Extended End Plate Research Articles

Semi-Rigid Analysis of Extended End Plate Connections Based on Correlation and Sensitivity

In traditional semi-rigid analysis of extended end plate connections is assumed to be deterministic parameters, most of moment-rotation models of the joint is determined by curve-fitting and statistically regressed with the test data. Those parameters of the models have little physical meanings and the effect of correlations between parameters is neglected. This paper deals with a semi-rigid joint of extended end plate connections based on correlation and sensitivity analysis. A numerical study was carried out and the finite element analysis was validated compared with the experimental results.The relative moment-rotation model was concluded based on correlations in parameters and probabilistic sentivity analysis. The relationship between height and width of steel beam was partial correlation, the relationship between thickness of steel beam flange and thickness of steel beam web was partial correlation. Height and width of steel beam, the distance of upper bolts to axle wire of steel beam were important sensitive parameters for the extended end plate connections.

Local Strength of a Compression Zone in Extended Endplate Beam-to-Column Connections Stiffened with Bolted Channels

Local Strength of a Compression Zone in Extended Endplate Beam-to-Column Connections Stiffened with Bolted Channels

Seismic performance of semi-rigid composite joints with a double-sided extended end-plate. Part II: Seismic simulations

The numerical model of the double-sided extended end-plate composite joint presented in Part I of this paper is used to evaluate the seismic performance of this joint when used in moment-resisting frames. For this purpose, three frames of different heights and spans were designed and analysed. Two pushover analyses, with uniform and modal lateral load, were performed to evaluate the ultimate capacity of the frame. Incremental dynamic analyses (IDAs) were also performed to evaluate the seismic properties of each frame using accelerograms that match three types of elastic response spectra. The data provided by the simulations has allowed us to obtain the behaviour factors of the composite frames that use this type of joint, and to ensure their improved behaviour under seismic actions.

The seismic performance of a semi-rigid composite joint with a double-sided extended end-plate. Part I: Experimental research

Composite structures exhibit higher stiffness than steel structures with similar ductility, and also show better performance to fire action. These benefits have led to an increase in the number of composite structures built in high seismic areas. The main objective of the experimental tests explained in this article is to obtain useful data about the seismic behaviour of a composite semi-rigid joint with a double-sided extended end-plate. A series of monotonic and cyclic quasi-static tests was performed to characterize the behaviour of this joint type against seismic actions. The tests were performed on interior and on exterior joints, and they have provided useful data about the ductility of the joint, the amount of energy dissipated and the degradation effects. This data was used to elaborate and calibrate a component-based model of the joint that is composed of two rotational springs, one for the shear panel behaviour and the other for the connection behaviour. This model is capable of simulating the joint behaviour and damage under cyclic loads with sufficient accuracy.

Experimental and numerical model for space steel and composite semi-rigid joints

An experimental investigation was made to study the behaviour of space steel and composite semi-rigid joints. The effect of loading from the minor direction on the main direction of semi-rigid joints was considered. Five full-scale tests were performed on semi-rigid space steel and composite extended endplates joints. A three-dimensional finite element model is proposed using ANSYS software for the analytical investigation. A comparative study between the present numerical model and the experimental results is presented to establish the validity of the proposed model. Also, an application was made on space frame to show the effect of joint rigidity using a beam-element model and this was verified with previous studies.

Evaluating a steel beam’s rigid connection to a concrete filled tubular column when submitted to dynamic load

Using prequalified connections during the structural design stage becomes increasingly necessary when developing structural engineering projects which include steel elements; this is so that the steel elements’ appropriate behavior can be ensured according to the structural system and seismic demand. Unfortunately, the international entities providing this type of information (i.e. FEMA) only have a limit series of prequalified connections and such series do not include rigid connections between steel beams and concrete filled tubular (CFT) columns having an extended end plate, which has become a very widespread building practice in Colombia. This paper describes the most important aspects of a study at the Universidad Nacional de Colombia concerning the behavior of a steel beam rigidly connected to a CFT-column, using six physical models having different width-thickness ratio (b/t) columns. ANSYS v.10 software was used for studying theoretical models (finite elements analysis) for comparative analysis of cyclic test theoretical and experimental results for each specimen presented for the qualification phase. The six tested specimens’ hysteretic curves are presented. Several conclusions are drawn concerning finite element validation for this type of connection and the influence of width-thickness ratio (b/t) variation and design recommendations for suitable behavior under dynamic loads when this type of connection was used.

