Experimental and theoretical analysis of the moment-rotation behaviour of stiffened extended end-plate connections

A new theoretical model to evaluate the moment-rotation (M-?) relationship for stiffened and extended steel beam-column end-plate connections has been derived in this paper. Based on a specific definition of the end-plate connection rotation, the end-plate connection is decomposed into several components, including the panel zone, bolt, end-plate and column flange. The complete loading-deformation process of each component is then analysed. Finally the loading-deformation process for the whole connection is obtained by superimposing the behaviour of each component. In addition, 5 joint tests have been conducted to verify the proposed analytical model. By comparing it with the test results, it has been concluded that this analytical model can evaluate the rotational behaviour of end-plate connections, as well as the moment-rotation (M-?) curve and the initial rotational stiffness accurately. Furthermore, it can analyse every contribution to the joint’s rotational deformation, such as the shear deformation of the panel zone, the bolt extension, the bending deformation of the end-plate and column flange, etc. This analytical model also provides moment-shear rotation (M-?_s) and moment-gap rotation () curves, which establish a reliable foundation for analysing the detailed rotational behaviour of end-plate connections.     

梁柱端板连接节点的初始转动刚度计算模型

首先利用分解法建立了梁柱螺栓端板连接节点的力学模型 ,然后基于梁板理论给出了节点初始转动刚度的解析公式。公式综合考虑了端板变形、柱翼缘以及螺栓对初始转动刚度的贡献 ,可方便地推广于平端板和外伸加劲端板连接初始转动刚度的计算。公式计算结果和试验结果以及有限元分析结果作了对比 ,吻合较好。同时给出了便于工程设计的简化公式。     

梁端受框架约束的平端板连接组合节点抗火性能试验研究

对梁端轴向约束作用下平端板螺栓连接组合节点的抗火性能进行了试验研究。试验共设计制作四个试件,一个为梁端无轴向约束的组合节点抗火试验试件、两个为梁端受框架约束的组合节点抗火试验试件,另一个梁端无轴向约束的组合节点试件作为对比试件,进行常温下受力性能试验,以研究梁端轴向约束对组合节点耐火性能的影响。试验结果表明,常温下组合节点因柱腹板受压屈曲而破坏。火灾作用下组合节点温度场分布不均匀,组合节点均出现梁下翼缘屈曲,但二者在梁下翼缘屈曲后的受力行为不同。梁端无轴向约束组合节点在梁下翼缘屈曲后承载力迅速降低;而梁端有框架约束的组合节点在梁下翼缘屈曲后由于钢梁出现悬链线效应（在梁大挠度情况下,梁内轴力由压力转为拉力来承受竖向荷载）,节点由压弯受力转为拉弯受力,表现出较好的承载能力和变形能力。试验反映了组合节点在结构中与梁的相互影响和共同作用,为理解火灾下组合节点在梁轴力影响下的结构反应、承载机理和破坏模式提供了依据。     

Finite element analysis of flush end-plate connections connected to column web

Eurocode 3: Part 1.8 (2005b) does not cover the empirical design for flush end-plate connections connected to column web. Thus, experimental works need to be performed to investigate the behaviour of the minor axis end-plate bolted connection. However, the experimental tests are expensive, tedious and time consuming to be conducted. Alternatively, finite element modelling and analysis can be adopted to predict the behaviour of the connection accurately. Five specimens of flush end-plate connections connected to column web with variable parameters have been tested and the results are compared with finite element analysis. Finite element models with enhanced strain solid and contact joint elements are used to stimulate the connection behaviour. The objective of this paper is to compare and validate the accuracy and reliability of the finite element model by correlating moment rotation (M-Φ) curves between the finite element model and experimental tests. The comparison shows a reasonable agreement between the predicted results from FEA and the experimental tests.     

地震作用下端板连接的特性

试验测试了循环荷载作用下的一组8个足尺的钢梁柱端板连接弯矩。研究的参数有端板厚度、螺钉直径、外伸端板加劲肋、柱加劲肋、齐平/外伸端板的类型。试验结果反映在弯矩能力曲线、转角刚度、转动能力和滞回曲线上。试验结果显示:延伸的端板连接有足够的强度、节点转动刚度、延性和抗震结构中要求的耗能能力。基于试验结果和分析,提出了在钢结构抗震设计中对端板连接弯矩的一些详细要求,为保证在地震作用下端板连接能够提供足够的转动能力和耗能能力,并使最终破坏模式为延性破坏,推荐了三种失效模式和相应的抵抗能力。为考虑端板连接向两侧延伸,本文还提出了一种双线性的运动硬化弯矩-转角(M-R)滞回模型。     

