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An Approximation Method for Configuration Optimization of Structures (구조물 형상최적화를 위한 근사해석법에 관한 연구)

  • Jang, Dong Jin;Hoon, Sang Hun
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.10 no.3
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    • pp.7-17
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    • 1990
  • The objective of this paper is to provide a method of optimizing are as of the members as well as shape of both truss and arch structures. The design process includes satisfaction of stress and Euler buckling stress constraints for truss and combined stress constraints for arch structures. In order to reduce the number of detailed finite element analysis, the Force Approximation Method is used. A finite element analysis of the initial structure is performed and the gradients of the member end forces are calculated with respect to the areas and nodal coordinates. The gradients are used to form an approximate structural analysis based on first order Taylor series expansions of the member end forces. Using move limits, a numerical optimizer minimizes the volume of the structure with information from the approximate structural analysis. Numerical examples are performed and compared with other methods to demonstrate the efficiency and reliability of the Force Approximation Method for shape optimization. It is shown that the number of finite element analysis is greatly reduced and that it leads to a highly efficient method of shape optimization of structures.

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Evaluation of Formability on Hydroformed Part for Automobile Based on Finite Element Analysis (유한요소해석에 의한 자동차용 관재액압성형 부품의 성형성 평가)

  • Song, Woo-Jin;Heo, Seong-Chan;Ku, Tae-Wan;Kim, Jeong;Kang, Beom-Soo
    • Transactions of Materials Processing
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    • v.17 no.1
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    • pp.52-58
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    • 2008
  • Tube hydroforming process is generally consisted with pre-bending, preforming and hydroforming processes. Among forming defects which may occur in tube hydroforming such as buckling, wrinkling and bursting, the wrinkling and bursting by local instability under excessive tensile stress mode were mainly caused by thinning phenomenon in the manufacturing process. Thus the accurate prediction and suitable evaluation of the thinning phenomenon play an important role in designing and producing the successfully hydroformed parts without any failures. In this work, the formability on hydroformed part for automobile, i.e. engine cradle, was evaluated using finite element analysis. The initial tube radius, loading path with axial feeding force and internal pressure, and preformed configuration after preforming process were considered as the dominant process parameters in total tube hydroforming process. The effects on these process parameters could be confirmed through the numerical experiments with respect to several kinds of finite element simulation conditions. The degree of enhancement on formability with each process parameters such as initial tube radius, loading path and preform configuration were also compared. Therefore, it is noted that the evaluation approach of the formability on hydroformed parts for lots of industrial fields proposed in this study will provide one of feasible methods to satisfy the increasing practical demands for the improvement of the formability in tube hydroforming processes.

Ultimate Behavior of Compression Flange Stiffened by Shear Stud on Double Composite Steel Box Girder (이중합성 강박스거더에서 전단연결재에 의해 보강된 압축플랜지의 극한거동에 관한 연구)

  • Lee, Doo Sung;Lee, Sung Chul;Suh, Suk Koo
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.28 no.4A
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    • pp.457-463
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    • 2008
  • The longitudinal stiffener performs its role to increase the local buckling strength by making simple support upon compression flange. In the recent researches, it is investigated that compression flange with point supports on certain arrangement reveals the same strength with longitudinal stiffeners. From this results, it is predictable that shear stud could perform the role of longitudinal stiffener if shear stud embedded in concrete satisfies the requirement to point-support under yield stress of the compression flange. In this study, the researches were performed to investigate the optimally required arrangement space of longitudinal point-support for which the shear stud replacing the longitudinal stiffeners and simultaneously determine the required numbers and space of shear stud for completely composite behavior between compression bottom flange and bottom concrete on the double composite girder system.

