• Computational Structural Engineering
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• v.29 no.2
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• pp.12-17
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• 2016

본 기사에서 대형 비정형 건축물의 시공 중 자동 모니터링 사례를 소개하였다. 소개한 사례에서는 무선 자동 계측 시스템을 이용하여 변형률계, 경사계, 변위계 등이 총 88개 설치되어 약 13개월 동안 장기 모니터링이 수행되었다. 무선 자동 계측시스템은 장기간의 데이터를 확보하고 데이터 간의 상관성 및 이력분석을 용이하게 하였다. 이를 통해 대상 구조물의 시공 중 안전성 및 안정성을 확보하고, 정밀 시공을 구현하는데 기여할 수 있었다.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05d
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• pp.300-305
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• 1996

격납건물용 콘크리트는 그 배합이 변경될 때마다 장기거동 특성시험 (크립, 건조수축, 탄성계수, 포아슨비, 열팽창계수 등)을 수행하여 그 시험결과를 설계회사가 텐돈의 인장 작업전까지 검토하게 되어 있으나, 이 중 크립(Creep)시험은 특성상 장기간이 소요되는 관계로 적시에 시험결과를 제공할 수 없는 경우가 종종 발생한다. 본 연구에서는 이 경우 유사한 배합비를 가진 콘크리트와의 물성치 대비 및 크립 변형율의 예측을 통하여 실험치가 허용치 이내에 드는 가를 분석하므로써, 사용된 콘크리트의 크립거동에 대한 안정성을 검토하였다.

• Journal of the Korea Concrete Institute
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• v.13 no.6
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• pp.629-636
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• 2001

To apply the research results to the design and the construction of the high rise buildings, long-term behavior of reinforced concrete structure have been widely studied. However, shoring and reshoring at early ages have not been considered in the most of studies. The removal of forms and shores has been dealt with one construction sequence. i.e. the deformation occurred at the early age before the removal of shore has been neglected. In this paper, two-dimensional frame analysis program for long-term behavior of reinforced concrete was developed. In the developed program, construction sequence including the settlement and the removal of shores is considered to predict axial force variation due to forms ,shores, and time-dependent concrete stiffness. Analysis results show that the time-dependent axial force of shores is reduced, and the redistributed axial force of the interior column is greater than the value by elastic analysis and that of the exterior column is smaller. In order to demonstrate the validity of this program, the test frame was constructed in sequence of the placement of concrete, form removal, reshoring, shore removal, and the application of additional load. The proposed program predicts experimental results well.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.2A
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• pp.401-409
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• 2006

This study presents basic information on the mechanical properties and long-term deformations of high-strength steel fiber reinforced concrete(HSFRC). The Influence of steel fiber on modulus of elasticity, compressive, splitting tensile and flexural strength, and drying shrinkage and creep of HSFRC are investigated, and flexural fracture toughness is evaluated. Test results show that Test results show that the effect of steel fibers on the compressive strength is negligible, and the modulus of elasticity of HSFRC increased with the increase of fiber volume fraction. And the effect of fiber volume fraction($V_f$) and aspect ratio($l_f/d_f$) on tensile strength, flexural strength and toughness is extremely prominent. It is observed that the flexural deflection corresponded to ultimate load increased with the increase of $V_f$ and $l_f/d_f$, and due to fiber arresting cracking, the shape of the descending branch of load-deflection tends towards gently. Also, the effect of addition of various amounts of fiber on the creep and shrinkage is obvious. Especially, the effect of adding fibers to high-strength concrete is more pronounced in reducing the drying shrinkage than the creep.

• Proceedings of the Korean Fiber Society Conference
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• 2001.10a
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• pp.95-99
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• 2001

토목섬유 (Geosynthetics) 중에서 사면, 옹벽 및 도로 보강을 위하여 사용되는 지오그리드는 고강력의 강도 및 적절한 신도가 필요하다. PP 또는 HDPE 의 지오그리드 등도 사용되고 있으나 creep성이 커서 장기적인 보강을 위해서는 사용에 제약을 받기도 하며, 열에 의한 변형이 쉬워 도로 시공시 변형이 발생할 수도 있다. (중략)

• Journal of the Korean Geotechnical Society
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• v.16 no.5
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• pp.149-155
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• 2000

응답변위법에서 이용되는 동지반강성계수의 적절한 평가법에 대한 제안을 하였다. 현재까지의 지진피해조사 및 장기간의 지진관측사례는 지반이 공진할 때의 변형모드가 지중구조물의 피해에 가장 직접적으로 관련이 있는 것으로 알려져 있다. 따라서, 지중구조물의 축방향의 지반의 변형모드와 그 타월 진동수를 특정하여 동지반강성계수를 평가했다. 동지반강성계수는 지반의 공진상태를 상정하고 있기 때문에 결과로써 지진파의 축방행 파장의 영향을 받지 않고, 관상구주물의 반경과 표층두께의 비, 표층두께에 대한 구조물의 매설위치, 표층지반과 기반의 임피단스비 라고 하는 3개의 무차원 변수에 의해 표현된다.

