Prediction of cyclic behavior of WUF-W connections with various weld access hole configurations using nonlinear FEA

The welded unreinforced flange-welded web (WUF-W) moment connection is one of seven prequalified connections for the special moment frames (SMF) specified in AISC 358-10. Previous studies reported that some WUF-W connections with a steep access hole slope failed before completing a loading cycle of 4% drift ratio. For investigating in detail the effect of access hole geometry including access hole slopes on the connection behavior, experimental tests require excessive costs and efforts because there are the large number of combinations of configuration parameters for access hole geometry. In this study, the cyclic behavior of WUF-W connections is evaluated using three-dimensional nonlinear finite element (FE) analyses with an adequate solid element and failure index. Based on the results of FEA, the effect of configuration parameters on the connection behavior is investigated.     

Investigation on the inelastic behavior of full-scale heavy clip-angle connections

This paper describes the investigation on the inelastic behavior of steel heavy clip-angle connections subjected to static loading. The work depends on the results of a large experimental investigation into the cyclic behavior of full-scale connections involving thick clip-angle components. The results of these experimental tests are described first, and then a methodology to simulate the response of clip-angle connections numerically using nonlinear finite element (FE) models is mainly treated in this study. Extensive studies utilizing numerous 3D models are discussed, including the introduction of the pretension force into the bolts and the effects of small changes in geometry on the deformation capacity of the angles. Generally, FE test results show a good agreement with experimental test results. These outcomes indicate that it is possible to model such connections successfully if care is exercised in the modeling phase. Moreover, these FE models provide useful instrumentation which is difficult to obtain during an experiment. They have widely been used to understand the parametric effect of connection components and establish a comprehensive study of their inelastic behavior including slip deformation and prying action.     

木销半榫节点转动性能试验研究与有限元分析

为研究木销半榫节点平面内的转动性能和节点区域木材损伤演化,通过木销半榫节点试件的单调加载试验和有限元分析研究了此类节点平面内的转动性能.试验研究表明,加载初期预钻孔附近木材会发生横纹劈裂破坏,随着荷载不断增加,榫头变截面处木材会出现顺纹受拉破坏.节点有限元分析结果表明,采用弹塑性损伤模型建立的有限元模型对于节点刚度和受...     

高层钢框架新型梁柱节点抗震性能试验研究

本文提出了三种焊接孔扩大型梁柱节点,完成了8个足尺试件在四种反复荷载历程下的破坏试验。对节点破坏模式和滞回曲线的比较分析表明,焊接质量是防止节点脆性破坏的首要保证,明显的焊接缺陷容易导致裂缝过早开始扩展,从而降低节点延性和耗能能力。节点局部构造尤其是焊接孔形状尺寸对于节点应力集中情况和节点破坏模式有很大影响。本文提出的焊接孔扩大型节点可以不同程度地缓解局部应力集中,同时通过采用较长的焊接孔,使节点破坏模式转变为梁翼缘的局部屈曲,降低了对接焊缝发生脆性破坏的可能,对节点延性有较大的改善作用。焊接孔扩大型节点构造也便于加工制作,是一种值得推荐的新型节点形式。     

Refined 3D finite element modeling of partially-restrained connections including slip

This study presents an approach for refined parametric three-dimensional (3D) analysis of partially-restrained (PR) bolted steel beam-column connections. The models include the effects of slip by utilizing a general contact scheme. Non-linear 3D continuum elements are used for all parts of the connection and the contact conditions between all the components are explicitly recognized. A method for applying pretension in the bolts is introduced and verified. The effect of several geometrical and material parameters on the overall moment–rotation response of two connection configurations subject to static loading is studied. Models with parameters drawn from a previous experimental study of top and bottom seat angle connections are generated in order to compare the analyses with test results, with good prediction shown by the 3D refined models. The proposed 3D modeling approach is general and can be applied for accurate modeling of a wide range of other types of PR connections. A pronounced effect of slip and friction, between the connection components is shown with connections having thicker (stiffer) seat angles. This study demonstrates the effects of clamping through the bolts and contact between the components on the overall non-linear moment–rotation response. Equivalent moment–rotation responses of pull-test simulations are compared to FE model responses of full connections without web angles. The moment–rotation from the pull test is shown to be equivalent to that of the full FE model for small rotations. As the rotation increases a softer response is shown by the pull tests.     

