• Journal of the Computational Structural Engineering Institute of Korea
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• v.33 no.6
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• pp.359-366
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• 2020

In this study, a simulation-based damage estimation method for helidecks is proposed using an artificial neural network. The structural members that share a connecting node in the helideck are regarded as a damage group, and a total of 37,400 damage scenarios are numerically generated by applying randomly assigned damage to up to three damage groups. Modal analysis is then performed for all the damage scenarios, which are selectively used as either training or validation or verification sets based on the purpose of use. An artificial neural network with three hidden layers is constructed using a PyTorch program to recognize the patterns of the modal responses of the helideck model under both damaged and undamaged states, and the network is successively trained to minimize the loss function. Finally, the estimated damage rate from the proposed artificial neural network is compared to the actual assigned damage rate using 400 verification scenarios to show that the neural network is able to estimate the location and amount of structural damage precisely.

• Journal of the Society of Naval Architects of Korea
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• v.56 no.5
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• pp.457-463
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• 2019

Damage control is a very important preliminary and primary activity to improve the survivability of naval ships by preventing spread of damage, and various types of onboard damage control training are conducted regularly on naval ships. The scenarios for these trainings should be well organized to improve the training efficiency. However, at present, it takes much time and effort to generate the training scenarios and there is a problem that the procedures and contents of the scenarios vary widely depending on the persons who generate, without the established methods and standards. In this paper, an efficient generation method of damage control onboard training scenarios has been established, especially for flood and fire o n naval ships. Also a computer program has been developed based on the established method. The results showed that this method and computer program reduce the time and effort to generate these scenarios, and it is hoped that the method be used as a ROK Navy Standard.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.6
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• pp.93-101
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• 2022

RC Slab bridges in Korea account for more than 70% of the total bridges for more than 20 years of service. As the number of aging structures increases, the importance of safety diagnosis and maintenance of structures increases. For highway bridges, cracks are a main cause of deck deterioration, which is very closely related to the decrease in bridge durability and service life. In addition, the damage rate of expansion joints and bearings accounts for approximately 73% higher than that of major members. Therefore, this study defined damage scenarios combined with devices damages and deck deterioration. The stress distribution and maximum stress on the deck were then evaluated using design vehicle load and daily temperature gradient for single and combined damage scenarios. Furthermore, this study performed damage-spread analysis and predicted condition ratings according to a deck deterioration model generated from the inspection and diagnosis history data of cracks. The heterogeneous damages combined with the member damages of expansion joints and bearings increased the rate of crack area and damage spread, which accelerated the time to reach the condition rating of C. Therefore, damage to bridge members requires proper and prompt repair and replacement, and otherwise it can cause the damage to bridge deck and the spread of the damage.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 2011.04a
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• pp.201-206
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• 2011

최근 국내에서는 대심도 터널 시공계획이 발표되면서 터널 구조물에 대한 방재 및 내화설계에 대한 관심이 높아지고 있다. 화재 발생 시 문제가 발생할 수 있는 콘크리트 라이닝의 내화설계를 위해서는 보다 구체적인 내화성능을 측정하기 위한 내화실험이 실시되어야 한다. 현재 국내에서는 건축물의 내화성능을 평가하기 위한 시험평가 방법이 제시되어 있는 상태이나 터널 구조물에 대한 시험법이나 성능평가는 거의 전무한 상황이다. 따라서 본 연구에서는 콘크리트 구조물의 화재손상 정도를 평가하기 위해 현장에서 사용되고 있는 터널 라이닝을 대상으로 화재 시 콘크리트 라이닝의 손상정도를 평가하였다. 실험은 대표적인 터널 화재시나리오 곡선인 RABT 화재 시나리오를 적용하였으며 폭렬방지에 효과적인 것으로 알려져있는 fiber cocktail(강섬유+폴리프로필렌섬유)의 혼입여부에 따른 성능평가도 함께 실시하였다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.1
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• pp.33-40
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• 2021

In recent years, many construction projects become large and complicated, and construction accidents also steadily increase, which grows interest in the safety and maintenance during construction. Many of the construction accidents are related to temporary construction and structures, but the safety evaluation and management during construction are unclear and indefinite due to the short operating period and continuous change in the formation of the temporary structure. The system support, which is one of the temporary structures to support the pouring load of concrete, was proposed to easily install and dismantle members with connection parts pre-manufactured. The use of the system support is increasing to improve the safety of the temporary structure during construction. However, the system support, which consists of multiple members, still has uncertainties in connectivity between members and supports of vertical members. Therefore, this study analyzed the structure, load, and accident cases of the system support to define the damage scenarios for member connection, support condition, and lateral displacement. The decrease rate of the critical load was analyzed according to the damage scenarios based on the defined unit structure of the system support. In addition, this study provided vulnerable members for each damage scenario, which could induce instability of the temporary structures during design, construction, and operation of the structure.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.19 no.3 s.73
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• pp.313-322
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• 2006

In the genetic algoricm (GA) based damage detection methods using vibration of structures, the selection of modal properties is important to improve the accuracy of damage detection. The objective of this study is to improve the accuracy of damage detection using natural frequency and modal strain energy, The following approaches are used to achieve the goal. First, modal strain energy is formulated and a new GA-based damage detection technique using natural frequency and modal strain energy is proposed. Next, to verify the efficiency of proposed technique, damage scenarios for free-free beam are designed and vibration modal tests of the target structure are conducted. Finally, the feasibility of the proposed technique is verified in comparison with other GA-based damage detection technique using natural frequency and mode shape.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.3C
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• pp.219-228
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• 2006

