Screw Connections Research Articles

Experimental and analytical behaviour of light gauge steel-fast growing timber composite shear connections

The shear performance of screw connections plays an essential role in the steel-timber composite (STC) members and structures. Plenty of monotonic push-out tests on the screw connections have been conducted, but there has been lack of cyclic tests for steel-timber screw connections. Seven groups of quasi-static tests on light gauge steel-fast growing timber screw connections are reported to research seismic performance, load capacity and failure modes. The use of fast growing timber is found not to degrade the hysteresis performance and increasing the diameter of self-tapping screws contributes to a significant improve in connection performance. Rope effect analysis and parametric analysis are further carried out based on ABAQUS finite element software. Furthermore, the applicability of Foschi and Folz theoretical model to the nonlinear load-slip behavior of the specimens is investigated, and the theoretical fitting results are in good agreement with the experimental results, and it is a meaningful study of the application of timber design experience to light gauge steel-fast growing timber composite structures.

Experimental Determination of the Coefficient of Friction on a Screw Joint

This paper deals with the coefficient of determination of screw connection friction between the thread and the matrix. The coefficient of friction was measured using a laboratory device with an M20 screw connection without any grease and, subsequently, plastic grease was added (CX80 silicone, lithium, and copper grease). When grease is added, the friction in the threads and screw heads is limited and consistently retained. When tightening by torque, which represents the prevailing assembly method in standard screwing practice, only part of the torque is effectively used to create axial force and pre-stress. The rest of the torque is employed in friction suppression between threads and converted into heat. In general, the coefficient of friction depends on diverse factors such as the roughness of the thread surface, the gradient angle of the helix, and the grease properties. The tightening torque represents a primary parameter in the experimental measurements, monitored using a digital torque spanner, and generates an axial force in the screw. Based on the aforementioned parameters, the objective of this paper was to monitor changes in the coefficient of friction between the thread of the screw and the matrix in the case of different grease types. The actual coefficient of friction was calculated through the exponential equation of the torque balance. First measured was the load of the bolted joint without the use of grease, where the average value of the coefficient of friction was 0.44732; this value served as a benchmark for comparison to the measurements with the use of grease. The measurements showed that the value of the friction coefficient was reduced by 30.57% when using lithium grease, by 40.56% when using silicone grease, and by 47.64% when using copper-based grease, making the latter the most suitable for the application. Without appropriate greasing, friction suppression was accompanied by extremely high torques, which resulted in insufficient screw prolongation.

Testing, numerical and analytical modelling of self-drilling screw connections between thin steel sheets in shear

The shear behaviour of self-drilling screw connections between thin steel sheets is investigated via experimental testing, numerical and analytical modelling in this paper. A total of nineteen sets of single-lap joint specimens with self-drilling screw connections were tested to failure under shear. The full force versus deformation curves were recorded, and three typical failure modes were obtained and were shown to be closely related to the ratio of the screw diameter to the sheet thickness. Prior to testing, constitutive responses of the employed thin steel sheets were acquired from tensile coupon tests, and were further represented by a three-stage model including an elastic branch, a plastic branch described by the Ludwik equations, and a damage branch defined by the Johnson–Cook model and the linear accumulation damage evolution law. Advanced finite element (FE) models of the screw connections were developed and validated against the obtained shear test results, and a parametric study on the influences of the sheet thickness and the screw diameter was carried out afterwards. Based on the obtained test and FE results, a new prediction model for the shear deformation behaviour of self-drilling screw connections was proposed and calibrated. The newly proposed prediction model was further introduced into the numerical models of the cold-formed box girders fabricated by self-drilling screws, the applicability of which was verified by the close agreement with the available experimental evidence.

