Tokyo Tech Strategic Research Field SSI Next-generation Social Infrastructure We Envision 2nd Session
Building a Resilient Society
Asst. Prof. Kazuya Mitsui, Asst. Prof. Kazuhide Nakayama
School of Environment and Society
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SSI has established four themes, “Building a Resilient Society,” “Designing Voices of the Earth,” “Creating Smart Cities,” and “Innovation,” to move toward the future society that we want to create. In this installment, Assistant Professor Kazuya Mitsui from the Department of Architecture and Building Engineering and Assistant Professor Kazuhide Nakayama from the Department of Civil and Environmental Engineering were featured on the topic of “Building a Resilient Society.” We spoke with them about their current research and other activities at SSI.
Moving toward lightweight, earthquake-resistant buildings
- First of all, what kind of research do you do, Assistant Professor Mitsui?
Mitsui: I am studying buildings, specifically “steel structural buildings” built using steel. Because of its superior strength to weight, steel is used in many buildings, from high-rise buildings in front of train stations to ordinary houses.
When an earthquake or typhoon causes shaking, buildings are damaged. The simplest way to reduce damage to buildings and improve their seismic performance is to increase the thickness of columns and beams, but this method consumes a lot of steel, which adds costs. In addition, since 2 tons of carbon dioxide are emitted in the process of manufacturing 1 ton of steel, it is undesirable to increase the amount of steel used here from the perspective of preventing global warming, which has been called for in recent years. It is generally believed that reducing the amount of steel will reduce the strength of a building, but I believe that controlling damage can improve seismic performance.
Therefore, our laboratory is researching techniques to minimize earthquake damage while reducing the amount of steel.
Asst. Prof. Mitsui
A focus on the physical phenomenon of “buckling”
A focus on the physical phenomenon of “buckling”
- What kind of research do you do exactly?
Mitsui: A unique aspect of our laboratory is that we focus on “buckling.” You have probably played a game where you push a desk pad or ruler, bending it to the breaking point. This is “buckling.” Buckling occurs not only in desk pads, but also in the members of a building, such as the columns and beams, and is one of the factors that cause buildings to collapse.
Buckling is often perceived as a bad phenomenon, but it can be predicted precisely based on mathematics. We are considering using this phenomenon to build control technology to generate buckling at targeted points and timing in steel structures and to make good use of buckling.
This technology allows us to predict which points of a building will accumulate damage and to what extent in the event of a major earthquake. It also allows for quick repairs. In a disaster-prone country like Japan, it is important to make buildings that are resistant to disasters, but even if one is damaged, it is easier to protect lives and property if the damage is done in the “right” way.
By thus controlling the phenomenon of buckling, the energy of an earthquake is concentrated and absorbed at specific points, thereby minimizing the damage caused by the natural disaster.
- Theoretical calculations can be used to derive how and in which parts of the building the buckling-prone points should be placed.
Mitsui: In the design of high-rise buildings, it is common practice to simulate the shaking of the building during an earthquake. For a precise simulation, data points such as “this column breaks down in this way” are essential. However, such data points are not abundant. Therefore, our laboratory investigates data on how columns and beams break by buckling through experiments and analysis.
Moving toward effective and efficient maintenance of concrete structures
Asst. Prof. Nakayama
- Next, what kind of research do you do, Assistant Professor Nakayama?
Nakayama: My research focuses on strategies for effective and efficient maintenance and management of concrete structures, as well as methods for evaluating the performance of structures that can be used as a basis for making decisions when considering strategies. The basic idea is to make minor alterations to things that are in good condition so that they can be used as long as possible, and revamp things that need to be rebuilt.
Deciding whether to continue using a concrete structure while making minor alterations to it or instead revamping it requires a basis for making the decision. Therefore, for structures such as tunnels and bridges, for example, periodic inspections are currently conducted once every five years. The main methods used are a “hammering test,” in which the concrete is tapped with a hammer to check for flaking or peeling, and a “close-up visual inspection,” in which the concrete surface is visually observed for changes and deformations. However, these require the assistance of skilled technicians. In addition, since public structures must be managed over a long period of time, inspection methods and data must be passed on to the next generation of technicians and engineers. With the number of technicians and engineers on the decline these days, we believe that there is a need for inspection methods that can provide inspection data that can be easily passed on to the next generation, regardless of the ability of them.
Therefore, I am studying methods related to performance evaluation of concrete structures in order to solve such problems.
Evaluate the condition of concrete and rebar using electrical (electrochemical) properties
- What exactly is the method?
Nakayama: There are two methods: one is to evaluate the electrochemical properties of rebar and the other is to evaluate the electrical properties of concrete.
First, let me talk about the method for evaluating electrochemical properties. For example, in Japan (an island nation), when salt and water from the sea permeate the concrete to some extent, the rebar begins to corrode. Rebar corrosion is a reaction in which iron is leached as iron ions, an electrochemical reaction involving the exchange of electrons. Therefore, by measuring the ease of electrochemical reaction of the rebar, the corrosive progression of the rebar inside the concrete can be evaluated.