SEISMIC DESIGN OF STEEL FRAMES WITH PARTIAL STRENGTH JOINTS

In the seismic design of steel frames, beam-to-column joints can be designed either as full strength joints, forcing the location of the plastic hinges at the beam ends, or as partial strength joints which have to dissipate the seismic input energy. Seismic codes provide specific design criteria for full strength joints, but there are no detailed recommendations dealing with partial strength connections. Therefore, in this paper, by means of a simplified model, such as a SDOF system, the requirements which partial strength joints have to possess, for designing steel frames characterised by seismic performances equivalent to those of steel frames with rigid full strength joints, are pointed out. Successively, starting from the above requirements, a new method for designing seismic resistant steel frames with extended end plate connections leading to the complete definition of the geometrical and mechanical parameters of the joints is proposed.

Ductility analysis of bolted extended end plate beam-to-column connections in the framework of the component method

The rotational behaviour of bolted extended end plate beam-to-column connections is evaluated in the context of the component method. The full moment-rotation response is characterized from the force-deformation curve of the individual joint components. The deformability of end plate connections is mostly governed by the bending of the column flange and/or end plate and tension elongation of the bolts. These components form the tension zone of the joint that can be modelled by means of

Parametric analysis of steel bolted end plate connections using finite element modeling

This paper presents and discusses results of parametric analyses on the behavior of bolted extended end plate connections using Finite Element (FE) modeling tools. The analyses were calibrated to experimental results that are also briefly reviewed in this paper. The analytical models took into account material nonlinearities, geometrical discontinuities and large displacements. Comparisons between numerical and experimental data for moment-rotation curves, displacements of the end plate, and forces on bolts showed satisfactory agreement. Phenomenological T-stub failure models were also used for calculations of the flexural strength for the end plate. These models clearly support the numerical results and show how the interaction between the end plate and the bolts changes the connections’ behavior. The results presented herein show that failures associated with either formation of yield lines in the plate (Mode 1) or bolt tension failure (Mode 3) are well-defined, while failures due to combinations of these mechanisms (Mode 2) represent levels of interaction between the end plate and bolts that are difficult to predict accurately. These results also indicate that the T-stub analogy has limitations in representing the yield lines at the end plate, leading to limitations both in accounting for prying action and in predicting values for strength and stiffness of the connection.

Experimental assessment of the ductility of extended end plate connections

An experimental investigation of eight statically loaded extended end plate moment connections was undertaken at the Delft University of Technology to provide insight into the behaviour of this joint type up to collapse. The specimens were designed to confine failure to the end plate and/or bolts without development of the full plastic moment capacity of the beam. The parameters investigated were the end plate thickness and steel grade. The results show that an increase in end plate thickness results in an increase in the connection flexural strength and stiffness and a decrease in rotation capacity. Similar conclusions are drawn for the effect of the end plate steel grade, though no major variations in the initial stiffness are observed. The failure modes involved weld failure in two test specimens, nut stripping in four tests and bolt fracture in the remaining, always after significant yielding of the end plate and bolt bending. Comparisons of the joint ductility and the corresponding equivalent T-stub for the end plate side are drawn.

반강접 접합부를 적용한 초대형 부유식 구조물 상부구조체의 2차 탄성해석

If semi-rigid connections are used for superstructures of very large floating structures (VLFS), the number of rigid connections can be reduced and more economical construction will be possible. In this study, considering service load and wave load in VLFS, the applicability of mixed use of rigid and semi-rigid connections have been studied using three types of connections for a four-bay eight-story frame. Three types of connections are used; top and seat-angle connections with double web-angle(TSD), extended end plate connections, steel tubular column with square external-diaphragm connections. ABAQUS(Finite element analysis program) is used for conducting second order elastic analysis.

An experimental study of the fire performance of non-sway loaded concrete-filled steel tubular column assemblies with extended end plate connections

