带或不带加劲肋螺栓连接端板性能试验及分析

给出了8个梁-柱、梁-梁外伸端板螺栓连接试样的试验结果,其中4个连接件在外伸端板处使用了加劲肋。将低阻力螺栓受拉区和受压区的失效模式进行对比,基于整体弯矩-转角曲线和螺栓拉应力的发展对试验结果进行分析。试验主要关注失效模式、阻力发展、刚度及扭转能力。将试验结果与按照EC3提供的方法得到的分析结果进行对比,评估该分析方法(包括分析外伸端板处使用了加劲肋的连接件)的准确性。     

火灾中外伸端板节点的弹簧模型和试验研究

为得到外伸端板节点的抗火性能,采用火灾试验炉对4个足尺H型钢进行了火灾行为的研究。从试验中得到了外伸端板节点试件的破坏特征和破坏模式。通过比较有无加劲肋以及不同厚度的端板的节点的抗火能力,分析了加劲肋和端板厚度对节点抗火能力的影响。此外,还描述了弹簧模型,用于预测外伸端板钢节点在高温下的性能。节点构成被认为由预先设定力学性能的弹簧构成,例如,刚度和强度。高温下的节点响应可以通过汇集构成、刚度和强度来预测,而刚度和强度的下降由中国现行的钢结构火灾安全技术规范建议的升温过程来设定。结果表明,模型计算结果与试验数据很吻合。     

Experimental study and spring-component modelling of extended end-plate joints in fire

In order to investigate the fire-resistant capacity of extended end-plate joints, an experimental study was performed by using a furnace on four full-scale specimens made with H-shaped steel. The failure characteristics and failure modes of the extended end-plate joint specimens in fire were obtained from the experiment. The influence of rib stiffeners and depth of end-plates on fire-resistant capacity of the joints was found by comparing the capacity of the joints with and without rib stiffeners and different depths of end-plate. In addition, this paper also describes a spring-component model employed for predicting the behaviour of extended endplate bare-steel joints at elevated temperature. The components of a joint are considered to consist of spring components with predefined mechanical properties, i.e. stiffness and strength. The response of the joints subjected to elevated temperature can be predicted by assembling components, the stiffness and strength of which are assumed to degrade with increasing temperatures based on the recommendations presented in the Chinese Technical Code on Fire Safety of Steel Building Structure. It is demonstrated that the results from the model agree with experimental data quite well.     

Analysis of a bolted T-stub strengthened by backing-plates with regard to Eurocode 3

The connection reinforcement by backing-plates, which is of low cost and simple to realize, can give performances which get closer to that of stiffeners in the tension zone. Currently, in the Eurocode 3, this reinforcement mode is considered only for resistance. The T-stub, a main component in the bolted connections under bending, is analysed at first in the non-reinforced stage as a calibration of the finite elements modelling approach. Then, the T-stub is reinforced by backing-plates with various geometrical configurations. The aim is to better understand the behaviour and the mechanical contribution of backing-plates considering the stiffness and the resistance. The 3D model developed in the finite elements software Cast3m takes into account elastic plastic behaviour of the materials, the large displacement and the unilateral contact between the connected parts. This model shows a good capacity to represent the available experimental results. The sensitivity analysis of T-stubs reinforced by backing-plates to various parameters such as the thickness of the backing-plate and the pre-tension force allows us to show that the contribution of the backing-plate in term of stiffness is significant in some cases and in particular with preloaded bolts. The T-stub behaviour is analysed on the basis of the global load-displacement curves, the evolution of the bolt load and the contact pressure due to the prying force effect. The analysis shows that the resistance of the T-stub increases in a significant way with the thickness of backing-plate. This increase has an upper limit due to the failure mode change which occurs for lower values of loads according to the analytical model, which gives a reserve of resistance for the reinforced T-stub.     

