• Journal of the Korea institute for structural maintenance and inspection
• /
• v.25 no.6
• /
• pp.131-142
• /
• 2021

For old piers constructed when seismic design code had not been developed, lap splices usually exist in plastic hinge region. Corrosion of rebars causes decreasement in cross-sectional area of rebar and deterioration of lap-splice behaviour, thereby reducing the seismic performance of the old piers. In this research, according to these characteristics of old piers, test specimens are designed and manufactured considering rebar corrosion, lap splice, seismic design details, and seismic reinforcement. These effects are investigated through experiments. As a result of these experiment, rebar corrosion as well as lap splice reduces displacement ductility. When seismic design details or steel-plate reinforcement are applied, sufficient displacement ductility is expressed. For non-seismically designed specimens, loosening of the lap splice of transverse rebars caused buckling of longitudinal rebars and crushing of core concrete in plastic hinge region . For seismically designed specimen, area-reducing and untying of transverse rebars due to corrosion of rebars caused buckling of longitudinal rebars and crushing of core concrete.

• Journal of the Korea Concrete Institute
• /
• v.22 no.5
• /
• pp.667-673
• /
• 2010

The near fault ground motion (NFGM) is characterized by a single long period velocity pulse with large magnitude. NFGMs have been observed in recent strong earthquakes, Northridge (1994), Japan Kobe (1995), Turkey Izmit (1999), China Sichuan (2008), Haiti (2010) etc. These strong earthquakes have caused considerable damage to infrastructures because the epicenter was close to the urban area, called as NFGM. Extensive research for the far field ground motion (FFGM) have been carried out in strong seismic region, but limited research have been done for NFGM in low or moderate seismic regions because of very few records. The purpose of this research is to investigate and analyze the seismic response of reinforced concrete bridge piers subjected to near-fault ground motions. The seismic performance of six RC bridge piers depending on three confinement steel ratios and three superstructure mass was investigated on the shaking table. From these experimental results, it was confirmed that the reduction of seismic performance was observed for test specimens with lower confinement steel ratio or more deck weight. The displacement ductility of RC bridge piers in terms of the stiffness degradation is proposed based on test results the shaking table.

• 한국석유지질학회:학술대회논문집
• /
• autumn
• /
• pp.73-79
• /
• 2000

해저지각 시추 프로그램 (Ocean Drilling Program: 이하 ODP 라함)은 해저 분지 연구를 통해서 지구의 진화와 구조를 밝히기 위해서 조직된 기구로 지구과학 분야에서는 세계에서 가장 규모가 크고 성공적인 연구사업을 추진하고 있다. 이 프로그램은 심해저시추 프로그램 (DSDP: Deep Sea Drilling Project)의 뒤를 이은 연구 사업으로 1983년부터 시작되었으며 지구 과학자들은 다양한 해저지질 및 지구물리 자료를 제공받고 있어 지구 지각과 해저 분지의 기원과 진화 및 구조에 대한 연구에 매우 커다란 도움을 받고있다. 한국은 2년 간의 가입 타당성 조사 끝에 1996년에 호주, 카나다와 콘소시움을 형성하여 ODP에 가입했고 그 후 대만이 합류하여 환태평양 콘소시움 (PacRim)을 이루었다. 한국이 ODP에 가입한 뒤 한국 사업단이 조직되고 정관이 제정되었으며 상임위원회, 과학위원회 및 사무국이 결성되었다. 아울러 한국이 ODP에 본격적으로 참여한 1998년이래 현재까지 두 명의 한국 과학자가 시추선에 승선하였고 승선 후 세계적으로 유명한 과학자들과 함께 공동 연구를 수행하고 있다. 한국이 ODP에 가입하게 됨에 따라 세계적으로 4곳의 시료저장소에 보관되어 있는 기존의 시추 시료 및 자료를 이용할 수 있으므로 국내 지구 과학자들은 시추선 승선 뿐 만이 아니라 ODP 시료와 자료를 적극 이용하여 국내 지구과학이 진일보하는 계기를 마련하게 되었다. 따라서, 한국 ODP 사업단의 개요와 활동, 그리고 향후 연구 사업의 방향을 소개하여 지구 과학을 연구하는 학계, 연구계 및 산업계에 종사하는 지구과학 전문가들에게 ODP 사업에 대한 이해를 증진시키고 시추선 승선과 시료 및 자료 이용에 대해 적극적으로 참여할 수 있는 정보를 제공코자 한다.정이 이뤄져야 할 것으로 보인다. 또한 내부파와 음파의 상대적인 진행 방향에 따라 음장변화가 크게 다를 것이 예상되므로 이를 규명하기 위해서는 궁극적으로 3차원적인 음장분포 연구가 필요하다. 음향센서를 해저면에 매설할 경우 수충의 수온변화와 센서 주변의 수온변화 사이에는 어느 정도의 시간지연이 존재하게 되므로 이에 대한 영향을 규명하는 것도 센서의 성능예측을 위해서 필요하리라 사료된다.가지는 심부 가스의 개발 성공률을 증가시키기 위하여 심부 가스가 존재하는 지역의 지질학적 부존 환경 및 조성상의 특성과 생산시 소요되는 생산비용을 심도에 따라 분석하고 생산에 수반되는 기술적 문제점들을 정리하였으며 마지막으로 향후 요구되는 연구 분야들을 제시하였다. 또한 참고로 현재 심부 가스의 경우 미국이 연구 개발 측면에서 가장 활발한 활동을 전개하고 있으며 그 결과 다수의 신뢰성 있는 자료들을 확보하고 있으므로 본 논문은 USGS와 Gas Research Institute(GRI)에서 제시한 자료에 근거하였다.ऀĀ耀Ā삱?⨀؀Ā Ā?⨀ጀĀ耀Ā?돀ꢘ?⨀硩?⨀ႎ?⨀?⨀넆돐쁖잖⨀쁖잖⨀／ࠐ?⨀焆덐瀆倆Āⶇ퍟ⶇ퍟ĀĀĀĀ磀鲕좗?⨀肤?⨀⁅Ⴅ?⨀쀃잖⨀䣙熸ጁ↏?⨀

