• Earthquakes and Structures
• /
• 제18권4호
• /
• pp.407-421
• /
• 2020

In-place analysis for offshore platforms is essentially required to make proper design for new structures and true assessment for existing structures, in addition to the structural integrity of platforms components under the maximum and minimum operating loads when subjected to the environmental conditions. In-place analysis have been executed to check that the structural member with all appurtenance's robustness have the capability to support the applied loads in either storm or operating conditions. A nonlinear finite element analysis is adopted for the platform structure above the seabed and pile-soil interaction to estimate the in-place behavior of a typical fixed offshore platform. The SACS software is utilized to calculate the dynamic characteristics of the platform model and the response of platform joints then the stresses at selected members, as well as their nodal displacements. The directions of environmental loads and water depth variations have significant effects in the results of the in-place analysis behavior. The most of bending moment responses of the piles are in the first fourth of pile penetration depth from pile head level. The axial deformations of piles in all load combinations cases of all piles are inversely proportional with penetration depth. The largest values of axial soil reaction are shown at the pile tips levels (the maximum penetration level). The most of lateral soil reactions resultant are in the first third of pile penetration depth from pile head level and approximately vanished after that penetration. The influence of the soil-structure interaction on the response of the jacket foundation predicts that the flexible foundation model is necessary to estimate the force responses demands of the offshore platform with a piled jacket-support structure well.

• Steel and Composite Structures
• /
• 제23권6호
• /
• pp.633-646
• /
• 2017

The compressive behavior of special-shaped concrete filled tube (CFT) mega column coupled with multiple cavities is studied by testing six columns subjected to cyclically uniaxial compressive load. The six columns include three pentagonal specimens and three hexagonal specimens. The influence of cavity construction, arrangement of reinforcement, concrete strength on failure feature, bearing capacity, stiffness, and residual deformation is examined. Experimental results show that cavity construction and reinforcements make it possible to form a combined confinement effect to in-filled concrete, and the two groups of special-shaped CFT columns show good elastic-plastic compressive behavior. As there is no axial bearing capacity calculation method currently available in any Code of practice for special-shaped CFT columns, values predicted by normal CFT column formulas in GB50936, CECS254, ACI-318, EC4, AISCI-LRFD, CECS159, and AIJ are compared with tested values. The calculated values are lower than the tested values for most columns, thus the predicted bearing capacity is safe. A reasonable calculation method by dividing concrete into active and inactive confined regions is proposed. And high accuracy shows in estimating special-shaped CFT columns either coupled with multiple cavities or not. In addition, a finite element method (FEM) analysis is conducted and the simulated results match the test well.

• Steel and Composite Structures
• /
• 제33권4호
• /
• pp.615-627
• /
• 2019

This paper aims to study the compressive behavior of circular hollow and concrete-filled steel tubular stub columns under simulated marine atmospheric corrosion. The specimens after salt spray corrosion were tested under axial compressive load. Steel grade and corrosion level were mainly considered in the study. The mechanical behavior of circular CFST specimens is compared with that of the corresponding hollow ones. Design methods for circular hollow and concrete-filled steel tubular stub columns are modified to consider the effect of marine atmospheric corrosion. The results show that linear fitting curves could be used to present the relationship between corrosion rate and the mechanical properties of steel after simulated marine atmospheric corrosion. The ultimate strength of hollow steel tubular and CFST columns decrease with the increase of corrosion rate while the ultimate displacement of those are hardly affected by corrosion rate. Increasing corrosion rate would change the failure of CFST stub column from ductile failure to brittle failure. Corrosion rate would decrease the ductility indexes of CFST columns, rather than those of hollow steel tubular columns. The confinement factor ${\xi}$ of CFST columns decreases with the increase of corrosion rate while the ratio between test value and nominal value shows an opposite trend. With considering marine atmospheric corrosion, the predicted axial strength of hollow steel tubular and CFST columns by Chinese standard agree well with the tested values while the predictions by Japanese standard seem conservative.

