End-plate Connections Research Articles

Cyclic behaviour of infilled steel frames with different beam-to-column connection types

Although numerous researchers demonstrated the significant difference in performance between the various beam-to-column connection types, most of the previous studies in the area of infilled steel frames focused on the behaviour of frames with welded connections. Therefore, there is a need for conducting studies on infilled steel frames with other common connection types (extended endplate with and without rib stiffeners, flush endplate and shear connections). In this paper, firstly, a two-dimensional finite-element model simulating the cyclic response of infilled steel frames was presented. The infill-frame interaction, as well as the interactions between connections' components, were properly modelled. Using the previously-validated model, a parametric study on infilled steel frames with five different beam-to-column connection types, under cyclic loading, was carried out. Several parameters, including infill material, fracture energy of masonry and infill thickness, were investigated. The results showed that the infilled frames with welded connections had the highest initial stiffness and load-carrying capacity. However, the infilled frames with extended endplate connections (without rib stiffeners) showed the greatest energy dissipation capacity and about 96% of the load-carrying capacity of frames with welded connections which indicates that this type of connection could have the best performance among the studied connection types. Finally, a simplified analytical model for estimating the stiffness and strength of infilled steel frames (with different beam-to-column connection types) subjected to lateral cyclic loading, was suggested.

Dynamic increase factor for progressive collapse of semi-rigid steel frames with extended endplate connection

As an extremely destructive accident, progressive collapse is defined as the spread of an initial local failure from element to element, resulting eventually in the collapse of an entire structure or disproportionately large of it. To prevent the occurrence of it and evaluate the ability of structure resisting progressive collapse, the nonlinear static procedure is usually adopted in the whole structure design process, which considered dynamic effect by utilizing Dynamic Increase Factor (DIF). In current researches, the determining of DIF is performed in full-rigid frame, however, the performance of beam-column connection in the majority of existing frame structures is not full-rigid. In this study, based on the component method proposed by EC3 guideline, the expression of extended endplate connection performance is further derived, and the connection performance is taken into consideration when evaluated the performance of structure resisting progressive collapse by applying the revised plastic P-M hinge. The DIF for structures with extended endplate beam-column connection have been determined and compared with the DIF permitted in current GSA guideline, the necessity of considering connection stiffness in determining the DIF have been proved.

Numerical testing of steel beam-to-column bolted extended end-plate connection with haunches

During the European research project entitled EQUALJOINTS (European pre-Qualified steel JOINTS) [1], which recently concluded, the matter of providing a set of pre-qualification procedures for moment resisting beam-to-column connections which are currently used in Europe has been addressed. During the experimental campaign 24 specimens with bolted extended end-plate connections with haunches were tested. The current paper presents the numerical model which has been developed such that numerical testing may be performed to further investigate specific details. In what concerns the material, an isotropic material model has been calibrated and used based on tensile tests of coupons extracted from the specimens to model the actual plastic behaviour. Moreover, the imperfections of the beam have been taken into account using a bucking analysis to model as accurate as possible the specimens tested. The interaction between parts has been modelled using contacts with different interaction laws. The model used for the bolt has been calibrated such that the preloading and failure replicate the behaviour of the actual bolts used in the experiments.

Numerical investigation of semi-rigid connection ultimate capacity

With the advances in computational analysis techniques and development of new design methods, new interests have arisen in structural engineering. In the last few years, with the increasing numbers of terrorist attacks, the study of robustness, progressive structural collapse and ultimate resistance of structures has grown exponentially, with various studies being published all over the world. In order to perform this study through computational analysis, it was necessary to develop a calibrated numerical model capable of representing the behaviour of structures in their final stage of resistance. This article presents an evaluation of semi-rigid connections through a numerical model considering the implementation of collapse and damage progression criteria calibrated against experimental tests. Afterwards, a parametric study was developed by varying the bolt diameters and endplate thickness of a flush endplate semi-rigid connection. The main parameters and criteria that rules the simulation of flush end-plate joints subject to damage were assessed, allowing that many different kind of studies with similar components could be performed, such as impact, explosion and column loss analysis. As an outcome, the bending moment-rotation curves of these connections are presented and it is shown that those with a larger bolt diameter were able to produce greater rotation, while an increase in the endplate thickness was able to provide a greater bending moment capacity.

