Behavior of beam-to-column moment connections under fire load

The welded flange-bolted web type moment connections are commonly used in the construction of modern steel buildings. The behavior of this type of connection under service load and seismic load has been studied extensively; however, the knowledge of its performance under fire load is limited. In this paper, the experimental studies of the welded flange-bolted web moment connections under fire loads are presented. Four full-size steel beam-to-column assemblages, with and without fire-proofing materials, were selected to simulate the moment connection commonly used in steel buildings. The fire load was simulated either by a steady state method to reach a fully-developed fire or by a transient state method following the standard temperature-time curve. Parametric studies were also conducted to examine the strength degradation of steel moment connection at elevated temperature. From these studies, it was found that the beam-to-column connection is able to retain its design strength up to 650 ^°C. However, the stiffness dropped to 25% of the value at ambient temperature. Ductile behaviors were observed on the connections, with necking and tearing at the top flange and local buckling at the bottom flange. It was also found that the stability and integrity of steel connections can be ensured if proper fire-proofing materials were provided.     

足尺钢梁柱刚性连接节点抗震性能试验研究

通过10个不同连接构造的足尺钢梁柱刚性连接节点的试验,研究了标准栓焊连接节点、标准全焊连接节点、梁翼缘加强型节点、梁翼缘局部削弱型节点以及梁贯通型节点在梁端往复荷载作用下的破坏过程、破坏形态、承载力和塑性变形能力等抗震性能。试验结果表明,梁翼缘局部切割削弱和梁翼缘加盖板节点的梁的极限塑性转角大于0.03,梁贯通型节点、梁下翼缘加腋节点和梁翼缘打孔节点的梁的极限塑性转角大于0.02,其余类型节点的都小于0.02。对实测的梁翼缘和腹板的应力分布的分析表明,梁根部翼缘处于三向应力状态,是其脆性断裂破坏的原因之一。建议钢框架梁柱连接优先采用梁翼缘加梯形盖板节点和梁下翼缘加腋节点。     

Application of fire-resistant steel to beam-to-column moment connections at elevated temperatures

This paper presents a new method of using fire-resistant steel to improve the fire-resistance of beam-to-column moment connections in steel structures. Two full-scale beam-to-column moment connection specimens were tested at elevated temperatures according to the standard ISO-834 fire to verify the feasibility of the proposed method. In addition, a detailed 3-D finite element model was developed to simulate the structural behavior of the column-tree moment connection specimens in fire. The fire test results show that the proposed method can effectively extend the fire endurance time, reduce structural deformation, and raise the critical temperature to failure for the beam-to-column moment connections. The numerical results obtained from the 3-D finite element analyses for the two specimens successfully simulated the fire test results.     

New moment-rotation equation for welded steel beam-to-column connections

A three-parameter tangent inverse equation is generically proposed for the non-linear moment-rotation (M-θ) relationship of semi-rigid steel beam-to-column connections. The parameters are the initial stiffness, the plastic stiffness, and a reference moment. Two commonly used welded moment connections are picked up for moment-rotation calculation and comparison between the results of the proposed model and those of a detailed nonlinear finite elements modeling. Semi-analytical equations are proposed for calculating the parameters containing basic factors affecting behavior of the connections. The coefficients of the equations are computed based on a data bank developed in this study using the finite element method. A large number of finite elements models covering the whole range of common dimensions of the above connections are analyzed. Accuracy of the finite element model is verified on the basis of the available test results from previous studies. Tensile tests for determination of material properties of weld to be used in the modeling are conducted. Comparison between the results of the semi-analytical equations and the finite element models shows that the proposed model is able to estimate the moment-rotation curves of the welded beam-to-column connections with very good accuracy.     

On the analytical model of beam-to-column semi-rigid connections, using plate theory

An analytical method is presented that can be used to determine the behavior of a particular steel beam-to-column extended end plate connection, in both linear and non-linear regions. This article demonstrates a closed form solution of the equations of deformation, for this type of connection. Besides, a step-by-step analytical procedure for establishment of the linear part of M-θ curve of this form of connection is developed. However, this technique can properly be extended to the non-linear regions, which is not considered in this article. The correctness of the results has been ascertained by a comparison, using non-linear finite element models as well as experimental approach; and very good agreement has been obtained. Furthermore, the writers believe that this method will efficiently serve design engineers in real design conditions.     

