Simulation of tensile bolts in finite element modeling of semi-rigid beam-to-column connections

This paper presents an innovative bolt model suitable for the three dimensional finite element analysis (FEA) of the semirigid beam-to-column bolted connections. The model is particularly useful for the moment-rotation relationship of beam-tocolumn connections, especially in cases where the connectors such as endplates, angles, T-stubs, are not particularly thin. In this paper, the bolt tensile behavior is firstly discussed by using a refined finite element model, in which the complex geometries of both external and internal threads were modeled. Then, the bolt behavior predicted by the commonly used models was compared with that of the refined FEA to appraise the accuracy of these models. The comparison shows most of the models commonly used can not predict accurately the axial stiffness, carrying capacity and ductility of bolt simultaneously. Afterwards, an innovative bolt model was proposed and the model accorded with the refined FEA for single bolts. Finally, the proposed model was applied to analyze the moment-rotation behavior of several experimented and well documented connections with different configurations. The results indicate that the proposed model is feasible and efficient.     

Moment-rotation behavior of bolted top-seat angle 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 top-seat angle connections may not be ignored when an accurate analysis of semi-rigid steel frames is desired. The goal of the current study is to find a new moment-rotation relation to estimate the behavior of connections of this type. Semi-analytical equations are proposed for this purpose based on the data bank, which is created using finite element simulation. Several refined 3D finite element models were created based on the previous experimental studies and their accuracy is examined through a comparison to test results from previous studies and other published numerical models. The presented new semi-analytical method covers some deficiencies of the previously proposed methods, and the accuracy of this approach is evaluated comparing its results with those of the other methods. The study is further extended, and the effect of axial force on the moment-rotation response of such connections is studied. This study shows that the axial tension load reduces the initial connection stiffness and moment capacity. The applicability of the presented method is evaluated, and it is shown that the model has the potential to estimate connection moment-rotation behavior under combined axial tension and moment loading.     

FE model of beam-to-column extended end-plate joints

The rotational behaviour of steel end-plate connections can be studied using the finite element method for the following three reasons: 1) such models are inexpensive and robust; 2) they allow the understanding of local effects which are difficult to measure accurately physically; and 3) they can be used to generate extensive parametric studies. This paper presents a full three-dimensional ANSYS finite element model of steel beam to column bolted extended end-plate joints for use to obtain their behaviour. The model includes: contact and sliding between different elements; bolt pre-tension; and geometric and material non-linearity.The model was calibrated and validated with experimental results found in the literature and with the model proposed by Eurocode 3. The results from the finite element analysis were verified by comparing the obtained moment-rotation curve of the joint. The procedure for determining the moment-rotation curve using finite element analysis is also given, together with a brief explanation of how the design moment resistance and the initial rotational stiffness of the joint are obtained.     

#br# 胶合木梁柱螺栓节点变异性分析

胶合木梁柱螺栓节点通常会受到木材材性和制造公差的影响，而表现出显著的变异性。为揭示节点变异性的关键影响因素并建立节点初始刚度和抗弯承载力预测模型，开展了节点变异性分析。采用已有试验结果验证确定性有限元模型的精度。考虑木材材性和螺孔间隙的随机分布规律，采用有限元方法计算胶合木梁柱螺栓连接节点初始刚度和抗弯承载力。根据统计方差分析结果确定节点初始刚度和抗弯承载力的关键影响因素。通过多项式回归拟合方法建立节点初始刚度和抗弯承载力的响应面方程。方差分析结果表明，销轴承压区顺纹和横纹方向弹性模量对于节点初始刚度的方差具有显著的影响，而螺孔间隙对于节点初始刚度也具有一定的影响；木材横纹抗拉强度和顺纹抗剪强度对于节点抗弯承载力的方差具有显著的影响，而螺孔间隙也会在一定程度上影响节点的抗弯承载力。针对随机生成的样本的计算结果表明，响应面方程能够准确预测节点的初始刚度和抗弯承载力。     

Behavior of bolted angle connections subjected to combined shear force and moment