Response of double angle and shear endplate connections at elevated temperatures

Double angle and shear endplate connections are considered simple-beam end framing connections designed to carry gravity loads only. However, during a fire event, additional thermal induced axial forces might develop in the beam and cause failure of the connection. This paper presents the results of finite element (FE) simulations on double angle and shear endplate connections assemblies in fire. FE simulations are validated against experimental results of double angle and shear endplate connections at elevated temperature. A detailed comparison of the variation of the axial force during the heating and cooling phases of a fire is made between the two connections covering the following parameters: load ratio, beam length, and double angle and shear endplate thickness and location. The results can help future design guidelines to account for the thermal induced forces and deformations in double angle and shear endplate connections during a fire.     

反复荷载作用下方钢管混凝土柱与钢梁连接节点非线性有限元分析

本文首先选择合适的本构模型作为约束混凝土循环本构模型的骨架曲线,提出了考虑局部屈曲和开裂的钢材循环本构关系;进而建立两类方钢管混凝土柱与钢梁连接节点———缀板焊接连接节点和穿芯螺栓-端板连接节点的空间非线性分析模型,对其在低周反复荷载作用下的滞回性能进行了非线性分析计算。结果表明:由有限元模型所得的单调荷载-位移曲线与试验所得的低周反复荷载作用下的骨架曲线极为相似,但在峰值荷载后差异较大;由有限元模型所得的在低周反复荷载作用下滞回曲线也与在反复荷载作用下试验所得的相一致。有限元模型能准确地预测上述两类节点的弹塑性行为和整体抗震性能,可用于节点滞回性能的非线性参数分析研究。     

Spannungsermittlung punktgelagerter Verglasungen unter Beanspruchung in Scheibenebene

Determination of the stress distribution of point supported glass structures under in‐plane loads. In this article a method for the determination of the stress distribution of point supported glass structures under the application of in‐plane loads is presented. To specify and calculate the load bearing of bolted connections in glass panels exact knowledge of the contact mechanisms and the parameters which influence the stress distribution around the hole is necessary. Due to the complex determination of the stress distribution mostly the structural safety is verified by full‐scale tests so far. An alternative is the numerical verification by finite element analysis (FEA). But therefore adequate program verifications are necessary. At first an approach for verifying the numerical model with an analytical solution is developed. To determine relevant results for design the verified FE‐model is used to examine the influences of different parameters on the stress distribution around the hole.     

Out-of-plane behaviour and FE modelling of a T-joint connection of thin-walled square tubes

Square hollow tubes with T-joint connections subjected to out-of-plane loading conditions are examined numerically. Finite element analysis (FEA) using 2D shell and 3D solid elements of relatively high density are used to determine the stresses in the joint and the joint's stiffness. The parameters describing the joint's stress concentration and the bending stiffness reduction are defined in terms of the thin-wall ratio (the ratio of side length to thickness of the tubes' cross-section) and the length of the longitudinal member and the geometric asymmetry of the T-joint connection. These parameters permit modelling accurately the tubes and the T-connection by simple one dimensional beam elements with certain modifications. The FEA of beam elements are significantly easier to prepare and analyze. To illustrate the correctness of the approach, a structure with a T-connection and dimensions typical for the agricultural industry is considered. It is shown that the modified beam models provide accurately all important information of the structural analysis (i.e. the stresses, displacements, reaction forces, and the natural frequencies) at substantially reduced computational effort in comparison with the complicated FE models built of shell or solid elements. This can be considered the main contribution of this research paper. Using a simplified FE analysis for design has always been attractive to practicing engineers.     

改进型钢结构梁柱节点非线性有限元分析

对 4种不同构造形式的钢框架梁柱节点进行了非线性有限元分析 ,研究了节点局部构造对应力分布、塑性区分布及极限承载力的影响 ,分析了焊接孔末端的应力分布状况。文中对不同节点的力学性能进行了分析比较 ,计算结果与试验结果吻合较好。     

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...     

