T-stub Connections Research Articles

Experimental and numerical investigation of novel triangular headed one-sided bolted T-stub connections

The reliable one-sided bolts constitute a vital component of fully bolted joints in demountable steel structures. In this study, an innovative triangular headed one-sided bolt (THOB) based on the traditional hexagon headed bolt (HHB) was proposed, and the tensile performance of T-stubs using the THOBs has been investigated through experimental and numerical approaches. Monotonic tensile tests were performed on 25 THOB bolted T-stubs to analyze the failure modes and load-carrying performance of the specimens. The test results disclosed that, beyond the three typical failure modes stipulated in the Eurocode 3, the specimens exhibited a characteristic failure mode, namely, limit groove pull-off failure. Finite element models, validated by the test results, were employed for the parametric analysis to compare the load-carrying performance of THOB bolted T-stubs with that of HHB bolted T-stubs. The finite element analysis results indicated that the average ratio of the plastic load-carrying capacity of THOB bolted T-stubs to HHB bolted T-stubs was close to 0.88. Furthermore, the load-carrying capacity of THOB bolted T-stubs was evaluated using existing specifications for comparison with the experimental and numerical results, and Eurocode 3 calculations for the plastic load-carrying capacities of THOB bolted T-stubs demonstrated a commendable level of precision. Finally design recommendations were put forward based on the test and finite element analysis results.

Moment capacity of cold-formed steel trusses with Howick Rivet Connectors: Tests, modelling and design

Cold-formed steel (CFS) trusses are increasingly used in lightweight building construction. A new type of pin-jointed connector, known as the Howick Rivet Connectors (HRCs), has been developed for CFS trusses. Previous studies focused on testing T-stub connections and shear strengths of CFS trusses with HRCs, providing insights into their structural performance and shear capacity. This paper extends the research by testing ten new CFS trusses with HRCs to determine their moment capacity. The study involved two different cross-sections: lipped channel sections and hat sections, used as truss chords. Variations in the number and locations of lateral supports were introduced to simulate different boundary conditions. A parametric study explored the effects of span-height ratio and variability in lateral support locations on truss strength and failure modes. Finally, the trusses with lipped section chords were designed according to the American Iron and Steel Institute (AISI 2016) and Australia/New Zealand standards (AS/NZS 2018), achieving an average test-to-design strength ratio of 0.86.

Experimental and numerical investigation on cyclic behavior of beam‑to‑column connection with a lateral steel slit damper

The objective of this research is to propose an innovative slit damper that can be installed in beam-to-column connections of steel structures as a fuse and energy dissipation device. These devices can be used as an effective and inexpensive way to mitigate earthquake risks to structures, and they can also improve the seismic behavior of building structures. Specifically, structures equipped with these devices can withstand more drift while their main members remain in an elastic state, thereby reducing the cost of rebuilding structures after earthquakes. In this study, four specimens were experimentally tested. Three beam-to-column connections were equipped with the proposed damper, and the fourth one was used as a reference sample. This damper can be referred to as a lateral slit damper (LSD). The test results show that all samples have stable and complete hysteresis curves without pinching. So, the LSDs can improve the ductility of beam-to-column connections. The test results showed that the innovative system can enhance the strength and ductility of the T-stub connection around 73 % and 21 %, respectively. To validate the LSD experimental findings, finite element models were employed for calibration. A numerical study using ABAQUS examined the system's hysteretic behavior under cyclic loading, revealing excellent agreement between the numerical and experimental results. Finally, the proposed LSDs demonstrate exceptional ductility, strength, effective hysteretic curves, and post-earthquake reparability. These qualities position it as a promising and practical damper for mitigating seismic risks in engineering structures.

