20-year history of activities of the International Research Center for Urban Infrastructure Safety Engineering (ICUS), Institute of Industrial Science, The University of Tokyo was reviewed in this paper. It also introduced the future plans of the entire Institute at that time as the background to the reorganization and establishment of ICUS from its predecessor, the International Center for Disaster-Mitigation Engineering (INCEDE). ICUS has achieved many achievements, such as creating more than 100 Ph. D holders from both Japan and overseas, and publishing more than 860 peerreviewed papers through 20 years of activities from its establishment in April 2001 to the end of March 2021. From 2021, the research divisions related to urban safety and disaster management is taken over the “Collaborative Research Organization on Knowledge of Disaster / Reconstruction”, and the research divisions related to urban infrastructure is taken over the “One Health One World Collaborative Research Organization”.
When dealing with the seismic ground motion stochastically that hits particular place, it is generally expressed that the probability of being hit by a ground motion with a seismic intensity of over 6 - with the next 30 years is 〇〇 %. However, with this index, it has been pointed out a problem in evaluating the probability of occurrence of an earthquake. The problem happens when probability of occurrence of different type earthquake, such as an active fault type and a plate boundary type, return periods of which are significantly different, is calculated for the same time length, such as the next 30 years. Therefore, in this study, the cumulative probability that indicates probability of an earthquake, which could have occurred up to now, is calculated. Then, subtracting this probability from 1, it is calculated as the probability remaining until the next event occurs (residual probability）. With this methodology, the probability of earthquake occurrence is expressed considering the influence of the return period and based on this probability, probability of expected ground motion distribution has been obtained.
At the time of the big events such as the Olympics Game or the international exhibition, extreme care is necessary for the crowd control including the time of the outbreak of emergency such as an earthquake, terrorism etc. And from the view point of crisis control, the risk management as the prior preparations for accident prevention and crisis management that fixed its eyes on outbreak of emergency are essential. In this article, we report the basic elements of the crowd control in the big events included the measures of the administration of pedestrian and facilities on ensuring the security of the pedestrian.
The aging of Japan's infrastructure and the decreasing number of skilled inspectors have become serious problems. In order to improve these problems, the industry, government, and academia are trying to utilize existing IoT technologies for infrastructure maintenance and management. In this paper, we will introduce some of the remote sensing technologies that have already been implemented in society, in particular the Mobile Mapping System, used for the management of roads and surroundings, and SAR satellite data analysis centered on InSAR processing, whose resolution and data volume have been improving with the launch of commercial satellites in recent years.
The purpose of this study is to design a road network in which autonomous vehicles, driver-operated vehicles, and pedestrians can move smoothly and safely, considering the interaction between moving entities at intersections and streets. Specifically, we propose a network optimization problem that focuses on multiple indices such as the number of crossings and travel time, as well as accounting for interactions at intersections and streets. Through the analysis of a virtual and a real road network, we aim to obtain a perspective on the design of roads with autonomous vehicles in the near future, such as the effectiveness of setting priority areas for autonomous vehicles.
The purpose of this study is to construct a disaster response workflow for each organization based on the analysis of issues related to pets in the event of a disaster for effective and efficient pet disaster response by the local government. This paper analyzed (1) the disaster response verification report and (2) the description status of the regional disaster prevention plan (RDPP). As a result, the RDPP could not cope with the problems in the past disaster response. In the future, to visualize the description of RDPPs while reflecting on the lessons learned from past disaster responses, this research will systematically construct a disaster response workflow using the Business Operation Support System (BOSS).
In this article, a deep learning algorithm to detect subsurface void from radar images by three-dimensional Convolutional Neural Network (3D-CNN) is developed. To obtain training data, producing 3D electromagnetic (EM) responses by three-dimensional finite difference time domain (3D-FDTD) method is not feasible, requiring large calculation cost. The methodology to reproduce 3D EM responses by two-dimensional finite difference time domain (2D-FDTD) method is proposed for the first time. The proposed method is validated by subsurface void measurement data. 3D-CNN trained by simulated data shows high performance indicating the effectiveness of 3D subsurface sensing.
Countless subsurface cavities are being generated under roads in the urban area. Some of them would collapse and may cause road cave-in accidents. In order to prevent this, the ground penetrating radar technique is effective to find cavities before their collapse. Appropriate repair treatment should be then carried out for the cavities according to their properties and collapsing risk. In this research, the effective countermeasure was developed for steps of survey, diagnosis, repair and prevention for subsurface cavities.
