Efficient tsunami countermeasures for bridges at coastal roads along Nankai Trough require a risk assessment of washout of superstructure due to tsunamis. This study uses a probabilistic hazard assessment method combining the random-phase tsunami model and the coRaL method to assess the probability of bridge superstructure washout risk considering the uncertainties in tsunami hazard prediction. The results of the safety assessment of coastal bridges in Wakayama Prefecture by the Nankai Trough megathrust earthquake tsunami show that the risk of bridge washout is increased in 16 bridges concerning the action force/strength ratio compared to the case of the Tokai-Tonankai-Nankai consolidated type earthquake model. The probabilistic tsunami hazard assessment method was used to quantitatively evaluate the washout risk of bridge superstructures by the return period. The effects of the bearing anchors and displacement-limiting structures as countermeasures were expressed by the increase in the critical tsunami height and the return period.

 We studied seismic and tsunami countermeasure technology using cushioning materials for disaster prevention and mitigation of structures in coastal areas. Here, we focused on the tsunami countermeasures, and investigated the use of cushioning materials to reduce wave pressure and stresses on the structure. The effect of wave pressure reduction was examined by tsunami model experiments, and the influence of stress reduction was evaluated by three-dimensional FEM analysis. The results of the model experiments showed that the wave pressure acting on the structure can be reduced by placing a cushioning material on the surface of the structure, and that it is possible to change the vertical distribution shape of wave pressure. The results of the three-dimensional FEM analysis confirmed that the stresses generated within the structure varied greatly depending on not only the magnitude of wave pressure but also the vertical distribution shape of wave pressure. Therefore, it is important to accurately set the distribution shape as well as the magnitude of wave pressure in order to properly evaluate the safety of structures against tsunamis.

 Most of the damage to gas pipelines caused by the Kobe Earthquake was due to ruptured joints in screw-jointed steel pipes. On the other hand, no damage was observed in polyethylene (PE) pipes, which are earthquake-resistant pipes. For this reason, the percentage of PE pipes installed has increased since the Kobe Earthquake. Therefore, it is necessary to consider the installation status of earthquake-resistant pipes when analyzing earthquake damage to gas pipelines. In this study, a numerical model of a one-dimensional piping system with various PE pipe installation ratios (PE pipe ratio) was developed to evaluate the relationship between PE pipe ratio and joint rupture rate. A numerical model was also constructed to reproduce the conditions of a pipeline in an area where an actual earthquake had occurred in the past. Ground displacement was calculated from the SI values and given to the model to verify the validity of the numerical simulation.

 This study investigated the impact of seismic countermeasures on the recovery process of production capacity using the business survey data following the 2022 Fukushima offshore earthquake. Firstly, the survey data were classified into two groups, the countermeasure group and the non-countermeasure group. Secondly, a dataset was created using propensity score matching to adjust for covariates. Finally, the effectiveness of seismic countermeasure implementation was verified based on the difference between the recovery curves with and without countermeasures. The results showed that countermeasures mainly aimed at early recovery, such as the formulation of a disaster response manual, BCP and securing emergency power supplies or fuel, reduced the expected number of recovery days until full recovery by 1 to 47%. The results quantitatively demonstrate a decrease in the expected number of recovery days until full recovery through the implementation of earthquake countermeasures, and are expected to be applied to the effective seismic risk management.

 Assessing the effectiveness of disaster risk reduction (DRR) education extends beyond the immediate outcomes of a single intervention to include its sustainability. While expert-led disaster education in schools can temporarily raise children’s awareness of disaster prevention, sustaining this awareness remains a challenge.

 In this study, we conducted a workshop for parents and children at a science museum and examined whether participants’ awareness of disaster prevention was sustained.

 The findings indicated that participants’ disaster preparedness awareness, which was raised by the workshop, endured even after one month. Factors that contributed to the sustained awareness included the unique learning environment provided by science museums, distinct from traditional school settings, and the importance of learning together with family members.

 In this study, we attempted to construct a damage discrimination model by machine learning of response acceleration time histories obtained from acceleration sensors installed in buildings, as a method for efficiently and quickly identifying damage states of wooden houses after an earthquake. First, we performed a number of seismic response analyses of a wooden house model to calculate the response acceleration time histories and response plasticity ratios, which were used as training data for machine learning. Then, Long Short-term Memory (LSTM) network and a one-dimensional convolutional neural network (1D CNN) were employed, and the obtained results were compared to construct an optimal discriminant model.

