Damage detection in plate structures using frequency response function and 2D-PCA

Khoshnoudian, Faramarz,Bokaeian, Vahid Techno-Press 2017 Smart Structures and Systems, An International Jou Vol.20 No.4

One of the suitable structural damage detection methods using vibrational characteristics are damage-index-based methods. In this study, a damage index for identifying damages in plate structures using frequency response function (FRF) data has been provided. One of the significant challenges of identifying the damages in plate structures is high number of degrees of freedom resulting in decreased damage identifying accuracy. On the other hand, FRF data are of high volume and this dramatically decreases the computing speed and increases the memory necessary to store the data, which makes the use of this method difficult. In this study, FRF data are compressed using two-dimensional principal component analysis (2D-PCA), and then converted into damage index vectors. The damage indices, each of which represents a specific condition of intact or damaged structures are stored in a database. After computing damage index of structure with unknown damage and using algorithm of lookup tables, the structural damage including the severity and location of the damage will be identified. In this study, damage detection accuracy using the proposed damage index in square-shaped structural plates with dimensions of 3, 7 and 10 meters and with boundary conditions of four simply supported edges (4S), three clamped edges (3C), and four clamped edges (4C) under various single and multiple-element damage scenarios have been studied. Furthermore, in order to model uncertainties of measurement, insensitivity of this method to noises in the data measured by applying values of 5, 10, 15 and 20 percent of normal Gaussian noise to FRF values is discussed.

피해자료 및 현장조사를 통한 공공건물 침수 손상함수 개발

이창희,김상호,황신범 한국방재학회 2019 한국방재학회논문집 Vol.19 No.6

홍수에 대한 피해평가는 홍수 위험 관리를 하는데 있어서 중요한 요소다. 홍수 피해를 추정하기 위해서 일반적으로 침수심별 손상함수가 사용된다. 미국, 유럽, 일본 등 주요 선진국에서는 과거의 홍수피해에 대한 분석과 전문가의 판단에 근거하여 침수심별 손상함수를 이용한 홍수 피해 추정 모형을 개발하였다. 그러나 이러한 손상함수는 개발된 지역 데이터를 기반으로 만들어 졌기 때문에 우리나라에서는 이를 그대로 적용할 수 없다. 이러한 문제를 해결하기 위해 본 연구에서는 공공건물에 대해서 우리나라의 실제 피해 데이터를 활용하여 손상함수를 개발하였다. 공제회로부터 획득한 각종 사고데이터와 현장조사에 의한 침수심 등을 이용하여 공공건물 건물유형별로 손상률을 산정하였다. 손상함수는 침수 피해에 따른 홍수피해액 추정을 가능하게 함으로써, 홍수피해저감 대책에 대한 비용대비 효과분석에 활용될 수 있다. Flood damage assessment is an important factor in flood risk management. Flood depth damage functions are commonly used to estimate flood damage. Major developed countries such as the US, Japan, and those of Europe have developed flood damage estimation models based on damage analyses of past flood cases as well as the judgment of flood experts. However, such damage procedures are not applicable to Korea, because they are based on data from regions in other developed countries. To solve this problem, this study developed damage functions using actual damage data from public buildings in Korea. Damage rates were calculated for each type of public building by utilizing various damage data obtained from the mutual aid association and the building register, and data on the depth of flooding, obtained through field surveys. The damage function can then be used to analyze the cost-effectiveness of flood damage reduction measures.

