diameter, was proposed through regression analysis. This formula serves as a technical reference for the safety evaluation of corroded bolt-ball joints and similar joints.

An efficient robotic-assisted bolt-ball joint looseness monitoring approach using CBAM-enhanced lightweight ResNet

Bolt-ball joints are widely used in space structures, and their looseness may lead to major safety accidents. The current bolt monitoring methods based on deep learning usually have high computational complexity, and it is difficult to guarantee its computational efficiency under practical scenario. To mitigate this problem, here in this paper, an efficient robotic-assisted bolt-ball joint looseness monitoring approach using convolutional block attention module (CBAM)-enhanced lightweight ResNet is proposed. Firstly, the robotic-assisted tapping method is applied to bolt-ball joints to generate audio signals, which are constructed into time-frequency maps by continuous wavelet transform. Secondly, the original ResNet is improved as a lightweight network, which successfully reduces model complexity, and employs time-frequency maps as input. Then, CBAM is introduced to capture global information and focus on the critical feature. Thus, the efficiency of feature extraction is significantly improved. Finally, by the overall optimized structure, a CBAM-enhanced lightweight ResNet model is established to monitor the bolt-ball joints looseness state accurately. Experimental results demonstrate the high efficiency while maintaining very lightweight structure of the proposed method, verifying the effectiveness and superiority of the robot-assisted approach using CBAM-enhanced lightweight ResNet over other methods.

The Effect of Preload Loss on the Mechanical Properties of Grid Structure Connected with Bolted-Ball Joints

Bolt-ball joints are widely adopted in grid structures due to their high installation accuracy and short construction period. Since the bolt is inside the joint, it is challenging to evaluate its health status from outside the structure. A finite-element plane-truss structure model, based on the actual grid structure, was constructed to investigate the influence of the rod’s preload on the overall stiffness and bearing capacity of the grid structure. Moreover, a model of the grid structure, with a bolt-ball joint connection, was constructed to analyze the influence of the preload loss in bolted-ball joints on the overall mechanical performance of the local members and structures. The results show that the release of preload on the outer web rod is less effective in terms of the overall stiffness and bearing capacity of the structure than on the inner web rod. The preload of the larger span direction rod plays an important role, and the preload of the upper chord has a greater impact, while the preload of the web rod and the upper chord in the smaller span direction has no significant effect on the normal stress in the surrounding rods.

Optimization of continuous drive friction welding process for AA6061-T6 circular pipe and conical head

Aluminum alloy double-layer grid structure with bolt-ball joint has the advantages of light weight, corrosion resistance, convenient construction, etc. However, when circular pipe and conical head are connected by fusion welding, its strength is low. In order to solve this problem, the continuous drive friction welding (CDFW) process of aluminum alloy circular pipe and conical head and its strength of joint were studied in this paper. Based on the orthogonal experiment scheme, the CDFW experiments were conducted on AA6061-T6 circular pipe, then the tensile tests were completed on the standard samples to obtain joint efficiency under different welding parameters. The optimum welding parameters were determined by the method of variance and range analysis. The microstructure of joints was characterized by hardness test, OM, XRD, SEM, etc. The test results show that parameters affecting joint efficiency are friction pressure, rotational speed and upsetting rotational speed in descending order. Under the optimal welding process, the joint efficiency can reach 87.0%, which is superior to fusion welding. The fracture form of the welded joint is a mixture of intergranular and ductile transgranular fracture. WNZ is the crucial region of the welded joint, where the grain growth is greatly influenced by friction pressure. The friction pressure of the optimal welded joint is moderate, so the grains in WNZ are fine and grow adequately. The hardness softening of the welded joint also has certain influence on its mechanical properties. The solid solubility of the optimal welding sample is high and alloy elements are stable in the Al matrix, so it exhibits good mechanical properties. Finally, the CDFW experiments and tensile tests of circular pipe and conical head were conducted, which verifies the effectiveness of the optimal welding parameters.

Comprehensive Investigations of the Effect of Bolt Tightness on Axial Behavior of a MERO Joint System: Experimental, FEM, and Soft Computing Approaches

In the present experimental study, 12 specimens were tested to assess and quantify the effects of bolt tightness on the overall behavior of a bolt-ball joint under uniaxial loading. A three-dimensional (3D) nonlinear finite-element (NFE) model with all geometrical complexities, including the threads, was developed to examine the significance of bolt tightness on overall behavior. Three types of parameters were studied, namely, tightness torque, material properties, and friction coefficients. The tests showed that the tightness torque moments had a significant effect on the axial stiffness of the specimens under compressive loading. Observations during the tests indicated that the bolt and sleeve had important roles in the load transferring mechanism. Based on the results of the current experimental study, the finite-element model (FEM) was verified against the test specimens. An acceptable qualitative agreement was observed between the FE models and the experiments for the axial behavior of the joint. It was found that the material properties had a significant role in changing the failure mode and load-bearing capacity. Based on experimental tests and NFE analyses, the present study provides a nonlinear model for determining the relationship between the torque and the preload using gene expression programming. It was concluded that the simplified formulation proposed in this study can calculate the relationship between the torque and the initial load against the bolt tightness database with good accuracy.

