Bolted Steel Connections Research Articles

Investigating the Effects of Adhesive on the Shear Capacity of Bolted Steel Connections

Recently, there has been a particular emphasis on the use of structural adhesives in steel connection systems. Applying adhesives that possess both high strength and flexibility would be highly advantageous for structural purposes. In this study, experimental tests are conducted on two main different types of steel-plate connections; namely, bolted connections and bolted connections with glue. The number of bolts ranged from one to eight for each connection type, such that a total of seven specimens of each type are tested. Additionally, one specimen with only glue is also tested for comparison. The findings indicated that the inclusion of up to four bolts with glue along the connection does not significantly increase the ultimate stress. This can be attributed to the non-uniform distribution of normal stresses, induced by the tightening of the small number of bolts that are not arranged across the entire connection region, on the capacity of the connection in the perpendicular direction. Thus, the connection could have been adequately established the same capacity through the use of adhesive alone. In contrast, the capacity is increased up to 60% and 100% when six or eight bolts are added, respectively, compared to the use of the connection with glue only. A three-dimensional finite-element analysis is developed based on the tested connections using ABAQUS/Explicit software. The glued interface between two steel plates is modelled using cohesive and damage criteria. The results are demonstrated to be consistent with the experimental findings. Keywords: ABAQUS, Adhesive, Bolts, Finite-element analysis, Shear, Steel connections

Bio‐based laminated truss structures with bolted steel connections: Experiment, modeling, and model‐updating

AbstractBio‐based laminated structures offer a timely solution to meet the pressing demand for resource‐efficient and environmentally responsible construction practices in civil engineering. Bolted connections are commonly used in truss joints and significantly impact their global mechanical behaviors. However, existing studies on the complex behavior of joints for integrated bio‐based structures are lacking. Based on previous work by the authors about joint behavior, this study seeks to experimentally investigate the axial behavior of bolted steel to laminated timber and bamboo (glubam) connections with slotted‐in steel plates in planar truss structures. First, cyclic tests were conducted on Bio‐based laminated planar truss structures to evaluate their global and local hysteretic behavior. The test matrix encompasses eight distinct connection configurations, carefully selected to assess the connection behavior of Laminated Veneer Lumber (LVL) and Glued Laminated Bamboo (glubam). Subsequently, through the incorporation of the hysteretic model for truss joints, an advanced hybrid truss model was developed within the OpenSees framework and successfully validated using experimental data. Finally, this study proposes and demonstrates the effectiveness of an efficient model‐updating framework, which combines the power of the genetic algorithm (GA) and neural network, resulting in a significantly enhanced accuracy of the model.

Failure mode and capacity prediction for bolted T-stub connections using ensemble learning

The present study utilizes machine learning (ML) algorithms, namely decision trees, and ensemble learning methods including bagging, random forests, gradient boosting, and extreme gradient boosting to identify the failure mode and predict the corresponding capacity of preloaded bolted T-stub steel connections subjected to tension. A nonlinear finite element model (FEM) was first developed and validated against experimental results from literature. Subsequently, a matrix of 3447 FEMs, covering a wide range of design parameters, were generated to train and test the ML models. In addition, to evaluate the significance of each input parameter in predicting the connections' capacity, different embedded feature selection techniques were employed. Furthermore, different interpretability methods were utilized to uncover the interrelationships between the input features and the modeled outputs to further interpret the developed Blackbox models. The results highlight the effectiveness of ML techniques in predicting the failure modes and corresponding capacity of bolted T-stub connections, supporting their potential as robust and rapid design tools which ensure adequate designs for new connections or effective assessments for existing ones.

Impact of partially damaged passive protection on the fire response of bolted steel connections using finite element analysis

This article aims to quantify the impact of a potential failure of passive fire protection on the ultimate response of a top and seat steel connection with double web angles. A numerical, finite element analysis scheme is proposed considering the real, semi-rigid behaviour of the connection, using unilateral contact-friction laws between the interfaces of the beam, the column, and the steel angles. The model has been validated by previous experimental research at ambient temperatures. Scenarios of unprotected connections, undamaged and partially damaged fire protections are numerically tested. A change in the failure mode and a reduction of the strength equal to 28% for standard fire and 35% for hydrocarbon fire arise for the model with the damaged protection. In this case, maximum temperatures locally at the beam reach the ones of the unprotected connection (900 °C), which is more than 800 °C higher than the connection with undamaged protection. Significant temperature increases of more than 288 °C and 406 °C for standard and hydrocarbon fires also arise on the top angle, compared to the model with undamaged fire protection.