Cyclic behaviour of bolted cold-formed steel moment connections: FE modelling including slip

In this paper a Finite Element (FE) procedure is described for simulating hysteretic moment–rotation behaviour and failure deformations of bolted cold-formed steel (CFS) moment connections. One of the main challenges in modelling the response of bolted connections is the presence of bolt slip. A series of six beam–column assemblies comprising CFS curved flange beams, a support column and a through plate were tested under cyclic loading. The moment–rotation behaviour of the connections was dominated either by flexure in the beams or by bolt slip in the connections. FE models presented in this paper incorporate geometrical imperfections of the beams, material properties obtained from tensile coupon tests and bolt slip to address these two types of behaviour. The updated FE models result in an accurate prediction of the hysteretic moment–rotation behaviour of the connections dominated by a flexural behaviour in the beams. A simplified cyclic slip model which allows slip at a specified reduced slip resistance load simulates reasonably well the hysteretic behaviour of connections dominated by bolt slip. Using the updated FE model, the failure modes of the connections predicted by the simulations also agree well with those observed in the experiments.     

基于OpenSEES的装配式混凝土框架节点数值模拟方法研究

装配式混凝土框架结构是目前应用最广的装配式结构体系之一,该结构中的梁柱连接节点是核心受力部位,不仅影响着整体结构的抗震性能,也直接关系到施工的便易性与经济性。针对不同类型装配式混凝土结构梁柱节点的非线性行为特征,文中基于OpenSEES软件系统地研究了其数值模拟方法,提出适用于湿式连接节点与干式连接节点的两类分析模型,并同时考虑如键槽、预应力、耗能件等局部构造措施的影响。为验证该文提出模型的有效性与准确性,进行10个不同类型的装配式节点低周反复加载试验的数值模拟,并给出各类型的建模参数取值。计算结果表明,文中提出的模拟方法不仅可以准确地反映节点的宏观力学行为（如峰值承载力、刚度退化等）,同时可以预测局部材料的微观受力状态与行为,可为今后的装配式混凝土节点建模分析提供参考。     

Seismic behavior of bolted beam-to-column connections for concrete filled steel tube

Concrete-filled steel tubes (CFT) have the advantage of high strength, high stiffness and being constructed quickly. However, because the behavior of the beam-to-column connection for CFT is complicated and its design has not been sufficiently verified, their use has been limited.In this paper, a new design of bolted beam-to-column connections for CFT is proposed. A mechanical model is established in order to derive theoretical equations for calculating the stiffness, the yielding shear strength and the ultimate shear strength of the panel zone. Also, a series of cyclic loading experiments have been conducted. The experimental results and theoretical results are very close, which demonstrates that the bolted connections have superior seismic resistance in stiffness, strength, ductility and energy dissipation mechanisms. From the laboratory studies, even though the story angular drift reaches 7% and the plastic angular displacement reaches 5%, the structure still stands. Those results indicate that the seismic resistance exceeds those specified in Taiwan and the US.     

加强式梁柱连接节点域初始刚度的计算方法研究

通过建立简化力学模型和修正节点域柱腹板的抗剪面积,提出一种较简便的节点域初始刚度计算方法,不仅能够灵活运用于柱翼缘和柱腹板加强的节点域刚度计算,也能够用于普通的未加强节点域的刚度计算.通过与试验和有限元结果的对比,表明本方法具有足够的精度,适于进行结构分析和参数研究.     

自复位钢框架节点有限元模拟及参数分析

研究了一种具有自复位能力的钢框架节点的力学性能.该节点在梁柱间通过角钢栓接,并沿梁长布置高强预应力钢绞线.通过对钢绞线施加预应力将梁柱压紧,使节点具备足够的抗弯刚度以满足正常使用情况下的功能性要求,钢绞线同时提供回复力,使节点在地震后具有自复位能力.采用通用有限元分析软件Abaqus 6.9建立节点模型,对9个足尺钢框...     

锈蚀钢筋混凝土压弯构件的恢复力模型

根据反复荷载下人工气候环境加速钢筋锈蚀的钢筋混凝土压弯构件力学性能的试验结果,提出了反复荷载作用下恢复力模型中与钢筋锈蚀率相关的特征参数计算公式,建立了锈蚀钢筋混凝土压弯构件的退化双折线恢复力模型,并与参考文献试验结果进行了对比,结果表明本研究建立的恢复力模型具有一定的适用性.     