Experimental and numerical studies on a new type of bolt-ball joint for spatial grid structures

The insufficient tightening due to workmanship and bolt loosen during the life cycle of spatial structures are common safety hazards in the installation process and the use stage of spatial structures. To tackle these problems, in this paper, a new type of bolt-ball joint with octagonal high-strength bolt is developed for conventional spatial structures. For this new type of node, the force was transmitted through the contact between the high-strength bolt and the inner wall of the octagonal sleeve, and the bolt is screwed into the bolt ball to avoid the shear forces on the pins. After installation, by checking whether the tail of the pin is flush with the outer surface of the sleeve, it will be easy to judge whether the high-strength bolt is properly tightened. To investigate the behavior of this new type of nodes, an experimental study on the tensile performance of octagonal high-strength bolts was performed. It is found that, the tensile strength of the octagonal high-strength bolts for this new type meets the requirements of the Chinese specification. Further detailed experimental studies and numerical simulations were carried out to investigate other nodes, namely steel-pipe, cone head/sealing plate nodes. The results show that the stress distribution and dimensions of the whole joints and the bearing capacity of the cone head are similar between the two nodes. The compressive test of the proposed new type of sleeve is also carried out, and the results show that the failure load is more than 3 times the required design value. Finally, the torsion bearing capacity test of this new type of node is carried out. The results show that the torsional bearing capacity of the new nodes during installation is much greater than that of the traditional ones.

If structure can exclaim: a novel robotic-assisted percussion method for spatial bolt-ball joint looseness detection

In proportion to the immense construction of spatial structures is the emergence of catastrophes related to structural damages (e.g. loose connections), thus rendering personal injury and property loss. It is therefore essential to detect spatial bolt looseness. Current methods for detecting spatial bolt looseness mostly focus on contact-type measurement, which may not be practical in some cases. Thus, inspired by the sound-based human diagnostic approach, we develop a novel percussion method using the Mel-frequency cepstral coefficient and the memory-augmented neural network in this article. In comparison with current investigations, the main contribution of this article is the detection of multi-bolt looseness for the first time with higher accuracy than prior methods. In particular, in terms of new data obtained via similar joints, the memory-augmented neural network can help avoid inefficient relearn and assimilate new data to provide accurate prediction with only a few data samples, which effectively improves the robustness of detection. Furthermore, percussion was implemented with a robotic arm instead of manual operation, which preliminarily explores the potential of implementing automation applications in real industries. Finally, experimental results demonstrate the effectiveness of the proposed method, which can guide future development of cyber-physics systems for structural health detection.

Effect of insufficient screwing depth of bolt on mechanical behavior of bolt-ball joint and stability of single-layer reticulated shell

This paper is aimed at exploring the mechanical behavior of bolt-ball joint with insufficient screwing depth of bolt. Such insufficient bolt connection was quantified as the thread screwing error. Experimental work was conducted to investigate the tensile behavior of the bolt-ball joint with insufficient bolt connection. It was found that three failure modes occurred in the joint, including the tube failure, bolt rod failure and thread failure. The tensile capacity of joint with thread failure decreased in an approximate linear manner with respect to the thread screwing error. A detailed finite element model of bolt–ball joint with thread part was established and verified by the tension test and a previous bending test. The moment-rotation curves of bolt–ball joint with insufficient bolt connection were obtained via the detailed model. These curves were then used to study the stability of Kiewitt 8 single-layer reticulated shells considering bolt-ball joints with insufficient bolt connection. The results showed that the stability capacity of reticulated shells with different rise-span ratios exhibited varied decrease. An obvious decrease occurred on the reticulated shells with 1/8 rise-span ratio. The proposed finite element methods provide a basic for the further parameter analysis of single-layer reticulated shells.

Numerical Investigation of the Behavior of MERO Joint System Under Combined Loading Regarding Helical Threads of Elements

A comprehensive finite element (FE) model of bolt-ball joint, as called MERO joint, is presented in this paper for a double layer grid structure. In double layer grids, the main internal forces are axial forces. The deflection and rotation patterns of the connector are studied under different loading conditions using the ABAQUS FE software. The applied forces on the connector are determined using displacement control. In order to take into account the connector effects in structural analysis, their behavior under combined loading should be predicted. To determine the load–displacement relationship of the MERO connection, numerical models were carried out on a connector of this type using of 3D FE method. The obtained load–displacement and moment- rotation relationships were used under different loads. The results of the FE simulation with experimental results have a good match. Compressive axial load increases the flexural stiffness of the connection and decreases the elastic bending moment. Furthermore, the equivalent stiffness of bolt with the whole of complexities was proposed.

