• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.10a
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• pp.69-72
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• 2004

A new three-node triangular shell element based on higher order zig-zag theory is developed for laminated composite shells with multiple delaminations. The present higher order zig-zag shell theory is described in a general curvilinear coordinate system and in general tensor notation. All the complicated curvatures of surface including twisting curvatures can be described in an exact manner in the present shell element because this element is based on geometrically exact surface representation. The displacement field of the proposed finite element includes slope of deflection, which requires continuity between element interfaces. Thus the nonconforming shape function of Specht's three-node triangular plate bending element is employed to interpolate out-of-plane displacement. The present element passes the bending and twisting patch tests in flat surface configurations. The developed element is evaluated through the eigenvalue problems of composite cylindrical shells with multiple delaminations. Through the numerical examples it is demonstrated that the proposed shell element is efficient because it has minimal degrees of freedom per node. The present shell element should serve as a powerful tool in the prediction of natural frequency and modes of multi-layered thick laminated shell structures with arbitrary-shaped multiple delaminations.

• Geomechanics and Engineering
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• v.38 no.4
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• pp.397-408
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• 2024

Buried box culverts are crucial elements of transportation infrastructure. However, their behavior under foundation loads is not well understood, indicating a significant gap in existing research. This study aims to bridge this gap by conducting a detailed numerical analysis using the Finite Element Method and Abaqus software. The research evaluates the behavior of buried box culverts by examining their interaction with surrounding soil and the pressures from surface foundation loads. Key variables such as embedment depth, culvert wall thickness, concrete material properties, foundation pressure, foundation width, soil elastic modulus, and friction angle are altered to understand their combined effects on structural response. The methodology employs a validated 2D numerical model under plane strain conditions. Parametric studies highlight the critical role of culvert depth (H) in influencing earth pressure and bending moments. Foundation pressure and width demonstrate complex interdependencies affecting culvert behavior. Variations in culvert materials' elastic modulus show minimal impact. It was found that the lower wall of the buried culvert experiences higher average pressure compared to the other two walls, due to the combined effects of the culvert's weight and down drag forces on the side walls. Furthermore, while the pressure distribution on the top and bottom walls is parabolic, the pressure on the side walls follows a different pattern, differing from that of the other two walls.

• Geomechanics and Engineering
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• v.35 no.6
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• pp.603-615
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• 2023

Population growth and urbanization prompted engineers to propose more sophisticated and efficient transportation methods, such as underground transit systems. However, due to limited urban space, it is necessary to construct these tunnels in close proximity to existing infrastructure like high-rise buildings and bridges. Battered piles have been widely used for their higher stiffness and bearing capacity compared to vertical piles, making them effective in resisting lateral loads from winds, soil pressures, and impacts. Considerable prior research has been concerned with understanding the vertical pile response to tunnel excavation. However, the three-dimensional effects of tunnelling on adjacent battered piled foundations are still not investigated. This study investigates the response of a single battered pile to tunnelling at three critical depths along the pile: near the pile shaft (S), next to the pile (T), and below the pile toe (B). An advanced hypoplastic model capable of capturing small strain stiffness is used to simulate clay behaviour. The computed results reveal that settlement and load transfer mechanisms along the battered pile, resulting from tunnelling, depend significantly on the tunnel's location relative the length of the pile. The largest settlement of the battered pile occurs in the case of T. Conversely, the greatest pile head deflection is caused by tunnelling near the pile shaft. The battered pile experiences "dragload" due to negative skin friction mobilization resulting from tunnel excavation in the case of S. The battered pile is susceptible to induced bending moments when tunnelling occurs near the pile shaft S whereas the magnitude of induced bending moment is minimal in the case of B.

• Structural Engineering and Mechanics
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• v.48 no.6
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• pp.791-807
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• 2013

Ultra High Performance Cementitious Composites with compressive strength 200MPa (UHPCC-200) is proposed for the structural design of super high hybrid wind turbine tower to gain durability, ductility and high strength design objectives. The minimal wall thickness is analyzed using basic bending and compression theory and is modified by a toque influence coefficient. Two cases of wall thickness combination of middle and bottom segment including varied ratio and constant ratio are considered within typical wall thickness dimension. Using nonlinear finite element analysis, the effects of wall thickness combinations with varied and constant ratio and prestress on the structural stress and lateral displacement are calculated and analyzed. The design limitation of the segmental wall thickness combinations is recommended.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1999.04a
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• pp.335-342
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• 1999

It is well known that l-girders are weak in torsion and it might be more economical to use a box girder, which has great torsional rigidity. The use of box beams does, however, present a potential problem in that cross-sectional distortions can induce large warping normal stresses and transverse bending stress. Accordingly a sufficient number of diaphragms are provided to make the distortional effects minimal. In engineering practice, diaphragms are spaced in 5m intervals without reasonable basis. It is considered to be noneconomical design to the almost design engineers, and it may produce the unsafe structural systems in special cases such as curved bridges with large initial curvature. These problems have not been solved for the lack of adequate tools of structural analysis. In this study, on the basis of the parametric studies, the design formulas for the distortional warping stress and the reasonable diaphragm spacing of box girder were presented.