 Logical residents, who initiate evacuation after receiving pre-determined information, are considered to have a significant influence on intuitive residents, who initiate evacuation based on the sense of urgency that is fostered in the community. In this research, we extended the existing definition of “logical residents” to include residents who make logical decisions to initiate action, and examined the relationship between “logical residents” and “intuitive residents”. The results of the analysis of 532 recordings of the Great East Japan Earthquake showed that (1) the ratio of logical to intuitive residents was 2:8 as a whole, (2) there were some regional difference in the ratio, depending on the ratio of potential logical residents increased or decreased depending on their disaster experience and disaster education, and the extent to which their decision conditions are met in the event of a disaster, (3) There is no difference between the two groups in terms of whether they evacuate to higher ground or to buildings.

 For structures and facilities in coastal areas, realization of effective countermeasures against tsunamis as well as strong earthquake motions is required. In this study, we proposed and researched the countermeasure technology based on the idea of seismic isolation and tsunami isolation to prevent and mitigate the disasters in coastal areas. In the safety evaluation of structures against tsunami, it is considered that the setting of distribution shape of wave pressure has a significant impact on the stress generated in the structures. Therefore, four shapes of wave pressure distribution, namely rectangular, pentagonal, trapezoidal, and triangular, were set and three-dimensional FEM analysis was performed. As a result, it was confirmed that the stress generated in the structure changed greatly depending on the distribution shape of the wave pressure, and that the generated stress increased more greatly when the rectangular shape was set than when the triangular shape was set. From these results, in order to practice appropriate safety evaluation, it is necessary to set the distribution shape of the wave pressure accurately.

 In this study, we propose and validate a method for modeling tsunami scenarios, which are the input in tsunami fragility assessment for nuclear power plants. Although one of methods to identify plant accident scenarios is to cover a wide variety of inundation scenarios, there are hundreds to thousands of tsunami sources for a plant, therefore, it is difficult to conduct inundation analyses on the site to all of them. In our method, to model the tsunami scenarios, the hazard contribution for each tsunami source was calculated, significant tsunami sources for the site are selected, and inundation analyses are conducted. Furthermore, the selected tsunami sources are grouped based on their features. Statistical studies for the features of tsunami sources and the variability of the inundation scenarios revealed the validation of our method and the relationship between the tsunami sources and inundation characteristics.

 We assume that a seismic motion record is one sample of seismic motions with certain source, path, and site characteristics, and propose a method to simulate acceleration time history by modeling the uncertainties as a stochastic process. We use the real part of the Fourier transform of each wave obtained by the wavelet transform. First, we verify the “standardized real part”, which is the real part without the effect of non-stationarity, is a stationary process, and simulate it as an autoregressive process. Calculating the real and imaginary parts from the simulated standardized real part, we simulate the waveforms by Fourier inversion. Finally, we confirm if the simulated waveforms can accurately reproduce the observation record.

 In the process of hazard mapping for liquefaction, it may be desired to use seismic response analysis with 3-D FEM for advanced prediction of liquefaction of large areas. However, the construction cost and calculation cost of the 3D FEM model are still too high to apply the method in practice. To solve these problems, the authors have developed “T-STRIKE”, a large-scale nonlinear finite element method program. This program incorporates constitutive laws for soil liquefaction. To verify the validity of the liquefaction hazard map using the developed program, we conducted a seismic response analysis with liquefaction on a real site using the supercomputer “Fugaku,” and the results were compared with those of other programs that have been used in practice. In addition, the results were compared with those of a one-dimensional horizontally layered ground model to demonstrate the usefulness of the 3-D analysis.

 Ground motion prediction models estimate ground motion intensities using parameters such as earthquake magnitude and fault distance. Gaussian process regression, one of the nonparametric methods, was used in this study to model the attenuation relations of peak ground acceleration (PGA). As an example of the analysis, the dataset of the 2016 Kumamoto earthquake sequence observed by K-NET and KiK-net was applied. The results show that the Gaussian process regression model underestimates the observed values in the near source area. This may be due to the difference in the density of observed values between the far field and the near field. In this paper, an original kernel function was proposed that can reflect the characteristics of seismic ground motion in the near source area. By using the proposed method, it is possible to construct a ground motion prediction model that can express the distribution of ground motion intensity in the whole field from near to far.

 For the purpose of evaluation and analysis of earthquake motion characteristics, we applied our developed method for characteristics extraction in the time-frequency domain. In this analysis, the method utilized a period-dependent feature vector based on the evolutionary power spectrum. Furthermore, the kernel density estimation was applied to the period-dependent feature vector. Next, for the comparison using to many earthquake motions, using the estimated density distribution, the singular value decomposition was applied.

