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Component based finite element model of structural connections
Abstract
This paper refers to component based finite element model (CBFEM). Design focussed component model (CM) is compared to design finite element (DFEM) and research finite elements models (RSFEM). Procedure for composition of a model based on usual production process is used in CBFEM. Method is demonstrated on two types of connections. CBFEM results are compared to results obtained by component method for portal frame eaves moment connection. Design of moment resistant column base is demonstrated for a case loaded by two directional bending moments and normal force.
... The connection components are grouped to examine joint momentrotational behavior and classification representation in a spring-shear model. Interactions between components incorporate boundary conditions to simulate the influence between the behavior of the connection elements for their consideration in the aggregate analysis of the connection structural performance [20]. The IDEA StatiCa software calculation procedure is supported by an extensive experimental validation campaign [16]. ...
... This unique calculation model provides excellent results, both from the point of view of precision and a speed analysis. Figure 2 illustrates the joint model as displayed by IDEA StatiCa. the behavior of the connection elements for their consideration in the aggregate analysis of the connection structural performance [20]. The IDEA StatiCa software calculation procedure is supported by an extensive experimental validation campaign [16]. ...
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The findings of this research can significantly contribute to the design and construction of efficient and safe steel joints for building structures.
Abstract
Structures must provide strength, stability, and stiffness to buildings and at the same time be efficient. This study addressed the effect of design elements and parameters on the strength of bolted lateral connections in steel beams under bending using the component-based finite element method. The variables evaluated were plate thickness, horizontal and vertical spacing between bolts, and geometric arrangement of bolts. Finite element software was used to evaluate the stress state of the junction plate, its plastic deformation, and bolt shear. A sensitivity analysis was performed to determine which bolt arrangements result in safer and more efficient designs using the same components. Stress distribution within the junction plate and plastic deformation values were used to evaluate the structural performance of the joints according to EuroCode 3. The results showed that placing bolts near the edge of a plate affected the bolts’ utilization, especially with thinner plates. Additionally, introducing an offset between central and outer bolt rows is not recommended as it worsened the stress distribution and the structural performance.
... Therefore, the 2D-FEM model herein presented has to be considered within the framework of research finite elements model (RSFEM) [28] using true stress-strain diagrams rather than design finite element model (DFEM) where design values of materials properties are commonly adopted [28]. ...
... Therefore, the 2D-FEM model herein presented has to be considered within the framework of research finite elements model (RSFEM) [28] using true stress-strain diagrams rather than design finite element model (DFEM) where design values of materials properties are commonly adopted [28]. ...
... In addition, due to the extremely high computational efforts, it is also not impractical to directly conduct the progressive collapse analysis of whole frame structures using full-scale solid FE models. Nowadays, a simplified analytical/numerical approach for the prediction of joint behaviors via CBFEM methods [17,18], which combines the analytical component method and the numerical finite element method, is needed to used for the fire-induced collapse analysis for whole frame structures. In above approach, the joint behavior is decomposed and substituted with a series of spring components, and each component is modeled with an equivalent nonlinear spring with a corresponding force-displacement relationship, rather than being simulated in detail using 3D solid elements. ...
... 1 which is developed based on CBFEM [23]. Full details about CBFEM and the process of its validation and verification is described in a book [24]. ...
The paper focuses on the design of fillet welds of regular structural steel. It presents a numerical design calculation (NDC) method for assessing weld resistance using the regular inclined shell element model (RISEM) in the finite element method (FEM). The NDC uses FEM, which helps to design the joints based on standardised procedures. Shell elements represent the stiffness of the weld and control its stresses in the plane, in which they are limited in analytical calculations. This work recommends a common inclined shell element with rigid links to represent the geometry and rigidity of fillet welds most accurately. The purpose RISEM model is based on stresses on the inclined shell element, using maximum equivalent stress as an indicator to calculate design weld resistance. This model is validated in the published experiments and verified in the analytical models offered by EN 1993–1-8:2006 and ANSI/AISC 360–16. Transverse and longitudinal fillet welded connections in both analytical models show a difference of 6%, except for the long weld, which diverges. While the European standard for fin plate welded connections is more conservative than the US standard, it still shows good agreement with a difference of less than 5% in both analytical models. RISEM results are safer by 13–16% for plate connections to unstiffened columns due to the missing fillet weld radius in the finite element (FE) model. The specially developed element for fillet weld presented, which prepared as a component of one of the set connectors prepared for the component-based finite element model (CBFEM).