Mechanical properties of bolted steel laminated flattened-bamboo lumber connections under cyclic loading

In beam-column systems, bolted steel connections in laminated composite structures are being increasingly employed for their superior mechanical performance. Laminated flattened-bamboo lumber (LFBL) is a newly engineered bamboo product and a promising structural material since its production process could achieve the high-efficiency utilization of bamboo resources. This research investigated the load–displacement behavior of bolted steel connections of LFBL under cyclic compression. A total of 30 specimens in 6 groups were tested to determine the hysteresis curves, the effects of the bolt number, and failure modes under cyclic compression parallel and perpendicular to the grain. The test results illustrated that splitting and crushing failure were the main failure modes. With the increase in bolt quantity, the maximum load and initial stiffness of all specimens were significantly increased, while the ductility slightly decreased. The theoretical models of the skeleton curves and the reloading and unloading curves under cyclic loads were put forward, and the proposed equations were able to predict the entire cyclic load–displacement response. This study is aimed at offering guidelines for LFBL applications in future construction engineering.

Bolted steel to laminated timber and glubam connections: Axial behavior and finite-element modeling

This study aims to characterize the axial monotonic and cyclic tensile behavior of bolted steel connections to laminated timber and bamboo, using slotted-in steel plates, and to provide a high-fidelity simulation using finite-element modeling. Forty-eight experimental tests were conducted, including eight different configurations, varying in material (Laminated Veneer Lumber (LVL) and Glued Laminated Bamboo (glubam)), number of bolts, and diameter of bolts, under tension, both monotonic and cyclic (three repetitions). The force and displacement were recorded, and used to define the initial stiffness, yielding strength, ultimate strength, ductility, viscous damping, and energy dissipation. The failure modes of the connections were monitored using Digital Image Correlation (DIC) techniques. A novel high-fidelity finite-element model integrating Hill’s yielding and element removal criteria was proposed to predict the mechanical performance and fracture behavior of the examined connections. The numerical simulation was validated by comparing the experimental load–displacement curves and the strain field measurements obtained with DIC. Finally, theoretical formulas for predicting the stiffness of bolted connections were proposed based on the FEM simulations.

Cyclic friction-slip behaviour of G350-steel bolted connections

In this study, an experimental program was performed to investigate the cyclic friction-slip behaviour of AS/NZS 3678–350 (G350) steel with different surface finishes. Fifteen bolted steel connections consisting of EN 1090–2 slip factor test assemblies with M16 bolts were prepared and tested with five commonly used surface finishes including inorganic zinc silicate (IZS), epoxy zinc primer (EZP), aliphatic acrylic polyurethane (PUR), abrasive blasted (SA2), and clean mill scale (CMS). The first initial force-slip stiffness and the first slip factor are reported for each surface finish and compared with the existing literature and design standards. An empirical model is proposed to predict the initial slip behaviour based on the first slip factor and initial stiffness, and its accuracy is demonstrated for the coated and uncoated steel. The effects of the cyclic load are then considered, and the cyclic slip factor and initial stiffness are evaluated and discussed. Finally, corresponding empirical models are proposed for the cyclic slip factor and friction-slip stiffness as a function of the cumulative displacement.

Seismic design of bolted beam to column connections in tubular steel structures – A review

Connections play an important role for the overall behaviour of steel structures. Considering seismic performance of steel buildings, tubular sections provide a better substitute as compared to wide flange sections during flexure, compression and torsion actions. In general, Tubular steel structures show better performance during earthquake motions; however, there are evidence where moment welded connections showed failures in joints. In the past decade, extensive research has been conducted on bolted connections for tubular steel sections. Comparatively, few research papers are available with reference to Beam to Column connections and Seismic conditions. The present work is a compilation of important events recorded during the evolvement of bolted steel connections, design codes as well as limitations in implementation of bolted connections for tubular steel structures. European codes are found as updated for performance-based design.

Evaluation of seismic performance of precast concrete walls with X-shaped steel plate bracings

Structures utilizing precast concrete walls have wide usage around the world, yet previous earthquakes have revealed the seismic performance of those walls is often deficient. These deficiencies can result in shear sliding at the wall base or brittle shear failure of the wall. These failure modes have been shown to be suppressed through the use of diagonal reinforcement in cast-in-situ walls, however, the tolerances and reinforcement geometry make the use of diagonal reinforcement in precast walls very difficult to achieve. In this paper, as an alternative to traditional diagonal reinforcement, X-shaped steel plate bracing was adopted in precast concrete walls and connected with welded joints. The experimental tests of four walls are presented, all of which incorporated the bracing and used either a cast-in-situ or bolted steel connection. The influence of the foundation connection and X-shaped steel plate bracing on the seismic performance of walls with different shear span ratios is described. The X-shaped steel plate bracing was found to effectively control shear sliding, with a greater decrease in shear sliding for walls with a lower shear span ratio. The bracing improved the peak strength of the walls, but the improvement varied with the angle of the bracing. The precast concrete walls with X-shaped steel plate bracing performed similar flexural failure modes to the reinforced concrete walls with a low shear span ratio but formed a plastic zone at the mid-height of the wall panel for the precast wall with a shear span ratio of 2.282. Numerical models developed for the precast concrete walls were able to estimate the force-displacement relationships.