 As a numerical example to demonstrate the effectiveness of the proposed method, the acceleration records observed from the 2011 Off the Pacific Coast of Tohoku Earthquake were used. Consequently, the characteristics of each earthquake motions was able to extract from the principal component scores obtained from the singular value decomposition.

 In the seismic design of road bridge specifications, when considering level 2 earthquake motion, the effects of various phase characteristics of earthquake motion are taken into account by selecting acceleration waveforms with phase characteristics that increase the nonlinear response of the bridge and inputting at least three waveforms. However, it is not clear whether the effects of phase characteristics on structures can be taken into account by inputting at least three waveforms for all types of structures. In this study, the appropriate number of input earthquake motions was examined using three different models of single piers as examples. As a result, it was statistically confirmed that at least three waveforms were input and the average of the response values was obtained with the same reliability as that obtained by inputting a large number of waves (about 20 waves).

 Dynamic vibrations are generated in road bridges due to steady actions such as traffic vibration, wind, and constant ground tremors, as well as unsteady actions such as earthquakes. Among them, steady-state effects act on road bridges even during earthquakes. In order to analyze vibration characteristics in detail, we need to clarify the influence of steady-state effects. In this study, we calculated the time-series changes in vibration characteristics using continuous acceleration records observed over a period of one month using a strong motion monitoring system, and analyzed the relationship with external factors. We focused on external factors such as traffic volume, temperature, and wind, and determined the correlation with time-series changes in vibration characteristics at each observation point. Furthermore, we showed the difference between a road bridge during an earthquake and at normal times based on the time-series changes in vibration characteristics.

 The authors have proposed a foundation composed of piles and soilbags. The authors have experimentally and analytically verified the superiority of the proposed structure over conventional foundations such as pile foundations for newly constructed structures. In this study, the authors proposed a method of reinforcing the foundation of existing structures by using additional piles, soilbags, and additional footings, and conducted test calculations together with the unreinforced structure and the reinforced structure with normal additional pile method. The results showed that the proposed method could suppress the rotational angle of the footing without increasing the inertia force excessively in the condition of foundation width of approximately 8 m after reinforcement, pier height of 10-15 m, and superstructure load of 6730 kN. The proposed method can be used as a reinforcement method for foundations such as existing wooden pile foundations and spread foundations, whose inertial force during large earthquakes is small before the reinforcement.

 The level of earthquake ground motions applied to critical facilities for the seismic design of nuclear power plants is increasing, and there is concern that liquefaction may occur even in dense ground. Furthermore, there is no established method for evaluating damage due to liquefaction for RC circular shafts, which have been increasingly adopted in recent years. In this paper, we first conducted a dynamic centrifuge test with the aim of establishing a damage evaluation method due to liquefaction in dense sand ground, targeting an RC circular shaft built in dense sandy ground. Through this test, we were able to understand the damage and acting loads on the RC circular shaft and obtained experimental data to verify the validity of the damage evaluation method. Next, we proposed a two-step damage evaluation method that combines response evaluation of structures and soil using 2D effective stress analysis and damage evaluation of structures using 3D non-linear analysis. In addition, we performed a reproduction analysis of a dynamic centrifuge test using the proposed method and confirmed that the proposed method can reproduce the damage caused by an earthquake in an RC circular shaft.

 In this paper, an analytical consideration was conducted to improve accuracy of the combination coefficient of inertia force and ground displacement for calculating the seismic response of pile foundation structures by the seismic deformation method. Specifically, linear dynamic analyses were conducted on various types of grounds and structures, and combination coefficients for the period ratios of grounds and structures were calculated. As a result, it is clarified that the correction coefficient  gradually decreases as the natural period of the ground T_g increases. Considering this tendency, we proposed a simple estimation method for the combination coefficients. In addition, it was confirmed that the proposed method can express the results of dynamic analysis more appropriately than the conventional method. The proposed method can improve the accuracy of the combination coefficients and calculate the seismic response values of structures more reasonable.

 This study was conducted to understand the effect of site nonlinearity of the ground on the seismic behavior of RC structure with pile foundation. First, a reproduction analysis of shaking table tests on a structure with pile foundation-soil system was performed. Then, the effect of site nonlinearity on the behavior of the structure was considered in this analytical model. As a result, it was confirmed that it is necessary to set the conditions so that the contribution of the ground to the target experiment becomes larger when conducting the shaking table tests on ground-structure simulating the natural ground. In addition, as a result of an analytical study under different ground conditions, it was found that the site nonlinearity has some effects on structural behavior when the shear strength of the near-surface ground is small and the nonlinear behavior during earthquakes is significant. However, the effect of site nonlinearity on the structure was confirmed to be very small for the seismic design of the structure.