... It is an analytical model without a corresponding numerical modelling method. A combination of the finite element and component methods was proposed for the characterisation of structural connections [31]. The material properties, shear deformation, extension, and bending of the entire joint were considered accurately in these models. ...
This study proposed a generalised and concise model consisting of spring-slider elements to characterise the nonlinear bending moment-rotation relationship of semi-rigid steel beam-to-column joints. First, the density function of the constitutive model was constructed based on the rotational characteristics of the joints. Second, the mathematical expression for the moment-rotation relationship of the constitutive model was derived. A method was developed to identify the parameters. Finally, after a discretisation method of the model was derived based on the strategy of evenly divided stiffness, the discrete model was applied to the numerical simulation of the rotation of the semi-rigid steel beam-to-column joints. It is observed that the proposed model accurately describes the rotation behaviour of semi-rigid connections in the entire rotation domain while reducing the degrees of freedom of the contact interfaces to improve the computing efficiency. There are six parameters in the model with a clear physical definition, which can be directly identified through macroscopic experiments. A high level of accuracy can be achieved by numerically calculating a discrete model using only five Jenkins elements.
... In all graphs the load levels in which the first plastification occurred in numerical models (the yield stress of material has been exceeded) and the load levels in which 5% plastic strain was reached (similar to [14]) are indicated. This value of plastic strain determines the limit state of the numerical model according to [15], Appendix C. ...
Subject of this paper is numerical modelling of steel assembling bolt connections of CHS (circular hollow sections) or L-profiles respectively in the FEM software ANSYS 12.0 and their subsequent comparison with performed laboratory experiments. Non-linear calculations with both plastic behavior of materials and influence of large deformations were taken into account. Comparison of results, in the form of load-deformation curves, showed that numerical models describe the basic behavior of those joints. The direct numerical model outputs were modified. This modification was made with respect to real laboratory conditions taking into account the effect of the trial press machine slip stiffness and the initial slip.
... However, these models include rigid bars, and they are not able to take into account the axial deformations and bending of the column. A combination of finite elements and component method was presented in (3) for the modelling of structural joints. However, they are CPU expensive, especially for nonlinear analysis. ...
The analysis and design of joints constitutes one of the most important aspects when designing steel structures. It is a common practice to model the joint behaviour by zero‐length rotational springs placed between the beam and corresponding column, or by mechanical models composed of springs and rigid bars. These models have serious limitations when considering the interactions between the shear, bending and axial forces and deformations of the panel zone.
In this research, a new approach based on the characterization of modal components is presented. First, the steel joint is modelled as a cruciform finite element of 12 degrees of freedom. Then, the stiffness matrix is decomposed in eigenvectors and eigenvalues. The eigenvectors provide information about the joint deformation modes, while the eigenvalues give information about the stiffness associated with each mode. To identify the main modes and their characteristics, a parametric study has been carried out for welded joints with and without stiffeners. For both cases, all combinations of IPE 120 to IPE 600 profiles for beams and HEA 160 to HEA 1000 profiles for columns have been studied. The only restraint imposed in the combination process is that the beam width be smaller than the column width.
First, the cruciform finite element stiffness matrices are obtained. Subsequently, a spectral decomposition is carried out using MATLAB, and then Python scripts are developed to classify the modes and eigenvalues. The statistical analysis of the results shows that after removing the three rigid solid modes the most relevant deformation modes are the shear and the two possible bending modes including their interaction. The remaining six modes correspond to deformation modes with high stiffness values that are not excited under common loading situations.
... Recently, a combination of the finite element method and the component method has been proposed for the characterization of structural connections [19]. These models take into account in an accurate manner the material properties, shear deformation, extension and bending of the complete joint. ...
This paper deals with the formulation of cruciform finite elements that model 2D steel joints for frame analysis. Three different cases are contemplated: single rectangular panels suitable for internal joints with beams of equal depth at both sides; trapezoidal panels for joints with beams of different depths at both sides and inclined stiffeners; and double rectangular panels for the case of joints with beams of different depths at both sides and with or without horizontal stiffeners in the panel zone.