In this paper, the effect of web angle dimensions on moment-rotation behavior of bolted top and seat angle connections, with double web angles is studied. Several 3D parametric finite element (FE) models are presented in this study whose geometrical and mechanical properties are used as parameters. In these models, all of the connection components, such as beam, column, angles and bolts are modeled using solid elements. The effect of interactions between components, such as slippage of bolts and frictional forces, are modeled using a surface contact algorithm. To evaluate the behavior of connection more precisely, bolt pretensioning force is applied on bolt shanks as the first load case. The results of this numerical modeling are compared with the results of experimental works done by other researchers and good agreement was observed. To study the influence of shear force on behavior of these connections, several models were analyzed using different values of shear force. The effect of important parameters, especially the effect of web angle dimension, is studied then. An equation is proposed to determine the reduction factor for initial rotational stiffness of connection using connection initial rotational stiffness, yield moment, the expected shear force and web angle dimension. The proposed equation is compared with other existing formulations and it was observed that the proposed model is a better estimator of connection behavior.     

高强螺栓延伸/齐平端板连接节点的有限元模拟

分析研究钢结构半刚性连接的受力性能（弯矩-转角关系）,可以采用实体有限元建立分析模型。主要介绍用C语言编写梁柱半刚性连接节点有限元模型前处理时的方法和技巧。     

Effect of shear force on the initial stiffness of top and seat angle connections with double web angles

This study focused on the moment-rotation behavior of bolted top and seat angles with double web angle connections, especially the initial stiffness of this type of connection under the combination of shear force and moment. Several 3D parametric finite element models are presented in this regard, with the geometrical and mechanical properties of connections are as parameters. In the models, all the connection components such as beam, column, angles and bolts are modeled using eight node brick elements. The effects of all component interactions, such as slippage of bolts and frictional forces, are modeled using a surface contact algorithm, and to evaluate the connection behavior more precisely, bolt pre-tensioning is applied on the bolts shanks as the first load case. The results of numerical modeling are compared with test results of experiments that have been done by researchers, and show good agreement with them. To evaluate the effect of shear force on the behavior of such connections, several models were analyzed under different magnitudes of shear force, and the results of the analyses showed that the shear force has a reducing effect on the initial stiffness of bolted angle connections. Therefore, an equation is proposed to determine the reduction factor of a connection’s initial stiffness in terms of the connection’s initial stiffness and yield moment in the case of no shear force, and any expected shear force that might be applied.     

Mechanical modeling of the nonlinear response of beam-to-column joints

A methodology for the estimation of the complete moment-rotation curve of structural beam-to-column joints is presented in this paper. The methodology is based on the component method and is materialized through appropriate mechanical models that are analyzed nonlinearly. The cases examined in this work include bolted connections with end-plates and with angles. Significant consideration is devoted to the reliable simulation of the tensile joint components that have the form of equivalent T-stubs, by application of a recently developed incremental T-stub model, for the calculation of their nonlinear force-displacement laws. The proposed methodology is evaluated against experimental tests and advanced finite element models in terms of stiffness, strength and rotational capacity, and its performance is found to be very satisfactory.     

半刚性连接无侧移组合框架梁挠度的简化计算

采用近似的线性节点刚度来反映连接的非线性弯矩-转角关系,提出了正常使用极限状态下半刚性连接无侧移组合框架梁挠度的简化计算方法。分析常用的几种线性节点刚度对组合框架挠度的影响,给出了可应用于实际设计的合理的线性割线刚度模型。通过与有限元方法计算结果比较,表明建议的简化方法具有可接受的精确度,而且对节点特征的线性简化不太敏感。     

高温下钢管混凝土结构节点的简化计算方法

本文在建立了高温下钢管混凝土柱一钢梁外加强环节点有限元分析模型的基础上,分析了在不同恒高温下环板宽度、钢管厚度、钢梁翼缘宽度和厚度、梁高等参数对节点抗弯承载力和初始刚度的影响.在此基础上建议了高温下节点抗弯承载力和初始刚度的简化计算方法,并用欧洲规范EC3的连接分类方法对高温下节点刚性进行了分析.     