Blind bolted moment connection to sides of hollow section columns

This paper presents the results of an experimental programme for a new blind bolted connection to unfilled hollow section (HS) columns under static loading. In this connection, channels with side plates connect beam flanges to the side face of HS columns. This is a simple alternative connection to typical face connections, i.e. the extended endplate connection or the T-stub connection (with T-stubs connecting the top and bottom flanges of the beam to the face of the column). The channel side plate connection was found to be much stiffer than a typical face connection and has the potential to achieve a rigid connection status for braced frames according to the EC3 classifications. Comparison of the test results and three dimensional finite element (FE) modelling indicates that the FE analyses can be used to predict the connection behaviour with sufficient accuracy. The preliminary investigation for the channel side plate connection shows promising results and forms the basis for the development of other blind bolted side connections for applications in the low rise construction industry.     

Blind bolted moment connection to sides of hollow section columns

This paper presents the results of an experimental programme for a new blind bolted connection to unfilled hollow section (HS) columns under static loading. In this connection, channels with side plates connect beam flanges to the side face of HS columns. This is a simple alternative connection to typical face connections, i.e. the extended endplate connection or the T-stub connection (with T-stubs connecting the top and bottom flanges of the beam to the face of the column). The channel side plate connection was found to be much stiffer than a typical face connection and has the potential to achieve a rigid connection status for braced frames according to the EC3 classifications. Comparison of the test results and three dimensional finite element (FE) modelling indicates that the FE analyses can be used to predict the connection behaviour with sufficient accuracy. The preliminary investigation for the channel side plate connection shows promising results and forms the basis for the development of other blind bolted side connections for applications in the low rise construction industry.     

Blind bolted T-stub connections to unfilled hollow section columns in low rise structures

This paper presents the results of an experimental program investigating blind bolted T-stub connections to unfilled hollow section columns in the tension and compression regions under static loading. The T-stub connection is proposed as an alternative connection to the welded connection currently used as a moment connection for unfilled hollow section columns in the Australian construction industry. The flexural performance of the T-stub connection, in terms of stiffness, has been evaluated in accordance with EC3 classifications and was found to behave as a semi rigid connection under serviceability loading. Results from the experiments have been compared with existing theoretical models that predict the maximum load the flexible column face can carry in the tension region before yielding occurs, and good agreement has been achieved. Furthermore, the experimental results have been used to validate a detailed three dimensional finite element (FE) model which simulates the proposed connection. The developed FE model in turn has been used to perform a sensitivity analysis which is presented in this paper.     

The in-plane behaviour and FE modeling of a T-joint connection of thin-walled square tubes

The behaviour of square hollow tubes with T-joints subjected to in-plane loading conditions is examined numerically. The stresses in the joint and its stiffness are determined from the finite element (FE) models using 2-D shell and 3-D solid elements. The parameters identifying the joint's stress concentration (ξ_m, ξ_b), and the bending stiffness reduction (α_K) are defined in terms of the ‘thin-wallness’ ratio (the side length to thickness) of the tube. These parameters permit modeling accurately the tubes and the T-connection by simple 1-D beam elements with certain properties modified. The FE models consisting of beam elements are significantly easier to prepare and analyze. The effectiveness of the approach is demonstrated by applying it to a structure with a T-connection and dimensions typical for the agricultural industry. It is shown that such beam models provide accurately all important information of the structural analysis (i.e., the stresses, displacements, reactions forces, and also the natural frequencies) at substantially reduced computational effort in comparison with the complicated FE models built of shell or solid elements.     

Mechanical performance of T-stub connections between square concrete filled steel tubular column and steel beam

传统的钢管混凝土柱-钢梁T形件节点易出现柱或者钢梁损伤严重的情况,不利于震后快速修复。以常规T形件和设置长槽孔T形件作为耗能构件,保证柱和梁损伤较小甚至不受损伤,实现耗能构件的可替换。对3个常规T形件节点和2个设置长槽孔T形件节点进行了数值模拟,分析了T形件翼缘厚度、T形件翼缘及腹板宽度、下T形件设置长槽孔、单边抗剪角钢等因素对节点滞回曲线、初始刚度、极限转角、延性系数、耗能能力的影响。研究结果表明：节点整体耗能较好,设置长槽孔T形件节点可显著提高节点延性,增加抗剪角钢的长槽孔T形件节点可显著提高节点耗能能力,该类节点滞回曲线呈饱满梭形,耗能表现为摩擦耗能和T形件塑性变形耗能共同作用;对于常规T形件节点,建议T形件翼缘厚度与腹板厚度的比值小于2.0。     

Investigation of fatigue resistance of fillet-welded tube connection details for sign support structures

