Flush End Plate Research Articles

Strength Evaluation of Flush End-Plate Connection Using Triangular Haunch in Pipe Rack

Strength Evaluation of Flush End-Plate Connection Using Triangular Haunch in Pipe Rack

Experimental and numerical investigations of seismic performance of stepped beam-column joints with different connection forms

The seismic resilience of prefabricated steel structures significantly depends on the design and construction of beam-column joints. To address the challenges related to the installation of prefabricated wall panels and overall system assembly, this study introduces a novel stepped beam-column joint. The effectiveness of different connection configurations on the seismic behavior of the joints was investigated. A series of cyclic tests were conducted on four joint specimens with different configurations, and their failure mechanisms, hysteretic curves, skeleton curves, stiffness degradation, load-bearing capacity, and energy dissipation capacity, were revealed. The experimental results showed that the stepped joint configuration offers favourable seismic performance, with notable asymmetry observed in the response patterns under positive and negative loading directions. Reducing the height of the stepped segment or the thickness of the end plate adversely affected the seismic performance, leading to early bolt failure. Consequently, a detailed finite element model of the stepped joint was developed and the model demonstrated satisfactory agreement with the experimental results. Furthermore, a parametric analysis focusing on variations in stepped segment's height was conducted, providing insights into optimization of the load-bearing capacity of the stepped joint. The difference in the performance between the stepped joints and traditional flush end plate joints is also highlighted.

Seismic performance of very short links in eccentrically braced substructures

Research on the seismic performance of eccentrically braced hybrid frames indicates that utilizing very short links can enhance structural stiffness and load capacity. However, there is limited investigation into their effectiveness within eccentrically braced substructures featuring flush end plate bolted connections. This study involves an experimental and numerical investigation to understand the behavior of very short shear links with flush endplates bolted connections in the substructure. An experimental study of 8 specimens was carried out, and the variables studied included loading protocol, links length ratio, flange thickness, and end plate thickness. The experimental results showed that the co-design methodology for flush endplates and bolts of very short links exhibited acceptable performance. Very short shear links bolted with flush endplates demonstrated an average overstrength coefficient of about 1.8 and an ultimate plastic rotation angle above 0.12 rad. Numerical analysis explored the effects of length ratio, web height-to-thickness ratio, and flange width-to-thickness ratio on overstrength behaviors and yield capacity of very short links. The analysis indicated that the length ratio was crucial in determining overstrength coefficients and the yield capacity of very short links. The study established modified formulas that consider the impact of different variables to more accurately determine overstrength behaviors and yield capacity based on formulas in the Chinese code.

Experimental and numerical investigation of the bending behavior in nontraditional steel beam-to-beam tip connections

This study aimed to conduct combined experimental testing and numerical studies on the static performance of tip beam-to-beam flush endplate moment connections. The research parameters considered were bolt layout, diameters, and end plate thickness. Three specimens consisting of two IPE 300 beams connected to a beam of section HEA 300 using two end plates were designed and assembled with different bolt configurations. The grade of the steel elements was S235, while that of the bolts was 8.8. A monotonic load was applied to the specimen during testing, revealing failure modes such as fractures in bolts, end plate bending, and necking loosening of bolts. The study presented and discussed the moment rotation relationship, rotation capacity, and initial stiffness for the three specimens. A finite element (FE) model was constructed based on the moment-rotation curves of the tested connections, and the numerical and experimental results showed good agreement. An extensive parametric study was conducted to investigate the effect of different end plate thicknesses and bolts of various diameters and configurations on the connection's behavior. The study revealed that increasing the bolts' row number in tension rather than increasing the number of bolts in a row significantly affects the ultimate capacity and ductility of the connection. A thick end plate increases the connection's rotation capacity but decreases its ductility. The study also introduced a simple approach based on virtual work to predict the connections' bending stiffness using load and deflection results.