RHS beam-to-column connection with web opening—parametric study and design guidelines

Connections between Rectangular Hollow Sections (RHS) have been a long-standing problem in steel construction but have received little attention from researchers. To ameliorate the situation, a new and efficient connection was proposed and evaluated by cyclic tests and finite element analysis. The connection consists of a channel connector welded to a column and bolted to a beam through a web opening. The validity of finite element analysis of the connection has also been established by comparing with test results in a companion paper. In this study, the necessary information for design is generated by finite element analyses and the influence of the various parameters is explained. The connection moment-rotation behaviour is represented by three parameters, namely, initial connection stiffness, ultimate moment capacity and the shape parameter. The variation of these parameters with the dimensions of the connecting element is presented. It is shown that the depth and thickness of the channel connectors are the primary parameters affecting the connection characteristics. It is also shown that the width-to-thickness ratio of the column web has a significant effect on the initial connection stiffness and should not be ignored in design. Other effects such as shear lag and stress intensity have a profound influence on the ultimate moment capacity of the connection. Empirical equations are presented to evaluate modal parameters based on a parametric study using finite element analysis. For the connection to be employed in seismic resistant frames, it is important to evaluate its ductility and energy dissipation capacity. Guidelines for their evaluation are also given. The results of finite element analyses are compared with simplified analysis to enable a better understanding of the distribution of forces and deformations at the initial and ultimate stages. This will be of great use in designing suitable connections between RHS sections.     

Evaluation of connection flexibility in cold formed steel racks

Steel storage racks are three-dimensional framed structures fabricated from cold formed steel sections, wherein hook-in end connectors are used to make beam-column connections which are basically boltless and semi-rigid in nature. Different types of beam end connectors with different geometry of the connected members are available, making it impossible to develop a generalized analytical model. Only very few theoretical models are available to evaluate the performance of the joints for some typical connectors. More often experimental evaluation and numerical studies are needed to predict the behaviour of every different type of connectors. In the present study eighteen experiments were conducted on a commercially available pallet rack connection by varying the most influencing parameters such as thickness of the column, depth of the connector and the depth of the beam. The main objective of this work is to quantify the beam to column joint, flexibility of commonly used pallet rack frame and to develop a general Frye-Morris type/three parameter power model type moment versus relative rotation relationship. A companion finite element shell model that simulates the experimental behaviour closely is developed using ABAQUS finite element software, which is also used for further parametric studies. Using the three major variables as size parameters, a Frye-Morris type of equation has been proposed. Some calibration studies have also been carried out. Using the ultimate moment capacity, initial connection stiffness and the shape parameter obtained, a three parameter power model has also been proposed to represent the moment-rotation behaviour of the boltless connections.     

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.     

Finite element simulation of new RHS column-to-I beam connections for avoiding tensile fracture

Many beam-to-column connections, consisting of rectangular hollow section (RHS) columns and wide flange I-beam connections, sustain brittle fracture of welded connections at the beam ends during a large earthquake. These fractures most frequently occur in regions around the beam bottom flange groove welds. A series of tests was conducted on an improved RHS column-to-I beam connection. The aim of the tests was to find possible solutions for avoiding premature occurrences of brittle fracture in RHS column-to-I beam connections. Research results show that the improved connection does not fail by fracture as observed in the conventional connections and has a larger energy dissipation capacity than the conventional types. This paper describes the finite element modeling method employed to analyze the new RHS column-to-I beam connection. The ABAQUS finite element package is used to simulate the experimental behavior, and three highly detailed 3D finite element models are created. These are complex models accounting for material nonlinearity, large deformation and contact behavior. The connection models have been analyzed through the elastic and plastic ranges up to failure. Comparisons with experimental data show that the models have high levels of accuracy.     

A simplified analytical method for unbraced composite frames with semi-rigid connections

The original Muto’s method for the lateral force analysis of conventional unbraced bare steel frames is first modified to incorporate the effects of semi-rigid beam-to-column connections. From which, equations for the calculation of the inter-storey drifts of these frames are formulated using first principles. By comparing the frame analytical results calculated from a rigorous finite element programme, it is shown that the proposed method gives reasonably accurate internal forces and inter-storey drifts estimations of a sway bare steel frame with semi-rigid connections. The proposed modified Muto’s method is then further developed for the manual analysis of unbraced composite frame systems by introducing an improved equivalent beam stiffness to account for the variation of the beam stiffness in the hogging and sagging moment regions. The accuracy of this simplified analytical method is verified by the rigorous finite element analysis of an unbraced composite frame with semi-rigid connections. Last, a parametric study is conducted to quantify the effects of semi-rigid connections on the inter-storey drifts of unbraced composite frames under lateral loads.     

