• Structural Engineering and Mechanics
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• 제11권5호
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• pp.519-534
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• 2001

The effect of the initial imperfections on the nonlinear behaviors and ultimate strength of the thin-walled members subjected to the axial loads, obtained by the finite element stability analysis, are examined. As the initial imperfections, the bucking mode shapes of the members are adopted. The buckling mode shapes of the thin-walled members are obtained by the transfer matrix method. In the finite element stability analysis, isoparametric degenerated shell element is used, and the geometrical and material nonlinearity are considered based on the Green Lagrange strain definition and the Prandtl-Reuss stress-strain relation following the von Mises yield criterion. The U-, box- and I-section members subjected to the axial loads are adopted for numerical examples, and the effects of the initial imperfections on the nonlinear behaviors and ultimate strength of the members are examined.

• Structural Engineering and Mechanics
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• 제15권2호
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• pp.225-238
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• 2003

In the present study, the finite strip analysis of a box girder to simulate a ship's hull model is carried out to investigate its inelastic post-buckling behavior and to predict its ultimate flexural strength. Residual stresses and initial geometrical imperfections are both considered in the combined material and geometrical nonlinear analysis. The von-Mises yield criterion and the Prandtl-Reuss flow theory of plasticity are applied in modeling the elasto-plastic behavior of material. The Newton-Raphson iterative process is also employed in the analysis to achieve convergence. The numerical results agree well with the experimental data. The effects of some material and geometrical parameters on the ultimate strength of the structure are also investigated.

• 대한조선학회논문집
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• 제56권4호
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• pp.316-326
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• 2019

In this paper, a methodology is presented for determining the optimal lamination of composite cylindrical structures subject to hydrostatic pressure. The strength criterion in association with the process of optimal design is the buckling collapse of composite cylinders under hydrostatic pressure loads. An empirical formula expressed in the form of the Merchant-Rankine equation is used to calculate the ultimate strength of filament-wound composite cylinders where genetic algorithm is applied for determining the optimized stacking sequences. It is shown that the optimized lamination provides improved collapse pressure loads. It is concluded that the developed method would be useful for the optimal lamination design of composite cylindrical structures.

• 대한조선학회논문집
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• 제43권5호
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• pp.604-610
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• 2006

Common structural rules of JBP(Joint Bulker Project) and JTP(Joint Tanker Project), which will come into effect in 2006, invoke the necessity of the ultimate limit state(ULS) design for ship structures. Even though the many applications of ULS analysis have been performed for ship structures, there have few studies carried out for deck machineries and their supporting structures. Recently four major Korean shipbuilders(DSME, HHI, HHIC, SHI) jointly developed and proposed a new design standards for mooring fittings and also proposed the SWL (Safety Working Load) obtained based on the first yield criterion. In this study, various ultimate strength analyses were performed for bollards and their foundation structures whose yield strengths were quantified by the research consortium. Prior to performing the ultimate strength analyses, the numerical calculation method was substantiated with the test results provided in the joint work report. Based upon the results of this study, it can be concluded that the reinforcements to increase the yield strength are not always resulted in the enhancement of the ultimate strength. Furthermore, the additional production costs for the reinforcements can not be rewarded by the ultimate strength. Therefore, another alternative arrangements should be developed in the view point of ultimate strength.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.104-107
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• 2004

The crack widths of reinforced concrete flexural members are influenced by repetitive fatigue loadings. The bond stress-slip relation is necessary to estimate these crack widths realistically. The purpose of the present study is, therefore, to propose a realistic model for bond stress-slip relation under repeated loading. To this end, several series of tests were conducted to explore the bond-slip behavior under repeated loadings. Three different bond stress levels with various number of load cycles were considered in the tests. The present tests indicate that the bond strength and the slip at peak bond stress are not influenced much by repeated loading if bond failure does not occur. However, the values of loaded slip and residual slip increase with the increase of load cycles. The bond stress after repeated loading approaches the ultimate bond stress under monotonic loading and the increase of bond stress after repeated loading becomes sharper as the number of repeated loads increases. The bond stress-slip relation after repeated loading was derived as a function of residual slip, bond stress level, and the number of load cycles. The models for slip and residual slip were also derived from the present test data. The number of cycles to bond slip failure was derived on the basis of safe fatigue criterion, i.e. maximum slip criterion at ultimate bond stress.

• Structural Engineering and Mechanics
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• 제55권5호
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• pp.953-964
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• 2015

A model has been proposed that can predict the ultimate torsional strength of single-box multi-cell reinforced concrete box girder under combined loading of bending, shear and torsion. Compared with the single-cell box girder, this model takes the influence of inner webs on the distribution of shear flow into account. According to the softening truss theory and thin walled tube theory, a failure criterion is presented and a ultimate torsional strength calculating procedure is established for single-box multi-cell reinforced concrete box girder under combined actions, which considers the effect of tensile stress among the concrete cracks, Mohr stress compatibility and the softened constitutive law of concrete. In this paper the computer program is also compiled to speed up the calculation. The model has been validated by comparing the predicted and experimental members loaded under torsion combined with different ratios of bending and shear. The theoretical torsional strength was in good agreement with the experimental results.