• Steel and Composite Structures
• /
• 제30권5호
• /
• pp.417-432
• /
• 2019

This paper presents the results of axial compression testing and numerical modeling on reinforced concrete columns (RCC) with normal concrete (NC) and high-strength concrete (HSC), RCC confined by glass-fiber reinforced plastic pipes (GRP) casing as well as carbon fiber reinforced polymer (CFRP), The major parameters evaluated in the experiments were the effects of concrete type, GRP casing and CFRP wrapping, as well as the number of CFRP layers. 12 cylindrical RCC ($150{\times}600mm$) were prepared and divided into two groups, NC and HSC. Each group was divided into two parts; with and without GRP casing. In each part, one column was without CFRP strengthening layer, a column was wrapped with one CFRP layer and another column with two CFRP layers. All columns were tested under concentrated compression load. Numerical modeling was performed using ABAQUS software and the results of which were compared with experimental findings. A good agreement was found between the results. Results indicated that the utilization of CFRP wrapping and GRP casing improved compression capacity and ductility of RCC. The addition of one and two layer-FRP wrapping increased capacity in the NC group to an average of 18.5% and 26.5% and in the HSC group to an average of 10.2% and 24.8%. Meanwhile, the utilization of GRP casing increased the capacity of the columns by 3 times in the NC group and 2.38 times in the HSC group. The results indicated that although both CFRP wrapping and GRP casing increased confinement, the GRP casing gave more increase capacity and ductility of the RCC due to higher confinement. Furthermore, the confinement effect was higher on NC group.

• 대한토목학회논문집
• /
• 제39권2호
• /
• pp.335-344
• /
• 2019

기존건물의 수직증축시, 추가되는 증축하중을 지지하기 위해서 기초를 보강하는 것은 필수적이다. 일반적으로 기초의 지지력을 증대시키고 침하를 감소시키기 위하여 마이크로파일공법이 널리 활용되고 있다. 본 연구에서는 기존의 마이크로파일에 전단키가 추가된 새로운 형식의 파형마이크로파일을 활용하여 연구를 수행하였다. 유한요소해석법(FEM)을 통해 기초보강시 파형마이크로파일의 하중침하거동과 하중분담율을 평가하였으며, 3가지 길이 다른 일반적인 마이크로파일들의 지지거동과 비교를 통해 보강효과를 확인하였다. 해석 결과, 파형마이크로파일의 지지력과 축강성이 일반 마이크로파일보다 크게 나타났으며, 이는 파형 마이크로파일의 전단키에 의한 효과인 것으로 판단된다. 또한, 수직증축 리모델링 시, 기존하중 대비 20 %의 증축하중이 재하될 때, 파형마이크로파일의 하중분담율이 동일한 길이의 일반 마이크로파일에 비해 약 40 % 증가하였으며, 보강효과는 길이 1~1.5배의 일반적인 마이크로파일보다 우수한 것으로 나타냈다.

• 대한기계학회논문집
• /
• 제14권5호
• /
• pp.1043-1058
• /
• 1990

본 연구에서는 전자기 성형법에 의한 원통형상의 가공재의 자유 확관성형 가 공에 대해서 유한요소해석법을 이용한 변형 및 응력해석을 수행하였다. 탄소성 재료 모형을 확장하여 변형 경화율이 변형률 및 변형률 속도의 지배를 받는 변형률 속도 종 속 탄소성 재료 모형을 도입하였고, 1차 제하 이후까지 포함하여 고속 성형시 변형률 속도 효과에 의해 발생하는 현상들에 대해서 연구하였다.결과의 비교 및 논의를 위 하여, 해석대상과 성형조건, 그리고 가공재에 작용하는 자기압력은 Suzuki의 것과 동 일한 것을 사용하였다.

• 한국지반공학회논문집
• /
• 제30권12호
• /
• pp.51-61
• /
• 2014

연구에서는 사질토 지반에서 개단말뚝의 지지력에 영향을 미치는 폐색효과를 조사하기 위하여 현장재하시험을 수행하였다. 현장재하시험은 직경이 다른 총 3본의 시험말뚝(508.0, 711.2, 914.4mm)을 제작하여 각각 동재하시험과 정재하시험을 실시하였다. 내주면마찰력과 외주면마찰력을 분리 측정하기 위하여 시험말뚝을 이중관으로 제작하였고, 외부말뚝의 안쪽과 내부말뚝의 바깥쪽 표면에 변형률계를 부착하였다. 정재하시험 결과, 내주면마찰력은 선단부로부터 총 관내토 길이의 약 18-34%의 부근에서 집중적으로 발생하였고, 이를 통해 말뚝 선단부근의 관내토가 내주면마찰력 발현에 큰 영향을 미치는 것을 알 수 있었다. 또한, 말뚝직경이 클수록 전체지지력에 대한 내주면마찰력과 순단면적의 선단지지력의 합의 비가 감소하는 것으로 나타났다. 그리고 말뚝의 폐색율을 정량화하기 위해 시험말뚝의 incremental filling ratio(IFR)를 측정하여 분석한 결과, SPT의 N값과 상관관계가 있는 것으로 나타났다.

