Experimental and numerical analysis of beam to column joints in steel structures

The behaviors such as extreme non-elastic response, constant changes in roughness and resistance, as well as formability under extreme loads such as earthquakes are the primary challenges in the modeling of beam-to-column connections. In this research, two modeling methods including mechanical and neural network methods have been presented in order to model the complex hysteresis behavior of beam-to-column connections with flange plate. First, the component-based mechanical model will be introduced in which every source of transformation has been shown only with geometrical and material properties. This is followed by the investigation of a neural network method for direct extraction of information out of experimental data. For the validation of behavioral curves as well as training of the neural network, the experiments were carried out on samples with real dimensions of beam-to-column connections with flange plate in the laboratory. At the end, the combinational modeling framework is presented. The comparisons reveal that the combinational modeling is able to display the complex narrowed hysteresis behavior of the beam-to-column connections with flange plate. This model has also been successfully employed for the prediction of the behavior of a newly designed connection.     

钢框架螺栓连接迟滞力学信息模型

强震作用下,钢和组合框架梁-柱螺栓连接节点的性能对其结构响应有着显著影响。其滞后响应表现为高度地无弹性特性以及刚度、强度和延展性的不断变化,从而影响结构的抗力。因此,为准确进行地震评估和设计,精确的螺栓连接滞回模型必不可少。提出了一种新的混合建模方法,可用于描述强震作用下框架螺栓连接节点复杂的滞回性能。该方法假定并非连接响应的所有特征均服从力学模型,因此,以信息为基础的替代方案是可行的。传统力学模型通过以信息为基础的模型单元对复合力学信息模型(HMIM)进行补充。信息单元了代表力学模型的各个方面。通过板件的翼缘连接展示了HMIM的效果,该连接表现出捏缩迟滞特性。     

Combination of mechanical and informational modeling to predict hysteresis behavior of I beam‐to‐CFT column connection

The behavior of beam‐to‐column connections is significantly complicated because it depends on the material, nonlinear relationship between different members, and contact of connecting elements. Their hysteretic response exhibits highly inelastic characteristics and continuous variation in stiffness, strength, and ductility. Therefore, accurate hysteretic models of bolted connections are essential to accurate seismic assessment and design. Composed (Hybrid) modeling approach is presented to represent the complex hysteretic behavior of I beam‐to‐concrete‐filled‐tube (CFT) column bolted connection. For the purpose in this study, experimental evaluation of I beam‐to‐CFT column connection with bolted end‐plate under cyclic loading is done. It must be mentioned to make the connection easily applicable practically and also prepare the column flanges continuity, a connection with the bolts penetrated into the CFT column are used since using the stiffeners in hollow sections is not easily applicable. In the composed mechanical–informational modeling framework, the conventional mechanical model is complemented by information‐based model components. Finally, moment–rotation curves of composed model have been compared with experimental results. Comparison showed that the composed model has a good agreement with experimental results. A newly designed specimen for validation purpose of the composed modeling was made and experimented. Composed model was well applied to predict the behavior of new connections. The presented results show that the composed model has a good ability to predict of hysteretic behavior.     

Investigation of Proposed Concrete Filled Steel Tube Connections under Reversed Cyclic Loading

Concrete-filled steel tube (CFT) columns are used in the primary lateral resistance systems. The objective of this research is to analyse the behavior of the steel beam to CFT column connections. A three-dimensional numerical model for simulating the behavior of CFT connections was developed with the aid of the general purpose nonlinear finite element analysis package ABAQUS. In this paper, 90 CFT connection specimens include simple and moment connections that were tested under reversed cyclic loading. Shear capacity of joint, moment-drift response, energy absorption, and displacement ductility were studied in those models. The results have indicated that, the hysteresis curve of CFT columns was plump; no pinch phenomenon can be found; the damage and degradation degree of the strength and stiffness of specimens is lower; and high energy dissipation capacity can be achieved. Improvement in the behavior of CFT connection depends on the beam characteristics and column features.     

Improved analytical model for special concentrically braced frames

Special Concentrically Braced Frames are commonly used as the seismic resisting system in buildings. Their inherent strength and stiffness assure serviceable performance during smaller, more frequent earthquakes. Inelastic tensile yield and post-buckling compressive deformations of the brace dominate performance during large seismic events. However, inelastic deformations of the brace place secondary yet significant inelastic deformation demands on beams, columns, and connections, which significantly affect the seismic performance. These response modes must be included in an analytical model of the system to capture the response. However, conventional practice uses beam–column elements for the brace, to simulate brace buckling, with pin-ended or rigid end connections; these computer models cannot capture the full range of SCBF behaviors. The research presented in this paper was undertaken to develop a modeling approach for SCBFs to more accurately predict their seismic performance. Beam–column elements are used for the braces, beams and columns and these elements include nonlinear geometric effects to simulate brace buckling. A new connection model is proposed to simulate the behavior of the gusset plate. The model parameters are based upon the member sizes, properties and connection designs. Simulated results are compared with experimental results and predictions from approaches more commonly used in practice. Although a step beyond models currently used in design practice, the proposed model remains simple in its implementation and is suitable for a wide range of practical applications. The proposed model provides accurate simulation of global behavior, while retaining simplicity and providing reasonable predictions for many local behaviors.     