Study on rotational behavior of bolted glulam beam-to-columnconnections with slotted-in steel plates

通过4组22个胶合木梁柱螺栓-钢填板足尺节点试件的单调和低周反复加载试验以及有限元数值模拟研究梁柱螺栓-钢填板节点的转动性能。试验研究表明,胶合木梁柱螺栓-钢填板节点性能主要取决于螺栓和螺孔周边木材的承压能力;节点加载初期的螺孔间隙和加载后期木材横纹裂缝张开均会导致节点刚度显著下降;同等条件下,节点初始刚度和极限弯矩随螺栓直径的减小而减小,节点初始刚度随螺栓边距的增加而减小。对试件进行有限元分析结果表明,基于有限元分析软件建立的节点三维实体模型对于节点的初始刚度和极限弯矩有较好的模拟精度（误差20％以内）。此外,模型参数分析表明,在更大取值范围内（螺栓直径12~28mm,螺栓边距30~70mm）,螺栓直径和边距对节点性能的影响与试验结果一致。     

梁柱盖板连接的滞回性能研究

盖板加强式梁柱刚性连接节点是使塑性铰外移以提高节点塑性变形的一种改进形式。为了研究梁柱盖板连接的滞回性能,在考虑材料、几何和接触状态非线性基础上,采用三维实体单元对梁柱盖板连接进行了循环加载有限元模拟。设计了4组共12个试件,研究了节点域厚度、梁高、盖板长度及轴压比等参数对盖板连接滞回性能的影响。有限元分析结果表明:大部分节点表现出良好的延性,梁端位移超过80mm;节点域厚度越厚,连接的承载力和刚度越高;梁高越大,连接的延性越差,可能会发生强梁弱柱破坏;盖板长度对节点性能没有显著影响;轴压比越大,节点的强度、刚度和延性会显著降低。     

应变率对全焊节点影响的试验和数值分析

对2个梁柱焊接节点的足尺试件进行动力试验。为了模拟试件的非线性动力性能,用纤维梁单元模拟梁、柱,用非线性旋转弹簧模拟焊接节点。对每一纤维,均采用Perzyna准则考虑应变率对梁、柱性能的影响。通过改进Richard静力模型模拟动力性能,考虑应变率对焊接节点的影响。Krawin-kler-Zoheri模型是标准累积塑性应变的函数,可根据应变率影响量化损伤和退化性能。将有限元分析软件DRAIN-2DX升级,建立模型并进行数值分析。与试验结果比较可知,考虑应变率影响和损伤累积的数值模拟能很好预测结构动力性能,甚至能预测焊接节点的破坏模式。     

Fracture prediction of welded steel connections using traditional fracture mechanics and calibrated micromechanics based models

Fracture resistance is of primary concern in the seismic design of beam-to-column connections in steel moment resisting frames (SMRFs). Micromechanics based fracture models such as the void growth model (VGM) and the stress modified critical strain (SMCS) model provide alternative approaches for ductile fracture prediction by relating micro-mechanisms of void nucleation, growth and coalescence to macroscopic stresses and strains. In this study, the VGM and SMCS models were calibrated for Q345 structural steel and the corresponding weld, through smooth notched tensile (SNT) tests and complementary continuum finite element models (FEMs). A series of seven local connections representing beam-to-column connections in SMRFs were tested under monotonic tensile loading and the specimen elongations at fracture critical point were obtained. The traditional J-integral based fracture mechanics and micromechanics based fracture models (VGM and SMCS) were applied to predict fracture in each tested local connection through refined three-dimensional FEM. Comparisons between these numerical approaches and experimental observations in prediction of fracture critical displacement, indicated that the VGM and SMCS models were able to predict fracture of welded connection with good accuracy, while the J-integral based approach resulted in quite conservative fracture prediction. This paper has bridged the gap between small-scale material tests and large-scale structural experiments in fracture evaluations.     

高温下耐火钢材梁柱抗弯连接的应用

介绍了使用耐火钢材的一个新方法,以提高钢结构中梁柱抗弯连接的耐火性。按照ISO-834标准,对两个足尺梁柱抗弯连接构件在高温条件下进行试验,以验证该方法的可行性。此外,采用一个详尽的三维有限元模型模拟梁柱抗弯连接在火中的结构性能。耐火试验结果表明:该方法可以有效延长构件的耐火时间,减小结构变形,同时提高梁柱抗弯连接破坏时的临界温度。三维有限元分析得到的数值结果也与试验结果具有很好的一致性。