 Many serious damages such as liquefaction and collapse of houses occurred by the 2018 Hokkaido Iburitobu Earthquake in Japan. Field investigation and inspection were conducted to study an effect of inclination of the house due to liquefaction on health problems of the residents. The outerwall inclination angle of 57 houses in liquefied sites of Sapporo City was measured. In addition, a questionnaire survey was conducted about one month after the earthquake. The results of this survey revealed the actual condition of inhabitant's health problems due to inclined houses induced by liquefaction.

 The first experiment uses a center-of-gravity sway measuring device. In this experiment, subjects were asked to lie in a supine position on a slight incline for 30 minutes, and then we examined the changes in their center of gravity sway and health conditions before and after they lay down.

 In this study, we performed a reproduction analysis of a centrifugal model experiment of an RC shaft buried in dense sandy ground (upper unsaturated layer, lower saturated layer) using effective stress analysis of the soil-structure interaction system. The two-dimensional effective stress analysis shows that by subjecting the ground to drainage conditions, it is possible to reproduce the softening behavior of the ground due to an increase in excess pore water pressure in a manner consistent with the experimental results. In the structure interaction analysis, we confirmed that the damage to the RC shaft and the maximum response displacement of the ground and structure could be evaluated generally well. In addition, due to the softening caused by the rise in excess pore water pressure in the lower saturated layer, the upper unsaturated layer, which maintains the rigidity of the ground, deforms together with the lower saturated layer, causing shear deformation in the RC shaft near the boundary.

 In recent years, the effects of crustal deformation caused by fault displacement on structures in addition to earthquake ground motions during earthquakes have been attracting attention. In such cases, the super-position of the two is also an issue, but it has been difficult to dynamically evaluate the effects with the evaluation methods that have been widely used up to now. In this study, we examined earthquake ground motions caused by the main fault activity and fault displacement of sub-faults using dynamic rupture simulation analysis that can dynamically evaluate earthquake ground motions and fault displacement, and found that the sub-fault activity occurs later than the main fault. The culvert was additionally modeled using RC nonlinear material to evaluate the effect of the culvert being subjected to sub-fault displacement. Comparison with static analysis results indicated that dynamic effects were limited.

 In the case of ground deformation caused by reverse fault at the Warren truss bridge service location, it was assumed that the parapet will slide and continue to slide even after impacting the lower chord member. FEM analyses conducted under the condition that the forced displacement through the parapet simultaneously acts on both lower chord members has shown that even a small forced displacement on the order of several centimeters can cause significant damage.In this study, elasto-plastic static and seismic response analyses were conducted under the condition that the forced displacement acts on only one of the lower members, which is on the safer side, and it was also examined whether the difference in the number of diameters affects the various responses. It was shown that when forced displacement acts on only one of the lower chords, more severe damage can occur even when the amount of forced displacement is about 1/4 compared to when forced displacement acts on both chords. There was no significant difference in damage behavior depending on the number of spans.

 This study examined and discussed the behavior of leaning-type retaining walls, which were reinforced at the bottom with soil nailing technique, during an earthquake. Initially, numerical analyses were carried out on the seismic behavior of leaning-type retaining walls before and after reinforcement with soil nailing targeted by small-scale model experiments in a past study. Subsequently, case studies by the numerical analyses using the L2 seismic motion assumed in railway design standards in Japan and experimental studies using small-scale model experiments were conducted on the seismic behavior of leaning-type retaining walls reinforced at the bottom with soil nailing. Consequently, the deformation suppression effect of retaining walls reinforced at the bottom with soil nailing was implied. On the other hand, the importance of examining the effects of earth pressure, ground resistance, and the resistance of reinforcing bars on the deformation mechanism of the wall and the degree of damage to the reinforcing bars were considered.

 The authors have been studying a method of joining reinforced piles with friction materials (hereafter referred to as “friction-jointed piles”). The friction-jointed piles are expected to exhibit hysteresis damping due to the sliding motion of the friction-jointed surfaces. In previous model tests, shear forces acting on the frictionally jointed surface were not directly measured, and there was a problem in verifying the hysteresis damping mechanism. In this study, the behavior of the friction-jointed piles was verified in detail, and the response acceleration suppression mechanism of the friction-jointed piles was verified. The results of the model experiment revealed that the friction-jointed surfaces exhibit hysteresis damping due to sliding. It was also suggested that by setting the introduced friction force at which the hysteresis damping is greatest, the predominant period, peak structure acceleration PSA, and SI values can be reduced, and that reinforcement is possible without compromising the safety of the train running.

