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Nonlinear inelastic analysis of steel-concrete composite beam-columns using the stability functions
박정웅,김승억 국제구조공학회 2008 Structural Engineering and Mechanics, An Int'l Jou Vol.30 No.6
In this study, a flexibility-based finite element method considering geometric and material nonlinearities is developed for analyzing steel-concrete frame structures. The stability functions obtained from the exact buckling solution of the beam-column subjected to end moments are used to accurately capture the second-order effects. The proposed method uses the force interpolation functions, including a moment magnification due to the axial force and lateral displacement. Thus, only one element per a physical member can account for the interaction between the bending moment and the axial force in a rational way. The proposed method applies the Newton method based on the load control and uses the secant stiffness method, which is computationally both efficient and stable. According to the evaluation result of this study, the proposed method consistently well predicts the nonlinear inelastic behavior of steel-concrete composite frames and gives good efficiency.
Force transfer mechanisms for reliable design of reinforced concrete deep beams
박정웅,김승억 국제구조공학회 2008 Structural Engineering and Mechanics, An Int'l Jou Vol.30 No.1
In this paper, a strut-and-tie model approach has been proposed to directly calculate the amount of reinforcements in deep beams, and the force transfer mechanisms for this approach were investigated using linear finite element analysis. The proposed strut-and-tie model provides quite similar force transfer mechanisms to the results of linear finite element analysis for the 28 deep beams. The loadcarrying capacities calculated from the proposed method are both accurate and conservative with little scatter or trends for the 214 deep beams. The deep beams have different concrete strengths including highstrength, various combinations of web reinforcements, and wide range of and a/d ratios. Good accuracy was also obtained using VecTor2, nonlinear finite element analysis tool based on the Modified Compression Field Theory. Since the proposed method provides a safe and reliable means for design of deep beams, this can serve to improve design provisions in future adjustments and development of design guidelines.
Structural and Optical Properties of Bandgap Engineered Bismuth Titanate by Cobalt Doping
박정웅 대한금속·재료학회 2013 METALS AND MATERIALS International Vol.19 No.6
The wide band gap of complex oxides is one of the major obstacles limiting their use in photovoltaic cells. To tune the bandgap of complex oxides, nano-sized bismuth titanate-based powders were synthesized by conventional solid reaction method. X-ray diffraction patterns confirmed that all powders were crystallized in an orthorhombic structure. The photoluminescence signal shows that there was no contribution to the optical bandgap from unwanted oxygen vacancy. The UV-vis absorption spectra of LaCo-BiT powder showed that the optical bandgap drastically decreased from 3.1eV to 2.5eV, while those of of BiT and La- BiT showed change in the optical bandgap. From these observations, we could experimentally confirm that cobalt atoms were responsible for the modification of the electronic structure in BiT-based oxides. This approach to controlling the bandgap could be applied to other complex oxides materials, such as other types of Aurivillius phase materials for use in emerging oxide optoelectronic and energy applications.
박정웅,안규백 대한용접·접합학회 2021 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2021 No.5
선박 및 해양구조물이 점차 고강도화될수록 구조 취성파괴에 대한 안전성은 감소된다. 특히 후판 용접부의 취성파괴에 대한 안전성은 더욱 중요시되고 있어 다양한 방법으로 용접부 설계에 대한 규정이 제정되고 있다. 이러한 취성파괴에 대한 평가를 하기 위해서는 먼저 모재에 대한 취성평가가 필요하다. 모재에 대한 취성평가는 실험에 의해 다양하게 제시되고 있으나 아직 해석적으로 구현하지 못하고 있다. 모재에 대한 취성파괴진전해석은 충격에 의한 균열을 촉진 및 진전 그리고 파괴역학을 포함한 광범위한 지식이 필요하다. 본 연구에서는 모재의 두께에 따른 후판의 균열진전해석을 수행하기 위해 모재실험에 의해 구한 KIC값을 이용하여 균열진전판단을 기준으로 설정하고 균열진전해석을 실시하였다. 균열진전해석결과는 균열진전 실험값과 비교하여 균열진전해석 결과의 신뢰성을 판단하였다.