Numerical Fracture analysis of prestressed concrete beams

Rabczuk, Timon,Zi, Goangseup Korea Concrete Institute 2008 International Journal of Concrete Structures and M Vol.2 No.2

Fracture of prestressed concrete beams is studied with a novel and robust three-dimensional meshfree method. The meshfree method describes the crack as a set of cohesive crack segments and avoids the representation of the crack surface. It is ideally suited for a large number of cracks. The crack is modeled by splitting particles into two particles on opposite sides of the crack segment and the shape functions of neighboring particles are modified in a way the discontinuous displacement field is captured appropriately. A simple, robust and efficient way to determine, on which side adjacent particles of the corresponding crack segment lies, is proposed. We will show that the method does not show any "mesh" orientation bias and captures complicated failure patterns of experimental data well.

Numerical Fracture analysis of prestressed concrete beams

Timon Rabczuk,Goangseup Zi 한국콘크리트학회 2008 International Journal of Concrete Structures and M Vol.2 No.2

Analysis of propagation characteristics of elastic waves in heterogeneous nanobeams employing a new two-step porosity-dependent homogenization scheme

Ebrahimi, Farzad,Dabbagh, Ali,Rabczuk, Timon,Tornabene, Francesco Techno-Press 2019 Advances in nano research Vol.7 No.2

The important effect of porosity on the mechanical behaviors of a continua makes it necessary to account for such an effect while analyzing a structure. motivated by this fact, a new two-step porosity dependent homogenization scheme is presented in this article to investigate the wave propagation responses of functionally graded (FG) porous nanobeams. In the introduced homogenization method, which is a modified form of the power-law model, the effects of porosity distributions are considered. Based on Hamilton's principle, the Navier equations are developed using the Euler-Bernoulli beam model. Thereafter, the constitutive equations are obtained employing the nonlocal elasticity theory of Eringen. Next, the governing equations are solved in order to reach the wave frequency. Once the validity of presented methodology is proved, a set of parametric studies are adapted to put emphasis on the role of each variant on the wave dispersion behaviors of porous FG nanobeams.

Thermal buckling analysis of embedded graphene-oxide powder-reinforced nanocomposite plates

Ebrahimi, Farzad,Nouraei, Mostafa,Dabbagh, Ali,Rabczuk, Timon Techno-Press 2019 Advances in nano research Vol.7 No.5

In this paper, thermal-buckling behavior of the functionally graded (FG) nanocomposite plates reinforced with graphene oxide powder (GOP) is studied under three types of thermal loading once the plate is supposed to be rested on a two-parameter elastic foundation. The effective material properties of the nanocomposite plate are considered to be graded continuously through the thickness according to the Halpin-Tsai micromechanical scheme. Four types of GOPs' distribution namely uniform (U), X, V and O, are considered in a comparative way in order to find out the most efficient model of GOPs' distribution for the purpose of improving the stability limit of the structure. The governing equations of the plate have been derived based on a refined higher-order shear deformation plate theory incorporated with Hamilton's principle and solved analytically via Navier's solution for a simply supported GOP reinforced (GOPR) nanocomposite plate. Some new results are obtained by applying different thermal loadings to the plate according to the GOPs' negative coefficient of thermal expansion and considering both Winkler-type and Pasternak-type foundation models. Besides, detailed parametric studies have been carried out to reveal the influences of the different types of thermal loading, weight fraction of GOP, aspect and length-to-thickness ratios, distribution type, elastic foundation constants and so on, on the critical buckling load of nanocomposite plates. Moreover, the effects of thermal loadings with various types of temperature rise are investigated comparatively according to the graphical results. It is explicitly shown that the buckling behavior of an FG nanocomposite plate is significantly influenced by these effects.