 Complex calculations are often required to accurately predict the complex behavior of geomaterials. It is difficult to evaluate consistent tangent moduli analytically, so that the numerical differentiation, in which the gradient is calculated from the change in stress when a small deformation perturbation is applied, is generally used to evaluate. However, the method using numerical differentiation requires multiple stress calculations, which is large computational cost. In this paper, we formulate the consistent tangent moduli using the Jacobi matrix of the return mapping equation used in the stress integration of elasto-plastic constitutive laws, and compare the calculation speed with that of numerical differentiation. As a result, it was found that the computation time using the analytically derived consistent tangent moduli was 1/5 of that using the numerical differentiation, and the computation speed was greatly improved.

 The seismic performance of underground linear structures is generally verified against member failure in the cross-sectional direction using two-dimensional seismic response analysis of soil-structure coupled systems. On the other hand, to verify the seismic performance of a single structure, a pushover analysis of the structure itself is sometimes performed. In a pushover analysis of a single structure, the force acting on the structure differs from that of a structure continuously surrounded by the surrounding ground, depending on how the boundary conditions, such as support points and loading points, are given. Therefore, in this study we proposed reasonable boundary conditions for pushover analysis of the cross-section of RC box culvert using a fiber model that considers material nonlinearity.

 To reasonably evaluate the safety of slopes during earthquakes, it is important to know how various characteristics of seismic waves affect the susceptibility of slopes to collapse. In this study, we focused on amplitude and frequency as indices that characterize seismic waves and investigated them by two-dimensional elasto-plastic finite element analysis using many sinusoidal waves consisting of combinations of these indices. First, the distributions of the absolute acceleration response and residual displacement of the slope are characterized by their dependence on the amplitude and frequency of the input wave. Furthermore, it is shown that the residual displacement on the slope shoulder can be large not only in the frequency band where the frequency of the input wave is close to the natural frequency of the slope and the response is large due to resonance, but also in the band where the frequency is small if the amplitude of the input wave is sufficiently large.

 In this research, as one of the studies on the seismic performance of existing PC road bridges designed based on the level 1 seismic ground motion, load tests were conducted on anchor bolts connecting the bearings and the superstructures with five combinations of vertical seismic force and horizontal seismic force. The load-carrying capacity and damage behavior of the anchor bolts up to the ultimate stage were confirmed and the seismic performance was investigated based on the test results. It was confirmed that the ratio of maximum tensile load to dead load was 1.05 in the case of vertical load only, and the ratio of maximum horizontal load to dead load was 1.16 to 2.06 in the four cases of vertical load and horizontal load. It is considered that the anchor bolts can be expected to resist not only the level 1 seismic ground motion considered in the design, but also the level 2 seismic ground motion of the current design standard.

 Recently, spherical sliding bearings have attracted attention as a new seismic isolation bearing mechanism that differs from conventional laminated rubber bearings. When a spherical sliding bearing is applied to existing bridges as a seismic retrofit, it is necessary to consider the effect of different ground type by modeling the structure including the ground. In this study, nonlinear dynamic analyses were conducted on bridge models with spherical sliding bearings and different ground type in order to investigate the effects of different ground type on the dynamic response of existing bridges seismically retrofitted by spherical sliding bearings. The results showed that the dynamic response of the model was affected by ground type, and that the difference in response values was small when solid ground, which suggests that solid ground could be preferable when spherical sliding bearings are applied to existing bridges as seismic reinforcement.

 The spherical sliding bearings in this study are seismic isolation bearings that are expected to replace the existing steel bearings in the seismic retrofit of bridges. Sliding bearings have velocity, temperature, and surface pressure dependency. However, the effects of the temperature dependency of the friction coefficient on the dynamic behavior have not been fully understood. Therefore, in this study, a series of shaking table tests were conducted using two types of sliders with two different friction coefficients, medium and low-friction types, at three different ambient temperatures. The results showed that the coefficient of friction for the medium-friction type decreased with an increase in ambient temperature, while no clear temperature dependence was observed for the low-friction type. Furthermore, the experimental results were simulated well by nonlinear time history analyses considering the temperature and velocity dependency on the friction coefficient in the model.