Experimental and Theoretical Study on High Strength Steel Extended Endplate Connections After Fire

In order to reveal more information and better understanding on the behavior and failure mechanisms of high strength steel (HSS) extended endplate connections at ambient temperature and after fire, an experimental and theoretical study has been conducted and presented in this paper. The provisions of Eurocode 3 are verified with the test results. Because strength of bolts decreases more rapidly than that of structural steels, failure modes of endplate connections may change after fire. Hence, a series of equations are proposed to predict failure modes of endplate connections after fire. Furthermore, FE simulations which can predicate the performance of HSS extended endplate connections with reasonable accuracy are adopted to study the behaviors of the connections after cooling down from various fire temperatures and to validate the accuracy of the proposed equations. Moreover, a parametric study is carried out to explore an optimization design method. It is found that the current provisions of EC3 can justifiably predict failure modes and plastic flexural resistances of HSS extended endplate connections both at ambient temperature and cooling down from 550 °C, but it is not the case for their initial rotational stiffness and rotation capacity. In order to avoid brittle failure mode of endplate connections after fire, appropriately increasing the diameter or grade of bolts in the design is suggested. What is more, the match of steel grade and thickness of column flange and endplate as well as beam should be considered in the optimization design of beam-column endplate connections.     

梁柱端板连接节点的滞回性能试验研究

为了研究钢框架中梁柱端板连接节点的滞回性能,本文进行了8个节点试件的循环加载试验,其中有7个试件的柱端施加了轴向压力,4个端板设置了加劲肋。试验结果表明:端板连接具有良好的延性和耗能能力,节点的转角都超过了0.03rad;端板刚度是影响节点滞回性能和极限承载力的决定性因素;端板较薄时,端板加劲肋不但可以显著提高端板刚度,而且可以延缓梁翼缘与端板间焊缝的开裂,有效提高承载力,减小撬力。最后根据试验结果提出了设计和施工建议。     

Investigation on the Collapse Behavior of Diagonal Stiffened Composite Plate Girders Subjected to Shear Loading

In this study, a new analytical method is presented to estimate the shear capacity of diagonally stiffened steel–concrete composite plate girders. This method is formulated based on tension field action in steel girder web and failure mechanism of concrete slab deck. To validate the accuracy of the proposed method, the obtained results are compared with three-dimensional finite element analysis of composite plate girders with different configuration of stiffeners. The results of analytical and numerical investigations indicate that the proposed method can accurately estimate the ultimate shear capacity of composite plate girders. In addition, it is shown that the diagonal stiffeners on one hand can reduce the buckling effects of shear panel of girders and on the other hand can increase the strength of elastic shear buckling and ultimate shear capacity of girders well in comparison with the unstiffened thin steel plate girders.     

The effect of axial beam force on moment–rotation curve of top and seat angels connections

Bolted top and seat angle connections are mainly designed to sustain gravitational loads of simply supported steel beams. However, the inherent flexural resistance of such connections may not be ignored when an accurate analysis of semirigid steel frames is desired. Current research aims at studying moment–rotation behaviour of this type under combined moment and axial tension force. Several refined three‐dimensional finite element models are created based on the previous experimental studies, and their accuracy is examined trough a comparison to test results from previous experimental studies. This study showed that the axial tension force reduces the connection initial stiffness and moment capacity. Based on the results obtained from analysing a series of finite element models under combined axial tension and moment loading, an equation is presented to estimate the affected moment–rotation response of such connections in terms of the connection geometrical properties, its moment–rotation response in the case of zero axial force and an expected axial tension force. Copyright © 2009 John Wiley & Sons, Ltd.     

Numerical and experimental analyses of multiple-dowel steel-to-timber joints in tension perpendicular to grain

The behaviour of dowel-type steel-to-timber joints loaded in tension perpendicular to grain is analyzed experimentally and numerically. Two main types of failures are observed in the experiments such as wood splitting and embedding. The experimental results are used to validate a three-dimensional (3D) non-linear finite element model. The non-linear model uses the Hill criterion to control the plastic yielding of wood material. The Hoffman failure criterion, controlling the damage evolution in wood, is used to take into account the brittle failure in shear and tension perpendicular to grain. The comparison with experimental results shows that the numerical results are in good agreement with them. The validated model is used to investigate the effect of some influential parameters on the splitting strength of the joints loaded in tension perpendicular to grain. Besides, the splitting strengths given by the numerical model are used to evaluate the accuracy of some analytical formulae available in the literature.     

