Flush End Plate Research Articles

Failures and Prediction Methods of Lateral Buckling Strength of H-Shaped Beams Connected by Flush End Plates

This paper presents boundary conditions for lateral buckling of the H-shaped beams connected to columns by flush end plates which fall into the lateral buckling following the out of plane plastic deformations of the flush end plates. The study is conducted by the following procedure: First, the behavior of the connection is researched by the no buckling experiment under the cyclic loading. As a result, it is found that the relationship between the out of plane plastic deformations of the endplates and the bending moment at the beam end can be predicted. Next, the FEM analyses of the rigid-frame structures consist of the slender beams having flush end plates connection and the structures consist of the beams having rigid connection are conducted to research the stress conditions in the tension flanges and the compression flanges of the beams during falling into lateral buckling. As a result, it is found that the rigid connection is restraining warping of the beam more tightly than the flush end plates connection, then the maximum bending moment strength against lateral buckling of the beams connected by rigid connections is higher than those of the beams connected by flush endplate. We recommend that the boundary conditions for the lateral buckling of the beams connected by flush end plates should be regarded to be different from those of the beams connected by the rigid connections.

Initial rotational stiffness of minor-axis flush end-plate connections

The semi-rigid performance of minor-axis connections is important in the study of overall framework. Experiments were conducted on minor-axis flush end-plate connections under a monotonic load. Numerical simulations were carried out using the finite-element package ABAQUS and compared with the experimental results. The initial rotational stiffness of the connection was calculated using the equivalent T-stub in tension and EC3 component method, and the calculated veracity is discussed. The results show that under the action of a negative bending moment, the failure modes of the minor-axis flush end-plate connection are the out-of-plane bending deformation of the end-plate, local buckling of the bottom flange of the beam, and bending deformation of the bolts. The minor-axis flush end-plate connection is a typical semi-rigid connection. However, the deformations of the flush end-plate could not be accurately calculated using the equivalent T-stub in the tension of EC3 methods. The initial rotational stiffness calculated using the method was much larger than that obtained using the experiment and finite-element analysis. The equivalent simulation is not appropriate if the out-of-plane bending stiffness of the flush end-plate is not obtained accurately.

Seismic behaviour of gravity load designed flush end-plate joints

Flush end-plate (FEP) beam-to-column joints are commonly used for gravity load resisting parts in steel multistorey buildings. However, in seismic resisting structures FEP joints should also provide rotation capacity consistent with the global structural displacements. The current version of EN1993-1-8 recommends a criterion aiming at controlling the thickness of the end-plate in order to avoid brittle failure of the connection, which has been developed for monotonic loading conditions assuming elastic-perfectly plastic behaviour of the connection's components in line with the theory of the component method. Hence, contrary to the design philosophy of the hierarchy of resistances implemented in EN1998-1, the over strength and the hardening of the plastic components are not directly accounted for. In light of these considerations, this paper describes and discusses the results obtained from parametric finite element simulations aiming at investigating the moment-rotation response of FEP joints under cyclic actions. The influence of bolt diameter, thickness of end-plate, number of bolt rows and shape of beam profile on the joint response is discussed and design requirements are proposed to enhance the ductility of the joints.

Dynamic increase factor for progressive collapse analysis of semi-rigid steel frames

An empirical and efficient method is presented for calculating the dynamic increase factor to amplify the applied loads on the affected bays of a steel frame structure with semi-rigid connections. The nonlinear static alternate path analysis is used to evaluate the dynamic responses. First, the polynomial models of the extended end plate and the top and seat connection are modified, and the proposed polynomial model of the flush end plate connection shows good agreement as compared with experimental results. Next, a beam model with nonlinear spring elements and plastic hinges is utilized to incorporate the combined effect of connection flexibility and material nonlinearity. A new step-by-step analysis procedure is established to obtain quickly the dynamic increase factor based on a combination of the pushdown analysis and nonlinear dynamic analysis. Finally, the modified dynamic increase factor equation, defined as a function of the maximum ratio value of energy demand to energy capacity of an affected beam, is derived by curve fitting data points generated by the different analysis cases with different column removal scenarios and five types of semi-rigid connections.

