Recent Advances in Structural Health Monitoring

Maria Q. Feng 한국비파괴검사학회 2007 한국비파괴검사학회지 Vol.27 No.6

Recent Advances in Structural Health Monitoring

Feng, Maria Q. The Korean Society for Nondestructive Testing 2007 한국비파괴검사학회지 Vol.27 No.6

Emerging sensor-based structural health monitoring (SHM) technology can play an important role in inspecting and securing the safety of aging civil infrastructure, a worldwide problem. However, implementation of SHM in civil infrastructure faces a significant challenge due to the lack of suitable sensors and reliable methods for interpreting sensor data. This paper reviews recent efforts and advances made in addressing this challenge, with example sensor hardware and software developed in the author's research center. It is proposed to integrate real-time continuous monitoring using on structure sensors for global structural integrity evaluation with targeted NDE inspection for local damage assessment.

Periodic seismic performance evaluation of highway bridges using structural health monitoring system

이진학,김두기,Maria Q. Feng 국제구조공학회 2009 Structural Engineering and Mechanics, An Int'l Jou Vol.31 No.5

In this study, the periodic seismic performance evaluation scheme is proposed using a structural health monitoring system in terms of seismic fragility. An instrumented highway bridge is used to demonstrate the evaluation procedure involving (1) measuring ambient vibration of a bridge under general vehicle loadings, (2) identifying modal parameters from the measured acceleration data by applying output-only modal identification method, (3) updating a preliminary finite element model (obtained from structural design drawings) with the identified modal parameters using real-coded genetic algorithm, (4) analyzing nonlinear response time histories of the structure under earthquake excitations, and finally (5) developing fragility curves represented by a log-normal distribution function using maximum likelihood estimation. It is found that the seismic fragility of a highway bridge can be updated using extracted modal parameters and can also be monitored further by utilizing the instrumented structural health monitoring system.

Deflection of Buried Prestressed Concrete Cylinder Pipe with Soil-Pipe Interaction

Yongjei Lee,Maria Q. Feng,이은택 대한토목학회 2014 KSCE JOURNAL OF CIVIL ENGINEERING Vol.18 No.7

The deflection of the buried pipe is a function of the load on the pipe, and also the load on the pipe is a function of the deflection. It is a typical soil-pipe interaction. The vertical deflection of buried pipe with the soil properties has been relatively well studied, however, there is no proper and practical guideline on the horizontal deflection of buried pipe considering the soil-pipe interaction. In practice, the horizontal deflection is considered as the same as the vertical deflection and it provides unnecessary conservative design. In this study, the deflection of buried prestressed concrete cylinder pipe is measured using a selected soil model. A finite element model is built to reflect the soil properties, as well as the backfill and in-situ condition. An equation for horizontal deflection of buried pipe considering soil-pipe interaction is proposed.

Long-Term Monitoring and Analysis of a Curved Concrete Box-Girder Bridge

Sungchil Lee,Maria Q. Feng,Seok-Hee Hong,Young-Soo Chung 한국콘크리트학회 2008 International Journal of Concrete Structures and M Vol.2 No.2

Autonomous pothole detection using deep region-based convolutional neural network with cloud computing

Longxi Luo,Maria Q. Feng,Jianping Wu,Ryan Y. Leung 국제구조공학회 2019 Smart Structures and Systems, An International Jou Vol.24 No.6

Road surface deteriorations such as potholes have caused motorists heavy monetary damages every year. However, effective road condition monitoring has been a continuing challenge to road owners. Depth cameras have a small field of view and can be easily affected by vehicle bouncing. Traditional image processing methods based on algorithms such as segmentation cannot adapt to varying environmental and camera scenarios. In recent years, novel object detection methods based on deep learning algorithms have produced good results in detecting typical objects, such as faces, vehicles, structures and more, even in scenarios with changing object distances, camera angles, lighting conditions, etc. Therefore, in this study, a Deep Learning Pothole Detector (DLPD) based on the deep region-based convolutional neural network is proposed for autonomous detection of potholes from images. About 900 images with potholes and road surface conditions are collected and divided into training and testing data. Parameters of the network in the DLPD are calibrated based on sensitivity tests. Then, the calibrated DLPD is trained by the training data and applied to the 215 testing images to evaluate its performance. It is demonstrated that potholes can be automatically detected with high average precision over 93%. Potholes can be differentiated from manholes by training and applying a manhole-pothole classifier which is constructed using the convolutional neural network layers in DLPD. Repeated detection of the same potholes can be prevented through feature matching of the newly detected pothole with previously detected potholes within a small region.