Numerical evaluation of the effects of fire on steel connections; Part 2: Model results

The resistance of beam-to-column connections to fire is an important consideration for the design of steel moment frames. The authors seek to study the effect of fire on such connections using finite element modeling in ABAQUS. The previously published first part of this paper detailed and validated the simulation technique by comparing model results to experimental results reported elsewhere in the literature. This, the second part of the paper, seeks to demonstrate the performance of four types of connections exposed to thermal loading: (1) bolted end plate, (2) bolted cover plate, (3) bolted tee, and (4) welded cover plate. A numerical study was performed to quantify the effects of thermal loading on beam buckling, displacement, rotation, connection stiffness, and moment-rotation behavior at temperatures between 20 and 900 °C. The bolted end plate connection exhibited the highest resistance to thermal loading with a significantly lower degree of degradation in connection performance compared to the other three connection types.

Numerical Study on Ultimate Deformation and Resistance Capacity of Bolted T-Stub Connection

Disproportionate or progressive collapse is a phenomenon in which entire structure or large part of it collapses because of the local failure of a structure. Resistance to such progressive collapse depends on continuity between elements and ductility of the connections. The ductility of commonly used bolted end plate connections may depend on the T-stub component of the connection. The aim of this paper is to study the behaviour of T-stub components of beam to column end plate bolted connections under large deformation demands associated with column loss scenario. For this purpose, a parametric study is carried out to evaluate the ultimate strength and deformation capacity considering two parameters i.e. distance between the bolts and endplate thickness. Based on the experimental data, numerical model has been validated and employed in a parametric numerical study aimed at improving the response under large deformation demands. The study indicate significant role of bolts in development of catenary forces since the ultimate tensile capacity of T-stub after undergoing large deformation in a ductile failure mode was controlled by the failure of the bolts. Parametric study reveals much higher bolt force in comparison with displacement controlled induced axial force in the T-stub indicating failure of the bolts at much lower applied axial force.

Generalised component model for structural steel joints

This paper presents a generalised component model for structural steel joints that extends the Component Method to the post-ultimate and post-fracture ranges. In this approach, a tri-linear spring model was developed for each individual component to include their post-ultimate behaviour, and a new concept of the instantaneous centre of rotation was introduced to track the changing load condition of each series of springs in a multi-spring system. The proposed generalised component model can predict the full-rangeM − θ curves of multi-spring models containing any number of deformable springs, and does not pose numerical difficulties in the post-ultimate range where some springs unload. The method is potentially applicable to all types of steel joints. The paper presents the application of the method to recent experimental tests on bolted moment end plate connections, showing good agreement over the full range of behaviour including fracture. The paper also demonstrates the application of the method to produce the backbone curve for a hysteretic model for the bolted moment end-plate connection.

Experimental and numerical behaviour of blind bolted flush endplate composite connections

This research presents an experimental investigation and finite element model on the performance of composite beam-to-column flush end plate connections utilising blind bolts. Previous research recommended improvements to the design of these connections if they are required to withstand a low probability high consequence earthquake of a 1-in-2500 years return period. Therefore, two full-scale sub-assemblages of cruciform composite joints were tested under static and cyclic loading. The test results were used to establish the load-displacement characteristics of the connection. The experimental results demonstrated improved stiffness and strength when compared with a previous study. Two finite element models were developed and validated with the experimental data. Parametric studies were performed to investigate the influence of the thickness of equal angles, end plate thickness, shear connection ratio, reinforcement ratio and slab thickness on the connection behaviour.

