This research focuses on the transformation process of alternate bars during floods. The series of flume experiments were conducted to investigate the role of the period that flood discharge rising and decreasing. Firstly, unsteady flow supply to movable bed, alternate bars form as initial condition. And 4 cases were set considering unsteady condition that discharge change, so that we could search the change of bar formation and migration. We demonstrated that the decreasing phase of flood discharge is more critical for bar transformation compared to the rising phase. In contrast, the rising phase of flood discharge has a greater influence on bar migration, with higher rates of discharge increase significantly accelerating migration speed.

 Water level and flow rate are the basic hydraulic quantities that represent flood flows, and their observation is important. Recently, methods for estimating water surface velocities using image analysis such as PIV have been developed and put into practical use. The estimation of the flow regime during a flood event has been challenging due to the difficulty in measuring three-dimensional internal flow velocity profiles and bed levels. In this study, the water surface fluctuations measured at two points in a straight channel were discussed to estimate the surface stream-wise velocity and water depth, with a focus on the difference in the celerity between forward and backward gravity wave with various wave lengths. This was done as a first step to estimate the internal flow structures from the surface flow images. The water surface velocity and depth estimated from point measurements of water surface fluctuations were found to be in close agreement with the water surface velocity estimated from PIV data and actual water depth measurements. Furthermore, these values could be estimated from the water surface fluctuations.

 In this work, the mixed finite element method, in which the transverse shear stresses are taken as unknown variables, is applied to dynamic problems of the Mindlin–Reissner plate. The splitting time integrator that works as an explicit method for bending deformation and as an implicit method for transverse shear deformation is adopted. The proposed approach relaxes the restriction on the time interval of an explicit method for plate bending problems by employing an implicit scheme targeted at only the minor transverse shear deformation. Numerical experiments demonstrated that the proposed approach exhibits superior numerical properties compared to conventional time integrators in terms of time interval and accuracy.

 While seepage failure is an old engineering problem, numerical studies on seepage failure have been progressing in recent years with the improvement of computer performance. When discrete element method (DEM) is used to simulate this problem, the soil is usually represented by spherical particles larger than the actual soil particles to reduce the simulation cost. However, when the difference in shape and size between the DEM particles and the actual particles get larger, it becomes more difficult to simultaneously represent changes in the mechanical and hydraulic properties of the soil. In this study, a multilayer sphere model that can represent both the mechanical and hydraulic properties even when using relatively large DEM particles, was developed and its applicability to seepage failure simulation was confirmed through comparison with elemental experiments.

 This study investigates the influence of the inertial force term in shallow water simulations through a coastal forest. First, we formulate two patterns of 2D shallow water momentum equation which consider trees’ resistance as an external force term consisting of either the drag force or the combination of drag and inertial forces. To obtain the parameters characterizing drag and inertial force, we carry out the 3D numerical flow tests with the 3D tree model. Finally, we conduct several 2D dam break simulations by incorporating the evaluated parameters into the resistance force term. By comparing the wave arrival time and the inundation depth, we could argue that the existence of inertial force has the potential to affect the ultimate evaluation of disaster mitigation performance of trees if they are densely arranged.

 Full-scale bending tests of segment joints in shield tunnels are important for understanding and properly evaluating the behavior of joint sections. However full-scale tests are costly and time-consuming. Therefore, numerical analysis is expected to complement these tests. In this study, a modeling method for segment joints was proposed. This method is based on the behavior observed in full-scale joint bending experiments using a three-dimensional FEM analysis. Furthermore, model cases of a shield tunnel for railway were set up. A series of steps, from setting up the rotation characteristics by finite element analysis to the frame structural analysis of the shield tunnel, was shown to illustrate the usefulness of this study.

 Sleeper floating is a typical abnormality on railways, but it is difficult to detect visually and various assessment methods are being developed. On the other hand, although there have been reports of cases leading to damage of track components, evaluation methods for sleeper floating on bridges have not been investigated to the same extent as in roadbed sections. In this study, a full-field image measurement method based on digital image correlation was applied to video images taken from oblique angles below a bridge, and a homography transformation was used to develop a method for extracting all the floating sleepers on a single bridge in a single shot. As a result of applying the method to 18 sleepers on a bridge on a real railway line, it was found that seven sleepers were in a floating state based on the difference in displacement waveforms between the sleepers and the bridge directly below them, and that the estimated results were consistent with the results of the gap survey in the field.

