Smart Sensors for Safer Bridges:
A UC Davis-NTU Joint Research Effort

A. Bridge Scour

The erosion of soil, sand, and riverbed materials near bridge foundations due to flowing water (or wind in some cases) is a phenomenon known as bridge scour. Despite our awareness of its occurrence, bridge scour remains one of the deadliest causes of overwater bridge failures worldwide, particularly in the United States and in Taiwan. For instance, a notable scour-induced bridge collapse in the U.S. was the Schoharie Creek Interstate Highway Bridge incident (Mohawk River, NY) that happened on April 5, 1987. The 32-year-old bridge collapsed due to flood-induced extensive scouring at one of its piers, and 10 people lost their lives. In Taiwan, similar incidents have occurred as well. More recently in September of 2008, Typhoon Sinlaku brought heavy rainfall across many parts of Taiwan. The Houfeng Bridge collapsed due to flooding and severe scouring near one of its piers, although it was suspected that long-term riverbed degradation following the Chi-Chi Earthquake (in 1999) also contributed to its failure. Events like these could be traced back throughout the histories of both countries. Even worse is that overwater bridge collapses following scouring continue to occur and threaten public safety. The inability to monitor scour, detect damage, and direct repair efforts lead to ineffective infrastructure management, high maintenance costs, and unsafe structures. Thus, there is an urgent need to devise ways for us to track bridge scour and to warn the public of (and prevent) pending disaster.

It is important to note that a variety of technologies and techniques exist for monitoring bridge scour. One of the most common methods remains employing divers to conduct underwater visual inspections of bridge foundations. However, this approach is of limited effectiveness, especially since divers could only be deployed after typhoons or floods have subsided; in this case, loose sand and soil could refill scour holes, thereby leading to a false diagnosis that the bridge is safe and that damage has not occurred. Murky waters and turbulent conditions also add to the challenges of visual inspection. On the other hand, technologies such as sonar, vibration sensors, magnetic sliding collars, tilt sensors, and fiber optics have been implemented or are subjects of active research investigations. While some of these technologies offer great promise, they also suffer from limitations such as being expensive, inaccurate, inaccessible, and/or unreliable. In short, the civil engineering community remains very much open to finding a high-performance, affordable, and reliable sensor solution for monitoring the progression of bridge scour.

B. Research Activities

The overarching goal of my research project, which is funded by the U.S. National Science Foundation (NSF, Hazard Mitigation and Structural Engineering program), is to devise a sensing system that could directly measure the depth, shape, and overall topography of bridge scour holes and in real-time. The data generated would then be used to improve computational models of the bridge and flow environment, thereby improving our physical understanding of bridge scour phenomenon as well as enhancing the predictive capabilities of these models. The availability of such predictive models would be an invaluable tool for transportation agencies around the world for asset management and hazard mitigation purposes. In addition, another very important long-term goal is to examine U.S. and Taiwan bridge design codes and whether or not these results could contribute to improving design parameters for enhanced structural resilience against scour.

As a step towards this goal, I have been able to spend six months in the Department of Civil Engineering at the National Taiwan University (NTU) in Taipei (hosted by Chair and Prof. Liang-Jenq Leu), thanks to the generous support provided by the U.S. Fulbright Scholar Core Program. I have also had the pleasure of working with some of the leading experts in bridge scour research, namely Prof. Jihn-Sung Lai (Hydrotech Research Institute, NTU), Prof. Chin-Hsiung Loh (NTU), and Prof. Tzu-Kang Lin (National Chiao Tung University). The objective during my Fulbright tenure is to fabricate prototype bridge scour sensors and to use the unique testing facilities at NTU for characterizing sensor performance. While the research objectives are clearly defined, I am leveraging this unique opportunity as a catalyst for establishing longstanding and intimate research collaborations with NTU and other Taiwanese institutions.

The sensor designed for this project is based on embedding a piezoelectric polymer thin film in a waterproofed rod-like structure. The sensing concept is simple; the rod-like sensor strip would be initially buried underneath the riverbed, and scour would erode sediments to expose the sensor strip. Water (or fluid) flowing past the exposed sensor strip would excite it and cause it to vibrate. Since piezoelectric materials generate electrical charge in response to strain or deformation, the vibrating sensor strip would generate electricity of magnitude proportional to its physical vibration. More importantly, the amount of sensor exposure (i.e., scour depth, which is also the quantity that we seek to measure) would be proportional to how fast the sensor is vibrating (i.e., the sensor’s natural frequency at that particular exposed depth). Since natural frequency could be deduced from the piezoelectric sensor’s voltage output, one would be able to use this sensor to track the depth of the scour hole over time. An added benefit is that the sensor generates its own power and is thus suitable for field instrumentation and long-term use.