RC 슬래브교의 바닥판 균열 열화모델에 따른 이종손상 확산 분석

정현진,안효준,김재환,박기태,이종한 한국구조물진단유지관리공학회 2022 한국구조물진단유지관리공학회 논문집 Vol.26 No.6

국내 RC 슬래브교의 경우 공용연수가 20년 이상인 교량이 전체의 70% 이상을 차지하며, 노후화된 구조물의 수가 증가함에 따라 구조물의 안전 진단 및 유지관리의 중요성이 증가하는 실정이다. 고속도로 교량의 경우 바닥판 균열은 열화현상의 우선적인 원인이 되며, 교량 내구성및 사용수명 저하에 밀접한 관계가 있다. 또한 신축이음과 교량받침 등의 부재 손상으로 인한 손상 발생 비율이 약 73%로 주부재보다 높다. 따라서본 연구에서 교량 부재 손상과 바닥판 열화가 결합된 손상 시나리오를 정의하였다. 설계하중으로는 일교차를 고려한 온도 증감과 차랑햐중을 고려하여 개별 단일 손상 및 이종손상 시나리오 발생 시 바닥판 응력 분포와 최대 응력 발생 지점을 비교 분석하였다. 또한 바닥판 열화의 주요한 원인이 되는 균열의 점검 및 진단이력데이터 기반으로 공용연수 별 손상 시나리오에 대한 손상확산 분석 및 상태등급 예측을 수행하였다. 교량부재손상이 동반되어 발생하는 이종손상의 경우 단일손상 대비 균열 면적율과 손상확산율이 증가되며, 상태등급 C에 도달하는 시기도 매우 빠를 것으로 예측된다. 따라서 교량부재 손상이 발생하였을 때, 신속한 보수 및 교체가 이루어지지 않으면 바닥판의 손상 발생과 손상 확산으로 인한 2차 피해를 유발하는 원인이 될 수 있다. 따라서 바닥판 응답에 대한 지속적인 관찰과 대응이 필요할 것으로 판단된다. 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 structuresincreases, 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 accountsfor approximately 73% higher than that of major members. Therefore, this study defined damage scenarios combined with devices damages and deckdeterioration. The stress distribution and maximum stress on the deck were then evaluated using design vehicle load and daily temperature gradientfor single and combined damage scenarios. Furthermore, this study performed damage-spread analysis and predicted condition ratings according toa deck deterioration model generated from the inspection and diagnosis history data of cracks. The heterogeneous damages combined with the memberdamages of expansion joints and bearings increased the rate of crack area and damage spread, which accelerated the time to reach the condition ratingof C. Therefore, damage to bridge members requires proper and prompt repair and replacement, and otherwise it can cause the damage to bridge deckand the spread of the damage.

Damage detection for beam structures using an angle-between-string-and-horizon flexibility matrix

Yan, Guirong,Duan, Zhongdong,Ou, Jinping Techno-Press 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.36 No.5

The classical flexibility difference method detects damage by observing the difference of conventional deflection flexibility matrices between pre- and post-damaged states of a structure. This method is not able to identify multiple damage scenarios, and its criteria to identify damage depend upon the boundary conditions of structures. The key point behind the inability and dependence is revealed in this study. A more feasible flexibility for damage detection, the Angle-between-String-and-Horizon (ASH) flexibility, is proposed. The physical meaning of the new flexibility is given, and synthesis of the new flexibility matrix by modal frequencies and translational mode shapes is formulated. The damage indicators are extracted from the difference of ASH flexibility matrices between the pre- and post-damaged structures. One feature of the ASH flexibility is that the components in the ASH flexibility matrix are associated with elements instead of Nodes or DOFs. Therefore, the damage indicators based on the ASH flexibility are mapped to structural elements directly, and thus they can pinpoint the damaged elements, which is appealing to damage detection for complex structures. In addition, the change in the ASH flexibility caused by damage is not affected by boundary conditions, which simplifies the criteria to identify damage. Moreover, the proposed method can determine relatively the damage severity. Because the proposed damage indicator of an element mainly reflects the deflection change within the element itself, which significantly reduces the influence of the damage in one element on the damage indicators of other damaged elements, the proposed method can identify multiple damage locations. The viability of the proposed approach has been demonstrated by numerical examples and experimental tests on a cantilever beam and a simply supported beam.

Novel plastic hinge modification factors for damaged RC shear walls with bending performance

Komarizadehasl, Seyedmilad,Khanmohammadi, Mohammad Techno-Press 2021 Advances in concrete construction Vol.12 No.4

This paper introduces several new damage states for shear walls with flexural behavior damaged in an earthquake. These damage states are deducted by carefully interpretation of reported available test results of shear walls in the literature. Moreover, two methods for obtaining the plastic hinge modification factors of strength, stiffness and ductility capacity of the damaged shear walls with the flexural behavior are presented. A method based on secant stiffness at maximum displacement of each cycle of observed damage and the second method uses the reloading stiffness of the hysteresis curves consistent with damage levels. The later method introduced in this research is more reasonable for obtaining modification factors among the introduced methods. Using these factors, a reliable residual capacity for damaged structures can be assessed and the proper seismic retrofitting method can be followed. In this research, the effects of damages caused by various experimental tests have been studied on 43 reinforced concrete shear walls with flexural behavior. By introducing and describing the bending performance's damage levels, given the shear wall's observable condition such as cracks' width, concrete spalling and crushing, conditions of longitudinal and transvers rebars, 10 damage levels are introduced. The factors of modification of stiffness, strength, and the acceptable range of ductility of the member (𝜆k, 𝜆Q, and 𝜆D) were proposed for each level of damage. The results show that almost across all damage levels, the damage grew with increased drift. Nonetheless, stiffness and ductility modification factors are constant during the first damage states; they decrease dramatically after the third damage state (DS4). However, the reduction of the strength decreased gradually as of the fourth damage state. the results presented in current research are more reliable estimation of reduction factors in comparison with current approaches.

