Papers by M. Lezgy-Nazargah
Acta Mechanica, 2021
In this study, an efficient 1D finite element model (FEM) is presented for the axial–flexural buc... more In this study, an efficient 1D finite element model (FEM) is presented for the axial–flexural buckling, post-buckling and geometrically nonlinear analyses of thin-walled beams. The non-classical effects like transverse shear and normal flexibilities are incorporated in the formulation by adopting a new structural concept called equivalent layered composite cross-sectional (ELCS) modeling. In the framework of ELCS, the original cross section of the thin-walled beam is replaced with a layered composite cross section with equivalent stiffness. A layered global–local shear deformation theory is employed for representing the displacement fields of the beam. A full Green–Lagrange type of geometrically nonlinear FEM is developed to formulate the governing differential equations. The Newton–Raphson linearization approach is adopted for solving the nonlinear equations. The proposed FEM avoids the use of a shear correction factor and has a low number of degrees of freedom (DOFs). For the validation of the proposed model, various buckling, post-buckling and nonlinear bending tests are carried out and the obtained results are compared with the results of classical beam theories and 2D/3D finite element results. Comparisons of the results prove the efficiency and accuracy of the suggested formulation for stability and geometrically nonlinear analysis of thin-walled beams.
Composite Structures, 2018
Original Research Paper Received 04 December 2015 Accepted 12 January 2016 Available Online 14 Fe... more Original Research Paper Received 04 December 2015 Accepted 12 January 2016 Available Online 14 February 2016 finite element model has been introduced for static bending analysis of thick plates based on mixed plate variational formulation. refined Reissner's mixed variational theoy is employed to derive the governing equations in terms of the introduced transverse normal stress and displacement variables. The in-plane displacement components of the plate are described by combination of polynomial and exponential terms. Concerning the transverse displacement component, first-order polynomial is adopted. second-order expansion is considered for the variations of the transverse normal component of the stress tensor along the thickness direction of the plate. The boundary conditions of shear and normal tractions on the top and bottom surfaces of the plate are exactly satisfied. Based on the proposed mixed plate theory, four nodded compatible Hermitian rectangular element which ensur...
Thin-Walled Structures, 2021
Abstract A quasi-3D finite element model (FEM) with a low computational cost is presented for cou... more Abstract A quasi-3D finite element model (FEM) with a low computational cost is presented for coupled bending and torsional–warping analysis of thin-walled beams. The presented FEM converts the problem of 3D analysis of thin-walled beams into separated 2D cross-sectional and 1D modeling. The warping function over the cross-section of the thin-walled beams is firstly approximated, via a 2D FEM. Then, a 1D FEM is developed for computing the axial variations of the displacement field variables. For describing the kinematic of the thin-walled beam due to axial extension and bending, the concept of hypothetical equivalent layered composite cross-section (HELCS) is employed. Using the HELCS, the non-classical effects like transverse shear flexibility can be easily incorporated into the formulation. A refined sinus theory is employed to describe the displacement fields of the equivalent layered cross-section. In contrast to other refined models of literature, the present model does not require the calculation of any geometric, torsional and warping constants. For validation of the proposed model, comparisons are made with the results of 2D/3D finite element analysis as well as the numerical and analytical results reported by other researchers. The proposed model not only gives accurate results but also reduces the number of involved degrees-of-freedom (DOFs) significantly. Considering the effects of the restrained warping due to torsion, no need to use the shear correction factor, satisfaction of zero-conditions of shear stresses on the exterior surfaces of beams are other advantages of the proposed FEM.
European Journal of Mechanics - A/Solids, 2020
Structural Concrete, 2021
Steel and Composite Structures, 2018
The aim of this paper is to evaluate the accuracy and reliability of the available bond.slip laws... more The aim of this paper is to evaluate the accuracy and reliability of the available bond.slip laws which are being used for the numerical modeling of Fiber Reinforced Polymer (FRP)/concrete interfaces. For this purpose, a set of Reinforced Concrete (RC) beams retrofitted with external FRP were modeled using the 3D nonlinear Finite Element (FE) approach. All considered RC beams have been previously tested and the corresponding experimental data are available in the literature. The failure modes of these beams are concrete crushing, steel yielding and FRP debonding. Through comparison of the numerical and experimental results, the effectiveness of each FRP/concrete bond.slip model for the prediction of the structural behavior of externally retrofitted RC beams is assessed. The sensitivity of the numerical results against different modeling considerations of the concrete constitutive behavior and bond-slip laws has also been evaluated. The results show that the maximum allowable stress ...
