The Experts below are selected from a list of 324 Experts worldwide ranked by ideXlab platform
M. Ahmer Wadee - One of the best experts on this subject based on the ideXlab platform.
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Sensitivity to local imperfections in inelastic thin-walled Rectangular Hollow Section struts
Structures, 2019Co-Authors: Jiajia Shen, M. Ahmer WadeeAbstract:Abstract Mass efficient inelastic thin-walled Rectangular Hollow Section (RHS) struts practically always fail in a combination of local–global interactive buckling and material nonlinearity while also exhibiting high sensitivity to initial imperfections. Nonlinear finite element (FE) models for inelastic thin-walled RHS struts with pre-defined local and global geometric imperfections are developed within the commercial package Abaqus . Using a unified local imperfection measurement based on equal local bending energy, the effects of imperfect cross-Section profiles, imperfection wavelength and the degree of localization in the longitudinal direction on the ultimate load and the nonlinear equilibrium path are investigated for four characteristic length struts at different material yielding stress levels. The corresponding most severe imperfection profiles are determined and are found to be qualitatively different to the linear eigenmodes in all cases. Moreover, it is found that the most severe purely periodic imperfections may be used to provide a safe approximation of the ultimate load when the corresponding amplitude is constrained to the manufacturing tolerance level. An extensive parametric study on the wavelength of the most severe periodic imperfection profile is conducted and a relationship for this is proposed in terms of the normalized local slenderness, which compares excellently with the FE results.
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Local–global mode interaction in thin-walled inelastic Rectangular Hollow Section struts part 1: Nonlinear finite element analysis
Thin-Walled Structures, 2019Co-Authors: Jiajia Shen, M. Ahmer WadeeAbstract:Abstract Mass efficient thin-walled Rectangular Hollow Section (RHS) struts have been shown to be susceptible to local–global mode interaction and exhibit sensitivity to imperfections. Material nonlinearity may increase the imperfection sensitivity of such members further and affect the final failure mode. Nonlinear finite element (FE) models for welded inelastic thin-walled RHS struts with pre-defined local and global geometric imperfections alongside residual stresses are developed within the commercial package Abaqus and validated against two independent experimental studies. Based on the validated FE model, the effects of material nonlinearity and residual stresses from welding on the ultimate load, mechanical behaviour and the imperfection sensitivity of struts are investigated. A simplified method to determine the initial geometric imperfection amplitude introduced in the FE model with residual stresses explicitly modelled within the ECCS framework is proposed for the first time. The experimental and numerical results in conjunction with existing experimental results from the literature are employed in the companion paper for the assessment of the Effective Width Method and Direct Strength Method, which also forms the basis for a new set of design recommendations.
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Local–global mode interaction in thin-walled inelastic Rectangular Hollow Section struts part 2: Assessment of existing design guidance and new recommendations
Thin-Walled Structures, 2019Co-Authors: Jiajia Shen, M. Ahmer WadeeAbstract:Abstract The second part of the study on the local–global mode interaction in thin-walled inelastic Rectangular Hollow Section struts focuses on design guidance. Based on the validated finite element (FE) model from the companion paper, a framework for fully automating FE model generation, submission and post-processing for geometric and material nonlinear analysis with imperfections is first presented. The ultimate load data for specimens with different cross-Section aspect ratios, cross-Sectional slenderness, global slenderness and welding options are generated. The current design rules for thin-walled welded RHS struts are assessed using the numerical results and existing experimental results from the literature by means of structural reliability analysis in accordance with the methodology presented in Annex D of Eurocode EN1990. A modified Direct Strength Method (DSM) relationship is then proposed and it is demonstrated to provide superior ultimate load predictions than the current guidelines.
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Sensitivity of elastic thin-walled Rectangular Hollow Section struts to manufacturing tolerance level imperfections
Engineering Structures, 2018Co-Authors: Jiajia Shen, M. Ahmer WadeeAbstract:Abstract Finite element models for elastic thin-walled Rectangular Hollow Section (RHS) struts with pre-defined local and global geometric imperfections are developed within the commercial package Abaqus . A unified local imperfection measurement based on equal local bending energy is proposed. The effects of imperfect cross-Section profiles, imperfection wavelength in the longitudinal direction and the degree of imperfection localization on the ultimate load and equilibrium path are investigated and the most severe imperfection profiles are determined. A parametric study on the wavelength of the most severe local imperfection profile is conducted and a semi-empirical equation to approximate the corresponding wavelength is proposed. Moreover, an equation to calculate the global buckling load of thin-walled RHS struts with tolerance level doubly-symmetric cross-Section local imperfections is proposed.