Modelling of Bolted Endplate Connections Subjected to Bending Moment and Axial Force in Fire

This article presents an extensive application of component based method both at ambient and elevated temperatures. The analytical model is used to predict the connection behavior, with axial force in the connected beam being superposed. The formulas for the calculation of bending moment resistance and rotation stiffness are derived in the article. At the same time, two kinds of loading paths, proportional loading and non-proportional loading, are also thoroughly investigated. A total of 12 tests, in which the connection is subjected to proportional loading path, are utilized to validate the analytical model. At the same time, a 3D Finite Element Model using the ABAQUS is also presented to verify the analytical model. As to the connection under non-proportional loading path, 6 transient fire tests are chosen to verify the proposed model. Compared to the experimental results, the accuracy of the moment-rotation curves obtained from the analytical model are acceptable. Hence, the presented analytical model can be used to predict connection behavior under fire conditions, taking the influence of axial force into account.

Numerical simulation of bolted connections

Abstract This article presents the modeling of a complete bolted connection based on a model with one bolt connecting two or three plates. Initially, the behavior of this model with one bolt is analyzed by comparing it with existing bibliography for 3 different types of applied load: tension, shear and a combination of these two. This model includes all necessary considerations: contacts between the plates and the nut, head and shank of the bolt; contact between the plates, as well as friction between them; and pre-load on the bolt. The model also responds properly to loads parallel and perpendicular to the contact surface between the plates, including prying action effects. These calibrated models are then introduced as super-elements in empty spaces left on the full connection, through a relatively simple process using the finite element software ANSYS®. Upon filling these spaces, two complete connection models are evaluated: one with a single plate and one between two T-stubs. The results obtained with these models are compared with standard forecasts. These two connection types have a practical application in the way they will be analyzed, and also as part of more complex connections: bolted girder splices (in the region of web beam), beam-to-column connections with splice plates or end plate connections, beam splices with end-plates, etc.

Coupled testing-modeling approach to ultimate state computation of steel structure with connections for statics and dynamics

The moment-resistant steel frames are frequently used as a load-bearing structure of buildings. Global response of a moment-resistant frame structure strongly depends on connections behavior, which can significantly influence the response and load-bearing capacity of a steel frame structure. The analysis of a steel frame with included joints behavior is the main focus of this work. In particular, we analyze the behavior of two connection types through experimental tests, and we propose numerical beam model capable of representing connection behavior. The six experimental tests, under monotonic and cyclic loading, are performed for two different types of structural connections: end plate connection with an extended plate and end plate connection. The proposed damage-plasticity model of Reissner beam is able to capture both hardening and softening response under monotonic and cyclic loading. This model has 18 constitutive parameters, whose identification requires an elaborate procedure, which we illustrate in this work. We also present appropriate loading program and arrangement of measuring equipment, which is crucial for successful identification of constitutive parameters. Finally, throughout several practical examples, we illustrate that the steel structure connections are very important for correct prediction of the global steel frame structure response.

Evaluation of fragility functions with potential relevance for use in New Zealand

One barrier to adopting seismic loss estimation frameworks in New Zealand engineering practice is the lack of relevant fragility functions which provide probabilities of exceeding certain levels of damage (e.g. cracking of gypsum wallboards) for a given demand (e.g. interstorey drifts). This study seeks to address this need for four different building components; interior full-height steel-framed plasterboard partition walls, unbraced suspended ceilings, precast concrete cladding, and steel beam-column joints with extended bolted end-plate connections. Fragility functions were sourced from literature, and their potential for use in New Zealand is evaluated considering similarities in component detailing with local practices. Modifications to a number of fragility functions, including generalizations for easier adoption in practice, are proposed. A loss estimation case study of a 4-storey steel moment-resisting frame is performed to investigate the significance of fragility function selection. It is shown that the definition of damage states can have a noticeable influence on the assessment of incurred repair cost of individual building components. This indicates that fragility functions should be carefully selected, particularly if the performance evaluation of each individual component is of utmost importance. However, the observed difference in expected annual repair cost of the entire building was small, indicating that in cases where fragility functions are not readily applicable for use in New Zealand, other fragility functions may be used as placeholders without drastically altering the outcome of loss analysis for the entire building.