Mechanics of Advanced Materials and Structures, 2020
In this study, an accurate 1D finite element model with low degrees of freedom (DOFs) is presente... more In this study, an accurate 1D finite element model with low degrees of freedom (DOFs) is presented for the static extensional-shearing-bending analysis of curved thin-walled beams. In order to incorporate the nonclassical effects like transverse shear flexibility in the formulation, the concept of equivalent layered composite cross section (ELCS) is employed. Based on this new concept, the cross section of a thin-walled beam is replaced with an equivalent layered composite one. A global-local layered beam theory is employed to describe the displacement fields of the curved beams. A curved beam finite element with three nodes and 13 DOFs is developed for the approximation of the unknown variables of the displacement fields. For validation of the proposed model, the results of 1 D models of other researchers as well as the results of the 2D/3D finite element simulations (ABAQUS) are employed. Needlessness to the shear correction factor, satisfaction of zero-conditions of shear stresses on the upper and lower planes of the curved beam, high accuracy in the prediction of structural responses, and significant reduction in the time of computations are some of distinct features of the proposed finite element model.
Acta Mechanica, 2020
A precise global-local shear deformation theory is developed for the prediction of static and dyn... more A precise global-local shear deformation theory is developed for the prediction of static and dynamic behaviors of thin and thick layered curved beams. The effect of deepness is considered in the derivation of the proposed beam theory. Variations of the shear stress along the thickness direction of the curved beam are approximated by using a global parabolic shear stress function which is locally refined at each layer. The zero conditions of shear stresses on the boundary surfaces of the curved beam are exactly satisfied, and no shear correction coefficient is needed. One of the important features of the present theory is that it has only four unknown field variables, which is only one more than the first-order shear deformation theory. A displacement-based finite element model is employed for solving the governing equations. For validation, the results obtained from static and free vibration tests are compared with the results of three-dimensional (3D) finite element analysis, classical theories, and other advanced shear deformation beam theories. The obtained numerical results show that the present model can precisely predict static and free vibration responses of both shallow and deep composite beams with arbitrary boundary and layup conditions.
Archives of Civil and Mechanical Engineering, 2018
A novel mixed-field theory with relatively low number of unknown variables is introduced for bend... more A novel mixed-field theory with relatively low number of unknown variables is introduced for bending and vibration analysis of multi-layered composite plates. The presented plate theory is derived from a parametrized mixed variational principle which is introduced recently by the first author. A global-local kinematic with a layer-independent number of variables is assumed for the description of the displacements of the plate. The considered kinematic stratifies the displacement and transverse stress continuity conditions at the mutual interfaces of the layers. It also fulfill the homogenous boundary conditions of the shear stresses on the upper/lower surfaces of the plates without using the shear correction factor. One-unknown variable fields which satisfy a priori the continuity conditions at the adjacent interfaces between layers and the zero boundary conditions on the bounding surfaces are considered for the approximation of the transverse shear stresses. The transverse normal stress along the total thickness of the multi-layered plate is approximated via a quadratic polynomial. The presented mixed-field plate theory has been validated through comparison of the bending and vibration analysis results with those obtained from the three-dimensional (3D) theory of elasticity and the results of the other classical and high-order plate theories.
Acta Mechanica, 2016
Based on the parametrized mixed variational principle, a high-performance finite element model ha... more Based on the parametrized mixed variational principle, a high-performance finite element model has been developed for bending and vibration analysis of thick plates. The proposed mixed variational formulation combines the concept of Reissner's mixed variational theorem and Rong's generalized mixed variational theorem. In addition to unknown parameters of the displacement fields, the transverse normal component of the stress tensor is also assumed as the independent field variable in the present variational formulation. The latter allows the fulfillment of the boundary conditions of the transverse normal stress at the top and bottom surfaces of the plate in a natural way. The variational constraint of the transverse normal strain-displacement relations is relaxed via the parametrized Lagrange multipliers method. The functional of the proposed variational formulation contains an arbitrary free parameter, called the splitting factor. Simple formulations have been proposed for selecting the splitting factor which leads to the results of higher precision. The numerical results obtained from the proposed mixed formulation have been compared with the results of three-dimensional (3D) theory of elasticity and other plate theories available in the literature. The comparison study shows that the proposed parametrized mixed plate theory is capable of achieving the accuracy of nearly exact 3D solutions.
