• 콘크리트학회논문집
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• 제23권6호
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• pp.773-780
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• 2011

이 연구는 초대형 매스 구조물인 지하식 LNG 저장탱크의 바닥슬래브 및 측벽에 타설되는 매스 콘크리트의 재료특성, 배합조건, 양생조건 및 콘크리트의 타설시기와 초기온도, 외기온 등을 고려한 온도응력 해석 결과를 기술하였다. 해석 결과를 토대로 유해한 균열의 발생 가능성을 예측하고, 이를 방지하기 위한 방안을 제시하였다. 이 연구에서는 콘크리트의 단열온도 상승시험을 통하여 수화열 관리에 유리하다고 평가된 2종류(벨라이트 시멘트+석회석 미분말)의 최적배합조건을 선정하였다. 온도응력 해석의 결과에 따르면, 바닥슬래브 2단을 제외한 대부분의 분할타설 블록에서 관통균열지수가 1.2이상을 만족하였다. 바닥슬래브 2단의 경우 균열방지 대책으로 선행냉각 방안을 제시하였으며, 콘크리트의 초기온도를 $25^{\circ}C$ 범위에서 관리할 경우에는 대부분의 타설블록에서 관통균열지수 1.2이상을 만족하는 것으로 나타났다. 또한, 바닥슬래브의 경우, 표면균열지수가 1.2이상이기 때문에 양생조건을 준수하면 표면균열을 제어할 수 있으며, 측벽의 경우에도 표면균열지수가 1.0이상을 만족하기 때문에 균열의 수 및 폭을 제어할 수 있는 것으로 나타났다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 가을 학술발표회 논문집
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• pp.375-380
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• 2002

Tong-young LNG tank is a LNG storage tank of 140,000 kl, and it is composed of Bottom Slab(Annular, Center), Outer Wall, Ring Beam and Roof. Generally, when concrete temperature arise, the complex thermal stress of inner and outer part can cause serious thermal crack and damage at structure. So in this paper, for the control of this thermal crack, we did the concrete mix design with the base of fly-ash 30% substitute at binder, and through the computer modelling at Bottom Slab(Annular, Center), Outer Wall, Ring Beam and Roof, we studied the probability of thermal crack by thermal crack index.

• 한국철도학회논문집
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• 제7권4호
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• pp.312-318
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• 2004

The wall in a subway structure is easily subject to crack occurrence since its expansion and shrinkage associated with hydration heat reaction is constrained by the slab. The greater problem is that the crack in the wall may be developed to pass through thickness and eventually deteriorate the structure due to rusting of reinforced steel. Thus, this study aims at controlling thermal cracks as much as possible and determining an optimized size of concrete placement through hydration heat analysis. For this study, effects of placement height, length, temperature and types of cement on the thermal cracks were evaluated by temperature rise, thermal stress and crack index. As results of parametric study, it was found that placement height and length do not have an effect on the temperature rise but have significant one on thermal stress which relates to direct possibility of thermal crack occurrence. This means that proper selection of size balancing internal constraint with external one is much more important than reducing the placement height and length simply. In order to prevent from thermal cracks most effectively, in addition, it was noted to reduce placement temperature and to use the cement blended with mineral admixture.

• 대한토목학회논문집
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• 제38권3호
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• pp.467-475
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• 2018

지자체 도로예산 절감을 위해 소규모 지역도로의 통행환경을 고려한 소규모 지역도로 포장상태 평가 기준을 제시하고자 하였다. 지방 지자체에서 관리하는 지역도로의 경우 설계속도가 낮고 일정하지 않으며 중차량 통행량이 작아 비교적 중요도가 떨어지는 구간이다. 일반적으로 포장상태 조사에는 조사장비를 이용하나 고가의 운영비가 소요되어 소규모 지역도로 적용에는 효율성 문제가 발생한다. 본 연구에서는 소규모 지역도로에 적합한 새로운 포장상태 평가지수를 제시하였다. 소규모 지역도로의 포장상태 평가는 제시된 평가지수에 따라 3등급으로 구분하였으며, 전문가 설문조사를 통해 타당성을 검토하였다. 제시된 평가지수는 포장상태 설문조사 결과와 $R^2$가 0.88로 매우 높은 상관성이 높은 것으로 나타났다. 제한된 조건에서 육안 균열조사를 통해 산출된 포장상태평가지수는 소규모 지역도로에 활용이 가능하다. 또한 보다 경제적인 포장상태평가방법으로 지역도로 관리뿐 아니라 도로관리 예산절감에도 효과가 있을 것으로 기대된다.

• International Journal of Railway
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• 제7권1호
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• pp.8-15
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• 2014

Recently, in the total railroad construction field, concrete slab tracks have been adapted in place of ballast tracks. Because ballast tracks need frequent maintenance and are difficult to handle due to increasing maintenance costs, eventually concrete slab tracks were selected as an alternative. However, owing to the hydration heat reactions and temperature-affected shrinkage of the concrete, a variety of studies to solve maintenance problems related to concrete slab tracks are underway. This study analyzed characteristics of TQI values evaluating track irregularity, investigated the relationship between crack progress and TQI, and then evaluated the correlation between the two values. Through our analysis, we found that there is a need to supplement the problems of the current method and develop a track evaluation index which takes cracking into account. We also concluded that TQI is the main decision-making tool in track maintenance.

