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Jayawardena A.W.,University of Hong Kong | Jayawardena A.W.,Nippon Engineering Consultants Co.
Procedia IUTAM | Year: 2015

In this paper, an attempt is made to highlight the causes, effects and mitigation measures of hydro-meteorological disasters with special reference to data driven approaches of forecasting. Recognizing the fact that the frequency of occurrence of water related disasters as well as the consequent damages including human casualties are on the increase in recent years, mitigation measures have become a high priority issue in all vulnerable countries. Structural measures taken by developed countries cannot be applied to developing countries because of the high capital investment. Non- structural measures such as early warning systems are more appealing to developing countries. One of the most important components of an early warning system is a mathematical model that links the input variables to the corresponding output variable. Several approaches of model formulation are discussed and some examples of the more recent fuzzy logic approach to flood forecasting is presented. © 2013 The Authors. Published by Elsevier B.V.

Terajima T.,Kyoto University | Miyahira E.I.,Nippon Engineering Consultants Co. | Miyajima H.,Yokohama Rubber Company | Ochiai H.,Japan Forestry and Forest Products Research Institute | Hattori K.,Chiba University
Hydrological Processes | Year: 2014

Knowledge of the mechanisms of rain-induced shallow landslides can improve the prediction of their occurrence and mitigate subsequent sediment disasters. Here, we examine an artificial slope's subsurface hydrology and propose a new slope stability analysis that includes seepage force and the down-slope transfer of excess shear forces. We measured pore water pressure and volumetric water content immediately prior to a shallow landslide on an artificial sandy slope of 32°: The direction of the subsurface flow shifted from downward to parallel to the slope in the deepest part of the landslide mass, and this shift coincided with the start of soil displacement. A slope stability analysis that was restricted to individual segments of the landslide mass could not explain the initiation of the landslide; however, inclusion of the transfer of excess shear forces from up-slope to down-slope segments improved drastically the predictability. The improved stability analysis revealed that an unstable zone expanded down-slope with an increase in soil water content, showing that the down-slope soil initially supported the unstable up-slope soil; destabilization of this down-slope soil was the eventual trigger of total slope collapse. Initially, the effect of apparent soil cohesion was the most important factor promoting slope stability, but seepage force became the most important factor promoting slope instability closer to the landslide occurrence. These findings indicate that seepage forces, controlled by changes in direction and magnitude of saturated and unsaturated subsurface flows, may be the main cause of shallow landslides in sandy slopes. © 2013 John Wiley & Sons, Ltd.

Yamaguchi H.,Saitama University | Matsumoto Y.,Saitama University | Yoshioka T.,Nippon Engineering Consultants Co.
Smart Structures and Systems | Year: 2015

Structural health monitoring of steel truss bridge based on changes in modal properties was investigated in this study. Vibration measurements with five sensors were conducted at an existing Warren truss bridge with partial fractures in diagonal members before and after an emergency repair work. Modal properties identified by the Eigensystem Realization Algorithm showed evidences of increases in modal damping due to the damage in diagonal member. In order to understand the dynamic behavior of the bridge and possible mechanism of those increases in modal damping, theoretical modal analysis was conducted with three dimensional frame models. It was found that vibrations of the main truss could be coupled internally with local vibrations of diagonal members and the degree of coupling could change with structural changes in diagonal members. Additional vibration measurements with fifteen sensors were then conducted so as to understand the consistency of those theoretical findings with the actual dynamic behavior. Modal properties experimentally identified showed that the damping change caused by the damage in diagonal member described above could have occurred in a diagonal-coupled mode. The results in this study imply that damages in diagonal members could be detected from changes in modal damping of diagonal-coupled modes. Copyright © 2015 Techno-Press, Ltd.

Jayawardena A.W.,University of Hong Kong | Jayawardena A.W.,Nippon Engineering Consultants Co.
KSCE Journal of Civil Engineering | Year: 2015

Climate change and global warming are currently hot topics. There is no doubt that warming is taking place in some parts of the globe as evidenced by melting of ice caps and glaciers, sea level rises, temperature rises, among other changes. At the same time, skeptics are of the view that the issue is blown out of proportion, and that warming exists locally and that it is premature to conclude that it is a global phenomenon. Projections made into the future climate have many uncertainties. These include model uncertainties, data length and their representativeness, calibration and validation issues, and the logic of projecting into 100 years or more into the future with a relatively short window of observations. What is not made known to the public at large is a balanced view that highlights the real scientific evidence and limitations and uncertainties of their findings. As a result the general public do not get a balanced view of the issues and get to know only a partial truth and not the whole truth. In this paper, an attempt is made to revisit the issues in the light of available information, and to highlight the important role of increasing population, with the objective of giving a reasonably balanced view since opinions about the issues are either biased or divided. © 2015, Korean Society of Civil Engineers and Springer-Verlag Berlin Heidelberg.

Dammika A.J.,Saitama University | Kawarai K.,Saitama University | Yamaguchi H.,Saitama University | Matsumoto Y.,Saitama University | Yoshioka T.,Nippon Engineering Consultants Co.
Journal of Bridge Engineering | Year: 2015

Structural health monitoring (SHM) of bridges by visual inspection is not necessarily reliable as many damages are not discovered during the periodic inspection of bridges. A technique to assist in visual inspection is vibration-based SHM. It is believed that structural damages lead to changes in stiffness and damping properties, and change the dynamic characteristics of structures, such as natural frequency, mode shape, and modal damping ratio. Although changes in the modal damping ratio can be used as damage indicators in the field of vibration-based SHM, the method's accuracy remains concerning. This study investigated the analytical modal damping evaluation as a complementary method to the experimental SHM of bridges. An energy-based damping model was introduced to estimate the damping parameters of a steel arch bridge, such as the equivalent loss factors of structural components, and the modal damping ratios of the bridge were then analytically evaluated using the damping parameters. The results confirmed that the proposed methodology can identify the damping sources in steel bridges and their contributions to each modal damping ratio, and complements the experimental SHM of bridges. © 2014 American Society of Civil Engineers.

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