Experimental investigation of beam-to-column connection with SHN490 steel under cyclic loading

Seismic performance of beam-to-column connections used in the middle-low rise buildings was investigated through the cyclic loading test. Four joint specimens were prepared in accordance with the variables of material and connection type. In two cases of welded connection, the brittle fracture in weld did not occur but cracked at heat-affected zone (HAZ) and/or near weld access hole. In the connections with extended end-plate, punching failure followed by end-plate failure occurred at the flange of column around bolt head. The moment capacities based on failure modes were calculated and compared with the test results. The connections were classified as rigid, semi-rigid, flexible in terms of bending stiffness and strength.

     

A connection element for modelling end-plate connections in fire

In this paper a robust 2-noded connection element has been developed for modelling the bolted end-plate connection between a steel beam and column at elevated temperatures. The connection element allows the element nodes to be placed at the reference plane with offset and the non-uniform temperature distributions within the connection. In this model the connection failure due to bending, axial tension, compression and vertical shear are considered. The influence of the axial tensile force of the connected beam on the connection is also taken into account. This model has the advantages of both the previous simple and component-based models. A total of 23 fire tests were used to extensively validate the model. It can be seen that the current model is robust and has a capability to predict the behaviour of a bolted end-plate connection under fire attack with reasonable accuracy. Compared to the tested results the predictions of the current model were mainly on the conservative side. Hence, the model can be used for structural fire engineering design on steel-framed composite buildings. The idea described in this paper can also easily be applied to develop other kinds of connections, such as simple connections, column based connections or hollow section connections, and so on.     

多层钢框架半刚性端板连接的循环荷载试验研究

为研究多层钢框架半刚性梁柱端板连接的抗震性能,对8个不同构造端板连接足尺试件进行了循环荷载试验研究, 分析了端板厚度、螺栓直径、端板外伸加劲肋、柱腹板加劲肋、平齐式和外伸式等因素对节点承载力、转动刚度、极限转动 能力、耗能能力、延性和极限破坏状态的影响。试验结果表明,半刚性梁柱端板连接具有良好的延性和耗能能力,可以应用 于多层抗震钢框架中。根据试验结果及相关分析,提出了多层抗震钢框架中端板连接的标准构造为:两端外伸,设置柱腹 板加劲肋和三角形端板加劲肋,柱翼缘在端板外伸边缘上下各100mm范围内局部加厚,厚度与端板厚度相同。对提高端 板连接节点的抗震性能提出了宜采用大直径螺栓、中等厚度端板的设计建议。本文还在"强节点,弱构件"抗震设计一般原 则的基础上提出了"强连接,弱板件"的端板连接抗震设计概念。     

Influence of initial imperfection on the behaviour of extended bolted end-plate connections for portal frames

Initial imperfection in bolted end-plate connections is mainly induced by residual deformation of welding. Three typical initial imperfections, namely V-shape, C-shape and W-shape are identified in terms of the geometrical imperfection shapes for extended bolted end-plate connections based on a field study. Seven specimens of extended bolted end-plate connection, among which six specimens with V-shape initial imperfection and one without imperfection in the end-plates were tested, and the influence of the initial imperfection of the end-plate on the behaviour of the connections was investigated. Test results show that initial rotation stiffness of extended bolted end-plate joints decreases with increase of initial imperfection in the end-plate, however, the strength of the end-plate joints is only affected slightly by the imperfection. Besides, the thicker the end-plate is, the more reduction in the initial rotation stiffness relatively. Further parametric study on 14 extended bolted end-plate connections with three typical shapes of imperfections were conducted based on the finite element analysis. Among the three types of initial imperfection, the V-shape has the least influence, and the C-shape has the biggest influence on the initial rotation stiffness of the extended bolted end-plate joints. For initial geometrical imperfection in a V-shape, its influence on behaviour of extended bolted end-plate connections is negligible as far as the imperfection is limited to the criterion, giving H/300. The influence of initial imperfection in a W-shape on rotation stiffness should be acceptable if the initial imperfection is limited to the criterion. In the case of a C-shape initial imperfection in the end-plate, its influence on the rotation stiffness would be substantial; even it satisfies the requirement of the imperfection limit. The results of the study should be applicable to the bolted end-plate connections, whether flushed or extended end-plate beam to column joints in structural frames.     