• Journal of the Korea Concrete Institute
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• v.20 no.6
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• pp.765-772
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• 2008

For RC structures, long-term deformation occurs due to the inherent characteristics, which are creep and shrinkage. In terms of serviceability, it is important to limit deflection caused by the deformation to the allowable deflection. In the recent years, various repair and strengthening methods have been used to improve performance of the existing RC structures. One of the typical methods is FRP externally bonded method (EBR). Fiber reinforced polymer (FRP) has been used worldwide as repair and strengthening materials due to its superior properties. Besides, it has to offer improved strengthening performance not only under instantaneous load but sustained load. Therefore, accurate prediction method of deflection for the RC members externally bonded with FRP under sustained load is required. In this paper, three beams were fabricated. Two beams were externally strengthened with one of CFRP plate and GFRP plate respectively. Total three beams were superimposed under sustained load of 25 kN. During 470 days, deflections at midspan were obtained. Moreover, creep coefficients and shrinkage strains were calculated by using ACI-209 code and CEB-FIP code. In order to predict the deflection of the beams, EMM, AEMM, Branson's method and Mayer's method were used. Through the experiment, it was found that the specimen with CFRP plate has the most flexural capacity and Mayer's method is the most precise method to predict total long-term deflections.

• Journal of the Korea Concrete Institute
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• v.13 no.3
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• pp.268-276
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• 2001

A numerical model for the thermal response analysis of concrete structures is suggested. The model includes the stress-strain relationship, constitutive relationship, and multiaxial failure criteria at elevated temperature conditions. Modified Saenz's model was used to describe the stress-strain relationship at high temperatures. Concrete subjected to elevated temperatures undergoes rapid strain increase and dimensional instability. In order to explain those changes in mechanical properties, a constitutive model of concrete subjected to elevated temperature is proposed. The model consists of four strain components; free thermal creep strain, stress-induced (mechanical) strain, thermal creep strain, and transient strain due to moisture effects. The failure model employs modified Drucker-Prager model in order to describe the temperature dependent multiaxial failure criteria. Some numerical analyses are performed and compared with the experimental results to verify the proposed model. According to the comparison, the suggested material model gives reliable analytical results.

• Progress in Medical Physics
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• v.25 no.3
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• pp.139-142
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• 2014

The purpose of this study was to develop a system of clinical application of reconstructed dose that includes dose reconstruction, reconstructed dose registration between fractions of treatment, and dose-volume-histogram generation and to demonstrate the system on a deformable prostate phantom. To achieve this purpose, a deformable prostate phantom was embedded into a 20 cm-deep and 40 cm-wide water phantom. The phantom was CT scanned and the anatomical models of prostate, seminal vesicles, and rectum were contoured. A coplanar 4-field intensity modulated radiation therapy (IMRT) plan was used for this study. Organ deformation was simulated by inserting a "transrectal" balloon containing 20 ml of water. A new CT scan was obtained and the deformed structures were contoured. Dose responses in phantoms and electronic portal imaging device (EPID) were calculated by using the XVMC Monte Carlo code. The IMRT plan was delivered to the two phantoms and integrated EPID images were respectively acquired. Dose reconstruction was performed on these images using the calculated responses. The deformed phantom was registered to the original phantom using an in-house developed software based on the Demons algorithm. The transfer matrix for each voxel was obtained and used to correlate the two sets of the reconstructed dose to generate a cumulative reconstructed dose on the original phantom. Forwardly calculated planning dose in the original phantom was compared to the cumulative reconstructed dose from EPID in the original phantom. The prescribed 200 cGy isodose lines showed little difference with respect to the "prostate" and "seminal vesicles", but appreciable difference (3%) was observed at the dose level greater than 210 cGy. In the rectum, the reconstructed dose showed lower volume coverage by a few percent than the plan dose in the dose range of 150 to 200 cGy. Through this study, the system of clinical application of reconstructed dose was successfully developed and demonstrated. The organ deformation simulated in this study resulted in small but observable dose changes in the target and critical structure.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.4
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• pp.35-43
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• 2016

Recently, the pipeline system for waste transportation has been increasingly constructed as new solution for the waste collection and disposal system by constantly increasing domestic waste which issued as social problem. The pipeline system is constructed through long distance, so proper long-term monitoring system is necessary which available to detect the damage location for the effective maintenance. In this paper, the experimental study is carried out to evaluate the applicability of optical strain gauge sensor based on FBG for the long-term monitoring system. Three test parameters such as pressure leaking, blockage and deformation are considered as typical damages for real-scale pipeline test specimen. In order to measure flexural and volumetric strain and temperature, three FBG sensors are installed at each monitoring sections. From the test results, this study suggested effective methods of sensor installation and arrangement. Also the sensor spacing for the design of monitoring system using FBG sensor is derived by the correlation of distances from deformation between sensor responses.