Behaviour of column web component of steel beam-to-column joints at elevated temperatures

This paper presents an experimental investigation on stocky column web panels of semi-rigid beam-to-column joints exposed to fire conditions in order to verify an analytical prediction model. Recent experimental studies show that the degradation of material properties and high axial forces, due to restrained thermal expansion of beams at elevated temperatures, significantly affect the moment–rotation response of the joints. The component method originally established for the evaluation of the joint behaviour at ambient conditions can be adopted for elevated-temperature cases. Recently developed mechanical models for joints may not be accurate as the column web component is simultaneously subjected to bending moments and axial forces. This paper focuses on the component column web in shear in order to identify the key parameters which affect joint behaviour in shear at elevated temperatures. This experimental work was conducted on three extended end-plate connections subjected to both ambient and elevated temperature conditions. After validations by test results, detailed finite element simulations were performed for a series of parametric studies at other elevated temperatures. Both experimental and numerical results are finally compared with analytical predictions.     

Modelling of strengthened column web panel in bolted end-plate composite joints

This paper deals with the analytical modelling of the column web panel in steel and composite bolted end-plate beam-to-column joints. The strengthening of these joints by web doubler plates or haunches is investigated. A previous experimental programme carried out at INSA of Rennes-France has shown the limitation of the web panel design model proposed by Eurocode 3 part 1-8. In this paper, a new model is proposed where the main idea is the partition of the whole column web panel into sub-panels. This allows to take into account the non-uniform distribution of shear forces along the height of the column web panel. The behaviour of each sub-panel is described by an original non-linear spring model. This model is able to predict accurately both the elastic and inelastic responses of the sub-panels. The overall behaviour of the column web panel is then described by a spring serial system in shear where each spring represents a sub-panel. The model predictions are in good agreement with experimental results whereas the Eurocode model seems to be conservative.     

Performance of beam-to-column joints in fire—A review

This paper presents a state-of-the-art review on the behaviour of beam-to-column joints in fire and considers experimental and analytical research work on isolated joint configurations conducted with the prime objective of developing moment–rotation–temperature behaviour of joints. In addition, investigations on the effect of axial thrust on the behaviour of joints is presented because fire tests on a full-scale building, and observations from accidental fires, have demonstrated differences between the behaviour of joints when tested in isolation and considered as part of a complete building. Furthermore, joints that are routinely assumed as pinned at ambient temperature can provide considerable levels of both strength and stiffness at elevated temperature, albeit at large deformations, and this has been found to have a beneficial effect on the survival time of steel-framed buildings. It is noted that while FE analysis is capable of predicting accurately the performance of steel structures in fire, realistic models of joint performance are required. For this purpose, the use of a component approach for the prediction of joint performance is explained and appears to be a viable alternative to extensive joint testing or detailed FE analysis of joint details.     

Testing of composite steel top-and-seat-and-web angle joints at ambient and elevated temperatures: Part 2 — Elevated-temperature tests

An experimental programme of eight elevated-temperature tests on composite steel top-and-seat-and-web (TSW) angle joints was carried out to investigate the behaviour of this form of joints under fire conditions. It is found that the inherent strength and stiffness of composite joints can significantly improve the structural behaviour of steel framed structures under fire conditions. However, experimental works on composite steel TSW angle joints under fire conditions have not been published yet. To develop a versatile model to predict the joint moment-rotation characteristics, the authors have developed a component-based mechanical model for this form of joints. The objectives of this study are to ascertain the moment-rotation characteristic for this form of joint at elevated temperatures and to validate the authors’ mechanical model. The effects of some parameters on the overall joint behaviour, such as elevated temperatures, longitudinal shear strength of RC slabs, steel beam depth and bolt behaviour were observed and investigated. The mechanical model predictions are compared with the test results and showed good agreement.     

