We have carried out the benchmark tests of ground motion calculation using the numerical methods. In the case of the Kanto Plain in the previous reports, difference in later phases of ground motion can be seen mainly due to the grid interval modelling from participants. In the 2013 benchmark tests, the foreshock of the 2004 Kii Peninsula earthquake is targetted to focus on the long-period ground motions caused by faults in the Nankai Trough. In the blind calculation, differences were found in synthetic waveforms provided by 6 teams. For the cases which used the unified and simple models, results becomes similar. Finally we examined the effect of the Q values in surrounding damping area on reflected motion in waveforms of the long-period ground motion.
In order to confirm the validity of liquefaction countermeasures selected for the integration of roads and housing in an existing housing area, three dimensional FEM analyses (LIQCA3D11) were conducted. The whole model in which all blocks are modeled is used in the case of taking measures by only main construction methods. The partial model that four housing areas are selected from all blocks is used in the case of taking measures by a combination of main and sub construction methods.The dewatering method and the grid-form deep mixing wells method were chosen as main construction methods in the whole model.It was confirmed that effects of the countermeasures of the grid-form deep mixing wells method are limited by the analysis of the whole model and it is most effective to set all blocks including just below the housing to the countermeasure region by analytical results of the partial model.
In this study, we carried out evaluations of ground motion characteristics in natural slope and cut slope in Chiba city. We have carried out seismic observation at the top of slope and on the terrace. Then we confirm that large amplification of ground motion arise at top of the natural slope. Therefore, we made ground models estimated from survey and calculated transfer function by dynamic analysis of two dimensional finite element method. The results show more accurate characteristics of ground motion than that of one dimensional analysis. We conclude that the soft soil on natural slope at the edge of terrace causes a large amplification of earthquake motion.
We evaluated spatial variations (i.e. lagged coherency and standard deviation of Fourier amplitude ratio between observation points) of seismic ground motions in hard soil, focusing on the difference of depth levels and horizontal and vertical components in addition to the frequency and the horizontal distance between the observation points, using the strong motion records in the three-dimensional array observation system arranged in the Hamaoka Nuclear Power Station. We derived the statistical models of coherence and standard deviation of Fourier amplitude ratio based on the regression analyses concerning frequency and horizontal distance from the spatial variation features of seismic ground motions. As a result, it was shown that the coherency decreased with increasing frequency and the distance. the degree of the decrease in the vertical component was larger than that in the horizontal component, also it is larger shallow in depth levels. Furthermore, we indicated that in coherence obtained from the observed record has a sharp decline at a particular frequency, it corresponds to the minimum value of the transfer function with respect to the incident wave Its minimum value is the resonant frequency of the depth level shallower than, and is a nodes of vibration mode at the time of resonance in the depth level. On the other hand, the standard deviation of Fourier amplitude ratio under 5Hz increased with increasing frequency and the distance, but that was constant in the range greater than 5Hz.
In the conventional Ground Motion Prediction Equations (GMPE), site amplification term is represented by average S-wave velocity near surface at a site (AVS30) or by ground type(type I, II or III). However, there has been pointed out that large variation of the site amplification factor by earthquake magnitude. In order to solve this problem, we used borehole data and velocity structures provided by KiK-net and tried to create a regression equation of site amplification ratio of PGA and PGV from the surface to bedrock as the new site amplification term. We investigated the effect of source parameters and wave propagation parameters, in addition to the number of layers, the average S-wave velocity and thickness of each layer, on the ground amplification ratios of PGA and PGV of the horizontal components. As a result, we created a high precision regression formula of the site amplification ratio that can evaluate the dispersion due to each individual earthquake by introducing magnitude, dominant periods and soil parameters that reflect deep subsurface structure, instead of the AVS30 site amplification term used in conventional regression equations.
In this study, we try to replicate seismic responses of the R/C high-rise residential building, where the earthquake observation system has been activated for more than 15 years. During the 2011 off the pacific coast of Tohoku Earthquake, the seismic records were obtained simultaneously for the building and the surrounding soil, which enable us to evaluate the coupling dynamic behavior of the building, soil, and the piles. We adopted the Penzien-model for simulation analysis to evaluate the dynamic building-pile-soil interaction considering nonlinear behavior of both the building and the soil, which is validated by good agreement with recorded motions. Pile stresses during the Tohoku earthquake are estimated to approximate to crack level.
