Hieu Nguyen-Van's research while affiliated with Ho Chi Minh City University of Architecture and other places

This study presents a numerical model for buckling analysis of the functionally graded sandwich plates (FGSP) laid on the elastic foundation through the Moving Kriging interpolation-based meshless method using a refined quasi-3D third-order shear deformation theory. The in-plane displacements encompassed a new third-order polynomial in terms of the thickness coordinate, will satisfy the natural vanishing of transverse shear stresses on the top and bottom surfaces. Furthermore, the displacement fields approximated by only four variables with accounting for the thickness stretching effect can lead to the reduction of computational time. Comparison investigations are studied to justify the accuracy of the present method. The influence of the aspect ratios, gradient index, and elastic foundation parameters on the normalized buckling load of FGSP is also studied and discussed.

In this paper, a new refined quasi-3-dimensional logarithmic shear deformation theory (RQ-3DLSDT) and an advanced moving Kriging interpolation (AMKI) based-meshless method is combined for the first time to study the static bending, free vibration, and compressive buckling analysis of isotropic and sandwich functionally graded plates laid on elastic foundations. The RQ-3DLSDT considering the effect of thickness stretching based only on four-unknown variables to determine the displacement field leading to reduce computational efforts. The weak forms of the equilibrium equation are discretized and numerically solved by the AMKI mesh-free method employed a proposed quadric correlation function for getting stable solutions. The accuracy of the proposed formulations is confirmed through several numerical validations. Parametric studies are conducted to investigate the influences of foundation stiffness coefficients, gradient indices, aspect ratios, and schemes of the sandwich plate on mechanical behaviors of the functionally graded plates in this work.

This paper firstly presents numerical analyses of functionally graded porous plates/shells with graphene platelets (GPLs) reinforcement using a novel four-node quadrilateral element with five degrees of freedom per node, namely SQ4P, based on the first-order shear deformation theory and Chebyshev polynomials. The novelty of the present element is to use the high-order shape functions which satisfy the interpolation condition at the points based on Chebyshev polynomials to build the new flat four-node element for analysis of plate/shell structures. The Chebyshev polynomials are a sequence of orthogonal polynomials that are described recursively and the values of these polynomials belong to the interval [−1,1] as well as vanish at the Gauss points. Full Gauss quadrature rule is used to establish the stiffness matrix, geometric stiffness matrix, mass matrix and load vector. Various dispersions of GPLs and internal pores into the metal matrix through the thickness of structure are considered with the rule of a mixture and the Halpin–Tsai model for evaluating effective material properties across the thickness. The influence of weight fraction, porosity coefficient and dimensions of GPLs, distribution of GPLs and porosity into metal matrix are fully studied via several numerical examples from static bending to free vibration and buckling response. Numerical results and comparison with other solutions from available references suggest that the present element has enough reliability and validity to use in structural analysis. With regular and irregular meshes, these results are in close agreement with the exact solutions by using the suitable value for the order of the shape functions.

In this paper, a new three-node triangular plate element is proposed to analyze laminated composite plates based on the higher-order shear deformation theory (HSDT). Originating from the MITC3+ shell finite elements, the displacement fields of the HSDT are interpolated by usual linear functions of the three-node triangular element and a cubic supplemented function associated with a node located at the centroid of the element. The transverse shear strain fields are separately approximated according to the MITC3+ shear-locking removal technique. The edge-based smoothed (ES) strain method is employed to improve the in-plane strain fields. Applying the divergence theorem, the surface integration of the in-plane stiffness matrices is transformed into the line integration on the boundary of the smoothing domains. The performance of the so-called ES-MITC3+ plate elements is validated through several numerical examples. The numerical results of the static, frequency and buckling analyses when this new element is used converge to the exact solutions and agree well with those given in other references.