We attempted evaluation of amplification factor of maximum acceleration of surface layers for seismic hazard assessment. We focused that maximum acceleration and maximum velocity has a correlation under certain conditions and evaluated empirical relationship between maximum acceleration and maximum velocity using ground motion records at surface and underground. The amplification factor of the maximum acceleration was evaluated by applying these relationships to the amplification factor of the maximum velocity obtained in previous studies. Finally, we evaluated amplification factor distribution of the maximum acceleration in Yangon City using proposed method.
In this paper, the investigation results of the ceiling damage in a public hall and gymnasiums in Sendai and Fukushima city due to the off the Coast of Fukushima Earthquake on Feb. 13, 2021, are reported. Although no causalities and large-scale ceiling failure were not fortunately occurred in the investigated buildings, the similar ceiling damage had been occurred at the same buildings in past earthquakes. From the viewpoint of not only protecting human life but also maintaining functions, to break through the current situation where facility managers have no choice but to return to the original state for the government subsidy, various countermeasures and creation of a system that allows to positively adopt them are necessary.
Particle shape of a non-spherical particle (clump) was reconstructed with the application of X-ray computed tomography (μCT). Shapes of the generated clumps were quantitatively estimated and correlated with the number of spheres (Ns). Subsequently, granular assemblies were prepared using these clumps in DEM simulations. After isotropic consolidation, the void ratio (e0) and mean coordination number ( ) of granular assemblies were correlated with Ns and overall regularity (OR), respectively. The DEM results found Ns=25 for clumps is sufficient to represent the real particle shapes. Meanwhile, e0 and were found to decrease with the increase of OR.
Recently, several occurrences of cave-in on sandy ground have been reported. Previous research shows that the interparticle cohesion such as suction is essential for the stability of a subsurface cavity in sandy ground. In this research, suction measurement tests on granular materials were conducted using a simple suction measuring device. A series of simple model tests were also carried out to consider the contribution of suction to the stability of cavity. It was revealed that matric suction of sandy soil is affected by the grain size and shape under a given degree of saturation. Further, not only suction but also surface roughness, shape and formation of arch contribute to the stability of cavity.
The mechanical response of a granular assembly such as sandy soil is affected by the surface roughness of its constituent particles. However, such research has not been sufficiently conducted due to a lack of objective approaches to quantify the surface roughness. Recent advancement of optical interferometry technique enables accurate measurements of nano-order surface roughness. A difficulty is that surface roughness should be evaluated on the surface texture, isolated from the overall curvature of the grain shape. This contribution proposes a new objective approach to quantify the surface roughness of non-planar surfaces using Gaussian filter.
Subsurface cavities located deep underground potentially cause large-scale cave-ins. Radar survey has been applied to detect cavities in shallow ground with high accuracy, whereas there is no effective non-destructive exploration method for cavities deeper than 2m below the ground surface. In this research, surface wave survey, which is a method to estimate the S-wave velocity structure deep underground, was conducted at a cave-in site in Abira town, Hokkaido. It was confirmed that surface wave survey is an effective method for detecting loosening regions which become cavities later, and for estimating water channels which may cause cave-ins.
This paper reports on a model test which discuss about the disturbed area of ground soil due to insert the freezing tube of “small-scale freezing sampling” method, which can be adopted in common soil boring works and takes less cost than conventional freezing sampling method. This study is focused on the effect of water flow rate and insertion velocity during inserting the self-boring freezing tube, and the disturbance around the tube is evaluated by the soil density and soil hardness. According to the result, a better water flow rate and insertion velocity with less disturbance, and the effectiveness of self-boring can be observed. However, it can also be found that the amount of discharged sand is not enough due to the plugging phenomenon of sand which occurred at the end of the self-boring freezing tube.
Previous studies on shear energy or work under undrained cyclic loading have mainly focused on two aspects: the independence on effective stress path and the relationship between shear energy to liquefaction and other parameters. Based on these previous studies, this study aims to investigate the relationship between shear work required to liquefy (liquefaction work characteristics) and cyclic shear stress ratio using a simple numerical model. The results show that the proposed model reflects the experimental results well, while there is a dependence of shear work in the region of cyclic mobility on effective stress path.