Q690高强钢端板连接梁柱节点抗震性能试验研究

对3个齐平式端板螺栓连接节点试件进行低周反复荷载试验,其中1个为普通钢端板节点试件,另2个为Q690高强钢端板节点试件。通过改变端板和柱的尺寸与材料,得到普通钢与高强钢端板节点、刚性柱和非刚性柱节点的性能差别,并与欧洲规范EC3的计算结果进行对比。结果表明：Q690高强钢端板节点的受弯承载能力比Q345钢端板节点高30%,但因其端板弹性变形能力较强,易于导致螺栓破坏,因此,需提高螺栓的承载力以提高其延性;刚性柱节点的受弯承载能力与非刚性柱节点基本相同,但其转动能力、延性、耗能能力等抗震性能明显优于非刚性柱节点;EC3组件法普通钢节点承载能力的预测公式可直接用于高强钢端板节点,但转动刚度及破坏模式的预测方法并不适用于高强钢端板节点。     

Numerical study on seismic behaviors of steel frame end-plate connections

In order to study the seismic behaviors of steel frame end-plate connections, an efficient and accurate finite element model of ABAQUS was established subjected to cyclic loadings. Element types, material cyclic constitutive models and contact models for bolts, end plate and members were described. Geometry and material nonlinearity were adequately considered. The simulated results of numerical models were verified by typical quasi-static tests of end-plate connections, including both hysteretic curves and failure modes. It provided a strong tool for investigating the performances of this kind of connection. Based on the verified models, connections with different connection methods were established to investigate the effect of connection methods on behaviors of connections, including fully welded connection, extended end-plate connection and flush end-plate connection. The carrying capacity, initial stiffness, hysteretic behaviors, degraded characteristics, fracture tendency index, failure modes and energy dissipation capacity were compared and discussed in depth. The results showed that: If the beam and column are reliably connected, the extended end-plate connection can obtain the same ultimate carrying capacity and initial stiffness (monotonic behaviors) as the welded connection, however, their hysteretic curves, degradation developing curves, and fracture tendency were quite different. It indicated that the connection methods could significantly affect the cyclic behaviors. The stiffeners of end-plate connection could be treated as the first defense of connection, effectively changing the failure mode and avoiding brittle fracture. Therefore, in the high seismic zones, hysteretic behaviors, failure modes and seismic ductility should be taken into account comprehensively to choose the appropriate connection methods.     

Behaviour of composite beam-column flush end-plate connections subjected to low-probability, high-consequence loading

This paper aims to investigate the performance of beam-column flush end-plate connections when using blind bolts. The paper studies the strength on medium rise buildings in regions of medium to high seismicity. This paper presents the result of both experiments and finite element analysis on composite beam-column flush end-plate connections subjected to low-probability, high-consequence loading. The earthquake actions were determined using the earthquake code, AS1170.4, Standard Australia (2004) [44]. Considerable savings were apparent when moving from a pinned connection to a semi-rigid connection. Not only in terms of weight savings, but more importantly the ability to reduce the floor-to-floor heights, which can considerably reduce the cost of services and facades and subsequently mass and inertia of the structure. This can also result in more lettable floor space due to reduced column sizes and the possibility of adding another floor for the same total height compared with the pinned connection. The experimental studies and finite element analysis enables improvement to the design of the connections to be used in engineering practice.     

端板连接高强度螺栓群中和轴位置研究

为研究端板连接中高强度螺栓群的中和轴位置变化,对门式刚架外伸式端板连接进行了试验研究与理论计算.试验采用4种梁截面尺寸,选择端板厚度和端板加劲肋作为研究参数,对12个试件进行了单调加载试验,通过在螺栓杆无螺纹区开槽粘贴应变片测量了端板螺栓力的变化情况.理论计算系建立带弹性支座的连续梁模型模拟端板连接,将模型计算结果与试验结果比较分析,结果表明：加载过程中,螺栓群中和轴逐渐从其形心轴向受压区移动,但不超过受压翼缘内侧螺栓中心线;极限状态下,受拉翼缘和端板可简化为等效T型件.根据理论模型,进行了简单的参数分析,研究了撬力、端板厚度和螺栓排列等对连接性能的影响.最后结合试验结果及理论计算,对现有计算方法进行了评价.     

Optimum design of semi-rigid connections using metamodels

Considerable efforts were made in the past 15 years to develop strategies for the optimization of steel frames with semi-rigid connections, concentrating on the frames and not the connections, which were designed after the rest of the structure had been optimized. The analysis of semi-rigid connections requires the calculation of the moment-rotation curve (M_j-ϕ), which can be predicted using the Finite Element (FE) method. This is computationally expensive due to both the high number of degrees of freedom in the FE model and the nonlinear analysis required. In order to optimize such connections, a surrogate or metamodel of the FE model can be used. This paper puts forward a methodology for the optimal design of semi-rigid steel connections using metamodels generated with Kriging and Latin Hypercube, and optimized with the genetic algorithm method. This methodology was applied to two examples involving bolted extended end-plate connections, and was shown to work excellently at obtaining their optimal designs.     