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Punching Shear Strength of RC Slabs by Simple Truss Model (단순 트러스 모델에 의한 철근콘크리트 교량 바닥판의 펀칭전단강도)

  • Lee, Yongwoo;Hwang, Hoonhee
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.28 no.2A
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    • pp.187-196
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    • 2008
  • The punching shear strength of RC slabs is estimated analytically by the simple truss model. To avoid intrinsic difficulties in punching shear analysis of reinforced concrete slabs, the slabs were divided into three sub-structures as the punching cone and the remaining parts. The strength of the punching cone was evaluated by the stiffness of inclined strut. The stiffness of springs which control lateral displacement of the roller supports consists of the steel reinforcement which passed through the punching cone. Initial angle of struts was determined by curve fitting method of the experimental data with variable reinforcement ratio in order to compensate for uncertainties in the slab's punching shear, the simplification errors and the stiffness of the remaining sub-structures. The validity of computed punching shear strength by simple truss model was shown by comparing with experimental results. The punching shear strength, which was determined by snap-through critical load of shallow truss, can be used effectively to examine punching shear strength of RC slabs.

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IBS Beam Element for Nonlinear Seismic Analysis of Steel Moment Frames (강재 모멘트 골조의 비선형 지진 해석을 위한 IBS 보 요소)

  • Kim, Dal Sung;Kim, Dong Seong;Kim, Kee Dong;Ko, Man Gi
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.28 no.2A
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    • pp.233-242
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    • 2008
  • This study presents a non-prismatic beam element for modeling the elastic and inelastic behavior of steel beams, which have the post-Northridge(cover plate) connections in steel moment frames that are subjected to earthquake ground motions. The elastic stiffness matrix for non-prismatric members with increased beam section (IBS) connection is in the closed-form. The plasticity model is of a discrete type and is composed of a series of nonlinear hinges connected by rigid links. The hardening rules can model the inelastic behavior for monotonic and random cyclic loading, and the effects of local buckling. Moreover the determination of yield surfaces, stiffness parameters, and hardening (or softening) rule parameters for IBS beam element were described. Analytical results of the IBS beam element show good correlation with test data and FEM results.

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Evaluation of the Effect of Initial Condition of the Granular Assembly on the Bearing Capacity of the Shallow Foundation using Photoelastic Measurement Technique (광탄성 측정 기법을 이용한 입상체 초기 조건의 얕은 기초 지지력에 대한 영향 평가)

  • Shin, Sang-Young;Jung, Young-Hoon
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.36 no.3
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    • pp.471-491
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    • 2016
  • Traditional limit equilibrium method needs an assumption of the failure surface to calculate the bearing capapcity of the shallow foundation. From the viewpoint of the mechanics of granular materials, however, the failure of the soil mass is initated by the local buckling of the contact force chains. In this study we observed the directional distribution of the contact force chains in the granular assembly stacked by model particles subjected to the model shallow foundation during loading. Two sets of the assemblies with a regular structure and initially local imperfection were prepared for tests. Existence of the initial local imperfection has a significant effect on the directional distribution of the contact force chains. The bearing capacity of the assembly with local imperfection is only 67% the capacity of the assembly with the regular structure.

Analysis of Influential Factors on Ploughing Failure of Footwall Slope (Footwall 비탈면의 ploughing 파괴에 미치는 영향인자 분석)

  • Moon, Joon-Shik;Park, Woo-Jeong
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.36 no.4
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    • pp.659-665
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    • 2016
  • The limit equilibrium method (LEM) is commonly used for slope design and stability analysis because it is easy to simulate slope and requires short calculating time. However, LEM cannot adequately simulate ploughing failure in a footwall slope with a joint set dipping parallel with slope, e.g. bedding joint set. This study performed parametric study to analyze the influence factors on ploughing failure using UDEC which is a commercial two-dimensional DEM (Distinct Element Method)-based numerical program. The influence of joint structure and properties on stability of a footwall slope against ploughing failure was investigated, and the factor of safety was estimated using the shear strength reduction method. It was found that the stability of footwall slope against ploughing failure strongly relies on dip angle of conjugate joint, and the critical bedding joint spacing and the critical length of slab triggering ploughing failure are also affected by dip angle of conjugate joint. The results obtained from this study can be used for effective slope design and construction including reinforcement.