Contact resistance measurement methods for PEM fuel cell bipolar plates and power terminals

The electrical contact resistance is a key parameter for optimising both the bipolar plate of the polymer electrolyte membrane fuel cell (PEMFC) and the electrical contact of the power terminal of the stack. The contact resistance is affected by the conductivity, roughness, and hardness of the two contacting surfaces. Here, new, application-specific contact resistance measurement methods are proposed for both the stack power terminal, and the bipolar plate. The proposed methods are compared to methods from references as well as standards, and it is concluded that the uncertainty of the measurements can be reduced by changing the measurement setup, and that the influence of probe resistance on measurement results can be eliminated. Furthermore, the effect of different accelerated durability tests on the contact resistance of the power terminal is examined both on test coupons and on a prototype screw connection with an electroless NiP and an electroplated NiSn coatings. As expected, the NiSn coupons gives lower contact resistance after ageing as compared to the NiP. However, the increase in contact resistance seen on coupons after ageing is not observed on the prototype screw connection.

Numerical Modelling of Timber Beams with GFRP Pultruded Reinforcement

Timber structural members have been widely adopted and used in construction due to their inherent characteristics. The main objective of this work is to assess the performance of timber beams with GFRP pultruded beam reinforcement subjected to flexure. A finite element model (FEM) using ABAQUS FEM software is developed, aiming to provide a benchmark modelling procedure. The modelling method considers the fundamental role of the connections among timber beams, the reinforcing GFRP pultruded profile (adhesive and screw connections), and the grain direction in the timber. To understand the influence of the grain direction, different angles of deviations between the longitudinal direction (along the grain) and the beam axis are considered. The robustness of the developed FEM procedure is validated by the experimental results of timber beams with and without GFRP pultruded reinforcement under flexure. It is demonstrated that the angle of deviation (grain deviation) produces high reductions in the strength of unreinforced timber beams. However, this effect is minimal for GFRP-reinforced timber beams. The experimentally derived benchmark FEM procedure can be used as a computational tool for timber beams with GFRP pultruded reinforcement to capture the capacity, failure mode, and load–displacement response.

Design of sheathed built-up nested CFS channel studs in load-bearing LSF walls

Cold-formed steel built-up nested channel (NC) sections have been increasingly used to replace the commonly used lipped channel sections as the load-bearing studs of light gauge steel framed (LSF) walls with higher compression capacity. However, the related knowledge is limited and no research study has investigated such NC stud walls yet. In this study, an investigation was undertaken on the compression behaviour and capacity of LSF walls made of slender NC studs sheathed with gypsum plasterboards on both sides. Compression tests of sheathed NC studs were conducted first, which were then used in developing and validating suitable finite element models. The results obtained from tests and finite element models showed that plasterboards and stud-to-board screw connections had significant influence on the failure mode and compression capacity of sheathed NC studs, while the end fastener groups recommended in the current cold-formed steel design standards and the stud-to-stud screw connections had only marginal effects. Finally, a simple and conservative design method was proposed based on the Direct Strength Method equations in the current design standards. This paper presents the details of this research study, including the results, discussions and main findings.

Design of built-up back-to-back CFS channel compression members sheathed with gypsum plasterboards

Built-up back-to-back cold-formed steel channel (BC) members are increasingly used as studs for increasing the compression capacity of light gauge steel framed (LSF) walls, even though the knowledge of their behaviour is limited. In this study, the behaviour and capacities of LSF walls made of slender BC members sheathed with gypsum plasterboards on both sides were investigated using a series of compression tests and detailed finite element studies based on validated models. The numerical and experimental results showed that (1) screw connections of BC members had marginal effects on the compression capacities of the investigated sheathed BC members with non-staggered stud-to-board screw arrangement, and the capacities were mostly equal to twice the capacities of their individual members, (2) the restraints provided by the plasterboards and stud-to-board screw connections effectively prevented sheathed BC members from in-plane flexural buckling and considerably improved their compression capacities, and (3) the Direct Strength Method in the current design standards in combination with the guidelines and recommendations proposed in this study conservatively predicted the compression capacities of these members. Details of this research study, its results and findings are presented in this paper.