 It is needed seismic retrofitting methods that focus on the “loss of axial load carrying capacity”, but few studies have focused on this “loss of axial load-bearing capacity”. And there are currently no studies that consider the retrofitting method from the viewpoints of workability at the site and reduction of the load on the foundation. In this study, we proposed a method of seismic retrofitting hollow-section RC piers, in which the base is filled with air mortar and is rolled up, and verified the retrofitting effect by cyclic loading experiments using large hollow-section RC specimens. The experimental results showed that filling the base with air mortar and rolled up with steel plates can prevent loss of load-bearing capacity of the piers.

 Seismic response analysis was conducted to clarify the response of the bridge-pipeline-ground system when nonlinear behavior of the ground was considered, based on the damage caused by the 2016 Kumamoto earthquake. The results showed that: 1) nonlinear behavior of the embankment behind the abutment increases the response of the pipeline near the abutment; and 2) the increase in axial stress in the bridge-pipeline-ground system is strongly enhanced when the system is subjected to seismic waves in the bridge longitudinal direction. Furthermore, it was confirmed that 3) the response of the pipeline near the abutments can be significantly suppressed by seismic countermeasure to the pipeline elements near the abutments.

 The authors have developed a ‘metabolism seismic column’ designed to modify seismic performance under axial force and facilitate rapid restoration post-earthquakes. This metabolism seismic column features a double-layered base structure: The outer layer comprises a replaceable plastic zone intended to absorb seismic energy, while the inner part has a permanent hinge designed to support axial and shear forces under regular conditions. In this study, we improved the metabolism seismic steel column by organizing the functions of the bridge piers in order to improve the recoverability of the bridge structure after earthquakes. We specifically examined the impact of augmenting the axial stiffness of the permanent hinge on the column’s seismic performance and its post-earthquake recoverability using cyclic loading tests. The results indicate that enhancing the axial stiffness of the permanent hinge not only improved the seismic performance of the columns but also aided in post-earthquake restoration. This was attributed to the column’s ability to maintain the position of the upper structure due to the permanent hinge.

 This study revealed the dynamic responses of the Tsurumi Tsubasa Bridge (a long-period, cable-stayed bridge infrastructure on the Tokyo metropolitan expressway) by means of seismic response analyses of a three-dimensional nonlinear frame-structural model exposed to multi-input ground excitations in the 2011 off the Pacific coast of Tohoku earthquake. The modal characteristics were basically consistent with those of previous studies and depended on the modelling of elastic restraint cables and the boundary conditions around the vertical axes of the main towers. By performing a sensitivity analysis of the dominant model parameters of the subject bridge structure, we examined the effects of axial rigidity of the elastic restraint cable on the longitudinal and transverse motions of the bridge system and on the coupled dynamic responses of the nonlinear structural components.

 This study experimentally investigated the correlation between the residual performance of rubber bearings and nondestructive evaluation by the AE method. Shear tests simulating earthquake waveforms were conducted on rubber bearing specimens, followed by cyclic compression loading tests and AE measurements, and the correlation between AE measurement data and residual performance obtained from performance verification tests was investigated. As a result, it was confirmed that there was a correlation between the RMS of AE waveforms, and equivalent damping constants, indicating that the AE method could be used to evaluate residual performance.

 This study develops a multi layered rubber bearing that can improve horizontal displacement demand of bridge structures. Compared to the traditional single bearing, this system consists of two laminated rubber bearings piled-up on each other. Experiments were conducted to evaluate the shear force-deformation performance considering two piled arrangements. One-by-two, and four-by-two piled-up bearings. The results of the one-by-two bearing demonstrated that the equivalent shear stiffness and damping coefficient can be estimated at shear strain of ±175%. Strain hardening was initiated after the shear strain of ±250%. In addition, specimen four-by-two exhibited a consistent shear force deformations after several cycles.

 The superstructure weight of bridges and viaducts influences the behavior of bridges and viaducts during earthquakes, but in order to grasp it, a detailed load calculation is usually required. In this paper, we developed a simple method for estimating superstructure weight of railway bridges and viaducts. Specifically, the girder weight per unit length according to the type of girder, the weight of the track according to the type of track were arranged from existing literature, and an simple estimation formula for superstructure weight was created. Regarding the girders for which the superstructure weight is calculated in detail, the results of the estimation formula and the detailed calculation were compared, and it was confirmed that the superstructure weight can be estimated with a maximum error of about 10%. This result is expected to be applied to the efficient construction of seismic response analysis models for a huge number of railway bridges and viaducts.