Anti-progressive collapse performance and design method of novel T-stub connections

To address the insufficient anti-collapse capacity of T-stub connections due to premature failure, this study proposes a novel T-stub connection (NTC) by adding four V-shaped laminated plates. Monotonic loading tests are conducted on the T-stub web and V-shaped laminated plate to analyze the influence of geometric parameters on their deformation and load-bearing capacity. The working mechanism of NTC is investigated through the validated numerical models by analyzing the failure mode, impact force history, deformation pattern, internal force development, and energy dissipation. The research results indicate that, compared to the T-stub connection, the NTC exhibits two-phase failure characteristics, which begin with the fracture of the bolt-hole in the T-stub web, followed by the gradual straightening and eventual fracture of the V-shaped laminated plates. NTC undergoes three stages under impact loads: peak, oscillation, and platform stages. The addition of V-shaped laminated plates enhances the ductility of NTC by 93 %−130 % and its energy dissipation capacity by 189 %−235 %. This significant enhancement in deformation and energy dissipation capabilities can be attributed to the addition of the V-shaped laminated plates. The deformation and bearing capacity calculation formulas for both the T-stub web and V-shaped laminated plate are provided. Additionally, a design method for NTC is proposed based on theoretical analysis, and its rationality is verified through numerical examples involving three different sets of beam and column sections.

Bayesian optimization-based Model-Agnostic Meta-Learning: Application to predict maximum cyclic moment resistance of steel bolted T-stub connections

Accurately assessing the maximum moment resistance of steel bolted T-stub connections under cyclic loading is crucial for designing earthquake-resistant structures with such connections. Traditional methods based on design standards like ASCE 41-17 often lack precision. Recently, supervised machine learning techniques, particularly Artificial Neural Network (ANN), have been explored. However, conventional ANNs require substantial data for generalization, which is limited for steel bolted T-stub connections. To address these challenges, this study explores the feasibility of using the Model-Agnostic Meta-Learning (MAML) to predict the maximum cyclic moment resistance of steel bolted T-stub connections. MAML adapts task-specific model parameters rapidly and transfers knowledge across tasks to fine-tune global model parameters, potentially enhancing prediction accuracy with limited data. The MAML model is first optimized using Bayesian optimization with a Gaussian Process model to identify ideal hyperparameters. The optimized MAML model is then compared with two ANN models (one with optimized hyperparameters, another matching MAML's neural network architecture) and ASCE 41-17 method. Results demonstrate the optimized MAML model's superior generalization capabilities, offering a promising approach for steel bolted T-stub connections.

Exploration of the behavior and evolution features of beam-column joints with T-stub using the structural strain energy method

Based on the structural strain energy method, the work behavior of four T-stub connection joints under cyclic loading is analyzed to visualize their working behavior and failure evolution. The experimental strain data are modeled as generalized strain energy density (GSED) to characterize the structural stress state and the corresponding characteristic parameters, and the Mann-Kendall (M-K) criterion is formulated to determine the performance characteristic points (P and Q) of the joint Mj-Ej curves and to derive the starting point of structural continuity damage. Then, by analyzing the parameters of the joint working state (strain, deformation, joint energy dissipation, connection stiffness, bolt force and pry force), the trends of the joint stressing state curves before and after the critical loading are reflected. Finally, the feature point data interpolation (EDI) method is introduced to effectively expand the joint test data, visualize the change process of the strain/stress field, and deeply reveal the mechanical response mechanism and evolutionary degradation law behind it. The contribution of the above work is to quantitatively identify the P and Q characteristic points in the changing trend of the joint working state, to reveal the mechanical mechanism and the failure degradation law from the perspective of energy evolution, and to visualize the mutation of the field data before and after the P/Q using the EDI method, which is a generalized method that can be applied to the other progressive failure structures.