Behaviour of bolted rigid joint with endplate under localised fire scenario

The bolted endplate rigid connections in steel structures are used due to their robustness in distributing forces between the connected members. Though numerous studies have been performed to investigate the response of endplate connections under conventional fires representing uniform temperatures throughout the members (ISO-834, ASTM E119, etc.), the response of the same in case of localised fire is still not explored fully. The present paper focuses on an investigation of the behaviour of a moment resisting frame (MRF) assembled with flush endplate connection with bolts as connecting medium under localised fire scenario using Finite Element (FE) technique. A series of cases with different magnitudes of applied loads was investigated. In all the cases, the frames were heated up to failure with the localised fire source underneath the beam midspan and the corresponding failure modes were investigated. Experiments were performed on the samples of material at high temperature to gather a firsthand information on material characteristics. The frames experienced member failure at the zone of maximum temperature in the beam (midspan) for load level up to 30% of its ultimate capacity, whereas for load level above this, the frame failed at the connecting bolts of grade 5.6, which were maintained at room temperature. Based on the numerical study, it was observed that the provisions of IS 800:2007 were conservative than EN 1993-1-8:2005 in evaluating the safety of bolts under localised fire scenarios. Finally, parametric studies with the variation in connection geometry and configurations were performed, and design suggestions were recommended.

Performance of short links with flush and extended end plate connections using FEM analysis

AbstractEccentrically braced frames are commonly used as a seismic resistant system, due to the good balance of stiffness and ductility. Bolted links have been proposed in the past to allow replacing the damaged dissipative components following a strong earthquake. The goal of this research work is to investigate the influence of the connection type on the performance of bolted links using the Finite Element Analysis. Numerical models of links are first calibrated using past experimental tests. Modelling criteria adopted to replicate the experimental behaviour of the links highlighted in the tests are reported. The achieved results obtained regarding a flush end plate bolted link and an extended end plate bolted link with different lengths are then used as benchmark to assess the influence of the link length and type of connections adopted on the response of the links. The Finite Element Method is used to investigate alternative solutions to the tested ones. Finally, the investigated options are compared to determine the advantages and disadvantages of each solution.

Enhanced progressive collapse resistance of bolted beam-to-column connections with ductile stainless steel components

With the use of ductile stainless steel bolts and hot-rolled sections/plates as critical connection components, the progressive collapse resistance of bolted beam-to-column connections may be effectively enhanced at relatively low costs. To verify the viability of this concept, a comprehensive numerical study is performed to investigate the collapse-resisting performances of flush end-plate (FEP) and web angle (WA) connections equipped with stainless steel components. Through a detailed parametric study with various connection configurations and structural layouts, it is proved that the use of stainless steel components can produce remarkable enhancement to the collapse resistance of the connections. The average increase in dynamic load capacity is 30% for FEP connections using stainless steel bolts instead of carbon steel bolts. This average ratio can be as large as 109% for WA connections with the use of stainless steel bolts and web angles. These results clearly demonstrate the great potential of using stainless steel components in steel connections for collapse-resisting purposes. Similar concepts may be naturally applied in many other scenarios where the ductility of a few critical components controls the robustness of the entire system.

Simplified Modelling of Failure in High Strength Bolts under Combined Tension and Bending

Bolted connections are widely adopted in steel structures and their behaviour affects to a large extent the global response of the system. High-strength bolts of type HV are commonly employed. Under pure tension, these bolt assemblies usually fail by thread stripping. However, it was observed experimentally that, under combined tension and bending, the failure mode changes to fracture of the shank. The former loading condition commonly occurs in the case of thick extended end plate connections and the latter in the case of flush end plates. In order to analyse the behaviour of the structure, the finite element method (FEM) is usually employed. While there is a wealth of information on FEM modelling of bolts for standard loading conditions (e.g., tension), the authors are unaware of a model able to replicate both tension-only and combined tension and bending conditions. In this paper, a simplified approach to be used in the framework of FEM is proposed to model the behaviour of high-strength HV bolts which can replicate the failure mechanism of bolts under tension only and combined tension and bending. The bolt assembly is modelled with continuum elements, supplemented by a non-linear spring connecting the nut to the bolt shank. The spring captures the stiffness, resistance, and ductility of the bolt-to-nut threaded connection, reproducing the experimentally observed failure mode in the case of pure tension conditions. A simplified damage model is applied to the continuum finite elements used to model the bolt, which replicates shank failure under combined tension and bending as a result of large local stresses and strains occurring under these conditions. The proposed model captures with good accuracy the actual behaviour of high-strength HV bolts under tension only as well as under combined tension and bending.

