• 한국구조물진단유지관리공학회 논문집
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• 제7권3호
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• pp.157-165
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• 2003

섬유시트들로 보강된 철근 콘크리트보에서 섬유시트들의 정당한 파단변형률을 평가하기 위해 적층수를 달리한 120개의 섬유시트 인장시험편과 72개의 섬유보강 콘크리트보들에 대한 실험적 연구를 수행하였다. 철근콘크리트보는 세 종류의 인장철근비를 선택하였다. 인장시험에 의한 섬유시트 파단변형률은 섬유시트 적층수에 관계없이 기술자료에서 주어진 값보다 다소 낮게 나타났으며, 보에 부착된 섬유시트들의 파단변형률은 적층수가 증가할 때 감소하는 경향을 보여주었다. 본 연구에서는 이들 결과를 바탕으로 섬유시트들의 파단변형률을 평가하였다.

• 한국철도학회논문집
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• 제19권6호
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• pp.755-764
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• 2016

이 논문에서는, 변위-변형률 관계로부터 변위를 추정하는 선행 연구의 현장 적용성을 검토하기 위하여 실교량에 대한 현장재하실험을 실시하고, 그 결과에 대해 고찰하였다. 3경간 연속 IPC 거더 도로교 및 강합성 박스거더 경량전철 교량에 변위계 및 변형률 게이지를 부착하고, 재하차량에 의한 응답을 측정하였다. 현장재하실험을 통해 얻어진 실측 변형률을 변위로 변환시키기 위해 변위와 변형률의 관계를 이용하였다. 해석적인 방법으로 변위-변형률 관계를 도출하기 위해 연구대상 교량을 격자구조로 모형화하고 구조해석을 수행하였다. 연구결과, 사전 구조해석에 의해 얻어진 변위-변형률 관계와 실측 변형률을 이용하여 변위를 추정하여도 실용상 만족할 만한 결과를 도출할 수 있었다. 이 연구 결과는 향후 계측이 어려운 환경하에 놓여 있는 교량의 변위 측정에 널리 활용될 수 있을 것으로 기대된다.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2002년도 춘계학술대회 논문집
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• pp.271-276
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• 2002

Continuous loading is applied the sample has been developed to overcome some of the problems associated with the incremental loading consolidation test. Therefore, it is able to reduce the test time and provide a well defined the curve of effective stress versus strain due to continuous stress-strain points. Also, the constant rate of strain consolidation(CRSC) test has been accepted widely as a standard method in foreign countries because of its many advantages. However, in Korea the CRSC test has not been used in engineering practice and experimentally verified. Because there is not a precise criterion of testing despite consolidation characteristics are influenced on strain rate and Pore pressure ratio. Consequently, it is difficult to apply in engineering practice. In this study, artificial neural networks are applied to the estimation of th proper strain rate and pore pressure ratio of the CRSC test. This study shows the possibility of utilizing the artificial neural networks model of estimation of the strain rate and pore pressure ratio in the CRSC test.

• Smart Structures and Systems
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• 제20권1호
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• pp.11-22
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• 2017

The long-term effect of ambient temperature on bridge strain is an important and challenging problem. To investigate this issue, one year data of strain and ambient temperature of a long-span cable-stayed bridge is studied in this paper. The measured strain-time history is decomposed into two parts to obtain the strains due to vehicle load and temperature alone. A linear regression model between the temperature and the strain due to temperature is established. It is shown that for every $1^{\circ}C$ increase in temperature, the stress is increased by 0.148 MPa. Furthmore, the extreme value distributions of the strains due to vehicle load, temperature and the combination effect of them during the remaining service period are estimated by the average conditional exceedance rate approach. This approach avoids the problem of declustering of data to ensure independence. The estimated results demonstrate that the 95% quantile of the extreme strain distribution due to temperature is up to $1.488{\times}10^{-4}$ which is 2.38 times larger than that due to vehicle load. The study also indicates that the estimated extreme strain can reflect the long-term effect of temperature on bridge strain state, which has reference significance for the reliability estimation and safety assessment.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 춘계 학술발표회 초청강연 및 논문집
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• pp.494-504
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• 2008

Successful design, construction and maintenance of NATM tunnel demands prediction, control, stability estimation and monitoring of surface settlement, gradient and ground displacement with high accuracy. Back analysis using measured data and forward analysis have been and are indispensable tools to achieve this goal. Sakurai provided the hazard warning levels for assessing the stability of tunnels using the relation of critical strain and apparent Young's modulus. This paper performed the estimation of tunnel stability on construction. Firstly, the apparent Young's modulus concept and back analysis method is introduced for the assessment of tunnel safety during excavation a brief framework. Secondly, this paper deals with case study using "Apparent Young's modulus" and "Back analysis" for the purpose of estimating the stability of NATM tunnel in Korea. Finally, a general method that can be estimated the tunnel stability discussed by a flow chart.