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Length effects on interactive buckling in thin-walled Rectangular Hollow Section struts
Thin-Walled Structures, 2018Co-Authors: Jiajia Shen, M. Ahmer WadeeAbstract:Abstract A variational model formulated using analytical techniques describing the nonlinear coupling between local and global buckling modes within an elastic thin-walled Rectangular Hollow Section strut is presented. A system of nonlinear differential and integral equations subject to boundary conditions is derived and solved using numerical continuation techniques. The nonlinear behaviour of four representative lengths is investigated, which are characterized by the post-buckling equilibrium paths. The numerical results from the variational model are validated using a nonlinear finite element model and largely show excellent comparisons, particularly for the practically important ultimate load and the initial post-buckling behaviour. Boundaries for the four distinct length-dependent zones are identified and the most unstable zone is demonstrated to have a considerably narrower length range than previously determined for practical corner boundary conditions within the cross-Section.
Jiajia Shen - One of the best experts on this subject based on the ideXlab platform.
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local global mode interaction in thin walled inelastic Rectangular Hollow Section struts part 2 assessment of existing design guidance and new recommendations
Thin-walled Structures, 2019Co-Authors: Jiajia Shen, Ahmer M WadeeAbstract:Abstract The second part of the study on the local–global mode interaction in thin-walled inelastic Rectangular Hollow Section struts focuses on design guidance. Based on the validated finite element (FE) model from the companion paper, a framework for fully automating FE model generation, submission and post-processing for geometric and material nonlinear analysis with imperfections is first presented. The ultimate load data for specimens with different cross-Section aspect ratios, cross-Sectional slenderness, global slenderness and welding options are generated. The current design rules for thin-walled welded RHS struts are assessed using the numerical results and existing experimental results from the literature by means of structural reliability analysis in accordance with the methodology presented in Annex D of Eurocode EN1990. A modified Direct Strength Method (DSM) relationship is then proposed and it is demonstrated to provide superior ultimate load predictions than the current guidelines.
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local global mode interaction in thin walled inelastic Rectangular Hollow Section struts part 1 nonlinear finite element analysis
Thin-walled Structures, 2019Co-Authors: Jiajia Shen, Ahmer M WadeeAbstract:Abstract Mass efficient thin-walled Rectangular Hollow Section (RHS) struts have been shown to be susceptible to local–global mode interaction and exhibit sensitivity to imperfections. Material nonlinearity may increase the imperfection sensitivity of such members further and affect the final failure mode. Nonlinear finite element (FE) models for welded inelastic thin-walled RHS struts with pre-defined local and global geometric imperfections alongside residual stresses are developed within the commercial package Abaqus and validated against two independent experimental studies. Based on the validated FE model, the effects of material nonlinearity and residual stresses from welding on the ultimate load, mechanical behaviour and the imperfection sensitivity of struts are investigated. A simplified method to determine the initial geometric imperfection amplitude introduced in the FE model with residual stresses explicitly modelled within the ECCS framework is proposed for the first time. The experimental and numerical results in conjunction with existing experimental results from the literature are employed in the companion paper for the assessment of the Effective Width Method and Direct Strength Method, which also forms the basis for a new set of design recommendations.
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Sensitivity to local imperfections in inelastic thin-walled Rectangular Hollow Section struts
Structures, 2019Co-Authors: Jiajia Shen, M. Ahmer WadeeAbstract:Abstract Mass efficient inelastic thin-walled Rectangular Hollow Section (RHS) struts practically always fail in a combination of local–global interactive buckling and material nonlinearity while also exhibiting high sensitivity to initial imperfections. Nonlinear finite element (FE) models for inelastic thin-walled RHS struts with pre-defined local and global geometric imperfections are developed within the commercial package Abaqus . Using a unified local imperfection measurement based on equal local bending energy, the effects of imperfect cross-Section profiles, imperfection wavelength and the degree of localization in the longitudinal direction on the ultimate load and the nonlinear equilibrium path are investigated for four characteristic length struts at different material yielding stress levels. The corresponding most severe imperfection profiles are determined and are found to be qualitatively different to the linear eigenmodes in all cases. Moreover, it is found that the most severe purely periodic imperfections may be used to provide a safe approximation of the ultimate load when the corresponding amplitude is constrained to the manufacturing tolerance level. An extensive parametric study on the wavelength of the most severe periodic imperfection profile is conducted and a relationship for this is proposed in terms of the normalized local slenderness, which compares excellently with the FE results.