An optimal design approach for steel space frames with T-stub semi-rigid connections considering soil-structure interaction

An optimization technique for designing the steel space frame with T-stub semi-rigid connections and interaction between soil and structure is presented in this article. A three-parameter-based elastic foundation model is utilized to investigate soil-structure interactions (SSI). To enable two-way data transfer for all optimization methods, computer software was developed using C# version 17.8.6, which connects to SAP2000-OAPI version 22. Particle swarm optimization (PSO) and teaching-learning-based optimization (TLBO) are employed for optimal designs. These optimization techniques choose profile sections from a list, including 64W discrete sections from the American Institute of Steel Construction (AISC). The Load and Resistance Factor Design-American Institute of Steel Construction (LRFD-AISC) strength constraints, geometric constraints, inter-storey drift constraints, and displacement constraints are considered during optimization. The first phase entails creating optimal designs for two unique steel space frames that consider SSI but do not include T-stub semi-rigid connections. Following that, the same optimization procedures are carried out with T-stub semi-rigid connections. The parameters needed for the foundation model are obtained through soil surface displacements. Utilizing T-stub semi-rigid connections while considering the interaction between the structure and the soil produces increased structural weight.

Investigating the effectiveness of concentric welded anchor rods in column base plate connections: A numerical and experimental study

This study presents a new strategy for column base plate connections, which involves the utilization of welded anchor rods positioned concentrically beneath the base plate, in alignment with the connected column. The objective was to remove the eccentricity between the anchor rods and the column, thereby excluding the base plate from the load-transferring chain. A numerical study was performed to compare the cyclic behavior and uplift response of the proposed connection with conventional column base connections. Additionally, different weld types were investigated to connect the anchor rods to the base plate, and their efficiency was evaluated based on a comprehensive dataset of nine tests on equivalent base-plate T-stub connections with different base-plate thicknesses, anchor-rod strengths, and anchor-rod diameters. The numerical results showed that using welded anchor rods could remove the pinching from the hysteresis loops, as the anchor rods can effectively resist cyclic loads in both compression and tension. Furthermore, removing the eccentricity between the anchor rods and the column enhanced the uplift stiffness by approximately 31 %. The experimental results indicated that the failure mode was the fracture of anchor rods for all specimens, while the other components remained elastic. The specimens with high-strength anchor rods showed a brittle failure accompanied by a sudden drop in load, which coincided with the fracture of anchor rod in the softened heat-affected zone. All developed weld types successfully withstood the ultimate tensile strength of anchor rods upon fracturing.

Seismic fragility and resilience assessment of steel frame with replaceable T-stub connection components

Based on a rational design, steel beam-column joints with replaceable T-stub connection components (SBCJ-RTCCs) possess superior structural fuse performance and seismic resilience performance. To further evaluate the benefits of steel frames using RTCCs in terms of dynamic response, structural and non-structural components damage as well as seismic resilience, a 12-story steel frame equipped with RTCCs (SF-RTCCs) and a steel moment resisting frame (SMRF) were designed and established. On the basis of validating the simulation results with the experimental findings, the nonlinear dynamic analyses and incremental dynamic analysis (IDA) based seismic fragility analysis was performed. The results confirm that the introducing RTCCs into steel frames can significantly mitigate base shear and floor acceleration as well as produce a more uniform inter-story deformation and a more rational yielding mechanism. Meanwhile, the SF-RTCCs can obtain comparable collapse-resistant performance compared to SMRF, and both frames possess sufficient redundancy to resist structural collapse. Thanks to the lower floor acceleration responses, the SF-RTCCSs performs much better than SMRF in controlling non-structural components damage. After DBE excitations, the probabilities of RTCCs can be replaced by 1st class and 2nd class was 17.2 % and 84.9 %, respectively. After MCE excitations, RTCCs has about 29.3 % and 67.2 % probability that it can be replaced by 2nd class and 3rd class, respectively. Considering the lower economic losses, short repair time and fewer casualties, the rating of seismic resilience of SF-RTCCs was enhanced from one-star of SMRF to two-star.