 This study constructed a new 1D depth-integrated model for dam-break flows. The model used cubic functions for the depth profiles of downstream and vertical velocities. The model also used quadratic functions for the depth profile of pressure. The model used depth-averaged and moment equations as gov-erning equations. The model also handled non-hydrostatic pressure. The upwind and flux difference split-ting methods were used to discretize the governing equations. The Newton-Raphson method was used for the convergence calculation of the non-hydrostatic pressure term. The model was verified with experi-mental results of dam-break flow. The verifications showed that the model can reproduce the experimental dambreak flow results. The numerical results of the model were also compared with the numerical results of the shallow water flow equations. The comparison showed that the model provides improved reproducibility compared to the shallow water flow equation results. The verifications and comparison also showed that the convergence of the model needs to be improved.

 In recent years, Ice-Harbor fishways have been adopted in many rivers due to their high adaptability to flow fluctuations. Ice-Harbor fishway has two flow routes such as orifice and notch. Discharge coefficients of orifice and notch are not so clarified, because both coefficients were obtained from the fishway with only either orifice or notch. Both coefficients affect each other due to the three-dimensional nature of flow. When orifice and notch coexist, a shear layer forms at their boundary due to differences in flow velocity and direction, resulting in momentum exchange. In this study, discharge coefficients of orifice and notch in Ice-Harbor fishway were obtained by varying geometry and hydraulic conditions. It was found that those coefficients are controlled strongly by the ratio between weir thickness and approach flow depth. The equations of discharge coefficients of orifice and notch were suggested.

 In recent years, the utilization of 3D models in bridge management has been catching attention in order to improve the efficiency maintenance and the accuracy of damage diagnosis. There has been lots of research in which they construct 3D models using various data, including consturction drawings and point cloud data. However, there are some problems like the difficulty of applying their method to the vast number of existing bridges and the lack of accountability about the uncertainty and reliability of the models when they are constructed. In this research, the authors propose a 3D model construction method through the interpretation of bridge point cloud data using neural network learned generic shapes of bridge parts.

 In this paper, a method for generating a pseudo earthquake ground motion is proposed. In the method, we utilize strong motion records which was used in the generalized inversion technique (GIT) and estimated parameters of the GIT. First, source spectrum evaluated by the GIT and path effect used in the GIT are removed from Fourier amplitude spectrum of the strong motion record. Then, many site amplitude factors (as many as the number of earthquakes) are gained. Second, pseudo earthquake ground motions are generated based on the site amplitude factors and an arbitrarily selected earthquake ground motion. In the method, there is no need to rely on random numbers. Thus, pseudo earthquake ground motions which have natural continuity between frequency points in the Fourier amplitude spectrum can be obtained. Furthermore, we apply the proposed method in the case of KNG003 (one seismic observation station of the K-NET in Japan). Seismic coefficients, which is needed for designing port and harbor facilities and velocity power spectrum intensity (PSI) are calculated from the generated pseudo earthquake ground motions. Finally, mean and standard deviation of the seismic coefficients and the PSIs are calculated, and probability distribution of seismic coefficients are evaluated for the case study of the KNG003.

 In the design of temporary retaining wall, the stability of the excavation bottom against heaving is important factor in addition to the displacement and stress of the wall. The full-face ground improvement to increase the friction between the wall and the bottom is one of the common having suppressions. However, to clarify the behavior of excavation bottom is expected to lead to more economic heaving suppressions. In this paper, we worked on the model experiment and simulation analysis by soil-water coupled finite element method for the ground improved bottom. As a result, we clarified the characteristic behavior of the full-face or the grid-shape improved bottom focusing the displacement and stress of the bottom.

 A validation experiment for reinforced concrete beams without shear reinforcements was carried out to validate the computational models in the verification and validation (V&V). Eleven beam specimens and thirty cylindrical specimens were prepared simultaneously under the same conditions to reduce uncertainty in the experiment. The four-point bend tests and material tests were performed by one operator using the same test machine in a short period in order to reduce human errors associated with testing. The non-linear finite element analysis was used to simulate the same mechanical behavior as the experiments. The experimental and numerical results revealed that the experimental data obtained in this study were suitable for comparison with numerical analysis and applicable as a validation experiment for validating computational models in the V&V.

