• Geomechanics and Engineering
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• 제14권2호
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• pp.203-209
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• 2018

Reliable estimation of compressive as well as tensile in-situ stresses is critical in the design and analysis of underground structures and openings in rocks. Kaiser effect technique, which uses acoustic emission from rock specimens under cyclic load, is well established for the estimation of in-situ compressive stresses. This paper investigates the Kaiser effect on marble specimens under cyclic uniaxial compressive as well as cyclic uniaxial tensile conditions. The tensile behavior was studied by means of Brazilian tests. Each specimen was tested by applying the load in four loading cycles having magnitudes of 40%, 60%, 80% and 100% of the peak stress. The experimental results confirm the presence of Kaiser effect in marble specimens under both compressive and tensile loading conditions. Kaiser effect was found to be more dominant in the first two loading cycles and started disappearing as the applied stress approached the peak stress, where felicity effect became dominant instead. This behavior was observed to be consistent under both compressive and tensile loading conditions and can be applied for the estimation of in-situ rock stresses as a function of peak rock stress. At a micromechanical level, Kaiser effect is evident when the pre-existing stress is smaller than the crack damage stress and ambiguous when pre-existing stress exceeds the crack damage stress. Upon reaching the crack damage stress, the cracks begin to propagate and coalesce in an unstable manner. Hence acoustic emission observations through Kaiser effect analysis can help to estimate the crack damage stresses reliably thereby improving the efficiency of design parameters.

• 한국전산구조공학회논문집
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• 제25권1호
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• pp.81-89
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• 2012

본 연구에서는 무선 가속도 센서노드를 이용한 강 거더 볼트연결 부재의 진동기반 손상 모니터링 체계를 제안하였다. 이 같은 연구목표를 위해, 다음과 같은 연구를 수행하였다. 먼저, 무선 가속도 센서노드의 하드웨어 구성 및 내장된 작동 소프트웨어를 제시하였다. 다음으로, 강 거더 볼트연결 부재의 진동기반 손상 모니터링 체계를 제시하였다. 손상 모니터링 체계는 가속도 응답특성 분석을 통해 전역적 손상발생 경보 및 손상위치 추정을 수행한다. 전역적 손상발생 경보는 파워스펙트럼밀도의 상관계수를 적용하였다. 손상위치 추정은 고유 진동수기반 손상검색 기법과 모드형상기반 손상검색 기법을 적용하였다. 마지막으로, 모형 강 거더의 볼트연결 부재 손상을 식별하기 위한 진동기반 손상 모니터링 체계의 적용성을 검증하였다.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2003년도 추계학술대회 논문집
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• pp.64-69
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• 2003

This paper describes a study on the tearing damage of the ship's bottom plating during a grounding. It has been known widely that difference scaling laws are applied for bodies undergoing simultaneously plastic flow and crack propagation in the deformation of the plate tearing. Especially, the basic scaling law is not followed for the fracture. In this study plate cutting experiments for the geometrically similar models have been performed in order to verify the problem. From the experimental results, it has been observed that the cutting forces and energy for the larger models are significantly lower than those of the smaller models the damage become large. A simplified analytical method for the estimation of tearing is proposed based on the experiments and it has been observed that the results of the present formula are correlated very well with the experiments

• Tribology and Lubricants
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• 제17권1호
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• pp.16-21
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• 2001

The wear particles is released from the moving surfaces in gear systems of transmission and its morphology is directly related to the damage and failure to gear system from which the particles originated. It is the effective method for damage condition estimation of automobile transmission gear to observe wear debris in gear oil. We tested with new transmission and took out gear oil according to driving distance. To be applied to damage condition of gear system in transmission of automobile,4 shape parameters of wear particles in gear oil were calculated and wear volume were presumed with the image processing system.

• 대한기계학회논문집B
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• 제31권11호
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• pp.936-941
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• 2007

This paper is on the influence of gas explosion caused by Vapor Cloud Explosion(VCE). Also, it is to understand the influence of the booth for explosion experiment which is installed to let the trainees for legal education which is managed by IGTT(Institute or Gas Technology Training) know the riskiness of explosion. In this study, the influence of explosion shock wave caused by VCE in enclosure was calculated by using the Hopkinson's scaling law and the accident damage was estimated by applying the influence on the adjacent human into the probit model. As a result of the damage estimation conducted by using the probit model, both the damage possibility of explosion overpressure to human 8 meters away and that of shock wave to hurt 15 meters away showed nothing.