Enhancing Structural Resilience: Exploring the Novel Sleeve Method for Steel T-Stub Connections

A new sleeve device has been introduced with the aim of enhancing the performance of steel structures under extreme loading conditions. Previous research has primarily focused on numerical simulations of this sleeve's application, emphasizing the need for further investigation to validate its effectiveness. This research paper presents a numerical analysis that explores how the sleeve device influences the deformation capacity and strength of a bolt up to the point of failure. The study involved the use of a T-stub connection with multiple sleeves, each featuring different geometric parameters. To assess the impact on strength and deformation capacity, a comparison was drawn between these findings and the behavior of a T-stub bolted connection without using the sleeve. In addition, Finite Element (FE) models were employed for additional parametric studies. The test outcomes demonstrated a substantial increase in the deformability of the bolted connection when utilizing the sleeve device, all the while preserving the strength and initial stiffness of the bolts. This proposed sleeve method in the study significantly enhances the connection's capacity by delaying bolt failure.

Feasibility study of TSOB replacing standard high-strength bolt in T-stub connection

The feasibility study of T-head Square-neck One-side Bolt (TSOB) replacing Standard High-strength Bolt (SHB) in T-stub connections is conducted in this paper. Parametric analysis is carried out by means of finite element numerical simulation to reveal the effects of T-stub parameters and bolt parameters on the tensile performance of T-stub connections using SHBs and TSOBs. The plastic hinge theory is applied to explain the mechanism for the difference formation in tensile capacity between the two types of connections. The results show that the failure modes of TSOBs bolted T-stubs are the same as those of SHBs bolted T-stubs, including complete flange yielding, bolt failure with flange yielding, and bolt failure. For the failure of complete flange yielding, the tensile capacity of TSOBs bolted T-stubs is reduced by 7.2%∼16.4% compared with that of SHBs bolted T-stubs, whereas the modes of bolt failure with flange yielding and bolt failure do not cause a difference between the two types of connections in tensile response. Two modifications on design equation and design result by introducing hole type reduction factor and thickening flange for T-stub connections were proposed, respectively. The modified design methods can be used in the design of TSOBs bolted T-stubs and are identical to the design criteria of specifications Eurocode 3 and P398 for SHBs bolted T-stubs. Besides, the high-strength large hexagon nuts for steel structures and assembly classes of H12 and H13 recommended by GB/T 1229–2006 and GB/T 5277–1985 should be preferred for TSOBs bolted T-stubs. Moreover, horizontal slotted bolt holes are recommended for practical constructions, and the T-head aspect ratio of TSOB in the range of 1.6–2.0 does not affect T-stub tensile performance.

Steel Beam-to-Column Friction Joint under a Column Loss Scenario

FREEDAM joints have been recently seismically prequalified for applications in European seismically prone countries. Despite their excellent seismic response, FREEDAM joints are not purposely conceived for exceptional loading conditions, such as in the case of a column loss scenario. Therefore, a comprehensive parametric numerical study has been carried out to investigate the robustness of this type of joint, varying the geometry of the beam–column assembly and the associated friction device. The results of the performed finite-element simulations allowed the identification of the critical components of the joints such as the upper T-stub connecting the upper beam flange to the column. This component is characterized by significant demand, due to the concentration of tensile and shear forces when catenary action develops in the beam. In order to enhance the ductility of the beam-to-column joint under large imposed rotations, the details of the upper T-stub connection were modified and numerically analyzed. The obtained results allowed for the verifying of the effectiveness of the amended details as well as characterizing the evolution of the tensile forces in the bolts.

Seismic Performance Analysis of Semi-rigid Steel Frame Based on Panel Zone Mechanical Characteristics of the Joint Experiment Study

The panel zone, as an important part of the semi-rigid connection (SRC), can effectively affect the force transfer mechanism of the connection. This study aims to evaluate the panel zone mechanical characteristics through test on end-plate connection (EPC) and T-stub connection (TSC) under cyclic loading. Based on failure criteria, the mechanical properties of the panel zone are discussed, including the shear force, plastic energy dissipation, and failure modes. In light of the test studies, an effective and accurate numerical method in OpenSees platform for SRC with a behavior monitored by nonlinear rational springs is proposed. A 4 × 6 plane steel frame with SRC under the loading stimulation of 12 ground motions is conducted to testify the reliability of the model and analyze the panel zone behavior on the frame. The panel zones exhibit stable hysteresis characteristics and excellent ductility, and the analysis results of the effect of stiffness ratio between bolted connections and panel zone on frame energy consumption provide suggestions for structural energy dissipation design. The model conducts an accurate prediction of semi-rigid connection steel frames (SRCSFs) seismic behaviors considering the panel zone mechanical properties, and it can dramatically improve computing efficiency and is conducive to seismic design.