 Methodologies using track geometries measured on the traveling train are rapidly developing to estimate railway bridge deflections, which have been measured on site one by one. However, the theoretical relationship between track geometry and bridge deflection obtained using two-bogie track inspection vehicles frequently used in domestic railways and the bridge deflection estimation method remain unclear. This study theoretically derives that the maximum value of the difference between the two track geometries obtained by a two-bogie track inspection vehicle is proportional to the maximum value of bridge deflection. In addition, a method is developed to estimate bridge deflection using a conversion coefficient from the maximum value of track geometry difference. As a result of field validation on actual railway, the following findings were obtained. Estimation accuracy is low with conversion coefficients based on single beam theory due to the influence of adjacent bridge deflections. By using a simple correction method that can be applied when bridges of the same type are consecutive, the estimation accuracy can be improved to an error of about 5% for a target bridge.

 In order to detect the debris flow by observing the ground vibrations, the authors have been investigating the characteristics of ground vibrations induced by debris flow experiments. To detect the debris flow, it is common to attempt to receive large signals in the immediate vicinity of a steep mountain stream. However, it is not always possible to install the sensors under such advantageous conditions. Therefore, in this study, detecting the occurrence of debris flow based on the ground vibration obtained in the distant place from the source of debris flow was performed. Based on the ground vibration records observed in the debris flow experiments, ground vibration models focusing on the frequency characteristics were constructed. As a method of detecting debris flow, discrimination by the goodness-of-fit of this model with the observed record is proposed. Examination using experimental data demonstrated the effectiveness of the proposed method, including the avoidance of false detections for seismic ground motions.

 Geotechnical surveys are conducted to understand the spatial distribution of soil properties. However, due to cost and time constraints, these surveys are often limited and may not provide sufficient data. Therefore, it is preferable to effectively utilize indirect data, such as construction data, to reasonably estimate the spatial distribution of soil properties. In this paper, we propose a Gaussian process regression method that considers the cross-correlation with indirect data. The direct data used in numerical examples are SPT values from the Standard Penetration Test (SPT), and the indirect data are torque values obtained during pile construction. The proposed method is applied to both simulated data and actual measurement data. The estimation accuracy of the proposed method is validated through cross-validation, demonstrating that a more accurate spatial distribution can be estimated by utilizing indirect data.

 In order to implement asset management of road assets, it is necessary to estimate the pavement conditions that affect vehicle driving safety and ride comfort, and to implement appropriate repair cycles. A method is developed to identify the road surface roughness through observed running load response. One variate ARMA model is employed for inverse problems. Kalman filter is used for an online estimation procedure of road surface roughness. Numerically simulated data from 1DOF running load-surface roughness system was used for the verification of the method.

 In bridge construction, height management of the bridge deck is currently done through leveling surveys, which consume cost, time and effort. The authors have proposed a method for estimating vertical displacement of bridges during construction using measurements of rotation angles. This method formulates the estimation of bridge displacement through Bayesian inverse analysis, applying virtual forces to a three-dimensional finite element method (3D-FEM) model of the bridge. Hyperparameters, which control the probability distribution of the prior information and observation error, are determined by maximizing the marginal likelihood function. This approach was applied to a three span continuous PC rigid frame (corrugated steel web) box girder bridge under construction in Japan. To estimate the bridge's vertical displacement, sensors were installed on an overhang from one of the bridge's pillar, and the bridge was modeled using a 3D-FEM with 200 vertical virtual forces. These virtual forces were estimated from the measured data, and then used for the estimation of displacements. The results demonstrated good agreement between the estimated displacements and those measured by leveling surveys. Based on rotation angle observations, the displacement of the bridge is estimated with an accuracy of less than 3 mm when the estimates are compared to leveling survey displacements.

 This paper presents an inverse analysis method for estimating boundary conditions in a linear elastic body. The proposed method reconstructs the anti-plane wavefield using fundamental solutions and observation information. The reconstructed wavefield provides boundary values, including displacement and traction, and is utilized to estimate the boundary condition. In the estimation computation, our proposed method uses linear equations only, though other inverse analysis methods require nonlinear equations. To demonstrate the efficacy of our proposed method, we applied it to boundary condition estimation problems in both elastic halfspace and a finite domain. The validity of our proposed method is confirmed through the numerical results.

