• 한국해양공학회지
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• 제20권6호
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• pp.88-92
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• 2006

Large-scale model tests of welded topside joints were carried out to observe the fatigue behavior of API 2W Gr.50 steel produced by POSCO. The fatigue crack behaviors for various loading conditions were measured and investigated around the critical joint sections. The experimental results have been verified with numerical approaches and also compared with the AWS D1.1 and DnV RP-C203 design curves. The large-scale experiment models were fabricated, based on the actual operating east area fixed platform. The dimensions of the models were slightly modified to accommodate the test facilities and capacities. The fatigue test was carried out having ${\Delta}Q$ of T1=705.6kN, T2=749.7kN and T3=793.8kN. The three specimens were statically loaded 20 times, with various loadings of about 50kN intervalsbetween the maximum and minimum loads required in the fatigue tests. This loading removed the residual stress in the specimen before the fatigue tests. The topside joint crack was initiated from the brace heel, where the maximum tensile stress occurred. The API 2W Gr.50 steel satisfied the AWS D1.1 detail category C and DnV RP-C203 detail category F ${\Delta}S-N$ curve.

• Structural Engineering and Mechanics
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• 제64권5호
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• pp.621-640
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• 2017

This paper reports the numerical investigation conducted to study the influence of Local-Distortional (L-D) interaction mode buckling on post buckling strength erosion in fixed ended lipped channel cold formed steel columns. This investigation comprises of 81 column sections with various geometries and yield stresses that are carefully chosen to cover wide range of strength related parametric ratios like (i) distortional to local critical buckling stress ratio ($0.91{\leq}F_{CRD}/F_{CRL}{\leq}4.05$) (ii) non dimensional local slenderness ratio ($0.88{\leq}{\lambda}_L{\leq}3.54$) (iii) non-dimensional distortional slenderness ratio ($0.68{\leq}{\lambda}_D{\leq}3.23$) and (iv) yield to non-critical buckling stress ratio (0.45 to 10.4). The numerical investigation is carried out by conducting linear and non-linear shell finite element analysis (SFEA) using ABAQUS software. The non-linear SFEA includes both geometry and material non-linearity. The numerical results obtained are deeply analysed to understand the post buckling mechanics, failure modes and ultimate strength that are influenced by L-D interaction with respect to strength related parametric ratios. The ultimate strength data obtained from numerical analysis are compared with (i) the experimental tests data concerning L-D interaction mode buckling reported by other researchers (ii) column strength predicted by Direct Strength Method (DSM) column strength curves for local and distortional buckling specified in AISI S-100 (iii) strength predicted by available DSM based approaches that includes L-D interaction mode failure. The role of flange width to web depth ratio on post buckling strength erosion is reported. Then the paper concludes with merits and limitations of codified DSM and available DSM based approaches on accurate failure strength prediction.

• 한국구조물진단유지관리공학회 논문집
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• 제20권1호
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• pp.72-84
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• 2016

종래 브레이스시스템은 횡력저항 및 층변위제어에 효율적이며 골조물량 감소에 따른 경제성이 향상되어 일반적인 강구조 횡력저항시스템으로 적용되고 있다. 그러나 압축측에서 항복응력에 도달하기 전 가새의 좌굴이 발생하여 충분한 내력을 발휘하지 못하고, 내력열화형의 이력거동으로 불안정상태가 된다. 좌굴에 의한 내력저하 개선시스템으로 중심재를 구속하여 좌굴방지가 가능한 비좌굴가새는 심재의 항복 이후에도 안정적인 이력특성을 나타내어 종래 브레이스에 비하여 에너지흡수능력이 우수하다. 최근 10년간 미국, 일본 및 대만에서 매우 다양한 형상의 비좌굴가새가 제안되었으나, 기존의 실험연구에서는 그 형상이 매우 제한적인 경향을 보이고 있다. 본 연구에서는 조립형 Precast RC 보강재를 가지는 비좌굴가새를 제작하고 이력특성을 평가하기 위한 부재실험을 수행하였다. 또한 실험결과를 AISC(2005)의 요구조항과 비교하였다.