Advanced finite element modelling of stainless steel bolted T-stubs under large deformations

Following upon the recently published experimental and numerical studies on stainless steel bolted T-stubs in tension, this study reports the development and validation of an advanced FE model that reveals the effect of initial contact between the bolts and bolt holes and constructional imperfections on the response of stainless steel bolted T-stubs subjected to large deformations. Key simulation strategies regarding the modelling of bolts, initial position of the bolts, flange bowing effect due to the initial constructional imperfections and overcoming numerical instabilities are discussed. The developed FE model first validated against the available test data in the literature. The effect of pre-established contact between the bolts and bolt holes and constructional imperfections on the overall response of the bolted T-stubs are reported comprehensively by comparing the plastic and ultimate resistances with the experimental ones. Moreover, the membrane action developing in the flange influences the ductility reserve of the T-stub which has a vital role in case of progressive collapse and robustness scenarios. Therefore, by inspecting the stress distribution through the flange thickness at various locations along the T-stubs, effects of different modelling configurations on the flexural and the membrane component of the load transfer mechanism are revealed. A parametric study is performed to investigate the influence of all these aspects on resistance of T-stub connections. On the basis of the obtained results and the discussions, modelling recommendations for the simulation of stainless steel T-stubs are made.

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.

Investigating the T-stub connection with different web-to-flange joint configurations

This article evaluates the impact of different web-to-flange joints in the T-stub connection. Mechanical properties of T-stub components were evaluated by experimental tests and by finite element simulations. Three different web-to-flange junctions are evaluated: laminated components, fillet welding and full penetration welding. Generally, laminated and fillet welded T-stub profiles have been considered in the past to study the behavior of the tension zone in the end plate connections. However, in structures predominately subjected to low and high cycle dynamic loads, and susceptible to a fatigue crack, is mandatory full penetration welds execution. This article evaluates the influence of full penetrated welding in the behavior of the full component, and not only in the mechanical capacity of the weld and the weld area. This article analyses how the increment of the free span between the bolt position and the web modifies the position of plastic hinges in the vicinity of the web, with the consequent reduction of strength and stiffness. A total of 72 experimental samples with 8 different geometries were tested to evaluate the different behavior of the web-to-flange joint configuration. A detailed finite element model of the T-stub component has been developed for each joint configuration. The model has been calibrated with experimental results, and it is able to accurately capture the full range behavior of the T-stub featuring any failure model. From the results of the experimental tests and their validation by finite element analysis, it can be concluded that the welded T-stub connection has a lower mechanical resistance, with no significant differences between fillet welding and full penetration welding. And the effect of the type of welding is only seen in ductility, and not in resistance or stiffness. On average, the typologies with full penetration welding have a maximum displacement 1.43 times higher than the fillet welded one.

Experimental investigation of wire arc additively manufactured steel T-stub connections

This paper presents an experimental investigation into the structural response of wire arc additively manufactured (WAAM) steel T-stub connections subjected to tension. A total of eighty T-stub specimens featuring different printing strategies, bolt arrangements and geometric configurations were tested to failure. 3D laser scanning was employed to determine the specimen geometry, while digital image correlation (DIC) was used to monitor the strain and displacement fields during testing. Utilising the DIC data, a new method was introduced for the determination of the failure mode and key points on the load-deformation response of T-stub connections. The structural response of the WAAM T-stubs generally followed the anticipated trends, though the geometric irregularities resulted in a delay in the development of prying action in some specimens and the printing strategy was shown to have a clear influence on the load-carrying capacity. Finally, comparisons between the test results and the capacity predictions yielded by existing design equations were made; overall, reasonable agreement was achieved, but further research is required to establish reliable design rules that are specific to this form of manufacture.

