Tokyo Tech Strategic Research Field SSI        Next-generation Social Infrastructure We Envision       1st Session

Creating next-generation social infrastructure

Assoc. Prof. Nobuhiro Chijiwa 

School of Environment and Society

Beginning of activities by the SSI Young Researchers Working Group

Tokyo Tech established a working group consisting mainly of young researchers from the School of Environment and Society. The working group is initially composed of nine members. Going forward, SSI plans to increase the number of members and expand the activities of the working group. What is the next-generation social infrastructure do young researchers envision? To answer this question, we will hold discussions with the nine members over a total of five sessions. In the first session, we talked with Associate Professor Nobuhiro Chijiwa of the Department of Civil and Environmental Engineering, who serves as the leader of the young researchers working group. Associate Professor Chijiwa discussed the activity policy of the working group and the content of his own research.

Creating next-generation social infrastructure

Role to be fulfilled by the School of Environment and Society

—Associate Professor Chijiwa, your field of expertise is civil engineering and architecture. This field is responsible for social infrastructure and has a very strong relationship with society. Therefore, it is essential to build consensus with local residents. In regard to global environmental issues, similar challenges are faced when introducing renewable energy. It is clear that the School of Environment and Society has a closer relationship with society than other schools.

Chijiwa  At disaster sites, every minute counts, so triage and other consensus-building efforts occur immediately. However, since global warming is a phenomenon that is slowly destroying society , it is difficult to reach a consensus. Even so, damage from natural disasters has increased both in Japan and overseas due to abnormal weather conditions in recent years. As a result, all people are finally beginning to realize the urgency of preventing global warming. SSI plans to formulate guidelines for Tokyo Tech based on serious discussions about how to build a sustainable future society, including measures to prevent global warming.

Building a base where young researchers can freely exchange opinions

—What issues do you plan to address in the SSI young researchers working group?

Chijiwa  Although academic fields have become increasingly fragmented, it is impossible for a single field to solve social issues such as global warming. The importance of integrating different fields has been pointed out for some time. Nevertheless, the reality is that integration is not progressing.

The SSI young researchers working group believes that the first step is for members to share a common awareness of issues. Even within the School of Environment and Society, students with different fields of expertise have different cultural bases, and therefore perceive things differently. Working group members have high hopes for using SSI as an opportunity to expand their horizons by learning about fields in which they lack knowledge. Therefore, we are working to create a base where young researchers in the School of Environment and Society can freely exchange opinions.

After something has been researched and developed, it takes many years for society to actually accept that development. Therefore, it is extremely important for young researchers, who will lead society in the future, to frankly exchange their opinions on what kind of future society they would like to create and to consider the direction of initiatives. I hope that young researchers will be able to think freely and have fun while engaging in activities that contribute to solving social issues.

SSI is dealing with extremely complex subject matter. Accordingly, it is unlikely that the working group will be able to devise answers after only one or two years of activities. Nevertheless, by spreading the word about the existence of such a center for activities and raising awareness, we hope to gradually increase the number of participants in our discussions and grow into a larger movement.

Using simulations to conduct research on concrete buildings

The Great Hanshin-Awaji Earthquake caused the collapse of reinforced concrete structures that had been considered as unbreakable even in large earthquakes. This event was known as the “collapse of the myth of concrete safety.” Using a simulation system which he had developed, Professor Maekawa analyzed those structures and clarified the mechanism that caused the collapse of concrete pillars. Since then, I have heard that the evaluation of surrounding simulations in fields such as civil engineering and architectural have changed completely.

Afterwards, in conjunction with rapid improvements in the performance of computers, research and development became possible through the trinity of theory, experimentation, and computational science. In particular, in recent years, it has become possible to engage in design using CAD (Computer Aided Design) and perform 3D analysis on a computer. This made it possible to significantly reduce the number of experiments, thereby reducing costs and shortening the period for research and development.