This paper presents the results of an experimental study of the behaviour of concrete filled steel tubular column assemblies using extended end plate connections. The objectives of this study are to investigate the effects of rotational restraint on column bending moments and column effective lengths. Two series of column assemblies have been fire tested at the University of Manchester’s fire testing laboratory. In each test, a hot-finished rectangular steel tube of grade S275 and dimension of either RHS 200×100×5mm or RHS 200×100×12.5mm, filled with nominally C30 concrete, was connected to a pair of steel beams at one end using extended end plate connections. Each series of tests consist of four combinations of two levels of total axial load in the column, with either equal or unequal loads on the connected beams. Design calculations are performed by using a finite element heat transfer computer program (ABAQUS) in combination with the ambient temperature design method for composite columns in Eurocode 4 Part 1.1, but with modified composite cross-sectional capacities at elevated temperatures. Due to different thicknesses of the steel tubes, the two series of fire tests show different behaviour. For tests using the thinner tube, local buckling was observed. From the results of design calculations, it is found that the position of local buckling of the steel tube has direct influence on the effective length of a concrete filled column. The effective length of a concrete filled column with a pin end may be taken as the distance from the largest local buckle of the steel tube to the pin end. For tests using the thicker tube, no local buckling was observed. The results of design calculations suggest that the effective length of these columns can be determined according to the method in Eurocode 4 Part 1.2. For these test columns, this means that the column effective length should be taken as 0.7 times the column height. The design column bending moment may be taken as the unbalanced beam load acting eccentrically from the column centreline.

Non-linear analysis of the low-cycle fracture behaviour of isolated Tee stub connections

The present work deals with the numerical analysis of the low-cycle fracture behaviour of isolated Tee stub connections with partial fillet welds. The overall objective of the research is to assess the seismic performance of bolted partial strength beam-to-column joints under seismic loading; but first, the complexity of these joints is approached after understanding the behaviour of more simple geometries which govern the response. In fact, the study focuses on the low-cycle fracture behaviour of Tee stub connections that are elemental components of extended end plate connections with partial fillet welds. First, the general experimental program dealing with bolted end plate joints and component parts is presented. The program comprises sets of constant and variable displacement amplitude cyclic tests both on complete specimens and on components. Test results have shown good performance of bolted extended end plate moment joints under cyclic loading as well as that of fillet welds that represent an economic solution for thin and moderate extended end plates. Then, the connection material is characterized from a microstructural and fracture mechanics standpoint. Successively, detailed three-dimensional non-linear finite element analyses are carried out in order to tune model material parameters; whilst two-dimensional inelastic analyses are performed in a monotonic and cyclic loading regime to validate connection finite element models. Lastly, a parametric study is conducted in order to define details able to reduce loading-induced toughness demands. Analyses have inferred that fracture driving force demands, quantified in terms of crack tip opening displacements, are reduced by using fillet welds matching the end plate material, by limiting welding-induced residual stresses and by increasing the yield-to-ultimate strength ratio compatibly with plastic analysis requirements.

Cyclic tests on bolted steel and composite double-sided beam-to-column joints

This paper summarises results of the research performed at the Department of Steel Structures and Structural Mechanics from the Politehnica University of Timisoara, Romania, in order to evaluate the performance of beam-to-column extended end plate connections for steel and composite joints. It comprises laboratory tests on steel and composite joints, and numerical modelling of joints, based on tests. Tested joints are double-sided, with structural elements realised of welded steel sections. The columns are of cruciform cross-section, while the beams are of I section. Both monotonic and cyclic loading, symmetrically and antisymmetrically, has been applied. On the basis of tested joints, a refined computer model has been calibrated using a special connection element of the computer code DRAIN 2DX. In this way, a static/dynamic structural analysis of framed structures with real characteristics of the beam to column joints is possible.

Genetic algorithm based optimum design of nonlinear planar steel frames with various semi-rigid connections

A genetic algorithm based optimum design method is presented for nonlinear multistorey steel frames with semi-rigid connections. The design algorithm obtains optimum frame by selecting appropriate sections from standard steel section tables while satisfying the serviceability and strength limitations specified in BS5950. The algorithm accounts for the effect of the flexibility of the connections and the geometric non-linearity of the members. The semi-rigid connections are modeled with the Frye–Morris polynomial model. The values of the coefficients, such as the diameter of bolts, the gauge and the geometric dimensions of angles used in the standardization constants are obtained by designing each connection in the frame during the optimum design cycles. The effective length factors for columns, which are flexibly connected to beams, are obtained from the solution of the nonlinear interaction equation. Several steel frames with different beam to column connections, such as extended end plate, and top and seat angle with and without web cleat, are designed using the algorithm. Each design is carried out twice, with and without considering the geometric non-linearity. Comparison of optimum frames has shown that consideration of geometric non-linearity results in greater economy. It is also noticed that taking the realistic behavior of beam–column connection into account produces more appropriate and in some cases even lighter designs.