Quality indicators after discharge from the intensive care unit in 3 public hospitals

Although there are many researches on infilled steel frames with welded beam-to-column connections, however, few studies were undertaken to investigate the behaviour of these infilled structures but with other common connection types (extended endplate, flush endplate and header plate connections), particularly under combined vertical and horizontal loading. In this paper, firstly, a simplified numerical model of infilled steel frames under cyclic loading, considering the interactions between frames, infills and beam-to-column connections' components, was constructed. The model results were compared with experimental data for cyclically-loaded infilled frames, showing good agreement. Using the verified model, a parametric study on infilled steel frames with five different beam-to-column connection types, under vertical and cyclic horizontal loads, was performed. Several parameters, including vertical load level, infill thickness and vertical load application method, were investigated. The results showed that increasing the level of vertical load (uniformly distributed on the beam) minimised the difference in performance between the frames with welded connections and those with bolted connections. Under vertical loads of 0, 16% and 24% of the columns' axial capacity, the horizontal ultimate load of frames with header plate connections, was, respectively, 73%, 86% and 91% of that of frames with welded connections. Hence, when the infilled frames are subjected to relatively high levels of vertical load, utilising header plate connections may be a viable alternative to using welded connections. Furthermore, a simple analytical method for predicting the stiffness and load-carrying capacity of masonry-infilled steel frames (with different connection types) under vertical and horizontal loads, was proposed.

Capacity of semi-rigid composite joints in accommodating column loss

In the scenario of column loss, joints would be subjected to bending moment combined with a tensile force due to large vertical displacement, where tensile force plays a critical role in resisting progressive collapse of structure by providing the catenary force. In order to study the effect of tensile force on the behavior of semi-rigid composite joints in structures in the case of column loss, six semi-rigid flush endplate connections tests were conducted, which include pure flexural tests, pure tensile tests and combined flexural and tensile tests. The experimental results indicate that under pure bending moment condition, the semi-rigid composite joint displays sufficient rotation capacity for forming “catenary action”. It is characteristic of the semi-rigid composite joint that its moment capacity decreases in a linear manner together with the increase of tensile load. Also, the capacity of semi-rigid composite joints is compared with that of the full-welded rigid composite joints. The tensile strength of high-strength bolts would not exert any effect on the initial stiffness of semi-rigid joint, but bring about decline in the moment resistance and tensile resistance of semi-rigid joint. The joints tend to fail at “catenary phase” under tensile force. A simplified M-N correlation formula for composite joint is proposed to describe the behavior of joint in structures under column loss. The finite element model with material failure criterion can predict the fracture of bolt in semi-rigid composite joint.

Experimental and numerical analyses of blind bolted moment-resisting composite joints to CFST columns with RC slab

In this paper, experimental and numerical analyses were conducted to investigate the structural properties and failure modes of the blind bolted flush or extended end plate joints between concrete-filled steel tubular (CFST) columns and composite beams. The experimental program and the main results of the tests were elaborated. Four full-scale subassemblages beam-tocolumn exterior joints to hot-rolled and cold-formed CFST columns were tested. The failure modes and moment-rotation relation curves of the joints were evaluated. The test results showed that all specimens exhibited favorable strength and stiffness, and larger deformation capacities. Meanwhile, finite element analysis (FEA) modeling of the specimens was built and analyzed. The results obtained from the FEA modeling were satisfactory agreement with the experimental tests results. Then, an extensive parametric study was conducted to investigate the influence of various parameters on the moment capacity and rotation stiffness of composite joints under positive or negative moment. The experimental studies and numerical analyses can improve the design of the typed joints to be used in moment-resisting composite frames.

Numerical study on masonry-infilled steel frames under vertical and cyclic horizontal loads

Although there are many researches on infilled steel frames with welded beam-to-column connections, however, few studies were undertaken to investigate the behaviour of these infilled structures but with other common connection types (extended endplate, flush endplate and header plate connections), particularly under combined vertical and horizontal loading. In this paper, firstly, a simplified numerical model of infilled steel frames under cyclic loading, considering the interactions between frames, infills and beam-to-column connections' components, was constructed. The model results were compared with experimental data for cyclically-loaded infilled frames, showing good agreement. Using the verified model, a parametric study on infilled steel frames with five different beam-to-column connection types, under vertical and cyclic horizontal loads, was performed. Several parameters, including vertical load level, infill thickness and vertical load application method, were investigated. The results showed that increasing the level of vertical load (uniformly distributed on the beam) minimised the difference in performance between the frames with welded connections and those with bolted connections. Under vertical loads of 0, 16% and 24% of the columns' axial capacity, the horizontal ultimate load of frames with header plate connections, was, respectively, 73%, 86% and 91% of that of frames with welded connections. Hence, when the infilled frames are subjected to relatively high levels of vertical load, utilising header plate connections may be a viable alternative to using welded connections. Furthermore, a simple analytical method for predicting the stiffness and load-carrying capacity of masonry-infilled steel frames (with different connection types) under vertical and horizontal loads, was proposed.

