• Steel and Composite Structures
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• v.10 no.1
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• pp.45-67
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• 2010

Composite steel-concrete structures are employed extensively in modern high rise buildings and bridges. This concept has achieved wide spread acceptance because it guarantees economic benefits attributable to reduced construction time and large improvements in stiffness. Even though the combination of steel and concrete enhances the strength and stiffness of composite beams, the time-dependent behaviour of concrete may weaken the strength of the shear connection. When the concrete loses its strength, it will transfer its stresses to the structural steel through the shear studs. This behaviour will reduce the strength of the composite member. This paper presents the development of an accurate finite element model using ABAQUS to study the behaviour of shear connectors in push tests incorporating the time-dependent behaviour of concrete. The structure is modelled using three-dimensional solid elements for the structural steel beam, shear connectors, concrete slab and profiled steel sheeting. Adequate care is taken in the modelling of the concrete behaviour when creep is taken into account owing to the change in the elastic modulus with respect to time. The finite element analyses indicated that the slip ductility, the strength and the stiffness of the composite member were all reduced with respect to time. The results of this paper will prove useful in the modelling of the overall composite beam behaviour. Further experiments to validate the models presented herein will be conducted and reported at a later stage.

• Smart Structures and Systems
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• v.11 no.3
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• pp.241-259
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• 2013

This paper presents the optimum load-speed diagram evaluation for a linear micromotor, including multitude cantilever piezoelectric bimorphs, briefly. Each microbeam in the mechanism can be actuated in both axial and flexural modes simultaneously. For this design, we consider quasi-static and linear conditions, and a relatively new numerical method called the smoothed finite element method (S-FEM) is introduced here. For this purpose, after finding an optimum volume fraction for piezoelectric layers through a standard numerical method such as quadratic finite element method, the relevant load-speed curves of the optimized micromotor are examined and compared by deterministic topology optimization (DTO) design. In this regard, to avoid the overly stiff behavior in FEM modeling, a numerical method known as the cell-based smoothed finite element method (CS-FEM, as a branch of S-FEM) is applied for our DTO problem. The topology optimization procedure to find the optimal design is implemented using a solid isotropic material with a penalization (SIMP) approximation and a method of moving asymptotes (MMA) optimizer. Because of the higher efficiency and accuracy of S-FEMs with respect to standard FEMs, the main micromotor characteristics of our final DTO design using a softer CS-FEM are substantially improved.

• Korean Journal of Materials Research
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• v.20 no.9
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• pp.478-482
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• 2010

A series of molecular dynamic (MD), finite element (FE) and ab initio simulations are carried out to establish suitable modeling schemes for the continuum-based analysis of aluminum matrix nanocomposites reinforced with carbon nanotubes (CNTs). From a comparison of the MD with FE models and inferences based on bond structures and electron distributions, we propose that the effective thickness of a CNT wall for its continuum representation should be related to the graphitic inter-planar spacing of 3.4${\AA}$. We also show that shell element representation of a CNT structure in the FE models properly simulated the carbon-carbon covalent bonding and long-range interactions in terms of the load-displacement behaviors. Estimation of the effective interfacial elastic properties by ab initio simulations showed that the in-plane interfacial bond strength is negligibly weaker than the normal counterpart due to the nature of the weak secondary bonding at the CNT-Al interface. Therefore, we suggest that a third-phase solid element representation of the CNT-Al interface in nanocomposites is not physically meaningful and that spring or bar element representation of the weak interfacial bonding would be more appropriate as in the cases of polymer matrix counterparts. The possibility of treating the interface as a simply contacted phase boundary is also discussed.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.209-212
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• 2002

Since Berkhoff proposed the mild-slope equation in 1972, it has widely been used for calculation of shallow water wave transformation. Recently, it was extended to give an extended mild-slope equation, which includes the bottom slope squared term and bottom curvature term so as to be capable of modeling wave transformation on rapidly varying topography. These equations were derived by integrating the Laplace equation vertically. In the present study, we develop a finite element model to solve the Laplace equation directly while keeping the same computational efficiency as the mild-slope equation. This model assumes the vertical variation of wave potential as a cosine hyperbolic function as done in the derivation of the mild-slope equation, and the Galerkin method is used to discretize . The computational domain was discretized with proper finite elements, while the radiation condition at infinity was treated by introducing the concept of an infinite element. The upper boundary condition can be either free surface or a solid structure. The applicability of the developed model was verified through example analyses of two-dimensional wave reflection and transmission. .

• KCI Concrete Journal
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• v.13 no.1
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• pp.19-25
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• 2001

Based on the orthotropic hypoelasticity formulation, a constitutive material model of concrete taking account of triaxial stress state is presented. In this model, the ultimate strength surface of concrete in triaxial stress space is described by the Hsieh's four-parameter surface. On the other hand, the different ultimate strength surface of concrete in strain space is proposed in order to account for increasing ductility in high confinement pressure. Compressive ascending and descending behavior of concrete is considered. Concrete cracking behavior is considered as a smeared crack model, and after cracking, the tensile strain-softening behavior and the shear mechanism of cracked concrete are considered. The proposed constitutive model of concrete is compared with some results obtained from tests under the states of uniaxial, biaxial, and triaxial stresses. In triaxial compressive tests, the peak compressive stress from the predicted results agrees well with the experimental results, and ductility response under high confining pressure matches well the experimental result. The reinforcing bars embedded in concrete are considered as an isoparametric line element which could be easily incorporated into the isoparametric solid element of concrete, and the average stress - average strain relationship of the bar embedded in concrete is considered. From numerical examples for a reinforced concrete simple beam and a structural beam type member, the stress state of concrete in the vicinity of talc critical region is investigated.