On the analytical model of beam-to-column semi-rigid connections, using plate theory

An analytical method is presented that can be used to determine the behavior of a particular steel beam-to-column extended end plate connection, in both linear and non-linear regions. This article demonstrates a closed form solution of the equations of deformation, for this type of connection. Besides, a step-by-step analytical procedure for establishment of the linear part of M- θ curve of this form of connection is developed. However, this technique can properly be extended to the non-linear regions, which is not considered in this article. The correctness of the results has been ascertained by a comparison, using non-linear finite element models as well as experimental approach; and very good agreement has been obtained. Furthermore, the writers believe that this method will efficiently serve design engineers in real design conditions.

Cyclic Tests of Double-Sided Beam-to-Column Joints

This paper summarizes the results of the full-scale tests on beam-to-column joints, carried out within the experimental program of the COPERNICUS European research project at the “Politehnica” University of Timisoara, Romania. Two series of six double-sided joints with three different beam-to-column connection typologies have been tested under symmetrical and antisymmetrical cyclic loading. Three types of connections (extended end plate, welded, and with cover plates) have been investigated. The main parameters considered in this study are: (1) initial stiffness; (2) moment capacity; and (3) plastic rotation capacity. The obtained experimental values are compared to the theoretical predictions by means of Eurocode 3, Annex J. The antisymmetrical loading triggers the participation of the panel zone to plastic mechanism, which brings the following changes as compared to the symmetrical loading: (1) Increase of ductility; (2) decrease of moment capacity and initial stiffness; and (3) more stable energy dissipation through hysteretic loops. In any of the loading cases, the quality of welds is essential for appropriate cyclic behavior of the joints.

A hysteretic connection element and its applications

A hysteretic connection element for the simulation of hysteretic responses of connections is formulated and implemented in the non-linear finite element program DRAIN-3DX. In the formulation of the element, both stiffness-and-strength degradation and pinching are expressed as functions of damage state variables; meanwhile, damage is monitored and failure is detected by means of a damage index. In the implementation of the element, an automatic event definition algorithm is developed and an event-to-event solution scheme is followed. The element is applied to the simulation of hysteretic responses of unstiffened extended end plate connections, web panels, joints and frame substructures subject to cyclic reversal loading. Simulations are in good agreement with experimental data in terms of load-deformation relationship, strength, stiffness, and energy dissipation.

Cyclic loading of end plate moment connections

An experimental investigation of 15 cyclically loaded extended end plate connections was undertaken to assess the significance of some design parameters. The parameters investigated were beam size, bolt layout, end plate thickness, use of extension stiffeners, welding process, and weld preparation. Eleven of the 15 full-scale test specimens were designed to confine failure to the end plate and four were designed to develop the plastic moment capacity of the beam. Of the beam sizes tested (W360×51, W460×97, and W610×125) the W460×97 beam connections provided the most ductility. The relaxed bolt configuration provided more energy dissipation and connection ductility. The use of extension stiffeners improved the ability of the end plates to dissipate energy and increased the connection rotation at yield. An increase in end plate thickness results in an increase in the connection flexural strength. No significant difference in behaviour was observed between the connections fabricated using the shielded metal arc welding process and those fabricated using the flux-cored arc welding process. Bolt bending and loss of preload were observed in all the test specimens. End plate thickness prediction equations proposed by various researchers were evaluated by comparing predicted plate thickness with plate thickness used for the test specimens. New prediction equations that use yield lines in close agreement with those observed in the test specimens are proposed. The proposed prediction equations are able to predict the thickness of the end plate to within 13%. The proposed prediction equations are applicable to stiffened and unstiffened end plate moment connections with various bolt layouts. Extended end plate moment connections showed good potential for use in seismic zones.Key words: cyclic loading, energy absorption, extended end plates, moment connections, steel, yield line.

Basic issues in the finite element simulation of extended end plate connections

Numerical simulations of steel bolted connections performed with finite element models depend heavily upon constitutive relationships, step size, number of integration points, kinematic descriptions, element types and discretizations. The aforementioned items combined with complex non-linear phenomena which are commonly observed in connections render the finite element technique not attractive for this class of problems. In this paper these issues are scrutinized and both a legitimate methodology suitable to the analysis of extended end plate moment resisting connections and proper three-dimensional finite element models are established. These models are provided first for non-preloaded and preloaded bolted tee stubs which are proposed as benchmarks. Next, both a solid model and an assemblage of three-dimensional beam finite elements, viz. the spin, are proposed to model the bolt behaviour either in a rigorous or simplified fashion, respectively. Lastly, a three-dimensional non-linear finite element model suitable for the analysis of isolated extended end plate connections is proposed and validated.