Assessment of Design Approaches for Stainless‐Steel Joints Through an Equivalent FE Modelling Technique

AbstractConsidering the significant strain‐hardening and ductility characteristics of stainless steel and the influential role of beam to column joints in the overall response of structures, a clear understanding of their moment rotation behaviour appears fundamental. In the present study, a review of the European design code for three typical semi‐continuous beam‐to‐column joints (extended end plate, flush end plate and top‐and‐seat angle connections) is first carried out. Then, using a hybrid modelling strategy with uncoupled elastic‐plastic springs for the bolts and shell elements for the members, more refined 3D finite element (FE) models are developed and validated against available test results. An equivalent stress definition is then proposed for calculating the joint moment resistance. Finally, the initial rotational stiffness, moment resistance, rotation capacity, and failure patterns are used to evaluate critically the accuracy of the predictions of the European design code. As a result, the need for more comprehensive design guidance in accordance with the observed findings is pointed out.

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.

Investigating the Behavior of Steel Flush Endplate Connections at Elevated Temperatures Using FEM and ANN

Investigating the Behavior of Steel Flush Endplate Connections at Elevated Temperatures Using FEM and ANN

Revealing the nonlinear behavior of steel flush endplate connections using ANN-based hybrid models

Connections are crucial zones in steel buildings since they provide interaction between principal structural components (i.e., beams, columns) and provide stability to the entire building. Therefore, predicting the connection behavior remains essential to achieving safe structures. This paper proposes novel hybrid ANN-HPO models, which are made by integrating artificial neural networks (ANN) and hunter-prey optimization (HPO), for predicting the moment-rotation (M-θ) behavior of steel flush endplate (FEP) connections. For this purpose, a database of 121 steel FEP connections and corresponding data points of the M-θ curve is compiled to develop the ANN-HPO models. The geometric and material properties of the column, beam, endplate, and bolts are used as input variables. Meanwhile, the M-θ behavior, represented by the ultimate moment (Mu), the rotation at the ultimate moment (θu), the initial stiffness (Rki), the reference plastic rotation (θ0), and the shape parameter (n) are output variables. To assess the predictive power of the ANN-HPO model, the obtained results are compared with those of four recently robust machine learning (ML) models, including decision tree (DT), random forest (RF), gradient boosting regression tree (GBRT), and extreme gradient boosting (XGBoost). The comparison shows that the proposed ANN-HPO model has the best performance for predicting the M-θ behavior in the training and testing phases. Finally, a graphical user interface (GUI) application is developed to enable users to predict the M-θ behavior and reconstruct M-θ curves of steel FEP connections based on trained ANN-HPO models.

Rapid prediction of the ultimate moment of flush endplate connections at elevated temperatures through an artificial neural network

Steel connections are vulnerable structural components, and their failure can lead to the collapse of the whole structure in a fire. Hence, it is crucial to predict the connection behaviors accurately to enable a precise prediction of structural performance in the fire. This paper proposes an efficient approach for predicting the ultimate moment of flush endplate connections at elevated temperatures using the finite element method and an Artificial Neural Network (ANN). Firstly, a finite element model considering both geometric and material nonlinearities is developed and verified with existing experimental results conducted by others. Based on the validated finite element model, an ABAQUS plug-in, namely COinFIRE, is implemented in ABAQUS to facilitate the parametric study. Consequently, 886 finite models are generated and used as training data for developing the ANN model. Accordingly, the endplate thickness, the pitch of bolts, the bolt row distance, the outer edge distance, the gage distance, the bolt diameter, the number of bolt rows, and the material properties at elevated temperatures are considered input variables. Meanwhile, the output is the ultimate moment. The obtained results show that the proposed ANN model can accurately predict the ultimate moment of flush endplate connections (R2 = 1.0, 1.0, 1.0, RMSE = 0.811 kN.m, 1.627 kN.m, 1.256 kN.m, and a20-index = 1.0, 1.0, 1.0 for the training, testing and validation datasets, respectively). Finally, closed-form formulas and a graphical user interface (GUI) tool are developed to evaluate the ultimate moment of flush endplate connections at elevated temperatures for practical use. The proposed approach shows great promise as a powerful design tool for steel connections at elevated temperatures.