• Structural Engineering and Mechanics
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• 제47권6호
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• pp.757-771
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• 2013

We present a semi-rigid connection estimation method by using cross modal strain energy method. While rigid or pinned assumptions are adopted for steel frames in traditional modeling via finite element method, the actual behavior of the connections is usually neither. Semi-rigid joints enable connections to be modeled as partially restrained, which improves the quality of the model. To identify the connection stiffness and update the FE model, a newly-developed cross modal strain energy (CMSE) method is extended to incorporate the connection stiffness estimation. Meanwhile, the relations between the correction coefficients for the CMSE method are derived, which enables less modal information to be used in the estimation procedure. To illustrate the capability of the proposed parameter estimation algorithm, a four-story frame structure is demonstrated in the numerical studies. Several cases, including Semi-rigid joint(s) on single connection and on multi-connections, without and with measurement noise, are investigated. Numerical results indicate that an excellent updating is achievable and the connection stiffness can be estimated by CMSE method.

• Smart Structures and Systems
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• 제20권3호
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• pp.385-396
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• 2017

The recent advancements in sensing technologies allow us to record measurements from target structures at multiple locations and with relatively high spatial resolution. Such measurements can be used to develop data-driven methodologies for condition assessment, control, and health monitoring of target structures. One of the state-of-the-art technologies, Fiber Optic Strain Sensors (FOSS), is developed at NASA Armstrong Flight Research Center, and is based on Fiber Bragg Grating (FBG) sensors. These strain sensors are accurate, lightweight, and can provide almost continuous strain-field measurements along the length of the fiber. The strain measurements can then be used for real-time shape-sensing and operational load-estimation of complex structural systems. While several works have demonstrated the successful implementation of FOSS on large-scale real-life aerospace structures (i.e., airplane wings), there is paucity of studies in the literature that have investigated the potential of extending the application of FOSS into civil structures (e.g., tall buildings, bridges, etc.). This work assesses the feasibility of using FOSS to predict operational loads (e.g., wind loads) on chain-like structures. A thorough investigation is performed using analytical, computational, and experimental models of a 4-story steel building test specimen, developed at the University of Southern California. This study provides guidelines on the implementation of the FOSS technology on building-like structures, addresses the associated technical challenges, and suggests potential modifications to a load-estimation algorithm, to achieve a robust methodology for predicting operational loads using strain-field measurements.

• 한국구조물진단유지관리공학회 논문집
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• 제16권1호
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• pp.99-109
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• 2012

이 연구에서는 변형률계를 사용하여 변위를 추정하는 이론식을 제안 및 검증하고 하중 작용점과 크기를 추정하여 강재보의 건전도 평가 시스템을 개발하고자 하였다. 실험결과 160kN(항복하중의 56%)가력시 최대처짐 점에서 변형률계를 사용하여 얻는 처짐과 변위계의 측정처짐과의 오차율이 2%이내로 나타났으며 하중작용점 및 크기의 추정도 오차율1% 이내로 나타났다. 이를 통해 변형률계로 강재보의 변위 및 하중을 계측 할 수 있으며 나아가 변위계와 하중계의 생략으로 경제적인 센서설계를 할 수 있다. Lab VIEW로 구현된 건전도 평가 프로그램은 측정된 데이터가 일정 범위(강도 한계상태, 사용성 한계상태, 항복변형률)를 넘어설 때 단계별 경고를 발생하였고 변형률계 만으로 사용성한계상태와 강도한계상태를 동시에 모니터링 할 수 있었다.

• Structural Engineering and Mechanics
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• 제88권1호
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• pp.83-94
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• 2023

An accurate and highly efficient inverse element labelled iPCB is developed based on the inverse finite element method (iFEM) for real-time shape estimation of plane-curved structures (such as arch bridges) utilizing onboard strain data. This inverse problem, named shape sensing, is vital for the design of smart structures and structural health monitoring (SHM) procedures. The iPCB formulation is defined based on a least-squares variational principle that employs curved Timoshenko beam theory as its baseline. The accurate strain-displacement relationship considering tension-bending coupling is used to establish theoretical and measured section strains. The displacement fields of the isoparametric element iPCB are interpolated utilizing nonuniform rational B-spline (NURBS) basis functions, enabling exact geometric modelling even with a very coarse mesh density. The present formulation is completely free from membrane and shear locking. Numerical validation examples for different curved structures subjected to different loading conditions have been performed and have demonstrated the excellent prediction capability of iPCBs. The present formulation has also been shown to be practical and robust since relatively accurate predictions can be obtained even omitting the shear deformation contributions and considering polluted strain measures. The current element offers a promising tool for real-time shape estimation of plane-curved structures.

• 대한기계학회논문집A
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• 제27권2호
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• pp.239-246
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• 2003

This paper proposes engineering estimation equations of elastic-plastic J and COD fur axial through-wall cracked pipes under internal pressure. Based on detailed 3-D FE results based on deformation plasticity, the plastic influence functions for fully plastic J and COD solutions are tabulated as a function of the mean radius-to-thickness ratio, the normalized crack length. and the strain hardening. Based on these results, the GE/EPRI-type J and COD estimation equations are proposed and validated against the 3-D FE results based on deformation plasticity. For more general application to general stress-strain laws or to complex loading, the developed GE/EPRI-type solutions are re-formulated based on the reference stress concept. Such a reformulation provides simpler equations for J and COD, which are then further extended to combined internal pressure and bending. The proposed reference stress based J and COD estimation equations are compared with elastic-plastic 3-D FE results using actual stress-strain data for Type 316 stainless steels. The FE results for both internal pressure cases and combined internal pressure and bending cases compare very well with the proposed J and COD estimations.