Experimental Study on Ultimate Shear Strength of Horizontally Curved Plate Girder Web Panels (강곡선 플레이트거더 복부판의 극한전단강도에 관한 실험연구)

  • Lee, Doo Sung;Park, Chan Sik;Lee, Sung Chul
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.26 no.4A
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    • pp.727-734
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    • 2006
  • Although a limited number of experimental investigations and finite element analyses revealed that a curved web panel in practical design has a considerable reserve strength after the elastic buckling as a straight girder web panel, the current Guide Specifications for Horizontally Curved Steel Girder Highway Bridges (AASHTO, 2003) do not consider the postbuckling strength in the ultimate shear strength due to lack of a comprehensive study. In this study, the ultimate shear strength behavior of horizontally curved steel web panels was investigated through nonlinear finite element analysis and experimental test. It was found that curved web panels used in practical designs are able to develop the postbuckling strength that is equivalent to that of straight girder web panels having the same dimensional and material properties.

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Design modification and structural behavior study of a CFRP star sensor baffle

  • Vinyas, M.;Vishwas, M.;Venkatesha, C.S.;Rao, G. Srinivasa
    • Advances in aircraft and spacecraft science
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    • v.3 no.4
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    • pp.427-445
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    • 2016
  • Star sensors are the attitude estimation sensors of the satellite orbiting in its path. It gives information to the control station on the earth about where the satellite is heading towards. It captures the images of a predetermined reference star. By comparing this image with that of the one captured from the earth, exact position of the satellite is determined. In the process of imaging, stray lights are eliminated from reaching the optic lens by the mechanical enclosures of the star sensors called Baffles. Research in space domain in the last few years is mainly focused on increased payload capacity and reduction in launch cost. In this paper, a star sensor baffle made of Aluminium is considered for the study. In order to minimize the component weight, material wastage and to improve the structural performance, an alternate material to Aluminium is investigated. Carbon Fiber Reinforced Polymer is found to be a better substitute in this regard. Design optimisation studies are carried out by adopting suitable design modifications like implementing an additional L-shaped flange, Upward flange projections, downward flange projections etc. A better configuration of the baffle, satisfying the design requirements and achieving manufacturing feasibility is attained. Geometrical modeling of the baffle is done by using UNIGRAPHICS-Nx7.5(R). Structural behavior of the baffle is analysed by FE analysis such as normal mode analysis, linear static analysis, and linear buckling analysis using MSC/PATRAN(R), MSC-NASTRAN(R) as the solver to validate the stiffness, strength and stability requirements respectively. Effect of the layup sequence and the fiber orientation angle of the composite layup on the stiffness are also studied.

Forming Limit Prediction in Tube Hydroforming Processes by Using the FEM and FLSD (유한요소법과 FLSD를 이용한 관재 하이드로포밍 공정에서의 성형 한계 예측)

  • Kim S. W.;Kim J.;Lee J. H.;Kang B. S.
    • Transactions of Materials Processing
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    • v.14 no.6
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    • pp.527-532
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    • 2005
  • Among the failure modes which can occur in tube hydroforming such as wrinkling, bursting or buckling, the bursting by local instability under excessive tensile stresses is irrecoverable phenomenon. Thus, the accurate prediction of bursting condition plays an important role in producing the successfully hydroformed part without any defects. As the classical forming limit criteria, strain-based forming limit diagram (FLD) has widely used to predict the failure in sheet metal forming. However, it is known that the FLD is extremely dependant on strain path throughout the forming process. Furthermore, The application of FLD to hydroforming process, where strain path is no longer linear throughout forming process, may lead to misunderstanding for fracture initiation. In this work, stress-based forming limit diagram (FLSD), which is strain path-independent and more general, was applied to prediction of forming limit in tube hydroforming. Combined with the analytical FLSD determined from plastic instability theory, finite element analyses were carried out to find out the state of stresses during hydroforming operation, and then FLSD is utilized as forming limit criterion. In addition, the approach is verified by a series of bulge tests in view of bursting pressure and shows a good agreement. Consequently, it is shown that the approach proposed in this paper will provide a feasible method to satisfy the increasing practical demands for judging the forming severity in hydroforming processes.