Effect of boundary conditions on the behaviour of composite frames against progressive collapse

Boundary conditions, such as the horizontal and out-of-plane restraints, play an important role in structural resistance and deformation capacity of composite frames under column removal scenarios. Most studies only focused on interior frames with rigid horizontal and out-of-plane restraints, whereas limited data are available on the effects of weak restraints and out-of-plane rotations on the behaviour of composite frames against progressive collapse. In this study, a series of experimental tests were conducted on composite frames with different horizontal and out-of-plane restraints. Web cleat and flush end plate connections were used in the frames. Experimental results showed that when subject to in-plane loading, exterior composite frames could mobilise significant catenary action to mitigate progressive collapse and eventually column failure might occur under catenary action in bridging beams. For composite frames with out-of-plane rotation, the ultimate resistance was substantially reduced due to lateral torsional buckling of composite beams at large deformation stage. However, the flexural resistance of frames was less susceptible to boundary conditions compared to catenary action. Furthermore, bending moments at side columns were evaluated to gain insight into the behaviour of side columns under horizontal tension force at the catenary action stage. Moreover, component-based models were developed for composite frames and validated against test data. Design recommendations were provided in accordance with experimental and numerical results.

Thermal creep mechanical-based modeling for flush endplate connections in fire

A mechanical-based model is developed to predict the time-dependent effect (thermal creep) and the fast loading-rate behavior of flush endplate connections at elevated temperatures during a fire. The fast loading-rate behavior model consists of multi-linear springs that predict each component stiffness, strength, and rotation. The multi-linear springs temperature expressions are based on the ambient temperature formulations proposed in Eurocode3 Part 1.8 where material properties are considered temperature-dependent. To include the effect of thermal creep in the proposed model, a modified Burgers creep model is developed to predict the time-dependent connection rotation and temperature of flush endplate connections. The modified Burgers creep model consists of linear springs and viscous dashpots that predict the time-dependent connection rotation. The proposed model is validated against experimental results available in the literature and finite element (FE) simulations developed as a part of this study. Through explicit consideration of thermal creep effect, the proposed model helps providing important insights into fire-induced thermal stresses and deformations and their implications on designing of flush endplate connections in fire.

Behavior of beam-high performance fiber reinforced CFST column joints

This paper presents a serial of test results of beam-high performance fiber reinforced CFST column joints (beam-HPFR CFST column joints). A total of four exterior joints specimens are tested experimentally. The test parameters are the thickness of the flush end plate and the ratio of the steel fiber. Moment- relative rotation relationships of the current tested joints are discussed and their characteristics are evaluated in terms of initial stiffness, moment capacities and ductility. The results are analyzed and compared with the EC3 prediction. The results show that, the initial stiffness and the maximum deflection of the steel beam increases with increasing the steel fiber ratio. Likewise, the rotation capacity of beam-HPFR CFST column joints exceeds 0.04rad and increases up to 0.08rad by increasing the ratio of fiber. Hence, the ductility of the current joints satisfies the required ductility for the seismic provisions for special moment frames AISC, 2010. Finally, the finite element (FE) model using ABAQUS program is used based on the test geometry. The FE models are verified by comparing with the current experimental results. The FE model predicts well the complete moment-relative rotation curves for the tested specimens in terms of initial stiffness, strength, rotation capacity and maximum vertical displacement of beams. In addition, the failure mode of the FE provides good agreement with the experimental results.

Behaviour of Flush End-Plate Connection for Perforated Section

Behaviour of Flush End-Plate Connection for Perforated Section

Behaviour of bolted endplate composite joints to square and circular CFST columns

This paper presents the results of an experimental study on the structural performance of blind bolted endplate composite connections to concrete filled steel tubular (CFST) columns under static loading. Four full-scale sub-assemblages of cruciform composite joints representing the internal region of a composite frame were tested. The parameters varied were the shape of column sections and the type of endplates. The performance of the joints in terms of rotational stiffness, moment resistance and rotation capacity was evaluated to explore the effects of the shape of column sections and endplate types. An analytical model was also developed to predict the moment-rotation behaviour of composite joints. The experimental results indicated that both moment resistance and initial stiffness of the tested connections are considerably enhanced if the flush endplate and square column were replaced by the extended endplate and circular column, respectively.