• Geophysics and Geophysical Exploration
• /
• v.9 no.4
• /
• pp.261-270
• /
• 2006

Two-dimensional (2-D) inversion of magnetotelluric (MT) data for two survey lines having south-north direction from Jeju Island has been carried out. Broad band MT sounding curves with good quality could be gathered by performing audio-frequency magnetotelluric (AMT) survey during the MT survey and by operating the remote reference in Kyushu Island, Japan. Comparison of the 2-D inversion model using MT band only and that using both AMT and MT bands for the field data as well as for the data from numerical 2-D modeling said that high frequency information from AMT survey can be useful for interpreting not only the shallow part but also the deep structures, especially when the formation is resistive. The 2-D inversion models of field data show a thick layer having around 10 ohm-m in the depth of a few hundred meters throughout the survey area, which can be considered as the unconsolidated sedimentary layer. And they also show a conductive anomaly at the central part of each survey lines. It can be either the effect of the surrounding sea water, or the structures due to ancient volcanic events. But unfortunately by now, we do not have any further information about the anomaly.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2009.05a
• /
• pp.167-168
• /
• 2009

The CFT structure is applied to newly developed CFTA girder because of improvement of ductility deformation, stiffness and internal force of structure owing to the interaction between steel tube and core concrete. CFTA girder is the structure which can reduce tensile stress due to external loads by using its arch shape and prestress force. This paper proposed constructional stage procedure and represented analytical technique considering constructional stage to investigate the safety against bridge collapse on construction and on operation.

• Economic and Environmental Geology
• /
• v.51 no.3
• /
• pp.223-232
• /
• 2018

The viscous force of fluids and the capillary force acting on the pore network of the porous media are important factors determining the immiscible displacement during geological $CO_2$ sequestration, these were directly affected by geological formation conditions and injection conditions. This study aimed to observe the migration and distribution of injected fluid and pore water, and quantitatively investigate displacement efficiency on various injection temperatures. This study aimed to perform micromodel experiments by applying n-hexane used as a proxy fluid for supercritical $CO_2$. In this study, immiscible displacement process from beginning of n-hexane injection to equilibrium of the distribution of the n-hexane and pore water was observed. The images from experiment were used to observe the displacement pattern and estimate the areal displacment efficiency of the n-hexane. For investigate the affects of the injection temperatures on the migration in macroscopic, migration of n-hexane in single pore was analyzed. The measurement revealed that the displacement efficiency at equilibrium state decreases as the temperature increases. The result from experiments indicate that the temperatures can affect the displacement pattern by changing the viscous forces and the capillary forces. The experimental results could provide important fundamental information on reservoir conditions and fluid injection conditions during geological $CO_2$ sequestration.