Mechanical models for the analysis of bolted T-stub connections under cyclic loads

The mechanical models used to simulate the complete behavior of full-scale bolted T-stub connections under cyclic loads are mainly treated in this paper. These mechanical models are composed of individual T-stub components modeled as nonlinear spring elements in order to reliably reproduce their various response mechanisms interacting with one another in the connection. The hysteresis behaviors of the T-stub components including bolt/flange uplift, stem elongation, and relative slip deformation combined with bolt bearing are simulated by the multi-linear cyclic stiffness models characterized from their actual force–deformation response mechanisms each. The nonlinear component springs, which contain these idealized stiffness properties, are implemented into the user joint element produced based on the mechanical model so as to numerically generate the complete behavior of the full-scale connections with considerable accuracy. The analytical predictions performed on the joint element are evaluated against the experimental tests with respect to stiffness, strength, and deformation. Thus, the adequacy of the proposed modeling approach is verified through comparisons between analytical predictions and experimental test results. Finally, it can be shown that the mechanical model proposed in this study has the satisfactory potential to predict the response of the T-stub components as well as the behavior of the T-stub connections through analytical studies.     

混凝土十字形中柱的板柱连接抗震性能试验研究

通过两个大比例十字形中柱的板柱连接试件(其中一个试件配置抗冲切锚栓),在竖向荷载和低周反复水平荷载作用下的试验,探讨了十字形中柱的板柱连接在模拟地震作用下的裂缝形态、破坏特征、混凝土以及钢筋的应变、滞回特性、位移延性等一系列受力特性。试验研究表明,十字形中柱的板柱连接与传统方形中柱的板柱连接受力性能类似,两个试件的极限侧移比都远超过了1.5%的侧移比限值要求,因此在板柱结构中引入十字形柱是可行的;配置抗冲切锚栓可以显著地提高板柱连接的承载能力和延性。此外,根据试验给出了十字形中柱的冲切临界面形式,并提出了其类似极惯性矩的计算公式,从而使十字形中柱的板柱连接可以应用现行规范的方法进行承载力分析计算,采用该方法的分析结果与试验结果符合较好。     

A simplified numerical model for post-tensioned steel connections with bolted angles

Post-tensioned (PT) self-centering beam–column connections has been developed for its good seismic performance. Many researchers have investigated its mechanical behavior by numerical or experimental method. Prior researches have indicated that the analysis by elaborate FE models is very time consuming. To overcome this disadvantage, a simplified numerical model was established in this paper. The accuracy of results derived by this model was validated against prior investigations on interior PT connections with top-and-seat angles. Influence of initial PT force on mechanical behavior of PT connection was investigated. The Geometric and material nonlinearities, and strands can be considered in the modeling. A planar steel frame structure was established and hysteretic analysis was conducted. Results indicated that the computational cost can be greatly reduced by this model.     

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。     

方钢管混凝土柱与钢梁连接的拉伸试验研究

本文通过对带内隔板的十字形连接节点的拉伸试验,研究了方钢管混凝土柱与钢梁连接的结构性能。借助于在柱翼缘、梁翼缘和内隔板上的应变测量,分析了连接区域的应力传递机制。基于屈服线理论,并考虑连接区域的应变性能,提出了方钢管混凝土柱与钢梁连接的承载力方程,可供制订规范和工程设计参考     

Analytical study of beam-to-HSS/CFT column connections by trapezoidal external stiffener

Use of continuity plates in box columns is approved by design codes. To meet seismic parameters, considering performance problems and lack of confidence in the quality of the connections due to closed section, unsuitable vision and extreme welding and cutting at junction, continuity plates have been removed from the column and replaced by external stiffener. In this study, behavior of box beam-to-column connections with/without continuity plates, with external stiffener in two states with/without concrete (CFT/HSS) inside the column and finally reinforced connection by horizontal bar mats in CFT (Concrete Filled Tube) column have been studied by finite elements modeling and nonlinear analysis under monotonic and cyclic loadings. The results have shown that the use of external stiffener rather than continuity plate causes to increase 1% in rigidity and in turn 46.09% in strength. On the other hand, the use of filler concrete in column has caused to improve seismic behavior of the connection. When this connection containing the combination of external stiffeners and horizontal bar mats in CFT column is taken place, rigidity and strength parameters will be increased 3.01% and 108.8% respectively, compared to connections with no horizontal bar mats. In addition, the proposed connection has best performance in terms of both stress distribution and energy absorption and meets rigid connection criterion as well.     