 Real-time hybrid simulation (RTHS), in which loading tests and numerical analysis are conducted simultaneously, is considered to be one of the most effective methods for evaluating the dynamic performance of large-scale structures. On the other hand, an increase in calculation-task may affect the Continuous Hybrid Simulation Algorithm, which guarantees the smoothly actuator behaviour in RTHS, and may degrade the accuracy of simulation. In this study, we examined the effect of increased calculation-task on the accuracy of the RTHS, using theoretical equations and evaluating a virtual RTHS, and discussed the applicability of the Continuous Hybrid Simulation Algorithm to the RTHS. The results showed that even a slight increase in calculation-task significantly reduces simulation accuracy, and that calculation-task can be an important parameter of analytical model design in RTHS.

 The effects of low temperature environments on the historical properties of seismic isolation bearings were investigated for the HDR-S and SPR-S bearings using real-time / pseudo hybrid experiments. The results are discussed in terms of the effects of temperature setting on initial loading, loading rate, and equivalent stiffness/damping. The effect on initial loading was independent of the temperature setting, while the effect on loading rate tended to differ between the HDR-S and SPR-S bearings. The increase in equivalent shear stiffness with increasing internal temperature in the SPR-S bearing showed a different trend from that in previous studies. The effect of temperature setting on equivalent damping is relatively small.

 Commands to controller may exceed the speed capability of the dynamic testing machine in Real-Time Hybrid Simulation (RTHS) because commanded displacements are calculated sequentially during the test, unlike the commands of conventional dynamic testing are specified in advance. If the controller limits the velocity in the case of velocity limitation exists, the delay between the command displacement and the measured displacement increases. As a result, excessive delay compensation may cause higher-order vibration to be included in the command displacement, which may degrade test accuracy. Therefore, this study proposes the delay compensation algorithm for RTHS that takes into account the speed constraint of the dynamic testing machine. We propose an algorithm for generating a command signal that reduces the speed according to the speed constraint, and verify this algorithm conducting virtual RTHS and RTHS using dynamic actuator. The results show that the proposed algorithm works well and the proposed method can suppress higher-order vibration of the command displacement by the delay compensation method compared to conventional speed control by a controller.

 The observation of two magnitude 7 earthquakes at the same location, such as the 2016 Kumamoto earthquake, is unprecedented in the history of Japanese seismic observations and has made us aware of the possibility that seismically designed structures may experience multiple large seismic motions. In view of the possibility that bridges may also be subjected to multiple large seismic loads, the authors have investigated the hysteresis characteristics of single-column RC piers after being subjected to a loading history equivalent to one earthquake load using cyclic loading experiments. The results of previous experiments have shown that the ratio of the reduction in equivalent stiffness of the second loading to the first loading history has a linear relationship with the range of the first loading, but in this paper, the results of new loading experiments show that the ratio of the reduction of the equivalent stiffness has a linear relationship with the range of the first loading only up to the limit state 2. The paper details that the results of the new loading tests show that the rate of reduction of the equivalent stiffness has a linear relationship with the range of the first loading only up to the limit state 2.

 In the 1995 Southern Hyogo Prefecture Earthquake, many columnar attached structures, including TV poles for installing traffic flow monitoring cameras, suffered damage such as overturning. However, TV poles are elastically designed against dead load, live load and wind load, and the seismic load is not considered. In this study, as basic data for establishing a seismic performance assessment method for columnar attached structures and considering countermeasures, the damage mechanism was analyzed based on the reproduction analysis of a TV pole that was damaged by the Southern Hyogo Prefecture Earthquake. As a result, the bending moment at the base of the TV pole exceeded the design allowable value and it was found that the damage was consistent with the damage situation where the TV pole fell. Furthermore, as the upgrading of the reproduction analysis, analyses of the influence of plasticity of steel piers and ground uncertainty on the response of TV poles were analyzed. As a result, it was found that the response of the TV pole tends to increase when resonance between the bridge pier and the TV pole is likely to occur.

 As a seismic resilience measure for road bridges, a structure in which the lower plate setting bolts of the rubber bearings rupture between the initial yield strength of the piers and the maximum horizontal strength when the action exceeds the design seismic action is investigated. In this experiment, cyclic loading tests were conducted on a reinforced concrete bridge pier model to investigate the effect of rebars arrangement that provides the difference between the initial yield strength and the maximum horizontal strength of the piers. The pier model consists of large-diameter rebars placed in a crisscross pattern inside the columns in addition to the rebars normally required. From this study, the following results were obtained: (1) The lower plate setting bolts of rubber bearing ruptured after the initial yield strength; (2) It was confirmed that there was a difference between the initial yield strength and the maximum horizontal strength of the piers; (3) Column structures with large-diameter rebars arranged in a cross shape inside the pillars also failed due to the fracture of the axial rebars and the crushing of the core concrete, as with ordinary RC bridge piers.