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Local–global mode interaction in thin-walled inelastic Rectangular Hollow Section struts part 1: Nonlinear finite element analysis
Thin-Walled Structures, 2019Co-Authors: Jiajia Shen, M. Ahmer WadeeAbstract:Abstract Mass efficient thin-walled Rectangular Hollow Section (RHS) struts have been shown to be susceptible to local–global mode interaction and exhibit sensitivity to imperfections. Material nonlinearity may increase the imperfection sensitivity of such members further and affect the final failure mode. Nonlinear finite element (FE) models for welded inelastic thin-walled RHS struts with pre-defined local and global geometric imperfections alongside residual stresses are developed within the commercial package Abaqus and validated against two independent experimental studies. Based on the validated FE model, the effects of material nonlinearity and residual stresses from welding on the ultimate load, mechanical behaviour and the imperfection sensitivity of struts are investigated. A simplified method to determine the initial geometric imperfection amplitude introduced in the FE model with residual stresses explicitly modelled within the ECCS framework is proposed for the first time. The experimental and numerical results in conjunction with existing experimental results from the literature are employed in the companion paper for the assessment of the Effective Width Method and Direct Strength Method, which also forms the basis for a new set of design recommendations.
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Local–global mode interaction in thin-walled inelastic Rectangular Hollow Section struts part 2: Assessment of existing design guidance and new recommendations
Thin-Walled Structures, 2019Co-Authors: Jiajia Shen, M. Ahmer WadeeAbstract:Abstract The second part of the study on the local–global mode interaction in thin-walled inelastic Rectangular Hollow Section struts focuses on design guidance. Based on the validated finite element (FE) model from the companion paper, a framework for fully automating FE model generation, submission and post-processing for geometric and material nonlinear analysis with imperfections is first presented. The ultimate load data for specimens with different cross-Section aspect ratios, cross-Sectional slenderness, global slenderness and welding options are generated. The current design rules for thin-walled welded RHS struts are assessed using the numerical results and existing experimental results from the literature by means of structural reliability analysis in accordance with the methodology presented in Annex D of Eurocode EN1990. A modified Direct Strength Method (DSM) relationship is then proposed and it is demonstrated to provide superior ultimate load predictions than the current guidelines.
Adam J. Sadowski - One of the best experts on this subject based on the ideXlab platform.
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Interactive buckling in long thin-walled Rectangular Hollow Section struts
International Journal of Non-Linear Mechanics, 2017Co-Authors: Jiajia Shen, M. Ahmer Wadee, Adam J. SadowskiAbstract:Abstract An analytical model describing the nonlinear interaction between global and local buckling modes in long thin-walled Rectangular Hollow Section struts under pure compression founded on variational principles is presented. A system of nonlinear differential and integral equations subject to boundary conditions is formulated and solved using numerical continuation techniques. For the first time, the equilibrium behaviour of such struts with different cross-Section joint rigidities is highlighted with characteristically unstable interactive buckling paths and a progressive change in the local buckling wavelength. With increasing joint rigidity within the cross-Section, the severity of the unstable post-buckling behaviour is shown to be mollified. The results from the analytical model are validated using a nonlinear finite element model developed within the commercial package Abaqus and show excellent comparisons. A simplified method to calculate the local buckling load of the more compressed web undergoing global buckling and the corresponding global mode amplitude at the secondary bifurcation is also developed. Parametric studies on the effect of varying the length and cross-Section aspect ratio are also presented that demonstrate the effectiveness of the currently developed models.
Sami Pajunen - One of the best experts on this subject based on the ideXlab platform.
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Finite element model for Rectangular Hollow Section T joints
Rakenteiden Mekaniikka, 2018Co-Authors: Marsel Garifullin, Sami Pajunen, Kristo Mela, Markku HeinisuoAbstract:Major developments in hardware and software enable researchers and engineers to apply non-linear finite-element analyses to study the behavior of tubular structures. However, to provide reasonable results, constructed finite element models should be verified and validated with experimental data. This article develops a finite element model for high strength steel Rectangular Hollow Section T joints. The joints are considered under in-plane bending moment and axial brace loading. The paper determines the most suitable finite elements and the number of layers in the thickness direction for the numerical assessment of initial stiffness and modeling the whole action-deformation behavior of joints. Finally, the proposed FE model is validated with the series of experimental tests. The validation shows that the developed model properly captures the local behavior of tubular joints and can efficiently serve as a reliable tool in routine numerical analyses.