As the driving method of the frictional fine positioning system based on slow expansion and quick restoration of piezoelectric actuator, we demonstrate it is reasonable to use, rather than a high-power high-voltage amplifier, the combination of a dc source or an amplifier with a driving capacity of high-voltage but small-current and a MOSFET discharging switch to the ground. We also demonstrate a waveform redressing circuit without need of dedicated power source, which is useful when the restoration takes too much time due to a driver with insufficient performance or due to the cable inductance between the driver and the actuator.
Barely visible impact damages (BVIDs) in carbon fiber reinforced plastic (CFRP) mobility structures may seriously affect the safety of users. In this research, we attempted to establish a method to identify BVIDs in CFRP mobility structures. Using film-type actuators and sensors, changes in ultrasonic guided waves due to the damage were investigated in a broadband frequency range. As a result, we found that the delay time of the lowest antisymmetric (A0) mode increases linearly with increasing damage size. Moreover, the amplitude of A0 mode was found to be largely affected by the damage length in the wave propagation direction.
Structural health monitoring (SHM) techniques applicable in high-temperature environments are necessary for monitoring the integrity of heat-resistant civil structures. Acoustic emission (AE) detection can be potentially used to establish the real-time passive SHM method. Conventional AE sensors are made from piezoelectric materials, whose operational temperature is limited up to 200 °C. To solve the issue, we proposed a new AE sensing system based on a regenerated fiber Bragg grating (RFBG). The RFBG was fabricated by annealing the conventional FBG, then applied to detect simulated AE waves that were excited by a laser irradiation at temperatures up to 800 °C.
We proposed to utilize the response of the polymer to terahertz (THz) polarization as a non-destructive internal residual stress evaluation method for plastic molded products. PTFE samples with different residual stresses were manufactured and then the polarization dependence of the absorption coefficient was evaluated using THz time region spectroscopy. PTFE samples with lower residual stress showed almost no polarization dependence, whereas PTFE samples with higher residual stress showed large polarization dependence. In addition, we experimentally confirmed the correlation between THz polarization dependence and the dimensional change caused by residual stress. This paper revies the details about the principle and the verification.
The plastication process in the vent-type heating cylinder of the injection molding machine was visually analyzed. It was clarified that voids are formed in the molten resin in the channel of the second screw zone near the vent port. In the continuous plasticization process, the void space expanded toward the nozzle side as the screw rotation speed increased, due to an imbalance of the resin transport rates between the first and second screw zones. In the reciprocating plastication process, the material feed rate at the hopper inlet for controlling venting-up phenomena increased more than the increase in the screw rotation speed, due to the increase in the resin transport rate in the second screw zone.
In this research, we proposed a fixed-abrasive tool with spiral continuous pores on the surface in order to realize a fixed-abrasive tool capable of precision machining without causing loading. By winding a wire around the tool base, the contact between the tool and the workpiece was made into line contact, and continuous pores were always arranged nearby the abrasive grains. Through machining experiments using the prototype tool, the causes of loading are the formation of closed pores due to the high abrasive grain ratio, the surface contact between the tool and the workpiece, and the continuous pores around the abrasive grains. It was shown that the spiral fixed abrasive grain tool prepared in consideration of these factors can perform mirror surface processing without causing loading.
The influence of pre-strain on the uniform formability of thin foils is investigated in this study. A multi-pass microforming process combines pre-straining with RH assisted forming is introduced for the investigation. The testing systems of applying uniaxial pre-tension strain under RH and for biaxial tension using cupping tests were built up. The pre-strained samples indicated uniform temperature and strain distributions, confirming the feasibility of this area for the following cupping tests. The uniform formability of the foils illustrated an increasing-decreasing tendency as the applied pre-strain increased. The loading path was thought to be the main reason for this.
Injection molding in the process route for MID (Molded Interconnect Device) is possible to be replaced with laser sintering. Then, the hidden surface can be activated by switching the fabrication and activation in one laser irradiation process, which is difficult for the injection-mold method. Furthermore, the size of equipment and cost can be greatly reduced when the fabrication and activation are completed using only one CO2 laser. Therefore, this study clarifies the activation mechanisms of laser-sintered LDS (Laser Direct Structuring) materials by CO2 laser through the direct observation in process with a high-speed video camera. The results are compared with a fiber laser which is normally used for LDS.