 This paper proposes a seismic design flow for a four-pylon multi-span cable-stayed bridge of an unprecedented scale in the structural planning phase to realize the planning concept, and reports the details of the study based on the flow. The optimal support conditions for the basic structure of the bridge are studied, the structural characteristics are clarified based on these conditions, and a seismic strategy is established based on the evaluation of the fracture process by buckling eigenvalue analysis. Next, scenario seismic motions are set for the revised basic structure based on the bridge conditions, performance requirements are proposed, and verification results based on these requirements are presented. Finally, the damage sequence is confirmed by pushover analysis and incremental dynamic analysis, and it is verified that the desired failure process is achieved. The results show the effectiveness of the seismic structural planning flow in the structural planning phase.

 An analytical approach that can reproduce the cyclic behavior of ERW steel pipe columns, where significant residual plastic strains occur during the manufacturing process, was investigated. As a result, several requirements for conducting accurate analyses became evident. Firstly, it is necessary to employ the geometrically and materially nonlinear FE shell model capable of representing the cyclic local buckling behavior of steel pipes in the large plastic strain region. Therefore, the modified three-surface model with the expanding bounding surface that had been proposed by authors was utilized herein as the constitutive model of the steel pipe. Secondly, it is crucial to accurately predict the generated residual plastic strains by the shell FE analysis, considering the pipe manufacturing process. Then, these predicted residual plastic stains are explicitly introduced into the FE shell model of steel pipes with their virgin material. When the constitutive laws of the virgin material are unknown, a method for estimating the constitutive laws of the virgin material through inverse analysis has been proposed. In the inverse analysis, suitable constitutive laws for the virgin material are identified so that the tensile coupon test results of the pipes can be represented by an FE model that incorporates the calculated residual strains.

 The Japanese Handbook for Bridge bearings was revised in 2018, and the items on design hysteretic models and product property verification tests were changed. In the current edition of the Specifications for Highway Bridges and their Commentaries V, the nonlinear characteristics of seismic isolation rubber bearings are generally modeled as bilinear in the dynamic verification of seismic isolation bridges with rubber isolators. However, it has been confirmed that the force-displacement characteristics of actual products are dependent on the maximum experienced strain due to the Mullins effect and that hardening occurs when the shear strain increases. In this study, a design hysteretic model that takes into account the Mullins effect and hardening in seismic isolation rubber bearings was used to investigate the effect of this phenomenon on the seismic performance of bridges.

 In order to expand the scope of application of the newly proposed analysis method using equivalent plastic displacement at element failure proposed by the authors, a fracture analysis was performed on experimental specimens of steel bridge piers with unstiffened box section subjected to random cycle displacement s. As a result, both the crack initiation and propagation of the experiment could be accurately simulated. In addition, the same analysis was performed even with a small mesh size, and the difference in the mesh size was confirmed. When the mesh size was made smaller by about half, the analysis time increased by about 4 times, but there was no significant difference in the crack initiation and propagation.

 In the April 2016 Kumamoto earthquake, a slope failure occurred around the Aso Ohashi Bridge, which is believed to have been a contributing factor to the bridge collapse. In many cases, bridges in wide-area networks such as expressways are constructed adjacent to slopes due to constraints such as alignment conditions, etc., and it is possible that slope failures may affect bridges. However, not much research has been conducted on the effects of slope failure on bridges, and analytical methods have not yet been fully established. The authors have conducted a replicated analysis of the slope around the Aso Bridge using the finite area method, but there are still problems in reproducing the behavior of secondary collapse. In this study, we focused on the continuous slip that is a characteristic feature of slope failure, and examined a method to evaluate the phenomenon in which a primary collapse causes a secondary collapse.

 In this study, field investigations and 3D seismic response analysis were conducted on a skewed bridge that collapsed during the February 2023 earthquake in southern Turkey. The skewed bridge had pad-type rubber bearings, no anchor bar connecting the superstructure and substructure as is common in Japan, and displacement-limiting blocks on the acute-angle side of the bridge, which was severely damaged. It was concluded that the bridge fell due to the rotational behavior of the main girder caused by the collision of the main girder with the abutment due to strong seismic motion. Seismic response analysis was also conducted using the observation records near the damaged bridge as input. As a result, the impact of the main girder on the abutment breastwall and the rotational behavior of the main girder were reproduced, and the support area of the main girder was found to cause the bridge to unseat from the acute angle side of the abutment.