Finite element modelling of steel fin plate connections in fire

Recent structural collapses caused by fire have focused attention on research concerning fire safety in building design. Steel connections are an important component of any structural steel building, as they provide links between the principal structural members. The evaluation of the performance of steel connections at elevated temperatures has been a topic of several research programmes in the last few years. Determining the behaviour, available strength and stiffness of moment connections in fire conditions has been a dominant theme in these research works; however very little information on the behaviour of simple shear connections in fire conditions has been disseminated. Fin plate shear connections are easy to fabricate and install; as a result, they have gained popularity with fabricators because of their economy. In this research, the robustness of simple fin plate beam-to-column connections is being investigated under catenary tension from highly deflected beams in fire. A highly detailed three-dimensional (3-D) finite element (FE) model has been created using the ABAQUS software. This is a complex model accounting for material and geometric non-linearity, large deformation and contact behaviour. Contact is critical to model the shear behaviour of the joint, and contact elements have been used both at the bolt–hole interface and also at the surface between the web of the beam and the fin plate, taking into consideration friction between the surfaces. The connection model has been analysed through the elastic and plastic ranges up to failure. Bolt shear and bending, and plate and web bearing have been observed as failure modes. A comparison between available experimental data at ambient and elevated temperatures and other analytical results shows that the model has a high level of accuracy. When the connection model was extended to include an attached beam, it was found that it eventually experiences large tensile force when exposed to fire.     

Modeling of end-plate bolted composite connection in fire considering axial force effects

This paper proposes the development and validation of a simplified model, which is based on spring-component-based model, in an attempt to calculate the initial stiffness and ultimate moment capacity for flush end-plate composite joints at elevated temperatures. This method may be adopted as the basis of the flush end-plate joint design in high temperature. In this paper, the resulting axial force due to the expansion of the beam at elevated temperatures is considered as a significant influence on the moment bearing capacity of joints. A 3-D finite element model using ANSYS is presented to simulate the real response of flush end-plate composite joints with axial force at elevated temperatures. This model is verified by comparing the simulated temperature distribution and the behavior of the joint at ambient temperature with experimental results. Then the finite element model is used to validate the accuracy of the simplified component model. Close agreement is found between the results of the simplified component-based method and that of the finite-element method. Furthermore, a simplified model based on the three-parameter exponential model proposed by Kishi-Chen [15] to predict the moment–rotation relationship of the composite joint at elevated temperatures considering the effect of the axial force is proposed, the parameters in which is obtained based on the parametric analysis with the FE model. The proposed component model and moment–rotation relationship provide a convenient path for designers to assess the connection behavior in the semi-rigid frame analysis.     

Experimental behaviour of the reverse channel joint component at elevated and ambient temperatures

The reverse channel connection appears to have the best combination of desirable features under fire loading: moderate construction cost, ability to develop catenary action and extremely high ductility through deformation of the web channel (Ding and Wang, 2007). This paper presents the results of an experimental investigation of a reverse channel component conducted at the University of Coimbra as part of the European RFCS COMPFIRE Project, the main focus of which is to characterise the behaviour of steel joints that connect steel beams to concrete-filled tubular columns under natural fire loading. A series of tensile and compressive tests at ambient and elevated temperatures was conducted. The purposes of the experimental tests were to characterise the strength, stiffness and ductility of this joint component and to establish a relationship between force, displacement and temperature.     

Column Web Panel at Elevated Temperature

One of the most recent studied components in the connections of a steel structure exposed to elevated temperature is the column panel loaded in shear. A set of three tests were performed to confirm the analytical prediction model at the Czech Technical University in Prague. The model takes into account the distribution of the internal forces in the shear panel affected by the transfer of the forces by bolt rows in tension. Two panels were tested at ambient temperature and four panels at elevated temperature. The gas temperature in the furnace followed the temperature measured during the seventh Cardington large compartment test in 2003. This contribution is focused on the presentation of the experimental results and an analytical prediction model with a component method.     