Experimental study on seismic performance of column-column-beam joint in panelised steel-modular structure

This paper proposes a fully-bolted column-column-beam joint for panelised steel-modular structure, which splices the box columns with integral inner sleeve and connects the box columns with H-shaped beam via stiffened angle steels and flush endplate. Compared to the currently prevailing joints, the currently proposed joint exhibits good constructional performances for panelised modules, such as higher prefabrication rate, lower transportation and stacking costs for column modules. To evaluate the influences of different vertical splicing bolt types, column top thickness and angle steel thickness, four different configurations of the joints are designed to derive the optimal performance of the currently proposed joint. On the premise of significant enhanced constructional performances, pseudo static tests on four different full-scale joint specimens are implemented to evaluate the seismic performance of the currently proposed joint via analyses of the failure mode, hysteretic curve, strength, stiffness, rotation capacity, ductility and energy dissipation capacity of the joints. It mostly exhibits as semi-rigid joint to possess sufficient rotation and energy dissipation capacities. Through the tests, compared with the long stay bolts, it is preferable to apply high strength bolts for vertical splice to improve seismic performance. Thickening the column top significantly avails the flexural capacity, stiffness and energy dissipation capacities of the joints. On the other hand, thickening the angle steel slightly enhances the positive flexural capacity, stiffness, whereas it negates the rotation and energy dissipation capacities.

Experimental investigation and analytical modeling of steel beam-to-CFDST column connection

In this paper, a prefabricated connection between concrete-filled double-skin steel tubular (CFDST) column and steel beam with flush endplates and bidirectional bolts was developed. To investigate the effects of the endplate thickness, axial compression ratio, bolt diameter, concrete fill degree, and shape of the inner tube on the seismic performance of the connection, a series of pseudo-static tests were performed on six specimens. It was observed that the bending deformation of endplates, warpage of bolts, local buckling of beam flanges, and cracking of weld seams were typical failure modes. An increase in the endplate thickness and the replacement of the circular inner tube by the square inner tube significantly improved the ultimate strength of the connection. The ultimate strength of the connection was not sensitive to the axial compression ratio and bolt diameter, and it decreased as the concrete fill degree increased. The displacement ductility coefficients of the specimens were greater than 6.21. Higher ductility and accumulated energy dissipation were obtained by increasing the endplate thickness, axial compression ratio, bolt diameter, and replacing the circular inner tube with the square inner tube. The ductility and accumulated energy dissipation decreased as the concrete fill degree increased. Based on the component method, an analytical model of the initial rotational stiffness of the connection was developed. The mean and standard deviation of the ratios of predicted values to test values were 0.95 and 0.06, respectively.

Novel coupled modular steel structure and seismic tests on high-performance interconnection

Modular building registers the advanced stage of construction industrialization and the corner-supported steel modular building is the most widely applied. However, its structure, which is integrated by corner interconnections only, incurs the problems of structural redundancy and interconnection-assembly complexity. To this gap, this paper proposes the novel coupled modular steel structure and suitable interconnection, which significantly affects the overall structural response and assembly efficiency. Pseudo static tests of three full-scale cruciform joint specimens are implemented to study the seismic performance of interconnection. The results show that the currently proposed coupled modular steel structure could replace the incompletely-combined group-columns and laminated beams with single structural components to avoid the structural redundancy and reduce the assembly difficulty of interconnections. The proposed interconnection exhibits excellent seismic performance. Hysteretic loops of coupled beam and module beam are “bow” shape and “shuttle” shape, respectively, indicating their good hysteretic performance. Ultimate storey drift angles of coupled beam and module beam could reach 0.08–0.09 rad and 0.06–0.08 rad, respectively, which satisfy the requirement for SMF in ANSI/AISC 341-16 and indicate their excellent rotation capacity. The ductility coefficients of the specimens are 2.27–3.64 except for MC2, indicating their good ductility capacity. Adopting the flush end plate for coupled beam and high strength bolts for vertical splice is recommended for the interconnections to obtain better hysteretic performance and bearing capacity. This research provides brand new design for modular construction and references for future research on global response of coupled modular steel structure.