• Earthquakes and Structures
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• 제16권2호
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• pp.197-208
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• 2019

The objective of this study is to propose new seismic intensity parameters based on the Hilbert spectrum and to associate them with the seismic damage potential. In recent years the assessment of even more seismic features derived from the seismic acceleration time-histories was associated with the structural damage. For a better insight into the complex seismic acceleration time-history, Hilbert-Huang Transform (HHT) analysis is utilized for its processing, and the Hilbert spectrum is obtained. New proposed seismic intensity parameters based on the Hilbert spectrum are derived. The aim is to achieve a significant estimation of the seismic damage potential on structures from the proposed new intensity parameters confirmed by statistical methods. Park-Ang overall structural damage index is used to describe the postseismic damage status of structures. Thus, a set of recorded seismic accelerograms from all over the word is applied on a reinforced concrete frame structure, and the Park-Ang indices through nonlinear dynamic analysis are provided and considered subsequently as reference numerical values. Conventional seismic parameters, with well-known seismic structural damage interrelation, are evaluated for the same set of excitations. Statistical procedures, namely correlation study and multilinear regression analysis, are applied on the set of the conventional parameters and the set of proposed new parameters separately, to confirm their interrelation with the seismic structural damage. The regression models are used for the evaluation of the structural damage indices for every set of parameters, respectively. The predicted numerical values of the structural damage indices evaluated from the two sets of seismic intensity parameters are inter-compared with the reference values. The numerical results confirm the ability of the proposed Hilbert spectrum based new seismic intensity parameters to approximate the postseismic structural damage with a smaller Standard Error of Estimation than this accomplished of the conventional ones.

• Smart Structures and Systems
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• 제12권6호
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• pp.619-640
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• 2013

It is highly desirable to explore efficient algorithms for detecting structural damage of large size structural systems with limited input and output measurements. In this paper, a new structural damage detection algorithm based on substructure approach is proposed for large size structural systems with limited input and output measurements. Inter-connection effect between adjacent substructures is treated as 'additional unknown inputs' to substructures. Extended state vector of each substructure and its unknown excitations are estimated by sequential extended Kalman estimator and least-squares estimation, respectively. It is shown that the 'additional unknown inputs' can be estimated by the algorithm without the measurements on the substructure interface DOFs, which is superior to previous substructural identification approaches. Also, structural parameters and unknown excitation are estimated in a sequential manner, which simplifies the identification problem compared with other existing work. Structural damage can be detected from the degradation of the identified substructural element stiffness values. The performances of the proposed algorithm are demonstrated by several numerical examples and a lab experiment. Measurement noise effect is considered. Both the simulation results and experimental data validate that the proposed algorithm is viable for structural damage detection of large size structural systems with limited input and output measurements.

• KIEAE Journal
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• 제7권4호
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• pp.141-146
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• 2007

It is necessary to guarantee the safety, serviceability and durability of reinforced concrete structures over their service life. However, concrete structures represent a decrease in their durability due to the effects of external environments according to the passage of time, and such degradation in durability can cause structural degradation in materials. In concrete structures, some degradations in durability increase the corrosion of embedded rebars and also decrease the structural performance of materials. Thus, the structural condition assessment of RC materials damaged by corrosion of rebars becomes an important factor that judges needs to apply restoration. In order to detect the damage of reinforced concrete structures, a visual inspection, a nondestructive evaluation method(NDE) and a specific loading test have been employed. However, obscurities for visual inspection and inaccessible members raise difficulty in evaluating structure condition. For these reasons, detection of location and quantification of the damage in structures via structural response have been one of the very important topics in system identification research. The main objective of this project is to develope a methodologies for the damage identification via static responses of the members damaged by durability. Six reinforced concrete beams with variables of corrosion position and corrosion width were fabricated and the damage detections of corroded RC beams were performed by the optimization and the conjugate beam methods using static deflection. In results it is proved that the conjugate beam method could predict the damage of RC members practically.

• Structural Engineering and Mechanics
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• 제48권2호
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• pp.257-274
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• 2013

In this study, seismic performance of one story hinged precast buildings, which represents the majority of existing lightweight industrial building stock of Turkey, was assessed. A lot of precast buildings, constructed in one of the important seismic zones of western Turkey, were investigated and building inventories were prepared. By this method, structural properties of inventory buildings and damaged precast buildings in recent earthquakes were compared. Damage estimations based on nonlinear analysis methods have shown that estimated damage levels of inventory buildings and observed damage levels in recent earthquakes are similar. Accuracy of damage estimation study and the simplicity of the one story precast building models implied that rapid seismic performance assessment method for these buildings can be developed. In this assessment method, capacity curves and vibration periods of precast buildings were calculated by using structural properties of precast buildings. The proposed assessment method was applied to inventory buildings by using two different seismic demand scenarios which reflect moderate and soft soil conditions. Comparison of detailed analysis and rapid assessment methods have indicated that reliable seismic performance estimations can be performed by using proposed method. It is also observed that distribution of damage estimations is compatible in both scenarios.

• Spatial Information Research
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• 제18권1호
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• pp.49-56
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• 2010

시가지 범람 문제를 고려할 경우 침수심의 정량적인 수치계산에 의한 재해 위험을 평가하는 것이 중요하다. 본 연구에서는 2002년 막대한 시가지 침수 피해를 경험한 바 있는 삼척시를 대상으로 범람 모의 계산에 의한 시가지 침수피해 평가를 수행하였다, 입력자료의 변환과정에서 생길 수 있는 에러를 줄이기 위해 시가지 조도계수, 표고, 건물의 점유율 등은 ArcGIS에서 바로 전산화하여 시가지 범람모형을 구축하였으며 계산된 침수심을 토대로 격자별로 피해액을 산정하였다 본 연구를 통하여 강우유출, 침수심 모의 계산, 피해액의 정량적 산정이라는 일연의 과정이 통합적으로 수행되어 향후 시가지 배수계획에 기여할 것으로 기대된다.