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Chae B.-G.,Korea Institute of Geoscience and Mineral Resources | Kim M.-I.,Korea Infrastructure Safety and Technology Corporation
Environmental Earth Sciences | Year: 2012

An early warning system can be an effective measure to reduce the damage caused by landslides by facilitating the timely evacuation of residents from a landslide-prone area. Early detection of landslide triggering across a broad range of natural terrain types can be accomplished by monitoring rainfall and the physical property changes of soils in real time or near-real time. This study involved the installation of a real-time monitoring system to observe physical property changes in soils in a valley during rainfall events. This monitoring included the measurement of volumetric water content, which was compared with the results of laboratory flume tests to identify landslide indicators in the soils. The response of volumetric water content to rainfall events is more immediate than that of pore-water pressure, and volumetric water content retains its maximum value for some time before slope failure. Therefore, an alternative method for landslide monitoring can be based on the observation of volumetric water content and its changes over time at shallow soil depths. Although no landslide occurred, the field monitoring results showed a directly proportional relationship between the effective cumulative rainfall and the gradient of volumetric water content per unit time (t/t max). This preliminary study thus related slope failure to the volumetric water content gradient as a function of rainfall. Laboratory results showed that a high amount of rainfall and a high gradient of volumetric water content could induce slope failure. Based on these results, it is possible to suggest a threshold value of the volumetric water content gradient demarcating the conditions for slope stability and slope failure. This threshold can thus serve as the basis of an early warning system for landslides considering both rainfall and soil properties. © 2011 Springer-Verlag. Source

Park J.-W.,Korea Infrastructure Safety and Technology Corporation | Yoo J.-H.,Seoul National University of Science and Technology
Steel and Composite Structures | Year: 2015

This paper presents the experimental results of flexural and compression steel members strengthened with carbon fiber reinforced polymers (CFRP) sheets. In the flexural test, the five specimens were fabricated and the test parameters were the number of CFRP ply and the ratio of partial-length bonded CFRP sheets of specimen. The CFRP sheet strengthened steel beam had failure mode: CFRP sheet rupture at the mid span of steel beams. A maximum increase of 11.3% was achieved depending on the number of CFRP sheet ply and the length of CFRP sheet. In the compression test, the nine specimens were fabricated and the main parameters were: width-thickness ratio (b/t), the number of CFRP ply, and the length of the specimen. From the tests, for short columns it was observed that two sides would typically buckle outward and the other two sides would buckle inward. Also, for long columns, overall buckling was observed. A maximum increase of 57% was achieved in axial-load capacity when 3 layers of CFRP were used to wrap HSS columns of b/t = 60 transversely. Copyright © 2015 Techno-Press, Ltd. Source

Lee D.-S.,Inha UniversityIncheon | Kim S.-J.,Korea Infrastructure Safety and Technology Corporation | Cho Y.-H.,Yeungnam University | Jo J.-H.,Inha UniversityIncheon
Energy and Buildings | Year: 2015

Exterior venetian blinds (EVBs) are widely used in commercial and residential buildings, and show a high performance level for both shading and lighting purposes. However, an EVB installed over an open window also influences natural ventilation rates. In this study, applying the pressure loss rate of an EVB to wind-driven natural ventilation rates was proposed. A mock-up building was set that the EVB was installed on the front opening. Wind generator was installed toward the front opening in order to describe wind-driven cross ventilation in a single zone. To investigate wind pressure changes through the EVB plane, 16 pressure measuring taps were installed on each of the front and back side of the EVB plane. Various wind speeds were induced toward the front opening so as to derive the pressure loss rate for the four EVB slat angle cases (0°, 45°, 90°, and no shading). The pressure loss rates for each case were derived from the field measurements. The results show that the pressure loss rates have a range of 0.22 to 0.90. In addition, the measurement results indicated that an EVB can change the air velocity by about 50% based on the slat angle. Therefore, when an EVB is installed on a window opening, the effect of the EVB on wind-driven cross ventilation rate should be taken into account. © 2015 Elsevier B.V. Source

Choi T.,University of Seoul | Han J.,Korea Infrastructure Safety and Technology Corporation | Koo J.,University of Seoul
Desalination and Water Treatment | Year: 2015

Abstract: The water pipe is an important component of the tap water facility, and plays a role as critical as that of the blood vessel in the body. However, accurate diagnosis of its condition is very difficult because it is buried under the ground, even as pipe aging frequently leads to phenomena that threaten water quality such as pipe damage and water leakage. In order to maintain and improve the performance of the existing pipe network, planned examination, operation, and maintenance, as well as technologies for proper renewal, are required. Accordingly, the present research proposes a method that can be used for the maintenance of the pipe network in each water distribution block (WDB). For this purpose, the weighted performance indicator (PI) determined by means of PI and the analytic hierarchy process technique which allows evaluation for individual water WDBs, was applied to the ELECTRE technique which is a multi-factor decision-making method. This result may be used as a reference for water leakage maintenance and for the renewal and change of a WDB. The frequency of pipe accidents is expected to be reduced by appropriate plans set up beforehand. The research was conducted by investigating the 60 WDBs of both Sujeong-Gu and Joongwon-Gu in Seongnam City. The water pipe rehabilitation ranking of the 60 WDBs could be determined as a result. In order to determine the best R model out of the 16R models, a comparison was made of the correlation coefficient, rate of ranking conformance, mean square error, and mean absolute error. The result showed that the R12 model was the most suitable model, while the priority in the maintenance of the pipe network for each block could be determined. As a result, the blocks least suitable for first maintenance were determined to be Blocks 22, 48, 38, 18, and 32, whereas the most satisfactory ones were Blocks 42, 55, 23, 12, and 41. © 2014, © 2014 Balaban Desalination Publications. All rights reserved. Source

Moon D.Y.,Korea University | Zi G.,Korea University | Kim J.-H.,Korea University | Lee S.-J.,Korea University | Kim G.,Korea Infrastructure Safety and Technology Corporation
Engineering Structures | Year: 2010

The strain change of a seven-wire strand is experimentally investigated for two different detensioning procedures of a pretensioned concrete bar: flame-cutting and hydraulic-jacking. Based on the results of strain changes, it is confirmed that the prestressing force was stepwise transferred to concrete for several seconds according to the individual cut of different wires in the flame-cutting procedure. In the hydraulic-jacking procedure, the detensioning was smoothly accomplished in a time of about one second shorter than that of flame-cutting. It seems that the pattern of strain changes during the detensioning procedure is more important than the elapsed time for detensioning. In addition, the drop in the strain of each wire at the moment of flame-cutting was reduced by the installation of the debonded region. Moreover, the test results showed that the placing of stirrups has an insignificant effect on the strain change. In particular, the initial prestressing force was estimated simply from the elastic recovering strain of the strand after detensioning. The prestressing force obtained from the procedure was very close to that obtained from a load cell. © 2010 Elsevier Ltd. Source

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