Research

　The Nankai Trough Earthquake is expected to generate strong ground motions and massive tsunamis across a wide area of Japan from the Tokai to Kyushu regions, causing severe damages to structures and infrastructure along the Pacific coast. Such severe events would inevitably result in significant casualties and disaster waste. As countermeasures for such huge cascading hazards, including earthquakes and tsunamis, the development of high-strength structures alone is not sufficient; the management of the possibility of structural failures (reliability) and its impacts on regional infrastructure systems and recovery operations (risk and resilience) under multiple hazards are required. This study develops analytical frameworks to address these challenges. For example, reliability assessments of road structures under cascading seismic and tsunami hazards, as well as impact estimates of structural damage on road network connectivity, tsunami-induced casualties, and disaster waste disposal time, have been established. Furthermore, by incorporating other disasters such as floods and landslides caused by heavy rainfall, comprehensive multi-hazard frameworks have been developed to support disaster prevention and mitigation strategies.
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　Bridges are critical components of road and railway networks, requiring immediate post-earthquake usability to allow the passage of emergency vehicles. This study focuses on the development of damage-free structures capable of maintaining serviceability even in the immediate aftermath of strong seismic excitations and precast structures that can be deployed rapidly as emergency temporary bridges. To evaluate structural performance and optimize the design, the research integrates advanced techniques and instruments, including 3D printing, three-dimensional shake-tables, and finite element analysis. The damage-free structures employ a friction pendulum-based seismic isolation system, in which the sliding of a nylon pendulum reduces inertial forces and the inclination of the sliding surface suppresses residual displacements. On the other hand, precast reinforced concrete (RC) blocks with proposed connections that can be easily assembled and disassembled without specialized equipment are developed to deploy temporary emergency superstructures.
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　Climate change is expected to escalate loads and actions on structures and infrastructure, including increased tsunami intensity due to sea-level rise, elevated hydrodynamic forces and scouring depths on riverine bridges caused by extreme rainfall, and accelerated material deterioration from global warming. These effects present significant challenges to structural safety and risk management. Predicting such impacts involves substantial uncertainty and non-stationary phenomena that evolve dynamically over long-term periods. This study aims to evaluate the impacts of climate change on infrastructure and develop structural design methods that account for these effects. For instance, the risk assessment and tsunami insurance portfolio have been developed for coastal regions exposed to tsunami hazards intensified by sea-level rise. Moreover, a novel structural design methodology for river embankments has been developed, accounting for the combined effects of extreme rainfall and climate change. The research provides analytical foundations for assessing long-term (over 100-year) impacts of climate change on structures and developing climate-resilient engineering solutions.
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　Global warming has been intensified by a sharp increase in greenhouse gas emissions, demanding significant decarbonization of major CO2-emitting industries to realize a carbon-neutral society. Since the cement and concrete industry represents 7–8% of global CO₂ emissions, innovations of near zero-emission concrete using abundant resources are urgently needed. This study aims to develop a near zero-emission concrete using a novel decarbonized material, WMaCS® (Waseda Magnesium-based Carbon Sequestration materials). WMaCS, including raw materials of Sorel cement (MgO, MgCl2, and H2O) and magnesium carbonate (MC), are produced via technologies that utilizes CO2 captured from a power plant and reacts it with seawater-derived MgO. Blending Sorel cement with MC creates a denser SCMC binder with enhanced compressive strength, water resistance, and CO2 sequestration capacity, offering a promising pathway toward a next-generation sustainable concrete with near zero-emission concrete production. The study involves optimization of concrete mixtures to enhance concrete properties, structural performance evaluation of reinforced WMaCS concrete members, and durability assessment of concrete under environmental exposure. As WMaCS concrete has low alkalinity and high chloride concentration, the research also explores its practical applications as unreinforced precast blocks and wave-dissipating tetrapod, non-structural decorative façade panels, and non-metallic bars reinforced concrete members.
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　Since most structures and infrastructure in Japan were constructed during the period of rapid economic growth (1955-1973), efficient maintenance and management for the widespread aging bridges must be established. As a common deterioration mechanism of reinforced concrete (RC) structures, external actions such as chloride attacks lead to corrosion of steel reinforcement, which subsequently causes corrosion-induced cracking due to the expansion of corrosion products and a decrease in the long-term structural performance during their service life. As the structural performance of deteriorated RC structures depends on localized steel corrosion, modeling spatial variability in steel corrosion using the inspection data of corrosion crack widths is important for obtaining accurate evaluation of the long-term structural performance which in turn help enhance reliability-based life-cycle management. However, several studies show a very large dispersion in the relationship between corrosion crack width and steel corrosion at different corrosion levels, resulting in a limited accurate degree of prediction models based solely on empirical formulas. To address this challenge, this study proposes an integrated approach combining machine learning, structural analysis, image processing, and updating techniques to develop a novel structural performance evaluation methodology. The proposed system can assess the structural health of deteriorating concrete bridges using only images of corrosion-induced cracks captured by drones, allowing automated diagnosis of serviceability and the need for repair.
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　In RC and PC structures, reinforcing bars and PC strands are used to resist tensile stresses, whereas concrete primarily carries compressive stresses. They are widely used as primary structural components in bridges worldwide. Differences in stress states and reinforcement configuration between RC and PC structures lead to different mechanisms of corrosion initiation and deterioration, as well as in their effects on structural performance. However, the influence of these different corrosion mechanisms on the life-cycle reliability and seismic assessment of RC and PC structures remain unclear and need elucidation. This study aims to clarify the corrosion mechanisms and structural performance of deteriorating RC and PC structures, integrating experimental and computational investigations. For instance, a non-destructive monitoring method combining X-ray and digital image processing techniques are employed to investigate and quantify the spatial growth in steel corrosion in RC and PC structures. The experimental results are utilized to develop structural performance assessment methods that consider the effects of steel corrosion on the load-bearing capacity, ductility, failure mode, and seismic performance. The findings provide important insights for extending the service life of RC and PC structures and developing rational maintenance and management strategies.
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　Labor shortages in the construction industry are a growing concern in Japan due to declining birth rates and population aging. This study aims to address this challenge by developing a labor-saving fabrication process for precast pile members along with automatic non-destructive quality control methods. Specifically, steel fiber-reinforced concrete (SFRC) piles are manufactured using a centrifugal forming method, eliminating the need of shear reinforcement installation. SFRC is an innovative composite in which steel fibers can effectively improve post-cracking tensile strength of concrete and suppress cracks through well-orientated fibers. During centrifugal casting, rotational forces induce circumferential flow within the mold through surface friction, aligning the steel fibers perpendicular to the pile axis. The aligned steel fibers ensure reliable shear resistance and eliminate the need for traditional shear reinforcement, thereby achieving labor savings. Furthermore, the integrated system for automatic quality control of load-bearing capacity and shear behavior of SFRC piles is developed by integrating X-ray imaging and digital image processing techniques with finite element model.
List of Papers