The method of conducting experiments is also changing with the development of analysis technology. For example, simply conducting a large number of experiments is not sufficient to develop a good simulation model. Instead, it is necessary to search for experimental conditions that will have the greatest effect on your desired outcome, and then implement those conditions. Numerical analysis is an efficient means to search for such conditions. Moreover, when actually conducting an experiment, researchers can avoid overlooking important points by using analysis to predict the expected results in advance. If the experiment and predictions differ, researchers are able to immediately investigate the reasons for those differences, thereby enabling them to conduct efficient research. I was taught this style of research by Professor Maekawa. I recently heard that similar methods are being used by famous global companies.

Aiming to become a “doctor” for concrete buildings

—Simulation is now indispensable in all fields. Specifically, it fulfills an extremely important role in the fields of civil engineering and architecture.

Chijiwa  There are various types of deterioration in buildings, and each type of deterioration has a different effect. For example, the deterioration of one section may not pose a significant issue, but the deterioration of another section could be fatal. By conducting simulations that account for changes over time in the entire target structure, it is now possible to judge the severity of problems and to rationally decide on appropriate countermeasures. Therefore, I am currently focusing on research to increase the usefulness of simulations for the maintenance and management of buildings.

In particular, much of the infrastructure built in Japan during the period of high economic growth has deteriorated, and the reinforcing bars inside reinforced concrete structures are now rusting. However, the impact on structural performance will vary depending on where and to what extent the rusting occurs. My research aims to reliably determine the effects of rust, evaluate performance, and set usage limits.

When I was a student, my instructor Professor Maekawa told me that I should become a “doctor” for concrete. Furthermore, Professor Maekawa advised me to implement the philosophy of Eastern medicine; that is, to not only eliminate the root cause of disease, but also to rebalance the entire body so that it coexists as a single constituent. This is in contrast to how physicians who practice Western only treat the diseased part. This advice from Professor Maekawa still guides my research even today.

My future goals are to recommend optimal repair methods and predict the lifespan of buildings. The structure of a building is not the only important aspect; rather, it is also important how the building responds to typhoons and earthquakes. Therefore, I hope to implement a variety of perspectives in order to contribute to the development of safe and secure next-generation infrastructure.

Deciding to become a researcher after reading an essay written by my uncle when I was in elementary 

—Professor Chijiwa, could you please elaborate on why you chose this particular field of research?

Chijiwa  The first step in my journey came when I was an elementary school student. I became interested in concrete after reading an article about prestressed concrete in a book written by my uncle, who was researching concrete. The book was a collection of essays written for engineers.

Prestressed concrete is a material which prevents cracks by applying compressive stress (prestress) to concrete in advance in order to cancel out the tensile stress exerted on concrete by load. This allows the entire surface of the concrete to function effectively and extends the lifespan of concrete (Figure).

My uncle explained this principle in an easy-to-understand manner using mahjong tiles. I found his example to be extremely interesting. Anyone who has played mahjong or donjara knows that it is possible to lift up a line of multiple tiles by pressing them together at both ends and then lifting. This works even though the tiles are not glued together. Prestressed concrete bridges use exactly the same principle as this example. This creates a crack-free structure even while using concrete that is weak against tension. As an elementary school student, I didn’t understand any of the concrete-related technical terminology used in the book. Still, I learned that the core of cutting-edge technology is made using familiar ideas that even a child like myself could comprehend. I found this to be a moving experience.

During my doctoral course, I conducted research on reinforced concrete structures which cracked due to corrosion of the steel rods. However, after receiving my doctoral degree, I was advised by my mentor to stop focusing on cracks for the time being. At the same time, I decided to address the problem of deflection of prestressed concrete.

A bridge name Tsukiyono-ohashi Bridge stands on the Kanetsu Expressway, on the way from Tsukiyono Interchange to Naeba Ski Resort (Photograph). This bridge was built about 40 years ago. The design prediction stated that deflection would slowly increase over time, eventually reaching about 4 centimeters. In reality, a deflection of 15 centimeters had occurred. After this was reported at an international academic conference in 2008, a series of similar reports were around the world, and deflection became a global issue.

When I used the latest simulation system to recreate Tsukiyono-ohashi Bridge and calculated how the bridge would deflect after construction, I calculated deflection in line with the actual measurement. In simulations, researchers can perform various analyses by setting conditions that cannot be reproduced in reality. I took advantage of these characteristics to analyze the causes. As a result, in the design process, bridge deformation was predicted based on several years of experimental data using small laboratory test specimen. In contrast, the size and environment of actual bridge differed from the laboratory test specimen. I determined that this difference caused a discrepancy in deformation over time, and that this discrepancy was the cause of the difference between the design prediction and actual deflection.