Dynamics Modeling and Characterization of Sunk Screw Connection Structure in Small Rockets

Bolted flange joints are widely used in engineering structures. Sunk screw connection structures commonly used in small rockets and missiles exhibit significant nonlinear characteristics when subjected to forces. In this article, a study of the dynamic characteristics of sunk screw connection is conducted. A 3-dof trilinear dynamic model is proposed, based on the study of the stiffness characteristics of the connection structure and considering contact nonlinearities. The connection surface is simplified as two axial trilinear springs and a lateral linear spring. The motion of the system can be divided into nine regions by the turning point of the trilinear springs. So that the motion of the system in each region can be completely resolved, the dynamic characteristics of the 3-dof trilinear system under impulse load and simple harmonic load are studied by means of semi-numerical analytical method. It is found that the response frequency of the system remains unchanged under a small impulse load, and the response can be obtained by approximate analytical expressions. When the impulse load is large, the response frequency is fluctuant, which reflects the sensitivity of the nonlinear system to the magnitude of impulse load. Under the simple harmonic excitation of bending moment, the response frequency curve of the system presents good single peak characteristics when the excitation amplitude is small. When the amplitude is large, the peak frequency of the system shifts, and the phenomenon of multi-peak resonance is shown in a certain range.

Parametric study on the pull-out performance of screw connections in cold-formed thin-walled steel structures

Screw connections have been extensively used in cold-formed steel constructions due to convenient construction and high capacity. However, little attention has been paid to the pull-out performance and parametric effects of screw connections. In this paper, the pull-out performance of screw connections is experimentally and numerically investigated. The objective of this study is to develop a refined finite element (FE) model that can be used to parametrically analyze the pull-out performance of screw connections. Eight sets of experimental results are selected for comparison with the FE results to validate the accuracy of the FE model. Based on the validated FE model, parametric analyses of the main variables in screw connections are conducted to discuss the effects of the tensile strength, the steel plate thickness, screw diameter and the ratio of thread pitch to plate thickness on the pull-out performance of screw connections. The results indicate that the failure modes of specimens are mainly classified into screw hole extrusion and thread shear failure. It is also found that the tensile strength, the steel plate thickness, screw diameter and the ratio of thread pitch to plate thickness have significant effects on the pull-out resistance of screw connections. Particularly, the numerically obtained pull-out resistance are used to assess the accuracy of the codified design rules for screw connections, as given in the Chinese Code, North American Specification, British Standard and European Norm. The evaluation results reveal that the current design formulas are relatively conservative. The formula proposed by one referenced paper is insecure, while the distribution trend is basically consistent with the straight line of PS/PFEM = 1.0 (the ratio of the calculated values to the FE values is equal to1.0), therefore, it can be used as a good reference for calculating the pull-out resistance of screw connections. Besides, the modified design formula in this study has good applicability.

Experimental research on seismic performance of cold-formed thin-walled steel frames with braced shear panel

The traditional cold-formed thin-walled (CFTW) steel sheathed walls are prone to have misalignment at the joints of wall panels and the damage of self-tapping screw connections under earthquake, resulting in obvious pinching of the hysteretic curves. In order to improve the energy dissipation and shear bearing capacity of the lateral resisting member in CFTW steel structures, an innovative structure called CFTW steel structure with braced ductile shear panel (CFTW-BSP) was proposed in this paper. Four full-scale one-story one-bay CFTW-BSP specimens containing two X-shaped and two K-shaped brace specimens were designed and tested under horizontal cyclic loads. The effects of configuration types, shear panel aspect ratios and slotted holes were investigated by comparing the lateral performance. In addition, the replaceability of the shear panel damper was analyzed. In general, the specimens performed well with a stable and plump energy dissipation capacity. The plastic deformation concentrated on the shear panel before 2% interstory drift, and then the end stud bases yielded and cracks propagated near the hold-downs at the ultimate stage. The braces always remained elastic during the tests. For X-shaped brace specimens, the slotted holes on shear panel can improve the ductility but decrease the energy dissipation capacity of the structure. For K-shaped brace specimens, the lateral resistance of the structure can be improved by decreasing the shear panel aspect ratio.