적외선 화상기법을 이용한 시멘트 모트타르 특성의 실험적 평가

권성준(Kwon Seung-Jun),Maria Q. Feng 대한토목학회 2010 대한토목학회논문집 A Vol.30 No.1A

최근 들어 적외선을 이용하여 콘크리트 구조물의 결함 또는 공동 등을 평가하려는 비파괴 연구가 활발하게 진행되고 있으며 이는 유지관리기법의 중요한 부분을 이루고 있다. 적외선 화상분석(Infrared Thermography)을 콘크리트 표변에 적용할 경우 콘크리트의 표면온도는 표면을 구성하는 재질과 열적특성(비열, 열전도율, 열전달율)에 띠라 그 응답이 다르게 나타나 게 된다. 서로 다른 배합을 가지는 시멘트 모르타르에서는 공극률이 다르게 구성되고, 표면에서 공극률의 차이는 열에 노출된 뒤, 냉각되는 과정에서 열적 거동이 다르게 평가된다. 한편 이러한 공극률은 강도 및 염화물 확산계수와 같은 역학적/내구적 특성에 영향을 주기도 한다. 본 연구에서는 외부에서 열을 가하여 측정하는 능동방식(active type)을 이용하여, 표면의 온도변화를 분석하였다. 물-시멘트비 55%와 65%인 시멘트 모르타르 시편을 제작하였으며, 공극률, 압축강도, 염화물 확산계수 등의 물리적 특성값들이 평가되었다. 이후 동일한 실내조건(온도 20~22℃ 습도 55~60%)에서 적외선 화상분석 기법을 적용하였다. 시간의 경과에 따라 공극을 많이 포함하는 시편의 경우, 표면 온도가 상대적으로 증가하였으며, 온도가 일정해지는 시점(임계시점)이 단축되고 있음을 확인할 수 있었다. 이러한 특성은 콘크리트와 같이 공극과 골재를 가지고 있는 복합 재료의 품질 평가에 적용할 수 있음을 시사한다. 한편 공극률과 실험상수를 고려하여 공극률에 따라 변화하는 임계시간에 대한 계산식을 제안하였다. 본 논문에서는 시멘트 모르타르의 공극량의 변화에 따른 물리적 변화와 이에 따른 열특성 변화가 논의될 것이다. Recently, NDTs (Non-Destructive Techniques) using infrared camera are widely studied for detection of damage and void in RC (reinforced concrete) structures and they are also considered as an effective techniques for maintenance of infrastructures. The temperature on concrete surface depends on material and thermal properties such as specific heat, thermal conductivity, and thermal diffusion coefficient. Different porosity on cement mortar due to different mixture proportions can show different heat behavior in cooling stage. The porosity can affect physical and durability properties like strength and chloride diffusion coefficient as well. In this paper, active thermography which uses flash for heat induction is utilized and thermal characteristics on surface are evaluated. Samples of cement mortar with W/C (water to cement ratio) of 0.55 and 0.65 are prepared and physical properties like porosity, compressive strength, and chloride diffusion coefficient are evaluated. Then infrared thermography technique is carried out in a constant room condition (temperature 20~22°C and relative humidity 55~60%). The mortar samples with higher porosity shows higher residual temperature at the cooling stage and also shows reduced critical time which shows constant temperature due to back wall effect. Furthermore, simple equation for critical time of back wall effect is suggested with porosity and experimental constants. These characteristics indicate the applicability of infrared thermography as an NDT for quality assessment of cement based composite like concrete. Physical properties and thermal behavior in cement mortar with different porosity are analyzed in discussed in this paper.

Long-Term Monitoring and Analysis of a Curved Concrete Box-Girder Bridge

Lee, Sung-Chil,Feng, Maria Q.,Hong, Seok-Hee,Chung, Young-Soo Korea Concrete Institute 2008 International Journal of Concrete Structures and M Vol.2 No.2

Curved bridges are important components of a highway transportation network for connecting local roads and highways, but very few data have been collected in terms of their field performance. This paper presents two-years monitoring and system identification results of a curved concrete box-girder bridge, the West St. On-Ramp, under ambient traffic excitations. The authors permanently installed accelerometers on the bridge from the beginning of the bridge life. From the ambient vibration data sets collected over the two years, the element stiffness correction factors for the columns, the girder, and boundary springs were identified using the back-propagation neural network. The results showed that the element stiffness values were nearly 10% different from the initial design values. It was also observed that the traffic conditions heavily influence the dynamic characteristics of this curved bridge. Furthermore, a probability distribution model of the element stiffness was established for long-term monitoring and analysis of the bridge stiffness change.

탄산화에 노출된 콘크리트 구조물의 배합설계에 대한 연구

이성칠(Sung-Chil Lee),Maria, Q. Feng,권성준(Sung-Jun Kwon) 한국콘크리트학회 2010 콘크리트학회논문집 Vol.22 No.3

System identification of the suspension tower of Runyang Bridge based on ambient vibration tests

Zhijun Li,Dongming Feng,Maria Q. Feng,Xiuli Xu 국제구조공학회 2017 Smart Structures and Systems, An International Jou Vol.19 No.5

A series of field vibration tests are conducted on the Runyang Suspension Bridge during both the construction and operational stages. The purpose of this study is devoted to the analysis of the dynamic characteristics of the suspension tower. After the tower was erected, an array of accelerometers was deployed to study the evolution of its modal parameters during the construction process. Dynamic tests were first performed under the freestanding tower condition and then under the tower-cable condition after the superstructure was installed. Based on the identified modal parameters, the effect of the pile-soil-structure interaction on dynamic characteristics of the suspension tower is investigated. Moreover, the stiffness of the pile foundation is successfully identified using a probabilistic finite model updating method. Furthermore, challenges of identifying the dynamic properties of the tower from the coupled responses of the tower-cable system are discussed in detail. It\'s found that compared with the identified results from the freestanding tower, the longitudinal and torsional natural frequencies of the tower in the tower-cable system have changed significantly, while the lateral mode frequencies change slightly. The identified modal results from measurements by the structural health monitoring system further confirmed that the vibrations of the bridge subsystems (i.e., the tower, the suspended deck and the main cable) are strongly coupled with one another.