• Steel and Composite Structures
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• 제48권4호
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• pp.461-474
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• 2023

Concrete-filled steel tubes are among the most efficient compressive structural members because the strength of the concrete is enhanced given that the surrounding steel tube confines the concrete laterally and the steel tube is restrained with regard to inward deformation due to the concrete existing inside. Accurate estimations of the ultimate compressive strength of CFT are important for efficient designs of CFT members. In this study, an analytical procedure that directly formulates the interaction between the concrete and steel tube by considering the nonlinear Poisson effect and stress-strain curve of the concrete including the confinement effect is proposed. The failure stress of concrete and von-Mises failure yield criterion of steel were used to consider multi-dimensional stresses. To verify the prediction capabilities of the proposed analytical procedure, 99 circular CFT experimental data instances from other studies were used for a comparison with AISC, Eurocode 4, and other researchers' predictions. From the comparison, it was revealed that the proposed procedure more accurately predicted the ultimate compressive strength of a circular CFT regardless of the range of the design variables, in this case the concrete compressive strength, yield strength of the steel tube and diameter relative to the thickness ratio of the tube.

• Steel and Composite Structures
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• 제42권2호
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• pp.173-190
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• 2022

With the development of spatial structures, the joints are becoming more and more complex to connect tubular members of spatial structures. In this study, an approach is proposed to establish high-efficiency finite element model of multiplanar KTX-joint with the weld geometries accurately simulated. Ultimate bearing capacity the KTX-joint is determined by the criterion of deformation limit and failure mechanism of chord wall buckling is studied. Size effect of fillet weld on the joint ultimate bearing capacity is preliminarily investigated. Based on the validated finite element model, a parametric study is performed to investigate the effects of geometric and loading parameters of KT-plane brace members on ultimate bearing capacity of the KTX-joint. The effect mechanism is revealed and several design suggestions are proposed. Several simple reinforcement methods are adopted to constrain the chord wall buckling. It is concluded that the finite element model established by proposed approach is capable of simulating static behaviors of multiplanar KTX-joint; chord wall buckling with large indentation is the typical failure mode of multiplanar KTX-joint, which also increases chord wall displacements in the axis directions of brace members in orthogonal plane; ultimate bearing capacity of the KTX-joint increases approximately linearly with the increase of fillet weld size within the allowed range; the effect mechanism of geometric and loading parameters are revealed by the assumption of restraint region and interaction between adjacent KT-plane brace members; relatively large diameter ratio, small overlapping ratio and small included angle are suggested for the KTX-joint to achieve larger ultimate bearing capacity; the adopted simple reinforcement methods can effectively constrain the chord wall buckling with the design of KTX-joint converted into design of uniplanar KT-joint.

• Composites Research
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• 제13권1호
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• pp.33-39
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• 2000

복합재료 적층판의 최종강도를 점증적 파손 해석방법을 사용하여 예측하였다. 플라이 강도를 확률분포로 가정했을 경우와 상수로 가정했을 경우 각각의 최종강도를 예측하였다. 복합재료의 강도에 대한 확률분포인 Weibull 분포를 이용하여 임의의 강도 값을 얻은 후 이 값을 Tsai-Hill 파손식에 대입하여 파손여부를 판정하고 파손이 일어나면 재료의 물성을 떨어뜨렸다. 이 방법에 의해서 얻어진 결과를 플라이의 강도를 상수로 가정하여 해석한 경우와의 차이에 대하여 고찰하였다. 결과적으로 두 경우 모두 실험치와 약간의 오차를 보였지만 파손의 경향성에 있어서는 확률분포를 이용한 강도해석이 실험값과 더 근사한 결과를 보였다.

• 대한조선학회논문집
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• 제30권4호
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• pp.127-135
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• 1993

정확성과 단순성의 균형을 유지하면서 선박의 강도평가에 쉽게 적용할 수 있는 평판의 최종강도 간이추정식들을 도출하였다. 당 조선소의 건조선들 중 유조선과 산적화물선에 대한 선저부와 상갑판의 최종강도에 관련된 기하학적 변수들의 통계자료를 분석하여 구조특성을 살펴보고, 강도에 영향을 미치는 주요인수를 중심으로 하여 나머지 영향인자들을 확률분포에 따라 가중시켜 선종별로 평판의 최종강도 추정식을 제시하였다. 또한 저자들에[3-5] 의해 이미 제시된 새로운 좌굴평가식을 바탕으로 좌굴후거동에서 판의 중앙단부의 항복조건을 결부시켜 또하나의 최종강도 추정식을 제시하였다. 본 논문에서 제시한 간이식의 정확도를 실험식과 기존의 식[6, 7, 9]들과 비교 확인하였다.