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Umeyama M.,Tokyo Metroplitan University | Ishikawa N.,Tokyo Metroplitan University | Kobayashi R.,Tokyo Metropolitan Government
Proceedings of the Coastal Engineering Conference

The flow visualization technique was applied to the collision of two solitary waves propagating in the same and opposite directions. Measurements of the velocity and trajectory of the solitary waves were conducted using a particle image velocimetry (PIV) system consisting of an 8-W ND: YAG laser and a high-speed CCD camera. In the solitarywave interaction tests, we set up three kinds of velocity fields - smaller, taller, and compound waves in the rear-end collision tests, and right-running, left-running, and colliding waves in the head-on collision tests. Instantaneous and spatial surface profiles were measured using the image thresholding method in which the boundary plane between the air and water can be detected as the interface having the maximum luminance value. The measured run-up elevation of the colliding wave was compared with the theoretical elevation using a third-order perturbation solution. Based on a Eulerian-Lagrangian algorithm, the PIV result was applied to the particle tracking process that occurred in the two dimensional plane. Source

Tatsuoka F.,Tokyo University of Science | Munoz H.,Peruvian National University of Engineering | Kuroda T.,Tokyo Metropolitan Government | Kiyota T.,University of Tokyo | And 2 more authors.
Soils and Foundations

To examine whether and how the seismic stability of existing bridges can be substantially improved by integrating the girder, the abutments and the backfill, a series of shaking table tests were performed in 1 g. The tested small bridge models are (1) a conventional-type comprising a girder, supported by a pair of gravity-type abutments (without pile foundation) via bearings (fixed and movable), and unreinforced backfill, (2) the girder and the abutments of the above are integrated (without using bearings), (3) the backfill of the above is reinforced with two layers of large-diameter nails connected to the abutment top and the toe or the heel of the abutment footing and (4) the bottom nails of the above are replaced with longer ones connected to the toe of the abutment footing. Their dynamic behavior was analyzed as a damped single-degree-of-freedom system. The dynamic stability of the bridge was found to increase with an increase in (i) the dynamic strength against the response acceleration, (ii) the initial stiffness, (iii) the dynamic ductility (i.e., a smaller decreasing rate of stiffness during dynamic loading) and (iv) the damping ratio. When factors (ii) and (iii) are high enough, the natural frequency of a bridge can be kept much higher than the input frequency, and thus, the response acceleration can be kept low. All these factors can be improved by integrating the girder, the abutments and the backfill together with part of the supporting ground. In a series of static model tests, lateral cyclic displacements, caused by the seasonal thermal deformation of the girders with prototypes, were applied to the top of a small abutment model. The active failure in the backfill and the detrimental effects of large passive pressure, both developing due to the dual ratchet mechanism, can be effectively restrained by reinforcing the backfill and supporting the ground with nails connected to the top and the bottom of the abutments. © 2012 The Japanese Geotechnical Society. Source

Asamoto S.,Saitama University | Ohtsuka A.,Pacific Consultants Company Ltd | Kuwahara Y.,Tokyo Metropolitan Government | Miura C.,Tokyu Construction Company Ltd
Cement and Concrete Research

In this paper, the effects of actual environmental actions on shrinkage, creep and shrinkage cracking of concrete are studied comprehensively. Prismatic specimens of plain concrete were exposed to three sets of artificial outdoor conditions with or without solar radiation and rain to examine the shrinkage. For the purpose of studying shrinkage cracking behavior, prismatic concrete specimens with reinforcing steel were also subjected to the above conditions at the same time. The shrinkage behavior is described focusing on the effects of solar radiation and rain based on the moisture loss. The significant environment actions to induce shrinkage cracks are investigated from viewpoints of the amount of the shrinkage and the tensile strength. Finally, specific compressive creep behavior according to solar radiation and rainfall is discussed. It is found that rain can greatly inhibit the progresses of concrete shrinkage and creep while solar radiation is likely to promote shrinkage cracking and creep. © 2011 Elsevier Ltd. All rights reserved. Source

Tsukamoto Y.,Tokyo University of Science | Ishihara K.,Chuo University | Sawada S.,Oyo Corporation | Fujiwara S.,Tokyo Metropolitan Government
International Journal of Geomechanics

The settlements of structures resting on saturated sand deposits are examined in shaking table tests. Two series of tests are conducted to examine the effects of the duration of seismic shaking and the group effects of closely spaced foundations. The models of rigid circular foundations are founded on the surface of saturated clean fine sand, and seismically excited. The settlements of model foundations and the distributions of excess pore-water pressures induced around the model foundations are observed. In one of the test series, the settlements occurring during shaking are found to increase as the durations of shaking increase; however, the settlements occurring after the end of the shaking remain almost the same, regardless of the durations of shaking. The total settlements are, therefore, found to increase as the durations of shaking increase. In the other test series, the settlements occurring during shaking remain almost the same, regardless of the spacing. However, the settlements occurring after the end of shaking are different, where the more closely spaced foundations tend to be subjected to smaller settlements. © 2012 American Society of Civil Engineers. Source

Nishitani A.,Waseda University | Matsui C.,Tokyo Metropolitan Government | Hara Y.,Waseda University | Xiang P.,Waseda University | And 5 more authors.
Smart Structures and Systems

The authors' research group has developed a noncontact type of sensors which directly measure the inter-story drift displacements of a building during a seismic event. Soon after that event, such seismically-induced drift displacement data would provide structural engineers with useful information to judge how the stories have been damaged. This paper presents a scheme of estimating the story cumulative plastic deformation ratios based on such measured drift displacement information toward the building safety monitoring. The presented scheme requires the data of story drift displacements and the ground motion acceleration. The involved calculations are rather simple without any detailed information on structural elements required: the story hysteresis loops are first estimated and then the cumulative plastic deformation ratio of each story is evaluated from the estimated hysteresis. The effectiveness of the scheme is demonstrated by utilizing the data of full-scale building model experiment performed at E-defense and conducting numerical simulations. Copyright © 2015 Techno-Press, Ltd. Source

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