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 unfilled hollow section columns using extended T-stub with back face support

This paper presents the results of an experimental and analytical study into a new bolted moment connection between unfilled hollow section columns and open section beams, referred to herein as the extended T-stub connection with back face support. The connection is comprised of T-stubs connecting the top and bottom flanges of the beam to the face of the column and channels connecting the T-stubs to a backplate at the back face of the hollow section column. The addition of the channels to a standard T-stub connection helps to distribute the beam flange tension load to the back face of the hollow section column thus reducing demand on the flexible column face which often will compromise the stiffness of the connection. The extended T-stub connection with back face support was found to be comparable to a previously tested side connection and is much stiffer than a typical face connection. Comparison of the test results and three dimensional finite element (FE) model indicates that FE analysis can be used to predict the connection behaviour with sufficient accuracy. The experimental results and analytical sensitivity analysis demonstrate that this new connection can offer a robust and reliable moment connection for application in the low rise construction industry.     

Double-angle shear connections with small hollow structural section columns

This paper describes an experimental study on double-angle shear connections when used with small-size hollow structural section columns. Twelve connection specimens were tested to confirm the practice of either fitting the connection angles to the narrow column face by shortening the outstanding legs or by employing flare bevel groove welds. Test results demonstrated that both rotational and shear resistances of the connections were satisfactory when either of the two details was used. In the meantime, the flare bevel groove welds, made by a gas metal arc welding process, were also tested for the purpose of determining their effective throat.     

Dynamic response of hollow section frames with bolted moment connections

The behaviour of moment-resisting steel frames under various types of loads is dependent on the type of beam-to-column connections and their flexibilities. The extended end-plate connection is a practical field bolted moment connection that can be adopted in moment-resisting steel frames with hollow structural steel (HSS) columns, by using high strength blind bolts. The objective of this work was to study the behaviour of blind bolted extended end-plate connections for HSS columns under cyclic loading. With proper detailing and modelling of such connections, it has been possible to investigate the effect of joint flexibility on the response of the frame when subjected to dynamic loading and then to compare its response to that of a rigid frame. It is concluded that the proposed bolted joint behaves in a predictable manner that can be modelled and analysed using standard frame analysis programmes. The study also showed that the inclusion of the connection flexibility in frame analysis is essential to obtain a more realistic frame behaviour.     

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.     

Numerical investigation of net section failure in stainless steel bolted connections

Despite fundamental differences in the mechanical behaviour of stainless steel and carbon steel, design provisions for stainless steel connections in current standards essentially follow the rules for carbon steel with some limited modifications. For the case of net section capacity, the design rules from EN 1993-1-3 for cold-formed carbon steel have been adopted for stainless steel connections in EN 1993-1-4 and the SCI/Euro Inox Design Manual without any modification. In this paper, an investigation into the behaviour of stainless steel connections failing by net section rupture has been conducted. Numerical models for austenitic and ferritic stainless steel have been developed and validated against existing test results. The validated models were subsequently used to perform parametric studies to investigate the main parameters affecting the net section rupture of bolted connections; these include edge distance e₂ and bolt configuration. By studying the stress distribution along the net section for different edge distances and bolt arrangements, it was found that the ductility of stainless steel is sufficient to ensure extensive redistribution of stresses prior to fracture. Hence, a revised design equation (based on that given in EN 1993-1-3) for net section capacity of stainless steel connections has been proposed and its reliability demonstrated by means of statistical analysis.     

Seismic design of reduced beam section steel moment connections with bolted web attachment

Recent test results on reduced beam section (RBS) steel moment connections showed that specimens with a bolted web connection tend to perform poorly due to premature brittle fracture of the beam flange at the weld access hole. The measured strain data appeared to indicate that a higher incidence of base metal fracture in bolted web specimens is related, at least in part, to the increased demand on the beam flanges due to the web bolt slippage and the actual load transfer mechanism which is significantly different from that usually assumed in connection design. In this paper, the practice of providing web bolts uniformly along the beam depth was brought into question. A new seismic design procedure, which is more consistent with the actual load path identified from analytical and experimental studies, is proposed. A pilot test specimen designed by following the proposed procedure exhibited sufficient cyclic connection rotation capacity without fracture.     