Buckling behavior of a circular steel tube with a bolt–ball joint under installation eccentricity

An issue that frequently occurs during the installation of a spatial grid structure is that the tube exhibits bending under installation eccentricity, and the buckling stability of the tube significantly decreases. In the study, eccentric compression tests of circular steel tube with a bolt–ball joint are carried out, in which three types of joint specifications and three types of installation eccentricities are considered. The degradation characteristics of the buckling stability of circular steel tubes under different installation eccentricities are obtained via tests. Similar phenomena of tube buckling are observed under different installation eccentricities. Additionally, detailed finite element models with bolt threads are established via ANSYS. A comparison of simulation and test results indicate good agreement, and this confirms the validity of the numerical simulation method. Then, a total of eighteen simulation schemes for the buckling behavior of tube under different eccentricities are studied, regarding three different joint specifications with six tube specifications for each. The results indicate that the stability capacity decreases in an approximate linear manner with respect to the installation eccentricity in the range of 0–15 mm, which is consistent to the test results, and the decreasing speed slightly drops while the eccentricity goes large. A reduction factor is proposed as the reference for considering the reduction of stability capacity of the tube under different eccentricities in engineering design.

Analysis on mechanical property of tensile bolt-ball joint with sealing platein high temperature

Elastic-plastic solid finite element model of bolt-ball joint with sealing plate was established. The mechanical performance of bolt-ball joint in high temperature was performed with finite element analysis. The stress distribution, ultimate bearing capacity and failure mode of bolt-ball joint in high temperature were studied. The results show that bolt-ball joint is eventually damaged on the sealing plate by bent, and plastic penetrating zone along the thickness direction of sealing plate is discovered. The stress of screw threads is large, and stress of bolt ball is very small except the part near threads. The stress of bolt is large, but do not reach the yield strength. When the temperature higher, the ultimate bearing capacity of bolt-ball joint is smaller.

The stability and stressed skin effect analyses of an 80 m diameter single-layer latticed dome with bolt-ball joints

Recent researches have demonstrated that bolt-ball joints have a certain amount of flexural stiffness, so they should be classified as semi-rigid joints and it is possible to apply them on single-layer latticed domes. In order to study the stability and stressed skin effect of the latticed domes with bolt-ball joints, a series of nonlinear full-produce analyses were conducted on the basis of the design of an 80 m diameter single-layer latticed dome with bolt-ball joints, which is the main structure of the Shenbei New District citizen fitness center in Shenyang, China. Above all, the moment-rotation relations for bolt-ball joints, which were established based on numerical results, were introduced into the latticed dome numerical model. Then, the nonlinear stability analyses for the latticed dome in different construction stages were carried out by the above-mentioned numerical model under vertical loads and horizontal wind loads. The mechanical behaviors discussed in this investigation including the stability and the ultimate bearing capacity of the latticed dome in different construction stages, and the influence of the stressed skin effect on the stability of the latticed dome with decorated plates. The result shows that: after being properly designed, the latticed dome with bolt-ball joints can exhibit a good mechanical performance, and this successful application of bolt-ball joints on the Shenbei New District citizen fitness center can set an example project for the design of single-layer latticed domes with semi-rigid joints; under vertical loads, it is more dangerous for the 75% complete latticed dome, while the dangerous construction stage for horizontal wind loads is the 50% completed latticed dome; the stressed skin effect can increase the stability of latticed domes.

Damage Models and Assessment Methods

Damage assessment based on the vibration response of structures has been, in the last decades, an important research area in various engineering branches. It integrates knowledge from a variety of disciplines, such as mechanical and structural engineering, material science, computer science and signal processing, and data management. This special issue is dedicated to fundamental understanding of the vibrational behavior of damaged structures and to the development of methods and techniques that are able to tackle these specific problems. A number of 23 papers have been submitted, from which a total of 7 papers have been finally selected to integrate the present issue. Two among them are focused on failures in machineries: W. Wen et al. in the paper “Planetary Gearbox Fault Diagnosis Using Envelope Manifold Demodulation” extract fault characteristics from the vibration signals, since in “Undecimated Lifting Wavelet Packet Transform with Boundary Treatment for Machinery Incipient Fault Diagnosis” by L. Duan et al. a Volterra series assisted undecimated lifting wavelet packet transform is investigated for machinery incipient fault diagnosis. The presented approaches dramatically enhance the weak defect feature extraction. Damages in structural elements are the target of research presented in “Development of a Vehicle-Bridge-Soil Dynamic Interaction Model for Scour Damage Modelling” by L. Prendergast et al., “Feature Recognition forMine HoistingWire Rope Based on Magnetic Flux Leakage Signals” by Z. Zhao et al., and “Experimental Study on Progressive Collapse Performance of Frame with Specially Shaped Columns Subjected to Middle Column Removal” by T. Wang et al. A model updating strategy for bolt-ball joint stiffness characterization for health monitoring is presented in “Finite Element Model Fractional Steps Updating Strategy for Spatial Lattice Structures Based on Generalized Regression Neural Network” by C. Liu et al. An interesting method to perform efficient fatigue tests is proposed by Y. Jiang et al. in the paper “Experimental Design and Validation of an Accelerated Random Vibration Fatigue Testing Methodology.” They succeed to significantly reduce the test time and the sample size. The papers reflect, without doubt, significant researches and developments of this subject. We hope that readers will find all articles of the special issue useful and exciting and that the articles will stimulate further research activities in the area of damage assessment.