Comprehensive studies on the behaviors of high strength steel T-stubs with thin-walled flange at elevated temperatures

This paper presents the experimental, numerical, and theoretical studies aimed at investigating the fire behaviors of high strength Q690 steel T-stub connections. The experiments determined failure modes, load–displacement curves, ultimate displacement, ductility factors, and load capacities of the specimens at elevated temperatures. The rupture of the flange disappeared at temperatures exceeding 600 °C. A finite element model was established using ABAQUS software, validated by the experimental results, to explore the effect of bolt preload and bolt grade on the fire behaviors of T-stubs. The first yield resistance derived from experimental and numerical findings was compared with EC3 predictions, highlighting a severe underestimation by EC3 for high-strength steel T-stubs with thin-walled flanges. A theoretical model was subsequently proposed and validated against numerical and experimental outcomes, serving as the basis for a novel design method. This model accurately anticipates the progression of the plastic hinge line and the first yield resistance, suggesting the use of 2.0% yield strength of high-strength steel to calculate the first yield resistance of steel T-stubs.

Prediction of yield strength and prying action of TOBs bolted arc-shaped endplate

Based on the component method, the structural behavior of the arc-shaped endplate in Thread-fixed One-side Bolts (TOBs) bolted beam to circular steel column joint is investigated through the bolted arc-shaped T-stub to a thick enough steel tube connection in this paper. To properly identify the load-carrying capacity of the arc-shaped T-stub connection, the tensile strength of the arc-shaped flange and the tensile strength of the TOBs are of interest. According to EC3, the tensile strength of the arc-shaped flange is determined by different yield line patterns. In addition, the prying action, which is defined as the ratio of the vertical bolt force to the external force at the yield state, should be taken into account to determine the tensile resistance of the TOBs for thin flange. To explore different yield line patterns and the prying action induced by arc-shaped flange, Finite Element models are developed and validated. Subsequently, comprehensive parametric studies are conducted on multiple parameters with the validated model, including the flange thickness, flange width, flange curvature, bolt layout, and bolt diameter. According to the analysis results, three different yield line patterns for arc-shaped flanges are cataloged, which are the corner yielding pattern, group end yielding pattern, and double curvature pattern. Corresponding design methods are proposed to estimate the tensile strength of the arc-shaped flange and the prying action induced by the arc-shaped flange which show an acceptable error with the Finite Element results.

Structural fuse performance and earthquake-resilient performance of beam-column joints with replaceable T-stub

In order to ensure that steel frame systems have excellent structural fuse performance and earthquake-resilient performance on the basis of good seismic performance, a novel steel beam-column joint with replaceable T-stub connection components (SBCJ-RTCCs) was proposed. The pseudo-static cyclic tests of original and replaced specimens were carried out. As an extension of the experimental tests, numerical parametric analyses were performed to determine an optimal range of resistance capacity ratio to make a balance between the seismic performance, structural fuse performance and earthquake-resilient performance. The analysis results demonstrated that despite seismic performance of specimen with a small resistance capacity ratio is relatively weak, the structural fuse performance and earthquake-resilient performance performed well. With the increase of resistance capacity ratio, the seismic performance consisting of initial stiffness and bearing capacity gradually improved. However, the plasticity and damage would be shifted from RTCCs to non-fuse components, which adversely affected the structural fuse performance, despite the earthquake-resilient performance of specimen was still good. In terms of comprehensive consideration of seismic performance, structural fuse performance and earthquake-resilient performance, the resistance capacity ratio was suggested as 0.53–0.63. Moreover, a design procedure of SBCJ-RTCCs was proposed, and its rationality was validated by a design example RT-D. The result indicates that by adopting the proposed design procedure, the RT-D exhibited stable hysteretic behavior without experiencing strength degradation. The RTCCs can play the role of structural fuses by dissipating more than 90% of the input energy, which effectively protect the non-fuse components from damage.