Behaviour of welded T-end connection to rectangular hollow section (RHS) in axial tension

This paper presents the results of an experimental investigation of the behaviour of T-end connections welded to rectangular hollow section (RHS) members subjected to axial tension. A total of 19 specimens were tested to failure. Parameters considered for the investigation were the tube size and the cap plate thickness. The cleat plate thickness was kept constant for all tests. The cleat plate orientation relative to the tube was investigated and was found to affect the joint strength. There was evidence of shear lag taking place. The test results also revealed that the use of very thick cap plates (more than 20 mm) does not lead to increased joint capacity. The yield line analysis was used to predict the failure loads and a comparison is made with the test results.     

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.     

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.     

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。     

Numerical study and design of skewed X-type branch plate-to-circular hollow section connections

Structural systems, including space-frames, cable stayed roof systems and bridges, with elements that intersect at non-orthogonal angles necessitating rotated and complex connection geometries, have become commonplace. Non-orthogonal plate-to-circular hollow section (CHS) connections with branch members rotated about their own axis (skewed) have been absent in international literature and design guidelines. A numerical finite element parametric study is presented on the behaviour of skewed X-type plate-to-CHS connections loaded under branch plate tension. A total of 91 connections with wide-ranging values of geometric properties were modelled and analysed using commercially available finite element software. The numerical finite element analysis indicated a smooth sigmoidal (S-shaped) transition between longitudinal and transverse orthogonal extremes. A non-linear interpolation function was developed, for application between longitudinal and transverse design recommendations, that adequately predicts skewed connection behaviour over a wide range of geometric connection configurations. A partial design strength function for skewed X-type plate-to-CHS, which builds on existing design recommendations for non-skewed plate connections, is hence proposed with lower bound reduction (resistance) factors.     

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.     

Experimental and numerical assessment of stayed steel columns

Stayed steel columns may be used as compression-resisting members of a structure presenting high slenderness ratios and fast erection requirements. The system is able to sustain a wide range of load levels and lengths with economic and reliable structural solutions. Although this structural solution dates back from the 1960s its structural behaviour is not fully understood. This fact motivated a study of the system structural behaviour by means of an experimental program followed by finite element simulations aiming to determine the most efficient structural geometries and the corresponding steel ties pre-stress force magnitudes. A series of full-scale tests were executed in 12 m pre-stressed steel columns with a 90 mm diameter. Some of the main contributions of the current study are related to the conception, development and execution of new tri-dimensional full-scale tests and the development of a finite element model calibrated against these experiments. An extensive parametric analysis based on the calibrated finite element simulation was also performed focusing on the most significant parameters that could affect the structural response, i.e., column length and diameter, pre-stress force magnitude, among others. The test and numerical results will certainly contribute to the development of updated design procedures and formulae to be introduced in future structural design codes.     

钢梁-混凝土墙铰结连接节点嵌固弯矩的分析与计算

近年来,外钢框架-混凝土核心筒混合结构在我国高层建筑中逐渐增多。钢梁-混凝土墙铰结连接节点是这种混合结构中常用的一种节点形式,在其预埋件的设计计算中,需要考虑节点连接处嵌固弯矩的影响。本文针对现有嵌固弯矩近似计算方法需求解超越方程的问题,首先基于螺栓连接的剪力-变形本构关系,给出了嵌固弯矩的理论计算方法,随后基于螺栓群连接的近似受力分布,提出了近似弹塑性计算方法,并根据塑性极限分析理论提出了近似极限计算方法。两种方法可直接计算嵌固弯矩,无需求解超越方程,其中近似极限计算方法更为简单。通过与收集到的20个试验结果的对比分析,讨论了理论方法和本文提出的近似方法准确性。结果表明,本文提出的近似弹塑性计算方法比试验值偏大约2%,近似极限计算方法比试验值偏大约20%,偏于保守较多。     

A novel steel section for concrete-filled tubular columns

In modern structural constructions, concrete-filled steel tubular (CFT) columns have gradually become a central element in structural systems like tall buildings, bridges and so forth. The effective parameters on load carrying capacity of CFT columns are the bond between the steel and internal concrete, local buckling strength of steel tube, creep of concrete and loading conditions of column at connections. Considering these effective parameters, a novel section is suggested which can be used for columns of tall buildings and bridges with large spans. The main characteristic of the suggested steel section is internal longitudinal symmetric stiffeners. In the present study, a comparative investigation into the behavior of this novel section (with circular and octagonal shapes) and the most common used sections of CFT columns has been carried out under axial and cyclic loading. Having verified the finite element modeling, several different analyses have been undertaken. The results of the analyses clearly exhibit the increase in strength and ductility of the suggested novel section under axial and cyclic loading and therefore, its application is recommended in construction practice.     