In this study, a series of fire tests was carried out to evaluate fire-induced damage to structural members in tunnels. From the tests, the loss amount of concrete materials under the RWS scenario was slightly bigger than under the RABT fire scenario. Especially under the RWS fire scenario where the maximum temperature is over $1,200^{\circ}C$, the loss of concrete materials was mainly induced by melting. Generally, the loss of materials in reinforced concrete was slightly smaller than that in unreinforced concrete. Depending upon an applied fire scenario, fire-induced damage to shotcrete was quite different. From the realtime investigation of a specimen surface by a digital camcorder, it was proved that the material loss under the RABT fire scenario was mainly induced by spalling. However, it was also revealed that although fire-induced damage in the initial heating stage under the RWS was so close to that under the RABT, the material loss under the RWS at the later stage after 50 minutes elapsed since fire initiation was induced not by spalling but by melting.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.623-626
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• 2011

본 연구는 수중 강판에 존재하는 결함탐지를 위한 탄성파 유한요소 시뮬레이션이다. 일반적으로 수중 강판은 외부의 물로 인하여 결함의 탐지가 어렵다. 이러한 수중 강판의 결함탐지에는 잠수부가 수중 강판 표면에 비파괴 검사 장비를 활용하여 결함을 탐지하는 경우가 많으며 잠수부의 경험과 많은 시간이 소요되는 단점이 있다. 본 연구에서는 수중강판의 표면이 아닌 수중에서 탄성파를 발생시켰을 경우 수중 강판의 결함탐지 유한요소 시뮬레이션을 이용하여 손상의 위치와 손상의 크기에 따라 발생하는 응답을 알아보았다. 강판의 상하부에 기계적인 손상이 발생한 경우를 손상 시나리오로 가정하고 해석을 수행하였다. 손상이 없는 경우의 응답을 기준으로 강판의 상부와 하부에 기계적인 손상이 있는 경우에 발생하는 응답을 비교하였다. 동적유한요소 프로그램인 ANSYS/LS-DYNA를 사용하여 결함탐지 해석을 수행하였다. 결과적으로 손상의 종류에 따라 응답신호의 진폭 감소가 나타났으며 손상의 크기가 커질수록 진폭 감소가 커지는 결과를 나타내었다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.7 no.3
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• pp.147-156
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• 2003

In this paper, a damage detection method using mode shapes of truss structures is presented. The theory is formulated based on the changes in the modal strain energy in a truss type structures due to damage. To examine the feasibility, the theory is applied to an experimental data of a 1:6 scale model of a typical hexagonal truss structure. The experiment consists of 17 damage scenarios subjected to three different types of damage. The damage evaluation results show that the proposed method detects successfully damage in truss elements and also show that the performance of proposed method can be significantly impacted by the noise in the measurement data for small damage.

• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.469-469
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• 2016

본 연구에서는 지진해일 모의결과를 바탕으로 하여 지진해일모형 결과에 민감하게 작용할 수 있는 다양한 입력조건을 분석하였다. 우선 2004년 인도양 지진해일 모의를 위하여 다중격자체계를 갖추고 있는 COMCOT모형과 수심적분된 Boussinesq모형의 결합모형을 사용하였으며, 근해역에 지진해일 충격 및 피해산정 결과에 유효한 영향을 주는 입력인자를 파악하기 위하여 4가지의 시나리오를 설정하였다. 각 시나리오에서는 3개의 서로 다른 독립인자가 포함되었으며 이들은 배타적으로 결정되어 최소한의 시나리오로 다양한 분석이 가능하도록 하였다. 즉, 시나리오 1에서는 지진해일의 초기수면상태를 산정하기 위한 간략화된 단층모형을 적용하였고, 이 때 바닥마찰에 대한 고려는 배제되었다. 시나리오 2에서는 시나리오 1과 모든 조건은 동일하게 하였으나 유한단층 모형을 통해 초기수면상태를 산정하도록 하였다. 이처럼 유사하게 시나리오 3에서는 복잡한 지형 특성을 나타내는 몰디브 지역의 보다 정확한 해석을 위하여 몰디브 지역의 상세격자망을 추가적으로 다중격자체계에 포함시켰다. 마지막으로 바닥마찰항에 대한 민감도를 분석하기 위하여 시나리오 4에서는 바닥마찰항에 대한 고려를 포함시켰다. 또한, 4가지 시나리오 외에 결합모형의 성능을 평가하기 위하여, COMCOT모형만을 사용하는 시나리오를 추가적으로 설정하였다. 즉, 시나리오 1과 모든 조건은 동일하되 COMCOT모형만을 사용하도록 하였다. 설정된 조건에 따른 수치모의 결과, 지진해일 내습에 따른 해수위 변화는 각 시나리오별로 큰 차이를 보이지 않았으나, Boussinesq모형에 의한 지진해일의 동수역학적 거동은 COMCOT모형을 사용한 결과와 유의한 차이를 보였으며, 특히 파랑에 기인한 난류적 거동은 극명한 대조를 이루었다. 따라서, 본 연구결과를 통해 향후 파랑에 기인한 난류적 거동의 정확모의를 위해 수치해석에 따른 확산오차 및 바닥마찰항에 대한 면밀한 연구가 필요함을 시사하였다.