모드 유연도 기반 변위를 이용한 보 구조의 손상탐색기법

구기영 ( Koo Ki Young ),이종재 ( Lee Jong Jae ),윤정방 ( Yun Chung Bang ),허용학 ( Huh Yonghak ) 한국구조물진단유지관리공학회 2008 한국구조물진단유지관리공학회 학술발표대회 논문집 Vol.12 No.1

본 연구는 모드 유연도에 의해 산정되는 변위를 사용한 보 구조계의 손상탐색기법을 제안하였다. 일반적으로 구조계에 손상이 발생하면 추가처짐을 발생하게 되는데, 이에는 손상위치에 대한 정보가 포함되게 된다. 일반적으로 손상과 추가처짐의 관계는 매우 복잡한데, 본 연구에서는 새로운 하중개념 즉, 양모멘트 탐색하중(PBIL: Positive Bending Inspection Load)과 손상유발 활선변위(Damage-Induced Chord-wise Deflection: DI-CD)을 도입하여 간략한 손상과 추가처짐의 관계를 해석적으로 도출하였다. 이를 바탕으로 추가처짐을 사용한 손상위치탐색기법을 제안하였으며, 모형교량에 대한 실내실험을 통하여 제안된 기법이 성공적으로 경간 내부 뿐만 아니라 지점 근처의 손상도 성공적으로 규명함을 관찰할 수 있었다. In bridge structures, damage may induce an additional deflection which may naturally contain essential information about the damage. However, inverse mapping from the damage-induced deflection to the actual damage location and severity is generally complex, particularly for statically indeterminatesystems. In this paper, a new load concept, called the positive-bending-inspection-load (PBIL) is proposed to construct a simple inverse mapping from the damage-induced deflection to the actual damage location. From the theoretical investigations, it was proven that the damage-induced chord-wise deflection (DI-CD) hasthe maximum value with the abrupt change in its slope at the damage location under a PBIL. Hence, a novel damage localization method is proposed based on the DI-CD under a PBIL. Experimental verification study was also carried out on a two-span continuous bridge model with a steel box-girder. It was found that the proposed method clearly identified the damage existence and damage location for small damage cases with narrow cuts at the bottom flange.

2D-Dynamic Strain Energy를 이용한 모형사장교의 손상평가

허광희 ( Heo¸ Gwanghee ),이규 ( Lee Giu ),최만용 ( Choi¸ Mhan-young ),신형철 ( Shin Heung Chul ),이진옥 ( Chin Ok Lee ) 한국구조물진단유지관리공학회 2002 한국구조물진단유지관리공학회 학술발표대회 논문집 Vol.6 No.2

This paper aims to develop a method to designate damage points and assess their degrees in cable-stayed bridges by calculating the dynamic strain energy change on two-dimensional level. First of all, we present a method by which the damage index is obtained, and then we calculate a damage index using numerically obtained modal data according to the presented method. Next, all those data are classified into two categories: data before damage and ones after damage. And then the normalized damage index is calculated. In order to get modal data, we make up four damage scenarios: cable damage, single deck damage, one-direction double damage, and two-direction double damage. Each of Modal data from those damage scenarios were used to the tenth mode, and the degree of damage was made to be between three and nine percents in load capacity ratio. Although damage point is rather ambiguous in the double damage scenario, all in all, the damage points and its degree were relatively well designated in all damage scenarios.

Damage detection in beam-like structures using deflections obtained by modal flexibility matrices

Koo, Ki-Young,Lee, Jong-Jae,Yun, Chung-Bang,Kim, Jeong-Tae Techno-Press 2008 Smart Structures and Systems, An International Jou Vol.4 No.5

In bridge structures, damage may induce an additional deflection which may naturally contain essential information about the damage. However, inverse mapping from the damage-induced deflection to the actual damage location and severity is generally complex, particularly for statically indeterminate systems. In this paper, a new load concept, called the positive-bending-inspection-load (PBIL) is proposed to construct a simple inverse mapping from the damage-induced deflection to the actual damage location. A PBIL for an inspection region is defined as a load or a system of loads which guarantees the bending moment to be positive in the inspection region. From the theoretical investigations, it was proven that the damage-induced chord-wise deflection (DI-CD) has the maximum value with the abrupt change in its slope at the damage location under a PBIL. Hence, a novel damage localization method is proposed based on the DI-CD under a PBIL. The procedure may be summarized as: (1) identification of the modal flexibility matrices from acceleration measurements, (2) design for a PBIL for an inspection region of interest in a structure, (3) calculation of the chord-wise deflections for the PBIL using the modal flexibility matrices, and (4) damage localization by finding the location with the maximum DI-CD with the abrupt change in its slope within the inspection region. Procedures from (2)-(4) can be repeated for several inspection regions to cover the whole structure complementarily. Numerical verification studies were carried out on a simply supported beam and a three-span continuous beam model. Experimental verification study was also carried out on a two-span continuous beam structure with a steel box-girder. It was found that the proposed method can identify the damage existence and damage location for small damage cases with narrow cuts at the bottom flange.