Testing of composite steel top-and-seat-and-web angle joints at ambient and elevated temperatures, Part 1: Ambient tests

This paper presents six ambient tests on composite steel top-and-seat-and-web (TSW) angle joint specimens subject to monotonic loading. It is well known that the inherent strength and stiffness of composite semi-rigid joints can improve the structural behaviour of steel frame structures. However, experimental works on the composite steel TSW angle joints are very limited. The main objective of this study is to ascertain the ambient moment-rotation characteristics of composite steel TSW angle joints and to validate the authors’ mechanical model. The test results are presented and the joint failure modes are described. The effects of some parameters on the overall joint behaviour, such as longitudinal shear strengths of RC slabs, steel beam depths and tightening torques of bolts are investigated. With the development of a new joint component to represent the RC slab in tension, the authors’ mechanical model proves to be able to produce accurate and consistent predictions of the moment-rotation characteristics of composite steel TSW angle joints. The analytical results are compared with the test results and good agreement is achieved.     

Numerical and analytical investigations of steel beam-to-column joints at elevated temperatures

Several furnace tests on the behavior of steel beam-to-column end-plate joints at high temperatures have been reported in a previous paper. This paper presents a series of corresponding analytical and numerical investigations to study the behavior of these steel joints, in some cases taking account of the influence of thermal restraint. A “component-based” methodology has been utilized to analyze the mechanical response of steel end-plate joints at elevated temperatures, incorporating the beam web shear component together with those within the tension and compression zones of the connection. Effects from thermal restraints on steel joints have also been integrated into this approach. This analytical model was found to represent well the structural behavior in the tests, including the effects of thermal restraint. In order to set these results into their proper context, detailed finite element simulations of the tests were also performed. Both the component-based and numerical predictions provide acceptable correlations with the test behavior.     

交错桁架体系中桁架与柱的连接节点设计方法研究

交错桁架中桁架的上弦杆和端部斜腹杆在与柱连接之前,已经连在一起,在与柱连接时,上弦杆和端斜杆又分别采用节点板与柱相连,在设计时如何计算,没有发现有关的研究和设计方法报道。本文对该处的连接节点进行了二维有限元模拟研究,将实际情况与采用整体连接进行了对比分析,对二者节点区的轴力、剪力和弯矩的分布情况进行了比较,并用考虑节点区弹塑性、大变形和接触问题的三维模型进行了分析,结果表明,该节点可以按照连在一起的整体节点进行设计计算。     

钢筋混凝土框架节点受剪承载力简化计算模型

各国现行设计规范中的节点受剪承载力计算公式均为基于试验资料的半经验公式,缺乏合理理论模型支撑。在已有研究基础上,通过建立平衡方程、几何方程和物理方程对钢筋混凝土框架节点进行受力分析,建议了框架节点等效核心区在剪、压复合作用下的简化计算模型,并将国内外108个钢筋混凝土框架节点试件(包括常规中节点、边节点、变梁中节点等)受剪承载力的试验结果与该模型计算得到的理论结果进行对比。研究表明：基于简化模型计算得到的节点受剪承载力与试验结果吻合较好,与我国现行规范建议设计方法的计算结果相当,该建议方法有明确的力学计算模型,能较为合理地反映框架节点的受力机理,可为混凝土构件受剪分析模型化提供参考。     

Tying capacity of web cleat connections in fire,Part 2: Development of component-based model

The companion paper has reported the results from a test programme in which web cleat connections were subjected to various combinations of shear, tying and moment actions at elevated temperatures. These tests showed that web cleat connections have very good tying resistance and rotational capacity, mainly due to the large deformation of which the web cleats are capable. In this paper a mechanical model is developed to predict the behaviour of web cleats subjected to tying forces. This model considers the formation of four plastic hinges on each angle and the effect of the angles opening in enhancing their resistance. It is capable of representing the action of the angles in component-based models for web cleat connections, in which algorithms for other components, including bolts in tension, bolts in double shear and holes in bearing, are already available. Failure criteria determined from the tests have been introduced into the models for components such as web cleats and bolts in double shear. This enables the component-based assembly to predict the occurrence and the sequence of connection failure. The behaviour of the connection predicted by the component-based model shows good correlation with the test results, which indicates that the developed model can be adopted in structural frame analysis to consider connection failure.     