• Tribology and Lubricants
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• v.28 no.6
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• pp.278-282
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• 2012

Various bearings such as deep-groove ball bearings, angular-contact ball bearings, and roller bearings are used to support the load and to lubricate between the shaft and the housing. The bearings of potential rolling systems in a turbo pump are the deep-groove ball bearings as comparing with the bearings with rolling elements such as cylindrical rollers, tapered cylindrical rollers, and needle rollers. The deep-groove ball bearings consist of rolling elements, an inner raceway, an outer raceway and a retainer that maintain separation and help to lubricate the rolling element that is rotating in the raceways. In the case of water-lubricated ball bearings, however, fluid friction between the ball and raceways is affected by the entry direction of flow, rotation speed, and flow rate. In addition, this friction is the key factor affecting the bearing life cycles and reliability. In this paper, the characteristics of flow conditions corresponding to a deep-groove ball bearing are investigated numerically, with particular focus on the friction distribution on the rolling element, in order to extend the analysis to the area that experiences solid friction. A simple analysis model of fluid flow inside the water-lubricated ball bearing is analyzed with CFD, and the flow characteristics at high rotation speeds are presented.

• Structural Engineering and Mechanics
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• v.16 no.4
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• pp.391-404
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• 2003

Local reinforcement in dowel type timber joints is essential to improve ductility, to increase load carrying capacity and to reduce the risk of brittle failure, especially in the case of using solid dowel. In many types of reinforcing materials available today, DVW (densified veneer wood) has been demonstrated to be the most advantages in terms of compatibility, embedding performance and ductility. Preliminary studies show that using appropriately sized DVW discs bonded into the timber interfaces may be an effective way to reinforce the connection. In this paper, non-linear 3-dimensional finite element models, incorporating orthotropic and non-linear material behaviour, have been developed to simulate structural performance of the timber joints locally reinforced by DVW discs. Different contact algorithms were applied to simulate contact conditions in the joints. The models were validated by the corresponding structural tests. Correlation between the experimental results and the finite element simulations is reasonably good. Using validated finite element models, parametric studies were undertaken to investigate effects of the DVW disc sizes and the end distances on shear stresses and normal stresses in a possible failure plane in the joint.

• Computational Structural Engineering
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• v.7 no.2
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• pp.101-109
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• 1994

A degenerated cylindrical shell element for modeling glass fiber reinforced plastic pipes is developed and its performance for static structural analysis under internal uniform pressure is evaluated. The element is a nine node degenerated solid shell element with reduced integration technique, addition of nonconforming displacement modes, and assumed strain method to improve convergence of analysis. Several numerical examples are solved and compared with analytical solutions and other F.E.M programs, The results show that the increment of fiber orientation in the GFRP pipes with reference to the longitudinal axis cause less radial displacements and much stiffness in the pipes. This is reasonable since the internal pressure will primarily cause hoop stresses in the ring and 90-angle ply GFRP ring carry these efficiently in pure tension.

• International Journal of CAD/CAM
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• v.8 no.1
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• pp.1-10
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• 2009

This paper presents a topology optimization approach using element-free Galerkin method (EFGM) for the optimal design of compliant mechanisms with geometrically non-linearity. Meshless method has an advantage over the finite element method(FEM) because it is more capable of handling large deformation resulted from geometrical nonlinearity. Therefore, in this paper, EFGM is employed to discretize the governing equations and the bulk density field. The sensitivity analysis of the optimization problem is performed by incorporating the adjoint approach with the meshless method. The Lagrange multipliers method adjusted for imposition of both the concentrated and continuous essential boundary conditions in the EFGM is proposed in details. The optimization mathematical formulation is developed to convert the multi-criteria problem to an equivalent single-objective problem. The popularly applied interpolation scheme, solid isotropic material with penalization (SIMP), is used to indicate the dependence of material property upon on pseudo densities discretized to the integration points. A well studied numerical example has been applied to demonstrate the proposed approach works very well and the non-linear EFGM can obtain the better topologies than the linear EFGM to design large-displacement compliant mechanisms.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.18 no.3
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• pp.321-332
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• 2005

In this paper, the time-domain finite element formulations for axisymmetric linear viscoelastic problems, especially for the viscoelastic hollow sphere and cylinder, under various boundary conditions are presented with the theoretical solutions of them obtained by using the elastic-viscoelastic correspondence principle. It is assumed that the viscoelastic material behaves like a standard linear solid in distortion and elastically in dilatation. Numerical examples are solved based on the spherically symmetric, axisymmetric and plane strain finite element models. Good agreements are obtained between numerical and theoretical solutions, which shows the validity and accuracy of the presented method.