Stiffened and unstiffened fillet-welded tube-to-transverse plate connection details are widely used for mast-arm and base-plate connections for highway sign structures. However, due to repetitive wind loads, cyclic fatigue stresses are induced and they are the primary source of failure in welded connections at these locations. The resistance of fatigue critical details has been an on-going research topic because of limited experimental results and the variability in existing fatigue testing results. The main objective of this study is to evaluate fatigue resistance of fillet-welded tube connection details by utilizing the advanced fatigue tool in ANSYS Workbench platform. Finite Element (FE) models development and model validation using existing test data was presented. The resulting fatigue resistance from FE analysis was expressed in terms of fatigue life, fatigue damage, and fatigue safety factor to determine the fatigue performance of fillet-welded connections. Existing fatigue test data was grouped to perform a synthetic analysis and then analysis results were provided to determine input data and fatigue limit for the fatigue module. The local stress level at fatigue critical locations was evaluated using a static FE model for different number of stiffeners and boundary conditions. The results of this investigation provides fatigue resistance of fillet-welded connection details in the form of fatigue life, fatigue damage and safety factor for various connection parameters and structural conditions.     

Dynamic analysis of liquid storage tank under blast using coupled Euler–Lagrange formulation

A growing number of terror attacks all over the world have become a threat to the human civilization. In the last two decades, bomb blasts in crowded business areas, underground railway stations and busy roads have taken numerous lives and destroyed properties in different parts of the world. However, blast response of many important civil infrastructures has still not been well understood due to the complexities in their material behavior, loading and higher nonlinearities. One such example of important civil infrastructure is liquid storage tanks which are undividable parts of any society for storage of water, milk, liquid petroleum, chemicals in industries etc. Blast loading on liquid storage structures may lead to disaster due to water and milk crisis, health hazard owing to the spread of chemicals and fire hazard due to the spread of liquid fuel. Hence, understanding the dynamic behavior of liquid storage structures under blast loading through numerical simulations is of utmost importance. In the present study, three dimensional (3D) finite element (FE) simulations of a steel water storage tank for different tank aspect ratios, percentages of water stored in the tank, tank wall thicknesses, boundary conditions at the bottom of the tank and magnitudes of blast loading have been performed using the FE software Abaqus. The coupled Euler–Lagrange (CEL) formulation in Abaqus has been adopted herein which has the advantage of considering the coupling of structural mechanics and fluid mechanics fundamental equations. The maximum hoop stress and shear stress in the tank wall, the water sloshing heights in tanks and the energy response of the tanks have been studied. It is observed that stresses and liquid sloshing heights in the tank increase with decreasing scaled distance of the explosive material and increasing aspect ratio, i.e. height to radius ratio.     

Analysis of composite connections in unbraced frames subjected to wind and gravity loading

A comparison between a simplified and an advanced method of elastoplastic analysis is made for unbraced frames with composite connections. The advanced method implements a mechanical model to represent the composite node in unbraced frames, which allows considering the behavior of each component of the composite connection individually. This method includes the determination of a moment-rotation curve for loading-unloading-reloading, considering gravity and wind loading. Physical and geometrical nonlinearities are taken into account in the analysis. In the simplified method an appropriate analysis for practical purposes is implemented, on which the connections are considered semirigid for unloading and flexible for loading, after yielding by gravity loads. Second order effects are included using the P-Δ procedure. Finally, a comparison is made between the two methods attempting to transform both methods in a useful tool for composite connection design.     

Numerische Untersuchungen zur Ermüdungsbeanspruchung vorgespannter Ringflanschstöße mit Imperfektionen

Numerical investigations on the fatigue‐relevant bolt stresses in preloaded ring flange connections with imperfections. For the structural design of preloaded bolted ring flange connections in tower‐like steel structures (e.g. chimneys or wind turbine tubular towers), the fatigue assessment of the bolts is very important. Gaps between the contact surfaces before preloading (so‐called flange imperfections) may have a negative influence on the fatigue‐relevant bolt stresses. A FE‐model for imperfect ring flanges was built up and validated by means of the results of large‐scale tubular bending tests on flange connections. With the validated FE‐model, a parametric study on imperfectly simulated L‐flange connections having realistic dimensions of typical wind turbine towers was performed. The results enable differentiating the various gaping forms with regard to their negative influence on the bolt fatigue. This influence may not be neglected when assessing the fatigue safety of the bolts.