香港城市大学Lam教授学术报告通知(2018--57)


发布时间: 2018-09-13     浏览次数: 12

   目:The development of a probabilistic health monitoring system for railway ballast utilizing measured track vibration data

报告人:Ir Dr Paul Heung-fai LAMAssociate Professor,香港城市大学建筑与土木工程系

   间:2018914日上午930

   点:乐学楼1116

   要:

      For ballasted track systems, the ballast layer is an essential component that transfer the repeated heavy train load from the rails to the foundation. Although commercialized methods are available for the inspection of the rails, there is currently no commonly acceptable health monitoring method for the ballast, especially for the ballast region directly under the sleepers, which is critical for the safety of the ballasted track system. The mechanical properties of ballast is complicated, and it is believed that the stress-strain relationship is nonlinear under large amplitude vibration (e.g., train induced vibration). This presentation aims in studying the feasibility in developing a long-term health monitoring system for railway ballast by installing sensors on the track that capture the track vibration induced by the train. To achieve this goal, the nonlinear modeling of railway ballast in the rail-sleeper-ballast system is formulated first. A series of impact hammer tests that measure the track vibration under controlled impact forces were carried out. Structural model updating technique was then adopted to identify the nonlinear ballast stiffness of the system based on the measured vibration data. When the ballast is damaged, the ballast stiffness in supporting the track will be reduced. Therefore, it is possible to monitor the health condition of the ballast under the sleeper based on the identified ballast nonlinear ballast stiffness. Owing to the irregular shapes of ballast particles and high level of measurement noise, the model updating problem in identifying the nonlinear ballast stiffness is classified as unidentifiable. In this study, a new Bayesian method was developed to approximate the posterior probability density function (PDF) of the uncertain model parameters by samples generated from the multi-level Markov chain Monte Carlo (MCMC) simulation. Analysis of time-domain vibration data from the impact hammer test carried out on an indoor segment of a full-scale ballasted track with artificial ballast damage simulations showed high accuracy in detecting regions of damage and estimating the severity of damage; thus, demonstrating the feasibility of a possible extension of the proposed methodology for real-time and in-service track monitoring.


报告人简介:

       Ir Dr Paul Heung-fai LAM is currently associate professor in the Department of Architecture and Civil Engineering at the City University of Hong Kong. His research interest is structural dynamics, vibration measurement, modal identification, structural model updating and damage detection, Bayesian system identification, design and analysis of vertical axis wind turbine. Dr Lam has over 70 international journal papers published with over 30 keynotes and invited lectures/presentations. A total of HK$39,100,275 research grant has been funded.

Dr Lam is currently the President of the Hong Kong Society of Theoretical and Applied Mechanics (HKSTAM); Dr Lam is the Chairman (Education and Training) of the Hong Kong Construction Metal Structures Association (HKCMSA), and he is the key person in the promotion of Eurocodes in Hong Kong through organizing a series of technical seminars (Continuing Professional Development); and Dr Lam was elected as the General Secretary of the International Steering Committee (ISC) of the East Asia-Pacific Conference on Structural Engineering and Construction (EASEC), which is one of the most important structural engineering conference series in the region (EASEC has been held regularly every two years since 1986). Furthermore, Dr Lam is a committee member of ASCE Engineering Mechanics Institute (EMI) in both the “Structural Health Monitoring and Control” and “Dynamics” Committee.

Dr Lam is the guest editor of International Journal of Structural Stability and Dynamics (IJSSD) on the special issue on Structural Assessment and Health Monitoring. He is also the assistant editor of the Journal of Modeling in Mechanics & Materials. He is the editorial board member for International Journal of Lifecycle Performance Engineering, and the review editor for Structural Sensing of Frontiers in Built Environment.

Apart from research and professional leadership, Dr Lam dedicated tremendous effort in teaching and curriculum design. The Winner of Teaching Excellence Award (TEA) 2007/2008, a total of HK$1,172,000 teaching grant has been funded.