DSM design of LSF walls subject to distortional buckling

With the new advancements in constructions technologies, the use of cold-formed steel (CFS) construction is becoming popular due to its inherent advantages over conventional construction materials. These high performing CFS sections, such as the web stiffened lipped channel studs, are more likely to be subjected to distortional buckling under compression load. Although many numerical and experimental studies have been undertaken on unsheathed CFS columns subjected to distortional buckling, there is limited research on light gauge steel framed (LSF) walls subject to distortional buckling. The behaviour of sheathed wall studs is significantly different to that of columns due to the complicated boundary conditions provided by the stud-to-sheathing contact interactions and screw connections. Although CFS design standards recognize the sheathing boards as a means of providing lateral and rotational restraints, they do not provide any information on their effects on studs subject to distortional buckling. In this study, the suitability of currently available numerical modelling techniques on predicting the distortional buckling behaviour of LSF walls was investigated. It was identified that the distortional buckling capacity is highly sensitive to the in-plane restraints provided by screw connections. The effects of stud geometry, stiffness of screw connections and stud length on the distortional buckling capacity were investigated in a detailed numerical parametric study involving more than 3500 finite element analyses. Finally, the accuracy of the current direct strength method was investigated and suitable modifications are proposed. Moreover, alternative simplified design methods and their accuracy are also discussed.

Parametric Study of the Numerical Model of a Bolted Connection of Steel Structure for Photovoltaic Panels.

In the face of the reality that unexpectedly mobilized the governments of most central European countries (including Poland), the development of renewable energy sources (RES) seems to be an important direction. Therefore, both wind parks and solar farms will be constructed at double speed for energetic independence. This urgency makes the market of producers of structures for mounting solar panels also need to adapt quickly to the new situation. New constructions adapted to quick assembly with the use of nutless screw connections seem to be one of the best solutions. These structures must not only be easy and quick to install but also durable, which makes the connections resistant to cyclical loads. The speed of assembly of the substructure can be achieved precisely with the help of nutless connections, but their durability should be carefully analyzed. This article presents parametric analyses of the numerical model of this type of connection. The selection of appropriate numerical models for simulation is of key importance in the fatigue strength analysis of bolted connections. This article investigates two different models used in numerical fatigue analyses performed in the Abaqus FEA and FE-Safe program, namely, traditional bolt with nut and innovative self-tapping nutless bolt. Extended parametric analyses of both numerical models were carried out, which ultimately allowed optimization of the fatigue capacity of the connection.

Numerical modeling on shear performance of braced cold-formed steel composite walls

In this paper, the specific influence of diagonal braces on the hysteretic behaviors, including lateral stiffness, yield load, and load-bearing capacity, of braced composite cold-formed steel (CFS) walls have been investigated through the combination of previous experiment results and numerical analysis. A detailed modeling method using connector function in ABAQUS for simulating single screw connection has been introduced. Furthermore, the finite element models based on experimental specimens have been constructed, an excellent match of finite element analysis and experimental results are yielded to prepare for parametric analysis; five significant parameters, vertical load, panel splice type, screw spacing, section thickness of end studs, and diagonal braces, were considered in parametric analysis to in-depth investigate the hysteretic behavior of walls. Finally, some valued conclusions expected to be benefited engineering applications have been summarized.