A novel refined arctangent exponential shear deformation theory (RAESDT) is presented for analysis the mechanical behavior of both isotropic and sandwich FGM plates. Material properties are set to be isotropic at each point and varied across the thickness direction obeying to a power-law distribution of the volume fraction gradation with respect to FGM core or skins of the plate. Unlike high-order shear deformation plate theories based on five or more variables, the displacement field of the novel RAESDT using arctangent exponential variations in planed displacements were approximated by only four unknowns, satisfying naturally tangential stress-free conditions at the plate surfaces and leading to reduce computational efforts. In accordance with RAESDT and enhanced moving kriging interpolation (EMKI)-based meshfree method with a new quadrature correlation function is introduced for the numerical modeling. Numerical validations with different plate configurations, geometries, length to thickness ratios and boundaries conditions are conducted. The obtained results are compared with the corresponding solutions available in the literature showing the accuracy and efficiency of the present approach. ARTICLE HISTORY

In the present study, a novel quadrilateral element, namely SQ4C, combined with the Timoshenko beam element is proposed for the static and buckling analyses of stiffened plate/shell structures. The idea behind these elements is a treatment for shear locking as well as membrane locking arising from the framework of the first-order shear deformation theory and a mesh with curved shell geometry. Formulations with eccentricity are also presented in this paper for the general case. The static and buckling analysis solutions and comparison with other available numerical solutions are presented to illustrate the robustness of the proposed elements to stiffened plate/shell structures. This paper also helps engineers in supplementing their knowledge.

This paper deals with numerical analyses of laminated composite plate and shell structures using a new four-node quadrilateral flat shell element, namely SQ4C, based on the first-order shear deformation theory (FSDT) and a combined strain strategy. The main notion of the combined strain strategy is based on the combination of the membrane strain and shear strain related to tying points as well as bending strain with respect to cell-based smoothed finite element method. Many desirable characteristics and the enforcement of the SQ4C element are verified and proved through various numerical examples in static, frequency and buckling analyses of laminated composite plate and shell structures. Numerical results and comparison with other reference solutions suggest that the present element is accuracy, efficiency and removal of shear and membrane locking.

Human comfort is becoming a vital serviceability requirement when it comes to design of long-span floor systems, as evidenced by the development of international standards on human exposure to vibrations. This paper discusses experimental findings derived from dynamic testing of a real office floor of steel-concrete composite construction where annoying footfall-induced vibration had been reported by the floor tenants. The fundamental frequency of the problematic floor was determined using measurements obtained from a series of simple heel drop tests. The observed vibration levels of the floor under normal walking excitations was then benchmarked against acceptance criteria suggested by a number of widely used floor vibration design guides. From a human comfort perspective, it is found that the same floor can be classified as unacceptable by some guidelines but deemed extremely acceptable by the others. As response levels are translated inconsistently by various acceptance criteria, designers would hence be placed in a dilemma when deciding whether the existing floor really needs modification to enhance its serviceability.

This study develops a statistical relationship between the peak displacement of seismic isolation systems obtained from nonlinear time-history dynamic (NTH) analysis and the peak displacement predicted from an equivalent linear force procedure (ELF). Firstly, the effect of isolators’ mechanical property and excitation type and amplitude on the ratio between the peak displacement of an isolation system calculated from ELF procedure and the peak displacement determined from NTH are evaluated. The ELF procedure in ASCE/SEI 7–16 is employed to estimate the ELF peak displacement. The input ground motions for bidirectional NTH analysis are scaled following this code. The investigation of 540 numerical models subjected to four levels of excitation amplitude, represented by 50 pairs of ground motion, including near-field and far-field motions, reveals that both mechanical property of an isolation system and excitation type and amplitude affect the displacement ratio, where the post-yield stiffness of the isolation system and ground motion type have stronger influence than other parameters. These influences are then statistically processed. Based on the investigated data, a novel practical equation accounting for these parameters is proposed to predict the displacement ratio at different reliability levels.

This paper develops a computational model for nonlinear bending analysis of functionally graded (FG) plates using a four-node quadrilateral element SQ4T within the context of the first order shear deformation theory (FSDT). In particular, the construction of the nonlinear geometric equations are based on Total Lagrangian approach in which the motion at the present state compared with the initial state is considered to be large. Small strain-large displacement theory of von Kármán is used in nonlinear formulations of the quadrilateral element SQ4T with twice interpolation strategy (TIS). The solution of the nonlinear equilibrium equations is obtained by the iterative method of Newton-Raphson with the appropriate convergence criteria. The present numerical results are compared with the other numerical results available in the literature in order to demonstrate the effectiveness of the developed element. These results also contribute a better knowledge and understanding of nonlinear bending behaviors of these structures.