• Transactions of Materials Processing
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• v.19 no.4
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• pp.203-209
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• 2010

In the hot press forming process (HPF), a martensitic structure is obtained by controlling the cooling rate when cooling a boron sheet that is heated up to over $900^{\circ}C$. The HPF process has various advantages such as the improvement in formability and material properties and minimal spring back of the deformed materials. The factors related to the cooling rate depend on the heat transfer characteristics between heated materials and dies. Therefore, in this study, the cooling rate is controlled by adjusting the heat transfer coefficient of the material at the pressing process. And, the mechanical properties and microstructure of the deformed material is demonstrated during the HPF process where cold dies are used to form the heated steel plate. This is achieved by varying the major forming conditions that control the cooling rate regarded as the most important process parameter.

• Computers and Concrete
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• v.9 no.5
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• pp.327-340
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• 2012

The search for a design that meets both performance and safety, with minimal cost and lesser environmental impact was always the goal of structural engineers. In general, the design of conventional reinforced concrete structures is an iterative process based on rules of thumb established from the personal experience and intuition of the designer. However, such procedure makes the design process exhaustive and only occasionally leads to the best solution. In such context, this work presents the development and implementation of a mathematical formulation for obtaining optimal sections of reinforced concrete columns subjected to uniaxial flexural compression, based on the verification of strength proposed by the Brazilian standard NBR 6118 (ABNT 2007). To minimize the cost of the reinforced concrete columns, the Simulated Annealing optimization method was used, in which the amount and diameters of the reinforcement bars and the dimensions of the columns cross sections were considered as discrete variables. The results obtained were compared to those obtained from the conventional design procedure and other optimization methods, in an attempt to verify the influence of resistance class, variations in the magnitudes of bending moment and axial force, and material costs on the optimal design of reinforced concrete columns subjected to uniaxial flexural compression.

• Journal of Computational Design and Engineering
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• v.2 no.1
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• pp.67-72
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• 2015

Recently, along with the improvements of geometry modeling methods using sketch-based interface, there have been a lot of developments in research about generating surface model from 3D curves. However, surfacing a 3D curve network remains an ambiguous problem due to the lack of geometric information. In this paper, we propose a new algorithm for estimating the normal vectors of the 3D curves which accord closely with user intent. Bending energy is defined by utilizing RMF(Rotation-Minimizing Frame) of 3D curve, and we estimated this minimal energy frame as the one that accords design intent. The proposed algorithm is demonstrated with surface model creation of various curve networks. The algorithm of estimating geometric information in 3D curves which is proposed in this paper can be utilized to extract new information in the sketch-based modeling process. Also, a new framework of 3D modeling can be expected through the fusion between curve network and surface creating algorithm.

• International Union of Geodesy and Geophysics Korean Journal of Geophysical Research
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• v.25 no.1
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• pp.23-34
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• 1997

Seismic tomography using the graph theoretical method of ray tracing is performed in two synthetic data sets with laterally varying velocity structures. The straight-ray tomography shows so poor results in imaging the laterally varying velocity structure that the ray-traced tomographic techniques should be used. Conventional ray tracing methods have serious drawbacks, i.e. problems of convergence and local minima, when they are applied to seismic tomography. The graph theretical method finds good approximated raypaths in rapidly varying media even in shadow zones, where shooting methods meet with convergence problems. The graph theoretical method ensures the globally minimal traveltime raypath while bending methods often cause local minima problems. Especially, the graph theoretical method is efficient in case that many sources and receivers exist, since it can find the traveltimes and corresponding raypaths to all receivers from a specific source at one time. Moreover, the algorithm of graph theoretical method is easily applicable to the ray tracing in anisotropic media, and even to the three dimensional case. Among the row-active inversion techniques, the conjugate gradient (CG) method is used because of fast convergence and high efficiency. The iterative sequence of the ray tracing by the graph theoretical method and the inversion by the CG method is an efficient and robust algorithm for seismic tomography in laterally varying velocity structures.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.34 no.4
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• pp.3-13
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• 2018

Load bearing capacity of dowel type fasteners loaded perpendicular to the shear plane is determined based on Johansen's yield theory (Johansen, 1949). In case of inclined screws whose axis is no longer perpendicular, the ultimate load of connection increases because of additional axial withdrawal capacity. To calculate load bearing capacity for inclined screws, KBC2016 and Eurocode5 provide design equations using the combination of two effects; axial and bending strength. Although their equations have been validated for a long time, there is still minimal information how to apply them for concrete-CLT joints. Since there are not many test data available, engineers have to make certain assumptions and thus results may look inconsistent in practice. In this paper, authors would like to describe the current approach and assumptions indicated by KBC2016 and Eurocode 5 and how they match the experimental results in terms of shear strength of CLT-concrete connections. To fulfill the objective, several push-out tests were performed on nine different test specimens. Each specimen has different penetration angles and depths. By analyzing load-displacement curves, the maximum shear strength, stiffness, and ductility were obtained. Shear strength values were compared with the current design codes and theoretical equations proposed in this paper. Observations on stiffness and ductility were briefly discussed.