Furthermore, when I used this simulation to predict the future, I found that the progress of deflection has essentially stopped at the current amount and stabilized. Consequently, no action is needed. On the other hand, if engineers were to attempt to eliminate the deflection simply by pouring more concrete onto the road surface, it would further increase the burden placed on the bridge and amplify the deflection.

Simulations have now become indispensable in civil engineering and architecture. Similar to the diagnostic technology used by physicians, these simulations have evolved to the extent that appropriate treatment is possible.

What kind of future society will Japan construct in response to a declining birthrate and aging society?

—In regard to the SSI young researchers working group, you discussed the importance of exchanging opinions between researchers in different fields. Personally speaking, what kind of problem awareness do you have on a daily basis regarding the issue of exchange?

Chijiwa  Actually, until I came to Tokyo Tech, I didn’t give much thought to the fusion of different fields. However, upon joining Tokyo Tech in 2013, I was able to discuss the future of concrete engineering with Professor Mitsuyasu Iwanami, and started to realize that there was little point in simply researching structures.

For example, let’s imagine that a construction group is considering where to build a new road. The role of the structural designer comes after the route plan has been determined. Based on the conditions defined in the route plan, structural designers search for the optimal solution that will satisfy the required strength and durability. In urban areas where land is scarce, routes tend to be planned in coastal areas where rust is more likely to occur. This makes it necessary to consider durability during the design process. However, if the route could be moved slightly inland rather than along the coast, that change alone would suppress the deterioration of infrastructure and enable the construction of infrastructure that would function stably for a long time at low cost. In order to realize this kind of idea, it is not enough to only research individual buildings; rather, it is necessary to collaborate with related fields.

Furthermore, the deterioration of infrastructure built during the period of high economic growth became widely recognized after the accident caused by a falling ceiling plate in the Sasago Tunnel on December 2, 2012. Today, Japan has introduced systems for regular inspection of infrastructure, and renovation work is progressing in order of urgency. Even so, some projects do not proceed as planned due to lack of manpower and funding.

Japan is a nation with a declining birthrate and aging population. Depopulation is progressing, especially in rural areas. As such, a situation is emerging where it is difficult to maintain and manage infrastructure. However, the government cannot easily issue a statement such as “Due to a lack of manpower and funds, we are unable to manage the infrastructure situation. Consequently, we have decided to abolish the water pipes around your neighborhood. These pipes have few users and the population is unlikely to increase going forward. Residents should figure out how to procure their own water, or considering moving to a different location.” This kind of government response would be especially cruel to elderly people by forcing them to move from their homes of many years.

Currently, Japan is proposing concepts such as compact cities and smart cities as visions of future society. The future cannot be viewed as a simple extension of the past. Instead, we need to return to the basics and hold discussions on what kind of society we want and how we should build that society. In that respect, I believe that the SSI young researchers working group fulfills an important role. Please expect great things from our working group going forward.

—Thank you very much for your time today.

Nobuhiro Chijiwa 

Associate Professor, Department of Civil and Environmental Engineering, 

School of Environment and Society, Tokyo Institute of Technology

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2004: Graduated from the Department of Civil Engineering, Faculty of Engineering, the University of Tokyo

2006: Completed the Master Program, Department of Civil Engineering, Graduate School of Engineering, the University of Tokyo

2009: Completed the Doctoral Program, Department of Civil Engineering, Graduate School of Engineering, the University of Tokyo

2009: Project Assistant Professor of Global COE Program, "Global Center of Excellence for Sustainable Urban Regeneration," Graduate School of Engineering, the University of Tokyo

2012: Assistant Professor, Department of Civil and Environmental Engineering, Graduate School of Engineering, Tokyo Institute of Technology.

Since 2016: Current position.

Conducting research on the development of new materials and performance evaluation methods for reinforced concrete structures with the aim to contribute to the realization of a rich and sustainable society with concrete engineering as the primary expertise.

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Published: March 2024