The cruciform elements have 4 nodes with 3 degrees of freedom per node, and take into consideration, in a consistent and complete way, the stiffness properties (components in Eurocode), including those of the panel zone. The proposed elements allow modelling simple, rigid and semi-rigid connections. In addition, they take into account all the internal forces that coincide at the joint, and the eccentricities of the internal forces coming from the beams and columns that meet at the joint. Numerical examples are solved that compare the proposed approach with complete finite element models of sample frames. The results validate the approach and demonstrate its advantages.
... The research FEA model (RFEA), which is based on materially and geometrically nonlinear analysis with imperfections (GMNIA), is not suitable for the design of common joints, especially for time-consuming modelling, difficulties in entering the imperfections and the definition of the ultimate limit state. On the other hand, the component based FEA model (CBFEM) with material nonlinear analysis without imperfections and with the assessment of the components of bolts, welds and plates becomes an alternative approach to the design of joints as is described in Gödrich et al. (2014) and Wald et al. (2014). The design of fourth class stiffeners in the joints of steel structures takes into account local buckling of a slender compressed plate, shear buckling of a slender web panel and local buckling of a compressed plate between the bolts (see Kurejková et al. 2015). ...
The paper presents research in design of haunches in structural steel joints. Experimental results of six specimens of haunches with and without flanges are presented. Three specimens are without flanges and three specimens are supported by additional flanges. Flanges differ in stiffness to observe the increase in haunch resistances and the effect on buckling shapes. The research finite element model (RFEA) is studied by material and geometrical nonlinear finite element analysis with imperfections under the actual stress conditions and validated on the measured experimental data. The validity is demonstrated on the comparison of load-deflection curves, failure modes, stress distributions and yield line patterns. The stability analysis of a joint with a haunch is related to the research into component based finite element models of complex joints. The input and the results of the research finite element model are summarised in a benchmark case of a haunch with a flange. A numerical study illustrates the effect of the flange stiffness on the joint’s resistance. The effect is demonstrated on a simple arrangement with triangular stiffeners and on a beam-to-column joint. The main goal of the research is to verify proposed design procedure for stiffeners in steel joints.
Abstract
The study aims to address the lack of design techniques for welded rectangular hollow sections connections made with offset, i.e., where the members of the branch adjacent to the connection are laterally shifted away from the chord centreline towards the chord web. To estimate the plastic resistance of the laterally offset truss-type RHS T-connection, a theoretical investigation was conducted. As a result, an analytical model has been developed and verified against the outcomes of a series of non-linear numerical simulations. During the construction of the model, specific attention was paid to the most general case of the branch location relative to the chord web, namely, the scheme of connection where adjacent vertical faces of the branch and chord members are in different planes is considered as prevailing. The proposed analytical model is an extension of a plastic mechanism model for traditional stepped rectangular hollow sections (RHS) T-connections. The model predicts the yield load and the post-yield response of the connections under concentrated load. The model presented in this paper is compared with other recently proposed methods of analytically determining limit loads of offset connections, and it provides reliable results in yield load computation. Moreover, the model yields sufficient accuracy in predicting the ultimate load for the offset connections with matched faces of the chord web and brace lateral surface.
This paper introduces Component Based Finite Element Model (CBFEM) which is a numerical design model to analyze and design connections of steel structures with features demonstrated here on a portal frame eaves bolted connection. The connection in CBFEM procedure is analyzed by Finite Element Method FEM. The correct behavior of components is treated by introducing components that well represent its behavior in terms of initial stiffness, ultimate strength and deformation capacity, of bolts, welds etc. As for another FEM design procedures a special care is given to the validation and verification procedures which is demonstrated here in this contribution on example of portal frame eaves welded connection. In this paper, CBFEM is applied to analyze steel beams and columns also at elevated temperature. The main objective of this study is to verify the CBFEM for predicting the resistance of steel members and connections at elevated temperatures.
Steel connections in building projects are traditionally designed in Canada by the fabricator’s engineer using connection design software or spreadsheets, often supplemented by hand calculations. Implicit in these processes is the desire to optimize the net fabrication and erection costs based on several parameters such as material, task and process repetition, machinery availability, fabrication and erection constraints, and available optimization tools. This study aims to explore the realm of structural optimization by employing evolutionary algorithms to automate and optimize the design of steel shear connections. Evolutionary algorithms are search algorithms used within artificial intelligence to determine an optimal solution from a population of possible solutions within user-defined optimization criteria. A design optimization tool built using parametric modelling and connection design software utilizing component-based finite element modelling is applied to a shear end plate connection. The results are tested and compared against an example end plate connection design from the Canadian Handbook of Steel Construction. The optimization results showcase the potential of using evolutionary algorithms for steel connection design, and the practicality of the optimization tool for use in a professional environment is presented.