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Effect of welding residual stresses on local behavior of Rectangular Hollow Section joints. Part 2 – Parametric studies
2018Co-Authors: Marsel Garifullin, Kristo Mela, Markku Heinisuo, Benjamin Launert, Hartmut Pasternak, Sami PajunenAbstract:Welding residual stresses that occur in tubular joints after the welding process affect their structural behavior. To ensure that these stresses do not negatively act on the load-bearing capacity of joints, their influence should be carefully investigated. This paper represents the second part of a study that numerically evaluates the structural behavior of Rectangular Hollow Section T joints taking into account welding residual stresses. The finite element model developed in Part 1 is now used to evaluate their effect on the resistance and initial stiffness of tubular joints. The conducted parametric analyses show that welding residual stresses have a positive influence of 1–19 % on the plastic resistance of tubular joints and insignificantly reduce their initial stiffness. At the same time, the behavior of the considered joints is found not to depend on the welding sequence.
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effect of welding residual stresses on local behavior of Rectangular Hollow Section joints part 2 parametric studies
2018Co-Authors: Marsel Garifullin, Kristo Mela, Markku Heinisuo, Benjamin Launert, Hartmut Pasternak, Sami PajunenAbstract:Welding residual stresses that occur in tubular joints after the welding process affect their structural behavior. To ensure that these stresses do not negatively act on the load-bearing capacity of joints, their influence should be carefully investigated. This paper represents the second part of a study that numerically evaluates the structural behavior of Rectangular Hollow Section T joints taking into account welding residual stresses. The finite element model developed in Part 1 is now used to evaluate their effect on the resistance and initial stiffness of tubular joints. The conducted parametric analyses show that welding residual stresses have a positive influence of 1–19 % on the plastic resistance of tubular joints and insignificantly reduce their initial stiffness. At the same time, the behavior of the considered joints is found not to depend on the welding sequence.
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Effect of welding residual stresses on local behavior of Rectangular Hollow Section joints/Einfluss der Schweißeigenspannungen auf die Tragfähigkeit von Rechteck-Hohlprofil-KnotenTeil 2: Parameterstudien
Bauingenieur, 2018Co-Authors: Marsel Garifullin, Markku Heinisuo, Benjamin Launert, Hartmut Pasternak, K. Mela, Sami PajunenAbstract:Welding residual stresses that occur in tubular joints after the welding process affect their structural behavior. To ensure that these stresses do not negatively act on the load-bearing capacity of joints, their influence should be carefully investigated. This paper represents the second part of a study that numerically evaluates the structural behavior of Rectangular Hollow Section T joints taking into account welding residual stresses. The finite element model developed in Part 1 is now used to evaluate their effect on the resistance and initial stiffness of tubular joints. The conducted parametric analyses show that welding residual stresses have a positive influence of 1–19 % on the plastic resistance of tubular joints and insignificantly reduce their initial stiffness. At the same time, the behavior of the considered joints is found not to depend on the welding sequence.
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Initial rotational stiffness of tubular joints with axial force in chord
Rakenteiden Mekaniikka, 2017Co-Authors: Marsel Garifullin, Sami Pajunen, Kristo Mela, Markku HeinisuoAbstract:In the frame analysis, the local model of the joint must follow the behavior of the joint. When completing the elastic global analysis, the initial rotational stiffness of joints should be known to obtain reliable moment distributions in frames. This paper consists of two parts. The first one evaluates the existing calculation approach for the initial rotational stiffness of welded Rectangular Hollow Section T joints. The validation with the experimental data shows that the current approach significantly underestimates the initial rotational stiffness. An improvement for determining the initial stiffness of T joints is proposed. The second part deals with the influence of the axial force in the main member on the rotational stiffness of the joint. The conducted numerical study shows the extreme reduction of the initial stiffness, when the main member is loaded by axial loads. To consider this effect in the frame analysis, the paper proposes a chord stress function for the initial rotational stiffness for square Hollow Section T joints, using the curve fitting technique.
Marsel Garifullin - One of the best experts on this subject based on the ideXlab platform.