Experimental and numerical analysis of a halved and tabled traditional timber scarf joint

Traditionally constructed heavy timber trusses, found in timber framed buildings and bridges, employ various traditional joints, among them the lower chord scarf joint. This paper examines the behavior of a halved and tabled scarf joint, which was studied as an isolated structural component using experimental tests and finite element analyses. Experimental tests identified two different limit states for these particular scarf joints: shear failure parallel to grain and tension failure perpendicular to grain. The possibility of failure due to tension perpendicular to grain results from variations in grain angle and means that the limit state of shear failure parallel to grain, typically assumed in analysis and design, is unconservative. For the purposes of design and rehabilitation, the authors propose that the scarf joint be treated as a member subject to combined bending and axial tension forces. The results of the finite element analysis, performed using solid continuum elements in ABAQUS, are in good agreement with the experimental test results. In addition to finite element models, the authors use analytical spring models to demonstrate that when developing a two-dimensional model of a truss with lower chord scarf joints, serviceability limit states be checked with a model that reduces the lower chord section properties in the vicinity of the scarf joints.     

Shear strength of plate girder web panel at elevated temperature

This paper presents a theoretical model to predict the failure loads of plate girders with transverse stiffeners subjected to a specified constant temperature or isothermal condition. The work is based on classical plate girder theory at normal ambient conditions subjected to increasing load. The equations incorporating the temperature-dependent material properties and thermally-induced axial stress arising from surrounding structural restraint are derived. They can be used for the case when the plate girder is subjected to pure shear or to a combination of shear and axial stresses. To simplify the analysis, uniform temperature distribution is assumed within the full depth of web panel. Solution procedures are presented for the fire resistance analysis of web plate girder, either in terms of the shear strength corresponding to isothermal condition, or the limiting temperature for a prescribed set of constant shear force and axial thermal restraint. For both procedures, the predictions agree well with the finite element analyses.     

On the plastic tripping of flatbar stiffeners

A simple model for plastic tripping of the web of a stocky T-strut subjected to axial compression is presented and the complete collapse behaviour of the model is analysed. The model is an extension of the Shanley model which has been proved useful in the past in understanding several aspects of inelastic column buckling. The column material is assumed to be elastic perfectly plastic. A closed-form solution is obtained for the post-ultimate load shortening behaviour of the present model strut. This solution is compared with the available experimental results and the previous analytical predictions based on Murray's plastic mechanism approach. It is shown that the present results are in better agreement with the experimental results than the previous analytical solutions. The present model grasps the main features of the post-ultimate collapse phenomenon, including tripping of the web and elastic unloading in a part of the cross-section.     

钢纤维增强异形柱框架节点受力性能试验研究

为了解决异形柱框架节点的薄弱问题,对核心区应用钢纤维增强的异形柱框架中节点与同条件下未用钢纤维增强的异形柱框架中节点进行拟静力试验研究,对比分析异形柱框架中节点试件的破坏特征、中节点核心区的箍筋应变、混凝土应变及异形柱框架中节点的受剪性能,研究钢纤维增强的异形柱框架节点薄弱部位受力性能。研究结果表明:应用钢纤维增强的异形柱框架中节点试件的破坏特征得到改善;在异形柱框架节点核心区掺入钢纤维可以降低加载初期中节点核心区的箍筋应变,中节点腹板在平行于剪力方向的箍筋应变大于腹板垂直剪力方向的箍筋应变及翼缘处的箍筋应变;在中节点核心区掺入钢纤维可提高腹板混凝土的主拉应变和异形柱节点受剪承载力。     

The seismic performance of new detailing for RCS connections

Over the past few decades considerable experimental and numerical studies have been conducted on the Reinforced Concrete columns to Steel beams (RCS) connections. Most of those researches have focused on studying the joint failure modes and ultimate joint strength of specimens utilizing strong beams and columns with weak joints. In this paper, two interior RCS connections were designed based on the Strong Column–Weak Beam (SCWB) criterion. Both specimens were tested under quasi-static reversed cyclic loading. The tested specimens were modeled by a finite element method, which verified with experimental results. Several models with different joint details were investigated using the verified FEM. Lateral load–story drift response, vertical bearing stresses, joint shear forces, shear strains at the joints, and axial stresses of the joint stirrups were studied in those models. The results indicated that the performance of models directly depends on joint detailing, effectiveness of shear keys, and the amount of confinement provided for a joint region.