Safety Assessment for Capacity Design of Bolted Steel Connections in Tension

AbstractCapacity design for bolted connections in tension means that yielding of the gross cross‐section is decisive over the ultimate resistance of the net cross‐section. If the requirement for capacity design is met, ductile connection behavior is achieved, and brittle failure is avoided. However, in many practical cases the bolt holes are too large to satisfy the current capacity design requirement of EN 1993‐1‐1. In this capacity design requirement, both failure criteria involved, plastic resistance of the gross cross‐section and ultimate resistance of the net cross‐section, are considered independently with their own partial factors. This may be overly conservative. The goal of the research is to determine an improved capacity design requirement such that bigger bolt holes can be allowed without hampering safety. Both partial factors and the factor 0,9 in the net cross‐section resistance are combined in one factor. With the use of a Monte Carlo simulation a new capacity design requirement with its own combined factor is developed. Several distributions for dimensions and steel properties are used as input for the Monte Carlo simulation. The correlation between the yield stress and the ultimate strength is considered as well. In the Monte Carlo simulation, also a model factor is used. The current combined factor for the capacity design requirement is 1.39. Based on the research performed, it can be concluded that this is very conservative and that the value of the combined factor can be lowered to 1.05.

Axial-moment interaction for 2D extended end plate bolted steel connections. Experimental investigation and assessment of the initial imperfections

A study of axial–moment interactions of bolted connections with double extended end plates is presented in this paper. Six connections, subjected to pure compression and flexural compression were tested for this purpose. After the experimental campaign, finite element models were developed and calibrated to accurately reproduce the experimental results. The models included initial imperfections to capture the possible buckling failure modes in the column web and the beam flanges. Moreover, the models with and without initial imperfections were compared for different sizes of the imperfection. Finally, the results obtained from the experimental and the computational models provided sufficient and adequate information to construct an axial-moment interaction curve for the tested joints.

Response characteristics of flush end-plate connections

Flush end-plate (FEP) connections are one of the most popular bolted steel connections in construction practice. These connections possess a semi-rigid moment-rotation behavior that betwixt that of rigid and pinned connections. Nonetheless, they are commonly idealized as pinned connections in design and numerical simulations. This paper investigates the flexibility, strength and ductility of such connections in a holistic manner, based on a recently compiled comprehensive database of more than 420 specimens that were tested within the past 50 years. The paper describes the systematic methodology used to deduce response parameters from the moment-rotation curves. This includes deduction of the elastic, post-yield stiffnesses, the effective yield and maximum moments as well as the ultimate rotation at failure. The deduced parameters are made publically available to support further analysis by other researchers. The median value of each parameter and associated variability are quantified with respect to different connection topologies and loading histories. The data are then used to assess the connection classification and performance in terms of flexibility, strength and ductility based on existing standards.

Corrosion effect on structural behaviour of bolted steel connections under axial tension loads

Corrosion is one of the most important problems and is an inevitable event in metal structures exposed to environmental effects. Corrosion deterioration usually forms in steel and steel-concrete composite bridges and marine structures. Bolted connections in steel structures are the preferred connection types because of their ease of assembly and high strength. In this study, corrosion damages were created in steel plates with bolted connections and the axial load strength, ductility and behaviour of the steel members were investigated. Axial tensile tests have been carried out on steel plates with bolted connections exposed to corrosion at different rates (10% and 20% by mass). According to the axial tensile tests, decreases in average yield strength and average yield strain values were determined as 4% and 10% for 10% corroded specimens, and were determined as 16% and 27% for 20% corroded specimens having 4 mm thick plates, respectively. Similarly, for specimens having a thickness of 6 mm plate, average yield strength and average yield strain values decreased 3% and 5% for 10% corroded specimens, and 13% and 14% for 20% corroded specimens, respectively. Also, it was found that the ultimate strengths and average rupture strains decreased almost proportionally to the amount of corrosion. In addition, finite element analysis was performed in ANSYS program for bolted connections examined experimentally. In terms of ultimate tensile strength, the results were obtained with an average error of 4% in non-corroded 4 mm specimens and 6% in 10% and 20% corroded 4 mm specimens. For 6 mm plate thickness, these values of non-corroded, 10% and 20% corroded specimens were obtained as 9%, 5% and 3%, respectively.