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Finite element model for Rectangular Hollow Section T joints
Rakenteiden Mekaniikka, 2018Co-Authors: Marsel Garifullin, Sami Pajunen, Kristo Mela, Markku HeinisuoAbstract:Major developments in hardware and software enable researchers and engineers to apply non-linear finite-element analyses to study the behavior of tubular structures. However, to provide reasonable results, constructed finite element models should be verified and validated with experimental data. This article develops a finite element model for high strength steel Rectangular Hollow Section T joints. The joints are considered under in-plane bending moment and axial brace loading. The paper determines the most suitable finite elements and the number of layers in the thickness direction for the numerical assessment of initial stiffness and modeling the whole action-deformation behavior of joints. Finally, the proposed FE model is validated with the series of experimental tests. The validation shows that the developed model properly captures the local behavior of tubular joints and can efficiently serve as a reliable tool in routine numerical analyses.
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Effect of welding residual stresses on local behavior of Rectangular Hollow Section joints. Part 2 – Parametric studies
2018Co-Authors: Marsel Garifullin, Kristo Mela, Markku Heinisuo, Benjamin Launert, Hartmut Pasternak, Sami PajunenAbstract:Welding residual stresses that occur in tubular joints after the welding process affect their structural behavior. To ensure that these stresses do not negatively act on the load-bearing capacity of joints, their influence should be carefully investigated. This paper represents the second part of a study that numerically evaluates the structural behavior of Rectangular Hollow Section T joints taking into account welding residual stresses. The finite element model developed in Part 1 is now used to evaluate their effect on the resistance and initial stiffness of tubular joints. The conducted parametric analyses show that welding residual stresses have a positive influence of 1–19 % on the plastic resistance of tubular joints and insignificantly reduce their initial stiffness. At the same time, the behavior of the considered joints is found not to depend on the welding sequence.
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effect of welding residual stresses on local behavior of Rectangular Hollow Section joints part 2 parametric studies
2018Co-Authors: Marsel Garifullin, Kristo Mela, Markku Heinisuo, Benjamin Launert, Hartmut Pasternak, Sami PajunenAbstract:Welding residual stresses that occur in tubular joints after the welding process affect their structural behavior. To ensure that these stresses do not negatively act on the load-bearing capacity of joints, their influence should be carefully investigated. This paper represents the second part of a study that numerically evaluates the structural behavior of Rectangular Hollow Section T joints taking into account welding residual stresses. The finite element model developed in Part 1 is now used to evaluate their effect on the resistance and initial stiffness of tubular joints. The conducted parametric analyses show that welding residual stresses have a positive influence of 1–19 % on the plastic resistance of tubular joints and insignificantly reduce their initial stiffness. At the same time, the behavior of the considered joints is found not to depend on the welding sequence.
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Effect of welding residual stresses on local behavior of Rectangular Hollow Section joints/Einfluss der Schweißeigenspannungen auf die Tragfähigkeit von Rechteck-Hohlprofil-KnotenTeil 2: Parameterstudien
Bauingenieur, 2018Co-Authors: Marsel Garifullin, Markku Heinisuo, Benjamin Launert, Hartmut Pasternak, K. Mela, Sami PajunenAbstract:Welding residual stresses that occur in tubular joints after the welding process affect their structural behavior. To ensure that these stresses do not negatively act on the load-bearing capacity of joints, their influence should be carefully investigated. This paper represents the second part of a study that numerically evaluates the structural behavior of Rectangular Hollow Section T joints taking into account welding residual stresses. The finite element model developed in Part 1 is now used to evaluate their effect on the resistance and initial stiffness of tubular joints. The conducted parametric analyses show that welding residual stresses have a positive influence of 1–19 % on the plastic resistance of tubular joints and insignificantly reduce their initial stiffness. At the same time, the behavior of the considered joints is found not to depend on the welding sequence.
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Initial rotational stiffness of tubular joints with axial force in chord
Rakenteiden Mekaniikka, 2017Co-Authors: Marsel Garifullin, Sami Pajunen, Kristo Mela, Markku HeinisuoAbstract:In the frame analysis, the local model of the joint must follow the behavior of the joint. When completing the elastic global analysis, the initial rotational stiffness of joints should be known to obtain reliable moment distributions in frames. This paper consists of two parts. The first one evaluates the existing calculation approach for the initial rotational stiffness of welded Rectangular Hollow Section T joints. The validation with the experimental data shows that the current approach significantly underestimates the initial rotational stiffness. An improvement for determining the initial stiffness of T joints is proposed. The second part deals with the influence of the axial force in the main member on the rotational stiffness of the joint. The conducted numerical study shows the extreme reduction of the initial stiffness, when the main member is loaded by axial loads. To consider this effect in the frame analysis, the paper proposes a chord stress function for the initial rotational stiffness for square Hollow Section T joints, using the curve fitting technique.