Finite Element Model Fractional Steps Updating Strategy for Spatial Lattice Structures Based on Generalized Regression Neural Network

In order to get a more accurate finite element model of a spatial lattice structure with bolt-ball joints for health monitoring, a method of modifying the bolt-ball joint stiffness coefficient was proposed. Firstly, the beam element with adjustable stiffness was used in the joint zone in this paper to reveal the semirigid characteristic of the joint. Secondly, the value of stiffness reduction factor (ar) was limited in the range of[0.2,0.8]and the reference value (ar0) of it was suggested to be 0.5 based on referenced literatures. Finally, the finite element model fractional steps updating strategy based on neural network technique was applied and the limited measuring point information was used to form the network input parameter. A single-layer latticed cylindrical shell model with 157 joints and 414 tubes was used in a shaking TABLE test. Based on the measured modal data, the presented method was verified. The results show that this model updating technique can reflect the true dynamic characters of the shell structure better. Moreover, the neural network can be simplified considerably by using this algorithm. The method can be used for model updating of a latticed shell with bolt-ball joints and has great value in engineering practice.

Experimental and numerical studies on a single-layer cylindrical reticulated shell with semi-rigid joints

Most existing studies on single-layer spatial structures with semi-rigid joints were focused on spherical domes. The present paper analyzed the squared plan-form single-layer structures, examining the influence of joint-rigidity on the mechanical performances of the structures. An experiment has been conducted on a 5×6m single-layer cylindrical reticulated shell with semi-rigid bolt-ball joints. The mechanical performance of the latticed shell is investigated in detail. Finite element analysis (FEA) model of the latticed shell is established taking material and geometric nonlinearities into account. The results show that the behavior determined using the FEA models correlates well with the experimentally observed behavior for the single-layer structures with semi-rigid joints.

Experimental Study on the Mechanical Property of Visual Bolt-Ball Joint System

Grid structures with bolted spherical joints suffer impairment because of the “fake tightened-up” phenomenon. To prevent the “fake tightened-up” phenomenon, this study presents a new type of visual bolt-ball joint system that visually and effectively estimates the length of threads inserted into the bolt hole after adjusting the position of the fixed trip bolt and the location of the chute. The ultimate bearing capacity of the high-strength bolt and sleeve are studied via experiments. Results show that the failure section of high-strength bolts is the inclined section, which has a 60° angle to the direction of the screw, and a formula for calculating the ultimate bearing capacity is derived. Sleeves are compressed as their bearing failure is strength failure, which is due to yielding of the net section. A design method of the visual bolt-ball joint system is put forward according to the experimental results, and the safety of the visual bolt-ball joint is verified. Finally, the ductility and the fatigue performance of the visual bolt-ball joint are discussed in the paper.

Seismic Behaviour and Seismic Design of Single-Layer Reticulated Shells with Semi-Rigid Joint System

An investigation of the seismic behaviour and a design method for single-layer reticulated shells with semi-rigid joints is described in this paper. A semi-rigid joint system has some bending and rotational rigidity that lying between that of a rigid-joint and a pin-joint. The seismic capacity of Kiewit reticulated shells with bolt-ball joints is analyzed in detail on the basis of the bending rigidity of the bolt-ball joint reported by others. The change rules of natural frequency and seismic internal force coefficient are reviewed by analyzing of large-scale shells with different span, depth-to-span ratio, bending rigidity, roof load, section size of members and seismic wave parameters. The seismic internal force coefficient (under the influence of bending moment) for shells with a semi-rigid joint system is summarized statistically to provide the maximal seismic response envelop.

Advances on the Influence of Joint Stiffness on Mechanical Behavior of Single-Layer Reticulated Shell

The bolt-ball joints and welded hollow spherical joints are used frequently in the reticulated structures. Many researches on the influence of the bolt-ball joints stiffness on dynamic and static mechanical behavior of these structures are carried out by far. This paper reviews these researches, and points out the limitation as well, then the future work of which has been put forward. In addition, the progress made in our work team in this filed is illustrated.