Comparison of component method with experimental tests for flush end-plate connections using hot-rolled perwaja steel sections

A component method has been introduced by Steel Construction Institute to predict the moment resistance of partial strength connection. The design philosophy is taken directly from Eurocode 3 with strength checks on bolts, welds, and steel which have been modified to comply with BS 5950-1:2000. The accuracy of the method however needs to be validated with the experimental tests especially for hot-rolled sections other than typical British Section (BS). Six experimental tests on beam-to-column connections have been carried out for Flush End-Plate (FEP) connections consisting of variable parameters such as thickness of end-plate, size and number of bolts, size of columns, and beams. The tests were set-up using local hot-rolled steel sections known as Perwaja Section (PS) for beams and columns instead of typical British Section (BS). The strength of materials for end-plate, column and beam sections were tested for tensile strength and used in predicting the moment resistance for component method. The moment versus rotation of the test results were plotted and compared with the moment resistance derived from component method. The study concluded that the moment resistance of the tested flush end-plate connections was higher than the predicted moment resistance from component method which showed good agreement between the two moments. The study also concluded that the tested FEP connections met the requirements and criteria of partial strength connections.     

Bolted moment connections in drive-in and drive-through steel storage racks

The stability of steel storage racks, which are often unbraced, may depend solely on the pallet beam to upright connector and on the stiffness of the base plate to floor connection. This paper presents experimental results from cyclic tests performed on portal beam to upright bolted moment connections intended for cold-formed steel drive-in and drive-through storage racks. In storage racks, portal beams are typically connected to uprights by “tab connectors”, which are costly to manufacture and experience initial looseness. By simply bolting the portal beams to the uprights, bolted moment connections may represent a cost-effective alternative to “tab connectors”. A literature review shows that bolted moment connections between cold-formed steel members are economical and feasible. However, experimental results show a significant amount of looseness in the connection after an initial high moment-rotational stiffness. Being slender structures, storage racks are sensitive to the second-order P-Δ effect, and international racking specifications require the initial looseness of the tab connectors to be considered when analysing the stability of the rack in the down-aisle direction (sway motion). The non-linear cyclic behaviour of bolted moment connections is presented and explained herein. Based on finite element results, it is shown that, for drive-in and drive-through racks, the looseness in bolted moment connections can be ignored in ultimate limit states design. Finally, the paper concludes with proposing two methods, with different degree of complexity, for the design of drive-in and drive-through racks with bolted portal beam to upright bolted moment connections.     

框架梁柱平端板连接组合节点性能研究

对钢框架梁柱平端板连接组合节点进行了三维有限元模拟并用试验结果验证,进而对不同参数进行了分析,探讨了端板厚度、钢筋、螺栓、节点形式等对组合节点工作性能的影响。     

半刚性端板节点在循环荷载作用下的非线性有限元分析

运用有限元数值分析软件ABAQUS建立半刚性端板节点模型,对其在循环荷载作用下进行非线性有限元分析,并与相应的试验结果进行了比较验证.结果表明:用ABAQUS建立的有限元模型能够准确地模拟端板节点在循环荷载作用下的整体受力性能,为进一步运用该模型对各种不同形式和构造的端板节点进行全面的有限元非线性参数分析计算提供了正确依据.并分析得出了端板厚度、螺栓直径、螺栓布置、端板加劲肋等因素对端板节点承载力、极限转动能力、耗能能力和延性的影响特性,为半刚性端板节点的抗震设计提供了参考依据.     

钢框架梁柱端板连接节点的抗震设计方法

根据钢框架梁柱端板连接节点的试验研究和有限元分析结果 ,探讨了节点的传力及破坏机理 ,提出了端板连接节点的抗震设计方法和步骤 ,弥补了规范的空白 ,也为工程设计提供了一种参考。     

Experimental and analytical investigation of steel column bases

The present work is devoted to the experimental and analytical investigation of the steel column bases. Therefore, eight sets of tests, simulating the column to concrete foundation joint, were carried out. Beside, three-dimensional FEM models of the test specimens were constructed and analysed. Finally, the results of these experimental and FEM analyses were correlated with those obtained from an analytical formula proposed by the authors in a previous work, describing the relation among bending moment and angle of rotation (M-φ) of the column base. The verification among the results seems to be satisfactory.