• 한국전산구조공학회논문집
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• 제23권2호
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• pp.217-225
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• 2010

현재 국내에서 이루어지는 대부분의 강교량 설계는 종전의 결정론적인 안전율을 사용하는 허용응력설계법에 기초하고 있다. 그러나 국제적인 경향은 확률, 통계 및 신뢰성공학의 개념에 기반을 둔 합리적이며 경제적인 설계가 가능한 한계상태설계법이 설계법의 표준으로서 보편화되고 있는 실정이다. 이 논문에서는 강교량 설계기술의 국제적 경쟁력 확보를 위해 국내 환경여건과 지역적 특성이 고려된 강교량의 하중저항계수설계법 제정을 위한 기초연구의 일환으로, 특히 사용빈도가 상대적으로 높은 폐단면 강박스거더교에 대하여 AASHTO-LRFD 규정을 적용한 시험설계를 수행하였다. 다양한 단면변화에 따른 시험설계로부터 폐단면 강박스거더교의 LRFD 설계시 고려해야 하는 제반문제에 대하여 고찰하였으며, 계산의 효율성 확보와 오류방지를 위하여 Excel-기반 설계검토 프로그램을 개발하여 시험설계에 적용하였다. 또한 LRFD 설계 단면의 신뢰성해석을 통하여 대상교량의 정량적인 안전도수준을 평가하고 실제 적용된 목표 신뢰도지수가 만족되는지를 확인함으로써 이 연구에서 적용된 절차와 방법의 타당성을 검증하였다.

• 대한토목학회논문집
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• 제33권1호
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• pp.81-92
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• 2013

HSB를 적용한 플레이트거더의 압축플랜지 국부좌굴을 고려한 극한휨강도를 비선형 유한요소해석으로 분석하였다. 압축플랜지의 비탄성 국부좌굴 또는 소성항복이 휨강도를 지배하는 압축플랜지 세장비를 갖도록 해석대상 강거더를 선정하였다. HSB600 및 HSB800 강재로 제작된 균질단면 강거더와 HSB800 강재와 SM570-TMC 강재를 함께 적용한 하이브리드 단면을 고려하였으며, 일반강재와의 비교를 위하여 SM490-TMC 강거더에 대한 해석도 수행하였다. 비선형 유한요소해석 시에는 플랜지와 복부판을 쉘요소로 강재는 탄소성-변형경화 재료로 모델링하였으며, 초기변형과 단면의 잔류응력을 고려하였다. 비선형 유한요소해석 결과와 기존 문헌의 실험결과를 비교하여 유한요소 해석결과를 검증하였으며, 초기변형과 잔류응력이 극한휨강도에 미치는 영향을 분석하였다. 총 60개 해석대상 강거더의 휨극한강도를 유한요소해석으로 구하고, 도로교설계기준, AASHTO LRFD와 Eurocode 3의 설계규정으로 구한 휨강도와 비교하여 이들 규정의 HSB 강거더에 대한 적용성을 검토하였다.

• Advances in Computational Design
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• 제1권1호
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• pp.1-25
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• 2016

Domes are architectural and elegant structures which cover a vast area with no interrupting columns in the middle, and with suitable shapes can be also economical. Domes are built in a wide variety of forms and specialized terms are available to describe them. According to their form, domes are given special names such as network, lamella, Schwedler, ribbed, and geodesic domes. In this paper, an optimum topology design algorithm is performed using the enhanced colliding bodies optimization (ECBO) method. The network, lamella, ribbed and Schwedler domes are studied to determine the optimum number of rings, the optimum height of crown and tubular sections of these domes. The minimum volume of each dome is taken as the objective function. A simple procedure is defined to determine the dome structures configurations. This procedure includes calculating the joint coordinates and element constructions. The design constraints are implemented according to the provision of LRFD-AISC (Load and Resistance Factor Design-American Institute of Steel Constitution). The wind loading act on domes according to ASCE 7-05 (American Society of Civil Engineers). This paper will explore the efficiency of various type of domes and compare them at the first stage to investigate the performance of these domes under different kind of loading. At the second stage the wind load on optimum design of domes are investigated for Schwedler dome. Optimization process is performed via ECBO algorithm to demonstrate the effectiveness and robustness of the ECBO in creating optimal design for domes.

• Earthquakes and Structures
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• 제7권4호
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• pp.463-484
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• 2014

Solid piers with a rounded rectangular cross-section are widely used in railway bridges for high-speed trains in China. Compared to highway bridge piers, these railway bridge piers have a larger crosssection and less steel reinforcement. Existing material models cannot accurately predict the seismic behavior of this kind of railway bridge piers. This is because only a few parameters, such as axial load, longitudinal and transverse reinforcement, are taken into account. To enable a better understanding of the seismic behavior of this type of bridge pier, a simultaneous influence of the various parameters, i.e. ratio of height to thickness, axial load to concrete compressive strength ratio and longitudinal to transverse reinforcements, on the failure characteristics, hysteresis, skeleton curves, and displacement ductility were investigated. In total, nine model piers were tested under cyclic loading. The hysteretic response obtained from the experiments is compared with that obtained from numerical studies using existing material models. The experimental data shows that the hysteresis curves have significantly pinched characteristics that are associated with small longitudinal reinforcement ratios. The displacement ductility reduces with an increase in ratio of axial load to concrete compressive strength and longitudinal reinforcement ratio. The experimental results are largely in agreement with the numerical results obtained using Chang-Mander concrete model.