• Geomechanics and Engineering
• /
• 제24권4호
• /
• pp.389-397
• /
• 2021

Pile foundation is a typical form of bridge foundation and viaduct, and large-diameter rock-socketed piles are typically adopted in bridges with long span or high piers. To investigate the effect of a mountain slope with a deep overburden layer on the bearing characteristics of large-diameter rock-socketed piles, four centrifuge model tests of single piles on different slopes (0°, 15°, 30° and 45°) were carried out to investigate the effect of slope on the bearing characteristics of piles. In addition, three pile group tests with different slope (0°, 30° and 45°) were also performed to explore the effect of slope on the bearing characteristics of the pile group. The results of the single pile tests indicate that the slope with a deep overburden layer not only accelerates the drag force of the pile with the increasing slope, but also causes the bending moment to move down owing to the increase in the unsymmetrical pressure around the pile. As the slope increases from 0° to 45°, the drag force of the pile is significantly enlarged and the axial force of the pile reduces to beyond 12%. The position of the maximum bending moment of the pile shifts downward, while the magnitude becomes larger. Meanwhile, the slope results in the reduction in the shaft resistance of the pile, and the maximum value at the front side of the pile is 3.98% less than at its rear side at a 45° slope. The load-sharing ratio of the tip resistance of the pile is increased from 5.49% to 12.02%. The results of the pile group tests show that the increase in the slope enhances the uneven distribution of the pile top reaction and yields a larger bending moment and different settlements on the pile cap, which might cause safety issues to bridge structures.

• Steel and Composite Structures
• /
• 제44권1호
• /
• pp.81-89
• /
• 2022

The purposes of the present work it to study the effect of shear deformation on the static post-buckling response of simply supported functionally graded (FGM) axisymmetric beams based on classical, first-order, and higher-order shear deformation theories. The behavior of postbuckling is introduced based on geometric nonlinearity. The material properties of functionally graded materials (FGM) are assumed to be graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents. The equations of motion and the boundary conditions derived using Hamilton's principle. This article compares and addresses the efficiency, the applicability, and the limits of classical models, higher order models (CLT, FSDT, and HSDT) for the static post-buckling response of an asymmetrically simply supported FGM beam. The amplitude of the static post-buckling obtained a solving the nonlinear governing equations. The results showing the variation of the maximum post-buckling amplitude with the applied axial load presented, for different theory and different parameters of material and geometry. In conclusion: The shear effect found to have a significant contribution to the post-buckling behaviors of axisymmetric beams. As well as the classical beam theory CBT, underestimate the shear effect compared to higher order shear deformation theories HSDT.

• 한국강구조학회 논문집
• /
• 제15권1호
• /
• pp.1-8
• /
• 2003

콘크리트의 가격이 상대적으로 높고 콘크리트 부재의 중량이 중요시되는 곳에서 중공 기둥을 사용하는 것이 경제적이다. 낮은 축력비와 적당한 종방향 철근비에서의 중공기둥은 원형 R.C 기둥과 유사한 휨강도와 연성능력을 갖는다. 그러나 높은 종방향 철근비와 축력비를 갖는 중공기둥 안쪽면에서의 구속력 부족으로 인한 압괴로 취성적인 거동을 보인다. 그래서 중공기둥의 안쪽면에 강관을 삽입한다면 기둥의 취성적인 거동을 방지할 수 있다. 본 연구에서는 콘크리트 교각의 내부에 강관을 삽입하여, 재료비의 절감과 중량의 감소 및 중공교각의 연성을 증가시키고, 이의 해석을 위해 강관의 삽입효과를 나타낼 수 있는 해석 프로그램을 개발하여, 상용 프로그램의 원형기둥 및 중공기둥의 해석치와 비교하여 타당성을 입증하였다. 휨강도와 연성을 표현하기 위해서는 모멘트-곡률 해석법이 사용되었으며, 콘크리트의 구속효과를 나타내기 위해 Mander의 통합된 콘크리트 모델이 사용되었다. 이러한 결과를 토대로 하여 매개변수 해석을 수행하여 강관 보강 중공 R.C 기둥의 거동특성을 연구하였다.