Multi-level simulation studies on seismic performance evaluation of steel-sheathed cold-formed steel framing shear walls

Cold-formed steel (CFS) framing shear walls has been widely used as the lateral force resisting system of light-weight steel structures. While the behaviors of walls have been numerically studied, there is a need to develop more convenient and efficient modeling strategies. In this paper, a simulation framework consisting of component-level to system-level analysis for the seismic evaluation of steel-sheathed CFS walls was proposed by using OpenSees software. Based on the improved fastener-based method, refined numerical models were developed and validated against tests of steel sheathed CFS shear walls. Self-drilling screw connection tests were conducted to characterize the nonlinear properties of the member-to-sheathing connections as inputs in the models. Then, a set of structural archetypes were systematically analyzed by nonlinear static and incremental dynamic analysis in accordance with FEMA P695. The results showed that the proposed simulation framework could well capture the response of CFS walls and evaluate the seismic performance of structural system. The post-peak behavior of wall had a significant impact on the collapse resistance of the structure. The seismic response modification coefficient value was suggested (R = 4.25) for the high-performance steel-sheathed CFS framing shear walls studied in this paper.

A fully soft, self-powered vibration sensor by laser direct writing

Soft electronics are comprised of stretchable and user-friendly components that mechanically conform to complex surfaces and epidermis, extending their applicability over commercial electronics. Vibration sensors that detect operation conditions of common motions generally rely on rigid materials or tedious fabrications. Here, a fully soft self-powered vibration sensor (SSVS) engineered by laser-assisted fabrication is proposed. Different from its rigid counterparts, the device is constructed with entirely ductile materials including a liquid metal kernel and an elastic shell. Furthermore, laser direct writing elaborates intricate patterns and functional surfaces of SSVS in a rapid and mask-free manner. A ubiquitous IR laser combined with an origami-inspired transfer creates arbitrary out-of-plane electrodes on soft media, while a pulsed UV laser judiciously tunes nonstick microstructures to the liquid metal droplet. To demonstrate the capability on curved surfaces, the SSVS is interfaced with an exhaust silencer of an air compressor and detects failures of screw connection. Additionally, a cap reinforced by SSVS with wireless transmission is devised for motion monitoring, which effectively distinguishes slip from walking, jumping and running. This work affords promising routes toward monitoring complex machinery and remote guardianship for the vulnerable populations.

New predictive equations for tilting and bearing resistance of U-shaped shear connectors in composite cold-formed steel floor joists using neural networks and stepwise regression

Due to the low thickness of cold-formed steel (CFS) sections, welding of traditional studs on them is not recommended; and there is a need to use shear connectors suitable for this type of sections. In this paper, the behavior of U-shaped shear connectors as connectors compatible with CFS composite beams has been investigated, to offer practical relationships for predicting the ultimate strength of this type of connectors. Accordingly, after the development of finite element (FE) models with the ability to predict the ultimate strength of U-shaped connectors, their performance against experimental results was validated. Then, an extensive parametric study, consisting of 216 numerical samples, was accomplished to provide a reliable database. As the main and most important of this study, two methods of artificial neural networks and stepwise regression were developed, and practical formulations were proposed to predict the ultimate strength of U-shaped shear connectors in CFS composite beams. Finally, in addition to evaluating the accuracy of the proposed formulas, a comparison was made between them and the relationships proposed by AISI, AS/NZS and EC3 codes for CFS screw connections. The relationships presented in this paper can be used by practical engineers in the design process of CFS composite beams.

Cyclic performance of steel frame fabricated with cold-formed steel composite wall structure

In this study, a novel hybrid wall structure of a hot-rolled steel frame fabricated with a cold-formed steel (CFS) composite wall is proposed. Ceramsite concrete is lightweight concrete that is used in CFS composite walls. The seismic performances, including the failure mode, hysteretic behavior, shear capacity, stiffness, ductility, and energy dissipation performance, of four specimens of steel frame fabricated with CFS composite wall and one specimen of conventional CFS composite wall were evaluated under low-cyclic loading. The experimental results showed that the collaborative working performance of the steel frame and infilled CFS composite wall was optimum, and the proposed fabricated wall structure had a significant effect on the bearing capacity, stiffness, and energy dissipation capacity. The infilled CFS composite walls were damaged earlier than the steel frames. The damage was primarily characterized by the compressive failure at the corners of fillers, loss of diaphragm effect, screw connection failure, and bond-slip failure between the CFS framing and fillers. However, the steel frames exhibited no obvious damage, which effectively restrained the infilled CFS composite walls and prevented them from severe collapse. In addition, enhancing the strength of the fillers and increasing the section area of the studs improved the bearing capacity of the structure; however, they were detrimental to the ductility. Wall opening reduced the bearing capacity and initial stiffness of the structure; however, it improved the ductility. Furthermore, a superposition method was used to calculate the bearing capacity of the proposed structure. The calculated results showed a superior accuracy in comparison with the experimental results.