• Structural Engineering and Mechanics
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• 제68권6호
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• pp.747-760
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• 2018

In the present study, a methodology for developing fragilities of arch concrete dams to assess their performance against seismic hazards is introduced. Firstly, the probability risk and fragility curves are presented, followed by implementation and representation of the way this method is used. Amirkabir arch concrete dam was subjected to non-linear dynamic analyses. A modified three dimensional rotating smeared crack model was used to take the nonlinear behavior of mass concrete into account. The proposed model considers major characteristics of mass concrete. These characteristics are pre-softening behavior, softening initiation criteria, fracture energy conservation, suitable damping mechanism and strain rate effect. In the present analysis, complete fluid-structure interaction is included to account for appropriate fluid compressibility and absorptive reservoir boundary conditions. In this study, the Amirkabir arch concrete dam is subjected to a set of 8 three-component earthquakes each scaled to 10 increasing intensity levels. Using proposed nonlinear smeared crack model, nonlinear analysis is performed where the structure is subjected to a large set of scaled and un-scaled ground motions and the maximum responses are extracted for each one and plotted. Based on the results, fragility curves were plotted according to various and possible damages indexes. Discrete damage probabilities were calculated using statistical methods for each considered performance level and incremental nonlinear analysis. Then, fragility curves were constructed based on the lognormal distribution assumption. Two damage indexes were introduced and compared to one another. The results indicate that the dam has a proper stability under earthquake conditions at MCE level. Moreover, displacement damages index is more conservative and impractical in the fragility analysis than tensional damage index.

• 한국도로학회논문집
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• 제18권6호
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• pp.115-122
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• 2016

OBJECTIVES : This study develops an evaluation method, which is useful to inspect pavement condition of specific boroughs. This is because pavement condition is broadly divided into five grades via visual inspection, which does not consider the types of deteriorations, and is decided by an investigator having a subjective viewpoint. This visual inspection method is not a satisfactory method for accurate maintenance when various deteriorations occur. METHODS : The performance model considers several factors such as crack, rutting, and IRI. This method is also modified from borough SPI based on SPI (Seoul Pavement Index). Considering limited budget of borough, PI (prediction index) is suggested, which is related to the grade of pavement condition evaluation and type of materials. Practical correlation review is also conducted with statistical verification by using the Monte Carlo simulation. RESULTS : The results of the study show that modified criteria are reasonable. First, the comparison between the visual inspection result and the SPI result indicates that the R-square value is sufficiently high. Second, through the common section, each evaluation method could be compared, and the result shows considerable similarity, which increases when the range is modified. Finally, PI for predicting remaining life and the random number SPI have common parts, which means that each indicator would be adequate to be used as an evaluation method. CONCLUSIONS : Comparison and analysis results show that the developed evaluation method is reasonable for specific boroughs where financial support is inadequate for the evaluation process by using the newer equipment. Moreover, for more accurate evaluation method, previous visual inspection data should be utilized, and the database of inspection equipment have to be collected.

• 콘크리트학회논문집
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• 제12권5호
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• pp.13-23
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• 2000

In this study, an flexural test on half-scale spliced PSC-I girder was conducted to verify the efficiency of the long span spliced girder as suggested by the Korean Highway Design Specification. The experimental results showed that the specimens developed a complex failure mode due to flexural-compression and torsional stress. The cracking moment of each girder was higher the experiment than was calulated by the ACI and the ultimate strength were the almost same. To estimate the safety and the structural efficiency of the spliced girder, the proposed Yielding Resistance Index(YRI) and ductility index by American Concrete Institutes were used based on the energy concept. The proposed YRI defined the ratio of crack resisting energy and the total energy calculated from load-displacement relationship. Based on the analysis of YRI and ductility index, the flexural behavior of the spliced girder was found to be efficient. Through the experimental results, the structural behavior of proposed spliced PSC I-type girder for long span bridge was found to be more efficient than the exsisting PSC I-type girders.

• 대한기계학회논문집A
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• 제30권9호
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• pp.1142-1147
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• 2006

A practical method for reducing the number of spot welds in automotive structures considering fatigue crack initiation life is suggested. At first, an influence index for the durability and the fatigue life of a spot weld itself is defined and then taken as the main effect of the DOE analysis. Spot welds that can be removed without serious reduction of durability through numerical experiments are selected by the results of DOE. The proposed method was applied to the shock tower and LCA(lower control arm) structure of a vehicle, which are important components in durability-related point of view.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 추계학술대회논문집
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• pp.603-606
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• 2006

We present a study on the development of a practical and quantitative technique for the assessment of the structural health condition with using piezoceramic(PZT) sensors. The electro-impedance-based technique with the PZT patches is very sensitive for evaluation of the incipient and small damage in a high frequency range, and however the commonly traditional modal analysis method is effective only for considerably larger damages in low frequency range. The paper presents the technique in detecting and characterizing real-time damage on the specimen that is an aluminum plate fastened with bolts and nuts by different torques and as well a plate with a crack. By using the special arrangement of the PZT sensors, the required longitudinal wave is generated through the specimen. A large number of experiments are conducted and the different conditions of the specimens, i.e. the location and extent of loosening bolts, and the plate with a crack are simulated. respectively. Since fixing and loosening the loosened bolt is controlled by a torque wrench, we can control exactly the experiment of the different torques. Compared with the simulated healthy condition, we can find whether or not there is a damage in the specimen with using an impedance analyzer with the PZT sensors. Several indices are discussed and used for assessing the different simulated damages. As for the location of bolt loosening, the RMSD is found to be the most appropriate index for numerical assessment and as well the RMSD shows strongly linear relationship for assessing the extent of the bolt loosening, and the frequency peak shift ${\Delta}F$ is used to assess the cracked plate. The possibility of repeatability of the pristine condition signatures is also presented and the appropriate frequency range and interval are uniquely selected through large numbers of experiments.