Component tests and numerical simulations of composite floor systems under progressive collapse

This paper presents experimental and numerical studies on the behaviour of components and composite floor system under column removal scenarios. Shear connectors, double angle-cleat connections and flush end plate connections were extracted from a three-dimensional composite floor system and tested under different loading conditions. The load-displacement curves of these components were compared with the results predicted from existing models. A simplified numerical model was developed to simulate the behaviour of composite floor systems subject to progressive collapse, in which the properties of springs were determined from component tests. The model was then validated against experimental results in terms of load-displacement relationship and failure mode. Finally, parametric studies were conducted to investigate the effects of slab thickness, aspect ratio and reinforcement. Numerical results suggested that the aspect ratio of slabs has the most significant effect on the load capacity of composite floor systems under progressive collapse scenarios.

End web stiffeners for connecting ductile replaceable links

The ability to restore the integrity of structural lateral systems that utilize steel links to inelastically deform in earthquakes can be improved through the use of replaceable links. Replaceable links can be removed when damaged, especially when isolated from the gravity carrying system, and can provide engineers greater design freedom with respect to structural stiffness and strength. To ensure that ductile inelastic deformation is isolated to the effective length of the replaceable link, robust connection details capable of sustaining large cyclic deformations are needed. An integrated numerical and experimental research program was performed to evaluate a bolted end plate connection detail which utilized fillet welds, instead of full joint penetration welds, between the links and end plates in an effort to simplify fabrication. Continuum finite-element methods were used to evaluate various end stiffener options to shift flange plastic strains caused by link deformation away from the welds. The results from that study informed the selection of cases evaluated in large-scale experiments. Cyclic pseudostatic tests were conducted to experimentally demonstrate the performance of the selected end-stiffener configurations. Results from the experimental investigation showed that ductile inelastic deformation within the effective length of the links can be achieved using a bolted end plate connection with fillet welds between the shear link and end plate by utilizing end stiffeners placed parallel to the web. Design recommendations for incorporating the end stiffeners are outlined based on the data and experiences gained.

An investigation of the behavior of header end-plate connections under monotonic loading

In seismically active regions such as Turkey, the context of the nonlinearity provided by a building is based on the behaviors of structural components; beams, columns and their connections constituting the seismic force resisting system of the structure. Of these members, beam-to-column connections can play a considerably important role even if they have a capability of limited stiffness and flexural strength. Structural steel connections are mainly classified as a pinned or a moment connection. However, some beam-to-column connections having limited stiffness and flexural strength, which are called semi-rigid connections such as header end-plate connections designed so as to transmit only shear forces, can be characterized by moment-rotation relationship. This paper investigates the behavior of header end-plate connections using finite element (FE) modeling. The FE models include material, geometrical and contact nonlinearities. FE modeling technique was first verified through the test results of the experimental research performed by Aggarwal (1990). Then the effect of header end-plate thickness upon moment-rotation relationship was investigated. According to the analyses results, in addition to shear stresses, axial tensile stresses have been observed to occur in the bolts at the tension side and thickness of the header end-plate and beam web play a governing role in the development of initial rotational stiffness and the flexural strength of header end-plate connections.