低周往复荷载作用下可变梁高装配式钢框架节点力学性能研究

在传统螺栓连接节点的基础上,提出一种可根据梁高在一定范围内调节节点连接高度的可变梁高装配式钢框架节点,适用于节点所连钢梁高度出现小范围变化时的情况。结合4个足尺试件在低周往复荷载作用下的试验研究及有限元分析,对采用不同L形连接件加强构造以及梁 柱连接对中方案时,节点的失效模式、滞回性能以及L形连接件的滑移情况进行了分析。结果表明,L形连接件的刚度将改变节点的受力性能,其椭圆螺栓孔构造会使节点在受力时产生一定的滑移,但该滑移对节点滞回性能的影响不明显;可忽略梁 柱连接对中方案对节点受力性能的影响;通过提高L形连接件的刚度,可使节点具有良好的滞回性能以及设计所期望的破坏模式;文中所采用的有限元分析方法可有效模拟节点滞回性能。该类节点可方便地应用于轻型装配式钢框架结构。     

混凝土T形边柱的板柱连接抗震性能试验研究

通过2个大比例T形边柱的板柱连接试件(其中1个试件配置抗冲切锚栓)在竖向荷载和低周反复水平荷载作用下的试验,探讨了T形边柱的板柱连接在模拟地震作用下的裂缝形态、破坏特征、混凝土以及钢筋的应变、滞回特性、位移延性等一系列受力特性。试验研究表明,T形边柱的板柱连接与传统方形边柱的板柱连接除破坏形态有所差异外,其受力性能基本类似,2个试件的极限侧移比都远超过了1.5%的侧移比限值要求,因此在板柱结构中引入T形边柱是可行的;配置抗冲切锚栓可以显著地提高T形边柱的板柱连接的承载能力和延性。此外,根据试验给出了T形边柱的冲切临界面形式,并提出了其类似极惯性矩的计算公式,从而使T形边柱的板柱连接可以应用现行规范的方法进行承载力分析计算,采用该方法的理论分析结果与试验结果符合较好。     

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.     

钢框架梁柱T型钢半刚性连接节点的性能研究

对实际工程中所采用的T型钢半刚性连接节点性能进行了研究,采用通用的有限元程序ANSYS对节点性能进行了非线性有限元分析,讨论了节点各组成要素对节点性能的影响。结果表明:柱翼缘厚度、T型钢翼缘厚度和连接螺栓竖向间距对节点性能影响较大,而柱腹板、T型钢腹板以及连接螺栓水平方向间距对节点性能影响较小,节点破坏主要由柱翼缘和T型钢翼缘控制。研究表明,T型钢梁柱连接节点属于半刚性连接节点,节点的半刚性对钢框架性能影响非常大,设计中不容忽视。     

矩形钢管柱与H型钢梁单边螺栓连接节点的抗震性能与恢复力模型研究

为研究矩形钢管柱与H型钢梁单边螺栓连接节点抗震性能,对5个单边高强螺栓连接节点试件和1个常规高强螺栓连接节点试件进行了拟静力试验,研究了矩形钢管柱与H型钢梁单边螺栓连接节点破坏模式、滞回曲线、骨架曲线、延性、耗能、刚度退化等抗震性能指标,对比了单边高强螺栓与常规高强螺栓连接节点抗震性能的差异性;分析了节点构造参数对单边高强螺栓连接节点抗震性能的影响,根据节点滞回特性和单边高强螺栓受力特点提出了节点恢复力模型。研究结果表明:节点试件的破坏模式中单边高强螺栓均产生滑移现象;节点试件的滞回曲线捏缩严重,滞回曲线呈反S形,且有明显滑移直线段;节点试件初始转动刚度约为常规高强螺栓连接节点的70%,单边高强螺栓滑移使节点具有很大的转动变形能力,节点试件的极限转角为0.06～0.08 rad;节点的受弯承载力与常规高强螺栓连接节点基本一致,单边高强螺栓能够满足节点承载力设计要求;节点试件的等效黏滞阻尼系数为0.15～0.17,等效耗能系数为1.29～1.77,延性系数为1.62～2.26,其耗能和延性性能均低于常规高强螺栓连接节点;通过设置端板加劲肋可有效提高节点试件的抗震性能,设置内隔板对节点试件...     

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。     

上下翼缘角钢半刚性梁柱节点的力学性能研究

上下翼缘角钢梁柱节点是一种典型的半刚性梁柱节点。其节点各个组成部分的几何参数变化将导致其力学性能发生改变。采用非线性有限元分析方法,对这种节点进行精细模拟,从而得出影响其力学性能的主要参数。     

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.     

Experimental behaviour of steel reduced beam section to concrete-filled circular hollow section column connections

In this paper, five specimens of connections of reduced beam section (RBS) steel beam to concrete-filled steel tubular (CFST) circular hollow section (CHS) column using an external ring were tested. The experiments considered the hysteretic behaviour under combined constant axial load and cyclic lateral load. For comparison, three specimens of a weak-column without an RBS configuration steel beam to CFST column connection were tested under the same conditions. The axial load level of the CFST column, width of connection stiffening ring and RBS configuration were considered as the experimental parameters of their seismic behaviour. It was found that the lateral load (P) versus lateral deformation (Δ) hysteresis curves exhibited no obvious strength deterioration and stiffness degradation. The energy dissipation of the RBS connections is significantly improved when compared with weak-column connections. The concrete filled CHS columns failed as a weak-column connection and their energy dissipation capacity was reduced. It can be concluded that the RBS connections exhibit good seismic performance.