The accurate simulation of steel structures requires a precise model of the joint behaviour. The methods proposed by the steel codes are based on either rotating springs or involved models of springs and rigid bars. In this article, a precise method to model the stiffness of 2D bolted steel connections is presented. First, the joint is accurately modelled using finite elements (FE). Then, the FE model is condensed to a cruciform element of 4 nodes (12° of freedom) by constraining each side cross-section to a node located at its centre of gravity. Subsequently, forces are applied to each node to compute the flexibility matrix, which is then used to construct the stiffness matrix that is finally decomposed through singular value factorization. Following this procedure, a parametric study is conducted to build the training and validation sets of the metamodel. Kriging and Radial Basis Functions are chosen to metamodel and predict the stiffness matrices of the cases not included in the parametric study. Finally, steel structures are analysed with both complete finite elements and surrogate models, and the results are used to confirm the accuracy of the proposed method.
The paper is focused on a design approach to a T-stub component, which is key part in an analytical/numerical prediction of behaviour of the bolted end plate connections, by the Component Based Finite Element Method (CBFEM). The method combines the analytical Component Method and the numerical Finite Element Method (FEM). The distribution of internal forces is solved by the FEM. The connectors' behaviour is modelled by analytical models implemented into FEM as components. The method is developed for design of generally loaded complex joints with end plated where the distribution of internal forces is not clear. The resistance of the joint is controlled by limiting the plastic strain of plates and the strength of connectors, e.g. welds, bolts, and anchor bolts. The prediction of the initial stiffness and the deformation capacity is included natively. The T-stub in tension is investigated in this paper. CBFEM is verified on the research oriented model, which is validated against the authors' own experiments and the results from literature, and on the Component Method.
Connections are a key component of steel structures. Current methods of analysis of steel frames mostly rely on approximate joint models based on zero-length rotational springs or mechanical models of rigid bars and springs. A method is presented in this paper to accurately model the stiffness of 2D welded steel joints that is based on surrogate modelling. The joint modelling process starts by developing an accurate 4-node (12 degree of freedom) cruciform finite element from a complete finite element model using substructuring techniques. Then a modal decomposition of these matrices yields the eigenvalues and mode shapes that are used to develop the design points of the training and validation sets of the surrogate model. The modal decomposition leads to a reduced set of variables that accurately models the design space. A uniform Rectangular Grid of design sites is proposed. The Kriging method and Support Vector Machine Regression are used to generate the metamodels and predict the stiffness at untried sites. Both methods provide accurate results. Simulations of steel frames are performed to show the accuracy of the proposed surrogate modelling.
This paper deals with the performance evaluation of cruciform finite elements with 4 nodes and 12 degrees of freedom that model 2D steel joints with beams of unequal depth in frame analysis. These elements are capable of modelling joints that have double rectangular panels, with or without horizontal stiffeners in the panel zone, due to beams of different depths at both sides of the joint. In addition, these cruciform elements are suitable for simple, rigid and semi‐rigid connections and therefore can be used for the global analysis of semi‐rigid steel frames. The performance of these elements is assessed by analysing steel frames under different loading conditions, and comparing the results with complete finite element models.
The characteristics of these elements (stiffness and resistance) are generated by a previously proposed displacement based modal approach. All the forces and moments coming from the adjacent beams and columns concur at the joint, therefore, the complete force field in the panel zones is known with no need for a transformation parameter β (EC3‐Part 1.8). The proposed element also avoid the use of mechanical models (composed of springs and rigid bars) for frame analyses, which add complexity, numerical overhead —consequence of the larger number of degrees of freedom— and possible round off errors (due to the rigid bars) in the solution process.
In addition, since the real dimensions of the joint are included in the proposed elements, the eccentric moments are automatically taken into account. Also, the interaction between the deep and the shallow sides of the column double panels are considered. Numerical simulations and comparison with complete finite element models are carried out that show the validity and computational efficiency of these elements.
The paper presents research into the advanced design of stiffeners in structural steel joints. Experimental results of six specimens of haunches with and without flanges are presented. Three specimens are without flanges and three specimens are supported by additional flanges. Flanges differ in stiffness to observe the increase of haunch resistances and its effect on buckling shapes.