Application of steel channels as stiffeners in bolted moment connections

This paper proposes a stiffening method to meet some architectural needs. This method uses bolted channels as alternatives to both continuity and doubler plates in bolted moment-resistant beam-to-column connections. The present study investigates the performance of channels as stiffeners to: increase yield load in the tension zone of connection, gradually increase overall moment capacity of connection, and avert shear failure of the column web panel zone. We conducted experiments to examine the tension region of the connection loaded from T-stubs. The moment capacity of full connection was predicted by considering T-stub idealization and shear effects on the column web panel. T-stub tensile behavior and overall connection behavior were also monitored using three-dimensional finite element simulations in ANSYS simulation software because this problem is three-dimensional in nature. Effects of geometrical and material non-linearities on interaction among connecting members should be clarified. This study showed marked strength improvement in connection by use of channels. The performance of channel stiffeners was examined through comparison of results.     

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。     

Experimental investigation of extended end plate joints to concrete-filled steel tubular columns

An experimental programme to obtain the behaviour of blind bolted extended end plate joints to circular or square concrete-filled steel tubular (CFST) columns under monotonic loading has been conducted. In order to enhance the strength and stiffness of the connections, the anchorage extensions are provided to the blind bolts to link the connection back into the concrete with the tubular. This paper investigated the effect of the end plate thickness and the column section type on the static behaviour and failure modes of the tested connections. The structural performance of the blind bolted extended end plate connections was evaluated in terms of the moment–rotation relationship, connection rigidity, the deformation pattern and the strain response. The test results showed that the blind bolted extended end plate connection to CFST columns exhibits high strength and stiffness, while its connection rotation capacity satisfies the ductility requirement for earthquake resistance in aseismic region. The experimental studies also demonstrated that the strength and stiffness of the connections can be improved by providing anchorage extensions to the blind bolts, and utilising moderately thick end plates leads to joints approaching full strength for the extended end plate connections.     

Experimental and analytical studies on the cyclic behavior of end-plate joints of composite structural elements

The subject of this paper is the analysis of end-plate joints under cyclic and monotonic loading conditions by experimental and analytical studies. The experimental programs are performed on bolted end-plate type joints of composite members under cyclic loading conditions with the purpose to study the seismic response of the considered connection type. The performed experimental research is the second and third steps of an international research project started in 1999 between the Budapest University of Technology and Economics (BME), Hungary and the Technical University of Lisbon (IST), Portugal. The monotonic behavior of the tested joints is followed by the Eurocode standard design method to evaluate the moment resistance and rotational stiffness of the joint. The comparison of the design and the experimental results are performed by the envelope moment-rotation relationships of the hysteretic curves and the design moment-rotation diagram. On the basis of the comparison the modification of the design model is proposed. The monotonic moment-rotation diagram is extended to large rotation regions with the purpose of covering the whole cyclic diagrams until the final failure of the specimen. A semi-empirical method is proposed to approximate the cyclic hysteretic behavior of the studied joints, based on the knowledge of the monotonic moment-rotation curve. This prediction method is based on all the available test results for each behavior mode type (6 tests on steel and 12 tests on composite specimens). The calculated hysteretic curve follows the cycles by polygonal lines taking into consideration the experimental observations. The proposed method establishes the absorbed energy of the consecutive cycles in the case of the studied joint arrangement using standard loading history. The proposed method is applied and verified in the case of each observed failure mode type. By these experimental and analytical investigations the favorable seismic behavior can be derived for the studied joint type.     

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.     

Dynamic and static axial crushing of axially stiffened cylindrical shells

The axial impact of cylindrical tubes, which incorporate axial stiffeners, is examined in this paper. For comparison purposes, the effect of static loading is also studied. An examination is made into the influence of stiffener depth (T), number of stiffeners (N) and the effect of placing the stiffeners externally or internally.