Flexural–torsional performance of thin-walled steel hollow box columns subjected to a cyclic eccentric load

This paper investigates the seismic performance of steel hollow box sections. The test results obtained from the combined load tests were used to define the relationship among member performance, sectional aspect ratios and the load combinations. It was found from the comparisons that the flexural strength of members decreased when the torsion magnitude was increased. It was also observed that the reduction in flexural strength increased when the sectional aspect ratio was increased. An empirical expression for estimating member performance under three-dimensional loads is proposed for design references.     

Behaviour of concrete filled steel tubular (CFST) stub columns under eccentric partial compression

This paper investigates the behaviour of concrete filled steel tubular (CFST) stub columns subjected to eccentric partial compression. Twenty-eight specimens were tested and presented. The main parameters in test program include: (1) section type: circular, square and rectangular; (2) load eccentricity ratio (including uniaxial and biaxial loading): from 0 to 0.4; and (3) shape of the loading bearing plate (BP): circular, square, strip and rectangular. The test results indicated that, similar to the corresponding fully loaded CFST stub columns under eccentric loading, CFST stub columns under eccentric partial compression have generally reasonable bearing capacity and favorable ductility. A finite element analysis (FEA) model for CFST stub columns under eccentric partial compression is developed and the predicted performances are validated through measured results. The FEA model is then used to investigate the mechanisms of such composite columns further.     

An innovative model for predicting the displacement and rotation of column-tree moment connection under fire

In this study, we carried out nonlinear finite element simulations to predict the performance of a column-tree moment connection (CTMC) under fire and static loads. We also conducted a detailed parameter study based on five input variables, including the applied temperature, number of flange bolts, number of web bolts, length of the beam, and applied static loads. The first variable is changed among seven levels, whereas the other variables are changed among three levels. Employing the Taguchi method for variables 2–5 and their levels, 9 samples were designed for the parameter study, where each sample was exposed to 7 different temperatures yielding 63 outputs. The related variables for each output are imported for the training and testing of different surrogate models. These surrogate models include a multiple linear regression (MLR), multiple Ln equation regression (MLnER), an adaptive network-based fuzzy inference system (ANFIS), and gene expression programming (GEP). 44 samples were used for training randomly while the remaining samples were employed for testing. We show that GEP outperforms MLR, MLnER, and ANFIS. The results indicate that the rotation and deflection of the CTMC depend on the temperature. In addition, the fire resistance increases with a decrease in the beam length; thus, a shorter beam can increase the fire resistance of the building. The numbers of flanges and web bolts slightly affect the rotation and displacement of the CTMCs at temperatures of above 400°C.     

Behaviour of flush end plate joints to concrete-filled steel tubular columns

This paper presents the results of an experimental program for bolted moment connection joints of circular or square concrete filled steel tubular (CFST) columns, and H-shaped steel beams using high-strength blind bolts. In order to investigate the static performance and failure modes of the blind bolted connection, an experimental program was conducted involving four sub-assemblages of cruciform beam-to-column joints subjected to monotonic loading. Moment-rotation relationships of the tested connections were obtained and their performance was evaluated in terms of their stiffness, moment capacities and ductility. The test parameters varied were the column section type and the thickness of the end plate. The results showed that the proposed blind bolted connection, which behaves in a semi-rigid and partial strength manner according to the EC3 specification, displays reasonable strength and stiffness. The rotation capacity of this type of connection to square or circular CFST columns exceeds 70 mrad and this satisfies the ductility requirements for earthquake-resistance in most aseismic regions. The blind bolted connection is shown to be a reliable and effective solution for moment-resisting composite frame structures.