• The Journal of Engineering Geology
• /
• v.8 no.3
• /
• pp.285-296
• /
• 1998

As a part of the study for understanding the deep geological structure of the Ogcheon Zone, both gravity and geomagnetic surveys are performed. A 70km survey line of which direction is nearly perpendicular to major faults in the southern tip of the Zone. The observed data are corrected and transformed into Bouguer and total magnetic intensity anomalies, respectively. Recent studies for petrology and geochemistry in the southwestern Ogcheon Zone in the vicinity of the survey line are reviewed for better interpretation. Both gravity and geomagnetic anomalies abruptly change around Janghung area, the southern boundary of the, Ogcheon Zone. This rapid increase of Bouguer anomaly around Janghung area can be explained by a deep seated normal fault with fairy large displacement between Precambrian gneisses and the denser intermediate plutonic rocks. It is believed that the fault acted an important role for the formation and evolution of the Ogcheon Zone. A pseudomagnetic intensity anomaly is calculated from the Bouguer anomaly assuming that the both anomalies are associated with the common source. From the origin of the survey line to the 50km point, the calculated anomaly coincides with observed magnetic anomaly. Whereas both anomalies show negative correlation in the outside 50km. From the residual Bouguer anomalies, the subterranean geological structure is provided through the iterative forward method. The initial model is obtained from informations about the surface geology as well as the results of the inverse method.

• Geophysics and Geophysical Exploration
• /
• v.6 no.1
• /
• pp.40-52
• /
• 2003

Despite the various opening models of the southwestern part of the East Sea (Japan Sea) between the Korean Peninsula and the Japan Arc, the continental margin of the Korean Peninsula remains unknown in crustal structure. As a result, continental rifting and subsequent seafloor spreading processes to explain the opening of the East Sea have not been adequately addressed. We investigated crustal and sedimentary velocity structures across the Korean margin into the adjacent Ulleung Basin from multichannel seismic reflection and ocean bottom seismometer data. The Ulleung Basin shows crustal velocity structure typical of oceanic although its crustal thickness of about 10 km is greater than normal. The continental margin documents rapid transition from continental to oceanic crust, exhibiting a remarkable decrease in crustal thickness accompanied by shallowing of Moho over a distance of about 50 km. The crustal model of the margin is characterized by a high-velocity (up to 7.4 km/s) lower crustal (HVLC) layer that is thicker than 10 km under the slope base and pinches out seawards. The HVLC layer is interpreted as magmatic underplating emplaced during continental rifting In response to high upper mantle temperature. The acoustic basement of the slope base shows an igneous stratigraphy developed by massive volcanic eruption. These features suggest that the evolution of the Korean margin can be explained by the processes occurring at volcanic rifted margins. Global earthquake tomography supports our interpretation by defining the abnormally hot upper mantle across the Korean margin and in the Ulleung Basin.

• Economic and Environmental Geology
• /
• v.35 no.5
• /
• pp.455-463
• /
• 2002

There have been few geophysical studies on the crustal structure of the continent-ocean zone around the middle eastern part of Korean peninsula, because of the lack of database in both land and ocean. The area for the study on the internal crustal structure using gravity data is bounded by the latitude of 37$^{\circ}$-38"N and longitude of 128$^{\circ}$-132$^{\circ}$E. WCA correction is applied to shipborne gravity data to integrate with gravity anomalies obtained on land. The high frequency components of the shipborne gravity data which are considered as the noise on survey track are effectively removed by means of correlating with satellite gravity data. The corrected shipborne free-air gravity anomaly is integrated with the Bouguer gravity anomaly on land under the same condition. The integrated gravity anomaly is divided into four areas for power spectrum analysis. The depths of Moho discontinuity increases gradually from inland to Ulleung basin. As the result of modeling based on power spectrum analysis, Moho discontinuity depth is about 33-35 km in the continental zone of Korea and 18-28 km at the continental margin. Such structural character is well elucidated in changing gravity data around Ulleung basin. The depths of Moho discontinuity in the southern ocean of Ulleung-island is 16--17 km, which is much lower than in the land. The result of crustal structure modeling in this study is similar to that computed by prior seismic exploration around this area.

• Geophysics and Geophysical Exploration
• /
• v.19 no.3
• /
• pp.111-120
• /
• 2016

In order to enhance the connectivity of fracture network as fluid path in enhanced/engineered geothermal system (EGS), the exact locating of hydraulic fractured zone is very important. Hydraulic fractures can be tracked by locating of microseismic events which are occurred during hydraulic fracture stimulation at each stage. However, since the subsurface velocity is changed due to hydraulic fracturing at each stage, in order to find out the exact location of microseismic events, we have to consider the velocity change due to hydraulic fracturing at previous stage when we perform the mapping of microseimic events at the next stage. In this study, we have modified 3D locating algorithm of microseismic data which was developed by Kim et al. (2015) and have developed 3D velocity update algorithm using occurred microseismic data. Eikonal equation which can efficiently calculate traveltime for complex velocity model at anywhere without shadow zone is used as forward engine in our inversion. Computational cost is dramatically reduced by using Fresnel volume approach to construct Jacobian matrix in velocity inversion. Through the numerical test which simulates the geothermal survey geometry, we demonstrated that the initial velocity model was updated by using microseismic data. In addition, we confirmed that relocation results of microseismic events by using updated velocity model became closer to true locations.