Experimentally validated FEA models of HF2V damage free steel connections for use in full structural analyses

Desombre, Jonathan,Rodgers, Geoffrey W.,MacRae, Gregory A.,Rabczuk, Timon,Dhakal, Rajesh P.,Chase, J. Geoffrey Techno-Press 2011 Structural Engineering and Mechanics, An Int'l Jou Vol.37 No.4

The aim of this research is to model the behaviour of recently developed high force to volume (HF2V) passive energy dissipation devices using a simple finite element (FE) model. Thus, the end result will be suitable for use in a standard FE code to enable computationally fast and efficient analysis and design. Two models are developed. First, a detailed axial model that models an experimental setup is created to validate the approach versus experimental results. Second, a computationally and geometrically simpler equivalent rotational hinge element model is presented. Both models are created in ABAQUS, a standard nonlinear FE code. The elastic, plastic and damping properties of the elements used to model the HF2V devices are based on results from a series of quasi-static force-displacement loops and velocity based tests of these HF2V devices. Comparison of the FE model results with the experimental results from a half scale steel beam-column sub-assembly are within 10% error. The rotational model matches the output of the more complex and computationally expensive axial element model. The simpler model will allow computationally efficient non-linear analysis of large structures with many degrees of freedom, while the more complex and physically accurate axial model will allow detailed analysis of joint connection architecture. Their high correlation to experimental results helps better guarantee the fidelity of the results of such investigations.

A Cell - based Smoothed Finite Element Method for Free Vibration and Buckling Analysis of Shells

Chien Thai-Hoang,Nhon Nguyen-Thanh,Hung Nguyen-Xuan,Timon Rabczuk,Stephane Bordas 대한토목학회 2011 KSCE JOURNAL OF CIVIL ENGINEERING Vol.15 No.2

This paper further extends a cell-based smoothed finite element method for free vibration and buckling analysis of shells. A fournode quadrilateral Mindlin-Reissner shell element with a gradient smoothing operator is adopted. The membrane-bending and geometrical stiffness matrices are computed along the boundaries of the smoothing cells while the shear stiffness matrix is calculated by an independent interpolation in the natural coordinates as in the MITC4 (the Mixed Interpolation of Tensorial Components)element. Various numerical results are compared with existing exact and numerical solutions and they are in good agreement. The advantage of the present formulation is that it retains higher accurate than the MITC4 element even for heavily distorted meshes without increasing the computational cost.

Fracture properties prediction of clay/epoxy nanocomposites with interphase zones using a phase field model

Msekh, Mohammed A.,Cuong, N.H.,Zi, G.,Areias, P.,Zhuang, X.,Rabczuk, Timon Elsevier 2018 Engineering fracture mechanics Vol.188 No.-

<P><B>Abstract</B></P> <P>We predict the macroscopic tensile strength and fracture toughness of fully exfoliated nano silicate clay epoxy composites accounting for the interphase behavior between the polymeric matrix and clay reinforcement. A phase field approach is employed to model fracture in the matrix and the interphase zone of the polymeric nanocomposites (PNCs) while the stiff clay platelets are considered as linear elastic material. The effect of the interphase zones, e.g. thickness and mechanical properties (Young’s modulus and strain energy release rate) on the tensile strength, and fracture parameters of the composite is studied in detail. The dissipation energy due to fracture in the PNCs is extracted for different thicknesses and properties of the interphase zones. We show through numerical experiments that the interphase thickness has the most influence on the tensile strength while the critical strain energy release rate of the interphase zones affects the dissipation energy depending on the interphase zone thickness.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A phase field model for fracture in heterogeneous structure. </LI> <LI> A hybrid hierarchical/concurrent multiscale method for fracture in polymer-matrix composites. </LI> <LI> A phase field model for matrix and interphase fracture in polymer-matrix composites. </LI> <LI> Extraction of fracture related material properties for various input parameters, particularly for the interphase zone. </LI> </UL> </P>

Experimentally validated FEA models of HF2V damage free steel connections for use in full structural analyses

Jonathan Desombre,Geoffrey W. Rodgers,Gregory A. MacRae,Timon Rabczuk,Rajesh P. Dhakal,J. Geoffrey Chase 국제구조공학회 2011 Structural Engineering and Mechanics, An Int'l Jou Vol.37 No.4