高强螺栓灌浆套管端板拼接节点试验研究

本文提出了一种新型H形截面钢高强螺栓端板拼接节点，即容错度较好的高强螺栓灌浆套管端板拼接节点。为研究此节点的受力性能，实验设计了2个足尺试件，对其进行静力加载破坏试验，分析节点的受力特性、承载力性能、高强螺栓的拉力分布规律及破坏模式，并同时设计2个试件与该节点对应的高强螺栓端板拼接节点进行受力性能的对比。试验结果表明：相较于高强螺栓端板拼接节点，该节点的抗弯承载力及延性提高较显著；抗剪承载力基本相同；受压区螺栓的拉力分布基本一致，受拉区螺栓的拉力分布，随着荷载的增大，其拉力始终小于高强螺栓端板拼接节点的受拉区螺栓。研究表明此节点由于端板上可以适当地开大螺栓孔径的大小而不影响其受力性能，故可以有效地解决高强螺栓的安装难度，便于施工现场安装。 A new type of flush endplate connection, named better-tolerance high-strength bolted grouted sleeve flush endplate connection, was developed for splice H-shape steel. In this paper, the static loading failure tests were conducted on two specimens in order to evaluate load transfer mechanism, strength capacity, tensile force distribution of high-strength bolts and failure mode of this type of connection, furthermore, the other two specimens of its corresponding type of high-strength bolted flush endplate connections were designed to compare their mechanical performances. The experimental results indicate that by comparing with high-strength bolted flush endplate connections, the bending capacity and ductility of high-strength bolted grouted sleeve flush endplate connections increases remarkably, the shearing capacity and the tension distribution of the bolts in the compression zone is basically the same, but with the increase of the load, the tension distribution of bolts in tension zone is smaller than the high-strength bolt endplate flush endplate connections. The results show that since the bolt aperture can be properly opened largely without affecting its mechanical performance, so this type of connection can effectively solve the installation difficulty of high-strength bolts, and facilitate to install at construction sites.

Modelling and behaviour of beam-to-column connections under axial force and cyclic bending

Many experimental and numerical studies were conducted to study the cyclic behaviour of steel beam-to-column connections; however, most of the proposed numerical works developed sophisticated three-dimensional solid models. In this paper, firstly, simplified finite element models of steel beam-to-column connections under cyclic loading were established using three- and two-dimensional shell models. Element types and steel cyclic constitutive models were described. The interactions between connection components (bolts, members and endplate) were accurately modelled to simulate the actual behaviour of connections. Both material and geometric nonlinearities were considered. The suggested finite element models showed good agreement with experimental results (hysteretic curves and failure modes) for a cyclically loaded endplate connection. Usually the steel connections are subjected to bending and axial force. In some situations, the axial force on the beam may reach sufficient large values which can lead to a considerable effect on the connections behaviour. Therefore, using the suggested two-dimensional shell model, a numerical parametric study on different connection types (fully welded, extended endplate, flush endplate and header plate connections), under combined axial force and cyclic bending, was performed. The carrying capacity, initial stiffness, hysteretic behaviour and energy dissipation capacity were compared and discussed. The results indicated that the level and direction of axial force significantly modified the connection response. The ultimate capacity of welded, extended endplate and header plate connections, under axial compression force equal to 35% of the beam axial plastic resistance, was, respectively, 74%, 126% and 169% of that of the same connections without axial force.

Computational modelling of the moment-rotation relationship for deconstructable flush end plate beam-to-column composite joints

This paper presents a three-dimensional finite element modelling of an innovative flush end plate semi-rigid beam-to-column composite joint comprising deconstructable post-installed friction-grip bolted shear connectors. The moment versus rotation relationship for these prototype joints subjected to a hogging bending moment with the influence of partial shear connection is investigated using ABAQUS software. This relationship is an indicator of the ductility of a composite joint and is a necessity for a semi-rigid frame analysis. A detailed finite element model of the connection region including the precast concrete slab, steel beam, flush end-plate, bolted shear connectors and the steel column is developed in the paper. Material and geometrical non-linearities as well as the non-linearity of the interfaces are incorporated in the model. The accuracy and reliability of the numerical formulation are verified against experimental data reported elsewhere. In addition, a composite joint with partial shear connection is constructed and tested in this study, and the numerical predictions are compared with the test results. An extensive parametric study is then conducted, using several parameters that include the degree of shear connection, reinforcement ratio, thickness of the precast concrete slab, spacing of bolted shear connectors, size of the bolts in the connection zone, thickness of the flush end plate, steel grade for the beam, column and end plate and the column flange thickness. Finally, moment versus rotation models for deconstructable flush end plate beam-to-column composite joint are proposed, and it is demonstrated that the design models developed can also be used for composite joints with high strength steel components.