Experimental investigation of lateral resistance of CFS walls with rigid diagonal bracings

In this study, monotonic and reversed-cyclic loading tests were conducted on six diagonally reinforced cold-formed steel (CFS) shear walls sheathed with a gypsum board (GYP) and a magnesium crystal board (MCB), respectively, to evaluate the effects of sheathing panels and different types of diagonal bracings on the shear capacity, lateral stiffness, ductility, and energy dissipation capacity of CFS shear walls. The results revealed that the stiffness of the skeleton, the sheathing material, the performance of the screw connections, and the construction of the splice of the wall panels have a distinct effect on the shear performance of the wall. The cooperative work effect of the rigid and strap bracings was excellent, and the ultimate strength and lateral stiffness of the wall were effectively improved by using an extra steel strap bracing. The shear performance of the wall sheathed with the MCB was higher than that of the wall sheathed with the GYP. When a flat steel strap was used to connect the panel splices, the torsion of the flat steel strap reduced the overall performance of the wall panels. This should be considered in practical engineering applications.

Experimental and analytical study of Friction Connection for seismic retrofit with Cross‐Laminated Timber (CLT) panels

AbstractWithin the European project e‐SAFE (Energy and Seismic AFfordable rEnovation solutions), this paper presents the experimental tests and modeling attempts for a class of Asymmetric Friction Connections (AFCs) tested in the laboratories of the Norwegian University of Life Sciences. The AFCs are part of the seismic retrofitting solution, called e‐CLT, based on installing Cross‐Laminated Timber (CLT) panels in reinforced concrete structures using friction connections. The authors carried out experimental tests on AFCs fixed with screws to a CLT panel to observe the contribution of timber to the total dissipation performance. The investigation is based on 20 cyclic test data with two different setups. The main one includes a CLT panel and screw connection, while the second one isolates the friction behaviour to evaluate the influence of the screw connection. A modified LuGre hysteresis model for friction is developed to simulate the experimental cyclic response of the tested specimen. The model possesses a direct physical meaning, and it explicitly depends on the slip force and the pre‐slip stiffness. The optimized model is used to assess the performance of the AFC by varying the pre‐slip stiffness and the slip force.

Machine learning based screw drive state detection for unfastening screw connections

The electrification of the transport sector, limited primary materials, and the resulting need for a circular economy drives the automated disassembly of End of Life battery systems. Environmental influences and improper maintenance may cause stripped screw drives. Industrial screw drivers and nut runners evaluate unfastening operations in binary form as OK and NOK (Not OK). However, deeper evaluations such as the detection of stripped screw drives are necessary to decide between destructive and non-destructive disassembly and the resulting tool selection. This paper presents a novel supervised learning based approach for detecting stripped screw drives during the positive locking phase of unfastening operations by using intrinsic data (torque of the screw driver), where the bit or nut are inserted inside the screw drive. The basis of this work is an experimental data set with more than 1,000 unfastening operations from a manual and robot-based test bench, which includes four screw drive types: Torx, Phillips, external hexagon, and internal hexagon. A comparison between multilayer perceptrons (MLPs) and convolutional neural networks (CNNs) have been examined using the experimental data set. Additionally, the reliability and accuracy of the proposed approach have been examined. The findings from this paper demonstrate the feasibility of CNN-based detection for a revolution number lower than one, which is one revolution better than the state of the art techniques, a screw size and screw drive independent detection of stripped screw drives. The CNN model gives an accuracy of 0.98 to predict the screw drive state.