Steel and Composite Structures, 2015
Thin-Walled Structures, 2017
Based on a generalized layered global-local beam (GLGB) theory, a computationally low cost finite... more Based on a generalized layered global-local beam (GLGB) theory, a computationally low cost finite element model is presented for the elasto-plastic analysis of thin-walled beams. In the employed GLGB theory, the crosssection of the thin-walled beam is replaced with an equivalent layered composite one. For describing the displacement fields of the equivalent layered composite beam, the double superposition hypothesis in conjugate with an exponential shear stress function is employed. In contrast to the most of available advanced onedimensional (1D) models proposed for thin-walled structures, the effects of the transverse normal stress and transverse flexibility are considered in the present GLGB theory. The proposed GLGB theory does not need the incorporation of any shear correction factor and it has only one general unknown parameter more than Timoshenko's beam theory. For plasticity modeling, von Mises yield criterion is employed. The non-linear 1D finite element formulations are solved using Newton-Raphson algorithm. The proposed nonlinear finite element model is validated through comparison with the three-dimensional (3D) finite element and other similar theoretical models available in the literature.
Mechanics of Advanced Materials and Structures, 2015
ABSTRACT An efficient and computationally low cost finite element (FE) model is developed for dyn... more ABSTRACT An efficient and computationally low cost finite element (FE) model is developed for dynamic free and forced response of sandwich beams with embedded shear piezoelectric layers based on a coupled refined high-order global-local theory. Contrary to most of the available models, all of the kinematic and stress boundary conditions are ensured at the interfaces of the shear piezoelectric layers. Moreover, both the electrical-induced strains components and transverse flexibility are taken into account for the first time in the present theory. For validation of the proposed model, various free and forced vibration tests for thin and thick sandwich beams are carried out. For various electrical and mechanical boundary conditions, excellent agreement has been found between the results obtained from the proposed formulation with previously published and the coupled two-dimensional (2D) FE results.
Thin-Walled Structures, 2019
Thin-Walled Structures, 2011
... 30] introduced a generalized globallocal higher order theory for the composite laminates. ..... more ... 30] introduced a generalized globallocal higher order theory for the composite laminates. ... developed for analyzing and controlling of the smart laminated piezoelectric beams by Beheshti ... Numerical results of the written computer code whose algorithm is based on the present ...
European Journal of Mechanics - A/Solids
Scientia Iranica
The available three-dimensional (3D) solutions reported for the analysis of Functionally Graded P... more The available three-dimensional (3D) solutions reported for the analysis of Functionally Graded Piezoelectric (FGP) laminates are based on this simplifying assumption that the FGP layer consists of a number of homogeneous sub-layers. The accuracy of these formulations not only is dependent on the number of sub-layers, but also leads to inaccurate results in the prediction of higher natural frequencies of the FGP laminates. In the present paper, a 3D Peano series solution is developed for the cylindrical bending vibration of the FGP laminates. This novel formulation exactly satis es the equations of motion, the charge equation, and the boundary and interface conditions of the continuously nonhomogeneous piezoelectric layers. The obtained solution is exact because no a priori assumption for the displacement components and the electric potential along the thickness direction of FGP layers is introduced. The in uences of the di erent functionally gradient material properties and di erent electric boundary conditions on the natural frequencies and mode shapes of the FGP laminate have also been studied through examples. The present solution and its obtained numerical results can be employed to assess the accuracy of di erent FGP laminated beam/plate theories. It can also be used for FGP vibration behavior comprehension purposes.
Journal of Mechanics, 2015
In this study, a fully micromechanical model based on iso-field assumptions is developed for comp... more In this study, a fully micromechanical model based on iso-field assumptions is developed for computing the effective coupled thermo-electro-elastic material properties of Macro Fiber Composites (MFCs) in the linear regime. The explicit formulations are derived using the thermo-electro-elastic constitutive equations under the iso-field assumptions and multiple loading conditions. The effects of piezoelectric fiber volume fraction and matrix properties on the effective material constants of MFCs are studied through some examples. In order to validate the accuracy of the present micromechanical formulations, comparisons have been made with other results available in the literature.
European Journal of Mechanics - A/Solids, 2015
An isogeometric formulation based on non-uniform rational B-spline (NURBS) basis functions is pre... more An isogeometric formulation based on non-uniform rational B-spline (NURBS) basis functions is presented for the analysis of laminated composite beams. A refined sinus model is considered in deriving the governing equations using the principle of virtual work. This refined sinus model does not require shear correction factor and ensures continuity conditions for displacements, transverse shear stresses as well as boundary conditions on the upper and lower surfaces of the laminated beam. It is important to notice that the number of the mechanical unknowns is independent of the number of layers. The proposed isogeometric finite element does not suffer from shear locking. Both static and vibration mechanical tests for thin and thick laminate beams are presented in order to validate the capability of the proposed isogeometric formulation. For different boundary conditions, fiber orientations and lay-up number, excellent agreement is found between the results obtained from the present formulation and reference results from open literature or finite element reference solutions.
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Papers by M. Lezgy-Nazargah