 Evaluating the residual capacity of seismically isolated bridges using vibration measurements in the operational condition is important from a life cycle management perspective. For this purpose, it is necessary to quantify the uncertainty in the hysteresis characteristics of rubber bearings, taking into account not only the ageing deterioration but also the spatial variability. In this study, a five-span seismically isolated bridge is modelled as a 2-dimensional finite element model and Bayesian model updating is performed using its seismic response data. The posterior distribution of a total of 20 model parameters is inferred using the transitional Markov chain Monte Carlo sampler. The results show that, by observing multiple points on either the girder or pier tops, the posterior distribution can accurately infer the varying hysteresis characteristics of the rubber bearings on different piers.

 In recent years, crucial damages to humans and structures caused by the impact due to natural disasters such as tornadoes and volcanic eruptions have occured. Projectiles have various shapes and it is necessary to elucidate the effect that the shape of the flying objects on the failure characteristics of RC slabs. This study investigated impact response of RC slabs subjeted projectile impact with different tip shapes. In the experimental study, impact tests were conducted for RC slabs by using different projectile tip shapes, and the crack properties and impact response were investigated. Then, numerical investigation to confirm the reproducibility of the experiment and to consider the impact response of the RC slabs was conducted. Solely the flat type projectile caused scabbing failure at 60 m/s, and the shear force generated in the RC slabs was the largest in the flat type projectile.

 In this study, experimental and numerical investigations were carried out for the response characteristics and scabbing of RC slabs subjected to repeated projectile impact. In the experiments, the thickness and reinforcement arrangement of RC slabs were varied to investigate the characteristics of scabbing and the acceleration on the back surface of the RC slab under repeated impact. In the numerical study, the reproducibility of the scabbing of the RC slab under repeated projectile impact was examined.

 Stress concentration significantly influences fatigue performance of welded joints. While it is possible to evaluate the stress concentration of arbitrary shapes by FEM analysis of measured data, it requires a considerable computational cost. Therefore, an evaluation formula that allows for a simple estimation of the stress concentration factor has been proposed. A method that facilitates the unified evaluation of all geometry parameters has also been proposed. Some certain issues of a similar method that have been used for multi-section analysis have been pointed out. Consequently, this study aims to develop a technique for evaluating the dominant factors affecting fatigue performance based on multi-sectional shape analysis of welded joints. The study confirmed that the prediction accuracy of crack initiation location was high when the median value was used among the stress concentration factors (𝐾𝑡) of multiple cross-sections. Additionally, through the evaluation of fatigue performance, it was confirmed that the misalignment and angular deformation are two important factors that significantly affect the fatigue performance of welded joints.

 Bouldery debris flows exert large impact forces, causing sighnificant damage to open Sabo dams and residential areas. Observations of damage to these dams suggest that the forces acting on the dams vary locally depending on the riverbed morphology and the sediment and boulders already trapped. This study analytically examines debris flow loads in conditions involving a movable bed and pre-deposited gravel using Distinct Element Method. The results reveal that pre-deposited gravel significantly affects the maximum load exerted on the entire dam, with particularly large loads occurring at the points where the front of debris flow impacts each step height of the dam. Additionally, using contact force diagram and velocity vector diagrams, the causes of the reduction in debris flow load due to the influence of pre-deposited gravel were analyzed from the flow process to the point of impact.

 This study aims to investigate the effect of the size and shape of the front wall on blast pressure characteristics surrounding box-type structures by conducting explosion tests and numerical simulations. Prior to the tests, the method for evaluating blast pressure characteristics proposed by the Unified Facilities Criteria was described, and its concept was discussed. Then, explosion tests using C-4 high explosives were conducted to investigate the blast effects on two test specimens with different front wall widths. The test results showed a significant change in blast impulse acting on the front wall and top roof by varying the width of the front wall. The test results were then reproduced by numerical simulations. Based on the simulated results, the correlation between size, shape of the front wall, and the difference in blast duration as well as blast impulse was discussed.