Haunches with and without flanges are validated by numerical model to tests and resistances are calculated and evaluated. The research finite element model (RFEM) is studied by material and geometrical nonlinear finite element analysis with imperfections under the actual stress conditions and validated on the measured experimental data. The quality of prediction is demonstrated on the comparison of load‐deflection curves and failure modes. The stability analysis of a joint with a haunch is used for design Component Based Finite Element Models (CBFEM) of complex joints. RFEM allows verifying the design FEM model (DFEM) and component based FEM model (CBFEM) developed for the design of complex joints in steel structures. To avoid local buckling of slender plates in CBFEM a design procedure is proposed and verified on research finite element model (RFEM). It is proposed to use a combination of material nonlinear analysis without imperfections with buckling analysis in CBFEM. The verification is shown on an example of a haunch in a welded portal frame joint. The stiffener is studied by numerical analysis, resistances and critical loads are determined in RFEM and CBFEM and results are compared. A numerical study illustrates the effect of the haunch's thickness on the joint's resistance.
The only way to prove correctness of simulated results by Finite Element Analyse (FEA) is through a methodical System response quantity process. Without this approval are the results of FEA meaningless and cannot be used in design process for making any decisions. The System response quantity consist of validation, which compares the numerical solution with the experimental data, of verification, which compares computational solutions with highly accurate analytical or numerical solution, and of benchmark cases, the examples for check of the software and its user on approved and simplified input and output.
In the eighties FEA of structural connection was treated by some researchers as a non‐scientific matter. Two decades later it was already a necessarily extension of experimental and analytical work. Today computational analysis, in particular computational mechanics and fluid dynamics, is commonly used as a catalyst of many research fields and an indispensable design tool. The recommendation for design by advanced modelling in structural steel is ready to be used in Chapter 5 and Annex C of EN 1993‐1‐5:2005 [1]. Development of modern general‐purpose software and decreasing cost of computational resources facilitate this trend. The FEA of structural connection is the coming step in structural steel design. As the computational tools become more readily available and easier to use even by relatively inexperienced engineers the proper procedure should be employed when judging the results of computational analysis.
This paper describes the System response quantity for Component Based Finite Element Model (CBFEM) which is a multilevel FEA method to analyse and design connections of steel structures, see [2]. The steel plates in connection are analysed in CBFEM procedure by FEA. The proper behaviour of components is treated by introducing a components representing well its behaviour in term of initial stiffness, ultimate resistance and deformation capacity, of bolts, welds etc. To help with this process is prepared a contribution, which summarises the history of achievements of FEA application in structural connections. Contribution shows the currents trends in advanced modelling of connection components and differences of the research oriented design oriented models. The particular attention is dedicated to design models of generally loaded endplates.
This paper presents the application of the component method to steel column bases. The decomposition of the connection into components is described. An analytical model is presented to determine the moment resistance and the rotational stiffness of column bases under axial forces. The analytical model is verified with test results. A sensitivity study of the base plate thickness and the anchor bolt length is presented.
A single and unified concept for the design of structural joints in building frames made of any material has been developed in recent years, and is now widely implemented in European design codes. In the present paper, this concept is presented, its merits as far as the economy of a project are demonstrated, and practical design tools for its application in daily practice are briefly described. The paper also contains references to user's manuals and design handbooks.
The behaviour of steel joints is complex and requires the proper consideration of a multitude of phenomena, ranging from material non-linearity (plasticity, strain-hardening), non-linear contact and slip, geometrical non-linearity (local instability) to residual stress conditions, and complicated geometrical configurations. The component method is widely accepted as the practical approach in predicting the behaviour of steel joints and it provides detailed procedures to evaluate the strength and initial stiffness of steel joints, as specified in Eurocode 3.Current safety concerns for steel structures require that steel joints are designed to perform adequately under a wider range of loading conditions: besides standard static loading conditions, fire and seismic loading must often be considered. In addition, robustness requirements impose that joints present a minimum level of resistance for any arbitrary loading. Predicting the 3-D behaviour of steel joints under arbitrary loading must thus be achieved in a practical way.This paper presents the results of a series of experimental developments that attempt to contribute to the knowledge of the 3D behaviour of steel joints, under static and dynamic conditions, and to discuss a possible framework for these general conditions that is in line with the principles of the component method.