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Chūō-ku, Japan

Katakura K.,Meitoku Engineering Laboratory | Akamatsu R.,Toin University of Yokohama | Sugimoto T.,Toin University of Yokohama | Utagawa N.,Sato Kogyo Co.
Japanese Journal of Applied Physics | Year: 2014

We study a noncontact inspection method for large-scale structures such as tunnels and bridges. This method involves the use of a high-powered sound source and a scanning laser Doppler vibrometer (SLDV). In our previous study, we proposed a tone burst wave method to improve the signal-to-noise ratio (SNR) of the measured result. Using this method, a defect that was difficult to detect using our previous method was detected. In this study, we examined the detectable size and depth of the defect by using a model wall with circular defects. The distance between the sound source and the concrete test piece was 5m, and the output sound pressure was about 100 dB near the surface of the concrete test piece. As the transmitted wave, tone burst waves with different center frequencies from 500 to 7000 Hz were used. A conventional investigation by the hammer method was also simultaneously carried out for comparison and almost identical performance was confirmed. From the experimental result, we confirmed that the bending resonance frequency detected was proportional to the depth of the circular defect, and was in inverse proportion to the plane size (area) coincident to the analytical result for a circular plate. We also found that the vibration energy of the defect shows a strong dependency on its depth. Therefore, the possibility of defect depth estimation using the resonance frequency and the vibration energy ratio is expected. In the future, a practical investigation system that will replace the hammer method might be developed. © 2014 The Japan Society of Applied Physics.

Akamatsu R.,Toin University of Yokohama | Utagawa N.,Sato Kogyo Co. | Sugimoto T.,Toin University of Yokohama | Katakura K.,Laboratory
IEEE International Ultrasonics Symposium, IUS | Year: 2013

We propose a new non-contact acoustic imaging method for nondestructive inspection using a high-power directional sound source and a S canning Laser Doppler Vibrometer (SLDV). In this method, vibration velocities on concrete surface, which is generated by an air borne sound, is measured with the SLDV. As a high-power directional sound source, an LRAD (Long Range Acoustic Device) is employed. Near a targeted concrete surface, very high sound pressure is required to excite the concrete wall. However, while the sound wave is emitted, the SLDV is vibrated by the sound wave. Thus, the vibration of the SLDV affects the signal-to-noise ratio. This paper describes about tone burst wave method for an improvement of the signal-to-noise ratio. Consequently, the signal to noise ratio of 12 dB was improved than using a chirp wave. © 2013 IEEE.

Uno Y.,Sato Kogyo Co. | Kimura S.,Kanazawa Institute of Technology
Life-Cycle of Structural Systems: Design, Assessment, Maintenance and Management - Proceedings of the 4th International Symposium on Life-Cycle Civil Engineering, IALCCE 2014 | Year: 2015

In this paper, the authors propose a method to evaluate quantitatively the spalling risk of the lining concrete and the spalling risk variation model in a road tunnel, the method is based on probability theory. A concrete risk shall be evaluated by economic loss. The spalling phenomenon can convert them into each economic loss which the administrator and user of a tunnel receive. Furthermore, the prevention technology to spalling by using fiber sheet is proposed. This method is applied to seven tunnels including the site under construction as of March, 2014. As a result, the verification is presented certainly at these construction sites. © 2015 Taylor & Francis Group, London.

Uemura K.,Tokyo City University | Sasaki T.,Kyokado Engineering Co. | Shimada S.,Kyokado Co. | Suemasa N.,Tokyo City University | Nagao K.,Sato Kogyo Co.
Proceedings of the International Offshore and Polar Engineering Conference | Year: 2015

Reasonable infusion materials are investigated using white carbon in this study. White Carbon, hereinafter written as WC, is aggregate silica micro-particles and the size of independent particle is several tens μm in diameter. Although the effect of the liquefaction countermeasure method using WC is to increase the density of sandy ground by injecting it, regular WC is relatively too large to be injected into the ground. Therefore, regular WC has to be grinded into much finer particles in order to grout them into sandy ground. In this study, a micro bubble generator was suggested to grind WC efficiently, utilizing the phenomenon of vortex breaking. In this paper, a series of grain size analysis of WC grinded by the micro bubble generator were conducted and infiltrating injection tests injecting the grinded WC were carried out in order to examine the feasibility of the WC injection method proposed. As a result, it was confirmed that the finer WC was able to permeate sandy ground. Copyright © 2015 by the International Society of Offshore and Polar Engineers (ISOPE).

Nguyen D.L.,Ho Chi Minh City University of Transport | Nguyen D.L.,Nagaoka University of Technology | Ohtsuka S.,Nagaoka University of Technology | Hoshina T.,Sato Kogyo Co. | Isobe K.,Hokkaido University
Soils and Foundations | Year: 2016

Currently, many formulas are used to calculate the ultimate bearing capacity. However, these formulas have disadvantages when being applied in practice since they can only be applied for calculating simple footing shapes and uniform grounds. Most formulas do not take into account the size effect of the footing on the ultimate bearing capacity, except for the formula by the Architectural Institute of Japan. The advantage of using the finite element method (FEM) is its applicability to non-uniform grounds, for example, multi-layered and improved grounds, and to complicated footing shapes under three-dimensional conditions. FEM greatly improves the accuracy in estimating the ultimate bearing capacity. The objective of this study is to propose a rigid plastic constitutive equation using the non-linear shear strength property against the confining pressure. The constitutive equation was built based on experiments for the non-linear shear strength property against the confining pressure reported by Tatsuoka and other researchers. The results from tests on Toyoura sand and various other kinds of sand indicated that, although the internal friction angle differs among sandy soils, the normalized internal friction angle decreases with an increase in the normalized first stress invariant for various sands despite dispersion in the data. This property always holds irrespective of the reference value of the confining pressure in the normalization of the internal friction angle. The applicability of the proposed rigid plastic equation was proved by comparing it to the ultimate bearing capacity formula by the Architectural Institute of Japan, which is an experimental formula that takes into account the size effect of the footing. The results of rigid plastic finite element method (RPFEM) with the proposed constitutive equation were found to be similar to those obtained with the Architectural Institute of Japan's formula. It is clear that RPFEM, with the use of the non-linear shear strength against the confining pressure, provides good estimations of the ultimate bearing capacity of the footing by taking account of the size effect of the footing. © 2016 Japanese Geotechnical Society.

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