A dynamic centrifuge test and a static cyclic loading test were performed on a soil-footing model to investigate superstructure response and ultimate bearing capacity of a shallow foundation during strong shaking. A residual rotation angle of the shallow foundation after the dynamic test was 1/200 rad, even though the estimated ultimate bearing capacity during strong shaking was less than the self-weight of the footing and the measured overturning moment acting on the footing reached the ultimate overturning moment. The ultimate bearing capacity during strong shaking determines the ultimate overturning moment, but it does not affect the overturning of a shallow foundation structure when the safety factor of bearing capacity during static conditions is large.
Based on analysis of data from hydraulic experiments for bridge deck models with or without overhangs, tsunami fluid forces acting on a bridge deck subjected to surging waves on dry bed were idealized by analyzing the relations between tsunami fluid forces and four dominant parameters: tsunami inundation depth, increase rate of tsunami inundation depth, tsunami velocity, and wave celerity. Normalized horizontal pressure acting on a bridge deck without overhangs was 1.16 times higher than those with overhangs in the range of Fr =1.80 which is a higher Froude number. Normalized vertical pressure is classified into five categories from μ1 to μ5 in the time series: μ1 occurred only for the model with overhangs, μ2 without overhangs showed higher values than μ2 with overhangs in the range of less than Fr =1.50, μ3 without overhangs varied from negative to positive values in the range of Fr =1.00 to Fr =1.80, μ4 and μ5 which mean vertical pressure on bridge deck in quasi stationary stage were nearly close to both models with or without overhangs.
When we evaluate the structural characteristic of traditional wooden structures, it is useful way to estimate vibration characteristics from micro-tremor measured data. In this study, we conducted micro-tremor measurements and excitation tests on Chofuku-ji Hondo in Ikoma City, Nara pref. and estimated the natural frequency, the damping ratio, and so on. Moreover, we made the analysis model of the building, and made sure of the differences between analytic and measured values by eigenvalue analysis.
For the purpose of promotion of the mid-rise timber building, we tried to design glued laminated timber frame structures of semi-fireproof construction, and designed the structural and fire resistance specifications. In this paper, it was confirmed in the experiment structural performance of tensile-bolted joints designed based on the trial design. For tensile-bolted joint, we examined the maximum strength of the bolt to the fracture toughness of the failure mode type. The Bolts were designed with the upper limit of 5% of the yield stress and the ultimate strength. By the experiment, it was confirmed experimentally that the validity of the mechanism assurance design of brittle failure mode prevention.
During the 2011 off the Pacific coast of Tohoku Earthquake, many residents living coastal area used car for their evacuation from mega Tsunami. Due to the rapidly increased traffic demand in road network and also trouble of traffic signals, heavy traffic congestions occurred in the road network. At first, this research investigated the condition of car evacuation in Kesennuma city. Secondly, tsunami evacuation simulation system was developed. Thirdly, several counter-measures for safer tsunami evacuation were developed and proposed. Finally, the scenario of roads widening proposed by Kesennuma city was evaluated using the simulation system. As a result, it was clarified that decreasing of car generation is an effective countermeasure to modify the road traffic flow and that it could not solve the problems in car evacuation perfectly.
Iwaki City, Fukushima Prefecture faced water outage two times due to the Tohoku earthquake that occurred on March 11, 2011 as well as due to its following earthquake that occurred on April 11, 2011. It is rare that the big earthquakes with different mechanism occur in a short term of one month. In this study, the pipeline damage of Iwaki City due to these earthquakes were focused on and it was tried to clarify seismic vulnerability of pipe attribute based on the earthquake damage analysis on water-supply pipeline. As the result of analysis on the seismic vulnerability factors of pipe material, pipe diameter and its micro-topography, the seismic vulnerabilities on pipe diameter and material were very similar between two earthquakes. The seismic vulnerability on pipe diameter was also similar to that in earthquakes in the past, while the vinyl chloride pipe was evaluated to be stronger. The micro-topography factor does not always need to add seismic vulnerability depending on the evaluation of seismic motion.
Basic study on an implementation of mean square of acceleration amplitudes to the waveform inversion is examined, in preparation for its application to a short period source inversion. First, a mean square procedure between random waves is confirmed to show a linear approximation. Next, numerical experiments are practiced using SGF results from fault models based on the Taisho Kanto Earthquake. If 6 site records around the fault model are available, short period radiating areas are almost reconstructed. Though the experiment was practiced under ideal conditions, the proposed method was shown to be effective.