Structural health monitoring technique was applied to an aged arch dam, where long-term continuous observation of ambient vibration/seismic motion was performed over a span of three years and a half and where the predominant frequency variation along time was detected. As the result, the following was made clear, that is, the structural health of an aged arch dam can be evaluated through the monitoring of the predominant frequency variation which is detected as the result of the long-term continuous observation of ambient vibration/seismic motion.
This paper aims to describe the changes in the dynamic characteristics of two existing buildings in Miyagi Pref., Japan. One is a reinforced-concrete(RC) structure and the other is steel one. In this study, we found that the natural frequency of the RC structure is more strongly correlated with temperature in comparison with the steel structure. The temperature dependence of the natural frequencies is included in record indicating the amplitude dependence of the building’s dynamic characteristics, and corrections with temperature data can deliver more accurate estimations of a building’s structural soundness.
This paper discusses the new subjects of the liquefaction research regarding the liquefaction damage of the Great East Japan Disaster. Specifically, the subject about the liquefaction potential assessment, the subject about the evaluation of ground subsidence caused by liquefaction and the subject seen to generate the liquefaction damage of a river levee, etc. are discussed based on the damage observed or the experimental results. It has been shown that understanding current damage on the extension of the present technology has a limit, and that the prediction and countermeasure technology of the liquefaction damage based on a new concept is necessary.
A new liquefaction countermeasure for small structures was proposed to reduce liquefaction damage. In our approach, the ground below the perimeter of the foundation circumference is replaced by gravel, opening a drainage route to the ground surface. Centrifugal model tests confirmed the effectiveness of the proposed method. The method does not prevent liquefaction, but significantly reduces the degree of tilting of the structures.
The facilitation of a water supply is important to human life. So, the maintenance of a reliable water supply function during earthquake is strongly required. From such necessity, we studied the seismic response of a large underground purification reservoir by 3D dynamic analysis. As a result, it became clear that the stresses by earthquake motion will concentrate in the connections at the top of middle pillars inside the reservoir. In order to evaluate the seismic performance accurately, it is necessary to faithfully analyze the middle pillars according to the actual shape and arrangement.
This study proposed a concept on ductility assurance design of joints for a glued laminated timber frame using the upper 5% limit of tensile bolt unit stress when tensile bolt strain is 5%. In addition, the suitability of this concept for ductility assurance design of joints was verified by conducting a structural experiment on three tensile bolt type joints.
Simple evaluation of the degree of structural damage suffered by high-rise RC buildings after being subjected to strong ground motions is extremely important. For a large number of high-rise RC residential buildings for which strong-motion measurements or observations of microtremors before and after earthquakes have not been carried out, we developed a benchmark indicator allowing simple characterization—based on pseudovelocity response spectra for strong-motion records measured at ground points close to the building, as well as re-created waves and other data—of peak inter-story drift ratio values expected in a future major earthquake.
The city of Iwaki, located in Fukushima Prefecture, Japan, faced water outage twice because of the Tohoku earthquake that occurred on March 11, 2011, as well as the earthquake that followed on April 11, 2011. It is rare that two large earthquakes, each with different mechanisms, occur within a short period of one month. This study focuses on the pipeline damage in Iwaki due to these earthquakes and tries to clarify the seismic vulnerability of pipe attributes on the basis of the earthquake damage analysis on the water-supply pipeline. As the result of the analysis on the seismic vulnerability index of the pipe material, pipe diameter, and its geomorphological classification, the seismic vulnerabilities to pipe diameter and material were very similar between the two earthquakes. The seismic vulnerability to pipe diameter was also similar to that in earthquakes in the past, whereas polyvinyl chloride pipes (VPs) were evaluated to be stronger. The geomorphological classification factor does not always need to add seismic vulnerability depending on the evaluation of the seismic motion.
In the conventional design method, there is no particular method to judge the liquefaction phenomenon of the unusual soil such as volcanic ash soil. This study, in order to clarify and evaluate the liquefaction characteristics of volcanic ash soil, field investigations and a series of soil laboratory tests of volcanic ash ground were carried out. The field investigations and sampling were conducted in the areas where ground liquefaction occurred due to the 1993 Hokkaido-nansei-oki and the 2013 Tokachi-oki earthquakes. According to the results, the liquefaction strength ratio (RL) was underestimated when using the formulation of the conventional design method. Moreover, it was found that the estimated formulation RL need to be modified for evaluating the liquefaction phenomenon in volcanic ash soil.
The eighth meeting of the Microtremor Research Camp (MRC) was held in Ohno City, Fukui Prefecture from September 30th to October 2nd in 2016, and MRC carried out microtremor measurements in the Katsuyama Basin, which is constituted by deposits of the Kuzuryu River. These measurements consist of microarray measurements at 25 sites and single-point measurements at 67 sites. This paper reports the outline of these measurements and presents the distribution of predominant frequencies in the basin obtained by the analysis of horizontal-to-vertical spectrum ratio at single-point measurement sites. As a result, the large differences in the distribution of predominant frequencies and peak spectral amplitudes between the Quaternary terrace deposits and alluvial deposits are clarified.