The development of a component-based connection element for endplate connections in fire

This paper describes the development of a component-based element for endplate connections in fire. The reported research is part of an ongoing project aimed at understanding joint behaviour in fire. The paper summarises the derivation of the stiffness matrix of this new element, based on a spring model, and the incorporation of the element into the non-linear finite element program Vulcan. It also states the component characteristics that have been used for the individual zones of deformation in an endplate connection. Furthermore, the additional features of the element, necessary for correct response at elevated temperatures, such as the consideration of the temperature distributions across the connection as well as cooling and unloading, are summarised. The proposed element is then used to predict the moment–rotation curves of connection experiments at ambient and elevated temperatures. Finally, the advantages and limitations of the new high-temperature connection element are listed.     

Design equations for moment strength of RBS-B connections

Reduced Beam Section (RBS) moment connections are newly developed connections for Special Moment Resisting Frames (SMRF). This study focuses on Reduced Beam Section with Bolted web connections (RBS-B). Several experiments have demonstrated that some RBS-B connection specimens failed prior to reaching the plastic moment capacity of the reduced beam sections: this may be attributed to insufficient moment strength in the RBS-B connections. This study proposes a new procedure for accurately computing the moment strength for ensuring that a plastic hinge forms in the reduced-section region of the beam, as intended by design.     

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.     

Performance of built-up T-stubs for Double T moment connections

The behavior of built-up T-stubs subjected to tensile loading through the stem is studied through numerical and experimental models. The aim of the research is the determination of limit states that control the behavior of built-up T-stubs and the evaluation of the applicability of current design recommendations for double split tee moment connections when the split tees are replaced by built-up T-stubs. A series of one-half scale T-stubs specimens were tested under monotonically increasing tensile loads. The experimental results show significant overstrength with respect to that predicted by current design recommendations and differences between the expected and actual failure modes. No weld failures were observed. Detailed 3D finite element models of the specimens tested were created and subjected to monotonic tensile loads. The models reproduced the load–deformation response and failure modes of the test specimens and enabled an improved understanding of the location and level of damage of the built-up T. They can be used to study the cyclic response of these components.     

Requirements for moment connections in statically indeterminate timber structures

In statically indeterminate structures, connections play a vital role in the moment distribution. Demonstrated here is a method to evaluate the conditions, taking full advantage of the benefits offered by the indeterminate nature of the structures, and using the well-established, graphical beam-line method. This method shows how important the immediate load take-up is, the stiffness, the moment capacity of the connection and how it all affects the structural behaviour. The examples considered here use both the traditional non-reinforced dowel-type fastener connections and also timber connections reinforced with steel plates. They show that the minimum rotation requirements to achieve an effective structure are satisfied easily in contrast to requirements on stiffness. In this respect, timber connections with local reinforcement glued at the interface of the connection area offer more prospects.     

钢板-混凝土组合墙压弯承载力计算模型

基于全截面塑性理论,提出了钢板混凝土(SC)组合墙压弯承载力计算模型。试验与有限元计算结果均表明,该计算模型具备精度高和简单实用的双重特点。有限元计算结果还表明,对于剪跨比小于1.0的SC组合墙,建立的压弯模型不再适用,原因在于剪力的耦合作用不可忽略,建议加强对小剪跨比SC组合墙抗剪承载力试验和机理的研究。     

Modelling M–φ curves for standard beam-to-column connections

A 3-parameter exponential model to describe the non-linear M–φ relationship of flexible beam-to-column connections is proposed. The model only requires a determination of the parameters M_o, K_i, andK_p generated from a connection's dimensional details and material strength properties. Employing simplified connection behavioural models to approximate beam-to-column connection behaviour and from kinematic and equilibrium considerations, analytical expressions for evaluating the model parameters K_i and K_p are derived for standard beam-to-column connections; an empirical expression for evaluating the M_o-parameter is developed. The connection M–φ behaviour predicted by the model is compared with published connection test results and it is concluded that the model yields results in good agreement with actual connection test behaviour.     

国家游泳中心方钢管受弯连接节点加强试验研究

国家游泳中心多面体空间刚架的杆件与节点之间采用全熔透的对接焊缝连接。为避免焊缝脆性破坏先于钢材破坏,实现“强节点弱构件”的设计思想,确保结构具有良好的延性,有必要对焊缝连接节点进行适当加强。对方钢管杆端承受弯矩的连接,在未加强全熔透焊缝连接的基础上,提出了贴板加强及厚管加强两种加强方式,本文对这三种连接方式进行低周反复荷载试验。对滞回特性及延性系数的分析比较表明,贴板加强和厚管加强两种方式均可使塑性铰从弯矩最大的焊缝处外移,从而较为有效地改善节点的延性,而其中贴板加强型的效果更好。在此基础上,进一步对由强屈比较小的钢材加工而成的钢管节点进行试验,表明贴板加强的方式仍能有效改善节点的延性。