• 한국산학기술학회논문지
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• 제17권1호
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• pp.298-303
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• 2016

수직 및 수평의 원형단면 강관으로 구성된 공간프레임 타워는 강재량을 줄이면서도 풍하중의 영향을 완화시킬 수 있는 장점으로 다양한 목적으로 널리 적용되고 있다. 이러한 공간프레임 타워를 하나의 타워구조로 거동하게 하기 위해서는 수직 강관과 수평 강관의 연결부인 강관조인트의 강도 확보가 중요하다. 본 연구에서는 압축과 휨이 동시에 작용하는 강관 T조인트의 강도평가를 수행하였다. AISC, Eurocode3, ISO 19902의 3가지 강관조인트 설계기준을 검토하고, 주강관과 지강관의 세장비를 주요 매개변수로 한 비선형 유한요소해석을 통하여 축력과 모멘트에 대한 극한강도 상호작용을 설계식으로 제안하였다.

• Computers and Concrete
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• 제29권4호
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• pp.219-235
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• 2022

Strengthening slender reinforced concrete (RC) columns is a challenge. They are susceptible to overall buckling that induces bending moment and axial compression. This study presents the precise three-dimensional finite element modeling of slender RC columns strengthened with fiber-reinforced polymer (FRP) composites sheets with various patterns under concentric or eccentric compression. The slenderness ratio λ (height/width ratio) of the studied columns ranged from 15 to 35. First, to determine the optimal modeling procedure, nine alternative nonlinear finite element models were presented to simulate the experimental behavior of seven FRP-strengthened slender RC columns under eccentric compression. The models simulated concrete behavior under compression and tension, FRP laminate sheets with different fiber orientations, crack propagation, FRP-concrete interface, and eccentric compression. Then, the validated modeling procedure was applied to simulate 58 FRP-strengthened slender RC columns under compression with minor eccentricity to represent the inevitable geometric imperfections. The simulated columns showed two cross sections (square and rectangular), variable λ values (15, 22, and 35), and four strengthening patterns for FRP sheet layers (hoop H, longitudinal L, partial longitudinal L_w, and longitudinal coupled with hoop LH). For λ=15-22, pattern L showed the highest strengthening effectiveness, pattern L_w showed brittle failure, steel reinforcement bars exhibited compressive yielding, ties exhibited tensile yielding, and concrete failed under compression. For λ>22, pattern L_w outperformed pattern L in terms of the strengthening effectiveness relative to equivalent weight of FRP layers, steel reinforcement bars exhibited crossover tensile strain, and concrete failed under tension. Patterns H and LH (compared with pattern L) showed minor strengthening effectiveness.

• 한국재료학회지
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• 제32권3호
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• pp.168-179
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• 2022

Microbiologically Influenced Corrosion (MIC) occurring in underground buried pipes of API 5L X65 steel was investigated. MIC is a corrosion phenomenon caused by microorganisms in soil; it affects steel materials in wet atmosphere. The microstructure and mechanical properties resulting from MIC were analyzed by OM, SEM/EDS, and mapping. Corrosion of pipe cross section was composed of ① surface film, ② iron oxide, and ③ surface/internal microbial corrosive by-product similar to surface corrosion pattern. The surface film is an area where concentrations of C/O components are on average 65 %/16 %; the main components of Fe Oxide were measured and found to be 48Fe-42O. The MIC area is divided into surface and inner areas, where high concentrations of N of 6 %/5 % are detected, respectively, in addition to the C/O component. The high concentration of C/O components observed on pipe surfaces and cross sections is considered to be MIC due to the various bacteria present. It is assumed that this is related to the heat-shrinkable sheet, which is a corrosion-resistant coating layer that becomes the MIC by-product component. The MIC generated on the pipe surface and cross section is inferred to have a high concentration of N components. High concentrations of N components occur frequently on surface and inner regions; these regions were investigated and Na/Mg/Ca basic substances were found to have accumulated as well. Therefore, it is presumed that the corrosion of buried pipes is due to the MIC of the NRB (nitrate reducing bacteria) reaction in the soil.