Seismic performance and analytical model of CFDST joint with endplates and long bolts

Developing the prefabricated structures is an effective way to reduce carbon emission. At present, the research on the prefabricated concrete-filled double-skin steel tubular (CFDST) joints is insufficient. In this paper, a prefabricated steel beam to CFDST column joint was proposed. In order to investigate the seismic behavior of the joint, a series of pseudo-static tests were performed on four 1/2 scale specimens with consideration of the endplate type and the inner steel tube shape. The failure modes included bending deformation of the endplate, warpage of the bolts, fracture of the weld seam, and buckling of the steel beam flange. Besides, all specimens exhibited better hysteretic behavior, ductility, strength, and stiffness. The ultimate strength and the energy dissipation capacity of the joint with the extended endplate were higher than the joint with the flush endplate. The inner steel tube shape had limited impact on the seismic performance except that the inner circular steel tube can distinctly increase the energy dissipation capacity of the extended endplate joint. According to the classification method in EC3, the proposed prefabricated joint was the semi-rigid and partial-strength joint. Moreover, the strain analysis indicated that the yield pattern was from the steel beam flange to the endplate. In addition, a prediction method of moment resistance was proposed and verified by test results. The research results of this paper provide a design basis for the prefabricated CFDST structures.

Seismic performance of prefabricated joint for hollow CFDST column

While several studies have been conducted on the performance of concrete-filled double-skin steel tube (CFDST) members, only a few have evaluated the performance of prefabricated CFDST joints. In this study, we propose a prefabricated endplate bolted joint between the steel beam and CFDST column by performing a series of experiments while considering two effect parameters of the endplate type and thickness to achieve rapid construction and avoid wet work and on-site welding. Typical failure modes include plastic deformation of the endplate, local buckling of the flange end, slipping and fracture of the bolts, and fracture of the weld seam. Brittle fractures of bolts usually occur in the extended endplate joint and not in the flush endplate joint. In addition, the displacement ductility coefficients were all between 4.89 and 8.54, which indicated that the proposed joints possessed supreme ductility. Compared to the flush endplate, the extended endplate is capable of increasing the bearing capacity of the specimens by over 20%. Moreover, when the thickness of the endplate was increased to 8 mm, the maximum increment in the bearing capacity of the extended endplate joint and flush endplate joint increased by 35.91% and 30.88%, respectively. Based on the classification method in EC3, all specimens were the semi-rigid and partial strength joints. Furthermore, we propose a prediction method for the ultimate moment of the joint, which showed good agreement with the experimental results. We believe the results acquired in this study can provide a design basis for prefabricated CFDST structures.

Seismic tests and nonlinear model of beam-CFDST column joints with blind fasteners

In recent years, substantial research efforts have turned towards concrete filled double skin steel tubular (CFDST) column due to its superior mechanical performance. However, an effective and convenient connection method between a CFDST column and a beam still needs to be investigated in depth. This paper tried to adopt the blind bolting technology in a CFDST column to beam connection. A series of joint specimens were prefabricated and designed with different end plate types, column hollow ratios and beam types to carry out pseudo-dynamic tests. Excellent seismic performance was detected for all test specimens. It was observed that increasing the column hollow ratio could moderately increase the ultimate strength and the specimen with extended end plate had higher ultimate strength stiffness compared with that with flush end plate. To accurately capture the dynamic response for this type of joint, an analytical model was developed considering the shear performance of panel zone and moment-rotation behavior of connection. Shear strength of CFDST column panel zone was modified from that of CFST column panel zone based on the yield line method for including the contribution of confined compression strut. It indicated that two potential yield mechanism might appear depending on the column hollow ration (χ). The analytical model could well predict the test results. The research and analytical results provided an effective connection method to assemble a CFDST column to a beam and supply a feasible analytical model to predict the joint performance.

Experimental Database for Steel Flush End-Plate Connections

A comprehensive experimental database of bare steel and composite flush end-plate (FEP) connections, covering tests conducted within the last 50 years, was collated and made public. The database includes deduced and tabulated parameters defining the configuration, geometric and material properties, and observed deformation and failure modes for more than 360 test specimens. The database also includes the specimens’ monotonic/cyclic responses in the form of digital moment versus rotation data. The database will aid researchers and engineers in benchmarking empirical, mechanical, or continuum finite-element models; assessing the robustness of existing numerical modeling and designing methodologies for end-plate connections; and developing new predictive models or damage fragility functions. The database also serves as an exemplar for the systematic development of similar databases for other types of semirigid connections. A graphical interface was developed to aid users in exploring, filtering, and assessing the database.