Simulation and experimental verification of an original full-scale bamboo truss

This study examines experimentally and numerically the performance of a full-scale bamboo truss footbridge. The truss is built of multi-culm bamboo axial members with bolted steel connections, joined together via steel gusset plates. The study proposes a hierarchical simulation approach with the aid of existing and new material/structural member experimental test results. Specifically, it models first the non-linear (bilinear) behaviour of the multi-culm bamboo structural members, and then using the structural member model as building block, it creates a non-linear model of the entire truss structure. The proposed numerical simulations return realistic force–displacement response of the truss structure. The axial deformation of truss members is mostly due to bolt deformation and embedment, since the bamboo culms are significantly stiffer than the bolted connections. The simulated yielding and damage modes occur at similar locations in the truss structure as those observed experimentally. The simulated sequence of damage modes is affected by the natural variability of bamboo culms. Overall, the developed simulations are promising towards predicting via a hierarchical systematic modelling approach, the non-linear response of the bamboo structures, after modelling the behaviour of its multi-culm bamboo structural members.

Behavior of different bolted connection configurations in frames composed of cold-formed sections

Rigid bolted cold-formed steel connections have been very popular for their better distribution of straining actions and for better full-filling serviceability requirements. However, the behavior of every single element in the connection as well as the interaction between them is not clear due to its complex behavior. A nonlinear finite element parametric study was conducted on the apex knee connection of a portal frame constructed with cold-formed back-to-back double-lipped C sections for both the rafter and the column. These back-to-back lipped C sections, connected by gusset plates are used as beam and column members. Only the webs of lipped C sections are connected to the connection gusset plates with bolts. The section flanges are not connected to the columns for ease of construction. The study focused on investigating the effect of different parameters on the ultimate capacity and the failure mode of the eave connection. Studied parameters include different bolt configurations, bolt diameters, gusset plate thickness, the bolt pre-tensioning force, and the edge distance. The effect of bolt bearing on the C-section web was considered in the calculation of the capacity of the connection. Five modes of failure were identified namely; lateral out-of-plane buckling of the gusset plate, local buckling of the connected section, bolt bearing of C-section web and the gusset plate, tearing of C-section web. It was observed that bearing failure is the dominant mode of failure. However, in some cases, the lateral-out-of-plane buckling of the gusset plate takes place and causes the premature failure of the connections at low values of applied loads. The local failure of the connected sections occurs at the ultimate loading phase. Several observations were found and some useful recommendations for optimum connection configuration are suggested. A simple interaction design procedure for special configuration to calculate the resistance of the joint connection under moment, shear, and normal forces based on the bolt bearing failure for different bolt pitches is proposed.

A Review on Fracture Behaviour of Bolted Steel Connections at Elevated Temperature

A Review on Fracture Behaviour of Bolted Steel Connections at Elevated Temperature

Meshless numerical simulation of steel connections: application to the T‐stub component

AbstractFinite element analysis is a widely used simulation technique in steel design to analyze the structural behavior of structural components, such as beams, columns or connections. The major steps involved in finite element simulations are the definition of the basic parameters and the discretization in elements of the component, also known as preprocessing; the analysis of the model and the post‐processing by the representation and the interpretation of the obtained results. On the particular case of bolted connections, the most time‐consuming of these three phases is that of preprocessing, because on traditional finite element technology is required that the real geometry of the CAD model is simplified to be meshed and analyzed; this task is specifically severe and requires paying close attention on the case of components affected to concentration stresses. Nowadays, different techniques have been proposed and developed with this objective: reduce costs in terms of time and specialized human resources because the workflow is easier and simpler. One of these methods are the known as the meshfree methods, that do not require connection between nodes and are based on the interaction of the points of the geometry with the neighbors, so the processor analyzes taken as base the real CAD geometry and no simplifications are needed.On this paper is exposed the meshless method based on the theory of external approximations as an alternative to the classic finite element method. This method is based on the theory where all parts of the assembly are considered as different elements, and the approximation of displacements inside is arbitrary and not only by polynomials. The convergence of the simulation model is based on the external equilibrium of the assembly. The method is applied to a practical case: the simulation of the T‐stub connection. The T‐stub component corresponds to one T‐shaped steel profile bolted through their flanges and loaded through their web until collapse, and its behavior is similar to the tension zone of beam to column bolted end plate connections. The analysis of strength, stiffness and ductility have been widely investigated experimentally, by simulation and theoretically, and they are obtained from the force‐displacement characteristic curve. Information presented by Bursi and Jaspart on the paper “Benchmarks for finite element modelling of bolted steel connections” are considered to elaborate the models and to compare the results.