At NTU and the Hydrotech Research Institute, my work focused on improving the design of these sensor strips. Through funding provided by NSF’s Research Experiences for Undergraduates (REU) program, my student (Ms. Jennifer Yasui) was also able to spend her summer in Taiwan assisting with this project. We worked with a local company to waterproof the sensors, as well as to establish a more durable exterior packaging. With these prototype sensors fabricated and in place, testing is currently being conducted using one of NTU’s hydraulic flumes. These flumes provide a controlled environment in which bridge scour could be simulated, while the performance of these sensors could be tested and verified. My graduate student working on this project, Ms. Faezeh Azhari, is also conducting parallel testing at the University of California (UC), Davis. The data produced from both sets of experiments could also facilitate some of the numerical modeling research on bridge scour currently in progress at NTU and at UC Davis (in collaboration with Prof. Fabian Bombardelli, UC Davis). The last stage would be to conduct large-scale testing at the Taiwan Ministry of Economic Affairs, Water Resources Agency laboratory (in Xindian, New Taipei City). I expect that these experiments would be able to subject the sensors to more realistic test conditions and provide valuable data so that they could be improved and one day be used in the field.

C. Beyond Scour Research

Although the main purpose of my Fulbright research was to investigate a new sensing system for bridge scour monitoring, I was very fortunate to have met other researchers in Taiwan and utilized this opportunity to broaden my scope of research. For instance, we conducted scaled wind turbine shaking table tests at the National Center for Research on Earthquake Engineering (NCREE) in Taipei. The rich dataset generated and my close collaboration with the research team earned my position to serve on the thesis committees for two NTU Civil Engineering M.S. students. We are also preparing a journal paper for peer-review. In addition, I also started co-advising a Ph.D. student at NTU (Mr. Shieh-Kung Huang), and he will participate in another related project on wind turbine blade monitoring, which is also funded by NSF. Work is already underway to design a new wireless data acquisition system for interrogating nano-composite sensors embedded in these wind blades. Besides these activities at NTU, I have also met new collaborators and friends at National Cheng Kung University and National Kaoshiung First University of Science and Technology. We are exploring new ideas for future, internationally funded, collaborative projects on topics such as energy harvesting and establishing a smart materials summer school in Kaoshiung, among many others.

During my stay in Taiwan, I also had the great pleasure of working with NTU and NCREE local organization team to host the 10th International Workshop on Advanced Smart Materials and Smart Structures Technology and the 7th Asia-Pacific Summer School (APSS) on Smart Structures Technology. The conference and summer school were co-chaired by Prof. Chin-Hsiung Loh and Prof. Kuo-Chun Chang, both Distinguished Professors of Civil Engineering at NTU. The objective of the international workshop was to assess the current progress in smart materials and smart structures technology and to develop synergies among researchers working in various disciplines and from different countries. The workshop was a tremendous success, with nearly 100 international participants that traveled to NTU and NCREE. A total of eight keynote lectures, 22 paper presentations, and a technical tour was organized over the course of three days. Funding for this workshop was graciously provided by the Taiwan Ministry of Science and Technology, Taiwan Ministry of Education, and the U.S. Office of Naval Research Global.

In addition, approximately 50 of those participants were students from the U.S., Japan, South Korea, China, and Taiwan; most of these students remained in Taiwan for the three-week APSS summer school program at NTU, which is set to conclude on August 15, 2014. Besides lectures delivered by world renowned academic leaders working in the smart materials and structures fields, students were also involved with hands-on experiments where they conducted shaking table tests using the facilities at NCREE. The goal was to immediately apply what they learned in the classroom and to demonstrate that they could use different algorithms to detect damage occurring in a test structure (i.e., structural health monitoring) or to control its behavior during strong ground shaking (i.e., structural control). These activities would not

D. Personal Impact and Reflections

Besides the opportunities that the Fulbright Program has provided for my professional career, my family and I have had the most pleasant experience living in Taipei. It is the first time, since my wife (Sunny) and I graduated from Taipei American School in 2000, that we were able to spend a considerable amount of time living in Taiwan. Both of our immediate and extended families have always been in Taiwan, and we were able to reconnect with many of them. However, our most fruitful personal outcome after staying in Taiwan for an extended period of time is that we were deeply immersed in the local culture and language. Not only can my wife and I speak Mandarin more fluently, but I have also been able to, for the first time, give technical lectures in Mandarin when I visited various institutions throughout Taiwan. We are also extremely pleased that our son (Jacob), who is now 18-months-old, can understand and communicate with us in Mandarin. His first words (i.e., mom and dad) were also in Mandarin! All in all, we are thankful to all the faculty, staff, and students in the Department of Civil Engineering at NTU to make this trip possible, as well as to Fulbright Taiwan for this once-in-a-lifetime experience. Our sincere gratitude goes out to all the friends, families, colleagues, students, and strangers that have made our life in Taiwan a completely fabulous and unforgettable experience!

Short Biography:

Dr. Kenneth Loh joined the Department of Civil & Environmental Engineering at the University of California, Davis as an Assistant Professor in 2009 and was recently promoted to Associate Professor with tenure. He is also currently a U.S. Fulbright Scholar in Taiwan (2013-2014) and Visiting Associate Professor in the Department of Civil Engineering at the National Taiwan University (until December 2014). Prior to this, he received his B.S. degree in Civil Engineering from Johns Hopkins University in 2004. He continued his graduate studies at the University of Michigan, where he completed two M.S. degrees in Civil Engineering (2005) and Materials Science & Engineering (2008), as well as a Ph.D. in Civil Engineering in 2008. His research interests include multifunctional materials, nano-engineering, composites, advanced manufacturing, biologically inspired systems, and resilient structures. Dr. Loh’s recent honors include the Achenbach Medal, NSF CAREER Award, SPIE Senior Member honor, and multiple best paper awards.