Next, let me talk about the method for evaluating electrical properties. As I mentioned earlier, corrosion of rebar begins when deterioration factors such as salt and water reach a certain degree around the rebar. In other words, the ease of corrosion can likely be predicted by evaluating how fast the deterioration factors can move through the concrete portion of the structure from the surface to the rebar (the cover). The ease of migration of these deterioration factors in concrete is affected by the pore structure and water content of the concrete. There is also a correlation between the electrical properties of concrete and its pore structure and water content. If we can elucidate the correlation and controlling factors, we should be able to evaluate the ease of migration of deterioration factors in concrete, and thus the ease of corrosion of rebar, based on electrical properties, regardless of the type and condition of the concrete.
Based on these two methods, we aim to establish a performance evaluation method for reinforced concrete structures. We believe this will help to achieve sustainable maintenance while maintaining a high level of reliability.
- What are some of the difficulties in studying these methods?
Nakayama: Many infrastructures such as bridges and tunnels are huge, so evaluation of points and surfaces does not necessarily translate into an overall evaluation. What indicators, which parts, when, and with what degree of precision can be used to help maintain and manage the structure? This is a difficult issue and one that is currently being studied.
For example, we believe that inputting measurement data into the simulation being conducted by Associate Professor Nobuhiro Chijiwa (https://sites.google.com/view/ssiwg-en) to depict the future state of the structure in a virtual space will provide hints for solving the aforementioned issue.
We want to explore the path to a resilient society through collaboration between architectural and civil/environmental researchers
- Assistant Professor Mitsui, you specialize in steel structures and Assistant Professor Nakayama, you specialize in concrete engineering. What kind of collaboration do you expect at SSI in the future? The word “resilient” has the connotations of both “flexible” and “having the ability to recover.” What are your thoughts on this, especially from the perspective of creating a resilient society?
Mitsui: In Japan, the fields of architecture and civil engineering are separated, so there have been limited opportunities for me, an architect, and Assistant Professor Nakayama, a civil and environmental engineer, to interact with each other. However, architecture and civil engineering are fields with many technical similarities.
I believe that every university is conducting research in architecture and civil engineering based on the premise of a resilient society. In terms of what only Tokyo Tech SSI can do, SSI (which facilitates interdepartmental collaboration) has been added to a previously vertically divided organization, allowing researchers who had not previously interacted with each other to exchange opinions and explore together the path they should all be aiming for.
“SSI is conducting this kind of research to move toward a resilient society.” We believe that it is first and foremost important to disseminate this message to the broader world so that young researchers in various fields can work together to create a large movement.
Nakayama: As Assistant Professor Mitsui mentioned, I think it is important for SSI to have cross-disciplinary discussions and to coordinate the path that Tokyo Tech as a whole should aim for.
In addition, when aiming for a resilient society, cross-disciplinary integration within SSI is indispensable from an academic perspective as well. Buildings, houses, and other structures, and public structures such as roads and bridges, need to be conceived of as one town or region, rather than separately. In this respect, I have very high expectations for SSI and I strongly believe that we, the younger generation, must lead the way.
Mitsui: I completely agree. I believe that it will be more necessary than ever before for various experts to pool their wisdom, establish a single concept for each municipality or region, and achieve community development in line with that concept.
The other day, Assistant Professor Nakayama came up with the idea of creating a place on the Tokyo Tech campus for experiments that would be the preliminary stage for real world implementation, through SSI. It is often difficult to immediately implement research seeds from a university in the real world. Therefore, as an SSI project, we hope to build a structure for real world experimentation, and SSI members can use the structure as a testing ground in their own way, in addition to as a place for collaboration. I would like to work more actively in cooperation with Assistant Professor Nakayama as well.
- I look forward to the future endeavors of all the young researchers. Thank you very much for your time today.
Kazuya Mitsui
Assistant Professor, Department of Architecture and Building Engineering,
School of Environment and Society, Tokyo Institute of Technology
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2012.3: Graduated from Nagoya Institute of Technology
2014.3: Completed the Master Program, Nagoya Institute of Technology
2017.3: Completed the Doctoral Program, Nagoya Institute of Technology
2017.4: Nippon Steal Research & Development Laboratories
2019.7: Assistant Professor, Department of Architecture and Building Engineering, Tokyo Institute of Technology
Kazuhide Nakayama
Assistant Professor, Department of Civil and Environmental Engineering,
School of Environment and Society, Tokyo Institute of Technology
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2014.3: Graduated from Tokushima University
2016.3: Completed the Master Program, Tokushima University
2018.4: Assistant Professor, Department of Civil and Environmental Engineering, Tokyo Institute of Technology
2019.3: Completed the Doctoral Program, Tokushima University
Published: June 2024
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