Fracture behavior of high-strength bolted steel connections at elevated temperatures

In fire events, to utilize catenary effect and accommodate large deformation in beams demands a sufficient deformation capacity and ductility in steel bolted connections, which is not well considered in design practice. Therefore, for performance-based fire safety design, it becomes very essential to accurately predict the fracture behavior of steel bolted connections at elevated temperatures. However, experimentally predicting their fracture behavior is very costly at elevated temperatures and limited by the scale of structural components. Therefore, this paper proposes a numerical analysis approach and investigates the fracture behavior of high-strength bolted steel connections at elevated temperatures based on the validated numerical analysis approach. The temperature-dependent material properties including true stress-strain curves and fracture parameters in a three-stage fracture model (describing the pure tension, pure shear, and combined tension and shear fracture behavior) for high-strength ASTM A325 bolt and A572 Grade 50 steel are firstly calibrated from and validated against their tensile and shear test results. They are further validated against the test results on single-bolted and multi-bolted connections at elevated temperatures, which were not used in the calibration of these material properties. The validated material properties and fracture parameters are finally proposed for fracture prediction of different types of bolted connections under various loading conditions at elevated temperatures. This study shows the potential of reasonable prediction of the fracture behavior for the steel bolted connections at elevated temperatures and under complicated loading conditions using a numerical analysis approach. According to the numerical analysis results, the degradation of shear fracture resistance of A325 bolts at elevated temperatures is more significant than that of A572 Grade 50 steel plate, which may lead to a bolt shear failure mode for these connections with a large end distance at high temperatures (>400 °C). It is also found that the fracture failure mode can significantly influence the degradation of the load and deformation capacities of high-strength steel bolted connections at elevated temperatures. With the bolt shear failure mode, the degradation of load and deformation capacities of steel bolted connections are more significant than that with plate tearing-out failure mode.

Seismic Behavior of Innovative Precast Superimposed Concrete Shear Walls with Spiral Hoop and Bolted Steel Connections

Owing to the desirable bond strength and excellent workability, spiral hoop and bolted steel connectors are introduced to enhance the connecting performance of superimposed reinforced concrete shear wall (SRCSW) system. In order to investigate the seismic performance of SRCSWs, applying such connecting methods under flexure-shear interaction and flexural dominated status, two groups of precast (PC) specimens were constructed: one-story and two-story specimens. Seismic behavior in terms of crack patterns, load-displacement response, ductility, stiffness degradation, strain response, and deformation results of SRCSWs is evaluated by the quasistatic cyclic test. It is shown that the wall specimens with the proposed connectors exhibited similar failure mode to that of the cast-in-place (CIP) walls and possessed adequate seismic performance such as lateral resistance, ultimate drift ratio, and lateral stiffness besides the ease of erection. The strain responses and deformation results of the PC specimens under reversed cyclic loading were presented to evaluate the effectiveness of the introduced connections. The test results indicated that the PC walls adopting bolted steel connectors behaved better in force transmission and exhibited greater integrity characteristic compared with the specimens having spiral hoop connectors. Lastly, simplified finite element models considering the nonlinear slip behavior within the connection joint of SRCSWs were established and verified, which could provide sufficient accuracy and efficiency to predict the seismic response of the proposed wall system.

Stiffness metamodelling of 2D bolted extended end-plate steel connections using modal decomposition

The accurate simulation of steel structures requires a precise model of the joint behaviour. The methods proposed by the steel codes are based on either rotating springs or involved models of springs and rigid bars. In this article, a precise method to model the stiffness of 2D bolted steel connections is presented. First, the joint is accurately modelled using finite elements (FE). Then, the FE model is condensed to a cruciform element of 4 nodes (12° of freedom) by constraining each side cross-section to a node located at its centre of gravity. Subsequently, forces are applied to each node to compute the flexibility matrix, which is then used to construct the stiffness matrix that is finally decomposed through singular value factorization. Following this procedure, a parametric study is conducted to build the training and validation sets of the metamodel. Kriging and Radial Basis Functions are chosen to metamodel and predict the stiffness matrices of the cases not included in the parametric study. Finally, steel structures are analysed with both complete finite elements and surrogate models, and the results are used to confirm the accuracy of the proposed method.