The aim of this research is to model the behaviour of recently developed high force to volume (HF2V) passive energy dissipation devices using a simple finite element (FE) model. Thus, the end result will be suitable for use in a standard FE code to enable computationally fast and efficient analysis and design. Two models are developed. First, a detailed axial model that models an experimental setup is created to validate the approach versus experimental results. Second, a computationally and geometrically simpler equivalent rotational hinge element model is presented. Both models are created in ABAQUS, a standard nonlinear FE code. The elastic, plastic and damping properties of the elements used to model the HF2V devices are based on results from a series of quasi-static force-displacement loops and velocity based tests of these HF2V devices. Comparison of the FE model results with the experimental results from a half scale steel beam-column sub-assembly are within 10% error. The rotational model matches the output of the more complex and computationally expensive axial element model. The simpler model will allow computationally efficient non-linear analysis of large structures with many degrees of freedom, while the more complex and physically accurate axial model will allow detailed analysis of joint connection architecture. Their high correlation to experimental results helps better guarantee the fidelity of the results of such investigations.

A Cell-based Smoothed Finite Element Method for Three Dimensional Solid Structures

Hung Nguyen-Xuan,Hiep Vinh Nguyen,Stephane Bordas,Timon Rabczuk,Marc Duflot 대한토목학회 2012 KSCE JOURNAL OF CIVIL ENGINEERING Vol.16 No.7

This paper extends further the strain smoothing technique in finite elements to 8-noded hexahedral elements (CS-FEM-H8). The idea behind the present method is similar to the cell-based smoothed 4-noded quadrilateral finite elements (CS-FEM-Q4). In CSFEM,the smoothing domains are created based on elements, and each element can be further subdivided into 1 or several smoothing cells. It is observed that: 1) The CS-FEM using a single smoothing cell can produce higher stress accuracy, but insufficient rank and poor displacement accuracy; 2) The CS-FEM using several smoothing cells has proper rank, good displacement accuracy, but lower stress accuracy, especially for nearly incompressible and bending dominant problems. We therefore propose 1) an extension of strain smoothing to 8-noded hexahedral elements and 2) an alternative CS-FEM form, which associates the single smoothing cell issue with multi-smoothing cell one via a stabilization technique. Several numerical examples are provided to show the reliability and accuracy of the present formulation.

A stochastic computational method based on goal-oriented error estimation for heterogeneous geological materials

Ghorashi, S.Sh.,Lahmer, T.,Bagherzadeh, A.S.,Zi, G.,Rabczuk, T. Elsevier 2017 Engineering geology Vol.225 No.-

<P><B>Abstract</B></P> <P>Computational modeling of geological materials is challenging. Firstly, they are heterogeneous with numerous uncertainties in the input parameters and secondly, the computational cost of modeling geological structures is time consuming due to the large and different length scales involved. In this article, we propose an efficient computational method for heterogeneous geological materials based on goal oriented error estimation and adaptive mesh refinement. Instead of estimating the error in a specific norm, the proposed novel error estimation approach which is called dual-weighted residual error estimation, approximates the error with respect to the quantity of interest. The dual-weighted residual error estimation is a dual-based scheme which requires an adjoint problem. The adjoint or dual problem is described by defining the quantity of interest in a functional form. Then by solving the primal and dual problems, errors in terms of the specified quantities are calculated. In many applications in engineering geology, the material is heterogeneous. In such cases, the material properties can be regarded as random fields. This variety of material properties leads to non-uniform distributions of the solution gradients, e.g. stresses. Therefore, it is vital to apply a reliable error estimation approach to be able to do efficiently the mesh-adaptivity procedure with regard to varying material parameters with pre-defined correlation lengths. Hence, the proposed error estimator is extended by accounting for a random field model to describe the material properties. Local estimated errors are exploited in order to accomplish the mesh adaptivity procedure. The goal-oriented mesh adaptivity controls the local errors in terms of the prescribed quantities. Both refinement and coarsening processes are applied to raise the efficiency. The performance of the proposed computational approach is demonstrated for several examples.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Novel adaptive methods for geological materials </LI> <LI> The method accounts for random fields and heterogeneities. </LI> <LI> It is shown the method is computationally faster than other adaptive methods. </LI> </UL> </P>