 The authors invented an unconventional material model and proposed a methodology for the investigation of the crack propagation phenomenon under the elasto-plastic state utilizing the model. However, previous works are conducted only under the positive stress ratio 𝑅. Additionally, the effects of the elasto-plastic deformation and the accumulated damage accompanying crack growth have not been sufficiently considered, nor the impact of these factors on the evaluation accuracy. This paper suggested the unconventional method considering the history of deformation and the accumulated damage accompanying crack growth to follow the complexity of the contact changes after crack initiation. The accuracy of this methodology was verified for the crack propagation tests by SENT specimen conducted under the two different stress ratios 𝑅 and maximum loads. The obtained results exhibit good accuracy in predicting four experiments under different loading conditions.

 Recent abnormal weather conditions have caused debris flows larger than anticipated, resulting in reports of damage to steel pipe open Sabo dams. Therefore, it is essential to design structures with significant load-bearing capacity including large redundancy and robustness. This study examines the effects of flange joints of steel pipe open Sabo dams under debris flow fluid force on the load-bearing capacities. First, the flange joint is modelled as a beam model using the section division method. Next, the load-bearing capacities of a steel pipe open Sabo dam are evaluated by using the three-dimensional elastic-plastic analysis method. In other words, redundancy is assessed in two ways; the reserved strength beyond the yield strength for an undamaged structure, and the residual strength ratio of a damaged structure. Robustness is also defined as the ultimate strength ratio under eccentric debris flow conditions. Finaly, it was found from calculation results that the redundancy and robustness of the truss-type steel open dams were reduced due to the influence of joints.

 A seismic reinforcement method is being developed to reduce the cross-sectional forces generated in existing piles by sheet piles around the existing pile foundations. The reduction effect on the existing piles is caused by the group pile effect between the sheet pile and the existing pile, but the conventional evaluation method for the group pile effect cannot be applied because of the difference in stiffness and length between the sheet piles and the existing pile. In this study, horizontal loading tests were conducted using a two-dimensional model of aluminum lods laminated soil and a three-dimensional model of dry Toyoura sand. it was confirmed that the reduction of cross-sectional force of existing piles is caused by the reduction or blocking of compressive strain in the passive wedge region of the existing pile by the reinforced sheet pile, which reduces the subgrade reaction. Based on the results, a quantitative evaluation method for the reduction of cross-sectional force of existing piles caused by the group pile effect is proposed.

 Determining the response of a rockfall barrier with a chain link wire netting as the impact surface against falling rocks by means of model experiments could be economical. Previous study conducted by the authors revealed that the replica law is valid for model experiments where the chain link wire netting is subjected to static loads. On the other hand, its validity to low-velocity impacts was not clear. In this study, out-of-plane steel ball impact analyses were performed for full-scale and model chain link wire nettings with and without gravitational acceleration in order to analytically investigate the mechanical similarity of rhombic wire mesh. Then, similar out-of-plane steel ball impact tests with and without gravitational acceleration were conducted for a protective fence configuration with rhombic wire mesh as the block face and steel bars as supports, to analytically investigate the mechanical similarity of the chain link wire netting with and without gravitational acceleration.

 The Architectural Institute of Japan (AIJ) Guidelines for building foundation design propose a formula for calculating the ultimate vertical bearing capacity of spread foundations. In particular, the size effect on sandy ground is thought to be due to the decrease in the angle of shear resistance caused by high confining pressure and progressive failure. Generally, homogeneous and uniform soils are rare, and soil composition is often multi-layered, consisting of sand and clay. Previous studies have examined two-layered clay layers with different strengths, however alternating clay and sand layers taking into account the size effect have not yet been studied. Therefore, in this study, a two-layered soil system of sand and clay was examined using rigid-plastic finite element analysis. A higher-order function is used as a constitutive model for the soil to reproduce the size effect. Simplified formulas are presented for the upper sand layer, the lower clay layer, and the upper clay layer and lower sand layer, and the applicability of the simplified formulas is examined.

 The stability of triple circular and square tunnels in cohesive-frictional soils subjected to surcharge loading has been numerically investigated assuming plane strain conditions. The centre-to-centre distance appears as a new problem parameters. A continuous loading is applied to the ground surface, and a smooth interface condition is modelled. For a series of tunnel size-to-depth ratios and material properties, rigorous lower-and upper-bound solutions for the ultimate surcharge loading are obtained by applying finite element limit analysis techniques. For practical stability, the results are presented in the form of dimensionless stability charts.