The experimental results on mild steel specimens show that there are considerable differences between the static and dynamic modes of failure, and that an optimum T/D ratio may exist for a given value of N.     

螺栓端板连接节点加固后承载性能有限元分析

已有试验表明,螺栓端板连接梁柱节点具有良好的受力性能,但节点刚度较小,循环荷载作用下破坏模式以螺栓拉断为主。当建成的结构由于各种因素螺栓端板节点承载性能不能满足要求时,需要进行加固以提高节点刚度和承载力。改：善其抗震性能,本文提出了在柱腹板加斜向加劲肋,并对端板进行焊接的加固方案。有限元分析表明加固后节点的刚度、延性和承载力都得到提高。静力加载时,荷载一位移曲线在达到峰值后出现平缓的下降段;循环加载时,节点破坏模式是梁翼缘发生局部屈曲形成塑性较,滞回曲线饱满。由于使用了焊缝,节点有可能发生脆性破坏,加固中应尽量使用较小尺寸的焊缝,施工中也应保证焊缝的质量,减小残余应力。     

Yield line theory based loading capacity analytical model of bolted endplate connections to square hollow section columns

为研究螺栓端板连接方钢管柱的承载力,进行了11个连接件的单调静力试验,分析了钢管和螺栓的3种典型破坏模式,以及钢管管壁厚度、螺栓列距与直径、盲孔螺栓Hollo-bolt构造等因素对连接件承载力的影响,提出了预测该类连接承载力的改进屈服线计算模型。研究结果表明：螺栓端板连接方钢管柱的破坏模式与钢管管壁厚度以及螺栓列距相关,承载力随钢管厚度以及螺栓列距和直径的增大而增大;通过连接件整体位移和钢管管壁连接面竖向位移与荷载关系,按双线性屈服模型得出的承载力预测值与试验值相近;由连接件试验结果折算得到的预测结果可用于此类节点的屈服弯矩计算。基于屈服线理论建立的连接件承载力的计算模型的计算结果,与试验结果比较,二者吻合较好。     

Experimental model of the behaviour of bolted angles connections with stiffeners

This paper presents the experimental results of twenty full scale specimens of steel bolted connections beam-to-column with top-and-seat angles in six groups, labelled L91-tp8, L82-tp8, L73-tp8, L91-tp10, L82-tp10 and L73-tp10 groups (L=length of top-and-seat angle, tp=stiffener thickness of top-and-seat angle), under static loading. This study was undertaken to analyse the influence of angles and beams with stiffeners on the behaviour of the beam-to-column joints. The main parameters observed are the evolution of the resistance, the stiffness, the rotation capacity, the ductility of a joint, and the energy dissipation capacity. The aim was to provide necessary data to improve the Eurocode 3.     

Tests of single shear bolted connections of thin sheet steels at elevated temperatures—Part II: Transient state tests

A total of 62 single shear bolted connection specimens were tested using transient state test method. The specimens of single shear bolted connections were fabricated by three different thicknesses of thin sheet steels. The tests were conducted at three different load levels of 25%, 50% and 75% of the failure load at ambient temperature. The tendency of the test strength reduction of the single shear bolted connections conducted using the transient state test method is generally similar to that for the steady state test method. However, it is shown that the transient state test results are always conservative compared with the steady state test results. Three main failure modes, namely the bearing, tear out and net section tension, were observed in the transient state tests. The failure modes of the specimens in transient state tests for the load level of 0.25 of the failure load at ambient temperature are generally consistent with those specimens in the steady state tests.     

加劲T形连接件有限元分析

根据T形连接件与端板受拉区的相似性,利用有限元分析软件ANSYS对单向受拉T形件连接节点进行三维非线性有限元分析。给出了T形件连接节点弯矩-转角曲线、节点变形及螺栓撬力分布和变化规律等,并将有限元结果与试验结果进行了全面的比较。研究表明,有限元方法能够很好地分析无加劲和加劲T形件连接的受力性能。工程中常用的加劲肋达不到预想的加劲效果;螺栓撬力的分布和变化规律与端板加劲肋的形状和厚度有密切关系。