정적 변형률 데이터 기반 머신러닝에 의한 무도상 철도 판형교의 손상 탐지

문태욱 ( Taeuk Moon ),신수봉 ( Soobong Shin ) 한국구조물진단유지관리공학회 2020 한국구조물진단유지관리공학회 논문집 Vol.24 No.6

국내의 노후 철도교량이 증가함에 따라 노후화로 인한 유지관리비가 점점 증가하고 있으며, 지속적인 관리가 더욱 더 중요해지고 있다. 하지만 관리해야하는 노후 시설물은 증가하지만, 노후 시설물을 점검 및 진단을 할 수 있는 전문 인력은 부족해지고 있다. 이러한 문제를 해결하기 위해 본 연구는 정적 변형률 응답 데이터를 적용하여 AI 기술의 머신러닝 기법으로 구조물의 국부적인 손상을 탐지하는 개선된 학습모델을 제시하고자 한다. 손상탐지 머신러닝 학습 모델을 구성하기 위해 우선 무도상 철도 판형교의 설계도면을 참고하여 교량의 해석모델을 설정하였으며, 설정된 해석모델로 손상시나리오에 따른 정적변형률 데이터를 추출하여 통계적 기법을 이용해 교량의 신뢰도 기반의 Local 손상 지수를 제시하였다. 손상 탐지는 손상 유무 탐지, 크기 탐지, 위치 탐지 3단계의 과정을 수행하여 손상 크기 탐지에서 선형 회귀 모델을 추가로 고려해 임의의 손상을 탐지하였으며, 최종적으로 손상 탐지 머신러닝 분류 학습 모델과 회귀 모델을 이용한 임의의 손상 위치를 추정 및 검증하였다. As the number of aging railway bridges in Korea increases, maintenance costs due to aging are increasing and continuous management is becoming more important. However, while the number of old facilities to be managed increases, there is a shortage of professional personnel capable of inspecting and diagnosing these old facilities. To solve these problems, this study presents an improved model that can detect Local damage to structures using machine learning techniques of AI technology. To construct a damage detection machine learning model, an analysis model of the bridge was set by referring to the design drawing of a non-ballasted plate-girder railroad bridge. Static strain data according to the damage scenario was extracted with the analysis model, and the Local damage index based on the reliability of the bridge was presented using statistical techniques. Damage was performed in a three-step process of identifying the damage existence, the damage location, and the damage severity. In the estimation of the damage severity, a linear regression model was additionally considered to detect random damage. Finally, the random damage location was estimated and verified using a machine learning-based damage detection classification learning model and a regression model.

Damage detection for beam structures using an angle-between-string-and-horizon flexibility matrix

Guirong Yan,Zhongdong Duan,Jinping Ou 국제구조공학회 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.36 No.5

The classical flexibility difference method detects damage by observing the difference of conventional deflection flexibility matrices between pre- and post-damaged states of a structure. This method is not able to identify multiple damage scenarios, and its criteria to identify damage depend upon the boundary conditions of structures. The key point behind the inability and dependence is revealed in this study. A more feasible flexibility for damage detection, the Angle-between-String-and-Horizon (ASH) flexibility, is proposed. The physical meaning of the new flexibility is given, and synthesis of the new flexibility matrix by modal frequencies and translational mode shapes is formulated. The damage indicators are extracted from the difference of ASH flexibility matrices between the pre- and postdamaged structures. One feature of the ASH flexibility is that the components in the ASH flexibility matrix are associated with elements instead of Nodes or DOFs. Therefore, the damage indicators based on the ASH flexibility are mapped to structural elements directly, and thus they can pinpoint the damaged elements, which is appealing to damage detection for complex structures. In addition, the change in the ASH flexibility caused by damage is not affected by boundary conditions, which simplifies the criteria to identify damage. Moreover, the proposed method can determine relatively the damage severity. Because the proposed damage indicator of an element mainly reflects the deflection change within the element itself, which significantly reduces the influence of the damage in one element on the damage indicators of other damaged elements, the proposed method can identify multiple damage locations. The viability of the proposed approach has been demonstrated by numerical examples and experimental tests on a cantilever beam and a simply supported beam.