• Interaction and multiscale mechanics
• /
• 제2권1호
• /
• pp.69-89
• /
• 2009

Reinforced and prestressed concrete (RC and PC) thin walls are crucial to the safety and serviceability of structures subjected to shear. The shear strengths of elements in walls depend strongly on the softening of concrete struts in the principal compression direction due to the principal tension in the perpendicular direction. The past three decades have seen a rapid development of knowledge in shear of reinforced concrete structures. Various rational models have been proposed that are based on the smeared-crack concept and can satisfy Navier's three principles of mechanics of materials (i.e., stress equilibrium, strain compatibility and constitutive laws). The Cyclic Softened Membrane Model (CSMM) is one such rational model developed at the University of Houston, which is being efficiently used to predict the behavior of RC/PC structures critical in shear. CSMM for RC has already been implemented into finite element framework of OpenSees (Fenves 2005) to come up with a finite element program called Simulation of Reinforced Concrete Structures (SRCS) (Zhong 2005, Mo et al. 2008). CSMM for PC is being currently implemented into SRCS to make the program applicable to reinforced as well as prestressed concrete. The generalized program is called Simulation of Concrete Structures (SCS). In this paper, the CSMM for RC/PC in material scale is first introduced. Basically, the constitutive relationships of the materials, including uniaxial constitutive relationship of concrete, uniaxial constitutive relationships of reinforcements embedded in concrete and constitutive relationship of concrete in shear, are determined by testing RC/PC full-scale panels in a Universal Panel Tester available at the University of Houston. The formulation in element scale is then derived, including equilibrium and compatibility equations, relationship between biaxial strains and uniaxial strains, material stiffness matrix and RC plane stress element. Finally the formulated results with RC/PC plane stress elements are implemented in structure scale into a finite element program based on the framework of OpenSees to predict the structural behavior of RC/PC thin-walled structures subjected to earthquake-type loading. The accuracy of the multiscale modeling technique is validated by comparing the simulated responses of RC shear walls subjected to reversed cyclic loading and shake table excitations with test data. The response of a post tensioned precast column under reversed cyclic loads has also been simulated to check the accuracy of SCS which is currently under development. This multiscale modeling technique greatly improves the simulation capability of RC thin-walled structures available to researchers and engineers.

• 산업경영시스템학회지
• /
• 제31권1호
• /
• pp.41-48
• /
• 2008

Enhanced machine reliability has dramatically reduced the rate and number of railway accidents but for further reduction human error should be considered together that accounts for about 20% of the accidents. Therefore, the objective of this study was to suggest a new taxonomy of performance shaping factors (PSFs) that could be utilized to identify the causes of a human error associated with railway accidents. Four categories of human factor, task factor, environment factor, and organization factor and 14 sub-categories of physical state, psychological state, knowledge/experience/ability, information/communication, regulation/procedure, specific character of task, infrastructure, device/MMI, working environment, external environment, education, direction/management, system/atmosphere, and welfare/opportunity along with 131 specific factors was suggested by carefully reviewing 8 representative published taxonomy of Casualty Analysis Methodology for Maritime Operations (CASMET), Cognitive Reliability and Error Analysis Method (CREAM), Human Factors Analysis and Classification System (HFACS), Integrated Safety Investigation Methodology (ISIM), Korea-Human Performance Enhancement System (K-HPES), Rail safety and Standards Board (RSSB), $TapRoot^{(R)}$, and Technique for Retrospective and Predictive Analysis of Cognitive Errors (TRACEr). Then these were applied to the case of the railway accident occurred between Komo and Kyungsan stations in 2003 for verification. Both cause decision chart and why-because tree were developed and modified to aid the analyst to find causal factors from the suggested taxonomy. The taxonomy was well suited so that eight causes were found to explain the driver's error in the accident. The taxonomy of PSFs suggested in this study could cover from latent factors to direct causes of human errors related with railway accidents with systematic categorization.

• 한국광학회지
• /
• 제35권4호
• /
• pp.175-183
• /
• 2024

근래 광통신, 광센서, 양자광학 등의 다양한 연구 분야에서 광IC 소자를 이용한 광신호 처리 연구가 활발히 진행되고 있으며, 광IC 제작에 이용되는 재료들 중 특히 폴리머 재료는 고유의 특징을 바탕으로 폭넓게 연구개발되고 있다. 폴리머 기반 광IC 소자를 제작하기 위해서는 광도파로 단면 구조를 정확히 제작하기 위한 제작 공정을 확립하는 것이 중요하며, 특히 안정적인 소자 특성을 유지하고 대량생산 시의 수율을 높이기 위해서는 재현성이 높고 오차 수용 범위가 넓은 공정과 제작 조건을 설정하는 것이 필요하다. 본 연구에서는 원자층 증착(atomic layer deposition, ALD) 공정을 도입하여 폴리머 광도파로 소자를 효율적으로 제작할 수 있는 방법을 제안하였으며, 기존의 포토 레지스트나 금속 박막 증착을 이용하는 방법에 비해 광도파로 코어 형상을 더욱 정밀하게 제작할 수 있음을 확인하였다. 본 연구에서는 ALD 공정을 도입하여 코어의 크기가 1.8 × 1.6 ㎛²인 폴리이미드 광도파로를 제작하여 광도파로의 손실을 측정하고, 이와 함께 광파워 분배기인 다중모드 간섭(multi-mode interference) 광도파로 소자를 제작하여 특성을 측정하였다. 이때 기존의 제작과정에서 문제시되었던 에칭 마스크 층의 크랙 현상은 나타나지 않았으며, 광도파로 패턴 단면의 수직성도 우수하였고, 도파로의 전파손실 또한 1.5 dB/cm 이하로 양호하였다. 이로써 ALD 공정이 대량생산을 위한 폴리머 광소자 제작 공정에 적합한 방법임을 확인하였다.