고온에서의 엔드플레이트 접합부를 가진 H형강 보 거동에 관한 실험적 연구

고온에서의 엔드플레이트 접합부를 가진 H형강 보 거동에 관한 실험적 연구

Behavior of Extended End-Plate Steel Beam to Column Connections

Background: The main objective of this study is to simulate the behaviour of steel beam-to-column connections using the computer package of Finite Element Analysis (FEA) known as “ABAQUS”. Objective: This paper presents the investigations of extended End-Plate connections (EP). A one-model segment is examined under the impact of concentrated load and the exclusive boundary conditions were tested. The analysis of the nonlinear behaviour of the connection is a complicated science and needs to use programs to solve this problem. Experimental works are normally conducted for this type of studies which used more of money, time and effort. Therefore, with the availability of simulation applications, these problems can be addressed. Results and Conclusion: The results of the evaluation were compared with the experimental data from the available literature. In this case, nonlinearity materials were used. A sample study on EP connections was carried out using both material and geometric nonlinearities. The comparison of FEA results with corresponding experimental results confirms the correlation and convergence between them.

Progressive collapse behaviour of extended endplate connection to square hollow column via blind Hollo-Bolts

This paper investigated behaviour of two blind bolted extended endplate connections using Hollo-Bolts to square hollow section (SHS) column in full-scale beam-joint-beam assemblies under a scenario of inner column removal. The characteristics of the Hollo-Bolt were firstly examined by nine direct tension tests and six double shear tests, which demonstrated low pre-tension and anti-sliding capacity under recommended torques in comparison with the requirement for standard high strength slip-critical bolts. In two specimens with special configuration of reduced beam section (RBS) or thin column (TC), Hollo-Bolts were pulled out from column wall with different failure mechanism, one exhibiting shear failure of sleeve and the other combining closure of sleeve legs in Hollo-Bolts and enlarged bolt holes of column wall. Strain intensities at the connection region and load transfer mechanisms of flexural resistance and catenary mechanism were analysed in details. Results indicated that the premature failure of thin column wall disabled the full utilization of Hollo-Bolts strength and hence resulted in low level of stiffness and catenary resistance of the assembly, which implied the necessity of connected plates with sufficient thickness for satisfactory performance of Hollo-Bolt connections. In the comparison against other blind bolted connection and welded connection in normalised vertical resistance - normalised beam rotation curves, extended endplate connections using Hollo-Bolts presented lower initial normalised stiffness due to their limited pre-tensions, and lower level of catenary mechanism development due to the reduced strength of Hollo-Bolt under large deformation.

Experimental and Numerical Analysis on Full High Strength Steel Extended Endplate Connections in Fire

Full-scale experimental study and numerical analysis on behaviors and failure mechanisms of full high strength steel extended endplate connections in fire have been carried out and presented in this paper. The experimental behaviors of the connections were compared with the provisions of Eurocode 3. The test results show that the failure modes of the connections in fire are bolt failure with yielding of the flange, as same as those at ambient temperature. The failures of the bolts in fire are ductile while they are brittle at ambient temperature. The rotation capacity of the connections in fire is proved sufficient. What is more, at elevated temperature 550 °C, the plastic moment resistances of Q690 and Q960 full high strength steel endplate connections are only 40% of those at ambient temperature, while their initial rotation stiffness are 66 and 63% respectively. But the rotation capacities of Q690 and Q960 high strength steel endplate connections are 1.38 and 1.74 times of those at ambient temperature. Moreover, it is found that the component method Eurocode 3 proposed based on connections made of mild steels can be used to calculate plastic resistances and to predict failure modes of high strength steel endplate connections in fire, but it is not suitable to predict their stiffness. The suggestions about rotation capacity of connections in Eurocode 3 are found too conservative for high strength steel endplate connections in fire.

TWO SIMPLIFIED MODELS OF COLUMN WEB PANEL IN SHEAR

The paper presents behaviour of the column web panel in shear. The finite element method is employed to examine the resistance of a joint with an extended end plate connection. The FE model is validated to results of physical tests and verified by an analytical solution based on existing formulas. Finally, a parametric study is performed. The studied parameters include web panel thickness, bolt position and the column dimensions.