Experimental study on blind bolted connections to concrete-filled stainless steel columns

This paper studies the performance of blind bolted connections to concrete-filled stainless steel tubular columns. An experimental investigation was conducted on seven full-scale joints to study the effects of the following parameters: (a) presence of the floor slab or not; (b) with or without binding bars in the connection region; (c) type of steel used for the column (stainless or carbon steel); and (d) loading type (monotonic or cyclic). The experimental results demonstrated the good performance of the blind bolts in this type of connection. No bolt shank fracture was observed in any of the test specimens. The presence of the binding bars slightly enhanced the performance of the blind bolted connections, whereas the presence of composite slabs significantly affected the failure mode, initial stiffness, flexural resistance, and rotation capacity of the joints. Owing to the use of flush end plates, the joint without floor slab can be classified as nominally pinned joint according to EC3. But in the presence of the floor slab, the joint nearly reached its full strength and the stiffness was also significantly increased close to the limit for rigid sway frames. In addition, the test results indicated that the material type of the steel tube had no obvious influence on the joint performance. In contrast, the cyclic loading led to slightly decreased joint strength, but had more obvious detrimental influence on the joint stiffness.

Numerical Study of Deconstructable Flush End Plate Composite Joints to Concrete-filled Steel Tubular Columns

This paper describes a three-dimensional finite element modelling of an innovative flush end plate semi-rigid composite joint, to a concrete-filled steel tubular column, using high strength blind bolts. This innovative composite joint is formed by connecting a precast concrete slab to the top flange of a steel beam using post-installed friction-grip bolted shear connectors to facilitate the deconstructability of the entire system. A finite element model is developed using ABAQUS software to study the structural behaviour and failure modes of these prototype joints. Both geometrical and material non-linearities, as well as the non-linearity of the contacts and interfaces, are incorporated in the model. Four full-scale laboratory test specimens having deconstructable flush end plate composite semi-rigid joint to CFST columns using bind bolts are tested, with the results then used for validation of the finite element model. The proposed numerical models developed are used for conducting an extensive parametric study, in which the effects of the reinforcement ratio, thickness of the precast concrete slab, degree of shear connection, number of bolted shear connectors, size of the blind bolts in the connection zone and thickness of the flush end plate on the structural behaviour of the composite joint to concrete-filled columns are investigated. A design recommendation in the form of an empirical equation is then formulated.

Finite element analysis of HSS semi-rigid composite joints with precast concrete slabs and demountable bolted shear connectors

High-strength steel has a higher yield strength, greater corrosion resistance and superior toughness compared to mild steel, and its use can contribute to the sustainability of a steel structure by increasing its structural life whilst reducing steel usage and maintenance. In addition, using deconstructable steel-concrete composite floors can facilitate component recycling and reuse and can improve the sustainability of the building industry significantly by reducing energy consumption and construction waste at demolition. This paper investigates the structural behaviour of an innovative beam-to-column composite semi-rigid joint with deconstructable post-installed friction-grip bolted shear connectors and grade S690 high strength steel flush end plates. Non-linear continuum-based finite element models are developed and validated against results of four full-scale laboratory tests of this innovative joint. The validated finite element models are used for conducting an extensive parametric study in which the effects of the reinforcement ratio, thickness of the precast concrete slab, degree of shear connection, number of bolted shear connectors, size of the bolts in the connection zone, size of the steel beam and thickness of the flush end plate on the structural behaviour of a composite joint with deconstructable post-installed friction-grip bolted shear connectors and grade S690 high strength steel flush end plates are investigated. A simple analytical model is proposed to predict the moment capacity and rotation capacity of this type of composite joint.

Experimental study of sustainable high strength steel flush end plate beam-to-column composite joints with deconstructable bolted shear connectors

The design of engineering structures for deconstructability can reduce the energy and cost required for their demolition and for the disposal of their construction waste, and it also enhances the sustainability of a building by allowing for easy dismantling and the reuse or recycling of structural components and construction materials at the end of the service life of the building. In addition, using high performance materials such as high strength steel can improve the sustainability of a structure by providing for higher design stresses and accordingly reducing the self-weight of the structure. This paper describes the results of four full-scale beam-to-column deconstructable composite joints with high strength steel S690 flush end plates. The structural behaviour of the new system in conjunction with application of post-installed friction-grip bolted shear connectors for developing deconstructable composite floors is investigated. The test results show that the proposed composite beam-to-column joints can provide the required strength and ductility according to Eurocode 3 and Eurocode 4 specifications, and that the system can be easily deconstructed at the end of the service life of the structure as a proof of concept.